Six-Electron Reduction of LiIO₃ to LiOH in Aprotic Solvents and Implications for Li–O₂ Batteries

Batteries that leverage conversion reactions such as Li–O 2 batteries can offer increased gravimetric energy density over Li-ion batteries. Li–O 2 batteries with added LiI and H 2 O in the electrolyte that can form LiOH during discharge have been identified as potentially having high gravimetric energy density. Unfortunately, charging such Li–O 2 batteries can lead to the formation of parasitic LiIO 3 instead of O 2, where the impact of LiIO 3 on the cycle life of Li–O 2 batteries is not known. In this work, we study the six-electron reduction of LiIO 3 to LiOH to elucidate whether parasitic LiIO 3 in Li–O 2 batteries can be electrochemically active during discharge, as well as to assess the viability of a battery chemistry based on the conversion of LiIO 3 to LiOH. Drop-cast LiIO 3 electrodes were shown to form LiOH on discharge with carbon electrodes at voltages of 2.1–2.6 V Li using Raman spectroscopy and X-ray diffraction measurements. In addition, quantification using iodometric and acid–base titrations confirmed that the consumption of LiIO 3 and formation of LiOH during discharge was consistent with a six-electron reduction of LiIO 3 to LiOH. By studying the influence of solvent and water content on the discharge process, the overpotential during discharge was shown to linearly correlate with the logarithm of electrolyte viscosity divided by the solubility of LiIO 3, which suggests that the discharge process was limited by the mass transport of soluble LiIO 3 . While LiIO 3 electrodes have shown high gravimetric energy densities up to ∼1550 W h/kg LiIO 3 /H 2 O_react, significant challenges remain to be overcome to increase the rate capability and cyclability of this chemistry.