Chemical vs Electrochemical Formation of Li2CO3 as a Discharge Product in Li-O2/CO2 Batteries by Controlling the Superoxide Intermediate.

The Li-O2/CO2 battery with high capacity has recently been proposed as a new protocol to convert CO2. However, the fundamental mechanism for the reaction still remains hazy. Here, we investigated the discharge processes of Li-O2/CO2 (70%/30%) batteries in two solvents, dimethyl sulfoxide (DMSO) and 1,2-dimethoxyethane (DME). During discharge, both solvents initially show the reduction of oxygen. However, afterward, the solvent affects the reaction pathways of superoxide species by solvating Li+ with different strength, depending on the so-called donor number. More precisely, the initial formation of CO4•- is favored in DMSO at the expense of lithium superoxide formation that we observed in DME. Despite the different intermediate processes, X-ray diffraction showed that Li2CO3 was the final discharge product in both solvents. Moreover, we observed that CO2 cannot be reduced within the electrochemical stability window of DMSO and DME.