The study of surface film formation on noble-metal electrodes in alkyl carbonates/Li salt solutions, using simultaneous in situ AFM, EQCM, FTIR, and EIS

In this study, surface film formation on nonactive-metal electrodes was ana lyzed using several in situ spectroelectrochemical techniques. These techni ques included in situ Fourier transform infrared spectroscopy in both inter nal and external reflectance modes, impedance spectroscopy, electrochemical quartz crystal microbalance, and atomic force microscopy. The solutions st udied included ethylene carbonate-dimethyl carbonate (EC - DMC) and EC-tetr ahydrofurane (EC - THF) mixtures with Li salts, such as LiAsF6, LiPF6, LiCl O4, and LiBr, part of which are essential for practical Li ion batteries. T his work aimed to determine the onset of surface film formation, the impact of the solvent and salt used, and to compare the stability of the surface films formed in the various systems. The onset of surface film formation in these systems usually approximated 1.5 V (Li/Li+). EC reduction products, probably (CH2OCO2Li)(2), are dominant constituents in the surface films. Ho wever, in LiPF6 solutions, Li salt reduction products become dominant in th e surface films. The surface film formation is accompanied by an injection of charge which does not form stable surface species and by dissolution pro cesses of surface species (until the solution becomes saturated with them). The coherence of the data obtained from the four techniques mentioned abov e and the relative stability of the surface films formed in the various sol utions are discussed.