Anion‐Solvent Dual‐Sieving Effect Revolutionizes Li Deposition Kinetics for Garnet‐Based Solid‐State Lithium Batteries

Solid‐state batteries (SSBs) are promising candidates for next‐generation energy storage due to their high theoretical energy density. However, their practical application is hindered by Li/solid‐state electrolyte interfacial issues, including poor contact, lithium dendrites, and side reactions, while polarization under high current densities or areal capacities cannot be ignored. Herein, we report a multifunctional composite interlayer (BN‐ASDSI) composed of a flexible polymer scaffold, a sultone‐based electrolyte, and boron nitride (BN) to address these challenges. Benefiting from the Lewis acid‐base interaction, BN‐ASDSI exhibits an anion‐anchoring effect that induces a localized microelectric field, accelerating Li + transport while restricting anion mobility. Concurrently, the solvent‐repelling property of BN mitigates interfacial side reactions, synergistically promoting the formation of LiF‐rich inorganic solid‐state interface to stabilize the Li metal. Notably, the symmetric cell with BN‐ASDSI achieves an ultrahigh critical current density of 8.8 mA cm −2 . Most impressively, the LiFePO 4 SSB delivers stable operation for 1500 cycles at 6 C with a capacity retention >92%, while the high‐loading LiNi 0.83 Co 0.12 Mn 0.05 O 2 (17.2 mg cm −2 ) SSB exhibits a high discharge areal capacity of 3.2 mAh cm −2 at 1 C and retains 93% capacity after 80 cycles at 0.33 C, showcasing the practical potential of BN‐ASDSI enabled SSBs.