Synthesis And Aluminum Storage Properties Of Vanadium Sulfide And Nickel Sulfide Nanomaterials

With the large-scale consumption of fossil fuels and the increasing demand for energy,the development of sustainable energy equipment has become an urgent problem to be solved.Among all kinds of energy storage technologies,lithium-ion batteries are considered as an efficient energy storage device because of their high energy density and working voltage,and are widely used in production and life.However,due to the low reserves,high cost and low safety performance of lithium resources,the application of large-scale energy storage in the future is limited.Therefore,it is of great significance to develop a new generation of energy storage system with low cost,high safety and excellent electrochemical performance.Compared with lithium,metallic aluminum has more abundant reserves,higher capacity per unit of volume(8046 mAh cm^-3).Besides,aluminum is better operability and safety in the environment.Therefore,aluminum ion battery system which uses metal aluminum as negative electrode has become one of the most promising new energy storage devices and a research hotspot.However,due to the high charge density of aluminum ions and the large diffusion resistance in the materials,there is relatively a few cathode materials that can reversible achieve the intercalation/deintercalation mechanism of aluminum ion.Developing cathode materials capable of reversible de-embedding of aluminum ions is the biggest challenge in this field.Among them,transition metal chalcogenide has been extensively studied due to their unique anion framework structure,which can provide lower electronegativity,multiple oxidized states and coordination polyhedrons.Achieving reversible intercalation and deintercalation and obtaining higher electrochemical capacity.Therefore,it has been widely studied.In this paper,vanadium sulfide is taken as the research object.VS₂ nanosheet material was prepared by hydrothermal method.Graphene was coated by physical stirring method.Phase and morphology of VS₂ and G-VS₂ samples were characterized by advanced characterization methods.Batteries were assembled with aluminum-based ionic liquid electrolyte to study its aluminum storage performance.The mechanism of aluminum storage was systematically studied by in-situ and ex-situ XRD techniques.In order to obtain better cathode materials,nickel precursors were synthesized by hydrothermal method.NiS_x nanosheets were prepared by calcination and vulcanization,and their phase characterization and electrochemical properties were characterized.The aluminum storage properties of other vanadium/niobium chalcogenides VSe₂,NbSe₂ and NbS₂ were preliminarily explored,which could provide a reference for the study of other transition metal chalcogenides.The main results are as follows:?1?VS₂ nanosheet material was synthesized by one-step hydrothermal method.Graphene was coated on VS₂ sheet material by physical stirring method.Graphene-coated VS₂?G-VS₂?sheet material with well-preserved layered structure was obtained.For the first time,it was used as the cathode material of aluminum ion batteries.Based on the stable layered structure of vanadium disulfide and the good conductive framework network of graphene,the material maintained the structural stability during the reaction process,which made G-VS₂ show better electrochemical performance than VS₂.At current density of 20 mA g^-1,the discharge capacity of G-VS₂ is 493 mAh g^-1,186 mAh g^-1at 100 mA g^-1current density and 45 mAh g^-1after 50 cycles.?2?The aluminum storage mechanism of G-VS₂ was investigated by ex-situ XRD,SEM,Raman,TEM and XRD in-situ XRD.The results showed that show that the reaction mechanism of Al³⁺ions in G-VS₂ material during charging and discharging process is intercalation/deintercalation reaction.?3?The precursors of nano-flake nickel-base grown on graphene were synthesized by hydrothermal method.NiS_x nanoparticles were formed by calcination and vulcanization.The phase composition and morphology of NiS_x nanoparticles were characterized by XRD and SEM.As the cathode material of aluminum ion battery,it shows better cycle stability.The capacity is 31.9 mAh g^-11 after 100 cycles at current density of 100 mA g^-1.At the same time,VSe₂,NbSe₂ and NbS₂ were used as cathode materials for aluminum ion batteries to preliminarily explore their electrochemical properties.electrochemical properties.At current density of 50 mA g^-1,the discharge capacities are 23.9,31 and 10.4 mAh g^-1,respectively.