Lithium phosphosulfide electrolytes for solid-state batteries: Part II

Among the electrolytes designed for all solid-state batteries, the phosphosulfide electrolytes stand out with respect to their very high Li-ion conductivities. However, when in contact with metallic lithium anodes, there are remaining challenges to ensure long-term operation stability. Both issues, the Li-ion conductivity and the electrochemical stability vs. metallic lithium, are the subject of this review. After introducing the background for developing all solid-state Li-ion batteries with metallic lithium anode and providing a brief overview on four types of phosphosulfide electrolytes, in Part I of the review a compound treatment on the Li-P-S and the LiSICon type electrolytes had been given. Part II of the review will continue following the same schedule by discussing the chemistry, structure, processing and Li-ion conductivity of the LGPS and the Argyrodite-type phosphosulfides. Emphasis is put on the treatise of the chemistries supported by the consideration of specific phase diagrams and intra-type comparisons of the Li-ion conductivities at ambient temperature. In a summarizing section, inter-type comparisons among selected compositions of the Li-P-S type, the LiSICon-type, the LGPS-type and the Argyrodite-type phosphosulfides are addressed for the two main issues for electrolytes in all solid-state batteries, the Li-ion conductivities and the electrochemical stability vs. metallic lithium. The review is concluded with remarks on the status and the perspectives of the research on Li-ion conducting phosphosulfide electrolytes.