Interfacial redox behaviors of sulfide electrolytes in fast-charging all-solid-state lithium metal batteries

Sulfide solid electrolytes offer great opportunities to construct solid-state Li metal batteries with high energy density. The high ionic conductivity of well-developed sulfide electrolytes enables solid-state battery to operate at high current rates. However, sulfide electrolytes exhibit severe decomposition in working cells, constituting a significant obstacle for the practical applications of sulfide solid-state electrolytes. The decomposition behaviors of sulfides are complicated and strongly depend on the electrochemical windows, some of which are even regarded reversible during battery cycling. Herein, we investigate the redox behaviors of Li₇P₃S₁₁ sulfide solid electrolyte under different voltage windows, and their effects on interfacial transport and battery cycle lifetime. Moreover, Li metal | Li₄Ti₅O₁₂ (LTO) batteries are introduced to further probe the role of multiphase redox reactions on interfacial ion conduction. By regulating the redox behaviors of electrolytes through varying working voltage window, Li | LTO metal batteries enable a rapid charge/discharge process in 10 ​min (6 ​C) and lifespan of 600 cycles at 1 ​C with 85% capacity retention. An all-solid-state Li | LTO metal pouch cell is also assembled and exhibits a stable cycling performance with a capacity of 120 mAh g⁻¹. This work provides understandings about interfacial redox behaviors of sulfide electrolyte, presenting novel insights in the rational design of future solid-state lithium batteries with high-energy/power-density.