Synthesis and electrochemical properties of a composite LiMn0.63Fe0.37PO4 with Li3V2(PO4)3 for lithium-ion battery cathode materials

A composite materials LiMn_0.63Fe_0.37PO₄ with Li₃V₂(PO₄)₃ can be synthesized by a sol-gel method using N,N-dimethylformamide (DMF) as a dispersing agent. The structures, characteristics of the appearance, and electrochemical properties of the composites have been studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The composites contained LiMnPO₄/C (LMP/C), LiFePO₄/C (LFP/C), and Li₃V₂(PO₄)₃/C (LVP/C) phases with a nano-sized dispersion. The TEM images showed that the composites are crystalline with a grain size of 10–50 nm. The Mn2p, V2p, and Fe2p valence states were analyzed by X-ray photoelectron spectroscopy (XPS). The incorporation of LVP and LFP with LMP effectively enhanced the electrochemical kinetics of the LMP phase by a structural modification and shortened the lithium diffusion length in LMP. The capacity of the composite 0.79LiMn_0.63Fe_0.37PO₄·0.21Li₃V₂(PO₄)₃/C remained at 152.3 mAh g⁻¹ (94.7%) after 50 cycles at a 0.05 C rate. The composite exhibited excellent reversible capacities 159.4, 150, 140.1, 133.7 and 123.6 mAh g⁻¹ at charge-discharge rates of 0.05, 0.1, 0.2, 0.5 and 1 C, respectively.