In-situ Electrochemical Oxidation For Preparation Of High-performance Carbon Electrode Material For Supercapacitor

With high power density and ultra-long cycling life,supercapacitors have good application prospects in many fields,including electronic devices,electrical vehicles and energy storage,etc.However,the low energy density has always been a bottleneck to their further development.As the most popular electrode material for supercapacitors,porous carbon has a good application prospect due to their high electrical conductivity,good structural stability,adjustable morphological structure and abundant elemental doping.The introduction of electrochemically active oxygen-containing functional groups with multi-electron redox reactions to provide high pseudocapacitance is a promising strategy.And the mild and controlled electrochemical oxidation methods provide an efficient way to introduce oxygen species for carbon electrodes.Based on the in-situ electrochemical oxidation method for the controlled preparation of high specific energy carbon-based electrode materials,this thesis investigates the structure-function relationship between the structure,composition and electrochemical properties of the oxidized electrode from the selection and optimization of the electrochemical oxidation process and carbon precursor.And it proposes the influence law of the oxidation process and carbon precursor on the oxidized electrodes,which provides a feasible strategy for the controlled preparation of high specific energy carbon-based electrode materials.The main contents and results are as follows.（1）High specific capacitance supercapacitor electrode materials were prepared by in-situ cyclic voltammetry oxidation of activated carbon YP-50 electrode in a three-electrode system.The effects of oxidation potential window,oxidation sweep rate and oxidation cycles on the components and electrochemical properties of the oxidized electrodes were investigated.It was found that the optimal electrochemical properties could be obtained under the multiple cyclic voltammetry oxidation process with broad oxidation potential window and high oxidation sweep rate.Specifically,the stronger oxidation capacity in a broader oxidation potential window of-0.65～2 V facilitates a deeper oxidation degree to obtain higher oxygen content and specific capacitance,while the rapid oxidation process at a high sweep rate of 20 m V s^-1 endow a selective introduction of electrochemically active oxygen-containing functional groups dominated by C-OH/C=O groups and a well-maintained electric conductivity.Benefiting from the abundant electrochemically active oxygen components and favorable electric conductivity,the oxidized electrode delivered a high specific capacitance(533.9 F g^-1 at 1 A g^-1)and exhibited an excellent rate capability(78.3%at 20 A g^-1).Symmetrical supercapacitor with the oxidized electrodes achieved a high energy density of 11.45 W h kg^-1 at a power density of 500 W kg^-1,and maintained 94%of the initial specific capacitance after 10000 cycles.（2）Two-dimensional B,N co-doped carbon nanosheets were prepared and used as carbon precursors for the electrochemical oxidation.The B,N-doped carbon sheets possess high specific surface area and abundant heteroatom doping（1.45 at.%B content and 3.75 at.%N content）.During electrochemical oxidation,the two-dimensional sheet structure and high specific surface area could provide a high reactive phase interface.While the abundant B-and N-doping enhances the defect density and changes the electron cloud density distribution of the carbon skeleton,which promotes the efficient introduction of oxygen species.Moreover,the additional electrons and holes provided by B-and N-doping also endow a fast electron and charge transfer.In addition,the differences between the oxidized electrodes prepared by constant potential oxidation and cyclic voltammetry oxidation were further investigated.From the component characterization and electrochemical performance tests,the repeated high-potential oxidation and low-potential reduction during cyclic voltammetry oxidation were proved to facilitate the deeper oxidation and optimization of the oxygen species.The optimized oxidized electrode exhibited a super-high specific capacitance of 601.5 F g^-1 at 1 A g^-1 and a high capacitance retention of 74.8%at 20 A g^-1,which presented a further improved specific capacitance compared to oxidized commercial carbon electrodes.Besides,the oxidized electrode also maintained a good cycling stability,which retained 92.6%of initial capacitance after 8000 cycles.