Unravelling the Complex LiOH-Based Cathode Chemistry in Lithium-Oxygen Batteries.

The LiOH-based cathode chemistry has demonstrated potential for high-energy Li-O2 batteries. However, the understanding of such complex chemistry remains incomplete. Herein, we use the combined experimental methods with ab initio calculations to study LiOH chemistry. We provide a unified reaction mechanism for LiOH formation during discharge via net 4 e- oxygen reduction, in which Li2 O2 acts as intermediate in low water-content electrolyte but LiHO2 as intermediate in high water-content electrolyte. Besides, LiOH decomposes via 1 e- oxidation during charge, generating surface-reactive hydroxyl species that degrade organic electrolytes and generate protons. These protons lead to early removal of LiOH, followed by a new high-potential charge plateau (1 e- water oxidation). At following cycles, these accumulated protons lead to a new high-potential discharge plateau, corresponding to water formation. Our findings shed light on understanding of 4 e- cathode chemistries in metal-air batteries.

Seed Layer Formation on Carbon Electrodes to Control Li2O2 Discharge Products for Practical Li-O2 Batteries with High Energy Density and Reversibility.

The high theoretical energy densities of lithium-air batteries (LAB) make this technology an attractive energy storage system for future mobility applications. Li2O2 growth process on the cathode relies on the surrounding chemical environment of electrolytes. Low conductivity and strong reactivity of Li2O2 discharge products can cause overpotential and induce side reactions in LABs, respectively, eventually leading to poor cyclability. The capacity and reversibility of LABs are highly susceptible to the morphology of the Li2O2 discharge products. Here, we identify for the first time that a seed layer formed by the combination of a cathode and an electrolyte determines the morphology of Li2O2 discharge products. This seed layer led to its high reversibility with a large areal capacity (up to 10 mAh/cm2). Excellent OER (oxygen evolution reaction) was achieved by the formation of a favorable interface between the carbon electrode and electrolyte, minimizing the decomposition of the electrolyte. These remarkable improvements in LAB performance demonstrate critical progress toward advancing LAB into practical uses, which would exploit good reversibility of LABs in pouch-type cell arrangements with 1.34 Ah.