Controllable Construction Of Three-dimensional Vanadium Sulfides Micro-nano Architectures As Anodes For Improved Sodium Storage Performance

Two-dimensional layered VS₂ with the polytropic V valence,intrinsic metallic behavior,large interlayer distance,weak interlayer interaction,and one-dimensional chain-like VS₄ with the polytropic V/S valence,high content of S^-,large interchain distance,weak interaction between neighboring chains,have been regarded as very promising anode materials for sodium-ion batteries?SIBs?.However,the pulverization and charge transfer sluggishness of VS₂ and VS₄electrode materials lead to their worse cycling stability and rate performance.This paper develops a strategy that constructing the three-dimensional micro-nano structures with the space physical entrapment and the adjustable structure of building blocks to simultaneously improve the cycling stability and rate performance of vanadium sulfides?VS₂ and VS₄?.Meanwhile,the cooperative regulatory mechanism of microscopic and crystal structure has been explored,the electrochemical reaction mechanism has been illuminated,the synergistic enhancement mechanism of cycling stability and rate performance has been revealed,and the relationship model of three-dimensional micro-nano structure,Na⁺storage mechanism and electrochemical performance has been developed to provide the foundation for further enhancing the electrochemical performance and broadening the application field of vanadium sulfides materials.The detailed innovations as follows.?1?The crystalline VOOH-coated VS₂ microflowers?c-VS₂@VOOH?constructed from nanosheets are successfully prepared by a one-step hydrothermal method.The c-VS₂@VOOH as anode for SIBs delivers an excellent cycling stability of 330 mAh g^-1 after 150 cycles at 0.2 A g^-1.Particularly,c-VS₂@VOOH electrode can still afford a high reversible capacity of 356 and 224 mAh g^-1 even at 0.5 and 1.0 A g^-1,respectively.The high capacity,good stability and enhanced rate capability are mainly attributed to the highly efficient surface sensitization and protection of crystalline VOOH,which can dramatically improve the Na⁺diffusion and suppress the pulverization of VS₂nanosheets.Besides,ex-situ Raman and TEM reveal that the electrochemical reaction of c-VS₂@VOOH electrode between 0.50 and 3.00 V is mainly the intercalation reaction,and the conversion reaction mainly occurs below 0.50 V.?2?VS₂ nanoarchitectures comprised of the nanosheets with single-crystal and polycrystalline structure are respectively synthesized by a one-step solvothermal method,and the influence of crystallinity structure on their sodium storage properties is revealed.It is found that the single-crystal structure can largely enhance the Na⁺intercalation kinetics in the crystal lattice and the structure stability during charge/discharge process.Thus,the single-crystal VS₂electrode exhibits an enhanced rate capability and cycling performance,delivering a high capacity of 193 and 172 mAh g^-1 at a high rate of 0.5 and 1.0 A g^-1,and 403 mAh g^-1 after the following cycling test of 200 cycles at 0.2 A g^-1.?3?3D hierarchical VS₂ microrods assembled by nanosheets comprised of small VS₂ nano-grains are controllably synthesized by in-situ chemical etching approach.Results show that the addition amount of ethanol serving as etching agent has a great influence on the oriented growth and thickness-to-diameter ratio of VS₂ nano-grains.Moreover,?001?-oriented VS₂ nano-grains with larger thickness-to-diameter ratio expose more layer-edges and unsaturated S-edges,and then dramatically improve the intercalation kinetic,eventually lead to the enhancement of rate performance and cycling capacity.When applied as anode for SIBs,this material affords a high capacity of 255 and 230 mAh g^-1 even at a high rate of 1.0 and 2.0 A g^-1,and a reversible capacity of 350 mAh g^-1 is still achieved after the following cycling test of 200 cycles at 0.2 A g^-1.?4?Three novel 3D VS₄ nanoarchitectures are controllably synthesized by adjusting the pH of precursor solution based on a one-step hydrothermal method:nanorods?Nanorod-VS₄?,nanocones and nanobelts self-assembled VS₄microspheres.When serving as anode for SIBs,Nanorod-VS₄ exhibits the better electrochemical performances than the latter two,delivering a high reversible capacity of 225 mAh g^-1 at 0.5 A g^-1 after 200 cycles and that of 203 and 168mAh g^-1 even at 1.0 and 2.0 A g^-1,respectively.The remarkable sodium storage properties of the Nanorod-VS₄ electrode is mainly ascribed to the synergistic effect of the self-assembled structure of radial nanorods and the preferred orientation growth along?110?planes.Moreover,the reversible insertion reaction and diffusion-dominant Na⁺storage process between 0.50 and 3.00 V occurring in the Nanorod-VS₄ are clearly revealed based on the characterization of ex-situ XRD,Raman,TEM,and electrochemical kinetic analysis.?5?VS₄ microspheres assembled by the nano-units with different crystallinity are synthesized via a one-step template-free hydrothermal method.Results show that the electrochemical performances of VS₄ microspheres as anode for SIBs largely depend on the crystallinity,and decreasing the crystallinity of nano-units can dramatically enhance the pseudocapacitive behavior of VS₄ microspheres,which takes main responsibility for the improvement of sodium storage properties.VS₄ electrode with the lowest crystallinity delivers a high reversible capacity of 412 mAh g^-1 at 0.2 A g^-1 after230 cycles and that of 345 and 293 mAh g^-1 even at 1.0 and 2.0 A g^-1,respectively.Besides,the insertion mechanism is revealed within the selected voltage window of 0.50³.00 V based on the characterization of ex-situ XRD,XPS,TEM,and electrochemical kinetic analysis.This work is selected as the front cover of Nanoscale.?6?VS₄ microspheres winded by?110?-oriented nanotubes are successfully synthesized via a one-step hydrothermal method and the electrochemical performances of the VS₄ electrode as anode for SIBs are investigated in detail.With a?110?-oriented nanotube structure and a radially clew-like structure,the VS₄ electrode delivers the high rate capacities of 686,496 and 453 mAh g^-1 at0.05,0.2 and 1.0 A g^-1 in the voltage window of 0.01³.00 V.With a double physical entrapment for the expansion/shrinkage of nanotubes,the VS₄ electrode exhibits excellent cycling stability with the reversible capacity of 301 mAh g^-1 at0.2 A g^-1 after rate and following cycling test of 120 cycles in the voltage window of 0.50³.00 V.