锂离子电池正极材料LiMnPO4的改性研究-物理化学专业论文.docxVIP

ABSTRACT Olivine framed LiMnPO4 is one of the most promising cathode material for lithium ion batteries duo to its high voltage, high energy density, low cost, high thermal stability and environmental friendliness. However, the intrinsically low electronic and ionic conductivity limite its application. For the purpose of improving the electrochemical performances of LiMnPO4, a solid state reaction and a hydrothermal method are used to synthesize LiMnPO4. Besides, substitution and carbon coating are used to further improve the electrochemical performance of LiMnPO4 composite materials. The detailed works are as follows: LiMn0.5(V2/3)0.5PO4/C cathode material is synthesized by solid state reaction. The influence of calcination temperature, different carbon content and different carbon sources on the structure, morphology and electrochemical properties of LiMn0.5(V2/3)0.5PO4/C cathode material is investigated by XRD, SEM, TEM, EDX, EIS and Charge-discharge tests. The results show that 600 °C is the optimum calcination temperature and sample calcined at 600 °C shows regular particle morphology, uniform particle size distribution and small degree of aggregates. Adding appropriate amounts of carbon can not only prevent particle agglomeration or growth, but also improve the conductivity of the material. However, for the added carbon is electrochemically inert substance, the electrochemical performance will be affected when the carbon content is too high. The best carbon content is 10%. Carbon sources have little effect on the crystal structure and morphology of the samples, but it has a great influence on the electrochemical properties. SP is considered to be the best carbon source. The electrochemical performance test results show the initial discharge capacity of sample synthesized at optimal conditions is 113.1 mAh·g-1 at 0.1 C rate and the capacity is still as high as 90.6 mAh·g-1 at 25th cycle. A nutty-cake structural C-LiMn1-xFexPO4-LiFePO4 cathode materia