Gradient Borohydride-Sulfide Hybrid Electrolyte Enabling Interfacial Isolation in High-Performance Solid-State Li–Se Batteries

Sulfide-based solid-state electrolytes (SSEs) are attractive candidates for high-energy all-solid-state lithium-ion batteries due to their high ionic conductivity. However, the intrinsic chemical instability against Li metal leads to continuous interfacial degradation. Herein, we design a gradient hybrid electrolyte by introducing a borohydride-based interfacial buffer to achieve complete anode-electrolyte isolation without sacrificing energy density. The borohydride component, with its intrinsic reducibility and deformability, facilitates the formation of a stable solid electrolyte interphase (SEI) while maintaining ionic transport comparable to pristine sulfide SSEs. Benefiting from this interfacial stabilization, the hybrid SSE enables long-term cycling over 2000 h and delivers a high specific capacity of 516.3 mAh g–1 at 10 C with selenium cathode featuring dual-electron reactions. This study demonstrates that borohydride-mediated interfaces effectively suppress parasitic reactions and provide a universal and scalable strategy to unlock the potential of sulfide-based solid-state batteries.