Synthesis And Electrochemical Properties Of Electrodes Material LiFePO₄for Lithium Ion Battery

In1997, it was reported that the olivine LiFePO4can be reversiblely inserted and extract ed lithium ion and could be considered as the cathode material for lithium-ion batteries, especially for the hybrid electric vehicles. Because of its advantages such as good stability of stucture, the abundant resource, high safty, nontoxicity, environmentally benign and a high theoretical capacity of170mAh/g, LiFePO4attracted great research interests. However, LiFePO4has some serious disadvantages:low electronic conductivity and slow lithium ion diffusion dynamics thus limiting the rate capacity of the batteries. In this work, some studies about electronic conductivity were done via coating carbon on the surface of LiFePO4, that remarkablely improved the conductivity and the electrochemical performance of LiFePO4.The main points are as follows:(1) The citric acid as the reducing agent and chelate agent, LiAc、Fe(NO3)3、NH4H2PO4as the starting material, carbon black as the carbon resource, LiFePO4/C contaied the different amount of carbon black were synthesized by a sol-impregnation. The samples were characterized by X-ray diffraction (XRD), and transmission electron microscope (TEM), scanning electron microscope (SEM). We optimized LiFePO4/C with different amount of carbon black, the LiFePO4/C with the best electrochemical performance was synthesized. The sample of20%carbon black was the best one in its electrochemical properties. The diameter of particles was about100nm, and the deliver capacity was160mAh/g at0.1C, and after20cycles, the capacity retained as high as that in the first cycle.(2) The citric acid as the reducing agent and chelate agent, LiAc、Fe(NO3)3、NH4H2PO4as the starting material, the CMK-3as the carbon resource, by the co-precipitation with treatment of ultrasonic waves, the different carbon amount of LiFePO4/C were synthesized, the sapmles were characterized by XRD, TEM and EIS The sample with5%CMK-3holded the capacity of145mAh/g at0.1C.(3) The sphere polystyrene(PS) and the netlike polyethylene glycol(PEG) as the reducing agent and carbon resource, LiA、Fe(NO3)3、NH4H2PO4as the starting material. The sol-gol method was used to synthesize the LiFePO4/C composit. The sapmles were characterized by XRD, TEM and EIS. The materials had some special structure, and behaved outstanding electrochemical performances. The capacity was about148mAh/g at0.1C.