Preparation Of Nickel-cobalt Bimetallic Oxygen, Sulfur And Selenides And Their Lithium/sodium Storage Properties

Currently,the anode materials of commercial lithium ion batteries(LIBs)were carbon materials represented by graphite.Although carbon materials have the advantages of rich reserves,wide resources,stable electrochemical behaviors,etc.,owing to their low theoretical capacity,cycling instability and poor rate performance in high current density,the development of LIBs has been seriously hindered.Besides,with the blowout growth of the LIBs market,the supplies of lithium resources become insufficient which leads to the rising price.Due to the wide distribution and economic price of sodium resources,sodium ion batteries(SIBs)have begun to the focus of researchers.However,the research and development of SIBs is still in the preliminary stage.In order to promote the further development of energy storage devices,the anode materials with excellent Li⁺/Na⁺storage performance is indispensable.Inspired by the similar physical and chemical properties between the nickel and cobalt compounds.Mixing them may produce a strong synergistic effect,which could highly enhance the electrochemical performance of Ni-Co bimetallic electrode materials.Based on the above background,this paper has conducted the following research:(1)Due to the low price and simple preparation process of transition metal oxides,this paper selects nickel-cobalt bimetallic coordination polymer(Co NiCP)as the precursor,and improves the oxidation process to retain the in-situ generated carbon to form a flower-like layered carbon skeleton loaded with Co₃O₄ and NiO nanopratices(Co₃O₄/NiO/NC).The LIBs half-cell test results show Co₃O₄/NiO/NC has a relatively high capacity of 493 mAh g^-1 at a higher current(5000 mAg^-1).When the current density is 200 mAg^-1,Co₃O₄/NiO/NC electrode can maintain a capacity of 1390 mAh g^-1 over 100 cycles.When combinated with Li Fe PO₄ to assemble lithium-ion full batteries,it can have a capacity retention rate of 40.29%after 200cycles.(2)Through structure control,a nickel-cobalt bimetallic sulfide(CNC NiS₂/Co S₂)with a unique concave cubic structure is synthesized.And by coating with polydopamine,the sample forms a nitrogen-doped carbon layer during the annealing and carbonization process,which increases the active sites of the sample and improves the electronic conductivity.The prepared CNC NiS₂/Co S₂ shows extremely high sodium storage performance,and can have capacities as high as 848 and 583 mAh g^-1 when the current density is 100 mAg^-1 and 5000 mAg^-1,respectively.Furthermore,the cycling stability of CNC NiS₂/Co S₂is achieved 404 mAh g^-1after 900 cycles at 5000 mAg^-1.(3)Two-dimensional transition metal carbide(Ti₃C₂)and nickel-cobalt bimetallic selenide are combined to form Ti₃C₂few-layer nanosheets(Ti₃C₂/Co_0.5Ni_0.5Se₂)coated with two-dimensional nickel-cobalt selenides.Due to the strong synergistic effect of CoSe₂ and NiSe₂,compared with a single-component selenide,the energy storage performance of the prepared cobalt-nickel bimetallic selenide is enhanced.When assembled with sodium to form SIBs half-cells and tested at 1000 mAg^-1,Ti₃C₂/Co_0.5Ni_0.5Se₂ has a high first cycle coulombic efficiency(89%),and has a capacity of 338 mAh g^-1 even over 600 cycles.