Controlled Preparation Of MXene/Metal Sulfides Composites And Study On Its Capacitive Properties

Supercapacitor is a kind of highly efficient electrochemical energy storage device,which has the advantages of long cycle life,fast charging and discharging rate,etc.,and has a wide application prospect in electronic devices,storage backup system,hybrid electric vehicles,wind power and solar power generation and other fields.As one of the core elements of energy storage device,electrode material directly determines the electrochemical performance of energy storage system.Two dimensional material MXene(Ti₃C₂)is an ideal electrode material for supercapacitors because of its unique two-dimensional structure,excellent physical and chemical properties and electrochemical properties.However,the spontaneous collapse of layered structures and the inherent shortcomings of a single material severely limit their application in the field of energy storage.A new strategy to improve the performance of Ti₃C₂-based supercapacitors is to introduce other materials into the highly conductive Ti₃C₂.In this paper,transition metal sulfide(ZnS)was successfully introduced into the interlayer and surface of MXene by one-step solvothermal method,and a new type of composite MXene/ZnS was constructed.The composites has both the layered morphology of MXene and the marshmallow morphology of ZnS,thus constructing a reasonable spatial network structure.Based on the successful construction of the structure,the collapse defect of the MXene structure is suppressed,thus providing more surface active sites.At the same time,the addition of high conductivity ZnS can improve the energy storage performance of the composites.Therefore,the new composites has excellent supercapacitive properties,and its specific capacity reaches1956 F/g at 1 A/g,which is about 9.2 times that of MXene and 1.3 times that of ZnS.More importantly,the energy density of a supercapacitor assembled with the composite as a positive electrode can reach 31.8 Wh/kg.On this basis,the experimental scheme is optimized.First,the multilayer MXene was separated into flakes by mechanical methods to avoid irreversible agglomeration of MXene flakes due to strong van der Waals forces between the MXene layers.Then the spherical structure Co S₂ was introduced into the MXene nanosheet by one-step hydrothermal method,so as to construct a state of layered structure and spherical structure interwoven coexist,which is the new MXene/Co S₂ composites.Based on the good construction of the structure,the composites shows excellent supercapacitive properties.The capacity can reach 1320 F/g at 1 A/g.The superior specific capacity performance is due to the synergistic effect between the two different structures,which promotes the efficiency of transport between metal ions.The maximum energy density of a supercapacitor assembled with this material as a positive electrode can reach 28.8Wh/kg at a power density of 800 W/kg.On the basis of the previous two groups of experiments,in order to explore the electrochemical behavior of metal sulfides of Zn-Co-S ternary system and MXene,ternary sulfide ZnCo₂S₄ was combined with MXene nanosheets by electrostatic self-assembly method.Taking full advantage of the high specific surface area of MXene nanosheets and the high energy storage performance of core-shell ZnCo₂S₄,the specific capacitance of the composite can reach 1072 F/g and the capacitance retention of the composite is 94.6%after 5000 continuous charge and discharge.Moreover,the energy density is measured to be 30.46 Wh/kg at 1 A/g when the composite was used as positive electrode of supercapacitors.In conclusion,the combination of metal sulfide of Zn-Co-S ternary system and MXene can effectively improve the electrochemical performance of each other.This paper contains 57 figures,3 tables and 93 references.