Characterization of lithium electrode in lithium imides/ethylene carbonate and cyclic ether electrolytes - II. Surface chemistry

Chemical components of surface films of deposited lithium on nickel substrates in electrolytes with LiN (SO2CF3)(2)) (LiTFSI), LiN (SO2C2F5)(2) (LiBETI), LiPF6 solutes, and tetrahydrofuran solvents were characterized by Fourier-transform infrared, two-dimensional nuclear magnetic resonance (2D NMR), X-ray photoelectron spectroscopy, evolved gas analysis, and ion chromatograph in order to understand the electrochemical performance of lithium imide/cyclic ether-based electrolytes. The top layers of the surface film were ROCO2Li, Li2CO3, polymer constituents, and LiF. The inner layers of the surface film consisted of Li2O and carbide species. In imide/cyclic ether-based electrolytes, Li2S2O4 and Li2SO3 as outer layers, and Li2S as the inner layer were formed on a nickel substrate as reductive constituents of imide solute. We found that organic surface layers consisted of lithium etoxides, lithium ethylene dicarbonate (CH2OCO2Li)(2), polyethylene oxide, and lithium ethylene dicarbonate containing an oxyethylene unit by H-1, C-13, and 2D NMR. Li cycling efficiency affects not only the deposited lithium morphology but also chemical components. (C) 2004 The Electrochemical Society.