Improved electrochemical properties of (1 − x)LiFePO4·xLi3V2(PO4)3/C composites prepared by a novel sol–gel method

Abstract

In this study, (1 − x)LiFePO₄·xLi₃V₂(PO₄)₃/C (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1) composite cathode materials are synthesized using CH₃COOLi·2H₂O, Fe(CH₃COO)₂·4H₂O, V₂O₅, and H₃PO₄ as starting materials with N,N-dimethyl formamide as a dispersing agent using a novel sol–gel method. The structure, morphology, and electrochemical properties of the composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge–discharge measurements. XRD patterns of the compound indicate the coexistence of LiFePO₄ and Li₃V₂(PO₄)₃. Compared to pristine LiFePO₄ and Li₃V₂(PO₄)₃, the composite materials exhibit smaller particle size, which can facilitate Li⁺ extraction and insertion, thereby leading to an improvement in the electrochemical properties. Among all the composites synthesized, 0.8LiFePO₄·0.2Li₃V₂(PO₄)₃/C exhibits the best electrochemical performance with an initial specific discharge capacity of 158.7 mA h g⁻¹ at 0.1C in the voltage range of 2.5–4.3 V. When the current rate is increased to 5C and 10C, the capacity of 0.8LiFePO₄·0.2Li₃V₂(PO₄)₃/C is retained at 125.8 and 110.8 mA h g⁻¹, respectively, indicating the cycling stability of the composite.