Effects Of Carbon-Coated On The Properties Of LiFePO₄ Cathode Material

Olivine LiFePO4 has been a new kind of anode material for lithium-ion battery,because this material is cheap, high security, structural stability and no pollution, etc, however, it has a low electronic conductivity. In order to improve the conductivity properties of LiFePO4, the effects of carbon-coating on its performance were studied.LiFePO4 and carbon-coated LiFePO4/C composites were synthesized by two-step solid-state reaction. The crystal structures, morphologies of the composites were investigated by XRD, SEM measurement. The electrochemical performances of as-synthesized cathode materials were investigated by galvanostatic charge-discharge performance test and electrochemical impedance spectra measurement.LiFePO4 was prepared by high temperature soli-state method, and the effects of precalcining temperature, sintering temperature and sintering time were discussed. The results showed that the products precalcined at 450℃for 6h and then sintered at 700℃for 16h possess excellent electrochemical performances.LiFePO4/C composite material has been synthesized by carbon-coated reaction using glucose, lauric acid, cinnamic acid, PVA as conductive carbon source. The results showed that the addition of carbon had not affected the crystal structure of LiFePO4. The electrochemical resistance of LiFePO4 decrease significantly with the increase of carbon content, the discharge specific capacity and cycle capability and high-rate charge-discharge capability were all improved largely. The results showed that the best added dosages of glucose, lauric acid, cinnamic acid and PVA were 30%, 20%, 20% and 20%, respectively.Analysing electrochemical performances, crystalline structure and morphology of particles of LiFePO4 synthesized by the solid-state reaction with the aforementioned carbon sources, we could conclude that LiFePO4/C prepared by solid state reaction with PVA had a better capacity and cycle performance than the others. The specific discharge capacities of LiFePO4/C using PVA as carbon source were 146.3 mAh/g at 0.1C, 115.3 mAh/g at 0.2C, and 104.3 mAh/g at 0.5C, respectively, and after 50 cycles the specific discharge capacities of them were 129.3, 93, 84.3 mAh/g.