Application Of Transition Metal-sulfur Group Compound Electrode Materials And Study Of Energy Storage In Supercapacitors

With the dramatic depletion of fossil fuels,the growing demand for energy has prompted the scientific community to search for renewable and sustainable sources of energy.Supercapacitors(SCs)as a new energy storage technology for energy storage devices have attracted special interest from researchers due to their excellent cycle life,high power density and environmentally friendly and safe ultra-fast charging capability.However,currently,low energy density is a big drawback of supercapacitors.As shown by the equation E=1/2 CV²,the effective way to increase the energy density is to increase the operating voltage and specific capacity,respectively.Nickel-based materials have become the first choice for research due to their high theoretical specific capacity,high chemical and thermal stability,easy availability,environmental friendliness and low cost.However,their low multiplicity properties and low electrical conductivity have hindered their wide application.In this paper,a variety of transition metal compounds are prepared by hydrothermal method using nickel,tin and cobalt as metal sources,and the objective is to construct high power density and energy density supercapacitor energy storage devices.The objective is to design and synthesize hybrid supercapacitor energy storage devices with excellent energy storage performance and characterize their electrochemical energy storage behavior.1.A novel Ni Se₂/Sn Se₂ nanocomposite was successfully prepared as a supercapacitor electrode material by a two-step hydrothermal process.The composites prepared with different Ni/Sn ratios have different morphological and electrochemical properties.When the Ni/Sn ratio was 2.5:1,the composite had optimal electrochemical properties with a high specific capacity of 116 m A h g^-1 at a current density of 1 A g^-1and an excellent cycling stability of 80%capacitance retention after 4000 cycles.The prepared(Ni,Sn)Se₂-2.5 cathode material was assembled with activated carbon(AC)to form a(Ni,Sn)S₂-2.5//AC asymmetric supercapacitor(ASC)with a high energy density of 34.3 Wh kg^-1 at a power density of 855 W kg^-1.More importantly,the(Ni,Sn)Se₂-2.5//AC ASC has an initial specific capacitance retention rate of 82.3%after10,000 cycles of charge/discharge,which indicates that the energy storage device has excellent cycling stability.2.Graphene oxide(GO)was firstly prepared by Hummers'method,and r GO/Ni Co₂S₄ composites were synthesized by one-step hydrothermal synthesis as supercapacitor electrode materials by combining GO and metal organic framework(MOF)ZIF-67 as a template.The metal-organic backbone can be used as an excellent supercapacitor electrode material due to its high specific surface area and good morphology.The design combines GO as a template with ZIF-67,which can not only improve the charge transfer rate and reduce the diffusion resistance,but also increase the active sites.The synthesized r GO/Ni Co₂S₄ has excellent electrochemical performance as an electrode material,with a high specific capacity of 171 m Ah g^-1 at a current density of 1 A g^-1 and a multiplicative performance of 71.3%when the current density reaches 10 A g^-1.And the asymmetric supercapacitor(ASC)assembled with r GO/Ni Co₂S₄ as the positive electrode and AC as the negative electrode has a high energy density.The energy density can reach 41 Wh Kg^-1 when the power density is870 W kg^-1,and the cycle stability is excellent 88.2%after 5000 cycles at a current density of 5 A g^-1.Therefore,the synthesized r GO/Ni Co₂S₄ has a good prospect as an electrode material for supercapacitors.3.Porous Bi₂S₃/C materials were prepared by hydrothermal method using carbon polyhedra as templates.The carbon polyhedra were obtained by carbonization of ZIF-67 and subsequent acid treatment.This unique structure helps the electrode material to be fully exposed to the electrolyte solution and maintain the structural stability during the fast electrochemical reaction.As a result,this Bi₂S₃/C-3 was used as a supercapacitor electrode at a current density of 1 A g^-1 with a specific capacity of 62m A h g^-1.The capacitance was maintained at 72.2%after 1000 cycles.In addition,the asymmetric supercapacitor assembled by the previously successfully prepared tubular Ni S/Mo₂S₃ as the positive electrode and Bi₂S₃/C-3 as the negative electrode in the laboratory exhibited good electrochemical performance with a capacitance retention rate of 77.7%at 3000 cycles.