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Study on Composite Electrode Materials of Supercapacitors with Ultrahigh Energy Densities Based on Mesoporous Carbon Support Materials

Author: ZhangJing
Tutor: KangLong；KongLingBin
School: Lanzhou University of Technology
Course: Materials Science
Keywords: Supercapacitor Hybrid capacitor Mesoporous Carbon Nanocomposites Specific capacity Power density Energy density
CLC: TM53
Type: PhD thesis
Year: 2010
Downloads: 415
Quote: 1
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Abstract

The super capacitor is a new green energy storage device, the storage performance of the range between the secondary battery and a conventional capacitor. The main advantage of the super capacitors is the charge and discharge rate, high efficiency; its main drawback is the low energy density. How to improve the energy density of the supercapacitor is imminent. By two effective ways: one is to improve the capacitance value (C) of the electrode material according to to E = 1/2CV2 known, improve the energy density of the super capacitor. The conducted studies show that the performance super capacitors require high performance electrode material, the electrode material is not only required to have the properties of the general materials have solid redox and requires matching of the pore structure and specific surface area. Based on this, the paper has a porous structure, large specific surface area mesoporous carbon CMK-3 as a carrier, was successfully prepared Ni (OH) ₂ / CMK-3, Co. (OH) ₂ / CMK-3 and polypyrrole / CMK-3 three novel composite materials. The three new composite material has a unique porous structure and a large effective specific surface area, high specific capacitance value; way is to increase the capacitor working voltage (V) Another way to improve the energy density of the super-capacitors. To further optimize the potential window of three new composite materials in order to improve the energy density, the composite mesoporous carbon hybrid capacitor. Specific research contents are as follows: (1) will be successfully prepared mesoporous carbon CMK-3 as a carrier, using the liquid phase precipitation method of synthesis of Ni (OH) 2/CMK-3 and Co (OH) 2/CMK- 3 composite electrode materials. XRD, SEM, TEM and BET analysis of the microstructure and morphology of the electrode material. The study showed that: Ni (OH) in ₂ / CMK-3, and Co (OH) 2/CMK-3 composite electrode material having a large specific surface area and graded porous structures. Graded porous structure of the composite material, respectively, the presence of a microporous, mesoporous, macroporous, and the pore structure of the three different scales. Wherein the macroporous structure is piled up by the active material nanosheet formed \phase reactive ion diffusion to the electrode body to provide a conductive path, is conducive to reduce the ion diffusion resistance, so that the ion diffusion rate of speed; addition, CMK-3 mesoporous intramural microporous structure could provide a larger electric double layer capacitor. Composites, nano-sheet-like structure having a large specific surface area, is conducive to the full use of the electrode material is electrically active bit redox reaction occurs, so that the composite material has a very high specific capacitance value of the series. 5mA/cm ^{2 of the current density, Ni (OH) ₂ / CMK-3 (15wt% CMK-3), and Co (OH) 2/CMK-3 (20wt% CMK-3) complexes respectively having 2570 and 753F / g, the ultra-high ratio of capacitance values. CMK-CMK-3 (2) on the basis of (1), the process for the preparation of a surface modified by a chemical oxidative polymerization method will be modified in the different concentrations of HNO ₃ solution 3 (m-CMK-3) as a carrier, with the conductive polymer polypyrrole (PPy) combining the preparation to obtain PPy/m-CMK-3 composites. SEM results show that, of PPy thin layer is coated on the carbon fiber bundle of the carrier m-CMK-3, the composite structure of osteoporosis, was a three-dimensional porous structure, the increase in porosity, permeability improvement, and prompting the active ions in the electrolyte diffusion to the electrode surface and the body fairly, the occurrence of the oxidation-reduction reaction, produce large Faraday pseudocapacitive. m-CMK-3 content of 18 wt%, PPy/m-CMK-3 composites than the capacity of up to 427 F / g. m-CMK-3, three-dimensional porous structure and a large specific surface area and surface activity on the optimize PPy/m-CMK-3 composite material structure from the important role so that the active substance PPy more dispersed, improving the utilization of the PPy. In addition, a good conductor m-CMK-3 carrier will make PPy/m-CMK-3 composite electrode material resistivity decreases further improve the high-power characteristics of the electrodes and electrochemical cycle stability. (3) mesoporous carbon CMK-3 surface modification in the concentrated HNO ₃ solution surface oxygen functional groups to enhance the role of CMK-3 ratio of capacitance to 200 F, 145F / g / g. The introduction of oxygen-containing functional groups CMK-3 is more suitable for high-power supercapacitor applications. Taking into account the potential window of metal oxide and conductive polymer are narrower, and still need to further improve the power characteristics. CMK-3 material excellent conductive properties proposed to mesoporous carbon-based composite cathode surface modified mesoporous carbon negative electrode assembly of hybrid supercapacitor. Tested, based on Ni (OH) 2/CMK-3, Co (OH) 2/CMK-3 and hybrid capacitors PPy/m-CMK-3 composite electrode potential window has been greatly improved, three capacitors in 5mA The charge-discharge current, and its specific capacity for 92.5F / g, 122F / g and 57F / g and. The electrochemical performance improvement due to the large specific surface area and proper pore size distribution CMK-3 as a negative electrode, a nano-composite within a relatively wide potential window can procure unobstructed Faraday reaction, to maintain its excellent capacitive properties. Other hand, the improvement of the potential window a great extent on improving the power density and energy density of the capacitor, especially in a large current density advantage. In addition, three hybrid capacitor has excellent cycle stability, and maintained at 90% or more than the capacitance volume after 1000 cycles.}

Study on Composite Electrode Materials of Supercapacitors with Ultrahigh Energy Densities Based on Mesoporous Carbon Support Materials

Abstract

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