Gear‐Meshing Design Reduces Heterointerfacial Mass‐Transfer Barriers for Accelerated Li + Conduction in Composite Polymer Electrolytes

Composite polymer electrolytes (CPEs) are promising for all‐solid‐state lithium metal batteries (LMBs), yet their practical implementation is still hindered by sluggish Li + transport kinetics. This limitation is associated with heterointerfacial mass‐transfer barriers between inorganic fillers and polymer matrices. Herein, a gear‐meshing composite polymer electrolyte (GMCPE) is developed to reduce these barriers and enhance Li + transport kinetics in CPEs. In this design, the hydroxyl‐ and amino‐rich polydopamine (PDA) coating functions as a molecular gear‐like interfacial coupler, which meshes polymer chains to improve filler/polymer compatibility and anchors anions to promote Li‐salt dissociation, thereby liberating more mobile Li + . Meanwhile, the Al 2 O 3 with a low Li + diffusion barrier and the three‐dimensional (3D) polyacrylonitrile (PAN) framework synergistically construct continuous Li + transport pathways while reinforcing mechanical robustness. Consequently, GMCPE achieves an enhanced Li + transference number of 0.52 and an ionic conductivity of 0.5 mS cm −1 at 60 °C. Moreover, Li|GMCPE|Li symmetric cells exhibit stable dendrite‐free Li plating/stripping for over 4200 h. All‐solid‐state Li|GMCPE|LiFePO 4 cells maintain 84.7% capacity retention after 500 cycles at 1 C. This work provides a novel gear‐meshing interfacial design paradigm for advancing accelerated Li + transport in CPEs toward high‐performance all‐solid‐state LMBs.