Flaky Li‐Doped High‐Entropy Oxide Enables PEO‐Based Composite Solid Electrolyte with Extended Suitability for Lithium Metal Batteries

Abstract Poly(ethylene oxide) (PEO) as a solid‐state electrolyte faces critical limitations, including low ionic conductivity, a narrow electrochemical window, and poor mechanical strength. To address these issues, flaky lithium‐doped high‐entropy oxides (LHEO‐f) with abundant surface oxygen vacancies are synthesized via a facile microwave‐assisted deep eutectic solvent (DES) method and incorporated into PEO‐based composite solid electrolytes (CSEs). The flaky LHEO‐f fillers morphology increases the continuous contact surface area with polymer chains, while oxygen vacancies enhance interfacial interactions. This synergy diminishes polymer deformation and enhances the mechanical strength of the CSEs. Moreover, the surface defects of LHEO‐f improve interactions with the oxygen‐containing groups of the polymer matrix, facilitating Li‐ion migration. All‐solid‐state lithium metal batteries (ASSLMBs) with these CSEs demonstrate excellent high‐rate capacity and cycling stability. These findings reveal that the incorporation of LHEO‐f significantly bolsters the performance of PEO‐based CSEs, showcasing their potential for further advancement and practical application in the realm of solid‐state batteries.