The Preparation Of High Performance Carbon-based Composites And Investigation Of Microsupercapacitors

The miniaturization of energy storage devices and the modularization of electronic systems have greatly promoted the development of micro-supercapacitors.The electrode material is the key factor for micro-supercapacitors performance.The main carbon materials include two-dimensional（2D）layered graphene,carbon nanotube,carbon aerogels and so on.They have characteristics of high specific surface area,high crystallinity,adjustable pore structure and strong conductivity.Their preparation processes involved in precursor polycondensation,supercritical drying and carbonization.However,the complex processes will cause time and resource waste.And their conventional preparation process is difficult to adjust the pore size to match the ionic size of the electrolyte.It is easy to be oxidated,resulting in decreased conductivity.How to overcome the shortcomings of existing carbon electrode materials and keep their advantages as much as possible is of great practical significance for commercial applications.This dissertation focuses on the above problems and starts to research on a hybrid carbon material with boron and nitrogen atoms boron carbon nitrogen（BCN）in the application of micro supercapacitors.At the same time,high-performance BCN composite electrodes based micro supercapacitors were prepared by optimizing device configuration,preparation process,and electrolyte type matching according to the characteristics of different composite materials.The main research contents are as follows:1.This dissertation selects boric acid,sucrose,and melamine as the sources of B,C,and N elements respectively.The 3D BCN microsphere structure was prepared with template free using a simple and economical solvothermal method and annealing treatment next.The 3D-BCN-4 exhibited a maximum specific surface area of 1390.12m²·g^-1 and a highly layered pore structure.Furthermore,the 3D-BCN-4 microsphere electrode material was printed on a flexible plane by screen printing method to prepare all solid-state micro supercapacitors（MSCs）.In PVA-KOH electrolyte,a single MSC has a specific capacitance of 41.6 m F·cm^-2,a maximum energy density of 0.00832 m Wh·cm^-2,and a maximum power density of 2 m W·cm^-2.The energy storage mechanism of BCN electrodes was studied by the Dunn method.The results show that 3D BCN exhibits surface control and diffusion control energy storage characteristics.And the number of active sites of 3D BCN is up to that is higher by 63 times and 6.3 times compared to BN and PC.2.In order to further improve the specific capacity of 3D BCN based micro supercapacitors,this dissertation investigate the reaction process and growth mechanism of 3D BCN.The results showed 3D BCN electrode materials have relatively few active function groups and poor filming property problems.To solve these problems,MXene/BCN composites were prepared by etching and high-temperature calcined method.The addition of MXene nanosheets connected with 3D BCN provided more active functional groups for the composite electrode,improving the ion transport efficiency.At the same time,the flower-like structure formed by 3D BCN/MXene composites provides more contact sites,reducing MXene layer agglomeration.MSCs devices based on MXene/BCN electrode materials were fabricated using screen printing technology.The research results show that in the GCD test with a current density of 0.5m A·cm^-2,a specific capacitance of 89 m F·cm^-2 was demonstrated,with a maximum area energy density of 0.0124 m Wh·cm^-2 and a maximum area power density of 3.1 m W·cm^-2.After connecting the MSCs unit device with MXene/BCN-3 as the electrode material in series and in parallel,the red LED light can be lit.Spin-unrestricted DFT calculations were performed to show that formation of heterojunction between BCN and MXene can reduce the band gap of MXene/BCN and increase the electron transfer rate from valence to conduction band.The H⁺adsorption energy of BCN/MXene（2.587 e V）was 2.2 times that of BCN（1.184 e V）by caculated.3.In order to improve the film formation of 3D BCN as electrode material,increase its effective contact area,and thus improve the cycling stability of 3D BCN,this dissertation adopts to introduce 3D BCD into r GO nanosheets to form BCN/r GO cauliflower structure by freeze-drying and calcination method.Next,this dissertation uses two methods,screen printing and laser engraving,to prepare MSCs cells and their array devices.Electrochemical test analysis is also conducted,and the results show that the BCN/r GO composite material has good film-forming properties.The results showed that the BCN/r GO-3 composite material,as an electrode material,exhibited an excellent specific capacitance of 72.2 m F·cm^-2 in MSCs through screen printing at a current density of 0.1 m A·cm^-2.MSCs carved by laser exhibit better performance than screen printing.the specific capacitance can reach up to 179 m F·cm^-2.Due to the addition of laser,the introduction of laser can once again reduction of r GO more thoroughly and have better conductivity and can retain 91%of its initial capacitance after 10000 CV cycles.Furthermore,the MSCs array based BCN/r GO connected in series/parallel can be fabricated to achieve the demands in practical applications.The energy storage mechanism of BCN/r GO has been analysed according to Dunn method.MSCs based BCN/r GO materials with planar structures also exhibit ideal mechanical properties and cyclic stability.4.When preparing the above electrodes,it was found that the electrode materials were first needed to prepare a slurry which included to add conductive agents and adhesives ingredient.The addition of these auxiliary materials greatly reduces the utilization rate of BCN based composites,while the addition of adhesives also increases internal resistance.Therefore,in order to further improve the utilization rate of electrode materials,this dissertation uses CVD method to realize the in-situ growth of BCN nanowire materials on high temperature resistant carbon paper,and then through Magnetron sputtering Mo S₂ to be compounded with BCN to directly obtain Mo S₂/BCN composite electrode with shell core structure,which can be directly used for electrochemical testing;At the same time,EIS spectroscopy testing was conducted on the material and spin unrestricted DFT calculations were performed to study the electron transfer rate,kinetics,surface information,and electrochemical reaction rate of the material during the electrochemical composite process.Due to the shell core structure formed by the in-situ growth of BCN nanowires and Mo S₂nanosheets,which provides a fast carrier channel,this electrode has good electrochemical properties.The results show that at a current density of 0.25 A·g^-1,the specific capacitance of BCN/Mo S₂（50W）can reach 446.3 F·g^-1.At the same time,BCN/Mo S₂ electrodes are assembled into BCN/Mo S₂//BCN/Mo S₂ symmetrical supercapacitors.At the same time,the maximum energy density and power density values were calculated through equations,which were33.3 Wh·kg^-1 and 1.9 k W·kg^-1,respectively.