Progress on Halide Solid State Electrolytes: Structural Regulation, Interfacial Engineering, and Machine Learning Driven Paradigms

Abstract Halide solid state electrolytes are applicable for all-solid-state batteries due to their favorable ionic conductivity, desirable mechanical deformability, and wide electrochemical stability window. Here we review recent advances in both lithium-based and sodium-based halide electrolytes. Beginning with materials classification and synthesis methods, this review delves into the effects of crystal framework architecture, coordination environment, and the synergistic regulation of occupancy and vacancies on ion conduction mechanisms, particularly emphasizing the advantages of amorphous halide solid state electrolytes. The underlying origins of air instability and electrolyte/interface failure in halide-based batteries are systematically summarized, followed by a discussion of stability enhancement strategies, including elemental doping, interfacial engineering, and structural optimization. Notably, this review introduces a machine learning perspective, exploring its applications in materials screening, elucidation of ion transport mechanisms, and prediction of interfacial reactions. This review provides a theoretical foundation and technical guidance for the rational design of all-solid-state batteries.