Synthesis And Electrochemical Performance Of Lithium Nickel Vanadium Oxide

In recent years, with the development of portable devices and electric vehicles, lithium ion electrode materials with excellent electrochemical performance have attracted more and more attention. Among them, Li Ni VO4 with the spinel structure is receiving increasing attention due to its excellent cycle performance, high voltage platform. However, the development of the Li Ni VO4 material is restricted by these factors such as low specific capacity, high diffusion impedance, and the performance influenced by the different preparation methods. The electron mobility of the novel graphene can be up to 2 ×105 cm2/V·s, the thermal conductivity is up to 5000 W·m-1·K-1; the specific surface area is 2630 m2· g-1. Studies shown that the presence of the graphene can improve the electronic conductivity of the material, shorten the lithium ion diffusion path, and stabilize the material structure. The graphene as conductive additives can greatly improve the cycle stability of the lithium ion battery, large current charge and discharge performance, and safety performance. Based on these properties, the preparation method of the new Li Ni VO4 cathode material for lithium ion battery is expected to improve the performance of the materials.In this paper, Li Ni VO4 cathode materials were prepared by sol-gel method and hydrothermal method, in which V2O5 powder, H2O2, Li Ac and Ni(Ac)2·4 H2 O, hydrogen peroxide, graphite powder, concentrated sulfuric acid, phosphorus pentoxide and glycol as raw materials. Graphite oxide was prepared through the improved Hummers method and graphene supported Li Ni VO4 was synthesized using hydrothermal method. The morphology and structure of the as-prepared materials were characterized by scanning electron microscope(SEM), transmission electron microscope(TEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR). The electrochemical performance of the material as anode for Lithium-ion batteries was studied by galvanostatic charge-discharge, cycle life testing, and electrochemical impedance spectroscopy. Meantime, thermogravimetric analysis(TG) was tested to prove the thermal stability of the composites. The results are as follows:(1) The nanoscale graphene was synthesized by sodium borohydride instead of hydrazine hydrate, and the structure, morphology and composition of the composites were characterized through XRD, Raman, FT-IR, TG, SEM, and TEM. The results confirmed that the graphene has good dispersion, low cost, and safe by modified Hummers method.(2) The graphene supported Li Ni VO4 as anode material for lithium-ion batteries were prepared by sol-gel method and hydrothermal method. The XRD characteristic peak of the product showed that the samples derived from lower temperatures reveal the crystal shape. The SEM photos shown that the sample take on uniform coral shaped covered with nanospherical protrusions, the size of the spherical particles is about tens of nanometers, the nanostructure not only increases the specific surface area, increases the contact area of material and electrolyte, also provides plenty of embedded lithium ions with more active position. The first discharge and charge capacities are as high as 912 and 782 m Ah/g, respectively, with a coulomb efficiency of 85.7%. After 27 cycles, the coulomb efficiency is above 95%. It can be seen from the cyclic voltammograms that the cyclic voltammograms are overlap for five cycles. The results reveal that the electrode material has good electrochemical performance and may be as a promising anode material for lithium-ion batteries in the future.