Operando Investigation into Dynamic Evolution of Cathode-Electrolyte Interfaces in a Li-Ion Battery.

While Li-ion battery cathode-electrolyte interfaces (CEIs) have been extensively investigated in recent decades, accurately identifying the chemical nature and tracking the dynamics of the CEIs during electrochemical cycling still remain a grand challenge. Here we report our findings in the investigation into the dynamic evolution of the interface between a LiNi0.33Co0.33Mn0.33O2 (LNMC) cathode and an ethylene carbonate/dimethyl carbonate (EC/DMC)-based electrolyte using surface-enhanced Raman spectroscopy (SERS) performed on a model cell under typical battery operating conditions. In particular, the strong SERS activity provided by a monolayer of Au nanocubes deposited on a model LNMC electrode (additive-free) enables quasi-quantitative assessment of the CEI evolution during cycling, proving information vital to revealing the dynamics of the species adsorbed on the LNMC surface as a function of cell potential. Furthermore, our theoretical calculation, which is based on the interaction between a model interface-bound molecule and a model LNMC surface, agrees with our experimental observation. The carefully designed operando SERS platform has demonstrated high sensitivity, good surface specificity, and excellent compatibility with extensive electrochemical measurements; it is also applicable to fundamental studies of dynamic interfaces in other electrochemical energy storage and conversion systems.