Electrochemical Behavior of Nonflammable Organo-Fluorine Compounds for Lithium Ion Batteries

The electrochemical behavior of organo-fluorine compounds with antioxidation ability has been investigated. Oxidation currents of fluorine-compound-containing ethylene carbonate (EC)/diethyl carbonate (DEC) solutions were much smaller than those of EC/DEC and EC/DEC/propylene carbonate (PC) at potentials higher than 6 V vs Li/Li+. Electrochemical reduction of fluorine compounds started at ca. 2 V vs Li/Li+, higher than those for EC, DEC, and PC. However the first coulombic efficiencies for natural graphite electrodes in fluorine-compound-containing EC/DEC mixtures were nearly the same as those in EC/DEC without an increase in irreversible capacities. Furthermore the first coulombic efficiencies in fluorine-compound-containing EC/DEC/PC mixtures were much larger than those in EC/DEC/PC itself. The results show that the fluorine compounds used in the present study can be used as nonflammable solvents for lithium ion batteries.