Ultracapacitors

Here's a guest article that Olan Dantes from Farnell sent us, regarding Graphene and Super Capacitors:

Electronic devices can become smaller and smaller to the point that it becomes invisible to the naked eye. But no matter what size they can have, they will still produce a lot of heat. The interconnecting wires as well as the multitude of transistors inside these devices at nano and micro scales are more than capable of creating heat spots. There could have been nothing wrong with the produced heat if it didn't induce damage.

Electrograph is a new EU-funded three-years project that aims to develop graphene-based electrode materials for supercapacitors. The development target is a combination of graphene and graphene-based material as electrode materials, and use of room temperature ionic liquids (RTILs) as electrolyte. At the end of the project the performance of those materials is to be demonstrated in the functional model of supercapacitor. The project is led by the Fraunhofer Institute.

Scientific and Technical Goals:

• Production of graphene in volumes required and with properties adjusted for novel electronic components (electrodes/supercapacitors).
• To establish a feedback between material properties and design parameters.
• Optimizing overall performance of supercapacitors.
• To present a functional model of supercapacitor.
• Assessment of hazard and exposure associated with graphene materials as well as their life cycle impact.
• To identify the potential for value recovery from graphene electrodes.

Researchers from Stanford discovered that dipping super capacitor electrodes in a carbon nanotube solution can increase the charging capacity by up to 45%. The electrodes were made by a composite graphene and manganese oxide, and it turns out that the thin coating of more conductive material greatly boosted the capacitance of the electrodes.

Researchers from the National Institute for Materials Science managed to dramatically increase the energy density of supercapacitors - using a new electrode in which graphene nanosheets are stacked in a layered structure with carbon nanotubes sandwiched between the graphene layers.

The researchers designed and developed a graphene-based composite structure, in which graphene is used as the base material of the capacitor electrodes and carbon nanotubes (CNT) are inserted between the graphene sheets. In this structure graphene offers a far larger specific surface area (2630 m2/g) than the conventional materials and the CNTs function as spacers as well as conducting paths to enable adsorption of a larger quantity of electrolyte ions on the graphene surface. With this graphene-CNT composite as the capacitor electrodes, Professor Tang has obtained a high energy density of 62.8 Wh/kg and output power density of 58.5 kW/kg using organic electrolyte. By using an ionic liquid as the electrolyte, they have achieved an energy density of 155.6 Wh/kg, which is comparable to that of nickel metal hydride batteries.

Nanotek Instruments and its subsidiary Angstron Materials developed a new graphene-based energy storage device - something between a battery and a supercapacitor. The new device is called graphene surface-enabled lithium ion-exchanging cells, or surface-mediated cells (SMCs).

Nanotek says that even the first generation devices (which aren't optimized yet) feature fast recharge cycles - and already outperform both supercapacitors and lithium-ion batteries. Recharge time is 10 times faster than supercapcitor and 100 times faster than lithium ion while energy capacity is the same as Li-ion batteries and 30 times higher than conventional supercapacitors.

Stacking several separate layers of graphene is useful for several applications, such as supercapacitors. But stacked graphene forms a graphite-like mass, which makes it less useful. Researchers from Monash University in Australia discovered that keeping graphene wet can keep it from stacking.

The team got their idea from examining Graphene Paper - which is made by filter graphene suspended in water. The water acts as a spacer between the individual graphene layers.

Energy storage maker Maxwell Technologies said it received more than $500,000 in state and federal (US) funding for energy storage research and development programs. One of these programs is a testing and evaluation project of new graphene material produced by Nanotek Instruments. These testing are performed to determine how graphene might be used to increase the energy density of ultracapacitors.