Study Of Synthesis And Electrochemical Performance Of Co-based Oxide Composite Nanoarrays

Lithium-ion batteries (LIBs) have became the centre of material science field,because of their high energy density, high safety, long cycling stability and nomemory effect. Currently commercial graphite anode (~372mAh/g) is hard tomeet the demand of portable energy storage device. Transition metal oxides arepromising next generation LIB anodes due to their high electrochemical activityas well as ease of processing. Specifically, owing to its superior specific capacity,cobalt-based oxide material has attracted more interest, the specific capacities ofCoO and Co3O4reach700and890mAh/g, respectively. However, its relativelylow capacity retention and poor rate capability restricted its practical applicationas LIB anode. In this paper, novel composite nanostructures were designedthrough synthesizing various nanoarrays to enhance the cycling and rateperformance, and the relationships among structures, compositions andcorresponding electrochemical performance were also investigated. Our mainresearch work was as follows:Co3O4-Ni@Cu: A two-step strategic approach combing electrodepositing andhydrothermal reaction was proposed to synthesize three-dimensional Co3O4nanoarrays which were fabricated on the Cu substrate surface with a Ni-nanoseed-layer as interface. Firstly, a Ni-nanoseed-layer was prepared on a Cusubstrate by electrodepositing Ni, then Co3O4nanowires were in situ grown onthe Ni layer via a hydrothermal synthesis. The pre-electrodeposited Ni-nanoseed-layer on Cu substrate could improve the mechanical adhesion between Co3O4nanoarrays and substrates, and the conductivity effectively. When the as-obtainedmaterials were directly used as anode materials for LIBs, the electrodesmaintained a high capacity up to1150mAh/g at0.1C after30cycles, andshowed a good cycling stability and rate capability, while the Co3O4nanoarraysonly maintained a capacity of400mAh/g. Co3O4@Si@C: Three-dimensional foam-Ni was utilized as the currentcollector to prepare3D Co3O4@Si@C nanocomposite material. Ionic liquid wasinnovatively took as the electrolyte while constant-potential electrolysis was usedas the process, instead of traditional and complex sol-gel-reduction method. Theunique net structure of foam-Ni which has high surface area, could to increasethe mass of active material. The introduction of Si greatly improved the capacity,meanwhile the SiO2layer formed on the Si surface could inhibit the Si expanding.The carbon layer enhanced the conductivity to improve the rate performance. Theas-prepared Co3O4@Si@C nanoarrays exhibited more excellent electrochemicalperformance as anode materials for LIBs than Co3O4nanoarrays. Theymaintained a high charge/discharge capacity of more than400mAh/g after200cycles with a high current density of1000mAh/g, while pristine Co3O4nanoarrays maintained only a capacity of60mAh/g.