Basicity and Stability of Argyrodite Sulfide-Based Solid Electrolytes

Abstract

Argyrodite-type sulfide-based solid electrolyte Li6PS5Cl (LPSC) holds immense promise for solid-state battery applications. This is attributed to its stable structure and high ionic conductivity. Nonetheless, the persistent challenges involving the instability at the electrode/electrolyte interface and susceptibility to moisture present significant obstacles in material preparation and cell manufacturing processes. Our research has unveiled a noteworthy finding: the sulfur of the PS4 3− moiety is a Lewis-base active site to adsorb Lewis acid. It is found that the adsorption of CO2 on the sulfide electrolytes can enhance both the interfacial and electrochemical stability of the lithium and sulfide electrolyte interface. The formation of new S–CO2 bonds, confirmed using various analytical techniques, plays a pivotal role in modifying the interfacial behaviors of the sulfide electrolytes. Moreover, the LijCO2@LPSCjLTO shows an amazing result, with 62% capacity retention and ultra-high coulombic efficiency of 99.91% after 1000 cycles. Interestingly, the same concept was also applied to the high ionic conductivity sulfide-based superionic conductor Li10GeP2S12 (LGPS) system, which also has the PS4 3− moiety. A novel approach is also developed by utilization of the BBr3 gas as a Lewis base indicator to probe the strength of Lewis basicity of the sulfur sites of sulfide electrolytes. The basicity of the sulfide electrolytes can be correlated to the shift of 11B NMR peak. This correlation is further supported by the H2S generation rate when the electrolyte is exposed to a moisture atmosphere. This work not only provides a new pave towards enhancing stability at the sulfide electrolyte/lithium interface but profound insights into the basicity and moisture stability of sulfide electrolytes.