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.