IntroductionAll-solid-state batteries (ASSBs), which replace flammable organic-based liquid electrolytes into ion-conducting solids, are expected to address the safety challenges for conventional lithium-ion batteries. Solid-state electrolyte materials as the most important constituent in ASSBs can be classified as oxide, sulfide, and halide solid-state electrolytes according to the anion type in the structural framework. To improve the efficiency of solid-state electrolytes in ion transport, some research efforts focus on the structural features suitable for cation migration events. Zeolite is a type of inorganic crystalline material made up of vertex-connected TO4 tetrahedra (i.e., T = Si, Al, P, etc.) with ordered microporous structures. They have one-, two-, or three-dimensional channel systems and cation exchange capabilities, which make them ideal for use as fast ion conductors. Zeolite membranes with a close-packed structure have a low electronic conductivity (i.e., 1.5 × 10–10 S/cm), making them an ideal option for solid-state batteries due to the high stability to air components and ability to reduce dendrite growth. In this paper, the molecular dynamics (MD) simulations of zeolite structures of relatively large sizes were accelerated via training a machine learning interatomic potential function (MLIP) with a good generalization ability, in turn screening zeolite structural frameworks suitable for Na+ transport as promising solid-state electrolytes for sodium ions in ASSBs.MethodsThe zeolite structure was characterized using the Smooth Overlap of Atomic Positions (SOAP) descriptor method provided by a software package named DScribe. Ab initio arithmetic molecular dynamics (AIMD) data used to construct the training dataset were computed by the Vienna Ab initio Simulation Package (VASP). The projector-augmented-wave (PAW) pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) function were used for the first-principles calculations, and the centre of the -point in the Brillouin zone was chosen as the k-point, the NVT systematic and the Nos-Hoover thermostat were used for the simulations, and a Nos-mass corresponding to a period of 40 time steps was chosen (SMASS = 0, a simulation time-step of 1 fs, and a simulation temperature of 1000 K). The MLIP model was based on the Nos-Hoover model.The MLIP was fine-tuned based on a pretrained model of the Crystal Hamiltonian Graph Neural Network (CHGNet) with the energy and force calculated by AIMD as target values, and the model was trained with a learning rate of 10–3. The trained CHGNet potential function was embedded into the Atomic Simulation Environment (ASE) library to carry out the MD simulations under the NVT regime with a simulation step of 1 fs and a total simulation duration of 100 ps.Results and discussionThe CHGNet pretrained model is based on the first-principles computational data of more than 1.5 million inorganic structures in the Materials program database, and it needs to be fine-tuned via adding the relevant data to achieve the better results when used for the computation of specific systems. To ensure that the data in the training set are applicable to all zeolite structures in the Na–Si–Al–O quaternary, the SOAP descriptors are used to select the ten structures with the differences in structural frameworks for the construction of the dataset, and the model obtained by training is capable of achieving a superior generalization in terms of simulated temperatures and systems. The model is used to select 18 representative structures from 124 zeolite structures for MD simulations at 1200 K. In most of the structures, Na+ is moved slightly and adsorbed to the edge of the pore channel, and only Na+ in ACO framework (ICSD 027717) is able to achieve a high enough mean-square displacement (MSD) of more than 800 2, which is extrapolated to obtain a potential barrier of 0.25 eV and an extrapolated room temperature ionic conductivity of 2.66 mS/cm after supplementing the multi-temperature simulation data. This is promising to be investigated as an important zeolite-structured solid-state electrolyte.ConclusionsIn this work, different structures selected by SOAP descriptors were used to fine-tune the CHGNet potential function model to obtain MLIP with a better generalization ability in the Na–Si–Al–O quaternary system. Using this MLIP for MD simulations indicated that in most of the zeolite structures Naions could be adsorbed far away from the cavity centre and could not form a continuous transport channel, but the ACO framework (ICSD 027717) with a migration barrier of 0.25 eV and an extrapolated room-temperature ionic conductivity of 2.66 mS/cm occurred. Na+ ions could be transported rapidly with the help of a pore structure, and it could be considered as a solid-state sodium battery electrolyte material for further studies.

IntroductionUnderstanding electron behavior is crucial in secondary battery research, as electrons directly participate in electrochemical reactions. Over the past few decades, Goodenough and his co-workers developed an electron theory for secondary batteries, introducing the splitting of d-orbital energy levels in transition metals, which reconstructs the local crystal field. This theory has provided valuable insights for optimizing the structure and performance of battery materials. However, the theory is not easy to be handled and difficult to intuitively understand due to its reliance on complex atomic and molecular orbitals, as well as orbital hybridization theories. With the advancement of material science, particularly density functional theory (DFT) and first-principles high-throughput calculations in quantum crystallography, researchers can obtain more precise insights into electronic structures and key parameters, such as the Fermi energy levels, band structures near the Fermi level, electron state, and density of states (DOS). These electronic characteristics are vital for understanding the electrochemical performance of electrode materials in secondary battery. This study was to investigate the band structures of phosphate cathodes for sodium-ion batteries via the first-principles calculations in order to establish a qualitative and semi-quantitative correlation between electronic properties and electrochemical behavior.MethodsThree typical phosphate compounds, i.e., -NaVP2O7, Na3V2(PO4)2F3 and Na3V2(PO4)3, were selected as model materials. Their crystal structures were obtained from the Inorganic Crystal Structure Database (ICSD) and optimized by the Vienna Ab initio Simulation Package (VASP) with the Perdew–Burke–Ernzerhof (PBE) functional and projector-augmented wave (PAW) pseudopotentials. The key computational parameters included a plane-wave cutoff energy of 520 eV and Monkhorst–Pack k-point grids of 4×3×3 for -NaVP2O7, 3×3×2 for Na3V2(PO4)2F3 and 2×3×3 for Na3V2(PO4)3. The convergence criteria were set at 10–5 eV for energy and –0.01 eV/ for forces. The band structures and density of states (DOS) were initially calculated using optimized structures for theoretically perfect crystals. However, since the actual sodium ion content in some phosphate cathodes deviates from the perfect crystal, the structural modifications were implemented. For Na3V2(PO4)3, the unit cell was doubled, and the number of sodium ions was adjusted according to symmetry rules to align with practical requirements. For Na3V2(PO4)2F3, no unit cell expansion needed, but the number of sodium ions reduced based on symmetry considerations. For -NaVP2O7, no sodium ion adjustments required. After these corrections, the band structures and DOS were recalculated. The electrochemical performance was further validated through galvanostatic charge/discharge tests at 0.2 C, with the specific capacities and cycling stability evaluated for 50 cycles.Results and discussionHigh-throughput calculations can yield the more precise Fermi energies for the selected phosphate cathodes, with -NaVP2O7 at 2.06 eV, Na3V2(PO4)2F3 at 1.70 eV, and Na3V2(PO4)3 at 2.91 eV. Correspondingly, the bandgaps are determined to be 2.53 eV for -NaVP2O7, 2.74 eV for Na3V2(PO4)2F3, and 1.93 eV for Na3V2(PO4)3. These electronic parameters have a direct impact on the discharge voltages and conductivity of the materials. Note that -NaVP2O₇ with the minimum Fermi energy, achieves the maximum discharge voltage of 4.2 V, aligning with theoretical predictions that lower Fermi levels correspond to higher working voltages. Despite its relatively high Fermi level, Na3V2(PO4)3 maintains a stable 3.4 V platform due to its uniform energy band distribution near the Fermi level along the entire recommended band path, minimizing electron behavior changes and transition barriers. This uniform distribution facilitates consistent electron transport, resulting in an exceptional cycling stability with 99.4% capacity retention after 50 cycles. In contrast, -NaVP2O7 and Na3V2(PO4)2F3 exhibit non-uniform energy band distributions near the Fermi level, indicating multiple electron transition pathways that contribute to instable voltage plotforms. The discharge specific capacities of these materials are measured as 92.7 mA·h·g–1 for -NaVP2O7, 124 mA·h·g–1 for Na3V2(PO4)2F3 and 115.2 mA·h·g–1 for Na3V2(PO4)3. A correlation between the integral of DOS near the Fermi level band and the discharge specific capacity of electrode materials occurs. Higher integrals of DOS for conductive electrons near the Fermi level correspond to greater discharge capacities, as demonstrated in the comparative analysis of these electrode materials.ConclusionsThis study established a correlation between high-throughput quantum crystallography calculations and electrochemical performance in sodium-ion battery cathodes. The Fermi levels directly affected discharge voltages, with lower Fermi levels corresponding to higher working voltages. A uniform band structure near the Fermi level over the whole recommended band path improved a cycling stability. The integral of the DOS near the Fermi level could be a critical factor determining the specific capacity of electrode materials. In addition, high-throughput calculations also revealed that structural imperfections, such as uncertain atomic occupancy in Na3V2(PO4)2F3 and Na3V2(PO4)3, significantly could affect computational accuracy. The more precise Fermi energy values, band configurations, and DOS parameters were obtained via refining ion-occupancy corrections and implementing supercell expansions, providing deeper insights into fundamental electrochemical properties of these materials. These findings established a theoretical framework for designing next-generation battery materials via optimizing band structures for optimizing energy density and stability. This study could highlight a potential of high-throughput quantum crystallography calculations in predicting and improving electrochemical performance, thus offering a roadmap for the development of next-generation battery materials.

IntroductionDevelopment of new energy becomes popular due to the energy shortages and environmental pollution. The existing commercial secondary batteries are primarily lithium-ion batteries, which use organic solvents and lithium salts as electrolytes. These batteries have two significant drawbacks, i.e., global lithium resources are insufficient and unevenly distributed, and organic solvents are flammable, having safety risks. These drawbacks severely affect the further development of lithium-ion batteries. Sodium solid-state electrolytes (SSEs) are emerged as an ideal material for future battery electrolytes due to the high energy density, good thermal stability, strong mechanical rigidity, low cost and improved safety. This paper was to explore a potential sodium SSEs by a high-throughput screening method based on machine learning (ML) and first-principles calculations. The potential sodium SSEs were predicted by machine learning models and were validated through Ab initio molecular dynamics (AIMD) simulations. In addition, the conduction mechanism of sodium ions was also analyzed based on the results of the first-principles calculations.MethodsThe dataset of inorganic sodium-containing compounds was established before building ML models. All the data in this dataset were from the Materials Project database. Solid-state electrolytes have good thermodynamic stability and insulation. The materials with a band gap less than 1.5 eV or energy above hull greater than 0.03 eV/atom were excluded, resulting in a final dataset of 3631 sodium-containing inorganic compounds.To achieve the optimal performance of the regression model, we tried four ML algorithms, i.e., Random Forest (RF), eXtreme Gradient Boosting (XGBoost), Categorical Boosting (CatBoost), and K-Nearest Neighbors (KNN). Magpie (Materials Agnostic Platform for Informatics and Exploration) was used to obtain the crystal structure information into 145 attributes as the input of ML models. To validate the performance of the screened sodium solid-state electrolytes and further analyze the migration mechanism of sodium ions, AIMD simulations and CI-NEB (Climbing Image Nudged Elastic Band) calculations were conducted to calculate their ionic conductivity, activation energy, probability density distribution, van Hove correlation functions and energy barriers along specific diffusion paths.Results and discussionIn the four machine learning regression models, XGBoost has the optimum performance on both training and testing sets with R2 = 0.999 and 0.994, respectively, indicating its high accuracy and strong generalization ability. The XGBoost model is used to predict 3631 of sodium-containing inorganic compounds, discovering that 126 of them have a potential to be superior SSEs. We further screen these and select 14 compounds for AIMD simulations, among which four materials (i.e., Na3HfTiSi2PO12, Na3Bi(BO3)2, Na2LuPCO7 and Na2LuPWO8) show a high ionic conductivity and a low activation energy. Since the difference between the machine learning prediction and AIMD calculated value is within an order of magnitude, the high-throughput screening method used is reliable. Among the four candidate SSE materials, Na3HfTiSi2PO12 belongs to the NASICON family. A previous study indicates that Na3HfZrSi2PO12 is a promising sodium SSE material, which is similar to Na3HfTiSi2PO12, except that Ti is replaced by Zr, indirectly proving the reliability of the machine learning model prediction.To clarify the sodium ion migration mechanism, the motion trajectories of various particles in each compound are investigated. The results show that at all simulation temperatures, the diffusion of sodium ions is evident, while other ions remain relatively stable, forming reliable channels for sodium ion migration. From the distinct parts, the four materials exhibit migration correlation, indicating that sodium ions do not move independently but rather diffuse cooperatively, which contributes significantly to the ionic conductivity. The migration pathways of Na3Bi(BO3)2, Na2LuPCO7 and Na2LuPWO8 are discussed according to the probability density distributions. Moreover, the energy barrier of migration in Na2LuPCO7 shows that the maximum obstacle is to bypass the triangular plane formed by CO3 within the diffusion channel.ConclusionsWe used the best-performing XGBoost model to search the established dataset of 3631 inorganic sodium-containing compounds, identifying 126 compounds with a high ionic conductivity. Also, we selected 14 of the 126 compounds for AIMD simulations to calculate their ionic conductivity and activation energy, ultimately identifying four inorganic sodium-containing compounds (i.e., Na3HfTiSi2PO12, Na3Bi(BO3)2, Na2LuPCO7 and Na2LuPWO8) with a high ionic conductivity. We derived the van Hove correlation functions and probability density distributions based on the AIMD simulation results. It was indicated that the common characteristic of the four high ionic conductivity materials could be the presence of stable sodium ion diffusion channels with sodium ions migrating in a coordinated manner. Finally, the migration mechanism of sodium ions was analyzed based on the results of AIMD and CI-NEB.

IntroductionSodium-ion batteries with their abundant resource availability and low cost, show a tremendous potential in energy storage. Sodium-ion batteries emerge as a more economical alternative to lithium-ion batteries, making it highly attractive for large-scale grid energy storage applications. To enhance the competitiveness of sodium-ion batteries, the development of high-energy cathode materials is crucial. As a result, recent efforts are made to explore sodium-ion cathode materials, particularly sodium layered oxides and polyanion compounds. The most extensively studied polyanion sodium-ion cathode materials are vanadium phosphates (i.e., Na3V2(PO4)3 or NVP) and fluorophosphates (i.e., Na3V2(PO4)2F3 or NVPF). NVP with its sodium fast ion conductor (Na-superionic conductor, NASICON) structure is considered as a high-performance sodium-storage cathode material. The related experimental results indicate that the actual specific capacity of pure-phase NVP is lower than theoretical expectations, and its cycling stability is generally poor. Adjusting the composition and structure of NVP through elemental doping is an effective strategy to enhance its cycling reversibility, increase reversible capacity, and improve sodium ion diffusion kinetics. However, some challenges exist in accurately measuring the properties of sodium-ion cathode materials during experiments coupled with high trial-and-error costs and the lack of scientific theoretical guidance. This study was to utilize first-principles calculations to investigate the electronic structure characteristics of mixed polyanions doped with different transition metals, aiming to elucidate the conductivity mechanisms within polyanion systems. In addition, the microscopic processes of sodium ion insertion/extraction during the charge and discharge cycles of polyanion cathode materials were also analyzed via simulating all possible sodium ion migration pathways and calculating the corresponding energy barriers and voltage platforms in an ideally conductive polyanion system.MethodsSpin-polarized DFT calculations were used within the Vienna ab initio simulation package. The projector-augmented wave (PAW) method was applied to solve the ion-electron interactions in a periodic system. The generalized gradient approximation (GGA) with Perdew−Burke−Ernzerhof (PBE) functionals was used to take into consideration of the exchange-correlation interactions in the Kohn−Sham equations. A plane-wave basis set with a cutoff energy of 400eV was used to expand the Kohn–Sham valence states. A k-point mesh of dimensions of 3 × 3 × 1 was employed for the Brillouin zone integration. For calculating the electronic structure, a Monkhorst-Pack grid of 5 × 5 × 1 was sampled. The self-consistent field convergence criteria were set at 1 ×10–6 eV. All the structures were sufficiently relaxed until the force at each atom was less than 0.02eV∙–1. The climbing-image nudged elastic band (CI-NEB) was used to calculate the migration energy barrier corresponding to the migration path of Na ions. This is an effective way to find the saddle points of the ion diffusion energy. Five intermediate images were constructed between the initial and final states along the sodium ion diffusion path. The calculation formula of charge and discharge voltage is: V = (E(NaxMP) + (y–x)E(Na)–E(NayMP))/(y–x), where E(NayMP), E(NaxMP) and E(Na) indicate the discharge completion state, charging completion state and the energy of Na atoms, respectively.Results and discussionThe results show that Na3TiMn(PO4)3 and Na3TiFe(PO4)3 have more abundant electronic state near the Fermi level, compared to the original Na3V2(PO4)3. The conductivity of Na3TiMn(PO4)3 and Na3TiFe(PO4)3 is better than that of the original Na3V2(PO4)3, accelerating the kinetic process of electron transfer and ion extraction. The electronic structure characteristics of mixed polanion based on iron and manganese are analyzed, and the conductive mechanism of polyanionic system is proved via the first-principles calculations, which is helpful to screen the polanion cathode materials with an ideal conductivity.The CI-NEB method is used to calculate the three diffusion paths and energy barriers in polanionic cathode materials (i.e., Na3TiMn(PO4)3, Na3TiFe(PO4)3 and Na3V2(PO4)3). The energy barriers for diffusion paths 1 and 3 of the primitive Na3V2(PO4)3 are both 0.12eV. The energy barrier of diffusion path 2 is 0.11eV, which is better than that of diffusion path 1 and 3. For Na3TiMn(PO4)3 and Na3TiFe(PO4)3, the energy difference between the initial and final state structures is too large (i.e., 0.6eV) although the energy barrier of the diffusion path 1 is extremely low (i.e., only 0.04eV), which is not conducive to the cyclic diffusion of sodium ions in the cathode material from the thermodynamic perspective. Sodium at Na1 is not conducive to prolapse, and sodium at Na2 is easier to prolapse during diffusion. The structural characteristics of Na3MM'(PO4)3 and experimental studies both thus indicate that sodium prolapsed at different positions has different effects on the structure. In terms of diffusion paths 2 and 3, the energy difference between the initial and final structures is close to 0, and the corresponding diffusion energy barrier is between 0.12eV and 0.18eV, favoring the diffusive transport of sodium ions both thermodynamically and kinetically.As the charging process proceeds, the voltage gradually increases, while desodium and sodium value decreases. The Na2 position is the first sodium ion effluent, which is consistent with that of the experimental studies. The theoretical calculation shows that the voltage platform of Na3V2(PO4)3 changes, the structure of Na3V2(PO4)3 changes in the process of sodium extraction, and the voltage platform of Na3TiMn(PO4)3 and Na3TiFe(PO4)3 is more stable than the voltage platform of original Na3V2(PO4)3.ConclusionsThe structure and electronic characteristics of Na3V2(PO4)3, Ti, Cr, Mn, Fe and other transition group metals were investigated. The density of state electronic structure of Ti, Mn and Ti and Fe substituted Na3MM′(PO4)3 polyanionic sodium ion battery cathode material. The results showed that Na3TiMn(PO4)3 and Na3TiFe(PO4)3 had more abundant electronic states near the Fermi level, the conductivity of Na3TiMn(PO4)3 and Na3TiFe(PO4)3 was better than that of the original Na3V2(PO4)3, which could effectively enhance the conductivity and accelerate the kinetic process of electron transfer and ion extraction. We calculated three sodium ion diffusion paths, analyzed the three diffusion paths of sodium ion in polyanionic cathode materials (i.e., Na3TiMn(PO4)3, Na3TiFe(PO4)3 and Na3V2(PO4)3) and the corresponding energy barriers of 0.12–0.18eV , and explained that the materials Na3TiMn(PO4)3 and Na3TiFe(PO4)3 were thermodynamically and kinetically beneficial. The theoretical calculation further studied the influence of voltage platforms on cathode materials. Based on the electronic structure and ion diffusion path results, Na3TiMn(PO4)3 and Na3TiFe(PO4)3 were selected as NASICON sodium ion cathode materials with a superior comprehensive performance.

IntroductionZinc-air batteries have a significant promise for next-generation energy storage due to their low cost, high safety, high theoretical capacity, and abundant availability. Recently, we reported a new rechargeable zinc-air battery based on zinc peroxide chemistry. Compared to conventional zinc-air batteries, this neutral zinc-air battery exhibits higher reversibility and stability, making it a more promising candidate for secondary zinc-air batteries. However, the low energy efficiency of neutral zinc-air batteries remains a challenge. And the mechanism of these neutral zinc-air battery reactions is still unclear. In this work, we systematically investigated the reaction pathways of neutral zinc-air reaction by first-principles calculations.MethodsDensity Functional Theory calculations based on a software package named VASP was employed with PAW potentials and the PBE functional. The vdW interactions were corrected by the Grimme’s D3 method. The k-point mesh was generated by the Monkhorst-Pack scheme via Pymatgen with MPRelaxSet settings. A cutoff energy of 520 eV was utilized within a convergence criterion of 10–5 eV for self-consistent calculations. The convergence criterion for ionic relaxation was set to be 0.02 eV/. The calculations were performed by a slab model with a thickness of approximately 10 and a vacuum layer of greater than 15 .Results and discussionThere is a clear linear scaling relationship among the adsorption strengths of O*, ZnO2*, and ZnO4* in neutral zinc-air reactions. This relationship constrains the freedom in catalyst design, making it difficult to optimize all intermediate adsorption strengths simultaneously. Breaking this linear scaling relationship will be a focus of future research. The rate-determined step for both the four-electron and two-electron reactions in Ag (111) is the first electron transfer. A weaker ZnO4* adsorption makes the first reaction barrier as high as 0.78 eV at 1.2 V (vs. Zn/Zn2+). This result indicates that even with this metal catalyst, the discharge voltage of neutral zinc-air batteries remains smaller than that of alkaline batteries due to the limitation of linear scaling relationships.Among various catalysts, Pt (111) exhibits a lowest reaction barrier, indicating that Pt maintains a high catalytic activity in Zn2+-involved ORR processes. Conversely, the surface reactivity of Ru (111) and Co (001) catalyst surfaces is significantly greater than that of Ag (111), where over-strong ZnO4* adsorption makes the second electron transfer the rate-determined step. Meanwhile, the energy barrier of four-electron pathway is notably lower than that of two-electron transfer pathway, showing that the Ru (111) and Co (001) catalyst can favor a four-electron transfer reaction and form ZnO discharge products.The optimal O* adsorption free energy is found to be around -6 eV based on the linear scaling relationships. And Ag (111) and Pt (111) have relatively appropriate O* adsorption strengths. The neutral zinc-air catalytic activity of Ag and Pt can be further improved via increasing the d-band center. In addition, the calculations also reveal that catalysts with a strong reactivity favor a four-electron transfer pathway.ConclusionsThe theoretical calculation results showed that linear scaling relationships still had true among various adsorption intermediates in neutral zinc-air reactions. Oxygen adsorption strength and overpotential followed the Sabatier principle, indicating that a moderate strength (i.e., GO* ~ –6 eV) yielded an optimal catalytic activity. Among numerous catalysts, Ag and Pt exhibited an optimal surface reactivity with a high theoretical catalytic activity. Furthermore, employing catalysts with a strong surface reactivity, such as Co and Ru, represented a potential approach to achieve non-protonic four-electron zinc-air batteries.

IntroductionAs pivotal components in modern energy storage systems, lithium-ion batteries remain constrained by inherent limitations in safety and energy density associated with conventional liquid electrolytes. All-solid-state lithium-ion batteriesrepresent a promising technological pathway to synergistically enhance both energy density and intrinsic safety through the implementation of non-flammable solid-state electrolytes. However, the fundamental trade-off between ionic conductivity and chemical stability persists as a critical challenge in solid-state electrolyte development. The existing material systems exhibit some distinct limitations, i.e., sulfide-based solid-state electrolytes (e.g., Li10GeP2S12) demonstrate a superior ionic conductivity (~10⁻2 S/cm), but suffer from pronounced hygroscopic and oxidative instability, and oxide-based counterparts (e.g., Li₇La3Zr2O12) display exceptional environmental stability with inadequate ionic conduction performance. This challenge leads to extensive research into oxysulfide electrolyte systems that combine advantageous characteristics of both material classes through chemical composition.Recent researches on LiAlSO-based materials reveal that enhanced lithium-ion concentration and isoelectronic substitution of Al with Li–Be groups can significantly improve an ionic conductivity. However, the inherent biotoxicity of beryllium substantially elevates synthesis costs and complicates manufacturing processes. To address this limitation, this work was to propose a novel Li2MgSO electrolyte system for replacing beryllium with the homologous element magnesium. This study also investigated the structural stability, electronic characteristics, and lithium-ion transport mechanisms via utilizing the crystal structure prediction program (CALYPSO) and density functional theory (DFT) calculations. The complementary anion/cation substitution experiments could elucidate composition-property relationships, providing a theoretical foundation for developing cost-effective, high-performance solid-state electrolytes.MethodsThe crystal structure of Li2MgSO was predicted by theCALYPSO method with the particle swarm optimization algorithm. The total energy calculations and geometry optimizations were performed using the Vienna Ab initio Simulation Package (VASP) within the framework of density functional theory (DFT). The projector augmented wave (PAW) approach was used to describe the core-valence electron interaction. The generalized gradient approximation in the parameterization of Perdew, Burke, and Ernzerhof was used to describe the exchange-correlation potential. The plane-wave energy cut-off was set to 500eV. The geometric structures were fully relaxed until the residual force on each atom was less than 0.02 eV·–1, and the energy converged to less than 10–5 eV. The hybrid density functional calculation, which was more accurate for electronic band structure calculations, was used to calculate the electronic density of states. The phonon spectrum calculations were carried out based on density-functional perturbation theory, and the phonon dispersion relations and thermodynamic properties were derived by a software named PHONOPY. Bond Valence Site Energy (BVSE) was used to model the possible diffusion channels of Li ions in Li2MgSO. The migration barriers of Li ions were obtained by the climbing image nudged elastic band (CI-NEB) method. Ab initio molecular dynamics (AIMD) simulations were further employed to investigate the ion transport properties of Li2MgSO. The simulations were conducted in the canonical ensemble (NVT) using a Nos-Hoover thermostat at different spanning temperatures (i.e., 800–1600 K). Each simulation lasted for 40 000 steps with one time step of 1 fs.Results and discussionThe application of CALYPSO structural prediction program and first-principles calculations indicates that the ground-state configuration of Li2MgSO can crystallize in a P4ˉ21m space group symmetry. The phonon dispersion analysis reveals a complete absence of imaginary frequencies, confirming the lattice dynamic stability. Electronic structure characterization discloses a substantial band gap of 4.76 eV, satisfying a critical requirement for solid-state electrolytes via ensuring electrochemical stability against redox reactions.The mechanical property evaluation demonstrates the Young modulus of 66.81 GPa and the Pugh ratio of 1.93, indicative of superior crack propagation resistance and favorable ductile behavior, respectively. The collective computational evidence indicates that Li2MgSO exhibits a promising potential as a high-performance solid-state electrolyte, achieving an optimal balance in structural stability, wide electrochemical window, and mechanical properties.The BVSE and CI-NEB calculations reveal that there is a three-dimensional ion transport network in Li2MgSO, comprising two distinct pathways, i.e.,1) a 2D fast diffusion channel within the ab-plane of LiMgSO layers exhibiting a migration barrier of approximately 0.34 eV, and 2) the interlayers form three-dimensional interconnected channels with a low energy barrier (0.17 eV) through vacancy migration.This unique structure substantially enhances a lithium-ion mobility, thus leading to exceptional ionic transport performance.The AIMD simulations are used to investigate the ion migration characteristics of Li2MgSO, Li2MgSeO, and Li2ZnSO, yielding the activation energies of 0.68, 0.82 eV, and 0.35 eV for lithium diffusion, respectively.The mean square displacement (MSD) analysis reveals the comparative dynamics, i.e., lithium ions in Li2MgSeO displayed marginally reduce mobility relative to Li2MgSO, whereas Li2ZnSO exhibits a twofold increase in MSD values, indicating a superior ionic migration capability. These findings indicate cation-induced effects as the primary governing mechanism for ion transport in Li2MgSO systems, providing a strategic guidance for optimizing cationic species to engineer expanded transport channels and enhance ionic conductivity.ConclusionsThe theoretical calculations indicated that Li2MgSO had the excellent kinetic properties, mechanical stability, and a wide bandgap (4.76 eV). The ion transport kinetics analysis unveiled a unique three-dimensional ionic transport network in Li2MgSO, comprising interlayer migration channels and two-dimensional in-plane migration pathways, with low migration barriers favorable for rapid lithium-ion transport. From the systematic substitution studies of anions (Se) and cations (Zn), Li2ZnSO demonstrated the superior lithium-ion migration kinetics, compared to Li2MgSO and Li2MgSeO, indicating that lithium-ion migration in Li2MgSO system could be primarily regulated by cation-induced effects.

IntroductionLithium-ion batteries are currently the most widely used secondary batteries, extensively applied in electric vehicles, laptops, and smartphones. However, commercial lithium-ion batteries generally use flammable organic solvents, which pose safety issues such as leakage and self-ignition. As the demand for higher energy density grows in fields like aerospace and electric vehicles, the existing commercial lithium-ion batteries cannot available. All-solid-state lithium-ion batteries (ASSLBs) with a high energy density and a good safety become one of the ideal alternatives to address the issues of the existing lithium-ion batteries. However, the bottleneck for ASSLB applications is the lack of solid electrolyte (SE) materials with a high ionic conductivity and a good stability simultaneously. Recently, a novel class of revived ternary halide SEs represented by Li3InCl6 (LInC) has attracted much attention due to their high room temperature ionic conductivity, high oxidative stability, compatibility with high voltage cathodes, and particularly high humidity stability. However, there are still some application-related issues regarding LIC that remain unclear, such as mechanical and thermal properties, especially the Li-ion migration mechanisms. First-principles calculations can reveal the underlying mechanisms in an atomic scale, compared to experimental methods.This paper was to evaluate the fundamental physical properties required for LInC as a SE material and reveal the main factors for high ionic conductivity, thus providing methods for the improvement and application of LIC SE. The geometric and electric structure, mechanical and thermal properties, defect chemistry, and Li-ion migration mechanism of LIC were investigated, and the findings indicated that LIC could be used as a promising SE material for ASSLBs.MethodsIn this work, all the calculations were performed by first-principles methods based on density functional theory (DFT) implementing in a software named VASP (Vienna Ab initio Simulation Package). The interaction between ion cores and valence electrons was described by Projector-Augmented Wave (PAW) with a plane wave cutoff energy of 640 eV. The exchange-correlation functional was described by the Perdew-Burke-Ernzerhof (PBE) functional within the Generalized Gradient Approximation (GGA). During geometry relaxation, the numerical integration over the Brillouin zone was performed by the Monkhorst-Pack method with a k-point grid of 3×2×3; for electronic structure calculations, the grid is 5×3×5, and a Gaussian smearing was applied to the Fermi level with a width of 0.2 eV. The electronic structure and band structure of the system were calculated by hybrid density functionals based on the Heyd-Scuseria-Ernzerhof (HSE06) method. All atoms within the unit cell were fully relaxed with a convergence criterion of 10–5 eV/atom, and the interatomic forces were less than 0.01 eV/. In addition, for the calculation of defects and Li ion migration barriers, a supercell of 2×1×2 was also constructed, containing 24 Li, 8 In, and 48 Cl atoms. The Climb Image Nudged Elastic Band (CI-NEB) method was used to search for the migration path of Li+ and to calculate the migration barrier.Results and discussionWe modeled LInC crystal based on the XRD experimental data. LInC unit cell with C2/m space group exhibits the lattice constants (i.e., a = 6.63 , b = 11.34 , c = 6.46 , = = 90°, and = 112.0°), which are in good agreement with the experimental data. All Cl atoms fully occupy the 4i and 8j Wyckoff sites, In atoms partially occupy the 4g site within the plane (001), and Li atoms fully occupy the 4h and 2d sites within the plane (002). The band structure illustrates LIC with a bandgap of 4.71 eV, indicating a great theoretical electrochemical window. Furthermore, DFT calculations demonstrate that LInC possesses low elastic moduli with B=14.71 GPa, G=7.05 GPa, and E=18.24 GPa, which is smaller than those of Li10GeP2S12 (LGPS) and Li3YCl6 (LYC), and exhibits a high Pugh ratio (i.e., B/G=2.09), indicating its favorable mechanical properties and ductility. LInC can be suitable as a solid electrolyte for all-solid-state batteries. The defect chemistry and Li-ion migration of LInC show that although isolated VLi' with a formation energy of –1.43 eV can form spontaneously, VLi' migration barriers as high as 0.48 eV indicates that the contribution of VLi' to the conductivity of LInC is negligible. Similarly, despite presenting a low migration barrier of 0.17 eV in ab plane, isolated VLi' has a high formation energy of 4.75 eV, indicating a negligible contribution to conductivity of bulk LInC. For four considered neutral defect pairs, the defect formation energies and Li-ion migration barriers follow an order of VLi'-Lii' (0.24 eV) < InLi··-VLi' (0.44 eV) < VLi'-VCl· (0.48 eV) < LiIn''-Lii· (0.69 eV) and VLi'-Lii· (0.26 eV) < InLi··-VLi' (0.28 eV) < VLi'-VCl· (0.34 eV) < LiIn''-Lii· (0.67 eV), respectively. The results indicate that Frenkel defect pair VLi'-Lii· is the dominant defect type, playing a critical role in the high ionic conductivity of LInC. The contribution of InLi··-VLi' and VLi'-VCl· defect pairs to the ionic conductivity of LInC bulk is also not negligible. This work provides valuable insights for evaluating LInC as SE material, and elucidates some dominant factors for a high ionic conductivity of LInC.ConclusionsThis work systematically investigated the basic properties and Li-ion migration mechanisms of LInC by first-principles calculation methods. The results showed that LInC had high theoretical electrochemical window as well as good mechanical property and ductility. Furthermore, the VLi'-Lii· Frenkel defect pair with the low formation energy of 0.24 eV presented a low VLi' migration barrier of 0.26 eV, confirming that it could be the dominant defect type in LInC, and Li vacancies were the predominant carriers in LInC bulk. The findings of this work could provide a theoretical basis for the modification and application of LInC materials.

IntroductionLithium-ion batteries are widely used in electric vehicles due to their high energy density and environmental compatibility, but their safety and endurance are limited by liquid-state electrolytes. Solid-state electrolytes have attracted recent attention for their high safety and energy density, but their research faces some challenges. Artificial intelligence technologies, such as machine learning, can accelerate the discovery and optimization of solid-state electrolyte materials. However, extracting synthesis information from literature is time-consuming and prone to errors. Large language models (LLMs) become popular in the field of natural language processing. This paper was to propose the use of LLMs to automatically extract solid-state electrolyte synthesis information from literature via building datasets to train and fine-tune models.MethodsThe process of extracting synthesis information for solid-state electrolytes included five parts, i.e., literature downloading, parsing and processing, paragraph classification, information extraction, and synthesis process visualization. Initially, the downloaded XML documents were parsed to extract all paragraphs under the headings of "Experimental" or "Method". A classification dataset was constructed using these paragraphs, with the training set used to train and fine-tune a Bayesian model, a BERT model, and three different LLMs. The test set was used to evaluate the classification performance of different models. Three LLMs are fine-tuned using a dataset previously built for the extraction of synthesis information in inorganic catalysts, enabling them to complete the task of extracting synthesis information for solid-state electrolytes, outputting four parts of contents, i.e., product, raw materials, methods, and steps, and testing and evaluating with the synthesis paragraphs filtered by the classification models.Results and discussionThe NB model slightly underperforms the other models in terms of precision, recall, and F1 score. This may be attributed to the pre-training of LLMs and BERT on extensive text data and their fine-tuning on paragraph classification data, endowing them with strong language comprehension abilities. The comparable overall performance of the 3B and 8B models may be attributed to the 3B model being derived from the 8B model through pruning and knowledge distillation, resulting in similar performance characteristics. The classification task in this paper is limited to the classification of solid-state electrolyte synthesis paragraphs and the training and testing data are relatively scarce, the superior performance of the 7B model does not imply that it is always superior to other models. The comparison between the 3B and 8B models demonstrates that in certain scenarios, smaller-parameter models can outperform their larger-parameter counterparts. Therefore, it is not always necessary to pursue models with more parameters. Instead, reasonable choices should be made based on the specific requirements of the task. In misclassifications, there is a higher incidence of predicting label 0 as 1, which may be due to the inclusion of descriptions of electrode preparation and battery assembly in paragraphs about non-solid electrolytes, involving the use of electrolytes, leading to the model to misjudge these paragraphs as solid-state electrolyte paragraphs. To further enhance the classification performance of LLMs, the way prompts the construction of the dataset that can be adjusted to allow LLMs to better understand the subtle differences between different paragraphs.The three LLMs perform exceptionally well in the task of extracting synthesis information for solid-state electrolytes, demonstrating that the combination of pre-training and fine-tuning can fully leverage the text understanding and instruction following capabilities of large models, making them competent for the crucial task of extracting important information from the synthesis process of solid-state electrolytes. Moreover, the fine-tuning dataset used originates from the field of inorganic catalysts and shows excellent performance in the field of solid-state electrolytes, indicating a great generalization ability of large models. They learn the ability to extract structured information from unstructured text, rather than just extracting information about fixed materials and synthesis processes. The extraction effects of the 3B, 7B, and 8B models are comparable, indicating that the size of the model is not a sole factor determining performance. The design and training strategies of the models are equally important.ConclusionsIn the paragraph classification task, LLMs and BERT, benefiting from their pre-training on large-scale text data and fine-tuning for specific classification tasks, demonstrated classification performance that surpassed that of Bayesian models. Among the LLMs of different sizes, the 3B model, derived from the 8B model through pruning and knowledge distillation, showed similar classification effectiveness to the 8B model. The 7B model achieved an F1 score exceeding 0.9, thus highlighting its superior performance in handling such tasks.In the synthesis information extraction task, LLMs were fine-tuned using a dataset of inorganic catalyst synthesis information. The results showed that the F1 scores of all three models exceeded 0.9, demonstrating great generalization capabilities of LLMs. This indicated that LLMs could learn the ability to extract structured information from unstructured text, rather than just extracting information about fixed materials and synthesis processes. The extraction performance of the 3B model was slightly better than that of the 7B and 8B models, thus indicating that the number of parameters could not be a sole factor determining performance. The design and training strategies of the models could be equally important.

IntroductionIn lithium-ion batteries, electrode active particles are used to store and release lithium ions. The insertion and extraction of lithium ions are accompanied by a local deformation of the electrode active material, which can lead to mechanical degradation. Studies on the chemo-mechanical behavior of electrode particles can favor to improve the capacity and cycle life of batteries. Silicon has a super high capacity as an anode and is considered as a promising electrode material. However, its excessively high volume change rate hinders the further development of silicon electrodes. Two main reasons lead to mechanical failure of silicon electrode particles, i.e., the non-uniform volume change due to Li-ion concentration gradient, and the contact between particles upon lithium insertion induced volume expansion. Contacts between elastic deformable parts with simple morphologies are investigated based on the Hertz theory, which mainly analyzes contacts via calculating the contact area and indentation depth. Simulations of solids are mainly based on the Lagrangian description, which requires to create multiple systems and inter-system connections that are computationally complex. A phase-field model is developed with Eulerian description that can conveniently identify and distinguish the inside and outside of an object by the value of a variable “order parameter”. In addition, some examples for calculation the contact between electrode particles with different morphologies are also calculated to explore the ability of the proposed method.MethodsThe calculation model is based on 3 equations, i.e., the equilibrium equation, Cahn-Hilliard equation and the reference map equation. After splitting the Cahn-Hilliard equation into two parts, 4 variables v,&#x03D5;, , need to be calculated. The constitutive law is calculated through and contact force is calculated through the &#x03D5; of the contact bodies. Deformation gradient is decomposed into elastic part and lithium-intercalation-induced part. The elastic part is constructed on neo-Hookean theory, and lithium-intercalation-induced part is calculated through the concentration of Li. Elastic constants are also functions of the concentration as Si and Li both contribute to it. 4 PDEs are generated, including the Cahn-Hilliard equation, the equilibrium equation and the evolution equation of . After applying boundary conditions, the PDEs are transformed to weak forms. The simulations are performed by the finite element method.Results and discussionA simple elastic contact problem is simulated to verify the feasibility and accuracy of the method. The result is compared with the Hertz theory. The lithiation of electrode particles is then simulated. The electrode particles are initialized as cylinders with regular and irregular profiles. The figure of von Mises stress shows that the contact between particles with regular profile is equivalent to the contact between a nanowire and rigid plane. And particles show different behaviors when they start lithiation at different durations. Particles with irregular circle profile shows a higher stress when the contact with rigid plane while the stress is lower when contacting with other particles. That is because particles rotate when the irregular profiles contact, which releases part of the stress and expands the contact area. To exclude the effects of rotation, considering that friction and binder can impede rotation, an example of 1/4 electrode particles is simulated. Particle rotation has a significant effect on stress relief, especially in the final stages of expansion, where the maximum stress can be reduced by approximately 1/3. Finally, simulations are performed with a reference to the actual electrode particle morphology. The internal stress in the particles becomes stable at a certain point and no longer increases significantly with deeper lithiation.ConclusionsThe simulation modeling of the contact between solids was implemented based on the phase-field method, and its feasibility and accuracy were verified through a simple example. Subsequently, the simulations of the contact problem of the lithiation of electrode particles were carried out to investigate the deformation and stress state of electrode particles with different shapes when the contact occurs to show the region where mechanical degradation might occur. The simulation of electrode particles’ lithiation showed different behaviors when the profile changed. This was because particles with irregular profile rotate when contacts occured so that concave surface and convex surface coupled. However, smaller contact area resulted in higher stress when concave surface contacted with rigid plane. The final simulations were performed with a reference to the morphology of the electrode particles in the real situation. These simulations could provide a reference for the study of the lithiation behavior of electrode particles in Li-ion batteries, showing the possible sites of mechanical damage or fracture of the electrode particles when they squeezed against each other, which in turn could be expected to contribute to the optimal design of Li-ion batteries in the future.

IntroductionLithium-ion batteries (LIBs) are widely used in electric vehicles and electronic devices due to their high energy density and long cycle life. The migration rate of lithium ions in cathode materials significantly affects the rate performance of LIBs. Previous studies showed that there were certain differences in the migration energy of lithium ions in LiCoO2 materials at different concentrations of lithium vacancies, which could be due to the different interlayer distances caused by different concentrations of lithium vacancies. The construction of individual lithium vacancies in different supercells can lead to different concentrations of lithium vacancies, which in turn affects the parameters of the unit cell. In addition, the synergistic migration effect between lithium ions also lead to a decrease in the energy barrier for lithium-ion migration. This paper was to use first-principles calculations to investigate the effects of lithium vacancy concentration and synergistic migration on the lithium-ion migration energy in layered materials (i.e., LiCoO2, LiNiO2) and spinel material (i.e., LiMn2O4).MethodFirst principles calculations in this work were conducted using the DS-PAW package, which is based on the density functional theory (DFT) framework and the projector augmented wave (PAW) approach. The basis set is in the form of plane waves, and the cutoff energy is set to be 500 eV. The Monkhorst-Pack scheme was used to integrate the Brillouin zone. The calculations for the models of the Li1&#x2212;xCoO2 and Li1&#x2212;xNiO2 in supercells of 2×2×1, 3×3×1, and 4×4×1 were performed using the k-point meshes of 5×5×2, 3×3×2, and 2×2×2, respectively. The calculations for the models of the LixMn2O4 and LixTi2O4 in supercells of 1×1×1, 2×2×1, and 3×3×1 were performed using the k-point meshes of 3×3×3, 2×2×3, and 1×1×3, respectively. The exchange-correlation interactions were treated with Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) formalism. The strong correlation effects of the 3d electrons were considered by using the GGA+U method, with effective U value (Ueff) of 4.91, 5.00, and 3.50 eV for Co, Ni, and Mn, respectively. All atomic positions and cell parameters were relaxed using the conjugate gradient method until the maximum force on each atom was less than 0.03 eV/. The energy convergence criterion for the self-consistent field (SCF) loop was set to 10–5 eV. The activation barriers for Li-ion migration were determined through the climbing image nudged elastic band (CI-NEB) method, and the convergence criterion for the forces on the transition state images was set to 0.1 eV/.Results and discussionThe results show that in LiCoO2 material, the lithium-ion migration energy for the 2×2×1 supercell is significantly smaller than that of other supercells by using the CI-NEB method to calculate the lithium-ion migration energy barrier. This is because the 2×2×1 supercell of LiCoO2 has a higher concentration of lithium vacancies, which can increase the interlayer distance and decrease in the lithium-ion migration energy. In addition, there are still some differences in the energy for lithium ion migration when different supercells of LiCoO2 have the same interlayer distance. The synergistic migration effect of lithium ions can lead to a decrease in the energy for lithium ion migration when there are more lithium ion migration pathways in the LiCoO2 supercell when LiCoO2 is expanded to the same size. Also, the same pattern in LiNiO2 material occurs.The results show that the higher the concentration of lithium vacancies in spinel materials is, the smaller the energy for lithium ion migration will be, after applying the same treatment to spinel materials LiMn2O4 and LiTi2O4. Unlike layered materials, however, the synergistic migration effect of lithium ions in spinel materials does not have a significant impact on the energy for lithium ion migration. This is because the interaction between transition metals and lithium ions has a certain hindering effect on lithium ion migration when lithium ions migrate in spinel materials.ConclusionsThe calculation results indicated that in layered materials like LiCoO2 and LiNiO2, the lower the concentration of lithium vacancies was, the smaller the interlayer distance would be, thus increasing the activation barrier for lithium-ion migration. The migration energy barriers for lithium ions within the 3×3×1 and 4×4×1 supercells of LiCoO2 were similar, indicating that the energy barriers derived from these supercells could be considered as a representative of the migration energy barriers in the stoichiometric ratio of LiCoO2. The synergistic migration effect of lithium ions in layered materials reduced migration energy, while the synergistic migration effect of lithium ions in spinel materials was not significant.

IntroductionCompared with organic lithium-ion batteries, all-solid-state batteries are expected to improve battery safety and energy density simultaneously. They have attracted extensive attention. The ideal solid electrolyte material should have the basic properties of electronic insulation, wide electrochemical window, good interface compatibility and high ionic conductivity. Many types of solid electrolyte materials are reported, including oxides, sulfides, halides, borohydrides and phosphates, each of which has advantages and disadvantages. For instance, lithium-based halide and sulfide solid electrolytes have a high ionic conductivity but a narrow electrochemical window, and they are unstable to lithium metal negatives. The interface compatibility between oxide solid electrolyte and electrode is poor, and lithium dendrites grow rapidly along the grain boundary in oxide solid electrolyte. To further develop all-solid-state batteries with a higher energy density, a longer cycle life and a higher safety, solid electrolyte materials with excellent comprehensive performance must be designed. Anti-perovskite superionic conductors based on cluster anions have attracted much attention due to their potential applications in solid electrolytes for rechargeable batteries. However, little theoretical studies on the phase stability, electrochemical stability and interface compatibility of anti-perovskite X3OBH4(X=Li, Na) materials have been reported yet. In this work, the electronic structure, phase stability, electrochemical stability, interface compatibility, mechanical properties and ion transport properties of anti-perovskite X3OBH4(X=Li, Na) materials were systematically investigated via first-principles calculation.MethodsAll the calculations were performed based on density functional theory (DFT) by a projector augmented wave method, as implemented in the Vienna ab initio Simulation Package (VASP). The generalized gradient approximation (GGA) with Perdew–Burke–Ernzerhof (PBE) was applied to treat the electronic exchange-correlation interactions. The cutoff energy was set to 520 eV. The crystal structure was fully relaxed until the convergence criteria for each atomic force and energy were less than 0.02 eV/ and 10–5 eV, respectively. Based on electrochemical energy storage materials design platform (bmaterials.cn), the phase stability and interfacial stability (including electrochemical and chemical stability) of X3OBH4(X=Li, Na) were evaluated.Results and discussionThe results show that X3OBH4(X=Li, Na) is a thermodynamically metastable and wide-band insulator at 0 K, which is unstable at a high pressure. Based on the energy calculated by DFT, the phase diagrams of Na-NaBH4-O2 and Li-LiBH4-O2 are constructed, respectively, and the calculated Ehull of Li3OBH4 and Na3OBH4 is 52.4 meV/atom and 110.7 meV/atom, respectively. X3OBH4(X=Li, Na) is thermodynamically unstable at 0 K. Since the Ehull value is relatively small, it is possible to stabilize the compound through the regulation of external conditions such as high temperature, high pressure and high entropy. Based on the lithium (sodium) giant potential phase diagram of the constructed X-O-B-H quaternary system, the voltage distribution and phase equilibrium of X3OBH4(X=Li, Na) in the process of lithiation/delithiation are calculated by DFT. The electrochemical window range of X3OBH4(X=Li, Na) is 0.53–0.93 V and 0–0.41 V, respectively. The corresponding decomposition product XBH4(X=Li, Na) has a wide electrochemical stability window, which can protect the solid electrolyte. The calculated moduli of B, E and G of X3OBH4 (X=Li, Na) are greater than those of lithium (sodium) metal or even Li3PS4 electrolyte, indicating that X3OBH4 (X=Li, Na) can effectively block the growth of lithium (sodium) dendrites and has a good mechanical contact at the electrode/solid electrolyte interface. In addition, the low migration barriers of X3OBH4(X=Li, Na) are 0.34 eV and 0.35 eV, respectively, and the ionic conductivity at room temperature can reach 10–4 S/cm. The rotation of the superhalogen promotes the movement of the lithium/sodium ions, thereby increasing their ionic conductivity.ConclusionsThe electronic properties, phase stability, electrochemical stability, chemical stability, mechanical properties and ion transport mechanism of the anti-perovskite type X3OBH4(X=Li, Na) were systematically investigated via first-principles calculation. The results showed that the crystal structure of X3OBH4(X=Li, Na) could be a metastable electronic insulator with a wide band gap. Under electrochemical oxidation conditions, X3OBH4(X=Li, Na) could be thermodynamically unstable and easily oxidized at relatively high voltages. However, the decomposition products could form a protective layer at the interface, preventing the electrolyte from further reacting and providing an improved electrochemical stability. In addition, X3OBH4(X=Li, Na) also had a good interface compatibility with typical cathode materials. The calculated mechanical properties indicated that X3OBH4(X=Li, Na) was brittle. However, their relatively large shear modulus indicated that they could be stable for lithium/sodium metal dendrites growth. By CI-NEB calculation, X3OBH4(X=Li, Na) showed a low migration barrier. In summary, these theoretical results could favor to better understand the thermodynamic and kinetic processes of X3OBH4(X=Li, Na), and provide a theoretical guidance for the development of high-performance solid electrolytes.

IntroductionConventional liquid electrolyte-based lithium-ion batteries have achieved a great commercial success. However, their energy density has theoretical limits, and safety concerns such as electrolyte leakage and thermal runaway remain. Replacing liquid electrolytes with inorganic, nonflammable solid electrolytes can significantly enhance battery safety and potentially enable the application of lithium metal anode in all-solid-state batteries (ASSBs), thereby further improving the energy density. Recent development on solid electrolyte materials has advanced rapidly, with significant improvements in ionic conductivity. Among them, halide electrolytes exhibit a high oxidative stability (i.e., ~4 V) and an excellent compatibility with high-voltage cathodes. However, cations (e.g., Zr4+, Al3+, In3+, Y3+) in the electrolyte reduce when halide electrolytes come into contact with lithium metal, forming metallic or alloy phases. These electronically conductive phases could cause continuous electrolyte decomposition, ultimately leading to battery failure. To improve interfacial stability, some strategies such as electrolyte doping, introducing interfacial buffer layers, and employing bilayer solid electrolyte structures are implemented to suppress interfacial reactions. However, the selection of buffer layer materials remains limited to a few commonly used compounds, and the degradation mechanisms at the lithium metal/halide electrolyte interface are still unclear in the atomic scale. This study was to employ theoretical calculations to systematically analyze the interfacial reaction between halide electrolytes and lithium metal, including the electronic conductivity of interfacial reaction products and the effects of volume changes.MethodesThe reaction phase equilibria between two contacting solid materials could be constructed by the Pymatgen (Python Materials Genomics) module. Based on enthalpy data retrieved from the Materials Project (MP) database, the interfacial reaction energy was calculated to predict the thermodynamic stability of different materials. This approach is widely used to study the interfacial stability between electrolytes and electrodes in batteries. The fundamental principle is to conceptualize two contacting materials, A and B, as a pseudo-binary system:Cinterface(cA,cB)=xcA+1&#x2212;xcB(1)where x is the mole fraction of component A. The total energy of the pseudo-binary interfacial system can be described as the sum of the energies of components A and B, each weighted by their respective mole fractions:EinterfacecA,cB,x=xEcA+1&#x2212;xEcB(2)The interfacial reaction energy is described as the reaction energy of the pseudo-binary interfacial system minus the decomposition energies of components A and B:ED,mutualcA,cB,x=minx∈0,11NEeq,interfacexcA+1&#x2212;xcB&#x2212;xEDcA&#x2212;1&#x2212;xEDcB(3)where Eeq, interface is the interfacial reaction energy of the pseudo-binary interfacial system; ED(cA) and ED(cB) are the decomposition energies of components A and B, respectively; ED can be obtained by searching the chemical space of all elements of the components and constructing the phase diagram. N is the total number of atoms involved in the reaction. The molar percentage of the electronically conductive phase in the interfacial products is calculated and used as a descriptor for the electronic conductivity of the interphase layer after constructing the reaction phase equilibrium between A and B. The higher the molar percentage is, the stronger the electronic conductivity of the interface layer will be.For interface reaction phase equilibrium: xAA + xBB → xCC + xDD + xEE + …. The volume change rate Vc induced by the interfacial reaction can be calculated byVc=xCvC+xDvD+xEvE+&#x22EF;&#x2212;xAvA+xBvBxAvA+xBvA×100%(4)where x is the stoichiometric number of different components in the phase equilibrium; v is the volume of the reactant and product per unit molecule.Results and discussionThe properties of interphases formed between Li-metal and solid electrolyte play a crucial role in the performance of all-solid-state batteries (ASSBs). If the interphase layer exhibits a mixed electronic and ionic conductivity (MIEC), continuous electrolyte decomposition will occur during battery cycling, thus leading to an increased interfacial resistance and an accelerated performance degradation. The complex interfacial reactions generate various interphases, whose volumes may change relative to the reactants (lithium metal and electrolyte). If the interphase layer undergoes volume shrinkage, interfacial separation may occur, exacerbating the inhomogeneous distribution of the interfacial electric field and current. It promotes lithium dendrite nucleation and growth at the interface. The calculation results indicate that the CPP of the interphase layer between halide electrolytes and Li-metal exceeds 9%, leading to the formation of MIEC, which can accelerate electrolyte decomposition during cycling. In addition, the volume shrinkage of interfacial interphase layer (Vc < –17.4%) can also further intensify interfacial separation and dendrite growth. Therefore, optimizing electrolyte composition to reduce interfacial reactivity as well as minimizing CPP and Vc are critical for improving ASSB performance. Based on these interfacial reaction characteristics, selecting coating materials that effectively suppress interfacial reactivity, form a passivating interphase, and exhibit minimal volume changes can significantly enhance the interfacial stability between the Li-metal anode and the electrolyte.ConclusionsHalide electrolytes exhibited an intrinsic thermodynamic instability with Li-metal, originating from the reduction of metal cations in the electrolyte into metallic and alloy phases, with a CPP ranging from 9% to 20%. The presence of these electronically conductive phases rendered the interphases layer a MEIC, leading to continuous reduction of the electrolyte during battery cycling. Also, the interfacial reaction between Li-metal and Li-MF (M = Zr, Nb, Al, Ga, In, Ge, Sn) resulted in interphase layer that underwent volume contraction, with a volume change rate ranging from –36.2% to –17.4%. This could lead to interface separation and the formation of local voids at the interface, which was experimentally confirmed. These phenomena significantly impacted Li-metal deposition and dendrite growth, further deteriorating the performance of Li-metal ASSBs. Based on the interfacial reaction characteristics between Li-metal and halide electrolytes (Vc < –17.4%, CPP > 9%), high-throughput screening was performed to identify materials that could effectively passivate the interface and mitigate reaction-induced volume changes, thereby enhancing the performance of ASSBs. The screening identified binary materials like Li3N and Li3P, along with the ternary material Li9NS3. These materials were validated to enhance the stability of the Li-metal/electrolyte interface, confirming the scientific validity and effectiveness of the screening criteria.

IntroductionAqueous electrolytes have potential applications in electrochemical energy storage devices due to their intrinsic non-flammable properties. Though its electrochemical stability window is narrow and normally it is hard to form effective solid electrolyte interphase, some researchers conduct in-depth research and propose several related solutions. Water-in-salt (WiS) electrolytes, as one of super-concentrated aqueous electrolytes, become one of the most promising systems. Some studies indicate that they can maintain a good electrochemical performance in a wide temperature range. However, its microscopic mechanism is still unclear. Therefore, in this paper, the microscopic structure and dynamic properties of LiTFSI-based aqueous electrolytes were investigated via molecular dynamics simulations.MethodsAll-atom classical molecular dynamics simulations were performed by using a software package named LAMMPS. The calculated system was composed of Li cation, TFSI anion and water molecules. The 20 mol/kg salt concentration system was selected as a main research object, and the component ratio was LiTFS:H2O of 128:355. In addition, a system with a salt concentration of 3.5 mol/kg (LiTFSI:H2O of 32:507) was also used as a comparison for simultaneous study. The selection principle of the two systems was to be consistent with that of the previous work. The force field parameters also followed the previous selection, where the simulation results were verified via the experimental data. Each system was simulated at different temperatures (i.e., 253, 273, 298, 323 K, and 343 K). For each salt concentration system, a relatively large simulation box was established and randomly put the corresponding number of particles into the box. Afterwards, the equilibrium system at each temperature was obtained through the initial structure optimization, and the heating or cooling procedure under the NPT ensemble. Finally, the production runs of 100–200 ns was carried out under the NVT ensemble, and the results of this step were used for post-analysis. In the whole production runs, the simulation timestep was 1 fs, and the data output interval was 50 fs for stress tensors, 1 ps for unwrapped coordinates, and 10 ps for trajectory-based analysis.Results and discussionsThe RDF calculations indicate that in the super-concentrated system (20 mol/kg), it is hardly affected by temperature, and at a lower concentration (3.5 mol/kg), the peak value is slightly affected by temperature. This indicates that the microscopic solvation structure between Li and water molecules in the high concentration system is more thermodynamically stable. To further explain this phenomenon, we calculate the potential of mean force (PMF). The results show that the solvation binding energy and activation energy of Li–Ow in the high concentration system both are almost temperature-independent, while the low concentration system shows a certain temperature dependence for the activation energy differences of 1–2 kBT in the temperature range.Furthermore, the connection matrix analysis (where the red region represents a closer contact distance between the two atoms and a higher binding strength) show that this part is mainly from Li–Ow, Li–O, Hw–O, Hw–O four pairs. The first two pairs represent O atom from the first solvation shell of Li, and the latter two groups represent the hydrogen bonds. In addition, the yellow region represents that although the contact distance between atoms is relatively far (i.e., still within 3 ), the binding strength is still high, such as Li–Hw, Li–S, Hw–S, Ow–O, Ow–Ow, O–O pairs. The connection matrix also gives important information that the Li–Li pair is formed at a distance of about 3 , which is an interesting phenomenon.The properties of Li–Li dimers in high concentration systems are investigated. Through the RDF, the first peak appears at 3 , and the peak gradually increases as the temperature decreases, implying a more intense binding or a longer binding time. From the auto-correlation function (ACF) and the lifetime of the dimer existence, the ACF decreases rapidly with the increase of temperature, and the lifetime decreases significantly from 8500 ps to 160 ps, which is consistent with the Brownian motion and can also be confirmed via the analysis of dynamic properties.Also, the relationship among the viscosity, diffusion coefficient, ionic conductivity and their temperature dependence of the two studied systems is analyzed. In general, the dynamic properties are obviously affected by temperature, both in high concentration system and low concentration system. In the analysis of the ionic conductivity, the Haven ratio is calculated to characterize the effect of collective diffusion in the system. The results show that the collective diffusion behavior in the high concentration system significantly affects the ionic conductivity, and is independent of temperature. At a low concentration, the effect of collective diffusion on ionic conductivity changes with temperature, and the effect gradually disappears at high temperatures.ConclusionsIn this work, molecular dynamics simulations were used to investigate the microscopic structure and dynamic properties of a typical aqueous electrolyte at two concentrations and their performance in a wide temperature range. The thermal stability of the micro-solvation structure of the high concentration system was analyzed via the RDF and PMF, providing a microscopic explanation for the excellent performance of super-concentrated aqueous electrolyte at extreme temperatures. The analysis of the connection matrix could further clarify the microscopic picture of the studied system. The analysis of the properties of Li–Li dimers could be related to the structure and dynamic behavior. The study of dynamic properties such as viscosity, diffusivity and conductivity showed the intrinsic coupling between them and their relationship with structural properties. In particular, the coupling relationship between collective dynamics and conductivity in two different concentration electrolyte systems was proposed and compared.

IntroductionLithium-metal batteries (LMBs), as next-generation high-energy-density battery technologies, have attracted considerable attention due to their theoretical energy density (i.e., approximately 3860 mA·h/g), which far exceeds that of conventional lithium-ion batteries (LIBs). This makes LMBs highly promising for applications in electric vehicles, portable electronic devices, and other fields. Compared to conventional LIBs with a theoretical capacity of 372 mA·h/g for graphite anodes, LMBs can offer a longer battery life or a higher energy output, thus addressing the energy density bottleneck faced by the existing energy storage technologies. As a result, LMBs are widely regarded as an important direction for the future development of battery technologies. However, despite the significant advantages of LMBs in terms of energy density, the use of lithium metal anodes still has some challenges. Some issues like dendrite growth and instability of the solid electrolyte interphase (SEI) severely restrict their practical application. It is thus critical to suppress lithium dendrite growth and improve the stability of SEI.Although the existing studies propose the use of artificial interphase layers to optimize the stability and safety of lithium metal anodes, there is a lack of systematic theoretical guidance, particularly in terms of how to regulate the composition and structure of the interphase layer. This study was to construct functional artificial interphase layers on the lithium metal anode surface by molecular self-assembly techniques. This study also regulated the SEI performance via utilizing self-assembled molecules with varying fluorine contents, thus enhancing the stability and safety of lithium metal anodes and providing a theoretical basis for future interface layer design in lithium metal batteries.MethodsThis study used the density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations to systematically investigate the interaction and structural evolution of self-assembled molecules with different fluorine contents on lithium metal surfaces. The focus was to clarify how fluorine-terminated molecular structures could affect the performance of the organic-inorganic composite artificial interphase layer.The calculations were performed by a Vienna Ab-initio Simulation Package (VASP) based on the density functional theory. The VASP employs the projector-augmented wave (PAW) method and the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA). All the calculations used -point centered Brillouin zone sampling to ensure accuracy. The PAW method was used for electron-ion interactions with an energy cutoff of 450 eV. Convergence criteria for energy and force were set at 1×10–4 eV and 0.05 eV/, respectively. The van der Waals interactions were determined by the DFT-D3 method. The density of states (DOS), charge differential density, and Bader charge distribution were calculated to characterize an interfacial electronic behavior. Organic-inorganic composite interphase layers were constructed by the molecular models with varying fluorine termini (i.e., F1:C9H19F, F3:C9H17F3), and the molecular adsorption behavior was analyzed by coverage gradient models to evaluate the adsorption stability through formation energy calculations. The AIMD simulations were conducted to explore the dynamic behavior of the interphase layer. The 20 ps simulations were performed at 300 K (Nos-Hoover thermostat) with one time step of 1 fs. Lithium ion diffusion coefficients were calculated via mean square displacement (MSD), and the structural characteristics of the interphase layer were analyzed via radial distribution functions (RDF) and coordination numbers.Results and discussionThis study systematically reveals the regulatory mechanisms of fluorine-terminated self-assembled molecules on lithium metal anode interphase layers based on theoretical calculations and dynamic simulations. On the Li(100) lithium metal surface, higher fluorine content molecules (F3:C9H17F3) exhibit stronger interfacial binding capabilities. The fluorine groups at the molecule heads react with lithium to form LiF as molecular coverage increases, significantly reducing the system formation energy and thereby enhancing the stability and density of the interphase layer. At a high coverage, the fluorine atoms at the heads of F3 molecules reactwith lithium to form an amorphous LiF layer with a thickness of 6.2 (compared to 3.8 for the F1 system), substantially inhibiting interfacial structural relaxation. The DOS analysis indicates that in the LiF layer formed by the F3 system, Li–F orbitals overlap significantly at –7.5 eV, indicating a strong ionic bonding. The interfacial electrostatic potential is lower for the F3 system (–4.87 eV), and the thicker LiF layer formed by F3 molecules results in a a wider negative potential region, and more conducive to lithium ion intercalation/extraction. Lithium ion diffusion dynamics analysis shows that the interphase layer formed by trifluorinated molecules is more stable based on the AIMD simulations with a thickness of 6.2 and a lithium ion diffusion coefficient of 4.76×10–6 cm2/s, indicating a superior lithium ion transport performance. In contrast, the interphase layer formed by monofluorinated molecules has a lithium ion diffusion coefficient of 1.37×10–5 cm2/s, showing a relatively inferior lithium ion transport performance.ConclusionsThis study used the DFT and AIMD simulations to systematically explore the interaction processes of self-assembled molecules with varying fluorine contents on lithium metal surfaces, and investigate the regulatory effects of fluorine-terminated groups on the performance of the organic-inorganic composite artificial interphase layer. The introduction of fluorine-terminated groups optimized the electronic structure of lithium metal, promoted lithium ion diffusion, and effectively inhibited electron transmission to the organic molecular layer, thereby enhancing an interphase layer stability. Increasing fluorine content enhanced the ionic nature of Li–F bonds, significantly reducing lithium vacancy formation energy and bonding strength, and improving lithium ion migration capability in the interphase layer. The interphase layers formed by trifluorinated self-assembled molecules had thicker structures, higher lithium ion diffusion coefficients, and exhibited a superior stability. This research elucidated the regulatory mechanisms of fluorine-terminated self-assembled molecules on lithium metal anode interphase layers in the atomic scale, providing a theoretical foundation for the design of high-performance lithium anode interphase layers based on molecular engineering, and extended the application prospects of self-assembly technology in the field of energy storage.

IntroductionSolid polymer electrolytes (SPEs) are pivotal for advancing all-solid-state lithium batteries (ASSLBs) due to their flexibility, processability, and compatibility with existing manufacturing processes. However, their practical application is hindered due to their low ionic conductivity and insufficient mechanical strength at room temperature. The existing research focuses on enhancing ionic conductivity through lithium salt optimization, polymer modification, or nanoparticle incorporation, the interplay between mechanical deformation and electrochemical performance remains underexplored. Previous studies reported that the mechanical pre-deformation (e.g., stretching or compression) can alter the microstructure of SPEs, thereby affecting ion transport. A unified understanding of how mechanical pre-deformation synchronously improves both ionic conductivity and mechanical properties (i.e., critical for structural integrity during battery operation) is still lacking. This study was to address this gap via systematically investigating the mechanical-electrochemical coupling effects on poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide (PEO-LiTFSI) SPEs under mechanical pre-deformation. This work was to establish a predictive model for SPE performance optimization and provide guidelines for designing high-performance ASSLBs.MethodsPEO-LiTFSI membranes were synthesized by dissolving PEO (Mw=600000) and LiTFSI (mass ratio 1.000:0.404) in acetonitrile, followed by casting and drying under controlled humidity (H2O≤0.1 mg/L). The samples were subjected to tensile or compressive pre-strain (i.e., 10%–20% compression, 50%–80% tension) at elevated temperatures (above melting point) by universal testing machines, followed by rapid cooling to room temperature. The ionic conductivity was determined by electrochemical impedance spectroscopy (EIS) in a CHI660E workstation. The elastic modulus and yield strength were measured via quasi-static tensile tests. The free volume changes were analyzed by positron annihilation lifetime spectroscopy (PALS). Then, a coupled electrochemical-mechanical model was proposed in COMSOL to simulate the stress distribution and lithium diffusion in ASSLBs. The model incorporated temperature- and strain-dependent material parameters derived from the related experimental data.Results and discussionThis study reveals that the mechanical pre-deformation, particularly compression, significantly enhances both the ionic conductivity and mechanical properties of PEO-LiTFSI solid polymer electrolytes (SPEs). The results demonstrate that in the presence of 20% pre-compression, the ionic conductivity is increased by 4.4 times at 20 ℃, while the elastic modulus and yield strength can be enhanced by 1.60 times and 1.45 times, respectively. These enhancements are attributed to the microstructural changes induced by pre-deformation. The results by positron annihilation lifetime spectroscopy (PALS) confirm an 18% increase in normalized free volume (vf/vfo), which reduces Li+ migration barriers and facilitates ion transport. Polymer chain alignment under compression strengthens interchain interactions, countering a potential mechanical weakening from free volume expansion and improving stress distribution homogeneity. The simulations further validate these findings, showing that pre-compressed SPEs exhibit more uniform tensile stress near the electrolyte/electrode interface, thereby delaying the plastic deformation and extending the elastic working range. Despite a modest 7.7% increase in interfacial stress, the concurrent 17.5% increase in yield strength ensures a mechanical integrity during high-rate operation. In addition, a unified Arrhenius-based model incorporating temperature- and strain-dependent parameters accurately predicts the SPE behavior, with average relative errors of 8.4% for ionic conductivity and 3.6% for elastic modulus, confirming its utility for performance optimization. These results highlight the dual benefits of mechanical pre-compression, i.e., enhancing ion transport while fortifying structural robustness, and provide actionable insights for designing high-performance, durable all-solid-state lithium batteries.ConclusionsThis study demonstrated that the mechanical pre-compression (i.e., 10%–20% strain) could be an effective strategy to simultaneously enhance the ionic conductivity, elastic modulus, and yield strength of PEO-LiTFSI solid polymer electrolytes (SPEs), addressing critical challenges in their engineering application. The improvements could be attributed to the synergistic effects of increased free volume, facilitating Li&#x207A; ion transport and polymer chain orientation, which strengthening interchain interactions and homogenizes stress distribution. A unified Arrhenius-based model could capture the temperature- and strain-dependent evolution of SPE properties, enabling the predictive optimization for diverse operating conditions. The simulations further revealed that the pre-compressed SPEs exhibited more uniform interfacial stress profiles and higher mechanical resilience, expanding a usable rate capability of all-solid-state lithium batteries while maintaining structural integrity. These findings could establish mechanical pre-deformation as a viable pathway to design high-performance SPEs and advance the development of durable, high-energy-density solid-state batteries.

IntroductionSolid-state electrolytes are critical for advancing lithium-ion battery technologies due to their potential to provide higher safety, improved energy density, and better long-term stability, compared to conventional liquid electrolytes. Among solid-state electrolytes, sulfide-based materials such as Li6PS5Cl (LPSC) are especially promising because of their high ionic conductivity, low interface impedance, and mechanical flexibility. LPSC has an argyrodite structure that inherently offers abundant lithium-ion migration pathways, ensuring efficient ionic transport. However, practical applications of LPSC are often hindered in the presence of intrinsic defects, such as lithium vacancies and LiCl substitutions, thus altering the local atomic environments and macroscopic ionic transport properties. Conventional computational methods like ab initio molecular dynamics (AIMD) offer a quantum-level precision, but are computationally prohibitive in large scales, whereas classical empirical potentials lack the accuracy to capture complex defect-induced local rearrangements. Therefore, developing a computational method that combines quantum accuracy with large-scale simulations remains an important challenge.MethodsThis study used a deep learning-based large-atom model (DPA-SSE), employing a "pretraining–fine-tuning–distillation" strategy specifically designed for sulfide solid electrolytes. Initially, the model was pretrained based on extensive density functional theory (DFT) data covering diverse sulfide materials and defect structures. Subsequently, it was fine-tuned using a carefully selected subset of 551 high-value DFT configurations specifically related to LPSC and its defect environments, chosen from a larger dataset of 11631 configurations. These configurations included comprehensive DFT-calculated energies, atomic forces, and virial stress tensors. The fine-tuned model could achieve a quantum-level precision with a significantly reduced mean absolute error in predicting energies and forces. Finally, a distilled model was proposed via leveraging the fine-tuned model to label extensive datasets efficiently, enabling simulations of large-scale systems with thousands to millions of atoms in nanosecond time scales.Results and discussionThe molecular dynamics simulations are conducted to systematically investigate the effect of LiCl defect concentration on the ionic conductivity in LPSC at different temperatures by the distilled DPA-SSE model. At a lower temperature (i.e., 333 K), the simulations show that introducing LiCl defects moderately improves the ionic conductivity, compared to pristine LPSC, indicating that defects at a low concentration can create a beneficial local disorder facilitating ion transport. However, at an elevated temperature (i.e., 500 K), the simulations clearly demonstrate a negative correlation between ionic conductivity and increasing defect concentrations. Specifically, the measured ionic conductivities at different defect concentrations (i.e., 0%, 3.8%, and 7.7%) are approximately 3.23 × 10–2, 2.06 × 10–2 S/cm, and 1.36 × 10–2 S/cm, respectively. The reduced ionic conductivity at higher defect concentrations is attributed to an increased structural instability, leading to a partial decomposition or a significant rearrangement of PS4 tetrahedral units, which form critical frameworks for efficient ion migration. The radial distribution function (RDF) analysis further corroborates these findings, showing intensified local coordination and disrupted ion diffusion pathways at higher defect levels.ConclusionsThis work demonstrated the feasibility and effectiveness of using a deep learning-based large-atom model to accurately and efficiently simulate ionic transport in defect-rich sulfide solid electrolytes. The "pretraining–fine-tuning–distillation" approach significantly reduced the computational cost associated with conventional quantum mechanical simulations, while maintaining a high predictive accuracy. This study provided valuable theoretical insights that could inform the design and optimization of high-performance solid-state electrolytes via revealing the intricate relationship among defect concentrations, local structural dynamics and ionic conductivity. Moreover, the methodological framework presented could have a broad applicability, offering a powerful and scalable computational tool for studying a variety of complex materials in energy storage applications.

IntroductionSolid-state lithium batteries are regarded as a promising alternative to traditional lithium-ion batteries due to their high energy density and safety. The development of solid electrolytes with high ionic conductivity is key to their application. The lithium-ion transport mechanisms in solid electrolytes can be categorized into single-ion migration and multi-ion correlated migration. Generally, multi-ion correlated migration can significantly reduce energy barriers compared to single-ion migration, making the promotion of correlated migration a crucial principle in designing solid electrolyte materials with high ionic conductivity. Titanite-type LiTaSiO5 is a new oxide solid electrolyte, in which Zr&#x2084;&#x207A; doping at Ta&#x2075;&#x207A; site introduces excess lithium ions, facilitating correlated migration and significantly improving ionic conductivity. However, the relationship between lithium-ion distribution, correlated migration, and ionic transport properties still require in-depth investigation. In this study, ab initio molecular dynamics (AIMD) simulations were employed to investigate the possible Li sites and migration channels in the monoclinic titanite-type Li1+xTa1&#x2212;xZrxSiO5(x = 0, 0.125) systems. The relationships between lithium-ion distribution, the degree of correlated migration, and ionic transport properties were also elucidated.MethodsAIMD simulations were performed using the Vienna ab initio simulation package (VASP) with the plane wave projector augmented (PAW) method and the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional. For the pristine LiTaSiO5 (ICSD No. 39648, space group P21/c), a 2×2×2 supercell was constructed, containing 32 formula units (256 atoms total). For the Zr-doped system, four Ta5+ were substituted with Zr4+, with four additional Li+ ions incorporated to maintain charge neutrality. AIMD simulations were carried out for the canonical (NVT) ensemble using a Nos&#x2212;Hoover thermostat at four elevated temperatures (800, 1000, 1200, and 1400 K) with a time step of 2 fs. To enhance computational efficiency, the plane-wave basis set was determined with a cutoff energy of 400 eV and integration in reciprocal space was performed at the -point only. All the structures were heated from 100 K to targeted temperatures by velocity scaling over 2 ps, and then equilibrated at the desired temperature for 20 ps. The analysis of possible Li sites, jump events, and diffusion properties based on AIMD data was performed using our in-house developed code, which is integrated into our group’s computational platform for electrochemical energy storage materials design (bmaterials.cn).Results and discussionThe framework structure of the monoclinic titanite-type LiTaSiO5 consists of SiO4 tetrahedra and TaO6 octahedra. Through crystal structure analysis, we identified 11 distinct interstitial sites (It1–It11), where the It1 site corresponds to the Li1 lattice site while It2 and It3 sites align with two previously reported potential interstitial sites. Lithium ion migration exhibits strong preference for specific channels. At 800 K, 81.8% of jumps occur along the It2–Li1/It4–It7–It3–It7–Li1/It4–It2 channel ([101] direction) through elementary channels (Li1–It2, Li1–It7, It2–It4, It3–It7 and It4–It7), clearly identifying this as the optimal long-range migration channel. The non-unity occupation probabilities at all sites indicate Li+ disorder, with primary Li+ distribution at Li1, It2, It3, It4, and It7 sites. Previous studies confirm that Li1 is the lowest-energy stable site, while It2 and It3 serve as saddle points in the energy landscape. Zr doping significantly alters the Li+ distribution by increasing the Li+ concentration and promoting occupation of higher-energy sites. At 800 K, Li1 occupancy decreases from 41.8% to 33.1%, while It2 and It3 occupancies increase dramatically from 7.2% to 27.9% and from 7.4% to 24.3%, respectively. This redistribution, accompanied by increased configurational entropy, enhanced Li+ disorder and promotes low-energy-barrier correlated migration. As a result, the correlated migration percentage increases, the overall activation energy decreases, and the Li+ diffusion coefficient improves significantly.ConclusionsThe main conclusions of this study are summarized as following. The LiTaSiO5 unit cell contains 11 distinct types of interstitial sites and shows anisotropic lithium-ion transport along the [101] direction through the It2–Li1/It4–It7–It3–It7–Li1/It4–It2 channel. After Zr doping, the lithium-ion concentration increases, leading to higher occupancy of lithium ions at high-energy sites (It2/It3), more disordered lithium-ion distribution, and an increase configurational entropy. This Li distribution enhances the probability of low-energy-barrier correlated migration, resulting in a higher correlated migration percentage, reduced overall activation energy, and significantly improved ionic transport performance.The methodologies employed in this study are applicable to inorganic crystalline solid electrolytes with stable framework structures, which have been successfully applied in previous studies to several representative lithium/sodium solid electrolytes, such as LiTa2PO8 and Na3Zr2Si2PO12. However, these methods rely on the framework ions to identify the positions of lithium ions during the migration processes, making them unsuitable for certain specific solid electrolyte systems, such as amorphous solid electrolytes or those exhibiting the polyanion rotation effect.

As energy sources diminish and ecological damage escalates, exploring green energy conversion and storage technologies becomes crucial. Electrocatalysis effectively converts green energy into chemical energy through electricity. In general, these reactions occur at double-layer interfaces, amidst a complex interface environment. It is essential for advancing electrochemistry research and the development of green energy technologies to clarify the interplay of ion-electron interactions, local potentials and electric fields. In the past decades, some researches on surface electrocatalysis have made significant progress since the standard hydrogen electrode model proposed by Nrskov et al. The model has effectively explained some origins of catalytic performance, and predicted some catalytic activity trends. However, the model has some limitations. The “electrocatalysts” encompass both “electricity” and “catalysts”. In this model, ignoring the potential effect on the electronic properties of catalysts leads to the deviation from experimental results. In addition, the failure to consider the influence of the solution in theoretical calculations also becomes another factor affecting the reaction process.This review represented the development and application on the Fixed Potential Method (FPM) based on first-principles calculations in complex interfacial electrochemistry. FPM emerges as a powerful tool for elucidating electrochemical reaction mechanisms, predicting material properties, and optimizing the design of electrochemical systems. The FPM significantly enhances the accuracy of simulating electrochemical reactions via precisely controlling the Fermi level of the reaction system and maintaining a constant electrode potential throughout simulations. Nowadays, FPM is extensively applied in the field of electrocatalysis to investigate the potential effects on the mechanisms of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Some work on transition metal-doped graphene (TM@graphene) catalysts reveal that the applied potential significantly affects the adsorption capacity of catalytic intermediates, charge transfer processes, and reaction pathways. The charge states of reaction intermediates exhibit a strong linear dependence on the applied potential, highlighting the importance of potential effects in catalytic mechanisms. In the realm of lithium-ion batteries, FPM is used to investigate the phase transformation processes of electrode materials. Some studies show that activation polarization induces a phase transition from the 2H phase to the 1T’ phase in MoS2, which is crucial for understanding capacity fade in lithium-ion batteries. A research provides a theoretical framework for predicting phase transformations and discharge behavior via constructing an electrochemical phase diagram and fitting discharge curves based on zero-charge potential. In addition, FPM elucidates the concerted proton-electron transfer mechanism in proton migration within the electric double layer. Some studies demonstrate that proton migration from the outer Helmholtz layer to the electrode surface is accompanied by electron transfer, thus facilitating the migration process. The free energy changes during proton migration are affected by the applied potential and the local pH value gradient near the electrode surface, providing a theoretical basis for optimizing proton transport processes. These discoveries can enhance the comprehension of electrochemical interfacial reactions, and provide invaluable insights for the development of innovative catalysts and energy storage materials.Summary and prospectsFPM is proven to be an advanced computational method with broad application prospects in electrochemical research, such as exploring the potential effects in electrocatalytic water splitting, the activation polarization in the kinetics of lithium-ion batteries, and the concerted mechanism of proton-electron transfer within the electric double layer. These applications reveal the profound potential effects on the catalytic intermediate adsorption, charge transfer, and reaction pathways in both OER and ORR. Some researches on material phase transitions in lithium-ion batteries and their impact on battery performance also offer new avenues for improving cycle stability and energy density. Furthermore, studies on proton migration mechanisms provide theoretical guidance for optimizing proton transport at electrochemical interfaces, enhancing reaction selectivity, and boosting energy conversion efficiency. As computing power is enhanced and theoretical models are refined, the application of the FPM in electrochemical research becomes more widespread and in-depth. In addition, FPM enhances the accuracy and reliability of simulations, providing theoretical backing for the design of novel electrochemical materials, and shows promising potential for application in frontier fields like gate-controlled material phase transitions, magnetism, and electrosynthesis, offering innovative solutions to energy and environmental challenges with prospects.However, FPM has its limitations. It can control the system to achieve fractional electron numbers, thereby realizing the grand canonical ensemble for electrons, but the complex interactions among multiple atoms are difficult to accurately describe. As a result, it cannot achieve non-integer changes in ion numbers to maintain a constant chemical potential, particularly for the systems with dynamic ion concentrations at chemical reaction interfaces. It is possible that machine learning potential fitting approaches based on first-principles calculations can offer a way to balance accuracy with the advantages of large-scale simulations. Nevertheless, the development of machine learning potentials for constant potential simulations is still in its early stage. Therefore, addressing large-scale and complex simulations under constant potential remains a challenge in future theoretical developments.

IntroductionSelective catalytic reduction (SCR) technology is widely used due to the advantages of high denitrification efficiency and low operating cost. The existing commercial SCR catalysts are mainly vanadium-based catalysts with V2O5 as an active component, metal oxides WO3 and MoO3 as additives, and anatase TiO2 as a carrier. They have a good denitrification activity at 320–420 ℃, but have a poor activity at a low temperature. The denitrification activity of vanadium-based catalysts is mainly related to their redox capacity, acidic sites, and chemisorbed oxygen. In order to improve their denitrification activity, in this work, V-Mo-P/TiO2 catalysts were prepared by an impregnation-roasting method. The effect of roasting atmospheres (i.e., air, hydrogen, and nitrogen) on the active components and denitrification performance of vanadium-molybdenum-titanium catalysts (V–Mo–P/TiO2) was investigated.MethodsA certain amount of oxalic acid was added into deionized water and dissolved under stirring., Ammonium metavanadate was then added into the solution, heated at 100 ℃ and stirred until the solution became dark blue. Afterwards, ammonium molybdate and diammonium hydrogen phosphate were added into the solution. TiO2 was added and impregnated into the solution under stirring for 2 h, and then dried in an oven at 108 ℃ for 12 h to obtain a precursor of V–Mo–P/TiO2 catalysts. The precursor was ground, pressed, and sieved to 40–60 mesh and placed in a fixed-bed reactor, and then roasted in different gases (i.e., air, nitrogen, and hydrogen) at 450 ℃ for 4 h to obtain different catalyst samples, which were named Air-450 ℃, N2-450 ℃, and H2-450 ℃, respectively.The structure of the catalysts was analyzed by a model PANalytical X-Pert PRO MPD X-ray diffractometer (XRD, PANALYTEC Co., the Netherlands). The pore structure of the catalysts was determined by a model NOVA2200e specific surface area analyzer (Kantar Instruments Co., USA). The surface elemental valence of the catalysts was characterized by a model ESCALAB250Xi Instrument (Thermo Co., USA). The elemental valence states on the catalyst surface were determined by an X-ray photoelectron spectroscope (XPS). The redox capacity and surface acidity of the catalysts were characterized with H2-TPR and NH3-TPD, respectively, and the NO adsorption on the catalyst surface was determined with NO-TPDe. Pyridine adsorption test (Py-FT IR) was performed using a model PE Spectrum II infrared spectrometer (PerkinElmer Co., USA) to characterize the types and strengths of the acidic sites on the catalyst surface.The catalyst activity was tested in a fixed-bed reactor at a gas flow rate of 1400 mL/min, a NO concentration of 500 mg-Nm3, an O2 concentration of 8%, and an NH3:NO volume ratio of 1:1 at 80–300 ℃. The catalysts were used in a fixed-bed reactor with a gas flow rate of 1400 mL/min, a NO concentration of 500 mg-Nm3, an O2 concentration of 8%, and an NH3:NO volume ratio of 1:1. The denitrification tail gas was examined by a model OPTIMA7 flue gas analyzer (MRU Co., Germany) to calculate the denitrification efficiency of the catalyst.Results and discussionAt 100–250 ℃, the NO conversion of Air, N2, and H2 catalysts increases with the increase of temperature. Clearly, the denitrification performance of the catalysts obtained by roasting in three atmospheres is different, and the denitrification activity in different gases follows an order of Air > N2 > H2, in which the catalysts roasted in air have the optimum low-temperature catalytic activity.The ratios of V4+/(V4++V5+) in the catalysts roasted in air, nitrogen, and hydrogen are 0.440, 0.482, and 0.538, respectively, indicating that more V4+ is produced in a reducing atmosphere. Roasting in air can oxidize V4+ to V5+ to a certain extent, thus increasing the percentage of V5+ on the catalyst surface and the amount of chemisorbed oxygen O. From the results of H2-TPR reduction, the corresponding integral area sizes are Air-450 ℃> N2-450 ℃> H2-450 ℃, indicating that polymerized vanadium is more easily formed in air. From the results of the NH3-TPD desorption, the NH3 desorption of the Air-450 ℃ catalyst is more than that of other two catalysts, and the number of acidic sites is in the following order of Air-450 ℃> N2-450 ℃> H2-450 ℃. The results of Py-FT IR further show that the acidic sites on the surfaces of the three catalysts are mainly of B-acid and L-acid. Roasting in air can increase the number of B- and L-acidic sites of the catalysts simultaneously, in which the B-acidic sites increased integrated areas of the catalysts roasted in air, nitrogen, and hydrogen are 1695, 1254 and 481, respectively, which are also basically consistent with the results of the NH3-TPD characterization. The results of NO-TPD desorption indicate that the catalyst surface at Air-450 ℃ is more prone to forming highly active bridged or double-toothed nitrates. The V—O bond and B acidic sites in polymerized vanadium make it easier for the catalyst to adsorb and activate NH3 species, which then reacts rapidly with the bridged or double-dentate nitrates to generate N2 and H2O. The reaction process mainly follows the L–H mechanism. The abundant O on its surface accelerates the formation of NO oxidized to NO2, promoting a rapid SCR reaction. The V–Mo–P/TiO2 catalysts roasted in air are superior to those roasted in nitrogen and hydrogen in terms of NO removal in the low-temperature section.ConclusionsV–Mo–P/TiO2 catalysts for low-temperature denitrification were prepared by an impregnation method, and the denitrification activities of V–Mo–P/TiO2 catalysts roasted in air, nitrogen, and hydrogen atmospheres were investigated. The order of their catalytic activities was as follows: air > nitrogen > hydrogen. The results of H2-TPR and XPS revealed that the catalysts roasted in air had a larger proportion of exposed V5+ on their surfaces, and contained abundant chemisorbed oxygen O, which further accelerated the oxidation of NO to NO2, and participated in the “fast SCR” reaction of denitrification. Moreover, the catalysts roasted in air at 450 ℃ were characterized by NH3-TPD, Py-FT IR and NO-TPD, and the results indicated that the catalysts possessed more abundant B acid sites, and the B acid and polymerized vanadium were more prone to adsorption of activated NH3 species, which further reacted with the bridged and double-toothed nitrate formed on the surface of the catalysts to generate N2 and H2O, thus promoting the SCR denitrification reaction by L-H mechanism.

IntroductionPolyetherimide with its high glass transition temperature (i.e., 217 ℃) and melting point (i.e., 247 ℃) is considered as a promising high-temperature dielectric material. However, the – conjugated structure of its benzene rings leads to a sharp increase in conductivity loss at high temperatures and electric fields, thus reducing efficiency and energy storage density. Montmorillonite possesses a large bandgap and good insulation properties. Incorporating montmorillonite nanosheets into the polymer matrix is an effective approach to enhance the carrier transition barrier and dissipate carriers in the in-plane direction, thereby suppressing conduction current and improving the high-temperature energy storage performance of the polymer. However, the significant differences between the flexible matrix and the rigid inorganic filler pose some challenges for the compatibility at the organic-inorganic interface. In this paper, polyethylenimine was modified onto the surface of montmorillonite nanosheets to improve their interface compatibility with polyetherimide, allowing for uniform dispersion within the organic matrix. In addition, the impact of modified montmorillonite on the dielectric constant, breakdown strength and energy storage performance of polyetherimide composites was also investigated.MethodsThe modified montmorillonite was prepared via cation exchanging with polyethylenimine, and MMT/PEI composites were prepared by a tape casting method. PEI particles were firstly dissolved in NMP solvent under heating and stirring at 50 ℃ for 6 h. Once the PEI particles were completely dissolved, modified montmorillonite with a target content were firstly dispersed in the solvent under ultrasonication for 0.5 h. The resulting suspension was then cast onto a clean glass plate with a scraper and dried in a vacuum oven at 80 ℃ for 12 h. Afterwards, the material was dried at 200 ℃ for 4 h to completely remove the NMP solvent. The glass substrate was then placed in deionized water and left to stand for 10 min, allowing for the composites film to detach from the glass substrate, resulting in a composite film with a thickness of approximately 10 m.Results and DiscussionThe relative dielectric constant of the composites exhibits only a slight decrease in the frequency range of 102 Hz to106 Hz, indicating a good stability. The dielectric constant of the composites at 1000 Hz increases from 3.25 for pure PEI to 3.54, while the dielectric loss remains below 0.02 in the entire frequency range as the amount of montmorillonite increases. Moreover, the dielectric constant of the composites increases from 3.13 to 3.32 with the addition of montmorillonite at 150 ℃ and 1000 Hz. The dielectric loss remains at a low level. Thus, the dielectric breakdown strength of pure PEI at 150 ℃ is 429 MV/m. After introducing modified montmorillonite, the breakdown strength of the composites initially increases and then decreases. At a doping modified montmorillonite amount of 0.1%, the breakdown strength increases to 487.2 MV/m, and with a doping modified montmorillonite amount of 0.2%, it further increases to 507.5 MV/m. However, the breakdown strength decreases to 459.5 MV/m when the doping modified montmorillonite amount continues to increase. The discharge energy density of pure PEI at 150 ℃ and at 450 MV/m is 2.56 J/cm3, with an efficiency of only 72.5%. After introducing the modified montmorillonite nanosheets, the breakdown strength and dielectric constant of the composites both are enhanced, leading to an improvement in charge storage capability. At 0.1% of modified montmorillonite doping amount, the maximum discharge energy density increases to 3.17 J/cm3 at 150 ℃ and 500 MV/m, although the efficiency remains low at 77.8%. When the doping modified montmorillonite amount increases to 0.2%, the maximum discharge energy density reaches 3.15 J/cm3 at 150 ℃ and 450 MV/m, with the efficiency improving to 90.1%, thus meeting the standard operational requirements for film capacitors. At 150 ℃ and 500 MV/m, the discharge energy density further increases to 3.54 J/cm3, while the efficiency stabilizes at 86.7%. However, when the doping modified montmorillonite amount increases to 0.3%, the maximum discharge energy density and efficiency both decline. This indicates that an appropriate amount of montmorillonite nanosheets can effectively enhance the energy storage properties of PEI-based composites. The excessive doping can lead to a negative effect on the energy storage performance of composites, likely due to aggregation or suboptimal dispersion of the nanosheets.ConclusionsPolyethyleneimine molecules were effectively loaded onto the surface and interlayers of montmorillonite nanosheets through cation exchange. This process improved the dispersibility of the montmorillonite nanosheets in solvents and their compatibility with the polyetherimide matrix, ensuring the structural uniformity of the composite materials. After doping with modified montmorillonite, the energy storage performance of the composites exhibited the optimum performance observed at a doping modified montmorillonite amount of 0.2%. At this doping amount, the dielectric constant was 3.45 at 1000 Hz and 150 ℃, while the breakdown strength reached 507.5 MV/m. At an electric field strength of 450 MV/m, the charge-discharge efficiency achieved 90.1%, with a discharge energy density of 3.15 J/cm3; at 500 MV/m, the charge-discharge efficiency was 86.7%, and the maximum discharge energy density reached 3.54 J/cm3. The results of this work indicated that doping with montmorillonite nanosheets could be an effective strategy for enhancing the high-temperature energy storage performance of polyetherimide, paving a way for the development of high-strength, high-performance high-temperature dielectric polymers.

IntroductionFormaldehyde, as an indoor pollutant and carcinogen, exists commonly in building materials and furniture products, posing a serious threat to human health. To address this issue, cellulose aerogel materials with their porous network structure can effectively remove pollutants. Cellulose aerogels exhibit a great potential in the field of adsorption due to their advantages of abundant raw material sources and environmental friendliness. Chitosan, due to the presence of amino groups, is widely studied for various applications, particularly for formaldehyde adsorption. Its adsorption performance is especially remarkable, as it can form specific interactions with formaldehyde, enabling an efficient removal. In this paper, a commonly available poplar wood powder was used to directly extract cellulose from plant-based raw materials. Cellulose-chitosan composite aerogels were prepared by a sol-gel method for the adsorption of formaldehyde gas. The structure, morphology, and adsorption conditions of the composite aerogels were investigated to evaluate their performance.MethodsThe round-bottom flask containing formaldehyde aqueous solutions of different concentrations was placed in a heater of the gas device to vaporize the solution, allowing formaldehyde gas to fill the apparatus. After 2 h, the formaldehyde adsorption tests were initiated when the formaldehyde gas concentration in the device reached a stable level. Adsorption tests were conducted separately on chitosan, cellulose aerogel, and cellulose-chitosan composite aerogel. The adsorption experiment for chitosan lasted for 12 h, with samples collected every hour to measure the formaldehyde concentration. For cellulose aerogel and cellulose-chitosan composite aerogel, the adsorption experiments lasted for 2 h, with samples taken every 15 minutes to monitor the formaldehyde concentration.Results and discussionAt a formaldehyde concentration of 8 mg/m3, the formaldehyde adsorption capacities at equilibrium for CS, CA, and CCA were 0.412, 2.336 mg/g, and 15.681 mg/g, respectively. CS exhibits the minimum adsorption performance, while CCA shows the most significant adsorption effect, outperforming CA. The removal efficiencies are 53.85%, 74.06%, and 98.00%, respectively when using 1 mg, 3 mg, and 5 mg of CCA at an initial formaldehyde concentration of 8 mg/m3. The 5 mg dosage of CCA achieves a removal efficiency of close to 100%, making it the most economical option for formaldehyde removal. Formaldehyde adsorption tests are conducted on 5 mg of CCA at different formaldehyde concentrations ranging from 2 mg/m3 to 16 mg/m3. The adsorption capacity increases significantly as the concentration increases from 2 mg/m3 to 8 mg/m3, indicating that formaldehyde concentration affects the adsorption performance. The maximum formaldehyde adsorption capacities at equilibrium for CCA-1, CCA-2, and CCA-4, with chitosan proportions of 0.05%, 0.10%, and 0.20% (in mass), are 13.264, 15.681 mg/g, and 15.877 mg/g, respectively. The difference in maximum adsorption capacities between CCA-2 and CCA-4 is relatively small, indicating that the optimal chitosan proportion is 0.1% to avoid resource wastage.ConclusionsThe results showed that the cellulose-chitosan composite aerogel exhibited a superior formaldehyde adsorption performance, compared to cellulose aerogel and pure chitosan. A significant advantage of introducing chitosan was its ability to specifically bind with formaldehyde, effectively enhancing the adsorption performance and broadening the application scope of cellulose aerogels, thereby achieving a high-value utilization of plant-based raw materials. Moreover, the composite aerogel demonstrated an effective adsorption at different formaldehyde concentrations, further expanding its applicability under varying conditions. In summary, the cellulose-chitosan composite aerogel exhibited excellent formaldehyde removal capabilities, showing a great potential for applications, particularly in household environments.

IntroductionCadmium magnesium telluride (CdMgTe), as a group II-VI CdTe-based compound semiconductor, can be used in room-temperature radiation detection. However, CdMgTe crystals grown by melt methods often exhibit major defects like vacancies, dislocations, twins, and inclusions, severely impacting the crystal quality and detector performance. Some studies show that selenium (Se) can significantly reduce harmful defects like sub-boundary networks and Te inclusions in CdTe-based crystals, enhancing the crystal quality through its favorable segregation coefficient and intense solid-solution hardening effect. Therefore, in this paper, Se was introduced into CdMgTe crystals via vapor phase diffusion as an advanced annealing strategy to enhance the both crystal quality and detector performance. In addition, the effect of annealing time on the crystal defects, microhardness, optical and electrical properties, and detector performance was also investigated.MethodsThe annealing source was a high-purity Se (7N), and the slices with the dimensions of 5 mm×5 mm×2 mm were selected from an In-doped CdMgTe ingot grown by a modified vertical Bridgman method under Cd excess condition. Prior to annealing, the slices were mechanically polished with an MgO suspension and then treated with a 2% Br2-MeOH solution to eliminate scratches and any damaged layers. The slices and the source were positioned at opposite ends of a quartz annealing device, with quartz crucibles evacuated to a pressure of 10–5 Pa. The annealing temperature of both slice and source was selected at 773 K. Effect of annealing time on CdMgTe crystal properties was investigated at different holding time (i.e., 30, 60, 120 h, and 240 h). CdMgTe planar room-temperature radiation detectors were fabricated via evaporating Au electrodes onto the both sides of the annealed crystals.CdMgTe crystals before and after annealing in Se atmosphere were characterized by near-infrared spectrometry (NIR), X-ray photoelectron spectroscopy (XPS), infrared transmission microscopy (IRTM), field emission scanning electron microscopy (FESEM), infrared (IR) spectrometry, Raman spectrometry, and current-voltage (I–V) measurement. Room-temperature radiation detectors were prepared by evaporation of Au electrodes on both sides of CdMgTe crystals. The carrier mobility was determined by a time-of-flight (TOF) technology. The energy spectrum of the detectors was acquired by an ORTEC measurement system with uncollimated 241Am particles with an energy of 5.48 MeV as an irradiation source.Results and discussionThe band gap of the as-grown crystal is 1.505 eV, and annealing in Se atmosphere does not prevent the volatilization of Cd in CdMgTe crystals or reduce Te inclusions. After annealing, the maximum increase of the band gap is 0.042 eV. Se interacts with CdMgTe matrix via diffusion and chemisorption, forming chemical bonds that effectively result in the partial substitution of Se for Te., The solution strengthening effect of Se is more pronounced than that of Mg as the annealing time increases, causing that the microhardness initially decreases and then increases, which is lower than that of the as-grown crystal. The IR transmittance of the crystal after 120 h annealing is 63.6% , which approaches the theoretical value of 65%, thus satisfying a criterion for high-quality crystals. The peak intensity of A1(Te) is basically unchanged based on the Raman spectra. However, an increase in the peak intensity of TO(CdTe) and a decrease in that of LO(CdTe) indicate that the lattice integrity in the annealed crystal is compromised.CdMgTe crystal obtained under optimal annealing conditions is fabricated into an Au/CdMgTe/Au planar structure for the room-temperature radiation detector. TOF measurements show a remarkable increase in electron mobility (e), up to 344.47 cm2/(V·s). 241Am particle source with an energy of 5.48 MeV is used for detector energy spectrum testing. The optimal CdMgTe detector exhibits the performance with an energy resolution of 17.2% and a carrier mobility lifetime product ()e of 1.32×10–4 cm2/V. Annealing in a Se atmosphere can thus offer an effective approach to enhance the quality of CdTe-based crystals.ConclusionsAn advanced annealing strategy was adopted for enhancing the quality of CdMgTe single crystals for room-temperature radiation detectors. After annealing, a decrease in Cd content along with an increase in Mg content resulted in an expanded band gap. The microhardness and the IR transmittance of the crystals firstly decreased and then increased, and the resistivity gradually decreased as the annealing time increased, thus improving the crystal quality. The optimum condition of Se atmosphere annealing was at 773 K for 120 h. The optimal performance of the detector was an electron mobility (e) of 344.47 cm2/(V·s), an energy resolution of 17.2%, and a ()e product of 1.32×10–4 cm2/V for 241Am particles with an energy of 5.48 MeV.

IntroductionUltra-wide bandgap (UWBG) semiconductor materials have attracted extensive attention in the fields of optoelectronics, sensing systems, and high-power devices due to their high critical electric field, high-temperature resistance, and excellent photoelectric properties. In this paper, high-quality Sn4+-doped ZnGa2O4 crystals with a volume of approximately 10 cm3 were successfully obtained by the VGF method. The crystal structure of the grown Sn4+: ZnGa2O4 crystals was detected by single crystal X-ray diffraction (XRD), and their crystal quality was studied by high-resolution X-ray diffraction (HRXRD). In addition, the optical and electrical properties of the grown Sn4+: ZnGa2O4 crystals were investigated by UV-Vis spectroscopy, XPS, and Hall measurements. The results show that the optical properties are affected by the Sn4+ concentration, and it is demonstrated for the first time that the electrical properties of ZnGa2O4 single crystals can be controlled by the concentration of doped Sn4+. The carrier concentration of the grown Sn4+-doped ZnGa2O4 single crystal at room temperature is higher than that of previously studied ZnGa2O4 single crystals (1.39 × 1019 cm–3) and Sn4+-doped -Ga2O3 (3 × 1018 – 3 ×1019 cm–3). The improved photoelectric properties of ZnGa2O4 crystals after Sn4+ doping are expected to find applications in high-power devices and optoelectronic devices.MethodsZnGa2O4 bulk single crystals doped with Sn4+ were grown by the VGF method. High-purity (99.999%) Ga2O3, ZnO and SnO2 powders were used as starting materials. The three powders were mixed for 80 h at a speed of 40 revolutions per minute, and then the mixed powders were cold-pressed into blocks at a pressure of 2000 bar and calcined in air at 600 ℃ in an alumina crucible for 16 h. Subsequently, ZnGa2O4 bulk single crystals doped with Sn4+ were grown in a crucible with an inner diameter of 60 mm and a height of 60 mm. The furnace was heated to 1900 ℃at a rate of 250 ℃/h in an atmosphere of argon and 12% oxygen, and maintained at this temperature for about 2 h. Then the furnace was cooled slowly at a rate of 2–3 ℃ per minute. Sn4+ doped ZnGa2O4 bulk single crystals were obtained.Results and discussionXRD analysis indicates that the Sn4+-doped ZnGa2O4 crystal maintains a pure spinel phase without any impurity phases, and the lattice constant slightly increases due to the introduction of Sn4+. The high-resolution X-ray diffraction (HRXRD) results show that the full width at half maximum (FWHM) of the rocking curve of the crystal is only 82 arcsec, indicating excellent crystal quality. X-ray photoelectron spectroscopy (XPS) analysis confirms that Sn4+ mainly enters the octahedral sites of the lattice by replacing Ga3+. X-ray fluorescence spectroscopy (XRF) analysis indicates that Sn4+ is successfully doped into the crystal, but the actual doping concentration is lower than the theoretical value due to the volatility of SnO2. Optical performance tests show that Sn4+ doping slightly reduces the optical band gap of ZnGa2O4 crystals and increases the absorption in the near-infrared band, which is related to the increase in carrier concentration. Hall measurement results show that Sn4+ doping significantly increases the carrier concentration of the crystal (up to 3.32×1019 cm–3) and reduces the resistivity (0.006 ?cm), outperforming undoped ZnGa2O4 and Sn4+-doped -Ga2O3 crystals.ConclusionsIn this study, high-quality Sn4+-doped ZnGa2O4 single crystals with a volume of 10 cm3 were successfully grown by the vertical gradient freezing (VGF) method. The obtained Sn4+-doped ZnGa2O4 crystals showed no significant shift in diffraction peaks and a full width at half maximum (FWHM) of the rocking curve as low as 82 arc seconds, confirming the extremely high quality of the single crystals. X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectroscopy (XPS) analyses respectively confirmed the contents of Zn, Ga, O, and Sn elements, as well as the fact that Sn4+ were mainly incorporated into the ZnGa2O4 crystal by replacing Ga3+ at octahedral sites in the spinel structure. With the increase of Sn4+ doping concentration, the optical band gap of ZnGa2O4 crystals decreased to 4.58 eV and 4.56 eV, respectively. The introduction of Sn4+ did not cause significant changes in the cutoff absorption edge at about 275 nm, but increased absorption in the near-infrared wavelength range, which was related to the increase in carrier concentration. Hall measurements verified the effect of Sn4+ doping on the electrical properties of ZnGa2O4 single crystals. The results indicated that the introduction of Sn4+ significantly increased the carrier concentration of ZnGa2O4 crystals (2.65×1019–3.32×1019 cm–3) and decreased the resistivity (0.006–0.008 &#x0387;cm). These properties were superior to undoped ZnGa2O4 single crystals and Sn4+-doped -Ga2O3 single crystals. Overall, the Sn4+-doped ZnGa2O4 crystals grown in this study demonstrated significant application potential in power devices and solar-blind detection, and are expected to play a key role in the development of future high-power and high-frequency electronic and optoelectronic devices.

IntroductionIt is critical for large-scale energy storage to develop sodium-ion batteries (SIBs) due to their cost-effectiveness and abundant sodium resources. However, some challenges like sluggish kinetics from large Na&#x207A; radii and poor structural stability of electrode materials hinder their practical application. Transition metal sulfides (TMS) like SnS, NiS, and FeS exhibit high theoretical capacities, but suffer from some intrinsic drawbacks (i.e., low conductivity and severe volume expansion during cycling). To address these limitations, this study was to propose a novel strategy, i.e., designing a mixed-metal sulfide composite of (NiS/Cu2(Fe,Co,Ni)SnS&#xFF0C;/CNT) with heterointerfaces and multi-metal synergy. The integration of Fe, Co, Ni, Cu, and Sn could enhance electronic/ionic transport, mitigate volume changes, and leverage catalytic effects of transition metals. Carbon nanotube (CNT) were introduced to further improve conductivity and structural integrity. This mixed-metal sulfide composite exhibited the excellent performance at a ultra-high current density.MethodsThe composite was synthesized via a co-precipitation method and a subsequent high-temperature sulfidation. For NiS/Cu2(Fe,Co,Ni)SnS&#xFF0C;/CNT, stoichiometric amounts of FeSO&#xFF0C;, CoSO&#xFF0C;, NiSO&#xFF0C;, CuSO&#xFF0C;, and SnSO&#xFF0C; were dissolved and co-precipitated with NaOH. The CNT slurry was ultrasonically dispersed and incorporated into the precursor. After sulfidation with thioacetamide in N2 at 500 ℃, the final product was obtained. NiS/CNT (control sample) followed the similar process using only NiSO&#xFF0C;. The crystallinity, morphology, and elemental states of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). To evaluate their kinetics, rate capability and cycling stability, CR2032 half-cells assembled with Na metal counter electrodes were tested by cyclic voltammetry (CV), constant-current charge/discharge test, galvanostatic intermittent titration (GITT) and electrochemical impedance spectroscopy (EIS), respectively.Results and discussionThe results show that the complex consists of Cu2(Fe,Co,Ni)SnS&#xFF0C; and NiS biphasic phases, and the heterogeneous interfaces exist, which are confirmed by high-resolution transmission electron microscopy (HRTEM). The built-in electric field at the heterogeneous interface accelerates the charge transfer, and the multimetal synergy (Fe/Co/Ni/Cu/Sn) provides abundant catalytic sites and reduces the Na&#x207A; diffusion barrier (i.e., 32% reduction in the diffusion barrier according to density-functional theory calculations). The three-dimensional conductive network constructed by the CNTs inhibits the volume expansion efficiently (i.e., the thickness of the electrodes increases by only 37.9% after cycling, which is significantly lower than that of the NiS/CNT). For the electrochemical performance, NiS/Cu2(Fe, Co, Ni)SnS4/CNT exhibits an excellent high rate charge/discharge performance and a long cycle stability, and still maintains a discharge specific capacity of 626 mA·h·g–1 after 1000 cycles at a current density of 5 A·g–1, and 399 mA·h·g–1 after 8000 cycles at an ultra-high current density of 20 A·g–1. Capacitive-dominated storage and enhanced Na&#x207A; diffusivity outperform monometallic NiS/CNT. The TEM images and CV indicate a reversible phase transition between sulfide and Na2S, thus validating the reaction mechanism.ConclusionsThe built-in electric field formed by the heterogeneous interface and the synergistic effect of polymetallic cations could enhance the ion and charge transfer rate, and the reduction of polymetallic ions to metal monomers facilitated the ion and electron transport during the charging and discharging process, effectively suppressing the polysulfide shuttling phenomenon, thus decreasing the polarization of the battery. The introduction of carbon nanotubes provided electron transport paths, which further enhanced the structural stability of the material. This study could have a great potential of mixed metal sulfides for application in anode materials for sodium-ion batteries.

IntroductionEnergy, environment and industrial production are interconnected with the rapid development of the industrialization process, conventional fossil fuels are close to exhaustion, and the environment on which mankind depends for survival is seriously damaged. The development of efficient, clean and sustainable energy conversion and storage technology is thus an important research direction in scientific community. In this paper, in-situ Ni-doped CoMoO4 electrode materials were synthesized on acidified pretreated nickel foam with nickel chloride formed on hydrochloric acid pretreated nickel foam as a reactive nickel source. The capacitive properties of in-situ Ni-doped CoMoO4 electrode materials synthesized at different hydrothermal reaction temperatures were investigated.MethodsIn this work, 1 mmol Co(NO3)2·6H2O and 1 mmol Na2MoO4·2H2O were dissolved in 60 mL of deionized water (DI) and stirred for 30 min, and then the conventionally cleaned nickel foams and four pieces of acidified pretreated nickel foams were immersed into five beakers of the solutions above, respectively. The solutions were then transferred into a hydrothermal high-pressure reactor lined with polytetrafluoroethylene. The reactor was kept in an oven at different temperatures (i.e.,180, 120, 150, 180 ℃, and 200 ℃) for 12 h, respectively. The nickel foam was removed from the cooled reactor, washed and dried in a vacuum oven at 60 ℃ for 12 h. The synthesized materials were labeled as CoMoO4 (3.6 mg), Ni-CoMoO4-120 (3.93 mg), Ni-CoMoO4-150 (3.46 mg), Ni-CoMoO4-180 (4.88 mg), and Ni-CoMoO4-200 (7.54 mg), respectively.Results and DiscussionThe XRD pattern of CoMoO4 shows that the diffraction peaks at 13.1°, 23.3°, 26.4°, 27.3°, 33.7°, 36.6°, 38.9°, 41.7°, 47.4°, and 54.5° correspond to the crystal planes (001), (021), (002), 1ˉ12, 2ˉ22, (400), (040), (422), (222), (421), and 4ˉ40, respectively, of CoMoO4 (JCPDS 21–0868), indicating the effective synthesis of CoMoO4. However, CoMoO4 electrode material synthesized by in-situ Ni doping shows an overall shift of the XRD diffraction peak to the left. The SEM images show that compared to the undoped CoMoO4, Ni-doped CoMoO4 nanosheets at different reaction temperatures are uniformly nucleated and grown on the surface of Ni foam due to Ni ions provided by the nickel foam as a crystallization core, and there is almost no pore space between the nanosheets. The nanosheets are stacked together with mutual reliance and supported. The results of specific surface area measurements indicate that in-situ Ni-doped CoMoO4 has the maximum specific surface area at a hydrothermal temperature of 180 ℃. The results of CV and GCD tests show that the optimum specific capacitance of Ni-doped CoMoO4 electrode material can be obtained at 180 ℃.ConclusionsIn-situ Ni-doped CoMoO4 electrode materials were synthesized on acidified pretreated nickel foam by a hydrothermal method. The morphology of Ni-doped CoMoO4 electrode materials was controlled via modulating the hydrothermal temperatures (i.e., 120, 150, 180 ℃, and 200 ℃), in turn modulating the capacitive properties of CoMoO4 electrode materials. Compared to undoped CoMoO4, Ni-doped CoMoO4 nanosheets with different reaction temperatures uniformly nucleated and grew on the surface of nickel foam due to Ni ions provided by nickel foam as a crystallization core, and the pores between nanosheets became smaller. The nanosheets rely on each other to stack together and support. Ni-CoMoO4 was less prone to some problems like structural collapse and volume deformation when subjected to long-cycle charging and discharging, showing a better cycling performance. The optimum capacitance performance of Ni-doped CoMoO4 could be obtained at 180 ℃, with a high specific capacitance of 4680 mF·cm–2 at 5 mA·cm–2. The capacitance retention of the ASC device after 10000 cycles was 96%.

IntroductionSilver niobate (i.e., AgNbO3, AN) as a lead-free antiferroelectric material has a promising application in energy storage and photocatalysis. However, a lack of theoretical understanding due to the heterogeneity of ceramic microstructures affects its further development. In this study, high-quality [001]-oriented AN single crystal was grown with AgCl as a co-solvent. This crystal exhibited energy storage density and efficiency comparable to AN ceramic, along with superior photovoltaic performance. The [001]-oriented AN single crystal demonstrated exceptional withstand voltage characteristics, surpassing those of AN ceramic. This work could provide crucial insights into the optoelectronic performance of AN single crystals, paving a way for potential applications in high-energy storage capacitors, piezoelectric devices, and photocatalysis.MethodsIn this study, pure-phase raw materials were synthesized by a solid-state reaction method, followed by the growth of AN single crystals by a modified co-solvent method. The raw materials from Sinopharm Chemical Reagent Co., Ltd., China, were Ag2O (99.7% purity) and Nb2O5 (99.5% purity), which were ground, dried, and then calcined in an oxygen atmosphere at 900℃ for 6 h to obtain pure-phase AN. The raw materials were mixed with a specific amount of AgCl (99.5% purity), and heated in double corundum crucibles in an oxygen atmosphere at 1180 ℃ for melting. The melt was then slowly cooled to 1140 ℃ for nucleation and further cooled to room temperature to obtain single crystals. Finally, the residual AgCl was removed through ammonia treatment.Results and discussionThe [001]-oriented AgNbO3 (AN) single crystals exhibit higher phase transition temperatures, compared to conventional AN ceramics, due to their high crystallinity and specific orientation. These crystals also demonstrate exceptional optoelectronic properties, with a forbidden bandwidth of 2.82eV, enabling an effective UV absorption at below 440nm and stable visible light transmittance at above 470 nm. Furthermore, the [001]-oriented AN single crystal shows remarkable withstand voltage characteristics, maintaining a stability at a bias voltage of up to 190 V, significantly exceeding those of AN ceramic (i.e., ~10V). The leakage current increases linearly and symmetrically with voltage and optical power, highlighting their potential for high-voltage, high-power applications. In summary, the [001]-oriented AN single crystal offers unique advantages for photodetectors and optoelectronic devices due to their enhanced phase transition temperatures, superior optoelectronic properties, and exceptional withstand voltage characteristics. A future research can focus on further optimizing their performance and expanding their applications in optoelectronic technology.ConclusionsIn this study, high-quality [001]-oriented AgNbO3 (AN) single crystals were grown with AgCl as a co-solvent. The crystals exhibited comparable energy density and conversion efficiency to the same-composition ceramics with higher phase transition temperatures due to their crystallinity and orientation. The forbidden bandwidth of 2.82 eV enabled an effective UV light absorption at below 440 nm and a good visible light transmittance at above 470 nm. The crystals demonstrated excellent withstand voltage characteristics, maintaining a stability at high bias voltage and exhibiting a linear relationship between leakage current and voltage/optical power. These results could underscore a potential of [001]-oriented AN single crystal for high-voltage, high-power optoelectronic applications.

IntroductionLithium iron phosphate-graphite (LFP-C) batteries are widely used in various fields due to their high energy density, low cost, high safety, good rate performance, long cycle life, and environmental friendliness. However, prolonged calendar aging leads to increased internal resistance and capacity decay, thereby shortening their service life. In this work, the impacts of storage temperature and SOC on the calendar aging performance of LFP-C batteries were investigated. The results show that the capacity decay is more severe under high temperature and high SOC conditions. The structural evolution of the anode and cathode materials, as well as the cathode–electrolyte interphase (CEI) and solid electrolyte interphase (SEI) layers were analyzed. It is indicated that the structure of LiFePO4 cathode remains stable, while the degree of disorder in the graphite anode increases. The decomposition of the liquid electrolyte leads to an increase of LiF content in the CEI and SEI layers with decreasing Li2CO3 content in the SEI layer at 50 ℃.MethodsIn an inert atmosphere glove box, several LFP-C CR2025 coin cells were assembled. The cells were charged to the targeted SOC, and then divided into six groups and stored under different conditions (i.e., at 0°C-50%SOC, 0 ℃-100%SOC, 25 ℃-50%SOC, 25 ℃-100%SOC, 50 ℃-50%SOC, and 50 ℃-100%SOC) for one month. After storage, each group of cells was cycled at 1C to assess the impact of different storage conditions on the electrochemical performance of the cells. Other cells were disassembled, and then cleaned to obtain the positive and negative electrodes. The capacity degradation mechanisms of batteries during calendar aging were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive X-Ray spectroscopy (SEM-EDX), and X-ray photoelectron spectroscopy (XPS).Results and discussionAfter 1-month storage, the LFP - graphite coin cells are charged and discharged at 1 C for 300 cycles. The results show that the cells stored at 50 ℃ cannot deliver any capacity. The cells stored at 0 ℃ exhibit a significantly higher discharge capacity, compared to the cells stored at 25 ℃. The cycling performance results of the cells after storage at different states of charge (SOC) indicate that the discharge capacity of coin cells stored at 50% SOC is higher than that of cells stored at 100% SOC.It is revealed that there is a slight difference in the XRD patterns of LFP electrodes stored under various temperatures and SOC conditions, indicating that the structure of LFP maintains a high stability under various storage conditions. The XRD patterns of the graphite anodes also remain unchanged, and only the peaks attributed to the graphite and current collector Cu foil appear.The results by Raman spectroscopy indicate that the LFP material remains stable after storage, while the degree of disorder in the graphite anode increases significantly and becomes more pronounced with the increase of storage temperatures and SOC. The results by FTIR reveal the side reaction products on the surfaces of both the cathode and anode materials (i.e., Li2CO3, (CH2OCOOLi)2, and ROCO2Li).The results by SEM-EDX indicate that there is a slight change in the elemental ratio on the surface of the cathode electrodes after storage under different conditions, further validating the stability of the LFP material. The surface of graphite particles becomes rough after storage, and the content of fluorine and phosphorus elements on the surface of graphite anodes increases under high-temperature and high-SOC conditions.The results by XPS show that the content of LiF in the CEI layers increases with increasing the temperature and SOC. The storage temperature shows a more pronounced effect on the composition of the CEI rather than the SOC. The relative content of LiF and P—F in the SEI layers significantly increases, while the relative content of Li2CO3 decreases due to decomposition as the storage temperature increases.ConclusionsLiFePO4-graphite coin cells with different SOC (i.e., 50% and 100%) were stored at various temperatures (i.e., 0, 25 ℃ and 50 ℃) and for one month and then charged and discharged for 300 cycles. The results showed that cells stored at 50°C were completely inoperative. The battery capacity retention followed an order of 0 ℃-50%SOC > 0 ℃-100%SOC > 25 ℃-50%SOC > 2 ℃-100%SOC.It was revealed that the LFP cathode exhibited a structural stability as the storage temperature and SOC increased. Conversely, the degree of disorder of graphite anode increased, having a detrimental effect on the lithium ion migration. It was evident that the temperature could have a dominant influence on the composition of the CEI rather than SOC. The relative content of Li2CO3 decreased, while the relative content of LiF decreased within the CEI layers as the storage temperatures and SOC increased. In addition, the relative content of LiF and P—F increased in the SEI layers with temperature, and the temperature had a more significant effect rather than SOC on the SEI layer.

As a promising advanced energy device, the solid oxide fuel cell (SOFC) has garnered increasing attention in recent years due to rapid development and substantial achievements. Compared to other types of fuel cells, SOFCs have the advantages of an all-solid-state structure that facilitates assembly, a lack of reliance on precious metal catalysts, broad fuel compatibility, and favorable chemical reaction rates and transport kinetics. The SOFC electrode is a high-temperature-resistant, porous composite material with a complex geometric configuration at the microstructural level. These microstructural parameters play a crucial role in influencing SOFC performance. In fact, the cell's lifespan and efficiency are intimately tied to the microstructure of the electrode. Therefore, optimizing the microstructure of the anode is significant for addressing existing challenges in SOFC technology. Such optimization can lead to a deeper understanding of the mechanisms underlying the microstructure's functional role and provide a foundation for designing high-performance electrodes.At present, research on the optimization of SOFC anode microstructure spans multiple fields and approaches. Advances in experimental techniques and simulation methods have enabled the quantification and virtual reconstruction of the SOFC anode microstructure, while improved fabrication methods have provided a more reliable basis for structural control. Consequently, research on optimizing the SOFC anode microstructure is expanding, with numerous emerging simulation and experimental approaches. This paper firstly reviews the current research status on anode microstructure, covering key materials of SOFC, characterization methods, three-dimensional reconstruction, quantitative simulations, and fabrication techniques. Subsequently, progress in anode optimization research, including simulation, experimental preparation, novel simulation techniques, and innovative fabrication methods, is discussed. Overall, SOFC anode microstructure optimization research has evolved from single-parameter improvement toward multi-objective optimization, with the aim of achieving breakthroughs not only in electrochemical performance but also in thermal performance and stability. This paper concludes with a summary and perspective, providing insights to guide further research on SOFC anode microstructure optimization.Summary and prospectsTo enhance the performance and lifespan of SOFCs, the academic community has undertaken multidisciplinary and multifaceted optimization research. Among these efforts, optimizing the microstructure of electrodes has yielded increasingly reliable results and remains a focal area of study, with numerous innovative approaches continuously emerging. The integration of advanced optimization methods has deepened researchers' understanding of the relationship between anode microstructure and the overall performance of SOFCs, enabling the intentional design of specific microstructural morphologies and the preparation of real samples for validation. Multi-objective optimization is anticipated to play a prominent role in future microstructural studies, opening new pathways for developing SOFC samples with controllable morphologies to further advance microstructural optimization.Based on this foundation, the future directions for research include:1) Employing modern advanced characterization techniques to comprehensively quantify the evolution of SOFC microstructure throughout its lifecycle. Building upon current observation and three-dimensional reconstruction techniques, future research should systematically investigate microstructural changes in various states, including sintering preparation, operation, and degradation. Advances in image processing and analytical algorithms hold significant potential for providing a thorough understanding of SOFC microstructural behavior.2) Integrating simulation and experimental preparation closely to identify the most effective anode microstructure. By decorating anodes with materials featuring specific morphologies, researchers can design electrodes with superior performance, promoting research into gradient anodes and anode modification. Active design of anode microstructures, with extensive use of multi-objective optimization methods, will allow for the successful fabrication of electrodes that meet anticipated performance targets. Further stability-enhancing strategies for SOFC anodes could be achieved by adjusting operating conditions and preparation techniques.3) Increasing attention is being given to the combination of artificial intelligence (AI) and big data in SOFC optimization. Using machine learning to identify optimized parameters and ideal models, rather than relying on trial-and-error, can significantly streamline resource use. Deep learning will be a powerful tool in designing unique functional anodes. Additionally, nanoscale 3D printing—an economical and practical technology for producing electrodes with special microstructural features—holds great promise in microstructure optimization design and may facilitate the successful fabrication of advanced electrodes.

Room-temperature sodium-sulfur (RT Na–S) batteries are a potential candidate for next generation of large-scale energy storage systems due to their high energy density and low cost. Nevertheless, their practical application is seriously hindered by the "shuttle effect" of sodium polysulfides, sluggish conversion kinetics, sodium dendrite growth, and electrolyte instability. In view of the problems above, extensive strategies are proposed to enhance the battery performance, such as cathode material engineering, anode interface modification, and electrolyte optimization. The modification of the RT Na–S batteries electrolyte has attracted recent attention. However, there is a lack of summary regarding the optimization mechanisms and design principles of different electrolytes. This review represented the research progress and optimization mechanism of electrolyte designs (i.e., the selection of solvent molecules, sodium salts, and functional additives) as well as the development of high-concentration/locally high-concentration electrolytes and flame-retardant electrolytes based on the working principle and challenges of RT Na–S batteries. In addition, some future research directions for electrolyte regulation toward practical RT Na–S batteries were also summarized.Summary and prospectsIn summary, the rational design and optimization of electrolytes is an effective approach to enhancing the performance of RT Na–S batteries. This review outlines the working principles and major challenges faced by RT Na–S batteries and systematically discusses the research advancements in carbonate-based, ether-based electrolytes, and electrolyte additives for RT Na–S batteries. In RT Na–S batteries, carbonate, and ether-based electrolytes exhibit different properties. The solubility of NaPSs is lower in carbonate-based electrolytes, but they can undergo side reactions with the carbonate solvent, thus leading to the loss of active sulfur and consumption of the electrolyte. The design of carbonate electrolytes focuses on avoiding side reactions between the carbonate solvent and NaPSs, such as selecting appropriate solvents or additives to induce the formation of a stable CEI layer, preventing direct contact between the carbonate solvent and NaPSs. In contrast, NaPSs are more stable in ether-based electrolytes, but their high solubility in ether electrolytes results in severe shuttle effects and corrosion of the sodium metal anode. The design of ether-based electrolytes emphasizes the suppression of NaPSs shuttle effect and the interface modification of the sodium metal anode. This can be achieved via selecting specific solvents and additives that form coordination bonds with NaPSs and a stable SEI to inhibit NaPSs shuttle and stabilize the sodium metal anode. Some strategies involving high-concentration or localized high-concentration electrolytes have some positive effects in the design of both carbonate and ether-based electrolytes. In addition, the introduction of flame-retardant solvents into the electrolyte can also enhance the safety of the battery to some extent.Despite significant research progress on RT Na-S battery electrolytes, there are still some scientific problems to be addressed to promote the commercial application of RT Na-S batteries. Future research should be as follows:1) Theoretical calculations can be employed to reveal the dissolution and diffusion mechanisms of NaPSs in electrolytes, as well as the general interactions between solvent molecules, additives, and NaPSs. This can then enable the efficient screening of suitable solvents and additives for sodium-sulfur battery electrolytes through machine learning.2) The sodium metal used in the anode of sodium-sulfur batteries is excessive, which increases manufacturing costs and reduces energy density. Developing sodium-sulfur batteries with Na2S as a cathode and a current collector as an anode (i.e., anode-free sodium-sulfur batteries) represents a promising avenue for future development, as it can maximize the energy density of sodium-sulfur batteries. However, the sodium in anode-free sodium-sulfur batteries is limited as it is sourced from Na2S. It is thus necessary to develop electrolytes with a high coulombic efficiency to minimize sodium loss and enhance the cycling stability of the battery.3) Although the operating temperature of sodium-sulfur batteries reduces from high temperatures (~350 ℃) to room temperature, a future research should focus on the development of low-melting-point solvents or ionic liquids for the design of low-temperature electrolytes, to accommodate more extreme operating environments. It is of great significance to promote the practical application of sodium-sulfur batteries.4) Solid-state electrolytes can effectively suppress the shuttle effect of NaPSs and the growth of sodium dendrites, while also avoiding the risks associated with electrolyte leakage. Therefore, the development of novel solid-state electrolytes shows a great promise for enabling higher performance and safety sodium-sulfur batteries.

Planar solid oxide fuel cells (SOFCs) offer several advantages, i.e., high power density, simplified fabrication processes, and excellent stack compactness, thus making them the predominant architecture in SOFC technology. However, high-temperature sealing remains a major challenge for planar SOFC stacks. Sealing technology is critical in determining the safety, efficiency, and overall stability of SOFC systems. The sealing material as the core component of this technology directly affects the stack hermeticity, thereby impacting its power output and long-term operational reliability.Planar solid oxide fuel cells (SOFCs) utilize two primary sealing methods, i.e., compressive and rigid sealing, which are distinguished via the application of compressive load during the sealing process. Compressive sealing materials suitable for planar SOFCs include metal, mica-based, and ceramic-based compressive seals, each offering unique properties such as excellent deformability, high stability, and superior high-temperature resistance. 1) Metal Compressive Seals: Silver (Ag) is the most widely used metal compressive sealing material due to its outstanding ductility, chemical stability, and lower cost, compared to platinum and gold. However, Ag also has several drawbacks, including temperature sensitivity, low mechanical strength, and limited chemical stability under both oxidizing and reducing atmospheres, hindering its suitability for commercial SOFC applications. 2) Mica-based Compressive Seals: Mica-based compressive sealing materials feature a distinctive layered structure, with adjacent layers held together by weak K&#x207A; interactions. This unique arrangement enables an interlayer sliding under compressive stress, enhancing their adaptability as sealing materials. The main gas leakage pathways in mica-based compressive sealing materials occur through the mica itself and the contact interfaces between mica and adjacent components. These leakage pathways can be mitigated via introducing an intermediate layer or infiltrating with wetting materials. Thermiculite&#x00AE; 866 is one of the most commercially advanced mica-based compressive sealing materials. It is based upon the mineral vermiculite and contains no organic binder or any other organic component. Thermiculite&#x00AE; 866 is soft and highly conformable, allowing for both macro- and micro-sealing to be readily achieved. In addition, it also maintains its sealing properties without relaxation or creep, even under high-temperature conditions. 3) Ceramic-based Compressive Seals: Ceramic-based materials with a great thermal and chemical stability are challenging to use directly as compressive sealing materials for SOFCs, considering their ductility, thermal expansion coefficient (TEC), and chemical compatibility. However, it is feasible to modify the morphology, optimize the manufacturing process or incorporate metallic components to improve their deformability, making them suitable for seals. In summary, the development and optimization of compressive sealing materials are crucial for enhancing the performance and durability of planar SOFCs. Each type of sealing material presents distinct advantages and challenges, necessitating ongoing research to address these issues and improve SOFC technology.Rigid sealing materials generally provide a superior gas tightness, compared to compressive seals, making them a focal point in the development of planar solid oxide fuel cells (SOFCs). These rigid seals primarily encompass glass, glass-ceramic, and metal brazing techniques. 1) Glass and Glass-ceramic Seals: Glass and glass-ceramic materials are among the most commonly used sealing materials in planar SOFCs. Adjusting the phase composition or controlling the crystallization process of these materials allows for tailoring their TEC, effectively minimizing thermal expansion mismatches with adjacent cell components. However, solely designing the composition of glass sealants to meet comprehensive performance requirements, such as glass transition temperature (Tg), softening temperature (Ts), TEC, thermal stability, and mechanical strength, poses some challenges. Incorporating ceramics, mica, or glass fibers into glass sealants can significantly enhance their overall properties. A research indicates that glasses and particularly glass–ceramics are ideal sealant candidates due to their properties, including thermal expansion, can be tailored to be compatible with other fuel cell materials. 2) Metal Brazing: Brazing is a high-temperature joining technique wherein a molten metal filler material fills the gap between metal and ceramic components, interacting with the substrates and solidifying upon cooling to form a robust, hermetic joint. Brazing techniques are primarily categorized into active metal brazing (AMB) and air reaction brazing (RAB). AMB is typically conducted under vacuum or a protective gas atmosphere, leading to higher production costs, compared to RAB. The Ag-CuO system as one of the most preferred RAB materials faces several challenges, i.e., high TEC, poor chemical stability, and low mechanical strength, significantly hindering its long-term stability in SOFC applications. In summary, while rigid sealing materials offer superior gas tightness essential for the efficient operation of planar SOFCs, some challenges remain in optimizing their properties to ensure long-term stability and compatibility with other cell components. Ongoing research and development efforts focus on addressing these challenges to enhance the performance and durability of SOFC systems.Solid oxide fuel cells (SOFCs) hold a significant promise for efficient energy conversion, however, some challenges associated with sealing materials impede their widespread commercialization. Two primary causes of sealing failure are identified:1) Thermal Expansion Mismatch: Differences in the thermal expansion coefficients (TEC) between sealing materials and adjacent SOFC components can induce thermal stresses at high operating temperatures. These stresses may lead to the formation of pores and cracks, compromising the mechanical integrity of the seal and resulting in gas leakage.2) Decomposition and Interfacial Reactions: Exposure to high temperatures and environments with both oxidizing and reducing conditions can cause decomposition of sealing materials. In addition, chemical reactions at the interfaces between seals and SOFC components can also occur, ultimately leading to a sealing failure.Addressing these issues is crucial for the commercial application of SOFCs. Future research should focus on:1) Enhancing high-temperature stability and chemical compatibility: Developing materials that remain stable and chemically inert under SOFC operating conditions.2) Improving TEC matching: Tailoring the TEC of sealing materials to closely align with those of adjacent components to minimize thermal stresses.3) Enhancing resistance to chemical corrosion and oxidation: Creating seals that can withstand corrosive environments and resist oxidation over prolonged periods.4) Optimizing glass-ceramic formulations: Adjusting compositions to reduce crystallization tendencies, thereby improving mechanical properties and durability.5) Developing self-healing materials: Innovating materials capable of autonomously repairing minor damages, extending the operational lifespan of seals.6) Advancing cost-effective solutions: Streamlining manufacturing processes to reduce costs without compromising quality.7) Promoting environmentally friendly technologies: Ensuring that new sealing materials and processes with a minimal environmental impact, aligning with sustainable development goals.Summary and prospectsAdvancements in sealing materials are pivotal for the progression of solid oxide fuel cell (SOFC) technology. These materials must maintain a long-term stability under extreme operating conditions, i.e., high temperatures, elevated pressures, and chemically aggressive environments. In addition, they also require excellent thermal expansion compatibility and gas impermeability to ensure the structural integrity and operational longevity of SOFC stacks. Future developments in SOFC sealing materials should focus on glass-ceramic composites, offering superior chemical stability, tailored thermal expansion behavior, and robust mechanical properties at elevated temperatures. These characteristics make them well-suited for ensuring the long-term stability of SOFC systems. The microstructure of these composites can be engineered to enhance gas tightness, self-healing capabilities, and overall durability via optimizing the composition of glass and ceramic phases, as well as refining heat treatment processes. The development of high-performance glass-ceramic composite sealing materials will address the critical challenges associated with the existing SOFC sealing technologies, providing some essential solutions for the commercialization and large-scale deployment of SOFC systems. Advancements in this field will facilitate a widespread adoption of clean energy technologies, contributing to the global transition toward a low-carbon economy and sustainable energy infrastructure.