Insights into chemical substitution of metal halide solid-state electrolytes for all-solid-state lithium batteries

Abstract

Over a long period of time, frequent safety incidents in electric vehicles and portable electronics have raised concerns about modern energy storage devices, particularly lithium-ion batteries. However, the emergence of solid-state electrolytes (SSEs) with good thermal stability has eliminated potential safety hazards of conventional lithium-ion batteries, such as liquid electrolyte leakage and explosions, allowing all-solid-state batteries to attract intensive attention. Among all types of SSEs, halide SSEs have gained research focus owing to their high ionic conductivity, good mechanical malleability, and excellent chemical/electrochemical stability. They have risen to the forefront of SSE research within just a few years. This paper firstly summarizes state-of-the-art halide SSEs by briefly introducing various synthesis methods of halide SSEs and comparing their advantages and disadvantages. Secondly, it introduces the composition, structural types, and ionic conduction mechanisms of halide SSEs, analyzing their effects on ionic transport behavior mainly from three perspectives: anion polarizability, cation disorder and stacking faults. Primarily, it not only reviews typical substitution types for current halide SSEs, explaining how each type optimizes ion transport kinetics, but also focuses on chemical substitution strategies to improve the inherent thermodynamic stability window of halide SSEs and the complex electrode/SSE interface. Additionally, this work proposes potential future research directions to address the challenges in the development of halide SSEs. Overall, the review aims to provide fundamental understanding for designing new halide SSEs and their structural characterization.