Unraveling the Complex Role of Iodide Additives in Li-O2 Batteries

Lithium iodide (LiI) has garnered considerable attention in aprotic Li-O-2 batteries. However, the reaction mechanism is still under hot debate and is attracting increasing controversy due to contrasting observations. Herein, on the basis of thorough evidence, a relevant mechanism has been systematically illustrated. LiI has been revealed to promote the superoxide-related nucleophilic attack toward electrolyte by catalyzing the decomposition of peroxide intermediate, resulting in the accumulation of LiOH and other parasitic products. Also, they refuse to be oxidized by not only triiodide (I-3(-)) but also iodine (I-2), resulting in inevitable degradation. However, as a proton-donor, water can buffer the superoxide-related nucleophilic attack by reducing it to moderate hydroperoxide (HO2-). More importantly, the catalysis of iodide toward speroxide is restrained with the increase of alkalinity in water-contained electrolyte, resulting in the formation of Li2O2. Turning LiOH into Li2O2, the newly proposed mechanism leads to revolutionary reunderstanding toward the role of iodide and water in Li-O-2 battery systems.