Operando UV-visible spectroscopy evidence of the reactions of iodide as redox mediator in Li–O2 batteries

•A simple homemade Li/O2 cell has been built up for operando UV-visible spectroscopy.•Iodide redox mediator has been evaluated using this cell.•Triiodide formation during charge has been observed.•Side reactions associated to the use of iodine have also been identified.

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.

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