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.

Lithium-rich oxides are a promising class of positive electrode materials for next generation lithium-ion batteries, and oxygen plays a prominent role during electrochemical cycling either by forming peroxo-like species and/or by irreversibly forming oxygen gas during first charge. Here, we present Li-Fe-Te-O materials which show a tremendous amount of oxygen gas release. This oxygen release accounts for nearly all the capacity during the first charge and results in vacancies as seen by transmission electron microscopy. There is no oxidation of either metal during charge but significant changes in their environments. These changes are particularly extreme for tellurium. XRD and neutron powder diffraction both show limited changes during cycling and no appreciable change in lattice parameters. A density functional theory study of this material is performed and demonstrates that the holes created on some of the oxygen atoms upon oxidation are partially stabilized through the formation of shorter O-O bonds, i.e. (O 2 ) nspecies which on further delithiation show a spontaneous O 2 de-coordination from the cationic network and migration to the now empty lithium layer. The rate limiting step during charge is undoubtedly the diffusion of oxygen either out along the lithium layer or via columns of oxygen atoms.