Preparation And Sodium Storage Properties Of Composite Nickel-Cobalt-Based Nanofibers

The arrival of the"big data era"promotes the wide use and rapid development of intelligent portable electronic devices,in which lithium ion battery plays an irreplaceable role of the energy supply of the above electronic products because of its high efficiency,reliability and pollution-free.In addition,researchers are actively exploring semiconductor devices with integrated power sources or energy storage devices based on semiconductor devices,where battery components and integrated circuit components can be installed on the same semiconductor substrate.However,the reserves of lithium resources themselves are limited,and the huge demand gap aggravates the rising cost year by year.At the same time,due to the abundant natural reserves of sodium and the very similar physical and chemical properties of lithium,sodium ion battery have gradually become the most competitive new focus in the field of clean energy.At present,in terms of promoting the use of energy supply in integrated circuits,the primary problem that needs to be solved is to prepare suitable negative electrode materials for sodium ion battery.This thesis is based on the above and the consideration of meeting the energy demands of light weight,long battery life and cheap cost in integrated circuits.On the one hand,in terms of carbon coating,structural and doping,the thesis focuses on nickel and cobalt base selenide,carbon nanofibers composite material design,synthesis and mechanism of sodium.On the other hand,the thesis explores the electrochemical properties of composite material as anode material for sodium ion battery.The main results are listed as follows:(1)Transition metal selenides have high theoretical specific capacity,but their low conductivity and large volume change during the cycle process limit their practical application in sodium ion batteries.Therefore,in the second chapter of thesis,a graphene-coated carbon nanofiber composite loaded with Ni_0.85Se-Co_0.85Se particles(Ni_0.85Se-Co_0.85Se@G@CNFs)was successfully prepared by using electrospinning technology.The double coating of graphene and carbon nanofibers not only improves the conductivity of metal selenides,but also improves the conductivity of metal selenides.It can also provide strain buffer for the active material.As a anode electrode,Ni_0.85Se-Co_0.85Se@G@CNFs showed good electrochemical properties of sodium storage.At the current density of 100m A/g,the capacity reaches more than 500m Ah/g for the first time,and remains above 300m Ah/g after 100 cycles.At A high current density of 1 A/g,the capacity stabilizes at 184.4m Ah/g after 50 cycles.In addition,we also investigate the possible capacitance effect processes of electrode materials.The results show that the capacitance contributions of the fake materials are 63.2%,67.3%,70%,71.8%and 75.4%,respectively,at the scanning rates of 0.2,0.4,0.6,0.8 and1m V/s.(2)In the third chapter of this thesis,Ni_0.85Se-Co_0.85Se particles embedded in carbon nanofibers were successfully prepared by changing the experiment strategy,adding selenium powder directly into the precursor solution and using electrospinning technology(Ni_0.85Se-Co_0.85Se@CNFs-A).Similarly,the electrochemical properties of the composites were tested.When used as the anode of sodium ion battery,Ni_0.85Se-Co_0.85Se@CNFs-A has better electrochemical properties than the fibers obtained by conventional electrospinning method.At the current density of 100m A/g,the first capacity can reach 507.2m Ah/g,and the reversible specific capacity can reach325m Ah/g after 200 cycles.At a high current density of 1A/g,the capacity remains at201.3m A/g after 400 cycles.At the current density of 0.1,0.2,0.5,1,2 and 3m A/h,the reversible capacity is 367.98,331.12,302.73,268.26,234.77,201.17m Ah/g,respectively.