Synthesis And Electrochemical Properties Of Vanadium Sulfide/carbon Composites

With the environmental pollution and the decrease of resource reserves,the demand for new energy in modern society is growing further.Energy storage devices can store and transform energy.Electrode materials are one of the main factors affecting the performance of energy storage devices,so a lot of research has been carried out around the development of electrode materials with high capacity,good stability and environmental friendliness.China has abundant vanadium reserves,and the multiple valence states of vanadium are beneficial to the multi-electron REDOX reaction,which has excellent electrochemical properties.Among vanadium compounds,vanadium sulfide has a unique chain-like structure and high sulfur content,which can provide more ion entry and exit sites and promote the REDOX reaction,and is a promising electrode material.However,due to its poor conductivity and cycling stability,its extensive application is limited.In this paper,vanadium sulfide was combined with Carbon nanotubes（CNTs）and Graphene oxide（GO）,the reduced graphene oxide（r GO）is formed after hydrothermal treatment to improve the electrochemical properties of the carbon material by taking advantage of its excellent electrical conductivity and high stability.The electrochemical properties of the materials were tested by characterizing the composition,structure and morphology of the products combined with cyclic voltammetry,constant current charged-discharge and impedance testing.The results are as follows:（1）The petal-like VS₄/CNTs binary material was synthesized by hydrothermal method to investigate its performance on supercapacitors.First,we optimized the content of CNTs.It was found that the specific capacitance of VS₄/CNTs composites containing 0.02g carbon nanotubes reached 330 F g^-1(924 C g^-1)at the current density of 1 A·g^-1,which was higher than other ratios.At the same time,the electrochemical performance of the composite VS₄/CNTs was compared with that of monomaterals VS₂ and CNTs.It was found that the addition of carbon material improved the electrical conductivity of the composite,and showed excellent reversibility and electrochemical characteristics.The energy density（E）of the VS₄/CNTs SSC device is 4.55 Wh m^-2 and the power density is 2.75 Wh m^-2in the large voltage range of 2.2V at the current density of 0.5 m A cm^-2,and the capacity of the VS₄/CNTs SSC device can still remain 51%of the initial state after 5000 cycles.（2）The optimal ratio of binary material VS₄/CNTs was used to further synthesize ternary material VS₄/CNTs/r GO through hydrothermal method to improve the electrochemical performance of the supercapacitor.The layered sandwich structure of VS₄/CNTs/r GO can effectively reduce the accumulation of graphene sheets.In the three-electrode test system,the initial specific capacitance of VS₄/CNTs/r GO-0.04 with the best carbon ratio can reach 490.7F·g^-1(1374 C·g^-1)in the voltage range of-1.4～1.4V at the current density of 1 A·g^-1.Meanwhile,when 0.5 m A·cm^-2,the capacitance of VS₄/CNTs/r GO SSC device can reach 1003.5 m F·cm^-2(2207.6 m C·cm^-2),the highest energy density of the device is 6.75 Wh·m^-2(72.07 Wh·kg^-1),and the corresponding power density is 1.38 W·m^-2(14.69 W·kg^-1).（3）VS₄/rGO precursors were synthesized by hydrothermal method and calcined at different temperatures.The applications of the products at different calcination temperatures in zinc ion batteries were studied.At 250℃,the material still maintains the sandwich skeleton of the precursor,and VS₄ oxidizes into boned V₂O₅ and attaches to the upper and lower surfaces of the lamella,which is beneficial to ion transport and promote electrochemical reaction..The discharge capacitance of S-V₂O₅/r GO-250 is 475.2 m Ah·g^-1 at the current density of 0.5 A·g^-1.At the current density of 5 A·g^-1,the capacitance retention of the material is 86.1%after 1000cycles..The morphology of the material does not change significantly after cycling.At the same time,non-in-situ XRD,non-in-situ XPS and other methods were used to conduct in-depth research on the energy storage mechanism.