Controllable Preparation Of Niobium-Based Oxides For Lithium-Ion Storage

The development of green new energy requires the assistance of energy storage systems,so efficient and convenient energy storage technologies have caused extensive research.Among them,lithium-ion batteries have been widely used in electric vehicles and electronic products,due to their high energy density,long cycling life and environmental benignity and other advantages.However,with the rapid development of social economy,people have put forward higher and higher requirements for the performance of lithium-ion batteries.Therefore,under the premise of ensuring safety and economy,how to further improve the energy density,power density,cycling lifespan and etc.of lithium-ion batteries has become the current research focus.The electrode material,as the carrier of lithium-ions and electrons during the charging and discharging process,plays a decisive role in the above performance.Since the cathode material of lithium-ion batteries has almost approached its theoretical specific capacity in practical applications,the development of the excellent anode material is the key to elevate the performance of lithium-ion batteries.Among numerous anode materials,niobium-based oxides have attracted extensive attention in recent years,due to their advantages of higher theoretical specific capacity and better structural stability.However,the intrinsic conductivity of niobium-based oxides is lower,which limits their electrochemical lithium storage performance.Therefore,this article aims to improve the electrochemical performance of niobium-based oxides by compounding with carbon on the surface,exposing the highly reactive facet of the material and nanometering.The specific research content is as follows:（1）The Nb₂O₅@r GO nanocomposite with the r GO as the base,on which the flower-like Nb₂O₅ microsphere is orderly distributed was in situ synthesized by the hydrothermal method,and its electrochemical performance as the anode material for lithium-ion batteries was studied.The results show that compared with the pristine flower-like Nb₂O₅ microsphere,the reversible specific capacity,rate performance,cycling stability and conductivity of the Nb₂O₅@r GO nanocomposite are all improved.This is mainly because the introduction of high conductivity r GO can effectively enhance the conductivity of the electrode material,and can also prevent the agglomeration of the flower-like Nb₂O₅ microsphere,relieve the volume expansion of the flower-like Nb₂O₅ microsphere during the charging and discharging process.In addition,this work also explored the electrochemical performance of Nb₂O₅@r GO nanocomposites with different proportions.The results show that when the mass ratio of Nb₂O₅ to r GO is 2:1,the electrochemical performance of the Nb₂O₅@r GO nanocomposite is the best.（2）The previous work showed that the insertion and extraction of lithium-ions mainly occur on the（101）facet and（141）facet of the orthorhombic Na Nb O₃.Therefore,the adsorption energy of lithium-ions on the（101）facet and（141）facet of the orthorhombic Na Nb O₃ and the diffusion energy barrier of lithium-ions in the（101）facet and（141）facet of the orthorhombic Na Nb O₃were studied by the DFT calculation.The results show that the adsorption strength of lithium-ions on the（141）facet is much weaker than that of the（101）facet,and the diffusion rate of lithium-ions in the（101）facet is faster than that in the（141）facet.That is the fact,that the（101）facet of the orthorhombic Na Nb O₃ is the highly reactive facet of the orthorhombic Na Nb O₃.In order to verify the conclusion obtained from the DFT calculation,three kinds of Na Nb O₃ microcubes exposed to different degrees of the（101）facet were designed and synthesized by the hydrothermal method,and their electrochemical performance as the anode material for lithium-ion batteries was studied.The results show that three different sizes of Na Nb O₃ microcubes exposed to different degrees of the（101）facet do not show the phenomenon that the larger the specific surface area of the material,the better its lithium storage capability,but show the almost same lithium storage capability,which indicates that the（101）facet of the orthorhombic Na Nb O₃ is more conducive to the storage of lithium-ions than the（141）facet of the orthorhombic Na Nb O₃.（3）One-dimensional Fe Nb O₄nanochains composed of nanoparticles were synthesized by the electrospinning method and the subsequent heat treatment method,and their electrochemical performance as the anode material for lithium-ion batteries was studied.The results show that one-dimensional Fe Nb O₄ nanochains have high reversible specific capacity(at the current density of 0.1 A g^-1,the reversible specific capacity is 650 m Ah g^-1),excellent rate performance(at the current density of 2.5 A g^-1,the reversible specific capacity is 250 m Ah g^-1)and good cycling stability(keeping80%of the initial reversible specific capacity at the current density of 1.0 A g^-1 after500 cycles),which is mainly because one-dimensional Fe Nb O₄nanochains have a large specific surface area,which can promote the interface contact between Fe Nb O₄ and the electrolyte,thus reducing the transmission path of electrons and the diffusion distance of lithium-ions,and one-dimensional Fe Nb O₄nanochains also have a certain ability to withstand the crystal structure change during the charging and discharging process.