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Electrophoresis of Graphene Sheets into Porous Template for high energy density supercapacitor

IP.com Disclosure Number: IPCOM000205699D
Publication Date: 2011-Apr-05
Document File: 2 page(s) / 72K

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Abstract

Supercapacitors can be divided into two main categories based on their mode of energy storage: the redox supercapacitor and electric double-layer capacitors (EDLCs). The EDLCs is the most developed form of electrochemical capacitors and activated carbon is currently the most extensively examined and widely utilized electrode material in EDLCs.
While the power density of supercapacitors is very high, its energy density is still significantly lower than energy density of batteries or fuel cells. One way to increase the energy density is to increase the effective specific surface area (SSA) of the electrode materials. Activated carbon has a high SSA compared to other materials, but its practical value is limited by its mechanical strength. In addition it needs to be mixed with additives such as organic binder and carbon black in order to enhance its formability and electrical conductivity. This however reduces the SSA of active carbon significantly.

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Electrophoresis of Graphene Sheets into Porous Template for high energy density supercapacitor

Idea: Xiaoxiao Dong, Ph.D., CN-Shanghai

Supercapacitors can be divided into two main categories based on their mode of energy storage: the redox supercapacitor and electric double-layer capacitors (EDLCs). The EDLCs is the most developed form of electrochemical capacitors and activated carbon is currently the most extensively examined and widely utilized electrode material in EDLCs.

While the power density of supercapacitors is very high, its energy density is still significantly lower than energy density of batteries or fuel cells. One way to increase the energy density is to increase the effective specific surface area (SSA) of the electrode materials. Activated carbon has a high SSA compared to other materials, but its practical value is limited by its mechanical strength. In addition it needs to be mixed with additives such as organic binder and carbon black in order to enhance its formability and electrical conductivity. This however reduces the SSA of active carbon significantly.

Graphene is a one-atom-thick planar sheet of carbon atoms that are densely packed in a honeycomb crystal lattice. Due to this unique material structure, graphene possesses extraordinarily high SSA and in-plane electrical conductivity. The theoretical SSA of individual graphene sheets is more than twice as high as that of finely divided activated carbon. In addition, in mechanical strength it is comparable
to carbon nanotubes, which can be considered graphene with a twist. Graphene is believed to be a good material for supercapacitor electrodes due to its high surface area to mass ratio and excellent electrical conductivity. However, supercapacitors made out of graphene only are not competitive, because the nanometer scale graphene sheets tend to agglomerate into micron size particles. This inherently reduces the effective contact area between functional graphene sheet and electrolytes. In addition, the agglomeration also leads to randomly orientated graphene sheets causing the electrode's electrical conductivity to be reduced since graphene is only highly conductive into two dimensions.

In a known method the graphene is produced from a reduction of colloid of graphite oxide, a graphene-like, thin sheet with epoxide and hydroxyl groups attached to various sites. The resultant graphene powder contains small particles agglomerated from randomly orientated graphene. These are thin sheets, which can be mixed with binders and pressed into bulk graphene plates. Typically, agglomeration occurs after the reduction of graphite oxide.

It is the graphene sheets sticking on the surface of particles that contributes to electron storage. In other words, graphene sheets inside the particles are insulated from electrolytes and thus do not contribute to electro...