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

Abstract

A major fundamental challenge in a Li−CO 2 battery, which has not received due attention in comparison to the intricacies of CO 2 redox, is the CO 2 gas crossover toward the Li anode. The CO 2 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 CO 2 (or CO 2 /O 2 ) crossover. Irrespective of the gas, our studies convincingly reveal active Li metal conversion to majorly LiOH and Li 2 CO 3 , with LiOH being the dominant phase at higher cycle numbers. Depth profile X-ray photoelectron spectroscopy reveals additional SEI components, viz., Li 2 O, Li 2 S, LiF, and CF 3 , which exhibit a depth-dependent spatial distribution along with Li 2 CO 3 and LiOH. Analytical chemical investigations based on metalation reactions quantitatively reveal irreversible loss of active Li metal with successive cycling.