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 graphite electrodes in electrolyte solutions based on ethylene and dimethyl carbonates (EC-DMC) and the impact of the salt used [from the LiAsF6, LiClO4, LiPF6, LiBF4, and LiN(SO2CF3)(2) list]. The presence of some additives in solutions (e.g., Li2CO3, CO2, tributylamine) and the effect of the particle size of the carbon on the electrode's behavior were investigated. The correlation between the surface chemistry, the morphology, and the performance of Li and graphite electrodes was explored using surface sensitive Fourier transform infrared and x-ray and photoelectron spectroscopies, impedance spectroscopy, x-ray diffraction and scanning electron microscopy in conjunction with standard electrochemical techniques. Synthetic graphite anodes could be cycled (Li intercalation-deintercalation) hundreds of times at a capacity close to the optimal (x --> 1 in LixC6) in EC-DMC solutions due to the formation of highly stable and passivating surface films in which EC reduction products such as (CH2OCO2Li)(2) are the major constituents. The cycling efficiency of Li metal anodes in these solutions, however, is lower than that obtained in ethereal solutions and seems to be too low for Li-metal liquid electrolyte, rechargeable battery application. The connection between the solution composition and the electrode's performance is discussed.