Lithium phosphosulfide electrolytes for solid-state batteries: Part I

Abstract

A high performance and stable Li-ion conductive solid electrolyte is one of the key components for the future all-solid-state batteries with metallic lithium anodes. Phosphate, oxide and phosphosulfide-based inorganic solid electrolytes are currently under development. High ambient temperature Li-ion conductivities amounting up to 10-2 S cm-1 for the best performing electrolytes distinguish the phosphosulfides from the other material systems. Part I of the review starts with the motivation and background for the development of Li-phosphosulfide electrolytes followed by an overview of four different types of phosphosulfide electrolytes; the Li-P-S, thio-LiSICon, LGPS and the Argyrodite-type electrolytes. The core of part I is concerned with a detailed discussion of the phosphosulfide electrolyte types that have been under investigation already for a long time, the Li-P-S and the LiSICon. There is a multiplicity of different compositions within each of these types. The idea behind the outline of these sections is to point out the relations and differences between the different materials with respect to their chemistry related to the phase diagrams. Patterns for the relations among the materials identified in the phase diagrams are the base for a discussion of structure, processing and Li-ion conductivity within separate sections for each type and resulting in intra-type comparisons. The follow up part II will continue with a treatment of the more recently developed LGPS and Argyrodite-type electrolytes tracking the same concept, before addressing an inter-type comparison of ambient temperature Li-ion conductivities and the electrochemical stability of the electrolytes vs. metallic lithium. A final section in part II summarizes conclusions and provides perspectives for future research on Li-ion conductive phosphosulfide electrolytes.