Ultra-robust Single-Ion Conducting Composite Electrolytes for Stable Li-Metal Batteries

With significantly high lithium-ion (Li⁺) transport efficiency, single-ion conducting polymer electrolytes (SIPEs) often suffer from low ionic conductivity due to the covalently bonded anions to the polymer backbone. Adding plasticizers to SIPEs to improve ionic conductivity usually reduces the polymer matrix's mechanical robustness, negatively affecting overall performance as solid electrolytes. Herein, to surpass such a trade-off relationship, we successfully designed a single-ion conducting composite membrane (c-SIPM60) with cross-linked linear SIPEs and incorporated glass-mesh substrate, which shows a cation transport number close to 1, ultrahigh tensile strength of 22 MPa (modulus of 547.3 MPa), and high ionic conductivity of 1.2 × 10^-4 S/cm at 25 °C. The resultant Li/c-SIPM60/Li symmetric cell showed stable cycling performance up to 1200 h, and the LiFePO₄/c-SIPM60/Li cell presented good reversibility at C/10. Meanwhile, with additional lithium salts, a high cationic-transport composite membrane (c-HTPM60) was designed to increase the ionic conductivity with retained high Li⁺ transport efficiency. The LiFePO₄/c-HTPM60/Li cell exhibited a stable cycling performance with a capacity retention of >75.6% after 700 cycles at 25 °C. This work provides new insights into designing solid electrolytes with simultaneously high t_Li, ionic conductivity, and mechanical robustness, affording effective Li⁺ transport for energy storage systems.