To DISP or Not? The Far‐Reaching Reaction Mechanisms Underpinning Lithium‐Air Batteries

Abstract

The short history of research on Li‐O2 batteries has seen a remarkable number of mechanistic U‐turns over the years. From the initial use of carbonate electrolytes, that were then found to be entirely unsuitable, to the belief that (su)peroxide was solely responsible for degradation, before the more reactive singlet oxygen was found to form, to the hypothesis that capacity depends on a competing surface/solution mechanism before a practically exclusive solution mechanism was identified. Herein, we argue for an ever‐fresh look at the reported data without bias towards supposedly established explanations. We explain how the latest findings on rate and capacity limits, as well as the origin of side reactions, are connected via the disproportionation (DISP) step in the (dis)charge mechanism. Therefrom, directions emerge for the design of electrolytes and mediators on how to suppress side reactions and to enable high rate and high reversible capacity.

Determinants of the Surface Film during the Discharging Process in Lithium–Oxygen Batteries

“…Aprotic lithium–oxygen (Li–O 2 ) batteries based on the formation and decomposition of lithium peroxide (Li 2 O 2 ) have one of the highest specific energies of 3500 Wh kg –1 , attracting worldwide research interest. − However, many challenges remain before commercialization, and one of them is early cell death, where the practical specific capacity and specific energy are much lower than the theoretical values. − During discharge, oxygen is reduced to form solid lithium peroxide (Li 2 O 2 ), which would further react to form undesired byproducts, such as lithium carbonate, both accumulating within the porous electrode. The pore clogging, the surface passivation of desired insulating Li 2 O 2 products, and the formation of undesired byproducts all contribute to premature cell death, which is all dependent upon the formation of the discharge product Li 2 O 2 . ,− …”