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

Ionic Industries announces a process for economically mass-producing graphene micro supercapacitors

Sep 11, 2017

Ionic Industries recently announced a process for economically mass-producing graphene micro supercapacitors and added that its directors and key personnel have taken direct stakes in the company.

Ionic Industries' graphene supercapacitors patent image

Ionic stated that since it published the positive results on its graphene micro planar supercapacitors 2 years before, the company has been working toward developing a device that not only demonstrates similar performance but can be produced at scale to deliver an economically viable device.

NSF grant to fund development of inkjet-printed graphene-based water quality sensors

Sep 04, 2017

The National Science Foundation recently awarded University of Wisconsin-Milwaukee scientists $1.5 million to perfect a method of mass-producing graphene-based small water sensors using inkjet printing. The goal is to determine whether the process can be customized in order to scale up production and in a more economic way than traditional manufacturing methods.

Inkjet-printed graphene-based water quality sensors image

The graphene-based sensors, developed at UWM, reportedly outperform current technologies in accuracy, sensitivity and sensing speed. Their performance and size make them useful for continuously monitoring drinking water for miniscule traces of contaminants like lead.

Graphene Handbook

Researchers deem graphene biocompatible and proceed to grow graphene "fuzz"

Aug 19, 2017

Researchers at Carnegie Mellon University have determined that graphene is safe for neurons and non-neuronal cells and has long-term biocompatibility — opening the door for use in devices that interface with the nervous system. Following this new finding, the research team will begin to use graphene with different types of tissues to better understand cell physiology.

In a separate study, the team also found it was possible to grow graphene “fuzz”: a special kind of graphene in 3D. This was achieved by first creating a mesh of nanowires made of silicon, which acted as a surface for the graphene to grow on. Then, the team exposed the mesh to methane plasma, which resulted in carbon separating from the methane and depositing onto the mesh, forming graphene. After using various levels of methane plasma and letting the mesh “cook” for various lengths of time, the research team began to see tiny flakes or “fuzz” of graphene growing off the surface of the silicon nanowires. Unlike previous studies, the graphene was reportedly growing in three dimensions.

Manchester U team prints flexible GO-based supercapacitors on fabrics

Aug 14, 2017

Researchers from The University of Manchester recently demonstrated flexible graphene-based supercapacitors printed directly on to textiles using a simple screen-printing technique.

Manchester U prints GO-supercapacitors on fabrics image

The solid-state flexible supercapacitor device has been demonstrated by using conductive graphene-oxide ink to print onto cotton fabric. The printed electrodes reportedly exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate.

Graphene supercapacitor developer Zap&Go seeks to raise £2 million in an equity crowd-funding campaign

Aug 03, 2017

UK-based graphene and CNT supercapacitor developer Zap&Go launched an equity crowdfunding campaign with an aim to raise £2 million. Note that this is an equity campaign - which means that participants will get shares in the company.

The minimum investment is £10,000. This investment opportunity is open to global investors, but UK investors will qualify for the tax breaks provided by the Enterprise Investment Scheme (EIS). Interested investors should be aware of the risks in investing in a start-up such as Zap&Go of course. For more information please check Zap&Go's campaign page.