Preparation And Electrochemical Properties Of Potato Starch-based Carbon Microspheres And Manganese Oxide Composites For High Performance Supercapacitors

Supercapacitors have the advantages of high power density,rapid charge and discharge,long cycle life and environmental friendliness,and have the characteristics of traditional capacitors and batteries/fuel cells.They have attracted extensive attention in the field of portable electronic equipment and hybrid electric vehicles.Carbon electrode materials with biomass,minerals and starch as carbon sources have the advantages of wide source,good conductivity,low cost and high stability,and become the preferred electrode materials for supercapacitors in industry.However,the materials of carbon-based still have the fatal defects of lower specific capacitance and lower energy density,which seriously hinder their practical application and development.Transition metal oxides have the advantages of high specific capacitance,high energy density and low price,which have become a research hotspot.In recent years,high-performance supercapacitors are mainly composed of carbon materials and transition metal oxides.This composite material is composed of a double-layer capacitor and a Faraday pseudocapacitor,which not only improves the capacitance of supercapacitors,but also improves the cycle life and multiplier performance.In this paper,the preparation process of potato starch based microporous carbon microspheres was first investigated,and the influence of binder content on the electrochemical properties of potato starch based microporous carbon microspheres was investigated,and carbon materials for high-performance supercapacitors were screened.Then,the MnO/C composite was synthesized by high temperature gelatinization and high energy ball milling.The effects of heat treatment temperature and potato starch content on the microstructure and electrochemical properties of the composite were investigated.In order to obtain high-performance electrode materials,carbon nanotubes(CNTs)were used to modify MnO/C@CNTs to produce composites with three-dimensional conductive network structure,MnO/C@CNTs.The influence of CNTs content on the morphology and electrochemical properties of MnO/C@CNTs composites was investigated,and the electrochemical properties of MnO/C@CNTs as electrode materials of type 2032 asymmetric button supercapacitor were investigated.(1)Potato starch based microporous carbon microspheres were prepared by stabilization of(NH₄)₂HPO₄ and activation of KOH,which perfectly maintained the spherical structure of potato starch.Potato starch based microporous carbon microspheres have abundant microporous structures,with an average pore diameter of1.68 nm and a specific surface area of up to 2047.64 m²/g.The electrochemical properties of 3 wt.%,5 wt.%,7 wt.%.When the binder content was 5 wt.%,the specific capacitance and volume specific capacitance of potato starch based microporous carbon microspheres were 170.0 F/g and 142.8 F/cm³ respectively when the current density was 1 A/g.the specific capacitance reaches 112.5 F/g(at 30 A/g),the volume energy density is as high as 6.35 Wh/L,and the power density is 4725W/L,with good multiplier characteristics.This is mainly the result of improving charge transfer and electron/ion transfer in the electrode under the optimized binder content.(2)MnO/C composites coated with MnO in situ by potato starch microporous carbon microspheres were prepared through the process of high-temperature gelatinization and high-energy ball grinding.Heat treatment temperature(400 ^oC and500 ^oC and 600 ^oC and 700 ^oC)and potato starch content(20 wt.%,30 wt.%and 40wt.%,50 wt.%)of MnO/C in three electrodes system KOH aqueous solution as the electrolyte(3 M)in the electrochemical properties and the effect of and to assess the MnO/C with potato starch microporous carbon microspheres electrode pole piece assemble type 2023 asymmetric button the electrochemical properties of super capacitor.The results showed that the dispersion of MnO/C-600(30%)nanoparticles with particle size of 50-200 nm was the best when the content of potato starch was 30wt.%at 600 ^oC.The specific capacitance of MnO/C-600(30%)is 1278.0 F/g(at 0.2A/g)MnO/C-600(30%)still has a specific capacitance of 421.4 F/g(at 1 A/g).In addition,MnO/C-600(30%)also exhibits excellent electrochemical performance in asymmetric supercapacitors.The specific capacitance is 75.0 F/g at 1 A/g,and remains at 72.1%after 5000 cycles.MnO coating on potato starch improves the overall electrical conductivity,accelerates the diffusion rate of electrons/ions,and improves the electrochemical properties.(3)Under the above(2)optimization conditions,high temperature gelatinization and high energy ball grinding were used to obtain the MnO/C@CNTs composites with CNTs doped potato starch carbon coated MnO nanoparticles with good dispersion.The electrochemical properties of MnO/C@CNTs composites prepared with CNTs(0.5 wt.%,1 wt.%,1.5 wt.%)in a three-electrode system(3 M KOH aqueous solution as electrolyte)were investigated.It was found that when CNTs were1 wt.%,the nano particles and CNTs of the MnO/C@CNTs-1 composite were evenly distributed and showed the best electrochemical properties.Ac impedance test showed that MnO/C@CNTs-1 electrolyte resistance is 3.3?.The mass ratio capacitance is as high as 758.5 F/g,which is much higher than the mass ratio capacitance of MnO/C without CNTs doped composite(421.4 F/g),which indicates that proper incorporation of CNTs can effectively improve the conductivity between particles and greatly reduce the overall polarization of the material,thus improving its high electrochemical performance.In addition,the specific capacitance of the asymmetric button supercapacitor assembled by MnO/C@CNTs-1 at 1 A/g is 172.0 F/g,the voltage window is up to 1.4 V,and the capacitance retention rate after 5000 cycles is84.6%.The efficient three-dimensional conductive network constructed by mutual hinge of potato starch carbon and CNTs is the main reason for significantly improving the electrochemical properties of MnO/C.