Operando and ex situ Raman spectroscopies for evaluating carbon structural changes in anode-free-type sulfide-based all-solid-state Li-ion batteries

Abstract

Anode-free-type sulfide-based all-solid-state Li-ion batteries are promising candidates for achieving high energy density and cycle capability. Although the introduction of an Ag/C layer between the solid electrolyte and the current collector could further improve the cycle capability, its role during charge–discharge remains unclear. In this study, we applied operando/ex situ Raman spectroscopies to observe structural changes in the Ag/C layer. Operando Raman spectroscopy revealed significant changes in the peak shape, intensity ratio, and position of the D- and G-bands derived from carbon black, suggesting Li intercalation into carbon even though it exhibited an amorphous structure. Additionally, new peaks appeared and disappeared during charging and discharging, respectively, corresponding to the deposition and dissolution of metallic Li onto the current collector. In contrast, ex situ Raman spectroscopy exhibited gradual changes in the D- and G-bands despite the clear formation of a metallic Li deposition layer. Therefore, we discovered that amorphous carbon black undergoes Li intercalation during charging and rapid structural changes under dynamic (operando) conditions compared with static (ex situ) conditions.