Oxygen Vacancy‐Li2ZrO3: A New Choice for Boosting Homogenous Distribution and Transport of Lithium Ion in Composite Solid‐State Electrolytes

Abstract The low concentration and inhomogenous distribution of free lithium ion (Li + ) in composite polymer electrolytes (CPEs) greatly restrict the Li + transport, cycle stability and rate performance of all solid‐state batteries. In this work, lithium zirconate with superficial oxygen (O)‐vacancies (O‐LZO) is reported as a new Li + conductors for polyethylene oxide (PEO)‐based CPEs (PEO@O‐LZO). The O‐LZO demonstrates exceptional Li + transport capability, and its superficial O‐vacancies efficiently adsorb anions to facilitate the dissociation of lithium salts, leading a high concentration of free Li + in CPEs. Furthermore, the electropositive equilibrium charge layer of O‐vacancies avoids the aggregation of Li + near the filler and achieves a stable interface to promote the efficient and continuous Li + transport. These effects contribute to a high Li + conductivity of 1.63 × 10 −4 S cm −1 and a Li + migration number of 0.35 for PEO@O‐LZO at 40 °C. The assembled battery (LiFePO 4 /PEO@O‐LZO/Li) exhibits a capacity of 120 mAh g −1 at 3 C and stable cycling performance with an 80.5% capacity retention after 800 cycles at 1 C and 40 °C, maintaining excellent coulombic efficiency. This work provides a design principle of fillers to regulate Li + concentration and distribution in CPEs for efficient solid‐state lithium metal batteries.