Selective Oxygen Doping of Li_6.6Si_0.6Sb_0.4S₅I Electrolyte for Enhanced Air Stability and Electrochemical Performance

The argyrodite electrolyte Li_6.6Si_0.6Sb_0.4S₅I has garnered significant interest due to its high ionic conductivity of 9.0 mS cm^-1. However, its integration into composite cathodes is hindered by poor chemical and electrochemical stability, limiting its practical application. This study investigates an O doping strategy to enhance the overall performance of Li_6.6Si_0.6Sb_0.4S₅I. In contrast to previous studies, a comparative analysis of two different oxygen sources Li₂O and Sb₂O₅ is conducted. The results demonstrate that the electrochemical stability of the material obviously improves when Li₂O is used as the O source, while its air stability significantly enhances when Sb₂O₅ is used. Furthermore, Li_6.6Si_0.6Sb_0.4S₅I (and Li_6.6Si_0.6Sb_0.4S_4.9IO_0.1-Li₂O) is combined with Li₃InCl₆ (and Li_3.25InCl_5.75O_0.25) to fabricate different separator configurations. Through aging tests, the optimal separator configuration, Li_3.25InCl_5.75O_0.25/Li_6.6Si_0.6Sb_0.4S_4.9IO_0.1-Li₂O, is found. Batteries assembled with this separator exhibit stable performance over 800 cycles at an upper cutoff voltage of 3.9 V (vs. Li-In), while maintaining an excellent capacity retention rate of 80.2%.