Unveiling Mechanistic Origins of Enhanced Cycling Performance in Quasi-Solid-State Batteries with High-Concentration Electrolytes

All-solid-state lithium metal batteries are promising candidates for next-generation batteries. However, they face challenges due to poor interfacial properties between the solid electrolyte and electrode. In this study, to address these interfacial issues, a small amount of high-concentration liquid electrolyte (HCE), consisting of lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane, is incorporated between the solid electrolyte and Li metal to create a quasi-solid-state electrolyte (QSE) battery. Electrochemical measurements show that the QSE cell achieves a critical current density of similar to 10 mA cm- 2 and exhibits enhanced Li plating/stripping reversibility with uniform Li morphology. The mechanistic origins of this improved electrochemical performance of the QSE system were systematically investigated. We propose that HCE positively influences the interface by alleviating contact gaps and forming a LiF-rich inorganic solid electrolyte interface. Additionally, the QSE cell effectively mitigates contact loss from localized current and void formation, providing insights for designing favorable interfaces in solid-state battery systems.