Synergistic Study of Crosslinking and Filler Effect in Composite Solid Polymer Electrolytes for High‐Performance Lithium Metal Batteries

The inherent instability of lithium metal with liquid electrolytes, as well as the performance constraints of typical solid electrolytes, has long shifted efforts to develop lithium metal batteries (LMBs). This review contends that the design approach is evolving from simply combining materials to designing multifunctional, network matrices. We critically investigate the development of cross-linked composite solid polymer electrolytes (C-CSPEs) as constructed platforms in which the polymer matrix is not merely a passive host rather a vital, functionally intrinsic constituent. The crosslinking with appropriate filler enables C-CSPEs to achieve high ionic conductivity, mechanical strength, >4.5 V vs. Li/Li⁺ electrochemical stability window (ESW), and reduce electrode/electrolyte interfacial impedance. This review thoroughly analyzed performance criteria, ionic conductivity mechanism, synthesis methods (physical and chemical blending), and crosslinking approaches (thermal curing, photo or UV curing, and radiation-induced crosslinking) for C-CSPEs. We highlight innovative strategies revolutionizing the field including structural battery composites (SBCs) integrating energy storage with load bearing properties, 3D printing for customizing electrolyte infrastructure, artificial intelligence (AI)-assisted designs for optimize material performance, dynamic C-CSPEs for self-healing properties, and halide-based electrolytes enabling high-voltage stability. By combining these fundamental concepts, this review offers a strategic framework for moving C-CSPEs from a promising research issue to the foundation of feasible high-density LMBs.