Synthesis and electrochemical properties of Li3V2(P1−xBxO4)3/C cathode materials

Abstract

B-doped compounds Li₃V₂(P_1−xB_xO₄)₃/C (x = 0, 0.01, 0.03, and 0.07) are prepared by a sol–gel method. The crystal structure, morphology and electrochemical properties of B-doped Li₃V₂(PO₄)₃ are investigated. X-ray diffraction (XRD) analysis indicates that a B atom enters the crystal structure of Li₃V₂(PO₄)₃ but does not change the monoclinic structure. Cycle stability and rate performance measurements reveal that moderate B doping improves the electrochemical properties of Li₃V₂(PO₄)₃. Among all the B-doped samples, Li₃V₂(P_0.97B_0.03O₄)₃/C shows the largest initial discharge capacity, best cycle stability and rate performances. In the potential range of 3.0–4.3 V, Li₃V₂(P_0.97B_0.03O₄)₃/C delivers a discharge capacity of 127.5 mA h g⁻¹ at 0.2C rate, while at 20C the discharge capacity remains above 100 mA h g⁻¹. After 100 cycles, the discharge capacity retention is 98%. Moreover, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) curves indicate that B doping not only decreases the charge transfer resistance but also increases the Li-ion diffusion rate. The excellent electrochemical performance of Li₃V₂(P_0.97B_0.03O₄)₃/C can be attributed to its larger Li ion diffusion, smaller particle size, and higher structural stability and electronic conductivity induced by B doping.