Solvent-Dependent Oxidizing Power of LiI Redox Couples for Li-O2 Batteries

Li-O2 batteries offer higher gravimetric energy density than commercial Li-ion batteries. Despite this promise, catalyzing oxidation of discharge products, Li2O2 and LiOH, during charging remains an obstacle to improved cycle life and round-trip efficiency. In this work, reactions between LiI, a soluble redox mediator added to catalyze the charging process, and Li2O2 and LiOH are systematically investigated. We show that stronger solvation of Li+ and I− ions led to an increase in the oxidizing power of I3−, which allowed I3− to oxidize Li2O2 and LiOH in DMA, DMSO, and Me-Im, whereas in weaker solvents (G4, DME), the more oxidizing I2 was needed before a reaction could occur. We observed that Li2O2 was oxidized to O2, whereas LiOH reacts to form IO−, which could either disproportionate to LiIO3 or attack solvent molecules. This work clarifies significant misconceptions in these reactions and provides a thermodynamic and selectivity framework for understanding the role of LiI in Li-O2 batteries.