Poly(ethylene oxide)‐Based Composite Electrolyte with Lithium‐Doped High‐Entropy Oxide Ceramic Enabled Robust Solid‐State Lithium‐Metal Batteries

Abstract Solid polymer electrolytes using poly(ethylene oxide) (PEO) as matrix are mostly applied due to the superior Li + transfer ability of oxyethyl chain. However, the high crystallinity, low oxidation potential window, and insufficient mechanical strength hinder PEO deployment in solid‐state batteries. Here, a novel composite solid electrolyte combined PEO with a lithium‐doped high‐entropy oxide (Li 0.25 HEO) ceramic powder is presented, which exhibits excellent properties for solid‐state lithium metal battery applications. On one hand, the rich oxygen vacancies of Li 0.25 HEO surface are favorable to capturing anionic groups (e. g. TFSI − ), reinforcing the Li + dissociation. On the other hand, Li 0.25 HEO with abundant Lewis acid sites markedly promotes the PEO oxidation potential window. Additionally, the incorporation of Li 0.25 HEO ceramic powder can effectively inhibit the PEO crystallization and enhance the mechanic strength of the composite electrolyte as well. The assembled solid‐state lithium metal battery based on the composite solid electrolyte exhibits high rate capacity and durable cycle performance, showing potential development and application prospects.