Preparation And Performances Of Novel Environment-friendly Supercapacitors Based On Straw Biomass Carbon Materials

Supercapacitor,a kind of new type energy storage device between conventional capacitor and chemical battery,is considered to be the most appropriate,environmental friendly and sustainable clean energy owing to its outstanding merits,such as the ultra-high chanrge and discharge power,Faradaic level of large capacity,high energy density,wide working temperature range,and long service life,maintenance-free,cheapness and environmental friendliness.With the rapid development of the global economy,the energy crisis is becoming more and more serious,which highly stimulates the development of new energies and corresponding energy storage devices,especially supercapacitors.Comprehensive use of abundant biomass materials,plant waste in particular,can not only alleviate effectively the shortage of the fossil energy,but also reduce the environmental pollution deduced by the waste incineration,which will bring considerable economic,social and ecological benefit.In this thesis,some activated carbon mayerials were obtained by activating the plaent straws,and then,as the electrode materials of the supercapacitors their electrochemical properties were investigated in detail.The thesis consists of three parts as follows:1.With wheat straw and polyacrylonitrile?PAN?as raw materials,novel wheat-straw carbon nanofiber electrode materials for supercapacitors were prepared by an electrospinning method.When PAN was doped 10 % wheat-straw,the resulted composite nanofiber electrode material showed the highest specific capacitance of249.0 F/g at the current density of 0.4 A/g.The prepared supercapacitor possessed a good cyclic stabiity and the specific capacitance only reduced 3.6 % after 1000 cycles at a current density of 2 A/g.Using waste biomass resources to prepare the valuable energy materials not only improved utilization efficiency but also solved effectively environmental pollution problems to a certain extent.2.Use of biomass waste industrial hemp as raw materials,different mass ratio of KOH as activating agent,3D porous hemp-activated carbon?HM-ACs?have been successfully prepared in a simple chemical activation method.The porous carbon material HM-AC-3 prepared with the mass ratio of 3:1 of KOH had an extremely highspecific surface area 1934.26 m2/g.And when used as the electrode material,it also showed an excellent capacitance performance.The highest specific capacitance was1683.75 F/g at the current density of 1 A/g in three-electrode system and the specific capacitance was retained 91.6 % after 10000 charging-discharging cycles at the same current density.The assembled HM-AC-3//HM-AC-3 symmetric supercapacitor device possessed a wide operation voltage of 1.6 V and a high energy density of 16.16Wh/kg.At the same time.The results indicated that the prepared HM-ACs were novel and promising electrode materials.3.Ni₃S₂ nanosheets were in situ on the as-prepared 3D HM-AC@Ni foam substrate by a simple electrodeposition method,as a result,the Ni₃S₂,3D HM-AC and Ni foam composite electrodes without binder were obtained.The results showed that the prepared Ni₃S₂/3D HM-AC@Ni electrode with 3 cycles of electrodeposition had an excellent electrochemical performance and the specific capacitance was as high as2797.43 F/g at 1 A/g of current density in 6 M KOH electrolyte.Using the composite electrode as positive pole,3D HM-AC as negative pole,a novel all-solid-state?ASS?asymmetric supercapator 3D HM-AC//Ni₃S₂/3D HM-AC was successfully assembled.The ASS asymmetric supercapacitor possessed not only a wide working potential range?1.2 V?and a high specific capacitance?267.6 F/g,1 A/g?,but also a high energy density?55.32 Wh/Kg,1 A/g?and a high power density?1053.71W/Kg,1 A/g?,as well as good cyclic stability?83.47 % of capacitance rentention after10000cycles?,suggesting a very promising practical application potential.