Lithium-rich sulfide Li2Ti1−xSixS3 cathode materials optimized through Si-doping for high-capacity all-solid-state lithium-ion batteries

Abstract

High-capacity lithium-rich sulfide cathodes with superior conductivity over S or Li₂S materials are considered for all-solid-state lithium-ion batteries (ASSLBs), yet their capacity and rate performance require further improvement. In this work, lithium-rich sulfide cathodes Li₂Ti_1−xSi_xS₃ with a disordered rocksalt structure and layered structure are synthesized by high-energy ball milling and high-temperature annealing, respectively. The Si doping strategy is implemented to tune the microstructure of the lithium-rich sulfide cathode and to obtain high capacity and improved ionic conductivity. The partial replacement of Ti with Si increases the cationic disorder of rocksalt and layered Li₂Ti_1−xSi_xS₃, which further activates the anionic redox activity to enable a higher capacity than Li₂TiS₃. Moreover, the robust Si–S bonds induce distortions in the LiS₆ octahedral and adjacent tetrahedral vacancies, broadening the Li⁺ migration channels in the Li⁺ percolation network and enabling rapid Li⁺ migration capability. The optimized rocksalt Li₂Ti_1−xSi_xS₃ exhibits a higher specific capacity of 361 mA h g⁻¹ than rocksalt Li₂TiS₃ (295 mA h g⁻¹) at 0.3 C (120 mA g⁻¹), while the layered Li₂Ti_1−xSi_xS₃ has a higher capacity of 260 mA h g⁻¹ than the layered Li₂TiS₃ (140 mA h g⁻¹) at 0.3 C. An argyrodite-type sulfide solid-state electrolyte Li_5.25PS_4.25ClBr_0.75 with high Li⁺ conductivity (7.64 mS cm⁻¹) is designed to match with the rocksalt Li₂Ti_1−xSi_xS₃ cathode, and the assembled ASSLB achieves a high areal capacity density of 9.79 mA h cm⁻². The Si doping to tune the disordered structure provides an effective improvement approach for high-capacity rocksalt or layered sulfide cathodes and high-energy density ASSLBs.