doi:10.1016/j.elecom.2015.06.019

We monitored by means of UV-visible spectroscopy the formation and consumption of triiodide ion (I₃⁻), generated when iodide ion (I⁻) is used as redox mediator in lithium–oxygen batteries. Results evidence the initial formation of I₃⁻ during oxidation, and its decomposition during reduction. Correlation of absorbance with capacity is consistent with the mediation of peroxide oxidation above 3 V. Decrease of I₃⁻ absorbance and the appearance of a peak at a wavelength of 410 nm after 14 hours at open circuit voltage revealed side reactions associated to electrolyte degradation leading to the formation of HOI. This work shows that UV-visible spectroscopy is a valuable tool for following reactions involved in the operation of lithium–oxygen batteries based in the absorbance of the species formed or consumed.