The cathode reaction in the rechargeable Li-O2 battery is describe by the following reaction: O2 + 2e- + 2Li+ = Li2O2. Using redox mediators as soluble catalysts in ether solvents, it is possible on discharge to reduce O2 to Li2O2 at ½ the overpotential, without forming passivating films and with fewer side reactions, while on charge Li2O2 can be oxidized rapidly to O2 even when the former is not in contact with the electrode surface. As a result, cycling of an aprotic Li-O2 cell has been demonstrated with rates and capacities of several mA and mAh cm-2, respectively. Although ethers, if used in conjunction with mediators, exhibit improved solvent stability, they do not entirely solve the stability problem. The decomposition of the electrolyte solution in Li-O2 cells will be discussed in the context of the mechanism of Li2O2 formation and decomposition. Ultimately, the Li-O2 cell must operate in air. The effect of H2O in the gas stream, and hence in the electrolyte solution, on the mechanism of the O2/Li2O2 reaction and the consequences for the cell performance are important. The influence of H2O on the O2 reduction mechanism will be considered.

Mediating reactions at the cathode in Li-O2 batteries

256th National Meeting (2018)

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