Nickel Hydride No. 5 battery.Research progress of graphene composite materials in supercapacitors?

　　Carbon element widely exists in nature. In addition to the most well-known graphite and diamond, fullerene discovered in 1985 and carbon nanotubes discovered in 1991 have expanded the family of carbon materials. It also gives people a deeper understanding of the diversity of carbon elements. At the same time, nanotechnology triggered by fullerenes and carbon nanotubes is of extremely great significance to the development of human society in the future. As the latest member of carbon materials - graphene is a two-dimensional carbon atomic crystal with sp2 hybrid orbitals. It was discovered by Geim et al. of the University of Manchester in the UK in 2004 and can exist stably. It is currently the thinnest material in the world - Materials one atom thick. Graphene not only has excellent electrical properties (electron mobility can reach 200000cm2V-1s-1 at room temperature), is light in weight, has good thermal conductivity (5000Wm-1K-1), and has a large specific surface area (2630m2g-1), its Young's The modulus (1100GPa) and breaking strength (125GPa) are also comparable to carbon nanotubes, and they also have some unique properties, such as quantum Hall effect, quantum tunneling effect, etc. Due to the above unique nanostructure and excellent properties, graphene can be used in many advanced materials and devices, such as thin film materials, energy storage materials, liquid crystal materials, mechanical resonators, etc. Graphene is a single layer of graphite, and the raw materials are easily available, so it is cheap and not as expensive as carbon nanotubes. Therefore, graphene is expected to replace carbon nanotubes as a high-quality filler for polymer-based carbon nanocomposites. Among the many properties of graphene, including high specific surface area and good conductivity, 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 and is higher than other carbon materials. , is an ideal material for manufacturing supercapacitors.

　　Supercapacitors (Supercapacitors), also called electrochemical capacitors (Electrochemical capacitors), are a new energy storage device with an energy density and power density between traditional capacitors and batteries. Supercapacitors have the advantages of batteries and traditional capacitors, such as energy It has the characteristics of high density, high power density, fast charge and discharge, long cycle life, instantaneous large current discharge and no pollution to the environment. It is a new type of energy storage and energy-saving equipment developed in the past ten years.

　　Since graphene is an ideal filling material for supercapacitors, combining it with other materials to prepare supercapacitor materials has attracted much attention.

　　There are two main types of composite materials. The first is the composite of graphene and polymer conductive materials. Among them, the most studied is graphene and polyaniline composite materials. The second type is a composite of graphene and metal oxides, of which the most studied is graphene and manganese dioxide composites. This article mainly provides a brief review on the research on these two composite materials.

　　Graphene and polyaniline composite materials 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 composite materials using in-situ polymerization under acidic conditions and found that polyaniline was uniformly adsorbed on the surface of graphene or evenly dispersed between graphene sheets at a current density of 0.1A/ g, the specific capacitance is as high as 480F/g and has good cycleability.

　　Li et al. performed in-situ anodic electropolymerization on graphene sheets to generate polyaniline. The resulting composite material has a tensile strength of 12.6MPa and a high and stable electrochemical capacitance (weight specific volume is 233F/g and volume specific volume is 135F/g). cm3), exceeds many other carbon-based flexible electrodes now available and therefore holds great promise in flexible supercapacitors.

　　Shi et al. first formulated a stable mixture of chemically modified graphene and polyaniline fibers, and then obtained graphene/polyaniline fiber film composites through vacuum filtration. In these films, polyaniline fibers were evenly dispersed between graphene interlayers. , the composite material has stable mechanical properties and high flexibility, and can be bent at a large angle to obtain the desired shape. When the content of modified graphene is 44%, the capacitance is the largest at 210F/g.

　　Yan et al. reported that a composite paper of polyaniline and graphene was obtained through a simple and rapid solution mixing and in-situ polymerization method. This composite material has good electrical properties. It is worth mentioning that this composite paper has great application in biology. The field has potential application value. Wei et al. composited functionalized graphene and polyaniline nanoparticles to obtain a capacitance of 1046F/g, which is almost twice that of pure polyaniline materials.

　　The second type is a composite of graphene and metal oxides, of which the most studied is a composite of graphene and manganese dioxide. Wei et al. mixed potassium permanganate with graphene and used microwave radiation to reduce potassium permanganate into manganese dioxide. The reduced manganese dioxide was deposited on the surface of graphene. This composite material was used as the anode and activated carbon was used as the cathode. The capacitance is obtained to be 114F/g,

　　Supercapacitors that can cycle up to 1,000 times. Yang et al. obtained a multi-layer polydiallyldimethylammonium chloride-modified graphene and manganese dioxide composite material through a self-assembly method, which has high capacitance and high cycle times.

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