Sulfide solid electrolytes for all-solid-state lithium batteries: Structure, conductivity, stability and application

This review focuses on the research progress of sulfide solid electrolytes. Two systems of (100-x)Li2S-xP2S5 and Li2S-MxSy-P2S5 are systematically reviewed from four aspects, the crystal structure, conductivity, stability and application. The methods for preparing sulfide solid electrolytes are summarized, and, their advantages and disadvantages are compared and analysed. Sulfide solid electrolytes with high conductivities are closely related to their crystal structures, and they can be improved via doping, such as substitution doping, interstitial doping, dual-doping, etc. The conductivities are introduced and summarized according to their classifications. Experimental studies and theoretical results are discussed in parallel to illustrate the relationship between the conductivity and crystal structure. Furthermore, the stabilities of sulfide electrolytes with lithium metal, active materials, organic solvents and humid air are reviewed separately, and corresponding methods for improvement are proposed. Finally, according to the different functions of sulfide electrolytes in all-solid-state lithium batteries (ASSLBs), they are categorized and generalized scientifically in terms of composite electrolyte, buffer material and electrolyte. Additionally, the techniques proposed in the recent works to achieve sufficient contact between the sulfide solid electrolyte and the electrode in the ASSLBs are summarized. The present review aims to provide a thorough understanding of the properties of sulfide solid electrolytes, including conductivity, structure, and stability, to allow for more efficient and target-oriented research to improve the performance of sulfides-based ASSLBs.