Synthesis and electrochemical properties of xLiFePO4·(1−x)Na3V2(PO4)2F3/C composite for lithium-ion batteries

To improve the operating voltage and the rate performance of LiFePO4, the different ratios of the xLiFePO4·(1−x)Na3V2(PO4)2F3/C (LFP-NVPF/C) are synthesised via a carbothermal reduction method. The structure and morphology of the composite are analysed by X-ray diffraction (XRD) and electron microscopy. The as-prepared material is composed of a mixture of two phases: V-doped LFP and Fe-doped NVPF. Electrochemical tests show that the molar ratio of 9:1 is the optimum composition and the LFP-NVPF/C (x = 0.9) composite exhibits excellent performance with an initial discharge capacity of 151.2, 146.5, 120.6 and 100.2 mAh g−1 at 1.0, 2.0, 5.0 and 10 C, respectively, which is higher than that of single phase LFP/C, especially at high rates. According to the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the introduction of NVPF improves charge transfer and Li+ diffusion of LFP/C and provides excellent cycle stability at high rates.