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

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 degrees 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 x 10-4 S cm-1 at 35 degrees C), a high Li+ transference number (0.486 at 35 degrees 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 degrees C and 90.5% capacity retention over 100 cycles. The electrolyte also exhibits compatibility with high-voltage cathodes of LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2 for high-energy Li-metal batteries. These new insights shed light on the rational regulation of SPEs in advanced solid-state batteries.