Tailored Li₇P₃S₁₁ Electrolyte by In₂S₃ Doping Suppresses Electrochemical Decomposition for High-Performance All-Solid-State Lithium–Sulfur Batteries

The retentive functional intimate contact at the solid electrolyte/cathode interface and among the cathode components, for example, solid electrolyte, a conductive additive, and active material (S/Li2S), is essential for high-performance solid-state lithium–sulfur batteries. Currently, thiophosphate-based electrolytes are plagued by failure at the interfaces due to the intrinsically narrow electrochemical stability window, which in principle, derive uneven irreversible redox reactions at the triple point of contact, which result in sulfur- and phosphorus-enriched interphases (e.g., Li3P, P2SX, S, Li2Sn, etc.), retard Li+ conduction, and increase the interface resistance. Herein, structural tuning of Li7P3S11 was done using the In2S3 dopant, and the designed Li6.93P2.97In0.02S10.92 electrolyte presented better σLi+ of 2.9 mS cm–1 and enhanced air stability @ RT. Furthermore, In2S3 broadened the electrochemical stability window and suppressed the redox decomposition of Li7P3S11 at the interface in the Li2S-composite cathode layer, ensuring effective (ionic/electronic) conduction. Therefore, the Li2S/Li6.93P2.97In0.02S10.92/Li–In cell offers a high discharge capacity of 946.75 mA h g–1 with an ∼100% average Coulombic efficiency over 30 cycles. Moreover, the cell with Li6.93P2.97In0.02S10.92 presented a low interfacial resistance of 127 compared to 383 Ω for counterparts over 30 cycles, which could be benefitted from suppressed redox decomposition of the solid electrolyte and long-lasting intimate contact at the triple point of contact. Thus, the projected doping strategy developed a sulfide electrolyte to address the chemical/electrochemical stabilities and redox decomposition of sulfide electrolytes for the next-generation all-solid-state technologies.