Enhancing Electrochemical Performance in PEO/LLZTO Composite Solid Electrolyte via PEG Polymer Integration for Solid‐State Batteries

Composite solid electrolytes (CSE) are promising candidate materials that can complement the ionic conductivity and thermal and electrochemical stabilities of solid polymer electrolytes. In this study, the ionic conductivity, Li migration characteristics, and electrochemical stability are investigated of “polymer‐in‐ceramic”‐structured CSE sheet into which polyethylene glycol polymer is introduced. PEG10 CSE exhibits ionic conductivity twice as high as PEG0 CSE at 50 °C and shows high oxidation potential stability of 5.2 V. In addition, PEG10 CSE has high interfacial compatibility with Li metal, and LiFePO 4 /PEG10 CSE/Li cell evaluation confirms that PEG10 CSE has high discharge capacity, C‐rate performance, and cycle stability at 45 °C.