A COMPARATIVE-STUDY OF SYNTHETIC GRAPHITE AND LI ELECTRODES IN ELECTROLYTE-SOLUTIONS BASED ON ETHYLENE CARBONATE DIMETHYL CARBONATE MIXTURES

This work entails a comparative study of both Li and synthetic graphit e electrodes in electrolyte solutions based on ethylene and dimethyl c arbonates (EC-DMC) and the impact of the salt used [from the LiAsF6, L iClO4, LiPF6, LiBF4, and LiN(SO2CF3)(2) list]. The presence of some ad ditives in solutions (e.g., Li2CO3, CO2, tributylamine) and the effect of the particle size of the carbon on the electrode's behavior were i nvestigated. The correlation between the surface chemistry, the morpho logy, and the performance of Li and graphite electrodes was explored u sing surface sensitive Fourier transform infrared and x-ray and photoe lectron spectroscopies, impedance spectroscopy, x-ray diffraction and scanning electron microscopy in conjunction with standard electrochemi cal techniques. Synthetic graphite anodes could be cycled (Li intercal ation-deintercalation) hundreds of times at a capacity close to the op timal (x --> 1 in LixC6) in EC-DMC solutions due to the formation of h ighly stable and passivating surface films in which EC reduction produ cts such as (CH2OCO2Li)(2) are the major constituents. The cycling eff iciency of Li metal anodes in these solutions, however, is lower than that obtained in ethereal solutions and seems to be too low for Li-met al liquid electrolyte, rechargeable battery application. The connectio n between the solution composition and the electrode's performance is discussed.