Synergistic Effect of Sn-Substituted Argyrodite Solid Electrolyte with Enhanced Air Stability and Li Metal Compatibility for All-Solid-State Li Metal Batteries

Sulfide solid-state electrolytes (SSEs) are promising for all-solid-state Li metal batteries (ASSLMBs) due to their high ionic conductivity and mechanical strength. Despite these advantages, challenges, such as poor air stability and compatibility issues with Li metal, have hindered their widespread application. To solve these issues, we developed Li_6+<i>x</i>P_1–<i>x</i>Sn_<i>x</i>S₅Cl electrolytes with doping of Sn⁴⁺, replacing P⁵⁺ in Li₆PS₅Cl electrolyte. The Li_6.1P_0.9Sn_0.1S₅Cl electrolyte with optimized dopant concentrations shows improved ionic conductivity (2.14 × 10^–3 S cm^–1), enhanced moisture resistance, and superior compatibility with Li metal. The Li symmetric cell with Li_6.1P_0.9Sn_0.1S₅Cl electrolyte shows a good critical current density (CCD) of 0.68 mA cm^–2 and long-term cycling performance (over 600 h at 0.1 mA cm^–2) due to the Li–Sn alloy. Moreover, the assembled LiNi_0.8Co_0.1Mn_0.1O₂/Li cell with the Li_6.1P_0.9Sn_0.1S₅Cl electrolyte exhibits a high initial discharge capacity of 163.1 mAh g^–1 at 0.05 C. It shows a discharge capacity of 108.9 mAh g^–1 with a capacity retention rate of 75.4% after 60 cycles at 0.1 C. These results demonstrate the potential of Sn substitution in enhancing the electrochemical stability and overall performance of SSEs for next-generation battery technologies.