Investigation On The Preparation,Modification,and Sodium Storage Of Novel Metal Sulfide Hollow Nanocubes

As the global energy shortage becomes more and more serious,it is crucial to develop large-scale,reliable and efficient clean energy installations.Lithium-ion battery（LIBs）has become an indispensable energy storage device in People’s Daily life because of its compact structure and high energy/power density.However,the problems of uneven distribution of lithium resources and low crustal abundance have led to increasing costs of LIBs and difficulty in sustainably maintaining the expanding application market.Sodium ion batteries（SIBs）have comparable performance to LIBs,especially the wide distribution of sodium elements,abundant,they are considered to be an ideal substitute for LIBs.As we all know,as an important component of SIBs,the negative electrode material has a decisive impact on the overall performance of the battery.However,sodium ion radii are larger than lithium ion radii,resulting in larger volume effects and slower reaction kinetics during storage.Therefore,the search for anode materials suitable for sodium ion storage with high rate performance and long cycle life has attracted wide attention,among which metal sulfide has recently become the focus of research due to its high theoretical specific capacity and better redox activity.In view of this,this paper intends to design and construct a new type of metal sulfide with special structure and its modified materials,in order to improve its sodium storage performance as a negative electrode of SIBs.Specific research contents are as follows:Cu₂O cubes were prepared by coprecipitation method and used as hard film plates and self-sacrificing templates.Nitrogen-doped carbon coated Cu₂Mo S₄hierarchical bivalved hollow nanocubes were constructed by solvothermal,chemical etching,polydopamine coating and carbonization（Cu₂Mo S₄@NC）.When Cu₂Mo S₄@NC is used as the negative electrode of sodium ion battery,it shows excellent reversible capacity,magnification ability and cyclic stability,which is mainly related to its unique structure and composition.In addition,the electrode reaction kinetics of the material was studied to explain the evolution of its properties.In particular,in-situ XRD analysis reveals the stepby-step transformation mechanism of Cu₂Mo S₄@NC during natritization,suggesting that non-reactive components can be used as buffers or conductors to improve their sodium storage properties.More importantly,as a conceptual demonstration,the composite negative with the Na₃V₂（PO₄）₂F₃/C positive constitutes a full battery.The results show that the capacity of the battery remains 166 m Ah g^-1after 1000 cycles at the current density of 1.0 A g^-1.Using NiCl₂·6H₂O and Sn Cl₄·5H₂O as raw materials,sodium citrate as chelating agent and Na OH as precipitating agent,Ni Sn（OH）₆cube was prepared first,and then used as a self-sacrificing template.Through chemical vulcanization,etching,coating and carbonization,Ni Sn（OH）₆cube was obtained.Nitrogen doped carbon clad Ni S/Sn S doulleshell hollow nanocubes（Ni S/Sn S@NC）have been constructed successfully.Ni S/Sn S@NC composites show excellent rate capacity and cycle stability when used as anode of sodium ion batteries.In addition,in situ EIS and CV were used to investigate the reaction kinetics of the composite electrode.In particular,in situ XRD detection was used to effectively reveal the sodium behavior of the Ni S/Sn S@NC negative electrode,which confirmed the synergistic mechanism of the bimetallic sulfide components.Similarly,as a conceptual demonstration,the composite negative with the Na₃V₂（PO₄）₂F₃/C positive constitutes a full battery.Electrochemical tests showed that the capacity of the battery remained 267 m Ah g^-1after 1000 cycles at A current density of 2.0A g^-1.The above results can provide useful reference for the design,construction and optimization of SIBs anode materials,and is expected to accelerate the development and application of SIBs research.