The Study Of Long Fibrous Biomass-based Carbon Materials In Supercapacitors

Under the trend of rapid growth of energy consumption,people urgently need to find high-efficiency energy conversion and storage devices.Compared with other energy storage devices,supercapacitors have the advantages of high power density and long cycle stability,which have attracted widespread attention.The most widely studied and used electrode material in supercapacitors is carbon materials.Carbon materials include carbon nanotubes,graphene,activated carbon and so on.Considering the cost and processing difficulty,activated carbon is the most widely used.But the main source of activated carbon is fossil energy（coal,asphalt and other non-renewable energy）.The choice did not meet the national strategy of dual carbon for the development of clean energy and energy storage technology requirements.Therefore,sustainable biomass precursors become the first choice.The use of biomass as carbon precursor to prepare electrode materials for energy storage devices is significant to solve the energy crisis and environmental pollution.Based on the machine learning prediction of our group,it was found that long fibrous biomass may be suitable for the preparation of high-performance energy storage materials.This thesis prepared porous carbon materials by two-step pre-carbonization and activation method using three long-fiber biomasses:okra stems,piemarker stems and banana stems.The electrochemical performance of three long-fiber derived carbon materials in cell-type supercapacitors and flexible supercapacitors was investigated.It mainly includes the following contents:（1）A three-dimensional porous carbon material was prepared by carbonization-KOH activation using okra stem as a precursor.The structure of the prepared carbon materials under different activation temperature conditions and its electrochemical performance as electrodes of supercapacitors were discussed.In the three-electrode system,the okra stem-derived carbon electrode had a capacitance value of 632.8 F g^-1 at a current density of 0.2 A g^-1.In the two-electrode system,the carbon electrode was assembled into cell-type supercapacitor,the capacitance value reached 472 F g^-1 at 0.2 A g^-1.This value was at a high capacitance level compared with other biomass-based supercapacitors.Besides,the okra stem-based cell-type supercapacitors had excellent cycle stability.Then,it was used in the preparation of flexible supercapacitors.The capacitance value reached 199 F g^-1 at 0.2 A g^-1 in the two-electrode system,which provided an idea for the preparation of biomass-based flexible supercapacitors.（2）The porous carbon materials was prepared by carbonization-chemical activation method with piemarker stem as the precursor.The relationship between the structure of the porous carbon material at different activation temperatures and the performance applied to the supercapacitor was explored.When it was used in the cell-type supercapacitor,the capacitance reached up to 412 F g^-1 at 0.2 A g^-1 in the two-electrode system.The capacitance had almost no attenuation after 10000 constant current charge and discharge at 2 A g^-1.This presented ultra-high cycle stability.When extended to flexible supercapacitors,the capacitance reached 265 F g^-1 at 0.2 A g^-1 in the two-electrode system.This result was a higher capacitance level than the capacitance size of biomass-based flexible supercapacitors in recent years.（3）With banana stem as carbon precursor,the three-dimensional porous carbon materials was prepared by two-step carbonization-chemical activation method.The capacitance in the cell-type supercapacitor could reach 474 F g^-1 at 0.2 A g^-1.The carbon electrode prepared at this activation temperature could retain a higher capacitance after constant current charge and discharge for 10000 times at 2 A g^-1.The capacitance value in the flexible supercapacitor could reach up to 243 F g^-1.By summarizing the structural characteristics of the three biomass materials,the relationship between the structural characteristics of biomass carbon materials and the energy storage performance was explored,which pointed out the direction for the selection of biomass precursors.By summarizing the structural characteristics of three long fibrous biomass materials（okra stem,piemarker stem and banana stem）,the relationship between the structural characteristics of biomass-based carbon materials and the energy storage performance was explored.These results pointed out the direction for the selection of biomass precursors.