Transitioning away from fossil fuels means that electric vehicles will become evermore present. The issue, however, is that these come with their own problems, such as slower charging and sometimes shorter range. That is because EVs need batteries (most commonly Lithium-ion) to store their energy. To solve these problems, improvements in energy storage need to happen. We’re seeing several innovations in battery technology, such as cobalt-free, or sea-water batteries, but one of the most interesting energy storage solutions is graphene supercapacitors.
What are Supercapacitors
Supercapacitors, also known as Ultracapacitors, differ from regular capacitors in that they can store tremendous amounts of energy. Basic capacitors usually consist of two metal plates, separated by an insulator. Whilst 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 then disturbs the natural pull of the negative charge towards the positive one, creating an electric field. To discharge, electrons are given a path to the other side.
Supercapacitors also contain two metal plates (one positive, one negative), only coated with activated carbon. They are immersed in an electrolyte made of positive and negative ions dissolved in a solvent. During charging, ions from the electrolyte accumulate on the surface of each carbon-coated plate. Supercapacitors also store energy in an electric field, 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, each electrode ends up having two layers of charge coating (electric double-layer) during charging.
Supercapacitors vs Batteries
Supercapacitors store energy in an electric field and are what is known as “fast energy storage”. They have high power density, often a 1 000 000 + cycle lifetime and are very reliable. They also have the huge benefit of almost instant charging and discharging.
Batteries, on the other hand, operate based on a chemical reaction, which means they’re classified as “slow energy storage”. They have a high energy density, a 2000-3000 cycle lifetime, but are much slower to charge and discharge.
Because of their super-fast charging and discharging, supercapacitors have a wide range of applications, especially in the automotive industry. For instance, they can be used in regenerative braking or for faster cranking when starting an engine.
Larger supercapacitors can also be used in wind turbines, helping to smooth out the intermittent power supplied by the wind.
Other applications for this technology include supporting the grid, providing fast power in case of a blackout which could mean big losses for companies even if only for a few seconds.
Hybridising Batteries and Supercapacitors
Supercapacitors can already store much more energy than regular capacitors, however, they’re nowhere near the levels of batteries for the moment. But what if we could hybridise the two technologies, creating a super-fast charging, highly energy-dense storage system?
Supercapacitors and batteries work in different ways, one using an electric field and the other a chemical reaction, which makes hybridizing them complicated. Some companies, however, are having some success.
Skeleton Technologies, an Estonian supercapacitor firm, has already developed straightforward supercapacitors which used “curved graphene” for greater energy density.
This, however, was just the start for the Estonian company, as they are now working with the Karlsruhe Institute of Technology, in Germany, to use their technology in what they call a “SuperBattery”
“Cooperation between European energy storage companies is key for the EU to be a global leader in energy storage. We are delighted to have signed the SuperBattery development deal with Karlsruhe Institute of Technology and combine forces to bring to market a technology that will blow existing EV charging solutions out of the water.”Taavi Madiberk, CEO Skeleton Technologies
According to Skeleton, this battery could be charged in just 15 seconds. That coupled with its long lifetime could make the SuperBattery a perfect solution for the three main issues affecting electric vehicles: slow charging times, battery degradation, and range anxiety.
Like Skeleton, NAWA already manufactures supercapacitors. Based in Aix-en-Provence, this French company is using vertically aligned carbon nanotubes (VACNT) in their supercapacitors.
NAWA has now adapted the VACNT plates to operate also as battery-like electrodes, by thinning out the tubes to make room for coating them with the chemicals which batteries employ for their reactions. This also allows for the movement of lithium ions into and out of the spaces between the tubes.
Test have shown that the VACNT electrodes achieved an energy density of 500 wh/kg in one battery, almost double that of traditional lithium-ion batteries.
Whether this device will be a success relies on the cost of manufacturing. According to Ulrik Grape, NAWA’s chief executive, it could be easily integrated into an existing battery production line
Despite supercapacitors being rather unknown compared to traditional batteries, they are a very interesting energy storage solution, that has many applications. However, where this technology can really shine is when combined with traditional batteries to create the ultimate energy storage solution: fast charging, reliability, long life and high energy density. This of course isn’t easy, but if this hybrid battery proves to be viable, it could solve many of the problems which stop EV’s from becoming mainstream.
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