Controllable Preparation And Sodium Storage Properties Of Cobalt-nickel-based Heterostructure Sulfur/selenide

Lithium-ion batteries have been successfully applied to smart devices and electric vehicles due to their advantages of high energy density,long cycle life,and environmental friendliness.However,the limitation of uneven distribution of lithium sources hinders their application in large-scale energy storage systems in the future.Compared with lithium-ion batteries,sodium-ion batteries have aroused people's interest again and have great application potential in power grid energy storage systems because of the widely available sodium resources and low cost.At present,the lack of suitable anode materials limits the further development of sodium-ion batteries.Therefore,the development of high-performance anode materials for sodium-ion batteries is the major topic of current research.Metal chalcogenides,which include metal sulfides and selenides,have been paid close attention by the scientific community owing to their high theoretical capacity,various physical and chemical properties.However,the electrochemical performance of cobalt-nickel-based chalcogenides is not satisfactory due to their poor electrical conductivity and serious volume expansion effect during charge and discharge.In order to solve the above problems,the design and construction of metal chalcogenides with the heterogeneous structure to improve the electrochemical reaction kinetics and electrode structure stability can be effective methods.Furthermore,systematically studied their structural advantages and sodium storage mechanism are also needed.The main research works are as follows:1.Nitrogen-doped carbon protected heterostructured CoSe₂@NiSe₂ nanoflowers(CoSe₂@NiSe₂@NC)were prepared by in situ selenization,dopamine coating and annealing on cobalt-nickel metal-organic framework(CoNi-MOF).The 3D flower-like structure can effectively buffer the volume expansion of the electrode material by releasing the stress caused by a structural mutation in all directions.At the same time,the 2D nanosheets can provide a large specific surface area,full contact with electrolyte and mass transfer channels,and shorten the diffusion distance of electrons and Na ions.Therefore,the CoSe₂@NiSe₂@NC heterostructured nanoflowers exhibit good rate capability and cycling stability,it can maintain a high-rate capacity of 330 m A h g^-1 at3 A g^-1,and can cycle 100 times stably at 0.2A g^-1,with no obvious capacity attenuation.2.The above CoSe₂@NiSe₂@NC electrode electrochemical test results show that the heterostructured nanoflowers protected by N-doped carbon can improve the sodium storage performance,but the cycling performance is not very acceptable.Therefore,the in-situ carbon shell/carbon nanotube conductive network derived from MOFs was designed to improve the performance of sodium storage,using solution method to synthesize Ni-ZIF-67,through the epitaxial growth of ZIF-8,high-temperature carbonization,selenization,annealing process to prepare Ni₃Se₄@CoSe₂@C/CNTs heteropolyhedron.The conductive carbon shell/carbon nanotube network not only promotes the transport of Na ions and electrons but also can effectively accommodate the volume expansion,which further enhances the storage capacity of Na ions.Electrochemical test results show that Ni₃Se₄@CoSe₂@C/CNTs heteropolyhedron can deliver a high discharge capacity of 284 m A h g^-1 at 0.5 A g^-1 over 300 cycles.The reversible specific capacity can reach 243 m A h g^-1 after 600 cycles at 1 A g^-1.3.In the previous work,carbon coating on active material was used to improve sodium storage performance.Herein,the performance of sodium storage was optimized by the design and preparation of hollow structure,namely the preparation of nickel cobalt Prussian Blue analogue(Ni Co-PBA)by co-precipitation method.After sulfurization and hydrothermal process,the Re S₂ nanoarray was successfully coupled on the hollow Ni S₂@Co S₂ nanocubes(Ni S₂@Co S₂@Re S₂).The ultrathin Re S₂nanosheet can shorten the diffusion path of Na ions,the hollow nanocubes can buffer the volume expansion and structural strain caused by the conversion reaction,the coupling effect of heterointerface is beneficial to promote the electrochemical reaction kinetics.The prepared Ni S₂@Co S₂@Re S₂ electrode shows excellent sodium storage performance,with a reversible capacity of 297 m A h g^-1 at 3 A g^-1.When cycled at 1 A g^-1 for 500 cycles,the capacity remains at 396 mA h g^-1.