CO2 Crossover to the Li Anode and Its Implications on the Solid Electrolyte Interphase Composition in a Rechargeable Li-CO2 Battery

A major fundamental challenge in a Li-CO2 battery, which has not received due attention in comparison to the intricacies of CO2 redox, is the CO2 gas crossover toward the Li anode. The CO2 crossover during battery operation changes the Li chemical state and the composition of the proximate solid electrolyte interphase (SEI). Systematic ex situ Raman spectroscopy and X-ray diffraction investigations confirm continuous active Li metal depletion with successive cycles due to CO2 (or CO2/O-2) crossover. Irrespective of the gas, our studies convincingly reveal active Li metal conversion to majorly LiOH and Li2CO3, with LiOH being the dominant phase at higher cycle numbers. Depth profile X-ray photoelectron spectroscopy reveals additional SEI components, viz., Li2O, Li2S, LiF, and CF3, which exhibit a depth-dependent spatial distribution along with Li2CO3 and LiOH. Analytical chemical investigations based on metalation reactions quantitatively reveal irreversible loss of active Li metal with successive cycling.