Synthesis And Modification Of V₅S₈ As Anode Material For Sodium-ion Batteries

As a typical two-dimensional layered transition metal chorionic compound,V₅S₈ has the advantages of large layer spacing（1.132 nm）,small band gap（1.1 e V）and abundant active sites,which is suitable for the anode system of sodium ion batteries.However,due to its low conductivity and high volume expansion during charging and discharging,it is easy to lead to structural collapse,which affects the cycle and rate performance of the battery.In view of the above problems,this paper adopts solvothermal method to adjust the material morphology to synthesize hollow rod V₅S₈ and dominant crystal plane growth V₅S₈.Through the composite with carbon material,it not only improves the electrical conductivity of the material,but also effectively inhibits the volume expansion of the material,and improves the sodium storage performance of the material.The morphology changes of the materials were studied by electrochemical testing technology,and the sodium storage mechanism of the materials was explored by electrochemical means.The main research contents and results of this paper are as follows:（1）Using vanadium oxyacetyl acetonate as vanadium source,L-cysteine as sulfur source and NMP as solvent,V₅S₈ with nano-flake structure was synthesized by solvothermal method.When molybdenum rod（rod-shaped Mo O₃）is introduced as the growth matrix and simultaneously grows with sucrose,materials with rod-like structure can be synthesized.After that,the molybdenum rod is dissolved in ammonia water to obtain V₅S₈@C with hollow rod-like structure,which improves the specific surface area of the material,and carbon enhances the electrical conductivity of the material.As the anode material of sodium ion battery,the synthesized V₅S₈@C material can be cycled 100 times at 5 A g^-1 current density and still has A discharge capacity of 395.3 m Ah g^-1,showing excellent sodium storage performance.（2）The V₅S₈ material with vertical growth was obtained by using ammonium metadvanadate as vanadium source,L-cysteine as sulfur source,NMP as solvent,and Mo O₃ as growth matrix.The crystal growth was induced along a specific direction during the solvothermal process.At the same time,the V₅S₈ material was compounded with graphene to stabilize the material’s long cycle performance and improve the material’s rate performance.After300 cycles at 5 A g^-1 current density,the discharge capacity of the obtained material is 421.3 m Ah g^-1.It has a capacity of 350.6 m Ah g^-1 at 15 A g^-1,showing excellent rate performance and long cycle performance.