An in situ‐Fabricated Composite Polymer Electrolyte Containing Large‐Anion Lithium Salt for All‐Solid‐State LiFePO4/Li Batteries

Abstract In this work, we propose an in situ hydrolytic method to synthesize SiO 2 nanoparticles, which are incorporated in poly(ethylene oxide)‐based polymer in the presence of lithium salt with a large anion (lithium bis(oxalate) borate). When evaluated as the solid electrolyte for electrochemical performance in lithium batteries, the as‐prepared composite polymer electrolyte (CPE) exhibits an exciting ion conductivity of 1.9 mS/cm at 80 °C. Moreover, the CPE shows a decent Li + transference number up to 0.69 and wide electrochemical window of 5.05 V at 60 °C. Furthermore, the Li/LiFePO 4 cell assembled by the CPE exhibits an impressive capacity of 156.3 mAh/g at 60 °C under 0.05 C (1 C=160 mA/g). Considering the aspects mentioned above, the prepared CPE has the potential to be applied in practical high‐temperature batteries with a long‐term service life. More importantly, the synthetic strategy is favorable for enhancing both physical and electrochemical performance for solid electrolyte and may provide a new strategy for study and fabrication of lithium batteries.