There’s been lot of hype about graphene since 2004, when it was first discovered and hailed as one of the most important breakthroughs in materials since the plastics revolution a century ago. But since its introduction, graphene still hasn’t hit any truly mainstream products that we can see in our daily lives. But that’s starting to change. One product that was just recently announced could make a big impact in the renewable energy market. Let’s revisit graphene, supercapacitors, and when and where it’s going to start making an impact.
Almost two years ago I produced a video on graphene, discussing why it was taking so long for it to come to market. About a year ago I made another video on supercapacitors and if they might be the future of energy storage. I always try to keep perspective and reiterate that these things take time to go from lab to commercial and mass produced products. And when it comes to graphene … we’re still waiting. But just recently one of the companies I highlighted in my supercapacitor video, Skeleton Technologies, is finally delivering on the graphene promise.
But before diving straight into that, it’s a good idea to take a look at what supercapacitors (or ultracapacitors) are, why they’re important, and how graphene plays a roll in all of this.
Both batteries and capacitors are a method of storing energy, but lithium-ion batteries rely on chemical reactions to store and release their energy. They’re made up of a positive and negative side, which are called the cathode and anode. Those two sides are submerged in a liquid electrolyte and are separated by a micro perforated separator, which only allows ions to pass through. When the battery charges and discharges, the ions flow back and forth between the cathode and anode. During this process the battery is heating up, expanding and contracting. These reactions degrade the battery over time, giving batteries a limited lifespan. One benefit of battery technology is a very high specific energy, or what most of us refer to as energy density, so it can store a lot of energy for later use.
But capacitors are different, they don’t rely on chemical play in order to function. Instead, they store potential energy electrostatically. It’s basically capturing static electricity. Capacitors use a dielectric, or insulator, between their plates to separate the collection of positive and negative charges building on each plate. It’s this separation that allows the device to store energy and quickly release it1. One benefit of this is that a 3V capacitor now will still be a 3V capacitor in 15 or 20 years2. They don’t last forever, but they’re very consistent. While a lithium-ion battery may lose voltage capacity over time and with use. And unlike a battery, a capacitor has a much higher power capacity, which is how much power it can take or give at once. Think of it like water flowing through a hose. Capacitors have a very wide diameter hose, so they can charge and discharge in a fraction of the time … but they have a very low specific energy. It’s good for bursts of power, but not for storing large amounts for later use.
Supercapacitors kick things up a notch because it’s starting to venture towards a battery’s design and use an electrolyte on either side of an insulator. When current is applied ions build up on either side of the insulator and create a double-layer of charge.3
What makes a supercapacitor truly superior to a normal capacitor, or even a battery in some cases, is the distance between the metal plates. In a normal capacitor the distance is around 10-100 microns (a micron is one-thousandth of a millimeter). But in a supercapacitor that distance is narrowed to one-thousandth of a micron, and that smaller distance leads to a larger electric field — i.e. more energy storage.4 Not to mention, the carbon coated plates on supercapacitors increase the available surface area for storage capacity by up to 100,000 times. That’s a lot more energy available for use than a normal capacitor.
Companies like NAWA Technologies and Skeleton Technologies have been trying to take supercapacitors to the next level by incorporating graphene into the coating of the metal plates. In concept this can expand the conventional use of supercapacitors into markets like components for electric motorcycles, spacecrafts and wave energy technology.5 6
Graphene provides the next generation of supercapacitors with an interesting array of improvements. In particular, graphene offers substantially more surface area, giving supercapacitors even more capacity for energy storage. It’s another step closer to a battery. But in addition to that, graphene is ultralight, has unique elasticity and is incredibly strong.7
But to pump the brakes for a second, what’s graphene? To put it simply, it’s fundamentally a single layer of graphite – the material used to make pencils. But instead of having a three-dimensional crystalline structure like graphite, graphene is basically two-dimensional, meaning it’s just one atom thick, with the atoms arranged in a hexagonal lattice or honeycomb arrangement – a bit like chicken wire.
This structure is important because it allows each carbon atom to be covalently bonded, that is, sharing an electron pair, to three more around it, and the strength of these bonds is one of the main reasons why graphene is so strong and stable8. Another reason is because the electrons can move around more freely9 – and this is what makes graphene so good at conducting electricity and heat. In fact, it’s the most conductive material that we’ve ever come across.
And that’s where Skeleton Technologies recent product announcement comes in because they’re starting to deliver on the big promise of graphene supercapacitors. It’s no longer a question of if a product like this will come to market … it is.
Skeleton Technologies new line of ultracapacitors has a 72% increase in Wh/l compared to their non-graphene version in the same form factor. The new line uses what they call curved graphene. It’s a closely guarded secret for the company, but it was originally developed at Estonia’s University of Tartu in the 1990’s and is essentially tiny, crumpled-up graphene sheets.10 I had a chance to speak to Dr. Sebastian Pohlmann, the Vice President of Automotive & Business Development at Skeleton Technologies, about the product. One of the biggest challenges to bringing the new ultracapacitor to market was producing enough curved graphene.
“… these material developments take a long time and they always present unforeseen difficulties.” -Dr. Sebastian Pohlmann “What normally happens is it works in the lab and you move from synthesizing one gram, so that one teaspoon to maybe 10 grams or a hundred grams. So a little jar of material, and you do that and suddenly, you don’t get the same material that you thought you would get. Your synthesis doesn’t work anymore.” -Dr. Sebastian Pohlmann “…moving from this one gram to the first kilogram, that is the hardest part. And then it gets easier and easier and easier. I’m not saying easy, I’m saying easier.” -Dr. Sebastian Pohlmann
Figuring out how to effectively scale production from 1 gram, to 1 kilogram, to tons of it is a major undertaking. It’s like I mentioned earlier, it takes time to go from lab to mass market product. The hardest part isn’t really figuring out if something will work, but how to produce it at scale.
“…generally it’s easier to come up with concepts to make things better. What is hard is to come up with concepts that make any technology better that are commercially and industrially feasible. So you can come up with a thousand ways to make ultracapacitors better, the same way that you can come up with a thousand ways to make batteries better, but to find that one way to make it better that is cheap and effective and scalable, that is the hard part.” -Dr. Sebastian Pohlmann
So why does this matter? You’re not going to be seeing these ultracapactiors replacing the lithium ion batteries in your cars. Their specific energy is still dramatically lower than a battery, but the power capacity and how much it can deliver at once is where it shines. And they can pair nicely with lithium ion batteries, like helping to run the things in a car you normally don’t see. Things like the 12-Volt board that runs the lights, the autonomous driving function, your AC and more.
“And there, ultracapacitors can help a lot to make the energy storage that is used there, smaller, lighter, and safer. And that’s where curved graphene ultracapacitors specifically can help because they are already much, much smaller, they carry more punch in a smaller form factor. So you just make this whole application cheaper and lighter.” -Dr. Sebastian Pohlmann
Skeleton Technologies current products can be found helping to power major tram-systems in big European hubs like Warsaw and Mannheim.11 12 The higher capacity of the new curved graphene products can help save on space and weight.
“If you look at one specific application that we have is on top of trains or light rail trains, where you have ultracapacitors that store the energy when the train breaks and release it when the train accelerates, and that’s an application that can actually save a lot of energy. So in normal operation, that saves around 30% of energy. So today, you have maybe three strings of ultracapacitors on top. With our curved graphene solution, you can take one or two out, and that makes the whole solution lighter and leaves a lot of volume for other things, but also reduces the amount of peripheral systems that you have on that train.” -Dr. Sebastian Pohlmann
But when it comes to things like renewables, supercapacitors play a big roll. Their ultracapacitor modules are already being used in wind turbines to help manage the blade pitch control.13 The new graphene versions can provide the same amount of power and control in fewer modules. That means reduced space, reduced weight, and reduced cost. But supercapacitors also play a very large roll in grid scale energy storage systems.
“I asked my colleague who is actually dealing with all the wind and renewable energy segment and he told me, “Okay, a lot of wind energy is good, but it’s like candy. If you have too much of it, it might be bad because you actually destabilize the grids. If you have too much solar, too much wind, it’s what we are striving for, to have 100% of it, but if you have a 100% of it and we have no energy storage, you lack the foundation.” -Dr. Sebastian Pohlmann “Because ultracapacitors are able to deal with these very short peaks that normally are dealt with by the huge rotating turbines that we have on coal power plants and nuclear power plants and so on. The more you take these out and bring renewable energy in, the more you need reactive power storage, and that’s what ultracapacitors can do.” -Dr. Sebastian Pohlmann
So when are we going to start seeing Skeleton Technologies’ new curved graphene ultra capacitors in the market? Commercial production is currently set for 2023, but they’re sending samples to partners, mainly European customers and automotive OEMs, and getting feedback to make adjustments as they ramp up to full production. But they aren’t stopping there with curved graphene. This is just the beginning for what’s to come and Dr. Pohlmann teased a little bit about what’s coming next.
“…our next steps are using it in the so-called super battery technology, which we have developed over the past five years, basically, which we’re now slowly moving out of the lab into the actual application and industrialization phase, and that is a technology where we increase the energy density even further by combining the curved graphene with a specifically developed chemistry.” -Dr. Sebastian Pohlmann “It basically has 10 times the energy density that you have today in ultracapacitors, but it doesn’t have that power. So it’s filling the gap between the ultracapacitors and the batteries.” -Dr. Sebastian Pohlmann “So you can imagine it like a battery with maybe a fourth of the energy that you normally would have in a battery, but you can charge it in 20 seconds. So it’s something that really covers these 20 seconds to five minute gaps that ultracapacitors are not really good at, but batteries are also not really good at. So you can think about things like supporting fuel cells in the operation, you can think about any hybridization, a lot of grid applications, where you just need to cover a couple of minutes of power passing, a lot of applications in industrial grids where you have 3, 4, 5 minute power peaks that you need to shave off, all these things can be solved by the super battery technology.” -Dr. Sebastian Pohlmann
When it comes to graphene the media hype got a little out of control in the beginning, which set some unrealistic expectations of when we’d start benefiting from its capabilities. Fast forward to today and we’re finally starting to see technologies come to market that have a good chance of making an impact. I’m really excited to see where Skeleton Technologies takes their curved graphene products, and how other products like them will help benefits renewables and other sustainable technologies.
- How does an ultracap work?↩
- SCs vs. Batteries↩
- Machine Design – What’s the Difference Between Batteries and Capacitors?↩
- How UCs work and why they fall short↩
- The Design Museum↩
- New Atlas – Skeleton’s high-power Superbattery is more interesting than we thought↩
- Skeleton Tech – ultracap for wave energy↩
- Graphene based ultracap for ESA↩
- Graphene-based supercaps – explained↩
- Skeleton Technologies to provide ultracapacitor for Warsaw tram system↩
- Skeleton and ESA↩
- Skeleton Tech pitches ultracapacitors as wind turbine control solution↩