Study On Preparation And Electrochemical Properties Of Carbon-based Manganese Dioxide Composites

New energy storage materials have been a hot topic in the field of materials research.Supercapacitors,as a new type of energy storage equipment,have been widely used in various energy storage fields due to their advantages of fast charge and discharge,high power density and cycle stability.The use of waste biomass,building materials and other carbon materials as carbon sources to prepare a variety of new functionalized carbon nanomaterials is an effective method to improve the energy density of supercapacitors,and is also an important innovation to achieve sustainable development concepts.In this paper,a new MnO₂/carbon nanocomposite material was prepared by using carbonaceous waste,which effectively improved the energy storage performance of MnO₂.The main work of this paper is as follows:1.Nitrogen-doped porous hollow carbon spheres were successfully prepared by hydrothermal pre-carbonization and pyrolysis carbonization using natural yeast cells as carbon sources.The MnO₂ nanowires were deposited by in-situ hydrothermal reaction using nitrogen-doped porous hollow carbon spheres as templates.MnO₂ nanostructures with different morphologies and electrochemical properties were obtained in different reaction solution concentrations.The as-prepared composite exhibits a high specific capacitance of 255 F g^-1 in 1 M Na₂SO₄ electrolyte and at a current density of 1 A g^-1.The asymmetric supercapacitor was assembled by the composite material as the positive and the hollow carbon sphere as the negative.The maximum energy density operating at the 2.0 V voltage window is 41.4 Wh kg^-1 at a power density of 500 W kg^-1 and still maintains 23.0 Wh kg^-1 at a power density of 7901 W kg^-1.Moreover,it exhibits excellent cycling stability,retains approximately 93.9%of the capacitance after 5000cycles.This work is innovatively based on biomass energy,which effectively increases the energy density of supercapacitors and provides environmentally friendly strategies and new insights for the preparation of electrode materials.2.A high-quality flexible carbon fiber material was prepared by pyrolyzing the surface of the epoxy resin,using carbon fiber reinforced epoxy-based material recovered from construction waste as a carbon source.The as-prepared recycled carbon fiber has a diameter of 8?m and is the perfect substrate material for flexible electrode materials.Furthermore,PANI and MnO₂ were uniformly deposited on the recycled carbon fiber by one-step electrodeposition to form an active film.The recycled carbon fiber/PANI/MnO₂composite shows an excellent specific capacitance of 475.1 F g^-1 and capacitance retention of 86.1%after 5000 GCD cycles at 1 A g^-1 in 1 M Na₂SO₄ electrolyte.The composites optimized for electrodeposition time have more electroactive sites,faster ions and electron transfer,structural stability and higher conductivity,endowing the composites promising application prospect.3.The hollow porous activated carbon material was prepared by using lotus as a carbon source,and the activation mode was mainly activated by KOH,supplemented by activation of trona metal elements in plant conduits.The activated carbon material has a specific capacitance of 217 F g^-1 at a current density of 1 A g^-1,showing good energy storage.In addition,MnO₂ particles were formed in the hollow pipe of the activated carbon by the hydrothermal deposition reaction.The electrochemical performance was further improved by introducing a pseudocapacitance.The symmetric supercapacitor assembled with the composite material as positive and negative electrodes exhibits an energy density of 16.6 Wh kg^-1 at a power density of 123.7 W kg^-1,and the energy density remains 11.5 Wh kg^-1 at a high power density of 9651 W kg^-1.In addition,the capacitance retention rate reachs 87.1%after 5000 cycles,indicating that the material is an ideal supercapacitor electrode material.