Surface modification of graphite by coke coating for reduction of initial irreversible capacity in lithium secondary batteries

Surface modification of graphite to reduce the irreversible capacity loss during the first charging period of graphite anodes is described. For the surface modification, artificial graphite (Lonza KS44) is dispersed in a tetrahydrofuran/acetone solution which contains coal tar pitch. The solvent is then evaporated. The loaded pitch component is converted to coke by a heat treatment at 1000°C in argon atmosphere. The resulting coke-coated graphite has a smaller surface area than that of the pristine one. The reduction of surface area, which is due to the coverage of pores of <10 nm by the coke component, causes a decrease in the irreversible capacity on the first cycle. The extent of electrolyte decomposition, gas evolution and surface film growth is also less with the coke-coated graphite electrode.