Flexible sensors are considered as one of the most important elements of flexible electronics, which convert physiological signals into electrical signals in human health monitoring and human-machine interaction fields^{[1, 2]}. Flexible energy units are required to power flexible sensors for real applications, among which, flexible lithium-ion batteries serve as one of the best solution to the growing needs^[3]. Lithium-ion batteries (LIBs) with high energy density and stable cycling performance have already been used in portable electronics and flexible wearable electronics over the past decades^[4−7]. However, commercial anode candidates now for LIBs including the graphite and Li₄Ti₅O₁₂ are hampered by limited capacity (372 mA∙h∙g⁻¹ for graphite, 175 mA∙h∙g⁻¹ for Li₄Ti₅O₁₂) and poor rate capability, which can not address the requests of high capacity for modern electronic products^{[8, 9]}. Thereby, developing and utilizing potential electrode materials with high energy density, long cycling lifespan and stable high-rate capability performance have become one of emergencies in LIBs field^[10−13]. Group Ⅳ elements such as silicon-Si and tin-Sn as the electrode materials for LIBs prove to have high theoretical specific capacity (3579 mA∙h∙g⁻¹ for Si and 992 mA∙h∙g⁻¹ for Sn), low working potential and low cost, which are currently attracting attention. Unfortunately, bulk Si and Sn anodes usually suffer from large volume changes and fracture of the structures during lithium insertion and deinsertion process, and it will cause electrode pulverization and destroy the electronic connection between active materials, leading to poor cycle stability and low Coulombic efficiency^[14−17].

In fact, commercially available Si normally covered by slightly amorphous Si_x layer on the surface and the compound (Si/Si_x) in recent years have been considered as the potential alternatives for pure Si anode for LIBs, where Si_x layer can well control the volume expansion to improve Si electrodes through generating Li₂O and/or Li₄SiO₄ in the first cycle which can disperse uniformly with the simultaneously formed Si particles. Nevertheless, the cycle stability of Si_x anodes is still unsatisfactory due to the poor conductivity^[18−21]. Thus, to overcome the afore-mentioned problems of Sn and Si_x anodes, general and effective strategies are adopted by compositing them with carbon or graphene with reasonable nanostructures. For carbon-based composites, carbon as a conductive buffering media plays important roles in increasing the electrical conductivity and relieving the volume change, resulting in the enhancement of cycling stability and Coulombic efficiency^{[22, 23]}. For example, the amorphous carbon tube coated Sn nanoparticles composite anodes exhibited superior electrochemical performances for lithium-ion batteries. Mesoporous SiO_x@C particles were prepared and exhibited a superior specific capacity and outstanding rate capability when used as anodes for LIBs^{[24, 25]}.

To further improve these issues, here we showed the fabrication of three-dimensional Si/SiO_x/C and Sn/C microrods array consisting of nanospheres on carbon textiles via a direct and large-scale electrospraying followed with calcination treatment in inert ambience. As well known, electrospraying technique as a simple and low-cost synthetic method has been successfully used to prepare nano/micro-materials with unique microstructures. Specifically, the highly electropositive precursor droplets show strong electrostatic interactions with the negatively charged carbon textiles to instantly trigger a fast coagulation process, during which the uniformly nano spherical precursors are cumulated with each other to construct the macrostructure of microrods array on carbon textiles, and followed by carbonization treatment to get the final products. Usually, several advantages can be summarized by this electrode fabrication method: First, microrod arrays stacked with nanoparticles exhibit large aperture density which increases the contact areas between the electrode active materials and electrolyte, and provides more space to accommodate the volume expansion of electrode materials. Second, the carbon cloth with loose texture structure as current collector has a high strength and high specific surface, providing higher specific surface compared to other traditional metal substrates with planar surface. When used as LIBs anode materials, both Si/SiO_x/C@CC and Sn/C@CC products exhibit high battery capacity, good rate capability and stable cycling performance. By using Si/SiO_x/C@CC as a new binder-free anode, we assembled flexible soft pack lithium-ion battery with outstanding mechanical robustness and electrochemical performance, which can successfully light up the commercial LED lamp.

3-Aminoprppyltriethoxysilane (AMEO), stannic chloride pentahydrate (SnCl₄·5H₂O) and N, N-dimethylformamide (DMF) were purchased from Sinopharm Chemical Reagents Co., Shanghai, China. 1,2,4,5-Benzenetetracarboxylic anhydride (PDMA) and Bis(4-aminophenyl) ether (ODA) were supplied by Qi Fuqin Materials Technology Co., LTD. Shanghai, China.

Si/SiO_x/C@CC samples were synthesized from the simple electrospraying process and carbonization treatment. The precursor solution was first prepared by dissolving 3 g of AMEO and 1.1 g of ODA into 23 g of DMF solution under magnetic stirring for 10 min. Then 1 g of PDMA was added to the freshly prepared solution and kept stirring at room temperature (~25 ^oC). The transparent precursor solution was electrosprayed from the medical needle on a piece of carbon cloth with the diameter of 8 mm placed at distance of 15 cm with applied voltage of 24 kV and constant flow rate of 0.1 mL·h⁻¹ as shown in Fig. 1. The as-sprayed carbon cloth with products was then calcinated in an atmospheric CVD furnace at 800 °C for 2 h under N₂/H₂ with a heating rate of 5 °C·min⁻¹, resulting in the formation of Si/Si_x/C nanosphere arrays.

Furthermore, Sn/C@CC samples were prepared via this similar electrospraying method: 3 g SnCl₄·5H₂O was dissolved into 24 g DMF solution under magnetic stirring till the solution being transparent. Then 1.0 g of PDMA and 1.1 g ODA were respectively added into the above solution and kept stirring for 0.5 h. The precursor solution was then electrosprayed on the circular carbon cloth with the same process for the fabrication of Si/Si_x/C@CC samples. Finally, the electrosprayed carbon cloth with precursors was calcinated in N₂ gas at 700 °C for 2 h with a heating rate of 5 °C·min⁻¹ to obtain prepare Sn/C@CC sample.

The crystal structures of the as-synthesized products were investigated using X-ray diffraction (XRD, DMAX-RB), electron energy-loss spectroscopy (EELS, SUPRA 55) and energy dispersive X-ray spectroscopy line scan (EDX, JEM 2200FS). The chemical composition of the products was analyzed by X-ray photoelectron spectroscopy (XPS Thermo Escalab 250XI). Raman spectrum of the sample was collected using the Raman spectrometer (HR800). The size and morphology were characterized via field-emission scanning electron microscopy (FESEM, Zeiss Supra 55) and transmission electron microscope (TEM, JEM 2200FS). Thermogravimetric analysis (TGA) was performed on a thermal analyser (SDTA851e) from room temperature to 1000 °C with a heating rate of 10 °C in air.

During the fabrication of Li-ion batteries, the weight of active materials on carbon cloth should be determined by weight differential subtract method of the carbon cloth covered with active material and pure carbon textiles weighed in a high-precision analytical balance. The calculated loading density of the active materials of two samples was about 0.5−1.0 mg·cm⁻². The electrochemical behaviors of two products were studied by laboratory-made CR2032 type coin half-cells. A piece of the carbon textile with spraying products was used directly as the working electrode without any polymeric binder or conductive additive, and a traditional Celgard 2325 as the separator, pure lithium-foil as the counter electrode and 1 M LiPF₆ in EC-DMC (1 : 1 by volume) as the electrolyte.

In this work, the flexible liquid-state full cell was fabricated using the as-fabricated Si/Si_x/C@CC as anode, aluminum foil coated with commercial LiCoO₂ particles as cathode, LiPF₆ as the electrolyte, and the Celgard 2325 as separator, respectively. The solid-state flexible full cells were composed of Si/Si_x/C@CC anode, commercial LiCoO₂ cathode, Celgard 2325 separator, and PEO/garnet composite electrolyte containing LiTFS. Both cells were assembled in the Ar₂ filled glove box. Cyclic voltammetry (CV) measurements were performed on an electrochemical work station (CHI 760D, Shanghai). The galvanostatic cycling measurements were performed on LAND battery testing system (Wuhan, China).

The phase structure and the composition of the prepared Si/Si_x/C samples were characterized by XRD technique. Clearly, as shown in Fig. 2(a), only a broad peak in the range of 15°−35° corresponds to amorphous Si_x phase, which also overlapped with the peak (~24°) of amorphous carbon, demonstrating the formation of Si/Si_x/C composites on the carbon cloth^[26].

The morphology and microstructures of Si/Si_x/C composites on the carbon cloth were further characterized by SEM and TEM, respectively. Fig. 2(b) shows that Si/Si_x/C composites uniformly grew onto the surface of carbon cloth. The magnified SEM image in Fig. 2(c) further shows that the rod-like morphology of the Si/Si_x/C composites on carbon cloth from the electrospraying procedure for 8 h. TEM image in Fig. 2(d) remarkably confirms that large number of nanospheres assembled into rod-like structure with the diameter of about 3 μm and length up to about 4 μm. Fig. 2(e) shows the TEM image of a single Si/Si_x/C nanosphere with smooth surface and the diameter of about 120 nm. HRTEM characterization in Fig. 2(f) confirms the amorphous nature of the prepared Si/Si_x/C composites and no obvious interface was observed between Si_x and C phases, demonstrating that Si_x samples were well-distributed in carbon samples. The elemental mapping analysis of the single Si/Si_x/C nanosphere was shows in Fig. 2(g), clearly, three elements of Si, O, and C uniformly distribute in the single nanosphere and the EDS line scanning result in Fig. S1 further confirms the good distributions of several elements without abrupt change of the intensity.

The composition of the as-prepared Si/Si_x/C composites was further characterized by Raman spectrum in Fig. 2(h). Two main diffraction peaks located at about 1320 and 1597 cm⁻¹ are contributed to the defect-induced (D) mode and the stretching mode of C−C bonds (G) of graphite, respectively. XPS was carried out to further investigate the chemical state of Si/Si_x/C nanosphere arrays on carbon cloth. The survey spectrum of Si/Si_x/C composites shown in Fig. 2(i) displays significant Si, C, and O peaks, agreeing well with the EDS results. The Si 2p emission spectrum in Fig. 2(j) can be distinctly attributed to four types of Si species: Si⁴⁺ (104.4 eV), Si³⁺ (103.5 eV), Si²⁺ (102.5 eV) and Si⁺ (101.4 eV), respectively. Moreover, Si/Si_x/C composites were first etched by HF solution (16 wt%), specified as Si/Si_x/C-HF, as and then characterized by HRTEM and XPS techniques to verify the existence of Si. Fig. S2(a) shows the HRTEM image of Si/Si_x/C-HF, in which a small amount of lattice stripes can be observed and the d-spacings of 2.41 and 3.33 Å correspond to (102) plane and (100) plane of crystalline Si (PDF # 80-0005), respectively. The SEAD pattern further indicated the polycrystalline of Si/Si_x/C-HF. XPS spectra were further operated to prove the existence of Si. Clearly, the peak appeared at 99.5 eV is attributed to Si−Si bond in Fig. S2(b). All above results indicate that amorphous Si/Si_x/C composites with nanosphere arrays were prepared on the surface of carbon cloth from the simple electrospraying and calcination processes. Significantly, during the synthetic process, the electrospraying time is very critical to the formation of Si/Si_x/C nanosphere arrays. When the electrospraying time is less than 8 h, no obvious array structures were observed and only numerous nanospheres aggregated on the surface of carbon cloth as shown in Figs. S3(a) and S3(b).

The composition and microstructure of the as-synthesized Sn/C composites from the similar electrospraying process were also characterized in detail. As shown in Fig. 3(a), all diffraction peaks can be indexed to tetragonal Sn phase (JCPDS No. 04-0673) with a broad peak (2θ = 24°) of amorphous carbon, indicating the formation of Sn/C composites. SEM images in Figs. 3(b) and 3(c) show that Sn/C composites on carbon cloth have similar structure with the as-synthesized Si/Si_x/C nanosphere arrays. TEM image in Fig. 3(d) confirms that Sn/C composites were consisting of a great quantity of nanospheres with the diameter of about 130 nm. HRTEM image in Fig. 3(e) clearly illustrated that amorphous C exists in this nanosphere with crystalline Sn particles casually distributing on the surface of the nanosphere.

The clearly resolved lattice spacing was measured to be 0.33 and 0.29 nm, corresponding to the (110) and (200) d-spacing of tetragonal phase Sn, respectively. Fig. 3(f) shows the corresponding EDS elemental mapping analysis of a single Sn/C nanosphere. Specifically, Sn nanocrystals are arbitrarily encapsulated in amorphous C matrix and this will greatly reduce the volume effect of Sn during the Li-storage process. Fig. 3(g) shows the full-range XPS spectrum of the Sn/C sample, in which signals from Sn, C, and O were observed, confirming the successful synthesis of Sn/C nanosphere arrays on the carbon cloth substrate.

Finally, TG analysis was employed to determine the C content of both composites. As shown in Fig. 4(a), Si/Si_x/C composites start to reduce weight when the heating temperature increased to 400 °C, indicating the oxidation of amorphous carbon. Thus, both Si/Si_x/C and Sn/C composites show relatively high C content of 41.40% and 80.70% (Fig. 4(b)), respectively. The existence of amorphous carbon in both samples can enhance the conductivity and reduce the volume effect of electrodes during the intercalation/deintercalation process.

The electrochemical behavior of Si/Si_x/C@CC nanosphere arrays was evaluated by assembling coin-type half cells using Li foil as anode and Si/Si_x/C@CC composites as cathode. Fig. 5(a) shows the initial five CV curves of Si/Si_x/C@CC electrode with the scan rate of 0.1 mV∙s⁻¹ at the voltage range of 0.01−2.0 V. In the initial cycle, the irreversible peak at about 0.72 V in the cathodic process can be assigned to the formation of solid electrolyte interface (SEI) due to the decomposition of the electrolyte. The other irreversible peak at about 0.2 V is related to the reduction of Si_x into Li₄SiO₄ and Li₂O^[27], and corresponding reaction equations are as following:

1SiOx+2xLi++2xe−→xLi2O+Si,

2SiOx+xLi++xe−→(x/4)Li4SiO4+(1−x/4)Si.

In the anodic-scan process, two oxidation peaks at about 0.23 and 1.2 V can be attributed to the deintercalation process of Li−Si alloys and Li−C alloys, respectively, and corresponding reaction equations are as following:

3Si+yLi++ye−↔LiySi,

46C+zLi++ze−↔LizC6.

Another oxidation peak at ~0.3 V can be ascribed to deintercalation reaction of Li ions in carbon cloth substrate, which is agreement with results observed in the CV curve of pure CC^[28]. In the subsequent cycles, the main cathodic peak remained at ~0.2 V, corresponding to the lithiation of process of Si. During the anodic potential sweeps, two oxidation peaks around 0.23 and 1.2 V are almost unchanged relating to the delithiation of process. Fig. 5(b) further shows the galvanostatic charge/discharge profiles of Si/Si_x/C@CC nanosphere arrays with various cycles at the current density of 0.5 A∙g⁻¹ within a potential window of 0.01−2.0 V, respectively. Obviously, in the 1^st discharge profile, a flat plateau at about 0.7 V corresponds to the formation of SEI film during the lithiation process. In addition, Si/Si_x/C@CC electrode with nanosphere arrays deliver the initial discharge/charge specific capacity of 2150/1552 mA∙h∙g⁻¹, with a high Coulombic efficiency of 72.1%. In subsequent 20^th and 100^th charge/discharge cycles, Si/Si_x/C@CC electrodes deliver discharge/charge specific capacity of 1750/1500 and 1682/1487 mA∙h∙g⁻¹, respectively, revealing the excellent cycling stability of Si/Si_x/C@CC electrode. The rate performance of Si/Si_x/C@CC nanosphere arrays was further evaluated at different current densities and 10 cycles for each current density were performed. As shown in Fig. 5(c), the delivered capacities of the electrode were relatively stable at various current densities during cycling. Specifically, with the increase of the current density from 0.5, 1, 2, 3, 5 to 8 A∙g⁻¹, the discharge capacities were 1803, 1521, 1388, 1224, 1053, and 705 mA∙h∙g⁻¹, respectively. When the current density was back to the initial value of 0.5 A∙g⁻¹, the specific capacity also recovered to its original value of 1881 mA∙h∙g⁻¹, demonstrating the outstanding rate performance of Si/Si_x/C@CC electrode.

The cyclic performance of Si/Si_x/C@CC nanosphere arrays was exhibited in Fig. 5(d). Specifically, the composites delivered a high specific capacity of about 1750 mA∙h∙g⁻¹ at a current density of 0.5 A∙g⁻¹ higher than some reported work in literatures^[29−32] (Table 1 in Supporting Information). After 1050 cycles, the electrode still retained a high specific capacity of about 1388 mA∙h∙g⁻¹ with a high CE of 100%, exhibiting the superior reversibility and stability of Si/Si_x/C@CC electrode. The electrochemical impedance spectra of Si/Si_x/C@CC electrode were operated to understand the Li-storage mechanism of the electrodes. As shown in Fig. 5(e), The Nyquist plots of Si/Si_x/C@CC nanosphere arrays after 10 and 1050 cycles were composed of a depressed semicircle in the high-frequency zone and a sloping line in the low-frequency zone, respectively. Typically, the semicircle in high-frequency zone can be attributed to the charge transfer resistance (R_ct) on the electrode/electrolyte interface, and the sloping line is called the Warburg resistance, representing Li ion diffusion kinetics in the electrode. The Si/Si_x/C@CC electrodes show the charge transfer resistances of about 42 and 98 Ω after 10 and 1050 cycles, respectively, demonstrating the Si/Si_x/C@CC electrodes with array structure have good contact with the electrolyte. The morphology and microstructure of the electrodes after long cycling were further evaluated by SEM analysis and shown in Fig. S4. Obviously, after 1050 cycles, Si/Si_x/C electrodes still maintained spherical microstructure and an intimate contact with carbon cloth as shown in Figs. S4(a) and S4(b). Thus, spherical structure and the existence of amorphous Si_x and carbon can availably alleviate the volume expansion effect during the lithiation/delithiation process.

In situ XRD was performed to further investigate the intrinsic reaction mechanisms of Si/Si_x/C@CC electrode. As shown in Fig. 6(a), the in-situ cell was discharged from open circuit voltage to 0.01 V, and charged to 2.0 V. In the discharge process, two characteristic peaks located at 20.5° and 23.2° can be indexed to Li₂₁Si₅ phase, the two characteristic peaks in the bidimensional contour map gradually narrowed when the discharge time increased, suggesting the grain size of Li₂₁Si₅ is larger as the discharge reaction going on, which correspond to the lithiation of process of Si. In the process of charge, the situation was opposite, revealing high reversibility of Si/Si_x/C@CC electrodes. Fig. 6(b) shows the schematic illustration and operating mechanism of the rechargeable Si/Si_x/C@CC electrode. In this case, Si/Si_x/C@CC electrode exhibited high battery capacity, good rate capability and stable cycling lifespan, which can be attributed to the following aspects: Firstly, 3D Si/Si_x/C microrod arrays on carbon cloth with the loose textures provided more open spaces, as well as contact area for facile diffusion of the electrolyte, leading to a higher efficiency of lithiation and delithiation under the electrolyte penetration and providing a high capacity. Secondly, Si/Si_x/C microrod arrays sticked tightly to the carbon cloth had an outstanding electronic conductivity, which built up an expressway for charge transfer and Li⁺, enhancing the rate capability. When suffering from intercalation and deintercalation, the conglutinated nanospheres with strengthened mechanical property can prevent the microrod arrays from pulverization and fragmentation. In addition, the carbon layer acted as the secondary active component can buffer the volume expansion of Si_x during lithiation/delithiation and prolong the cycle life of the electrode.

The electrochemical property of Sn/C@CC electrode was also measured in the coin-cell system and the initial five CV curves with the voltage window ranging from 0.01 to 2 V at a scan rate of 0.1 mV∙s⁻¹ were displayed in Fig. 7(a). In the first cathodic process, a broad cathodic peak at about 0.72 V can be ascribed to the formation of the solid electrolyte interphase (SEI) layer and the alloying reaction of Li and Sn. The other reduction peak at 0.27 V can also be indicated the Li−Sn alloying reaction. Subsequently, the third reduction peak at about 0.14 V can be caused by the Li⁺ insertion into the amorphous carbon matrix. In the anodic-scan process, the oxidation peaks at about 0.3 and 0.7 V can be assigned to the delithiation of Li−Sn alloy. In sequential cathodic-scan process, two main reduction peaks at about 0.2 and 0.25 V can be assigned to the alloying reaction of Li⁺ insertion into Sn to form Li−Sn alloy, respectively^[33]. The oxidation peaks in sequential anodic-scan process have no obvious changes implying the good reversibility of the Sn/C@CC electrode for Li-storage device.

The discharge/charge curves of Sn/C@CC electrode for various cycles were shown in Fig. 7(b) at the current density of 0.5 A∙g⁻¹ within a voltage window of 0.01−2.0 V, respectively. Specially, the Sn/C@CC electrode with nanosphere arrays delivered an initial discharge/charge specific capacity of 1420/1170 mA∙h∙g⁻¹ with a high Coulombic efficiency (82.3%) during the 1^st cycle. Importantly, the Sn/C@CC electrode delivered slightly decreased discharge capacity of about 1250 mA∙h∙g⁻¹ for 100^th cycle, which is almost the same value with that for the 50^th cycle illustrating the high capacity and outstanding cycling stability of the electrode. Fig. 7(c) further showed the rate performance of the Sn/C@CC electrode at different discharge/charge current densities. Clearly, the Sn/C@CC electrode delivered the reduced discharge capacities of 736 mA∙h∙g⁻¹ at current densities of 3 A∙g⁻¹. When the current density decreased to 0.2 A∙g⁻¹, the Sn/C@CC electrode still remained a stable discharge capacity of 1503 mA∙h∙g⁻¹, indicating the excellent rate performance of the Sn/C@CC electrode. Fig. 7(d) depicted the discharge/charge capacities vs. cycle number at a current density of 0.5 A∙g⁻¹, in which the Sn/C@CC electrode delivered a stable specific capacity of about 1375 mA∙h∙g⁻¹ even after 500 cycles, exhibiting its good cycling performance and potential application for Li-storage batteries.

For instance, using Si/Si_x/C@CC nanosphere arrays as binder-free anode, commercial LiCoO₂ covered Al foil as cathode, LiPF₆ as electrolyte and the Celgard 2325 as separator, the full cell was fabricated to investigate the feasibility in commercial application of nanosphere arrays growing on the carbon cloth substrate as shown in Fig. 8(a). The Si/Si_x/C@CC//LiCoO₂ full cell was performed in the potential range of 2.5−3.9 V. Fig. 8(b) depicts the galvanostatic charge/discharge curves of full cell for the 1^st, 50^th, and 100^th cycle at the current density of 0.5 A∙g⁻¹, respectively. From the curves, the corresponding charge/discharge voltage plateau is about 3.7 V. The Si/Si_x/C@CC//LiCoO₂ full cell delivers irreversible discharge capacity of about 1620 mA∙h∙g⁻¹ in the first cycle and in subsequent 50^th and 100^th cycles, the charge/discharge curves were almost overlapped and remained discharge capacity of about 1280 mA∙h∙g⁻¹, revealing excellent stability of the full cell. Fig. 8(c) revealed the cycling performance of Si/Si_x/C@CC//LiCoO₂ full battery at a current density of 0.5 A∙g⁻¹ within a potential window of 2.5−3.9 V. Significantly, after 250 cycles, the full cell still maintained the reversible capacity of about 1350 mA∙h∙g⁻¹, demonstrating the excellent capacity retention of the full cell. The rate capability of the full cell was also tested at various current densities as shown in Fig. 8(d). With the increase of current density from 0.5, 1 to 2 A∙g⁻¹, the delivered discharge capacities were 1300, 985, and 800 mA∙h∙g⁻¹, respectively. When the current density returned to its initial value of 0.5 mA∙g⁻¹, the specific capacity also returned to 1190 mA∙h∙g⁻¹. Confirming the good rate performance of the Si/Si_x/C@CC//LiCoO₂ full cell.

To further investigate the practical applications of the flexible device, the safety performance of the full cell was also carried out at various humidity (H) parameters and temperature (T), respectively. As shown in Fig. 8(e), the Si/Si_x/C@CC//LiCoO₂ full cell remains the same discharge capacities of 1276 mA∙h∙g⁻¹ under the different humidity of 50%, 70%, and 90% for each 20 cycles. Fig. 8(f) further showed the reversible capacities of full battery cycled at 0.5 A∙g⁻¹ at different temperature. The full battery delivers a stable discharge capacity of about 1290 mA∙h∙g⁻¹ at various temperature of 45, 35, and 25 °C. When the temperature decreased to 10 °C, the delivered discharge capacity dropped to 1000 mA∙h∙g⁻¹. When the temperature finally returned to 25 °C, the initial capacity value of 1250 mA∙h∙g⁻¹ still recovered, revealing the stable electrochemical activity of the full battery. Mechanical flexibility of the full cell was also evaluated due to the great importance for potential applications in wearable electronics. Fig. 8(g) shows the voltage values of the Si/Si_x/C@CC/LiCoO₂ full battery under different bending angles of 0°, 30°, 60°, and 90°, respectively. Interestingly, the full battery still keeps a stable voltage value of about 3.45 V under various bending angles, indicating the good flexibility and mechanical stability of the device. Fig. 8(h) further shows that this full battery has the almost constant potential value under repeated bending condition, confirming the outstanding flexibility of the cell. The insets in Figs. 8(g) and 8(h) distinctly display that the as-fabricated full battery can effectively light a commercial green LED, even under the bending state. Solid-state lithium battery had caused widely concern in recent years due to the excellent safety. To demonstrate the applicability of Si/Si_x/C@CC in field of solid-state lithium battery, solid-state Si/SiO_x/C@CC//LiCoO₂ full batteries based on PEO-LLZTO-PEG-LiTFSI electrolyte were also assembled^[34]. Fig. S5 shows the charge−discharge curves of the solid battery in a voltage range of 2.5−3.9 V at a current density of 0.5 A∙g⁻¹ and the corresponding discharge capacity versus cycle number was shown in Fig. S5(b). Results show that the battery delivered an initial discharge capacity of 251 mA∙h∙g⁻¹ and gradually decreased to a stable value of 112 mA∙h∙g⁻¹ after 30 cycles. Importantly, the solid-state battery shows reversible capacity with a nearly constant value of ~120 mA∙h∙g⁻¹ during 80 cycles, implying that the interfaces between Si/Si_x/C@CC electrode and the electrolyte possess good stability during the charge/discharge cycle. All results demonstrate that both as-prepared Si/Si_x/C@CC and Sn/C@CC electrodes may be applied in futural energy storage field.

Three-dimensional Si/Si_x/C and Sn/C microrod arrays consisting of nanospheres grown on carbon cloth were prepared from the electrospraying process and subsequent calcination treatment. The Li-storage properties Si/Si_x/C and Sn/C composites as anode active materials were investigated for lithium rechargeable batteries. Comparing with Sn/C microrod arrays, Si/Si_x/C anode distinctly showcased a higher specific capacity of 1750 mA∙h∙g⁻¹, higher Coulombic efficiency of almost about 100% and much more cycling stability. We suggested that the improved performance can be attributed to the innovative Si and Sn-based architectures on carbon cloth, where those electrodes possessed good electronic conductivity and structural stability. The proposed strategy for fabrication of Si/Si_x/C and Sn/C electrodes was expected to be advantageous for mass-scale fabrication, and it would provide reference for the development of electrode materials for high-performance rechargeable lithium-ion batteries.