Study On Design Fabrication And Lithium Storage Property Of Copper Cobalt-based Binary Metal Oxides(Sulfides)

With the increase of renewable energy sources and the development of new energy vehicles,electrode materials with high capacity,long cycle life,rapid charge and good security for lithium ion batteries have gained great research effort in recent years.Compared with traditional carbon based anode materials,cobalt based metal oxides have attracted great interest for their high theoretical capacities.However,the poor conductivity,severe volume variation and high cost impede their practical applications.In respect of the issues above,cobalt are partially replaced with copper to synthesize copper cobalt binary metal oxide and sulfides,as copper possess higher conductivity and lower cost.Finally,three types of copper cobalt binary metal oxides?sulfides?with different nanosturctures were fabricated.The physical and chemical properties were thoroughly characterized,and electrochemical properties were intensively studied.CuCo₂O₄ nanoparticles with mesoporous were synthesized through solvothermal method.The average pore sizes of CuCo₂O₄ changed with different calcination temperatures.Larger pore size not only provide abundant channels for mass transfer and promote the electrode reactions,but also provide enough space to accommodate the volume variation during charge/discharge process and release the inner stress,thus enhancing the cycle performance and stability of the electrodes.CuCo₂O₄ nanoparticles obtained under 500?possess a large pore size of 13.2 nm and exhibit better cycle performance and rate capability.A discharge capacity of 543 mAh g^-1still could be remained after 100 cycles at 0.2 A g^-1.Discharge capacities of 894,754,587,436 and 256 mAh g^-1were delivered when the current densities were fixed at 0.1,0.2,0.5,1.0 and 2.0A g^-1,respectively.CuCo₂S₄ nanoparticles are anchored on reduced graphene oxide through a facile solvothermal method,and graphene were simultaneously doped with N and S,thus obtaining CuCo₂S₄@N/S codoped graphene composite.CuCo₂S₄ nanoparticles were effectively distributed on graphene,thus impeding the agglomeration of nanoparticles and enhance the conductivity of anode material.On the other hand,CuCo₂S₄ nanoparticles could impede the stack of graphene.Therefore,the composite possess better stability.According to the research on reaction mechanism,the excellent rate capability of this composite exhibits obvious capacitive storage behavior.The capacitive storage behavior effectively enhanced the rate capability to deliver a capacity of 328 mAh g^-1at 20 A g^-1.Through the mixed solvothermal method,CuCo₂O₄ hollow spheres were synthesized,then 3-aminopropyl trimethoxysilane were modified on graphene through electrostatic self-assembly.The addition of thiourea not only could convert CuCo₂O₄ to CuCo₂S₄,but also in-situ doped graphene with N and S,finally obtaining CuCo₂S₄ hollow sphere@N/S doped graphene.The inner space of hollow spheres could accommodate the volume variation during discharge/charge process,the thin shell could effectively increase the contact area of electrode material and electrolyte and shorten the diffusion distance of Li⁺.N/S doped graphene enhances the conductivity and further stabilize the structure of electrode materials.Benefiting from the merits above,CuCo₂S₄ hollow sphere@N/S doped graphene exhibits excellent lithium storage property.A high discharge capacity of541 mA h g^-1still could be remained after 600 cycles at 2 A g^-1.Discharge capacities of902,799,748,659 and 527 mAh g^-1were delivered when the current densities were fixed at 0.2,0.5,1,2 and 5 A g^-1,respectively...