Toward design of cation transport in solid-state battery electrolytes: Structure-dynamics relationships

Cation-conducting, solid-state electrolytes represent a burgeoning focus of battery research, offering the potential for enhanced safety profiles, durability, and wide electrochemical stability windows for high energy density. In this review, we focus primarily on the Li/Na ion conductivity as one of the requirements and limiting factors in development of solid-state electrolytes and secondarily on stability. We highlight experimental and computational methods leading to the current state of understanding of solid-state cation transport, with the goal of drawing out structure-property relationships that lead to design strategies. Topics covered include: descriptors and high-throughput search methodologies including machine learning for identification of fast cation conductors; defect chemistry and its relationship to conduction mechanisms including emerging understanding of frustration, disorder, and concerted ion migration; the impact of strain on transport; factors determining stability; and the role of microstructure and extended defects. We conclude certain sections and the overall review with an outlook for the field, offering ideas for necessary research directions to address knowledge and property gaps.