Preparation Of Negative Electrode Materials Based On Biomass Stems And Their Application In Supercapacitor

The sustainable conversion of biomass waste into porous carbon with unique electronic morphology and chemical structure has attracted wide attention in the field of energy storage.Biomass carbon materials,with abundant renewable precursors and ever-changing microstructure,have been playing an important role in practical energy storage devices.Transforming into electrode materials for supercapacitors,the waste biomass realizes the vision of turning waste into treasure,green life and reducing carbon emissions.Based on the properties of biomass-derived carbon materials,this thesis used sesamum indicum stem and abutilon theophrasti stem as carbon precursors,and prepared N and O co-doped porous carbon by simple carbonization and activation processes.The specific research contents are as follows:（1）In order to illustrate the specific effects of activators on activated carbon of biomass,waste sesamum indicum stem（SIS）were used as precursors to investigate the effects of different KOH activation ratios on the microstructure and electrochemical properties of sesamum indicum stem derived activated carbon（SISACs）.With the increase of KOH,O content showed an increasing trend.As a strong oxidizing agent,KOH had strong oxidation with carbon materials at high temperature,thus increasing oxygen content and etching non-oxygen atoms.Moreover,with the increase of KOH concentration,the roughness of the inner wall of pore diameter also increases,which verifies the effect of KOH as a strong oxidant on pore etching.Among them,the prepared SISAC-4 possesses superior electrochemical performance,high specific surface area(2012 m² g^-1)and abundant micropore structure（85%microporosity）.In addition,the SISAC-4 electrode showed excellent specific capacitance(284.6 F g^-1 at1 A g^-1),excellent magnification performance(57%at 15 A g^-1 with high current density),and excellent cyclic stability（98%after 5000 cycles）.（2）In order to further enhance the specific capacitance of biomass-derived carbon materials,a two-step activation method of KOH and ZnCl₂was explored to prepare biomass-derived carbon anode materials.N and O co-doped activated carbon was prepared from discarded abutilon theophrasti stem（ATS）as a precursor by a two-step activation method.The synergistic effect of KOH and ZnCl₂ on the microstructure and electrochemical properties of activated carbon（ATSACs）was discussed.Compared with ATSAC-4 and ATSAC-8,ATSAC-6 shows superior electrochemical performance.The optimized ATSAC-6 has a high surface area of 3783 m² g^-1 and a microporosity of94%,providing abundant electroactive sites for the adsorption of electrolyte ions.In addition,the ATSAC-6 electrode provides high specific capacitance(365.1 F g^-1 at 1 A g^-1),excellent rate performance(64%at high current density at 15 A g^-1)and long cycle stability（97%after 5000 cycles）.In addition,electrochemical studies have been conducted on KOH and[BMIM]BF₄/AN symmetric devices assembled with ATSAC-6 electrodes.KOH devices have higher specific capacities(Specific capacitance 74.81F g^-1 at 0.5 A g^-1 current density)and better cyclic stability（KOH device maintains 95%capacitance retention after 5000 cycles,while[BMIM]BF₄/AN device has only 80%capacitance retention）,[BMIM]BF₄/AN devices have a larger voltage window and a higher energy density(providing a high energy density of 51.83 Wh kg^-1 at a power density of 375 W kg^-1).Finally,the assembled devices are tested in series and parallel.Two[BMIM]BF₄/AN devices in series can supply power to 40 red LEDs continuously for 3 minutes.Two KOH devices in series can drive the small fan,indicating that continuous power supply can be achieved by connecting m KOH devices in series.Therefore,this paper provides a preparable strategy to transform waste biomass into active carbon through simple carbonization and activation,which lays a foundation for the large-scale development and application of supercapacitors.