At high voltages, Li-ion and Li-air batteries undergo unwanted electrochemical reactions that can permanently decrease the performance of the battery. Recent experiments studying off-gassing from NMC cathodes have yielded different results for the trends of O2, CO2, and CO gas production with varying Ni composition. Studies also disagree on the origin of the elements in the gas. Very recently, it was suggested that not only is Li2CO3 on NMC cathodes responsible for the majority of CO2 production [1] but that singlet oxygen is produced when Li2CO3 is bias above 3.82 V [2]. This and other studies suggest singlet oxygen production as a common degradation pathway in Li-ion, Li-air [3,4], and Na-air [5].

With the use of first principles methods, we attempt to reconcile these experimental works and propose a universal mechanism of singlet oxygen production. We will also discuss a way to experimentally verify our mechanism by varying the electrolyte, which we claim will change the onset potential of singlet oxygen production in a predictable way.

[1] 1. Renfrew, S. E. & McCloskey, B. D. Residual Lithium Carbonate Predominantly Accounts for First Cycle CO2and CO Outgassing of Li-Stoichiometric and Li-Rich Layered Transition-Metal Oxides. J. Am. Chem. Soc. (2017). doi:10.1021/jacs.7b08461

[2] 1. Mahne, N., Renfrew, S. E., McCloskey, B. D. & Freunberger, S. A. Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen. Angew. Chemie Int. Ed. (2018). doi:10.1002/anie.201802277

[3] 1. Mahne, N. et al. Singlet oxygen generation as a major cause for parasitic reactions during cycling of aprotic lithium-oxygen batteries. Nat. Energy (2017). doi:10.1038/nenergy.2017.36

[4] 1. Wandt, J., Jakes, P., Granwehr, J., Gasteiger, H. A. & Eichel, R.-A. Lithium–Air Batteries Singlet Oxygen Formationduring the Charging Process of an Aprotic Lithium–Oxygen Battery.

[5] 1. Schafzahl, L. et al. Singlet Oxygen during Cycling of the Aprotic Na-O2 Battery. Angew. Chemie Int. Ed. (2017). doi:10.1002/anie.201709351