Preparation And Performance Study Of LiFePO₄ As Cathode Material For Lithium Ion Battery

The positive active substances of the lithium-ion battery directly determine the performance of the power typed lithium-ion battery. LiFePO4 as the positive active material has many advantages such as stable structure, low cost and its safety. These make the LiFePO4 be the important positive acitive material for the power typed lithium-ion battery. To rise up the properties of LiFePO4 materials furtherly and reduce the manufacturing cost, a solution co-precipitation method with cheap Fe3+ iron raw material and hydrothermal synthesis method conditions are used to prepare high-performance cathode material LiFePO4 in this paper. In order to improve the conductivity and electrochemical properties of the LiFePO4 material, a carbon-coating method is applied into the prepared LiFePO4 powder to obtain LiFePO4/C.The electrochemical test, TG-DSC, XRD, SEM are used to analysize microstructure and the performances to optimize reaction conditions.The solution co-precipitation method was used with cheap Fe3+ iron raw material and the complexing agent citric acid. The XRD patterns showed that pure-phase LiFePO4 and carbon coated LiFePO4 were prepared after two stages heat treatment. When a sintering temperature was at 650℃for 6h, the properties of LiFePO4 was best. When 15wt.% glucose as carbon source was added to coat the LiFePO4, the initial specific discharge capativity of carbon-coated LiFePO4/C at 0.1C rate current density reaches to 132.7mAh·g-1, and the capacity stability maintained 130.9mAh·g-1 after 20 cycles. In a test cell, the prepared LiFePO4/C with acetylene black additive, presented the best charge-discharge capability.Utilizing hydrothermal synthesis method with (NH4)2Fe(SO4)2·6H2O, LiOH·H2O and NH4H2PO4 as the raw materials and citric acid as the complexing agent, the pure-phase was obtained and carbon coated LiFePO4 was prepared by sintering the mixure of the glucose. It turned out that the LiFePO4/C sample synthezed in 220℃for 6 h and followed by carbon coating shows the best electrochemical performance. The initial specific discharge capacity at 0.1 C rate current density was 128.3mAh·g-1.