Mitigating Oxidation of Li₇P₂S₈I‑Based Electrolytes in All-Solid-State Batteries: Cathode Coating versus Electrolyte Interface Engineering

Highly electro/chemical compatible solid-state electrolytes are essential for all-solid-state lithium batteries with high power density, and the integration of sulfide and halide electrolytes within a bilayer separator has garnered significant interest due to their enhanced electrochemical stabilities and improved ionic conductivities. Despite these advantages, current sulfide electrolytes do not adequately satisfy the criteria required for high-performance all-solid-state lithium batteries. In this context, we present the synthesis of Li₇P₂S₈I through a combination of ball-milling and heat treatment processes. The resulting Li₇P₂S₈I achieves an ionic conductivity of 1.8 × 10^–3 S cm^–1 and excellent air stability. Subsequently, the Li₂ZrO₃ coating layer and a bilayer separator comprising Li₇P₂S₈I as the anolyte and Li₃InCl₆ as the catholyte were constructed to evaluate its compatibility with the LiNi_0.7Mn_0.1Co_0.2O₂ cathode. Electrochemical analysis indicates that while Li₃InCl₆ is effective in reducing lithium loss from cathode materials, it reacts with Li₇P₂S₈I, leading to the formation of interphases that impede Li-ion transportation, consequently resulting in a more rapid capacity fade after cycling. Meanwhile, the Li-In/Li₇P₂S₈I/Li₂ZrO₃@LiNi_0.7Co_0.1Mn_0.2O₂ battery exhibits marginally reduced discharge capacities at identical C rates and superior cycling performances. These findings provide insights into the development of high-performance Li₇P₂S₈I-based all-solid-state batteries.