Interfacial engineering of composite solid electrolytes for high-performance solid-state lithium-metal batteries

Composite solid electrolytes (CSEs) combine the flexibility of polymers with the stability of inorganic electrolytes, making them promising candidates for next-generation solid-state lithium-metal batteries (LMBs). However, their practical application is limited by low room-temperature ionic conductivity, primarily due to poor polymer-inorganic interfacial compatibility that hinders Li + transport. In this work, we introduce a polymer-compatible ionic liquid (IL) to mediate the interphase between the polymer and ceramic components, simultaneously preventing ceramic particle aggregation for uniform dispersion and activating ceramic-polymer interfaces to construct continuous Li + transport pathways across ceramic domains and interfacial boundaries. The interfacial engineered CSEs exhibit a substantial enhancement in room-temperature ionic conductivity to 1.64 × 10 −3 S cm −1 . At the ambient temperature, the Li||Li symmetric cells demonstrate stable and reversible lithium plating/stripping for 4000 h, and the Li||LiFePO 4 cell delivers an initial specific capacity of 172.1 mAh g −1 at 0.5C with 90.4% capacity retention after 300 cycles. Furthermore, the Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 cells demonstrate stable performance even under high-voltage operation (4.5 V). This work provides a practical interfacial design strategy for developing high-. performance CSEs in the next-generation solid-state LMBs. • A polymer-compatible ionic liquid is introduced to mediate the polymer-ceramic interphase, preventing ceramic aggregation and activating interfacial Li + transport pathways. • The interfacial-engineered composite solid electrolytes (CSEs) achieve high room-temperature ionic conductivity of 1.64 × 10 −3 S cm −1 and enable stable Li plating/stripping over 4000 h in Li||Li cells. • The optimized CSEs deliver high electrochemical stability, with 90.4% capacity retention after 300 cycles in Li||LFP cells and excellent high-voltage tolerance (4.5 V) in Li||NCM811 cells.