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

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 (LiFePO₄/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.