The Research On Natural Mircocrystalline Graphite As Anode Materials For Li-ion Batteries

In order to receive a batter electrochemical performance, The natural microcrystalline graphite, which is purified and grinded, was modifidy by ways of different modification methods: coated by phenolic resin; surface oxidized-coated; intercalation oxidized- exfoliated-coated.The pyrolytic carbon-coated microcrystalline graphite was prepared by impregnating graphite into phenolic resin which is homemade, follwed by carbonization. the influences of the treat temperature and amount of resin for the electrical performances of natural microcrystalline graphite were discussed.The result shows that: The graphite is coverd by pyrolytic carbon without destructing its the crystal structure. the specific surface area of evaporated graphite increase with coating amount. When heating temperature is 950℃, coating amount is 3%, the initial reversible capacity increases to 334.3mAh·g-1 from 321.4mAh·g-1, the irreversible capacity of coated modified graphite was decreased from 75.8mAh·g-1 to 60.1mAh·g-1. Capacity retention after 30 cycles was increased from 65% to 91.1%.After oxidized by H2O2 and coated by phenolic resin, the change on the crystal structure, appearance, and electrical performance of nature graphite is studied. Oxidization didn't charge plate—sheet structure of natural graphite. The defect structure for surface of natural graphite was wiped off by H2O2 oxidized. Meanwhile, some crack or dent structure and nanometer-micropore was formed at the flank of natural graphite. It was used to enhance:the capacity for storing lithium-ion. the oxygenated group was formed at the crystal interface of nature graphite where is apt to decomposing electrolyte. Wetting between electrode and electrolyte was improved. Interface impedance of nature graphite was reduced, Enhance sticky abilities to amorphous carbon. after modified by liquid-phase oxidation method using H2O2 as oxidant, the irreversible capacity decreased from 75.8mAh·g-1 to 61.8mAh·g-1 and the initial reversible capacity increases to 350.6mAh·g-1 from 321.4mAh·g-1, the coulomb efficiency of first cycle for the oxidized sample increased to 83.9% from 80.1%, and the capacity retention after 30 cycles was increased to 92% after coated treatmeat. The natural microcrystalline graphite was processed by H2SO4+NaNO3 and expanded at high temperature, then coated by phenolic resin. the change on the crystal structure, appearance, and electrical performance of nature graphite is studied. The result shows that: The interlayer space of the sample was increased, and the room for expanding of the sample was reserved. Using this sample as anode material of lithium-ion batteries, the rate discharge performance and cycle performance were improved remarkably. This was because of the increasing of the interlayer space and reserving room for expanding resulted in the enlargement of Li-ion diffusion path and the decrease of the coating layer damage. The first cycle capacity of oxidize-expanded graphite was increased from 321.4mAh·g-1 (NG) to 361.7mAh·g-1. After coated by 5% resin, the initial reversible capacity is decreased from 361.7mAh·g-1 to 353.1mAh·g-1,but capacity retention after 30 cycles was increased to 91.2%.