Study of graphene composites in supercapacitors

Abstract: Since the discovery of graphene in 2004, research on graphene composites has been hot. This paper reviews the research progress of Polyaniline/graphene and manganese dioxide graphene composites in the electrode materials of supercapacitors and looks forward to the future application of these materials in the electrode materials of supercapacitors.

Xingruiguang; Liyanan

(Rare Earth College, Inner Mongolia University of Science and Technology, Baotou 014010)

Carbon is widely found in nature. In addition to the most well-known graphite and diamond, fullerenes discovered in 1985 and carbon nanotubes discovered in 1991 expanded the family of carbon materials. It also gives people a deeper understanding of the diversity of carbon. At the same time, the nanotechnology induced by fullerenes and carbon nanotubes has great significance for the development of human society in the future. As the latest member of the carbon material, graphene is a two-dimensional carbon atom crystal with an SP2 hybrid orbit. It was discovered by Geim of the University of Manchester in the United Kingdom in 2004 and can be stable. This is currently the world's thinnest material-monatomic thickness material. Graphene not only has excellent electrical properties(electron mobility up to 200000 cm2V-1s-1 at room temperature), light mass, good thermal conductivity(5000 Wm-1K-1), larger than the surface area(2630m2g-1), Its Young's modulus(1100 GPa) and fracture strength(125 GPa) are also comparable to carbon nanotubes, and they also have some unique properties, such as quantum Hall effect, quantum tunneling effect, and so on. Due to the above unique Nanostructures and excellent performance, graphene can be applied to many advanced materials and devices, such as thin film materials, energy storage materials, liquid crystal materials, and mechanical resonators. Graphene is a single layer of graphite, and the raw materials are easy to obtain, so it is cheap and not as expensive as carbon nanotubes. Therefore, graphene is expected to replace carbon nanotubes as high-quality fillings for polymer-based carbon nanocomposites. Among the many properties of graphene, the specific surface area is high and the conductivity is good. The most important thing is that the capacitance of graphene itself is 21μF/cm2, which reaches the upper limit of all carbon-based electric double layer capacitors, which is higher than other carbon materials. It is an ideal material for making supercapacitors.

Supercapacitors, also known as electrochemical capacitors, are a new type of energy storage device with an energy density and power density between conventional capacitors and batteries. Supercapacitors combine the advantages of batteries and conventional capacitors. Such as high energy density, high power density, fast charging and discharging, long cycle life, with instantaneous high current discharge and no pollution to the environment and other characteristics, it is a new type of energy storage and energy conservation equipment developed in the past decade.

Since graphene is an ideal Super capacitor filling material, it is of great concern to prepare Super capacitor materials by Compounding it with other materials.

There are two main types of composites. The first is the composite of graphene with polymer conductive materials, of which graphene and polyaniline composites are the most studied. The second is the compound of graphene with metal oxides, of which graphene and manganese dioxide composites are the most studied. This paper makes a brief summary of the research on these two kinds of composites.

Graphene and polyaniline composites are used in supercapacitor materials. In addition to the special properties of graphene mentioned above, polyaniline has the advantages of high conductivity, easy synthesis, and low monomer cost. Zhao et al. prepared polyaniline/graphene composites using in-situ polymerization under acidic conditions. It was found that polyaniline was evenly adsorbed on the surface of graphene, or evenly dispersed between graphene sheets. When the current density was 0.1 A/g, the capacitance was as high as 480F/g, and it has a good circulation.

Li et al. carried out in situ anodic electropolymerizations on graphene sheets to form polyaniline. The obtained composite had a tensile strength of 12.6 MPa and a high and stable electrochemical capacitance (weight specific volume 233 F/g, volume specific volume 135 F/ Cm3), which surpasses many other currently available carbon-based flexible electrodes, and therefore has great promise in flexible supercapacitors.

Shi et al. first combined chemically modified graphene with polyaniline fibers to form a stable mixture, and then obtained graphene/polyaniline fiber thin-film composites through vacuum filtration, where polyaniline fibers were evenly dispersed between graphene interlayers. The composite material has stable mechanical properties and high flexibility and can bend at a large angle to get the desired shape. When the modified graphene content is 44 %, the capacitance is the largest, 210F/g.

Yan et al. reported that the composite paper of polyaniline and graphene was obtained by a simple and rapid mixture of solutions and in situ polymerization. This composite material has good electrical properties. It is worth mentioning that this composite paper is in the biological field. Potential application value. Wei et al. combined functional graphene with polyaniline nanoparticles to obtain a 1046F/g capacitor, which is almost twice that of pure polyaniline materials.

The second is the compound of graphene and metal oxides, of which the most studied is the composite material of graphene and manganese dioxide. Wei et al. mixed potassium permanganate with graphene, reduced potassium permanganate to manganese dioxide by microwave radiation, and reduced manganese dioxide were deposited on the surface of graphene. Such a composite material was used as an anode, and activated carbon was used as a cathode to obtain a capacitor. 114F/g,

The number of cycles can reach 1000 times to get a supercapacitor. Yang et al. obtained a multi-layer polydiallyldimethylammonium chloride-modified composite of monetite and manganese dioxide by self-assembly method with higher capacitance and higher cycle times.

In summary, with the continuous progress of society, the continuous consumption of resources, and the continuous development of the economy, graphene composites will surely play an extremely important role in the future electronic field.

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