Halide solid electrolytes: composition tuning, structural design, and performance optimization for all-solid-state lithium batteries

Halide solid electrolytes have become key candidate materials for all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity, wide electrochemical window, and good compatibility with high-voltage cathodes. This paper reviews their material chemistry, crystal structure, synthesis, and characterization methods, with a focus on analyzing the composition–structure–performance relationship, and explores the effects of halogen types and their mixtures on ion transport and stability. Meanwhile, it analyzes the challenges at the cathode/anode interface and summarizes strategies such as element doping, interface engineering, and mechanical performance and moisture resistance optimization. Despite significant progress in the laboratory, practical applications are still constrained by issues such as high cost, moisture sensitivity, and unstable interfaces with lithium metal. In the future, efforts should be focused on low-cost alternatives, improved moisture resistance, and multi-functional interface design, combined with high-throughput computing and advanced characterization, to accelerate the industrialization process in high-energy-density ASSLBs.