Fabrication Of Cobalt-Based Bimetallic Oxide Materials And Their Lithium Storage Properties

In recent years,as the most promising electrochemical energy storage devices,lithium ion batteries?LIBs?have been widely utilized in various fields like portable electronics and emerging electric vehicles,because of their unique features in terms of high energy density,high operating voltage,low self-discharge rate,no memory effect,long-life cycling.However,the conventional graphite-based anodes for LIBs could hardly meet the urgent demands on high energy density and large-scale energy storage due to the low theoretical capacity(372 mA h g^-1).Thus,it is essential to seek other alternative anode materials with higher capacity,better rate capacity and longer cycling life.Due to the enhanced electrocatalytic activity and the synergistic effects in multiple metal species,cobalt-based bimetallic oxides generally deliver superior electrochemical performance.However,these materials usually suffer serious volume changes during the electrochemical cycling process,which could result in some pulverization and fragmentation,and even cause the active materials to peel off the current collector.To address these issues,more efforts have been devoted to designing a variety of reasonable nanostructures by reducing the size and controlling the morphology in our work,which aim to avoid rapid capacity fading induced by huge volume changes.The main research contents and conclusions are as follows:?1?Wrinkled-paper-like ZnCo₂O₄ nanoflakes as anode for LIBs.Wrinkled-paper-like ZnCo₂O₄ nanoflakes were sythesized on Ni foam substrate by a facile hydrothermal synthesis and a post-annealing treatment.As an anode for lithium-ion batteries,it exhibits excellent cyclability and outstanding rate capability.It delivers a high reversible capacity of 1138 mAh g^-1 after 500 cycles at the current density of 1 A g^-1.Even tested at the current density of 12.8 A g^-1,the electrode also displays a high discharge capacity of 407 mAh g^-1.The remarkable lithium storage performance may be attributed to the good contact between the active materials and the conductive collector,and the stable 3D network structure of the interconnected macro-mesoporous nanoflakes,which can not only provide more diffusion paths for Li⁺and the electron,but also effectively alleviate the volume change during the charge-discharge process.?2?Hollow octahedra-like NiCo₂O₄ cages as anode for LIBs.Hollow octahedra-like NiCo₂O₄ cages were prepared by a facile template-assisted strategy.CuO octahedra acted as hard templates,while hydroxypropyl cellulose?HPC?as a film-forming agent,the octahedra-like NiCo₂O₄@CuO nanostructures consisted of nanosheets were prepared by a facile water bath method.Then,the CuO templates were in situ removed by dissolving into a diluted ammonium hydroxide solution,and finally formed hollow octahedra-like NiCo₂O₄ cages.When evaluated as anode for lithium ion batteries,it exhibits superior lithium ion storage performance with excellent cyclability and great rate capability.It delivers a high reversible capacity of 793 mAh g^-1 after 100 cycles at the current density of 0.2 A g^-1.At a high current density of 1.4 A g^-1,its reversible capacity remains 377 mAh g^-1.?3?Uniform mesoporous Ni_xCo_3-xO₄ nanospheres as anode for LIBs.Uniform mesoporous Ni_xCo_3-xO₄ nanospheres were prepared by a facile solvothermal method combined with an ion-etching procedure.Firstly,the trimesic acid was used as the organic ligands,and Co²⁺ions were selected as the skeleton metal to prepare uniform spherical Co-BTC precursors.Then,the Co-BTC precursors were gradually etched and exchanged by immersed into alcohol solution containing nickel ions.Finally,after an annealing treatment,mesoporous Ni_xCo_3-xO₄ nanospheres were obtained.When evaluated as anode for lithium ion batteries,the electrode exhibits superior lithium ion storage performance with excellent cyclability and great rate capability.It delivers a high reversible capacity of 821 mAh g^-1 after 400 cycles at the current density of 1 A g^-1.Even tested at a high current density of 6 A g^-1,the electrode also displays a high discharge capacity of 429 mAh g^-1.?4?Hollow NiCo₂O₄ nanotubes derived from alginate as anode for LIBs.Hollow NiCo₂O₄ nanotubes were prepared by the chelate reaction between metallic ions and the functional groups in sodium alginate.One-dimensional sodium alginate nanofibers were firstly synthesized by a facile centrifugal spinning technology,which then chelated with Ni²⁺and Co²⁺ions to form unique“egg-box”structure.Finally,NiCo₂O₄ nanotubes were obtained by an annealing treatment.When evaluated as anode for lithium ion batteries,the electrode exhibits superior lithium ion storage performance with great rate capability and excellent cyclability.The electrode delivers a high reversible capacity of 684 mAh g^-1 at the current density of 8 A g^-1.It also displays a high reversible capacity of 949 mAh g^-1 after 800 cycles at the current density of 1 A g^-1.