Effects Of Ni、Fe Doping On Properties Of V₂O₅ Thin Film Electrode

Vanadium pentoxide（V₂O₅） has been very promising and valuable researching cathode material for lithium-ion batteries because of its good lithium embed performance, high theoretical capacity, abundant and low cost. However, the development of lithium-ion batteries with V₂O₅ as cathode materials was limited for its poor structural stability, short cycle life and the oxidation of electrolyte in the charge-discharge cycle. It was found by many researches that the performance of V₂O₅ was improved well with the optimization of synthesis process and doping modification.. In this paper, V₂O₅ thin films doped by Ni, Fe were prepared with sol-gel method. XRD, SEM, XPS and the electrochemical analysis has been employed to characterize and analyze the structures and surface morphology of V₂O₅ thin films. What’s more, the effects of doping Ni and Fe on the electrochemical performance of V₂O₅ thin films had been researched.Results of XRD, SEM showed that the crystal structure of Ni and Fe doped V₂O₅ thin films were standard orthogonal crystal,the same as pure V₂O₅. Ni-doped V₂O₅ thin film, which was uniform distribution, regular shape, clear interface and dense accumulation, was formed of nanorudes with the length of 350⁵10 nm, width of 30nm⁷0 nm, thickness of 10³0 nm, while Fe-doped V₂O₅ thin film was composed of nanoplates with the length of 360⁵40 nm, width of 150²20 nm, thickness of 90¹60nm. Doping V₂O₅ thin film had a larger surface area, which can increased the contact area between V₂O₅ thin film and electrolyte solution, contributed to the improvement of the cycling stability and specific capacity. The results of XPS indicated that the structure stability of V₂O₅ thin filmwas improved the increase of the content of V4+ owing to doping Ni.Cyclic Voltammetry and Chronopotentiometry results displayed that can improve the electrochemical performance of V₂O₅ thin films could be improved by doping appropriate Ni and Fe and the fading rate restrained effectively. The capacities of Ni-doped V₂O₅ thin films were enhanced firstly and then decreased with the increased of the content of Ni, and the optimum content was 2%. Under the current density of 33.20 μ A/cm2, the discharge and charge capacities of V₂O₅ thin film were up to 725 m Ah·g-1 and 764 m Ah·g-1. After 100 cycles, the charge and discharge capacities were 458 m Ah·g-1 and 431 m Ah·g-1, with fading rates of 0.57% and 0.35% per cycle. When the current density increased 4 times, the discharge capacity just decreased 18%, and showed a good rate performance. The capacities of Fe-doped V₂O₅ thin film increased with the increased of the content of Fe. But the sol was instable when the content of doping Fe was more than 1.2%, so the suitable doping content of Fe was 1.2%. Under the current density of 33.20 μ A/cm2, the discharge and charge capacities of V₂O₅ thin film were up to 744 m Ah·g-1 and 767 m Ah·g-1,while fall down to 548 m Ah·g-1 and 529 m Ah·g-1after 45 cycles, with fading rate of 0.58% and 0.65% per cycle. When the current density increased 3 times, the discharge capacity only decreased 6%, suggested that Fe-doped V₂O₅ thin film had good rate performance.The electrochemical properties of V₂O₅ thin film electrode could be improved significantly due to the enhancement of the surface area and structure stability by doping appropriate amount Ni or Fe. However, the fading rate of Ni-doped V₂O₅ thin film electrode was lower than that of Fe-doped V₂O₅ thin film electrode, so Ni-doped V₂O₅ thin film electrode showed a better electrochemical properties.