Clarification of Solvent Effects on Discharge Products in Li-O2 Batteries through a Titration Method.

As a substitute for the current lithium-ion batteries, rechargeable lithium oxygen batteries have attracted much attention because of their theoretically high energy density, but many challenges continue to exist. For the development of these batteries, understanding and controlling the main discharge product Li2O2 (lithium peroxide) are of paramount importance. Here, we comparatively analyzed the amount of Li2O2 in the cathodes discharged at various discharge capacities and current densities in dimethyl sulfoxide (DMSO) and tetraethylene glycol dimethyl ether (TEGDME) solvents. The precise assessment entailed revisiting and revising the UV-vis titration analysis. The amount of Li2O2 electrochemically formed in DMSO was less than that formed in TEGDME at the same capacity and even at a much higher full discharge capacity in DMSO than in TEGDME. On the basis of our analytical experimental results, this unexpected result was ascribed to the presence of soluble LiO2-like intermediates that remained in the DMSO solvent and the chemical transformation of Li2O2 to LiOH, both of which originated from the inherent properties of the DMSO solvent.