Chemical vs Electrochemical Formation of LiCO as a Discharge Product in Li-O/CO Batteries by Controlling the Superoxide Intermediate.

The Li-O/CO battery with high capacity has recently been proposed as a new protocol to convert CO. However, the fundamental mechanism for the reaction still remains hazy. Here, we investigated the discharge processes of Li-O/CO (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 CO 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 LiCO was the final discharge product in both solvents. Moreover, we observed that CO cannot be reduced within the electrochemical stability window of DMSO and DME.