High-capacity and long-cycle life Li2S−V2S3−V2O3−LiI bifunctional materials for all-solid-state Li/S batteries

All-solid-state batteries have been attracting worldwide attention because of their safety and high energy density. Lithium sulfide (Li₂S)-based active materials are attractive due to their high theoretical capacity. The positive electrodes with Li₂S active materials generally require mixing with solid electrolytes and conductive carbons in the positive electrode layer due to their insulating nature. Recently, a material concept of “electrode-electrolyte bifunctional materials” has been proposed. They function as active materials and solid electrolytes without being mixed with conductive additives, leading to an improvement in the energy density of the all-solid-state batteries. However, most of the electrode–electrolyte bifunctional materials suffer from degradation of battery performance after long cycles. In this study, we developed electrode-electrolyte bifunctional materials in the system Li₂S−V₂S₃−V₂O₃−LiI. The addition of V₂O₃ into Li₂S−V₂S₃−LiI enhances conductive properties and structural stability during cycling owing to the mixed–anion effect. In particular, an all-solid-state battery with 90(0.75Li₂S·0.225V₂S₃·0.025V₂O₃)·10LiI (mol%) exhibited a high capacity of 430 mAh g⁻¹ at 25 °C and retained 97.4 % of the initial discharge capacity even after 300 cycles. It is believed our findings will pave the way for developing positive electrodes with high capacity and long cycle life for all-solid-state batteries.