Enhancing the Moisture Stability and Electrochemical Performances of Li6PS5Cl Solid Electrolytes through Ga Substitution

Sulfide solid electrolytes are attracting much attention as a next-generation electrolyte material due to their high ionic conductivity and appropriate mechanical properties. Among them, Li-argyrodite exhibits ultrahigh Li-ion conductivity and has the possibility of process expansion, so it is a material that has been extensively studied in academia and industry. However, due to the high reactivity of S and the weak P-S bond, there are electrochemical and air stability issues, such as undesirable reactions at the interface with the active material in the composite electrode during charge/discharge cycling and reacting readily with moisture in the atmosphere. Herein, we report solid-electrolyte with the composition Li6+2xGaxP1-xS5Cl (x = 0, 0.013, 0.025, 0.038, 0.05, 0.075) in which P is substituted with softer acid Ga, based on Hard and Soft Acids and Bases (HSAB) theory. In the half-cell charge/discharge experiment using synthesized electrolytes for cathode composite, the cell using Li6.1Ga0.05P0.95S5Cl shows a higher capacity retention rate after 50 cycles, and XPS analysis confirmed that lower electrolyte decomposition compared to the cell using Li6PS5Cl. This demonstrates that the electrochemical stability of the solid electrolyte is improved with Ga substitution. Further, the dry air exposure test confirms that the air stability of Li6PS5Cl is increased by Ga substitution. Finally, the Cyclic Voltammetry (CV) tests show that Ga-substitution enhanced the stability against Li-metal.