PEO‐Based Solid Composite Polymer Electrolyte for High Capacity Retention All‐Solid‐State Lithium Metal Battery

Abstract The limited ionic conductivity at room temperature and the constrained electrochemical window of poly(ethylene oxide) (PEO) pose significant obstacles that hinder its broader utilization in high‐energy‐density lithium metal batteries. The garnet‐type material Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is recognized as a highly promising active filler for enhancing the performance of PEO‐based solid polymer electrolytes (SPEs). However, its performance is still limited by its high interfacial resistance. In this study, a novel hybrid filler‐designed SPE is employed to achieve excellent electrochemical performance for both the lithium metal anode and the LiFePO4 cathode. The solid composite membrane containing hybrid fillers achieves a maximum ionic conductivity of 1.9 × 10−4 S cm−1 and a Li+ transference number of 0.67 at 40 °C, respectively. Additionally, the Li/Li symmetric cells demonstrate a smooth and stable process for 2000 h at a current density of 0.1 mA cm−2. Furthermore, the LiFePO4/Li battery delivers a high‐rate capacity of 159.2 mAh g−1 at 1 C, along with a capacity retention of 95.2% after 400 cycles. These results validate that employing a composite of both active and inactive fillers is an effective strategy for achieving superior performance in all‐solid‐state lithium metal batteries (ASSLMBs).