Enhancing Solid-State Li-Ion Batteries with MOF–Polymer Composite Electrolytes—Effect Mechanisms and Interface Engineering

Solid-state batteries (SSBs) are regarded as one of the most promising next-generation energy storage technologies due to their high energy density and improved safety. To achieve this goal, the development of solid-state electrolytes with high ionic conductivity and low interfacial resistance is essential. In recent years, composite polymer electrolytes (CPEs) have garnered extensive attention due to their ability to combine the intrinsic flexibility of polymers with the enhanced ionic conductivity and mechanical robustness provided by inorganic fillers. Metal-organic frameworks (MOFs), characterized by tunable pore structures, high surface areas, and excellent thermal and mechanical stability, are considered ideal fillers for constructing MOF-polymer composite electrolytes (MPCEs). This review summarizes the performance enhancement mechanisms of MPCEs and strategies for electrode-electrolyte interface stability. First, the primary preparation methods of MPCEs are introduced. Subsequently, the roles of MOFs in regulating ionic transport, suppressing dendrite growth, improving electrochemical stability, and optimizing the solid electrolyte interphase (SEI) layer are discussed. In addition, various interface engineering strategies are highlighted, including in situ polymerization of the polymer matrix, in situ growth of MOF fillers, integration of liquid plasticizers forming gel-like ionic conductor, and design of composite electrode to enhance interfacial compatibility and stability. Finally, the significant challenges and future research directions of MPCEs are outlined. This review provides valuable insights into the rational design of MPCEs and offers guidance for the development and practical application of high-performance SSBs.