Micro-scale mismatches of electrically conductive and mechanically resilient regimes in Li-variant sulfide conductors

Abstract

Li-ion-conductive sulfide electrolytes have attracted significant attention with regard to the development of superior solid-state batteries owing to their high ionic conductivity and ductile mechanical properties. Nevertheless, the relationship between the variations in Li content resulting from extraction and insertion in sulfide electrolytes and their subsequent influence on the electrochemical and mechanical properties remains unelucidated. In this study, we simulated the electrochemical operating conditions of glass sulfides through experimental and computational methods. Our investigation focused on the microscale reversibility of their electrochemical and mechanical properties. In Li-variant glass sulfides, (Li₂S)_0.75(1−x)(P₂S₅)_0.25S_0.75x, we demonstrated that 50% Li deficiency induced polymerization, resulting in a 98% decrease in Li-ion conductivity. Furthermore, we posit that changes in the mechanical properties of solid electrolytes during plastic deformation can be evaluated using Pugh’s ratio. In the case of Li deficiency, the Pugh’s ratio is reduced by 24%, and the solid electrolyte becomes extremely brittle. Interface deterioration in solid-state batteries is accelerated by the irreversible elastic hardening resulting from delithiation and polymerization of solid electrolytes during continuous electrochemical cycling. These evaluation approaches, which are based on Li-variant glass sulfides, afford guidelines for designing electrolytes suitable for cathodes.