Carbon-based Composite Supercapacitor Electrode Materials From Corncob Sponge And Tobacco Stem

Supercapacitors are important novel energy storage devices,but their low energy density needs to be improved.Carbon materials with high specific area and conductivity are often employed as electrodes in supercapacitors.Biochar is a potential candidate for supercapacitor electrodes because of the wide choice of raw materials,low cost and high conductivity.Structure and electrochemical performance of the biochar vary be-tween different raw materials.In this thesis,two kinds of typical agricultural by-prod-ucts,corncob sponge and tobacco stems,were used as carbon source to produce bio-mass carbon materials,and were made into nano carbon materials and composites to improve the electrochemical performances.The main contents are as follows:1.The honeycomb-like carbonized corncob sponge was obtained by pyrolysis of the corncob sponge,and the effect of the carbonization temperature on the electrochem-ical properties of the carbonized corncob sponge was investigated.Then the carbonized corncob sponge was used as reducing agents to prepare carbonized corncob sponge/Mn O₂ composite by hydrothermal reaction with KMn O₄.Under different hy-drothermal reaction conditions,the Mn O₂ formed on the carbon surface had different structure and morphology,and the electrochemical performance also changed conse-quently.The resulting carbonized corncob sponge/Mn O₂ sample had a maximum spe-cific capacitance of 161.7 F·g^-1(1 A·g^-1),which was further assembled with commer-cial activated charcoal to form an asymmetric capacitor.At a high power density of2466.2 W·kg^-1,the energy density of the capacitor was 4.0Wh·kg^-1.And the capaci-tance retention reached 92.3%over the 1,000-cycle test.2.The corncob sponge was soaked in a multi-walled carbon nanotube/ethylene-vinyl acetate（CNT/EVA）dispersion to produce a corncob sponge/CNT/EVA compo-site carbon source.Taking use of the pro-carbonization effect of CNT and soft template effect of surfactant,the composite carbon source was converted into a carbon material with a carbon nano bowl array structure after a one-step heat treatment.This carbon nano bowl array structure endowed the resulting material with a larger specific surface area and a higher capacitance.CCP-850-5 sample had a specific capacity of 213.4 F·g^-1(0.5 A·g^-1),and it was assembled into a solid-state capacitor as electrodes,which had an energy density of 0.98Wh·kg^-1 at a high power density of 8000 W·kg^-1 and excellent cycling stability with a capacitance retention of 92.5%over 10,000 cycles.3.A novel N,S co-doped activated carbon material with an ultra-high specific area was produced using tobacco stems as the carbon source,KOH as the activating agents and thiourea as the doping agent.KOH activation resulted in a large number of meso-pores around 2 nm,giving the tobacco stem activated carbon a large specific surface area and double-layer capacitance.The specific surface area of the samples could be up to 3733 m²·g^-1,while the maximum specific capacitance of samples obtained was up to281.3 F·g^-1(1 A·g^-1).The doping of N and S elements could significantly improve the electrochemical properties of the tobacco stem activated carbon,and the specific ca-pacitance could be increased to as high as 422.5 F·g^-1 at the current density of 1 A·g^-1.4.Ni-Co precursors were first grown on the surface of the prepared tobacco stem activated carbon by hydrothermal method.And the precursors were converted into ATC/Ni Co₂O₄ composite and ATC/Ni Co₂S₄ composite by pyrolysis method and hy-drothermal ion-exchange method,respectively.The performance of ATC/Ni Co₂S₄composite was better than that of ATC/Ni Co₂O₄ composite,demonstrating that Ni Co₂S₄ had a more significant effect on the specific capacitance of carbon substrate then Ni Co₂O₄.The performance of ATC/Ni Co₂S₄ composite was also better than pure Ni Co₂S₄ and ATC-3,demonstrating that the ATC substrate and Ni Co₂S₄ can play a complementary role.The specific capacitance of ATC/Ni Co₂S₄ reached 867.6 F·g^-1 at a current density of 1 A·g^-1,and even under a high current density of 10 A·g^-1,the sam-ples still retains a specific capacitance of 531.1 F·g^-1.