Lithium‐Rich Li2TiS3 Cathode Enables High‐Energy Sulfide All‐Solid‐State Lithium Batteries

Abstract Outstanding interfacial issues exist between oxide cathodes and sulfide electrolytes in all‐solid‐state lithium batteries (ASSLBs), while high‐capacity Li‐rich sulfide cathodes are gaining attention for application. Herein, a sulfide cathode active material Li 2 TiS 3 (LTS) that is chemically compatible with sulfide solid electrolytes, is used in high‐performance Li 6 PS 5 Cl‐based ASSLBs at room temperature. The batteries demonstrate a maximum discharge capacity of 423.2 mAh g −1 (910 Wh kg −1 based on Li 2 TiS 3 ) with 95% capacity retention after 100 cycles at 0.1 C (0.33 mA cm −2 ). Traces of elemental sulfur on the surface of LTS are mainly responsible for the excessive Li‐intercalation and the capacity exceedance. The Li 6 PS 5 Cl is also found to offer a nonnegligible capacity (at least 27% of excess capacity) by comparing the Li 6 PS 5 Cl‐based and Li 3 YCl 6 ‐based cells using Li 2 TiS 3 as cathode active material. During long cycling, the amorphization and degradation of Li 2 TiS 3 and Li 6 PS 5 Cl cause capacity decay. The electrochemical kinetics of Li 6 PS 5 Cl‐based cells are evaluated as a reference to further exploit the potential of Li 2 TiS 3 material for practical applications in ASSLBs. Overall, this superior Li‐rich sulfide material is an attractive alternative to oxide cathodes for the development of high‐performance ASSLBs.