Study On The Preparation And Electrochemical Rroperties Of New Metallic Material Ni-V-O By Ionic Liquid Thermal Synthesis

With the rapid development of electric vehicles/hybrid vehicles and smart grids,the development of large-scale energy storage systems has become a hot topic in lithium-ion battery technology research.Nickel vanadate（NiVO）has become a class of anode materials for lithium ion batteries with potential applications due to its high theoretical capacity,excellent safety performance,lower cost,and simple synthesis process.Ionic liquids are often introduced into the synthesis of inorganic nanomaterials because of their low vapor pressure,good thermal stability,strong dissolving ability,recyclability,and environmental friendliness.It has good application prospects in the preparation of porous materials and materials with special morphologies.At present,although there are many literatures on the synthesis of vanadates,the use of ionic liquid thermosynthesis to prepare nickel vanadate materials has not been reported.In this paper,nickel vanadate materials are prepared by ionic liquid thermal synthesis,in which ionic liquids serve as both green solvents and template agents.The composition,morphology and structure of the prepared materials were investigated in detail,and the lithium intercalation properties were preliminary investigated.The specific research contents and conclusions are as follows:（1）Ionic liquid（1-Butyl-3-methylimidazolium Bromide（[Bmim]Br））as green solvent and templating agent,Ni（NO₃）₂·6H₂O as nickel source,and NH₄VO₃ as vanadium source.A simple one-step ionic liquid thermal synthesis method successfully prepared 3D crosslinked coral-like vanadium-based materials at different times and temperatures.The structure,morphology,specific surface area and valence state of elements were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,N₂ adsorption desorption and specific surface area measurement,and X-ray photoelectron spectroscopy（XPS）,and applied it to the anode of lithium-ion battery for preliminary electrochemical performance research.The effects of different time and temperature on the morphology and surface structure of Ni-V₂O₅ material precursors and final Ni-V₂O₅-IL materials are investigated in detail.First,the reaction time was investigated at 180℃,and the differences in material morphology under different reaction times were compared.According to scanning electron microscopy,it was found that the products were mainly large particles at 12 hours of reaction,and some of the particles surface became smooth and had a tendency to change to coral-like antennae at 24 hours of reaction,but they were still mainly large particles;When reacted for 36-48 h,3D cross-linked coral-like structures have been formed in some places,but there are still many irregular large particles;after 60-72 h,most of them have developed into 3D cross-linked coral-like structures with smooth surfaces,Uniform appearance.It shows that the formation process should generally follow the dissolution-recrystallization process,in which the ionic liquid plays a role in controlling morphological growth.The reaction time was controlled to 72 h to investigate the reaction temperature.The results showed that no solid was obtained when reacted at 120℃for 72 h;reacted at 140℃for 72 h,and the morphology was a granular product with uniform size;when reacted at 160℃for 72 h,a large number of3D cross-linked products were apparently,but not as smooth as at 180°C.Therefore,it can be roughly verified that it is a dissolution-crystal formation mechanism.As a negative electrode material for lithium-ion batteries,the specific capacity was maintained at 764.9 mAh·g^-1 after 300 cycles at a current density of 300 mA·g^-1,which was much higher than that of massive vanadate synthesized in an aqueous solution(306.8 mAh·g^-1).The nickel material exhibits high specific capacity and excellent cycle performance compared to nickel vanadate materials synthesized in aqueous solution.（2）Because the size of the vanadium-based material synthesized in the upper part is still large and the specific surface area is low,the specific capacity of the electrode is still not too high.Phosphorus doping can significantly enhance the electrochemical performance of carbon-based materials,and the sizes of the synthesized nickel phosphate nanofibers and vanadyl phosphate nanoparticles in the ionic liquid are both about 50 nm.This section continues to dope the above nickel vanadate materials with an appropriate amount of phosphorus to reduce the size of the nickel vanadate material,increase the specific surface area,and then enhance its electrochemical performance.Therefore,the ionic liquid thermal synthesis method was used to successfully design and prepare a phosphorus-doped vanadium-based material（P-NiVO-IL）.Its particle size is reduced to 50-100 nm,but its morphology is granular rather than 3D crosslinked,and the material shows excellent electrochemical performance.At a current density of300 mA·g^-1,after 300 cycles,the specific capacity is 1174.6 mAh·g^-1,which is much higher than the undoped nickel vanadate prepared by the ionic liquid thermal synthesis method and Nickel vanadate synthesized in aqueous solution.Phosphorus-doped nickel vanadate has great advantages.（3）Based on the first part,the ionic liquid（1-butyl-3-methylimidazole bromide（[Bmim]Br））is used as the green solvent and template agent,LiOH is used as the dopant,and Ni（NO₃）₂·6H₂O was the nickel source and NH₄VO₃ was the vanadium source.A lithium-doped vanadium-based material（Li-NiVO-IL）was successfully prepared by ionic liquid thermal synthesis.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,N₂ adsorption desorption and specific surface area determination and X-ray photoelectron spectroscopy（XPS）were used to characterize the structure,morphology,specific surface area and element valence,and the effects of lithium doping in different proportions on their electrochemical performance were discussed.They were applied to the negative electrode of lithium-ion batteries,and their electrochemical performance was preliminary studied.