The Institute of Physics made new progress in the research of carbon nanotube thin film supercapacitors

Recently, the "Nanomaterials and Mesoscopic Physics" research group of Advanced Materials and Structure Analysis Laboratory of Institute of Physics, Chinese Academy of Sciences / Beijing National Laboratory for Condensed Matter Physics (Preparation) proposed a simple structure, light weight, high energy density and high power density Carbon nanotube film compact supercapacitor and preparation method thereof. Related research results were published in Energy & Environmental Science (2011, 4, 1440).

The development of energy storage devices with long cycle life, high specific energy and high power density has always been one of the hot topics concerned by researchers in many fields. With the development of social technology, the requirements for power supply in many fields, such as electric vehicles, have greatly increased, and have far exceeded the battery's ability to withstand. Although the power of the traditional capacitor is very large, its energy density is limited, and it cannot meet the actual needs. Supercapacitors, also called electrochemical capacitors, have performances between traditional capacitors and batteries, and have the characteristics of high specific energy of batteries and high specific power of traditional capacitors. Supercapacitors have important applications in hybrid vehicles, high-power radars, mobile phone information backup power supplies, laptop computers and batteryless remote controls. With the development of portable electronic devices, the traditional way of assembling supercapacitors has been far from satisfying the development of current electronic devices. Supercapacitors are developing in the direction of lightness and simplicity.

Carbon nanotubes have a high specific surface area and electrical conductivity and are an ideal electrode material for supercapacitors. At present, mainly by mixing carbon nanotubes with a conductive polymer, and then applying the mixture to a conductive substrate or directly depositing a pure carbon nanotube film on the substrate as an electrode material. However, the addition of polymer will reduce the conductivity and porosity of the carbon tube thin-film electrode, which will adversely affect the transfer of charge in the electrode and the diffusion of ions in the electrolyte pores in the electrolyte, resulting in a decrease in the power density of the supercapacitor. However, the pure carbon nanotube film has high conductivity and porous structure, can effectively overcome the influence of the conductive polymer on the electrode, and can be directly used as the electrode material of the supercapacitor. However, the above two types of carbon nanotube electrodes have to be laid flat on metal foils or other substrates. The use of the substrate will increase the weight of the supercapacitor, and the flexibility of the metal foil or other substrates is poor. Therefore, the current carbon nanotube-based supercapacitor is still a traditional button structure, that is, a sandwich structure. How to use carbon nanotubes to construct high-performance compact supercapacitors is a development direction of carbon nanotube supercapacitors in the future.

The Nanomaterials and Mesoscopic Physics Research Group of the Institute of Physics has been devoted to the research of carbon nanotube film preparation, physical properties and application foundation for many years, and has achieved a series of results (Nano. Lett. 2007, 7, 2307; Adv. Mater. 2009, 21 , 603; Nano. Lett. 2009, 9, 2855). Recently, Dr. Niu Zhiqiang, Researcher Zhou Weiya, and Academician Xie Sishen of the research group cooperated with Dr. Chen Jun of Institute of Intelligent Polymers, University of Wollongong, Australia, and Dr. Li Hong, Researcher of Clean Energy Laboratory E01, Ph.D. Supporting the characteristics of high conductivity, high mechanical properties, and high self-adsorption of flexible carbon nanotube films, a simple carbon nanotube film supercapacitor with simple structure, light weight, high energy density and power density and its preparation are proposed method.

They used the organic solution tiling method to control the self-adsorption of directly grown carbon nanotube films, and assembled any number of carbon nanotube films very flatly and firmly onto the membrane of the supercapacitor, effectively reducing carbon nanotubes. The connection resistance between the films is helpful to improve the power density of the carbon nanotube film electrode. Moreover, this method breaks through the limitations of the directly grown carbon nanotube film area and thickness in the preparation of thin-film electrodes, and is expected to address the demand for the electrode material area and thickness of large-capacity carbon nanotube supercapacitors. They used the carbon nanotube film with regular size and surface shape obtained by the above method directly as electrode material and current collector, and assembled into a high-performance compact supercapacitor by winding. This design and assembly technology not only effectively eliminates the contact resistance between the carbon nanotube film and the metal current collector, but also simplifies the structure of the supercapacitor and reduces the weight of the supercapacitor, which is practical for the carbon nanotube film supercapacitor. Application is of great significance.

The experimental results show that the compact supercapacitor exhibits ideal electric double layer capacitance behavior, and exhibits a good current response when the potential is reversed. The charge and discharge efficiency of the carbon nanotube thin film supercapacitor reaches 99%, and the calculated quality The specific capacitance is 35 F / g, the energy density is 43.7 Wh / kg, and the maximum power density is 197.3 kW / kg. This is much greater than the energy density (1-10 Wh / kg) and power density (2-10 kW / kg) of conventional supercapacitors currently made with activated carbon materials. In addition, the compact supercapacitor also exhibits excellent frequency characteristics.

This work was supported by relevant projects of the Chinese Academy of Sciences, the National Natural Science Foundation of China, the Ministry of Science and Technology and the Beijing Municipal Education Commission.

Figure 1 Schematic diagram of the preparation process of a simple supercapacitor of carbon nanotube film

Fig. 2 (a) Optical photo of the flat carbon nanotube diaphragm; (b) Optical photo of the winding process of the flat carbon tube diaphragm; (c) Optical photo of the simple supercapacitor with carbon nanotube film; (d) Carbon nano An optical photo of an example of a tube thin film supercapacitor providing power to a device.

Figure 3 (a) CV curves of carbon nanotube thin film supercapacitors at different scanning rates; (b) specific capacitance of carbon nanotube thin film supercapacitors as a function of scanning rate; (c) carbon nanotube thin film supercapacitors 2V Under the charge and discharge curve; (d) Nyquist pattern of carbon nanotube thin film supercapacitor.

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