Ethylmethylcarbonate, a promising solvent for Li-ion rechargeable batteries

Ethylmethylcarbonate (EMC) has been found to be a promising solvent for rechargeable Li-ion batteries. Graphite electrodes, which are usually sensitive to the composition of the electrolyte solution, can be successfully cycled at high reversible capacities in several Li salt solutions in this solvent (LiAsF{sub 6}, LiPF{sub 6}, etc.). These results are interesting because lithium ions cannot intercalate into graphite in diethyl carbonate solutions and cycle poorly in dimethyl carbonate solutions. To understand the high compatibility of EMC for Li-ion battery systems as compared with the other two open-chain alkyl carbonates mentioned above, the surface chemistry developed in both Li and carbon electrodes in EMC solution was studied and compared with that developed on these electrodes in other alkyl carbonate solutions. Basically, the major surface species formed on both electrodes in EMC include ROLi, ROCO{sub 2}Li, and Li{sub 2}CO{sub 3} species. The uniqueness of EMC as a battery solvent is discussed in light of these studies.