The Synthesis And Research On LiFePO₄/C As Cathode Materials For Lithium Ion Battery

Lithium-ion battery is mainly made up of anode material,cathode material and the anode material electrolyte. As a lithium-ion battery anode material,LiFePO₄/C has some advantages, such as the good cycle performance, green pollution-free, etc. Its theoretical specific capacity has reached 170 m Ah/g. However,in a practical application, its actual specific capacity is far lower than the theoretical specific capacity for low conductivity. Typically, the methods of improving included carbon- coating, ion doping, nanocrystallization, etc.The LiFePO₄ of the pure phase was fabricated by hydrothermal method in this paper. and then was coated by glucose, carbon nanotubes to study the effects of the electrochemical performance of LiFePO₄/C of different carbon sources and its mechanism of action. Then the LiFePO₄/C of the different shape were obtained by adjusting water and glycol of different ratios in the process of hydrothermal preparation of LiFePO₄. And their electrochemical properties were test further, the results show that:1.The sample of LiFePO₄ prepared have bigger particle size and serious reunion by the Hydrothermal method for the effect of strong polarity of the water. It size is about 2-3um.The sample size is smaller and the dispersibility is good after replacing the solution with ethylene glycol.It size is about 100 nm.Because of the influence of ethylene glycol can be adsorbed on the surface of the crystal,the nucleation process.2.The LiFePO₄ of the pure phase fabricated was coated by carbon, whose discharge specific capacity is 122 m Ah/g for the amount of glucose of 10%wt at 0.1C ratio. Because of the addition of glucose can fully improve the electrical conductivity of the sample. And the LiFePO₄ particles size are smaller by the solvent hot method. The LiFePO₄/C of the three-dimensional network structure combined with carbon nanotube of the different quality have the highest discharge specific capacity, whose discharge specific capacity is 154.6m Ah/g when the amount of carbon nanotubes is 4% wt. Because of the addition of carbon nanotubes can fully improve the electrical conductivity of the sample. Then the LiFePO₄ prepared werecoated by the method of mixed sintering of the mass fraction of 4% carbon nanotubes and 10% glucose to study the effects of the electrochemical performance of LiFePO₄/C and its mechanism of action on different carbon sources.3.The LiFePO₄ have different microstructure in the solvent of different rations of water and ethylene glycol under the condition of pH = 5 by hydrothermal method.The sample prepared has good electrochemical performance when the volume ratio of water and ethylene glycol is 1:1, whose discharge specific capacity is 147 m Ah/g in 0.1 C ratio.Because of the particle size of the sample is the smallest,the sample has the best electrochemical performance.