Enhanced air/electrochemical stability and Li-ion conductivity of argyrodite-type Li5.5+x(P1−xGex)S4.5Cl1.5 ceramic solid electrolytes for all-solid-state batteries

Li-containing argyrodites, particularly Li 5.5 PS 4.5 Cl 1.5 , are key ceramic solid electrolytes with high ionic conductivity (∼10 mS cm –1 at room temperature), making them promising candidates for all-solid-state lithium batteries (ASSBs). However, their poor air and electrochemical stability limit their application as electrolytes for ASSBs. This study attempts to address these issues by Ge 4+ substitution involving the forming of Li 5.5+ x (P 1− x Ge x )S 4.5 Cl 1.5 solid solutions (0 ≤ x  ≤ 0.10). The optimized composition, Li 5.56 (P 0.9 Ge 0.1 )S 4.5 Cl 1.5 , exhibits improved air and electrochemical stability and a higher ionic conductivity of 13.2 mS cm –1 . When used in a lab-scale ASSB, this electrolyte achieved an initial discharge capacity of 106.4 mAh g –1 , retaining 89.3 mAh g –1 after 100 cycles with 98.9 % cycling efficiency. This work provides insights into the improving air and electrochemical stability of Li 5.5 PS 4.5 Cl 1.5 solid electrolytes for ASSBs.