Preparation And Electrochemical Performance Of Coal-tar Pitch Based Hard Carbon Anode Materials For Lithium Ion Batteries

Lithium-ion battery is one of the most promising battery systems used in electric vehicles. Developing hard carbons with high rate capacity has become a research focus in this field. However, the systematic studies of hard carbon anodes for lithium ion batteries, including the efficient systhesis of hard carbon materials, the effects of carbonization temperature and composite conductive agent on the electrochemical performance of hard carbon, and the further improvement in rate performance of hard carbon anode are still limited. This thesis developed a cheap and efficient way to prepare hard carbon material and investigated the relationship between structure and electrochemical performance of hard carbon. Eventually, the coal-tar pitch based hard carbon anode material with excellent rate performance was achieved. The main results of this thesis are summarized as follows:(1) The synthesis of coal-tar pitch based hard carbon. Coal-tar pitch was chosen as raw material. Firstly, the oxidized pitch spheres were prepared through pitch concocting process, spheres formation process and pitch sphere oxidation process. After pre-carbonization at800℃, ball-milling and ultimately carbonization at above1000℃, the oxidized pitch spheres were made into coal-tar pitch based hard carbon.(2) The effects of carbonization temperature on the electrochemical performance of coal-tar pitch based hard carbon materials. As the carbonization temperature increased from1000℃to1600℃, the specific surface area and pore volume of hard carbon decreased, and the interlayer distance of graphite crystallite also decreased. Thus, with the increase of carbonization temperature, the first discharge capacity reduced from407mAh/g to149mAh/g with the first coulumbic efficiency from65%to83%. and the rate capacity decreased from128.5mAh/g to50.8mAh/g (after50cycles at2C). Comprehensively considering the advantages of the first coulumbic efficiency and the rate performance, the carbonization tempature of1300℃was chosen as the optimization.(3) The comparasion of coal-tar pitch based hard carbon with the commercial hard carbon anode. The results suggested that coal-tar pitch based hard carbon prepared in this study has better cycle stability and rate performance compared with the commercial hard carbon.(4) The effects of composite conductive agent on the electrochemical performance of coal-tar pitch based hard carbon. The results indicated that hard carbon added with acetylene black/carbon nano-tube composite conductive agent has more excellent rate performance than that added with acetylene black only. After adding acetylene black/carbon nano-tube composite conductive agent, the rate capacity of hard carbon after300cycles at2C is120.6mAh/g, and the capacity retention ratio is99.4%.