Enhanced air stability and interfacial compatibility of Li-argyrodite sulfide electrolyte triggered by CuBr co-substitution for all-solid-state lithium batteries

As a class of candidate materials for all-solid-state lithium batteries (ASSLBs), Li-argyrodite electrolytes have drawn extensive attention due to their cheap raw materials, high ionic conductivity, and suitable mechanical properties. However, poor Li incompatibility and inferior air stability of the sulfide electrolytes have seriously hindered their practical applications. Herein, novel argyrodite-based Li6–2xCuxPS5-xBr1+x (0 ≤ x ≤ 0.4) electrolytes are synthesized via CuBr co-substituting to overcome above obstacles. Theoretical calculations predict that Cu+ prefers to replace the Li+ site instead of P5+ site, which is further confirmed by the X-ray diffraction and Raman measurement. The optimized Li5.6Cu0.2PS4.8Br1.2 electrolyte possesses a high ionic conductivity of 3.65 mS cm−1. The ab initio molecular dynamics (AIMD) simulations testify that the incorporation of Br‒ facilitates the inter-cage jumps of Li+, resulting in an improved long-range Li+ migration. Besides, such a modified electrolyte represents enhanced Li compatibility and good air stability compared to pristine Li6PS5Br. The constructed ASSLBs with the Li5.6Cu0.2PS4.8Br1.2 electrolyte also exhibit cycling stability and rate capability. As a result, it is a promising path to develop CuBr co-substituted argyrodite electrolytes for ASSLBs.