Interface Engineering via Ceria Coating Reconciles Ion Transport and Lithium Compatibility in Composite Polymer Electrolytes

ABSTRACT Composite polymer electrolytes (CPEs) exhibit considerable potential for solid−state lithium−metal batteries (SLBs). However, incompatibilities between the various components in the electrolyte continue to hinder the full realization of its performance and practical applications. In this work, a multifunctional ceria interfacial layer is proposed to achieve uniform dispersion of ceramic fillers and facilitated interfacial transport of lithium ions in CPEs. At the same time, the physical barrier provided by this multifunctional interface layer prevents direct contact between the ceramic filler and the lithium metal, thereby avoiding potentially harmful side reactions that could further lead to a performance deterioration in battery cycling. Owing to the introduction of this multifunctional interface layer, the CPE exhibits high ionic conductivity (0.772 mS cm −1 ) and Li–ion transference number (0.626), with a wide electrochemical window (5.03 V). Furthermore, the Li|CPE|Li symmetric cell exhibits a lithium deposition/stripping capacity exceeding 1500 h at room temperature, indicating the CPE's excellent ability to suppress interfacial side reactions. Li|CPE|NCM811 cells retained a capacity of 77% after 350 cycles, whilst pouch cells retained 76% after 300 stable cycles at room temperature and 0.5 C. The method of optimizing ceramic fillers offers new insights into the design of novel composite solid–state electrolytes for SLBs.