Of Lifepo <sub> 4 </ Sub> Compounds In Hydrothermal Synthesis, Modification And Electrochemical Performance

LiFePO₄ powders were synthesized by three different reacting conditions (solid state reactions at high temperatures, mechanochemical activation and hydrothermal synthesis). The samples were characterized by XRD, SEM, granularity analysis etc. Results showed that only the LiFePO₄ powders gotten by hydrothermal processes were pure phase, regular sheet with 2 urn, better performance compared with the products prepared by the other methods.In the process of the hydrothermal synthesis, we researched the effect of technological conditions on crystal structure and electrochemical performance. The results showed that the reaction temperature, reaction time and fill rate were important factors. The optimum process of synthesizing LiFePO₄ read as follows: the mixture was reactioned at 190℃ for 6 h, and the fill rate was 90%. The low rate recharge-discharge characteristic of the sample is best, the 1st recharge-discharge capacity at 0.1C rate were 140.2 mAh.g^-1 and 132.9 mAh.g^-1.In order to improve the electrochemical performance of products, prepared LiFePO₄/C by doping carbon and LiFe₀.9Mg₀.1PO₄ (LiFe₀.9Mn₀.1PO₄) by doping metal ion. The effect of doping ways on the materials was investigated. The experiment results showed that doping carbon and doping metal ion would not change the crystal structure; doping carbon can enhance the specific capacity and cycle characteristic at low rate. The chemical diffusion coefficient of lithium ion in the crystal lattice was increased and high rate characteristic of the materials was improved after doping metal ion.