Preparation And Properties Of Lithium Iron Phosphate Cathode Materials

Olivine type cathode material is considered to be the most promising cathode material for lithium-ion batteries,because it has the advantages of friendliness environment,richness resources,low price,and good safety performances.Because of the limitation of the crystal structure of LiFePO4 results in poor conductivity and ion diffusion properties,low specific capacity and poor large current discharge performance.Therefore,improving the electronic conductivity and diffusion of ions of the material has become the focus of researchers' attention.In this paper,LiFePO4/C materials were synthesized by carbon thermal reduction and mixed solvent thermal method,respectively,and modified by carbon coating.The structure,morphology,carbon content and electrochemical performance of materials were also analyzed by means of XRD,SEM,TEM,element analyzer,AC impedance and electrochemical techniques.Iron phosphate as iron and phosphorus source,lithium carbonate as lithium source,were selected to synthesize LiFePO4/C by the carbon thermal reduction method.The effects of different iron phosphate materials,sintering temperatures,carbon source and carbon contents on the morphologies and electrochemical properties of the composites were investigated.The optimal synthesis conditions are as follows,glucose is used as carbon source,the molar ratio of FePO4,lithium carbonate and glucose is 2:1.03:0.35,and calcination temperature is 700 ?.Under this condition,the discharge specific capacities are 160.0 and 104.9 mAh/g at 0.2 C and 10 C,respectively.When the carbon content is 0.40,the discharge specific capacity of LiFeP04/C composite is 106.3 mAh/g at dicharge rate of 10 C,and the discharge capacity remains 99.2%at 1 C after 200 times cycles.Lithium phosphate,phosphoric acid and ferrous sulfate heptahydrateas as raw materials were selected to synthesize LiFePO4/C by mixed solvent thermal method.The effects of different solvents,solvent ratio and the amount of template on the morphologies and electrochemical properties of the composites were studyed.The optimal synthesis conditions are as follows,the mixture of PEG-H2O is used as solution to prepare LiFePO4/C composites,the solvent volume ratio of the mixed solution is 50%,and the template content is 3 mmol.Under this condition,the synthesized LiFePO4/C composite preferentially grows along(020)crystal face,the first discharge capacity is 152.3 mAh/g at 0.2 C,and the discharge specific capacity at 10C magnification is still 99.2 mAh/g.