Electrochemical Li-insertion processes into carbons produced by milling graphitic powders: The impact of the carbons' surface chemistry

Carbon powders were prepared by milling graphite particles in different atmospheres including air, highly pure argon, nitrogen, and CO2. Part of the samples was further exposed to air after milling. The carbonaceous materials thus obtained were tested as Li-insertion anodes in nonaqueous Li salt solutions. It was found that the atmosphere in which the active mass was prepared had a pronounced impact on the specific surface area of the particles obtained, probably due to the effect of surface groups on the carbons developed in the milling process. It was also found that the atmosphere to which the powders were exposed had a remarkable impact on the electrochemical behavior of the carbon electrodes in Li-insertion processes. The milling of the graphite produces highly reactive carbon surface sites, which react readily with active gases such as oxygen and CO2. The surface groups thus formed influence the surface chemistry developed on these electrodes in solutions. Since the electrochemical behavior of Li-C insertion electrodes depends strongly on the nature of the passivation films developed on these electrodes at low potentials, the milling atmosphere strongly influences their electrochemical behavior. The electrochemical processes were studied by chronopotentiometry, cyclic voltammetry, and impedance spectroscopy, the electrodes' structure and morphology were explored by X-ray diffraction and scanning electron microscopy, and the carbons' surface chemistry was studied by Fourier transform infrared and X-ray photoelectron spectroscopy. (C) 2001 The Electrochemical Society.