Oxidative modification of natural graphite for use as the anode of a lithium ion battery

Natural graphite was modified by oxidation with a mixture of sulfuric acid (98%) and hydrogen peroxide (30%) with a volume ratio of 1∶1, followed by a heat treatment under argon at 900 ℃ for 3 h to overcome its disadvantages of the presence of active surface groups and volume changes produced by the intercalation/deintercalation of Li ions. Results showed that the graphitic layers of the expanded graphite were exfoliated and grain size increased from 26.8 to 35.2 nm after the modification. Constant current charging-discharging and cyclic voltammetry indicated that its high rate performance and cyclic stability were improved. The capacity retention ratio increased from 45.7% for the natural graphite to 81.3% for the modified one in the 50th cycle.