Regulating Interfacial Chemistry to Boost Ionic Transport and Interface Stability of Composite Solid‐State Electrolytes for High‐Performance Solid‐State Lithium Metal Batteries

Abstract Composite solid‐state electrolytes (CSSEs) that combine the benefits of inorganic and polymer electrolytes hold great potential for solid‐state lithium metal batteries (SSLMBs) due to their high ionic conductivity and superior mechanical properties. However, their overall performance is severely hindered by several practical challenges, including inorganic component aggregation, poor interface behavior, and limited Li + transport. Here, a unique ultrathin coating of triaminopropyl triethoxysilane with a bifunctional structure is introduced that effectively bridges the inorganic fillers (Li 1+x Al x Ti 2‐x (PO 4 ) 3 , LATP) and the polyvinylidene fluoride hexafluoropropylene /polyethylene oxide polymer matrix, thereby enabling high‐performance CSSEs (referred to as SLPH). This design prevents LATP particle agglomeration, improves interfacial compatibility, and ensures the enrichment and fast transport of Li + within SLPH. Consequently, the SLPH exhibits a low ionic conduction energy barrier ( E a = 0.462 eV), desirable ionic conductivity (4.19 × 10 −4 S cm −1 at 60 °C), and a high Li + transference number ( = 0.694). As a result, SSLMBs with SLPH, including Li| SLPH |Li symmetric cells, LiFePO 4 | SLPH |Li coin‐type, and pouch cells, demonstrate superior rate capability and long‐time cycling stability. This work underscores the significance of surface functionalization of inorganic electrolytes to create a stable solid‐solid interface and enhance ionic conduction, paving the way for high‐performance CSSEs in SSLMBs.