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 (M_w=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 (v_f/v_fo), 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⁺ 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.