Enhancing the high rate performance of synergistic hybrid LiFePO4·LiVPO4F/C cathode for lithium ion battery

Abstract

The (1-x)LiFePO4·xLiVPO4F/C (x = 0, 0.05, 0.10, 0.20, 0.40, 0.60, 0.80, 1) composites with high rate performance were successfully prepared by an improved solid-phase method. Their physicochemical properties were characterized by different test instruments. Through X-ray Diffractometer and structural refinement, it was found that modification with certain amount of LiVPO4F on the LiFePO4 material induced bi-phase co-existence with mutual doping. By Scanning Electron Microscope and Transmission Electron Microscopy detection assisted with Energy Dispersion Spectrum and Fast Fourier Transform analysis, it can be confirmed that the composite material was evenly distributed. Sample 0.9LiFePO4·0.1LiVPO4F/C had the highest specific capacity and specific energy in all samples, with its discharge capacity of 137.4, 129.0, 121.4, 109.6 and 94.0 mAh g−1 at the rate of 3C, 5C, 7C, 10C and 15C, respectively. Furthermore, at the rate of 15C, the specific energy of 0.9LiFePO4·0.1LiVPO4F/C was more than 2 times of that of sample LiFePO4/C. After 800 cycles at 10C, the capacity retention ratio still maintained at 91.42%. Compared with the untreated material, sample 0.9LiFePO4·0.1LiVPO4F/C possessed smaller impedance and larger lithium diffusion coefficient, which is conducive to improve the electrochemical properties of LiFePO4 materials. It indicated that the heterogeneous double active phase shows good synergistic effect.