Investigation On Fabrication And Properties Of Graphite/Hard Carbon Composite Materials For Li-ion Battery

In this paper, two kinds of pyrolytic carbon were prepared through hightemperature solid phase with the boron-doped phenolic resin and coal tar pitch as rawmaterials. Besides, the pyrolysis process was optimized and the electrochemicalproperties of the two pyrolytic carbon were studied.; The phenolic resin pyrolyticcarbon/pitch pyrolytic carbon composite materials were prepared by carbon surfacecoating; The rate performance of graphite was improved by surface modified,includingcoating by the phenolic resin pyrolytic carbon and pitch pyrolytic carbon. Meanwhile,the electrochemical properties of pitch pyrolytic carbon/graphene composite materialswas stidied.The materials which was obtained through pyrolysis of the boron-containingphenolic resin material had a reversible capacity of246mAh/g and kept a capacityretention of98%; Through the electrochemical properties of pitch pyrolytic carbon ofdifferent temperature, the700℃had the highest capacity, it could be up to about564mAh/g, however with a poor cyclic performance,412mAh/g was left through50cycles; but at800℃,900℃,1000℃, the cyclic performance was excellent, nodecreace happened through50cycles. The pyrolytic carbon kept a capacity of350mAh/g,300mAh/g,270mAh/g at800℃,900℃,1000℃respectively. Consideringthe capacity and efficiency, the temperature800℃was determined as the thermaltemperature. And pyrolysis rate and pyrolysis time was studied, the final conclusionheating rate to5℃/min, pyrolysis time was3h.The phenolic resin pyrolytic carbon/pitch pyrolytic carbon composite materialswas prepared through carbon coating. The influence of the proportion of pitch on theelectrochemical properties of materials was studied, finally reached the conclusion: theratio of3:1was the best program with a capacity of310mAh/g and efficiency of61%which was much higher than phenolic resin pyrolytic carbon.The rate performance of pitch pyrolytic carbon was increased through theaddition of graphene. Through the experiment,the rate performance was greatlyimproved because of the excellent electron conductivity and high capacity of thegraphene. The capacity could reach280mAh/g,250mAh/g and200mAh/g with thecurrent of1C(372mA/g),2C(744mA/g) and5C(1860mA/g) respectively.The pitch was used to be the precursor of the carbon coating of graphie. When thecoating amount reached the10%, the rate performance of the materials was the bestwith a capacity of350mAh/g at the curent of1C(372mAh/g). Besides, the direct mechanical mixing of graphite and pyrolytic carbon could reach a capacity of340mAh/g and the efficiency could reach76%.