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.

Graphical abstract

中文翻译：

---

溶胶-凝胶法合成钒过量Li3V2(PO4)3-LiVOPO4/C复合正极材料的结构和电化学表征

为了提高锂离子电池正极的容量和电化学性能，非化学计量、钒过量（V-excess）Li ₃ V ₂ (PO ₄ ) ₃ -LiVOPO ₄ /C (LVP-LVOP/C)复合正极材料通过一步柠檬酸辅助溶胶-凝胶法合成，并在温度（300-900°C）下烧结。X 射线衍射和透射电子显微镜结果表明主要的 Li ₃ V ₂ (PO ₄ ) ₃和次要的 LiVOPO ₄相共存和X射线光电子能谱结果也表明钒的价态为+4和+3。在800°C烧结的样品表现出最好的电化学性能，在0.2 C时最高放电容量为140 mAh g ^-1，在2.8-4.3 V的电压范围内高于Li ₃ V ₂ (PO ₄ ) ₃的理论容量。复合材料显示出显着提高的稳定性，可逆容量为130、115和108 mAh g ^-1 分别以 0.3 C、0.5 C 和 1 C 的速率循环 300、500 和 1000 次后。此外，复合材料 LVP-LVOP/C 在 0.2 至 10 C 的各种电流密度下显示出优异的倍率性能。我们的研究表明，这种新型复合材料显着提高了电化学性能、电子电导率、锂离子扩散以及 LiVOPO ₄对通过容纳额外的锂离子来提高容量。结果表明，该研究对于开发 V 过量正极非常有希望，因为 V 过量复合材料表现出比纯相 Li ₃ V ₂ (PO ₄ ) ₃更好的性能。

图形概要