Effect of Nanophase Li₃PO₄ and Li₄P₂O on the Electrochemical Performance of LiFePO₄ Cathode Materials.

The Li3PO4 modified LiFePO4/C and Li4P2O7 modified LiFePO4/C cathode materials were synthesized by in-situ synthesis method, respectively. Phase compositions and microstructures of the products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM). Results indicate that Li3PO4 and Li4P2O7 can sufficiently coat on the LiFePO4 surface and does not alter LiFePO4 crystal structure. The electrochemical behavior of cathode materials was analyzed using galvanostatic measurement and cyclic voltammetry (CV). Compared with Li3PO4, the existence of Li4P2O7 can better improve the electrochemical performance of LiFePO4 cathode materials in specific capability and lithium ion diffusion of cathode materials. The charge-discharge specific capacity and apparent lithium ion diffusion coefficient increase with Li4P2O7 content and maximizes around the Li4P2O7 content is 5 wt%. The results indicated that the Li4P2O7 adding enhances the lithium ion diffusion rate of LiFePO4. However, because of the interface fracture between Li4P2O7 and LiFePO4 particles during charging and discharging process, the cycling performance of Li4P2O7 modified LiFePO4/C cathode materials is very poor.