The Superiority of Asymmetric Alkyl Methyl Carbonates

The electrochemical behavior of graphite electrodes cycled galvanostatically versus Li metal in electrolyte solutions containing LiPF{sub 6}, LiC(SO{sub 2}CF{sub 3}){sub 3}, and LiN(SO{sub 2}C{sub 2}F{sub 5}){sub 2} in ethyl and methyl alkyl carbonates was studied. The solvents include ethyl methyl, ethyl propyl, methyl propyl, isopropyl methyl, and isopropyl ethyl carbonates. The use of asymmetric, aliphatic alkyl methyl carbonates is shown to be essential to achieve both high capacity and long cycle life with graphite electrodes in Li-ion batteries.