Structural and electrochemical characterization of vanadium-excess Li3V2(PO4)3-LiVOPO4/C composite cathode material synthesized by sol–gel method

To improve capacity and electrochemical performance of the cathode of Li-ion batteries, non-stoichiometric, vanadium-excess (V-excess) Li3V2(PO4)3-LiVOPO4/C (LVP-LVOP/C) composite cathode materials are synthesized by a single-step citric acid assisted sol–gel method and sintered at temperatures (300–900 °C). X-ray diffraction and transmission electron microscope results indicate that major Li3V2(PO4)3 and minor LiVOPO4 phases coexist and X-ray photoelectron spectroscopy results also show that the valance state of vanadium is + 4 and + 3. The sample sintered at 800 °C shows the best electrochemical performance with the highest discharge capacity of 140 mAh g−1 at 0.2 C, higher than the theoretical capacity of Li3V2(PO4)3 in the voltage range 2.8–4.3 V. The composite material displays remarkably improved stability exhibiting reversible capacity of 130, 115, and 108 mAh g−1 after 300, 500, and 1000 cycles at the rate of 0.3 C, 0.5 C, and 1 C, respectively. Additionally, the composite LVP-LVOP/C shows superior rate performance at various current densities from 0.2 to 10 C. Our study reveals that the novel composite material considerably enhances electrochemical performance, electronic conductivity, Li-ion diffusion, and contribution of LiVOPO4 to capacity by accommodating extra Li-ions to enhance capacity. The results demonstrate that the study is highly promising for the development of V-excess cathodes as V-excess composite materials exhibit better performance than pure phase Li3V2(PO4)3.