Interface failure mechanisms and engineering strategies in sulfide and halide solid electrolytes for lithium metal solid-state batteries

Abstract

Researchers widely regard lithium-metal solid-state batteries (SSBs) as a promising next-generation energy storage technology. They offer substantially higher theoretical energy density and improved safety compared to conventional lithium-ion batteries (LIBs). Among solid electrolytes (SEs), sulfide and halide chemistries stand out due to their high ionic conductivity (>10 –3  S cm -1 ) and compatibility with high-voltage cathodes (>4.5 V). However, both face significant challenges at the Li-electrolyte interface. This instability manifests as dendrite penetration, electrochemical decomposition, void formation, and mechanical failure. The dominant failure modes and their severity differ between sulfides and halides. This mini-review provides a comparative analysis of interfacial failure mechanisms in sulfide and halide systems. It also evaluates mitigation strategies, including interface engineering, electrolyte chemistry, microstructure design, mechanical reinforcement, and in situ diagnostic techniques, and highlights the trade-offs of each approach. We conclude with a forward-looking roadmap that prioritizes hybrid designs and targeted interface stabilization strategies to accelerate the development of practical, high-performance Li-metal SSBs. This mini-review aims to guide researchers toward material-class-specific solutions that balance conductivity, stability, and manufacturability.