Preparation And Electrochemical Performance Of Electrodes Derived From Needle Coke/Polymer Electrospun Carbon Fibers

Supercapacitors have great applications in the fields of national defense,civil use,etc.,and are a new type of energy storage device with great development prospects in the development and application of new energy.Nano/micron-scale electrode materials can provide more storage space for charge storage.The nano-micron carbon fibers prepared via electrospinning have the characteristics of wide source of raw materials,good controllable structure and remarkable industrialization characteristics,so it has become an optimal way for the preparation of electrode materials for supercapacitors.In this paper,the high-energy ball milling method is used to prepare nano-micron-sized needle coke particles as raw materials;then under the action of ultrasonic cavitation,the needle coke is surface-modified with a surfactant to obtain a good compatibility with the fiber-forming polymer modified needle coke: After the needle coke/polymer ultrafine fibers are prepared via electrospinning,activated carbon fiber with high carbonization rate,conductivity and electrochemical stability is prepared through the process of carbonization and activation.In addition,this paper studies the dispersibility and dispersion mechanism of modified needle coke in the strong polar solvent DMF.At the same time,the morphology and structure of the prepared needle coke/polymer derived composite fibers and its carbon fibers are systematically studied.Analysis,and investigated the application of its active composite carbon fiber electrode material in supercapacitors.The main research contents and results are as follows:(1)Study on the preparation and surface modification of ultrafine needle coke.The needle coke is crushed by different crushing methods,and analyzed and characterized by a variety of test methods.The results show that the particle size of the needle coke prepared by the high-energy planetary ball milling method is the smallest.In order to improve the dispersibility of ultrafine needle coke in N,N'-dimethylformamide(DMF),a variety of surfactants were used to study the surface modification of ultrafine needle coke particles.The needle coke is further broken with an ultrasonic cell pulverizer,and the soft agglomeration inside the needle coke is opened.At the same time,under the action of ultrasonic cavitation,active sites can be obtained on the surface of the needle coke,which improves the modification effect of the surface modifier.The results showed that needle coke modified with silane coupling agent(KH-570)and polycarboxylate sodium salt(5040)do not delaminate after standing in DMF for 3days.The factors and mechanisms affecting the dispersion stability of surface-modified needle coke particles in DMF were studied.The results show that under the action of ultrasonic cavitation,the surface modifier has a good physical and chemical effect on the surface of the needle coke,resulting in a good compatibility between the surface-modified needle coke,the fiber-forming polymer and the solvent.Thus,a uniform and stable electrospinning precursor is obtained.(2)Preparation of needle coke/polyacrylonitrile(PAN)derived ultrafine carbon fiber electrode materials and its electrochemical performance.Using PAN as the fiber-forming polymer,adding different contents of surface modified ultrafine needle coke,the needle coke/PAN electrospun fiber is prepared by the electrospinning method.Then,the needle coke-based activated carbon fibers are obtained through pre-oxidation,carbonization and activation processes.The composition,morphology and electrochemical properties of the needle coke composite fiber and activated carbon fiber with different content were analyzed and characterized.The results show that compared with pure PAN-based carbon fiber,the carbonization rate of needle coke/PAN-based carbon fiber is higher and the degree of graphitization is higher.The electrochemical test of needle coke/PAN derived carbon fiber shows that when PAN:needle coke=5:10,the electrode materials prepared by it shows the best electrochemical performance.It has a specific capacitance of 173.8 F/g when the current density is 1 A/g,and its retention rate reaches 91% after 10,000charge-discharge cycles.(3)Preparation of needle coke/hybrid polymer derived ultrafine carbon fiber and its electrochemical performance.The deposition coating formed by PAN with high carbonization rate on the surface of needle coke particles will reduce the porosity and specific surface area of needle coke-based carbon.For this reason,polyvinylpyrrolidone(PVP)with low carbonization rate is used as the fiber-forming material,Preparation of needle coke/hybrid polymer-based ultra-fine carbon fiber.The composition,morphological structure and electrochemical performance of the research showed that when the fiber-forming polymer PAN:PVP=2:1,it is most suitable for compounding with different proportions of needle coke.The morphology and electrochemical properties of needle coke/hybrid polymer derived ultrafine carbon fibers were characterized.The results show that as the content of needle coke increases,a large number of needle coke particles are attached to the surface of the fiber and the surface roughness of the fiber increases.Electrochemical tests show that when PAN:PVP:Needle coke=5:2.5:7,the overall performance of the active electrode material is the best.The impedance is the smallest and the frequency response is the best;it has a specific capacitance of 182.3 F/g in the current density range of 1.0 A/g.After 10,000 charge and discharge cycles,the capacitance retention rate reaches 97.2%.