Preparation And Electrochemical Properties Of Biomass Carbon Based Materials And Their Composites

With the overuse of fossil fuels and the production of greenhouse gases,clean energy storage devices have attracted a lot of attention from many researchers and it is critical to create a new generation of energy storage and conversion devices.Considerable work has been invested in developing advanced energy storage devices and management systems to address the growing energy demand and environmental concerns.Supercapacitors have the advantages of high power density,fast charge rates,excellent rate capability and long cycle life,making them one of the most promising energy storage devices.Biomass carbon with its high specific surface area,porous structure and heteroatom self-doping characteristics is considered as one of the most promising candidates for supercapacitor-electrode materials.However,the relatively low specific capacitance of biomass carbon based electrode materials limits their application in supercapacitors.Ni-Co LDH has received increasing attention because of its high theoretical capacity,excellent electrochemical activity,environmental friendliness and low cost,but Ni-Co LDH has the problem of lower conductivity in practical applications.Therefore,in this study,biomass carbon material and its composite with Ni-Co LDH were used as substrates to prepare electrode materials with excellent electrochemical properties and used in supercapacitors as follows.(1)The heteroatom self-doped porous LLPC800-4 electrode material was prepared by a onestep carbonization activation method using rabbit tail based biomass carbon as the precursor.LLPC800-4 has a graded porous structure,abundant heteroatom doping,large SSA(2717.6 m2/g),and good electrical conductivity.The abundant heteroatom doping also improves the wettability of the material and further enhances its electrochemical properties.In the three-electrode system,LLPC800-4 exhibits a high specific capacitance of 403.3 F/g at 0.5 A/g.The assembled symmetrical supercapacitor LLPC800-4//LLPC800-4 shows a high energy density of 24.5 Wh/kg at a power density of 450 W/kg.It also shows excellent cycle stability(93.55%capacitance retention and 101.21%coulomb efficiency after 10,000 charge/discharge cycles)and excellent multiplier performance(about 76.4%capacitance retention when scaled from 0.5 A/g to 10 A/g).(2)To further enhance the number of active sites in biomass carbon materials,Ni-Co LDH was used as a composite pseudocapacitive material,and Ni-Co LDH nanoflowers were successfully grown on locust-based biomass carbon materials(A-BAC)by hydrothermal method to obtain ABAC@Ni-Co LDH composites with porous corallite-like structures.The natural structural framework in locusts enables A-BAC to form a special porous corallite structure,and Ni-Co LDH grown on the carbon skeleton of A-BAC can provide high capacitance,which makes A-BAC@NiCo LDH have excellent electrochemical properties.In the three-electrode system,A-BAC@Ni-Co LDH is able to exhibit a high specific capacitance of 910.6 F/g at 0.5 A/g.The assembled asymmetric supercapacitor has a high energy density of 35.7 Wh/kg at a power density of 375 W/kg,and it still has a capacitance retention of 82.54%after 5000 cycles.