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 LiNi0.7Mn0.1Co0.2O2 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/[email protected] 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.