Weakening Lithium‐Ion Coordination in Poly(Ethylene Oxide)‐Based Solid Polymer Electrolytes for High Performance Solid‐State Batteries

Abstract The high crystallinity of poly(ethylene oxide)‐based solid polymer electrolytes (PEO‐based SPEs) is viewed as a key barrier to their ambient‐temperature performance. Conventional approaches to mitigate crystallinity necessitate elevated operation temperatures of 50–60 °C. Interestingly, this work indicates that the predominant factor limiting ambient‐temperature performance is the robust coordination between lithium‐ion (Li ⁺ ) and ether oxygen (EO), rather than the crystallinity. By rationally tailoring the Li ⁺ concentration, this work effectively weakens the coordination strength, thereby enhancing the ambient‐temperature electrochemical performance. An optimal SPE with EO: Li ratio of 9:1 exhibits remarkable ionic conductivity (1.76 × 10 ⁻⁴ S cm ⁻¹ at 35 °C), a high Li ⁺ transference number (0.486 at 35 °C), and superior adhesion to electrodes in compression‐free pouch cells. The practical feasibility of the SPE is demonstrated in solid‐state Li‐LiFePO ₄ cells achieving a specific capacity of 149.66 mAh g ⁻¹ at 0.1 C and 35 °C and 90.5% capacity retention over 100 cycles. The electrolyte also exhibits compatibility with high‐voltage cathodes of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ and LiNi _0.8 Co _0.1 Mn _0.1 O ₂ for high‐energy Li‐metal batteries. These new insights shed light on the rational regulation of SPEs in advanced solid‐state batteries.