Suppression of Electrochemical and Chemical Degradation of Li₁₀GeP₂S₁₂ by an Elastomeric Artificial Solid Electrolyte Interphase

The family of thio-LISICON solid-state electrolytes (SSEs)is oneof the most promising material systems for the realization of fullysolid state batteries due to comparable performance with liquid electrolyte-basedcounterparts. Among this SSE family, Li10GeP2S12 (LGPS) is one of the most promising candidates dueto its high theoretical ionic conductivity (1 x 10(-2) S cm(-1)). However, the narrow electrochemical andchemical stability windows of LGPS make it unstable in direct contactwith both Li metal and conventional transition metal oxide cathodematerials, leading to dramatic degradation during battery cyclingand even during battery storage prior to battery operation. In thisstudy, we employ an elastomeric artificial solid electrolyte interphase(ASEI) as a protective layer grown directly on Li metal by electrochemicallypolymerizing 1,3-dioxolane prior to assembling Li/LGPS/Li test cells.This ASEI serves as a Li+-conducting interlayer capableof halving the chemical degradation rate as compared to untreatedpristine Li at the Li/LGPS interface, while also significantly loweringthe absolute impedance and overpotential of Li/LGPS/Li symmetric cellsduring galvanostatic cycling at 0.1 mA h cm(-2). Theelemental composition and spatial structure of this ASEI layer wereinvestigated using X-ray photoelectron spectroscopy and scanning electronmicroscopy characterization techniques. Density functional theorycalculations were performed to understand the impact of the elastomericASEI layer on chemical aging at the Li/LGPS interface.