Research On Cooperative Coupling Of Transition Metal Co-X(X=Mo,Cu) Sulfides And Oxides For Supercapacitor Performance

Supercapacitors have been widely concerned by researchers due to their high discharge power,fast charge-discharge rate,long cycle life and environmental friendliness.Recently,carbon based materials,conductive polymers and transition metal oxides/hydroxides as the main electrode materials for supercapacitors can not meet the practical application needs of human due to low energy density,poor recycling stability and slow electron transfer rate.Therefore,it is very necessary to design new electrode materials and improve energy density and stability of electrode materials.Herein,according to the synergistic coupling effect of transition metal Co-X（X=Mo,Cu）sulfide and oxide,several new transition metal sulfide and oxide composite electrode materials have been prepared and applied to supercapacitors.Through electrochemical test,they show excellent energy storage characteristics.The specific content is described as follows:1.The Co-Mo-O-S composite material with a spherical flower cluster structure was prepared by hydrothermal method.And the electrochemical test shows that when the discharge current density is 1 A·g^-1,the specific capacitance of Co-Mo-O-S is 1142 F·g^-1.After 3,000 cycles;only 9%of the initial capacitance is lost.In this work,simple hydrothermal and vulcanization reactions were used to prepare the Co-Mo-O-S(Co₃S₄,MoS₂ and Mo₈O₂₃)composites with special morphology.When Co-Mo-O-S was used as the positive electrode and redox graphene oxide（r GO）as the negative electrode,the assembled water-based asymmetric supercapacitor could provide a high energy density of67.6 Wh·kg^-1,so it is expected to be widely used in energy storage devices.2.A stable and controllable core-shell nanobar-like Cu Co₂S₄@Co Mo O₄ composite material was grown on nickel foam（NF）substrate.The ultra-high specific capacitance of2058 F·g^-1(5557 m F·cm^-2)was delivered at the current density of 1 m A·cm^-2.The maximum energy density of the water-based asymmetric device assembled by activated carbon（AC@NF）coated on NF as the negative electrode and Cu Co₂S₄@Co Mo O₄@NF as the positive electrode was 45.73 Wh·kg^-1 at the power density of 198.8 W·kg^-1.After 3000cycles,it has a capacitance retention rate of 83%.The first principle（DFT）calculation proves that the coupling of Cu Co₂S₄ and Co Mo O₄ can improve electrochemical performance.3.The MoS₂-Cu₂O@Ti₃C₂ composite with 3D flexible self-supporting heterostructure was prepared by hydrothermal method and static precipitation self-assembly.By loading the Ti₃C₂ surface with MoS₂ nanosheets and filling the Ti₃C₂-MoS₂ layer gap with hard Cu₂O,the specific capacitance and cyclic stability of the composite can be improved simultaneously.With MoS₂-Cu₂O@Ti₃C₂ as the cathode and activated carbon（AC）as the anode,the all-solid-state flexible asymmetric supercapacitors can show the maximum energy density of 60.5 Wh·kg^-1,and retain about 90%of the initial specific capacitance after 3000 cycles and having excellent mechanical flexibility under different bending angles.This study provides a new strategy for the development of flexible supercapacitor electrode materials with excellent electrochemical properties.