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

The primary factor limiting the operation of poly(ethylene oxide)-based solid electrolytes at ambient temperature is strong ionic coordination, rather than high crystallinity. Consequently, the strategy of weakening coordination by increasing Li⁺ concentration facilitates excellent electrochemical performance and ambient-temperature operation of solid-state lithium-metal batteries. Furthermore, the stable operation of high-voltage batteries and compression-free pouch batteries further demonstrates the broad applicability of this strategy.

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-LiFePO₄ 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_0.6Co_0.2Mn_0.2O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ for high-energy Li-metal batteries. These new insights shed light on the rational regulation of SPEs in advanced solid-state batteries.