Achilles' Heel of Lithium-Air Batteries: Lithium Carbonate.

The lithium-air battery (LAB) is envisaged as an ultimate energy storage device because of its highest theoretical specific energy among all known batteries. However, parasitic reactions bring about vexing issues on the efficiency and longevity of the LAB, among which the formation and decomposition of lithium carbonate Li CO is of paramount importance. The discovery of Li CO as the main discharge product in carbonate-based electrolytes once brought researchers to "the end of the idyll" in the early 2010s. In the past few years, tremendous efforts have been made to understand the formation and decomposition mechanisms of Li CO , as well as to conceive novel chemical/material strategies to suppress the Li CO formation and to facilitate the Li CO decomposition. Moreover, the study on Li CO in LABs is opening up a new research field in energy technology. Considering the rapid development and innumerous emerging issues, it is timely to recapitulate the current understandings, define the ambiguities and the scientific gaps, and discuss topics of high priority for future research, which is the aim of this Minireview.