Preparation And Electrochemical Properties Of MXene/CNTs Composite Fibers

With the rapid development of wearable and portable electronic products,flexible supercapacitors are widely concerned by researchers.Electrode materials are the most important components of flexible supercapacitors.Therefore,it is of great significance to develop structural and functional integrated electrode materials with light weight,good flexibility and high storage capacity.Carbon nanotube fibers have the advantages of excellent electrical conductivity,good flexibility and high mechanical strength,which make them an ideal electrode material for flexible supercapacitors.However,due to the dual-layer energy storage mechanism,their specific capacity and energy density are relatively low.Therefore,the introduction of pseudocapacitive active materials with excellent electrochemical performance into carbon nanotube fibers and the development of fiber electrode materials with excellent energy storage characteristics have become a hot topic in the research of carbon nanotube fibers in the field of supercapacitors,which has important research value and scientific significance.In this paper,polypyrrole（PPy）/MXene（Ti₃C₂）composites were prepared by in-situ hydrofluoric acid generation and in-situ polymerization.The process parameters such as reaction concentration,reaction time and ultrasonic treatment were optimized in the preparation process.The morphology,structure and electrochemical properties of the obtained MXene materials and PPy/MXene composites were studied.The stable preparation of MXene and the functional modification of PPy of MXene were realized.Using carbon nanotubes（CNTs）and MXene as raw materials,biomolecular sodium hyaluronate（HA）as dispersing agent and ionic binder,the process of preparing fibers by wet spinning method was optimized.Flexible MXene/CNTs composite fiber electrode materials with uniform shape,controllable length and excellent mechanical,electrical and electrochemical properties were prepared.Studies showed that MXene/CNTs composite fibers prepared when the composite ratio of MXene to CNTs was 1:1 had the best comprehensive performance.Young’s modulus is 3.31±0.33 GPa,fracture strength is 56.68±3.99 MPa,resistivity is 0.51±0.05Ω·mm and specific capacitance is 30.98±3.02 m F/cm².At the same time,MXene/CNTs composite fiber has good flexibility and stability.After 3000 folding and unfolding tests,its resistance retention rate is still above 98.5%.With CNTs and PPy/MXene composite materials as raw materials,HA as dispersant and ionic adhesive,wet spinning method was used to prepare good conductivity,high strength,good flexibility,excellent electrochemical performance of PPy/MXene/CNTs composite fiber electrode materials.Young’s modulus,fracture strength and resistivity of PPy/MXene/CNTs composites were 3.37±0.33 GPa,54.65±1.88 MPa and 0.39±0.02Ω·mm,respectively.When the composite ratio of PPy,MXene and CNTs was 0.5:1:1.5,the specific capacitance of prepared PPy/MXene/CNTs composite fiber was 2.5 times that of MXene/CNTs composite fiber.The planar asymmetric supercapacitor was constructed by using MXene/CNTs composite fiber as negative electrode material,PPy/MXene/CNTs composite fiber as positive electrode material,and H₃PO₄/PVA gel as gel electrolyte.The stable operating voltage window of the supercapacitor is increased to 2 V,and the energy density and power density are 1.20 m W/cm²and 8.22μwh/cm²,respectively.Under the condition of large Angle bending,the deviation rate between the capacitor value and the normal capacitance value is less than 4.14%,which has good flexibility and stability.