Structure and Electrochemical Performance of LiFePO4 Cathode with Coating Super Iron Conductor Li3 V2(PO4)3

The composite 9LiFePO4@Li3 V2(PO4)3 was prepared by coating super ion conductor Li3 V2(PO4)3 on the surface of LiFePO4 particles through mechanical activation method.X-ray diffraction,scanning electron microscopy,high resolution transmission electron microscopy,energy disperse spectroscopy and electrochemical measurements were used to evaluate the properties of the cathodes.The coated LiFePO4 contains olivine LiFePO4,monoclinic Li3 V2(PO4)3 and orthorhombic Li3 PO4 phases.As LiFePO4 particles are encapsulated with a layer of Li3 V2(PO4)3 and some V3+ ions are incorporated into the olivine structure,the LiFePO4 lattice parameters decrease.Subsequently,the exchange current density and lithium ion diffusion coefficients of coated LiFePO4 are separately improved one order of magnitude.Electrochemical measurements indicate that the rate capability and cycle performance of coated LiFePO4 are significantly enhanced.Compared with bare LiFePO4,the first discharge capacity of coated LiFePO4 is raised 34.09% and 78.97% at 1C and 2C rates,while the capacity retention increases 27.77% and 65.54% after 150 cycles,respectively.Furthermore,the 9LiFePO4@Li3 V2(PO4)3 exhibits initial discharge capacity of 121.379 mA·h/g at the rate of 5C and its capacity retention is 94.03% after 350 cycles,while the pure LiFePO4 almost shows no capacity at the same rate.