Graphene supercapacitors

Graphene is a thin layer of pure carbon, tightly packed and bonded together in a hexagonal honeycomb lattice. It is widely regarded as a “wonder material” because it is endowed with an abundance of astonishing traits: it is the thinnest compound known to man at one atom thick, as well as the best known conductor. It also has amazing strength and light absorption traits and is even considered ecologically friendly and sustainable as carbon is widespread in nature and part of the human body.

Graphene is often suggested as a replacement for activated carbon in supercapacitors, in part due to its high relative surface area (which is even more substantial than that of activated carbon). The surface area is one of the limitations of capacitance and a higher surface area means a better electrostatic charge storage. In addition, graphene based supercapacitors will utilize its lightweight nature, elastic properties and mechanical strength.

Graphene-based supercapacitors are said to store almost as much energy as lithium-ion batteries, charge and discharge in seconds and maintain all this over tens of thousands of charging cycles. One of the ways to achieve this is by using a a highly porous form of graphene with a large internal surface area (made by packing graphene powder into a coin-shaped cell and then dry and press it).

What are supercapacitors?

Supercapacitors, also known as EDLC (electric double-layer capacitor) or Ultracapacitors, differ from regular capacitors in that they can store tremendous amounts of energy.

A basic capacitor usually consists of two metal plates, separated by an insulator (like air or a plastic film). During charging, electrons accumulate on one conductor and depart from the other. One side gains a negative charge while the other side builds a positive one. The insulator disturbs the natural pull of the negative charge towards the positive one, and that tension creates an electric field. Once electrons are given a path to the other side, discharge occurs.

Supercapacitors also contain two metal plates, only coated with a porous material known as activated carbon. They are immersed in an electrolyte made of positive and negative ions dissolved in a solvent. One plate is positive and the other is negative. During charging, ions from the electrolyte accumulate on the surface of each carbon-coated plate. Supercapacitors also store energy in an electric field that is formed between two oppositely charged particles, only they have the electrolyte in which an equal number of positive and negative ions is uniformly dispersed. Thus, during charging, each electrode ends up having two layers of charge coating (electric double-layer).



Supercapacitor design

Batteries and Supercapacitors

Unlike capacitors and supercapacitors, batteries store energy in a chemical reaction. This way, ions are inserted into the atomic structure of an electrode, instead of just clinging to it like in supercapacitors. This makes supercapacitors (and storing energy without chemical reactions in general) able to charge and discharge much faster than batteries. Due to the fact that a supercapacitor does not suffer the same wear and tear as a chemical reaction based battery, it can survive hundreds of thousands more charge and discharge cycles.

Supercapacitors boast a high energy storage capacity compared to regular capacitors, but they still lag behind batteries in that area. Supercapacitors are also usually more expensive per unit than batteries. Technically, it is possible to replace the battery of a cell phone with a supercapacitor, and it will charge much faster. Alas, it will not stay charged for long. Supercapacitors are very effective, however, at accepting or delivering a sudden surge of energy, which makes them a fitting partner for batteries. Primary energy sources such as internal combustion engines, fuel cells and batteries work well as a continuous source of low power, but cannot efficiently handle peak power demands or recapture energy because they discharge and recharge slowly. Supercapacitors deliver quick bursts of energy during peak power demands and then quickly store energy and capture excess power that's otherwise lost. In the example of an electric car, a supercapacitor can provide needed power for acceleration, while a battery provides range and recharges the supercapacitor between surges.

Supercapacitor vs Battery charge times

Common supercapacitor applications

Supercapacitors are currently used to harvest power from regenerative braking systems and release power to help hybrid buses accelerate, provide cranking power and voltage stabilization in start/stop systems, backup and peak power for automotive applications, assist in train acceleration, open aircraft doors in the event of power failures, help increase reliability and stability of the energy grid of blade pitch systems, capture energy and provide burst power to assist in lifting operations, provide energy to data centers between power failures and initiation of backup power systems, such as diesel generators or fuel cells and provide energy storage for firming the output of renewable installations and increasing grid stability.

Rivaling materials

Several materials exist that are researched and suggested to augment supercapacitors as much (or even more than) graphene. Among these materials are: hemp, that was used by Canadian researchers to develop hemp fibers that are at least as efficient as graphene ones in supercapacitor electrodes, Cigarette filters, which were used by Korean researchers to prepare a material for supercapacitor electrodes that exhibits a better rate capability and higher specific capacitance than conventional activated carbon and even higher than N-doped graphene or N-doped CNT electrodes.

Graphene supercapacitors commercialization

Graphene supercapacitors are already on the market, and several companies, including Skeleton Technology, the CRRC, ZapGoCharger, Angstron Materials and Sunvault Energy are developing such solutions. Read our Graphene Supercapacitors market report to learn more about this exciting market and how graphene will effect it.

Graphene supercapacitors market report

Further reading

Latest Graphene Supercapacitors news

Zap&Go awarded with $1.6 million from the EU to continue development of its graphene supercapacitor enhanced power tools

May 23, 2017

UK-based graphene supercapacitor developer Zap&Go announced that it was awarded with a $1.6 million USD from the European Union to perfect the prototype cordless tools powered by its fast-charging graphene supercapacitors.

ZapGo graphene supercapacitor powered tool prototype (PE Europe 2017)

Zap&Go initiated a self-funded feasibility study to embed its graphene supercapacitors in cordless tools. The company says that it has received commitments from major OEMs in joint development agreements. In this new EU-funded project, Zap&Go intends to further develop its power modules and electronics, integrating them with cordless tools such as vacuum cleaners and power drills, and finally build units to conduct customer trials.

Graphene supercapacitors minimize the need for pacemaker surgeries

May 18, 2017

Researchers from Egypt and the United States have reportedly created ultrathin, biocompatible supercapacitors that can be used as efficient and long-lasting power sources for implantable devices such as pacemakers, brain stimulators and more.

The scientists made the supercapacitors using graphene, a muscle protein and biofluids as electrolytes. The team reports that such supercapacitors can power pacemakers for a long time by utilizing protein and biofluids available in the body, reducing the need to perform surgery to replace drained power sources.

Graphene Handbook

Gas can turn laser-induced graphene superhydrophilic or superhydrophobic

May 17, 2017

Researchers at Rice University, who invented laser-induced graphene (LIG), in collaboration with researchers at Ben-Gurion University in Israel, have designed a way to make the spongy graphene either superhydrophobic or superhydrophilic.

Rice's superhydrophillic LIG image

Until recently, the Rice lab made LIG in open air only, using a laser to burn part of the way through a flexible polyimide sheet to get interconnected flakes of graphene. However, putting the polymer in a closed environment with various gases changed the product’s properties. Forming LIG in argon or hydrogen makes it superhydrophobic (extremely water-avoiding), a property highly beneficial for separating water from oil or de-icing surfaces. Forming it in oxygen or air makes it superhydrophilic (extremely water-attracting), making it highly soluble.

Malaysia's KTMB purchases electric trains with graphene-based supercapacitors

Apr 18, 2017

The Ministry of Transport, national operator KTMB in Malaysia and China's CRRC Zhuzhou Locomotive have signed a €180 million contract for the supply of 22 electric multiple-units of two types.

The order includes 13 EMUs with a capacity of more than 500 passengers, with a maximum speed of 100 km/h. These are said to be equipped with CRRC's graphene-based supercapacitors. CRRC said the 60 kF capacity energy storage would enable 85% of the braking energy to be recovered for use when accelerating.

Updates from Prof. James Tour's graphene lab at Rice University

Apr 09, 2017

Prof. James Tour's research lab in Rice University is one of the leading graphene research groups in the world, with several key technologies first discovered and developed there. Professor Tour is involved with several application areas - from de-icing coating to energy storage and quantum dots production. Prof. Tour was kind enough to share his time and update us on the latest research and commercialization efforts at his lab.

rice university laser process supercapacitor image

The Tour group is now commercializing two of its key technologies. First up is the laser-induced graphene (or LiG), which was reported first in 2014. This is a process in which graphene is formed on a flexible polyimide film using a room-temperature laser-based process. It is possible to pattern this graphene to create devices and as it is formed on a flexible film this easily enables flexible electronics applications.