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 Al₂O₃ 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|LiFePO₄ 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.