Lithium-ion Battery Negative Electrode Modified Graphite Materials

The electrochemical performances of graphite anode for Li-ion batteries were studied in this paper. Graphite samples with different particle size distributing were gained by sedimentation technology; some natural flake graphite were oxidized in air, and some were doped with metal oxidation such as Li2O and NiO. Those graphite materials were tested by means of X-ray diffraction technology; scanning electron microscopy; microelectrode cyclic voltammetry technology and galvanostatic charge/discharge technology. The main results were as following:1) With the increasing of the purity and the degree of graphitization, graphite has more sites for Li-ion and shaw larger reversible capacity.2) Diffusion was the key process of Li-ion intercalation/deintercalation from graphite negative electrode. When charge/dischargeing with high rate, large particles shaw low reversibel capacity because it were difficulty for Li-ion to intercalate/deintercalate thoroughly. Small particles also shaw low capacity because they has less sites for Li-ions, they had larger surface area and higher ratio of edge atom. During the first discharging process, more charge was consummated during the formation of solid electrolyte interface film and the anodes expressed larger irreversible capacity loss. The prople particle size of graphite anode was 10-20 micrometer.3) Surface oxidizing process at 500 C removed some sites with extra high reactivity and ultra-fine particle, which couled reduce the first irreversible capacity loss, improve the cyclic performance and reversible capacity, and better the performance at high current rate .4) The proper quantity coating of Li2O was assisted to form homogeneous SEI film, which could enlarge the first charge/discharge efficiency and better the cyclic performance. But how to asure the Li2O combine with graphite tightly, and what was the optimally contents of Li2O7 It was still to be studied further.5) The coating of NiO could react with electrolyte reversibly, but the reacting potential was much higher than the work potential of graphite anode, and the coating would reduce the first charge/discharge efficiency and cyclic performance.