Surface Study of Lithium–Air Battery Oxygen Cathodes in Different Solvent–Electrolyte pairs

The O₂/Li₂O₂ electrode reaction has been studied on low surface area Au electrodes in three solvent–electrolyte pairs (0.1 M LiPF₆/DMSO, LiPF₆/ACN, and LiBF₄/ACN) using an electrochemical cell coupled to UHV XPS spectrometer, EQCM, AFM, and DEMS. The XPS spectra of the surfaces after treatment at selected electrode potentials for the O₂ reduction and reoxidation of the surface show the presence of C and S from solvent decomposition and of F and P from electrolyte decomposition. Furthermore, Li 1s and O 1s peaks due to Li₂O₂ and decomposition products such as carbonate, organics, LiF, high oxidation sulfur, and phosphorus compounds were also observed. Using ACN instead of DMSO results in less solvent decomposition, whereas using LiBF₄ results in less electrolyte decomposition. XPS, AFM, and EQCM show that O₂ reduction products removal only takes place at very high overpotentials. In agreement with XPS which shows removal of carbonate surface species, DEMS confirms evolution of CO₂ and consumption of O₂ at 4.5 V, but LiF cannot be removed completely in a round trip of the Li–O₂ battery cathode