Skeleton's high-power Superbattery is more interesting than we thought

We got it wrong, folks. Working from a scant press release we'd now view as borderline misleading, we looked at the Superbattery from Estonia's Skeleton Technologies and assumed the company was talking about a hybrid power system combining lithium batteries with ultracapacitors – similar to other such arrangements we've written about in the past. And we covered it speculating as such, saying the company's carefully-worded 15-second EV charging claims came across as "possibly a bit disingenuous."

Skeleton got in touch to say no, this is not a hybrid battery/capacitor system, it's "a completely novel energy storage technology on a cell level", and offered us the chance to chat with Dr. Sebastian Pohlmann, the company's VP of innovation.

We had a very interesting chat with Dr. Pohlmann, and while the fast-charging Superbattery categorically won't be replacing the lithium-ion packs powering tomorrow's electric cars, it's a lot more interesting and promising than we originally thought.

Strap in for some battery geekery.

Batteries vs Ultracapacitors: a quick primer

Skeleton's current first-generation product offering is high-end ultracapacitors. According to Pohlmann, the company makes the most power-dense ultracaps available on the market today. Ultracapacitors operate a little like batteries in that they store electrical charge, but where batteries use a chemical reaction to store and release charge, capacitors store energy in an electric field.

As a result, capacitors can capture and release energy very quickly – near enough to instantly for practical purposes. That gives them an outstanding power density, a metric relating to maximum power input and output per weight. An electric car powered by ultracapacitors could charge up in a matter of seconds, and a relatively small pack could provide enough instant energy for you to really drop the hammer on a powerful drive system.

It wouldn't go very far, though, because ultracapacitors have terrible energy density when compared to lithium batteries. Where power is the rate of charge or discharge, expressed in watts, energy is the total amount of energy stored, expressed in watt-hours, and the much slower chemical processes that store energy in lithium-ion batteries let them store vastly more energy per weight than an ultracapacitor. Thus, lithium-powered EVs can offer a usable range, but tend to take ages to charge up.

Ultracapacitors give you as much as 60 times more power density than lithium-ion batteries, plus they work much better in extreme temperatures and can handle upwards of a million cycles, giving them much longer lifespans. The current Tesla Model 3 battery, though, can store about 37 times as much energy per weight as the best ultracaps on the market today, and that's the key reason why they continue to get all the EV gigs.

Skeleton has a second-gen product coming out sometime soon, called the SkelCap, that uses "curved graphene" to vastly increase the surface area of its electrodes, and Pohlmann says these devices will "have up to two times higher energy density compared to even the most advanced cells produced by our competitors." That's big news in the ultracapacitor world, but we're still only talking 15 watt-hours per kilogram, where a Tesla battery stores about 260 Wh/kg, with that figure set to rise significantly.

What's "curved graphene?"

It's a slightly dodgy name, for starters. Graphene is a form of carbon – a flat, single-layer sheet of carbon atoms locked together in a hexagonal honeycomb shape. It's a next-gen supermaterial with extraordinary properties that would revolutionize all sorts of industries if only anybody could work out how to produce it cheaply and in bulk.

"Any physicist will tell you that curved graphene does not exist," says Pohlmann; "graphene is always a flat sheet, that's the definition of graphene. Curved graphene, in that sense, is not graphene by definition. But it has the same hexagonal structure. It's like a sheet that's been crumpled up like a balled-up sheet of paper. So you've still got the same surface area of that sheet, and it's still accessible to the air around it. So it's very close to the structure of regular graphene, but you can use it better in certain applications."

Curved graphene is the single, closely guarded piece of IP at the core of Skeleton's business. Developed at Estonia's University of Tartu in the 1990s, and now refined into a secretive, low-cost, industrial-scale mass-manufacturing process by Skeleton, curved graphene is a black powder made up of tiny, crumpled-up graphene sheets.

It's not as ludicrously conductive as graphene, but it's still much more conductive than the typical activated carbon back powders used in electrodes. That ease of conduction explains how Skeleton claims "the power density of SkelCap ultracapacitors exceeds competitors' products by a factor of four." Low resistance also makes for higher efficiency, with "up to five times less energy lost to heat."

And because each particle is scrunched up instead of being a flat sheet, they can't stack up on top of one another. In an ultracapacitor electrode, where a greater surface area immediately increases your energy density, these balled-up sheets offer much more usable surface area than flat graphene. That explains how the second-gen SkelCaps will double their competitors' storage capacities.

Pohlmann won't be drawn too far on how the company makes this curved graphene, other than to say that it's "very different to the production of regular graphene ... Much easier. You put in bulk material and you get out a bulk material. It doesn't come out dispersed in a liquid ... The input materials are industrially available and very cheap all over the world, you can do that synthesis in Europe, Asia or the US, no problem."

The input materials, he stresses, do not include graphite; a significant point given that graphite is primarily mined in China and Australia, and Europe doesn't have a lot of naturally-occurring graphite.

So what is Skeleton's Superbattery?

After all that hefty preamble, we can finally discuss the Superbattery. At its heart, it can be described as being similar to one of these SkelCap ultracapacitor designs, but with its curved graphene electrodes flooded with a chemical electrolyte. Again, this electrolyte is somewhat of a secret sauce, and Pohlmann says "it's not the classic lithium-ion cell chemistry, it's something we developed specifically to work with the curved graphene."

The chemical electrolyte vastly boosts energy density, bringing it up to around 60 Wh/kg at the cell level, and the huge, crumpled surface area of the curved graphene in the electrodes enables charge to get in and out quickly, so power density is at least 10 times greater than a lithium battery. Indeed, it packs an even bigger immediate punch: "The power density in the first moments of charge or discharge is very similar to that of a typical ultracapacitor," says Pohlmann. "In the following 10 minutes, you still have a significantly higher power density than a high-powered lithium-ion battery. It's still in the ultracapacitor range, but maybe 5-6 times reduced power density."

So you end up with a new type of battery somewhere in between lithium and ultracaps, with 10 times the energy density of a current-gen ultracapacitor but a much greater ability than lithium to deliver large spikes of power quickly, as well as a longer lifespan thanks to reduced heat and resistance.

Which brings us back to our problems with that original press release, part of which read "extra fast charging time coupled with charging cycles counted in hundreds of thousands make the SuperBattery a perfect solution for the three main issues affecting electric vehicles: slow charging times, battery degradation, and range anxiety."

The Superbattery might be able to charge super quickly, in the range of 15 seconds, and it might last through hundreds of thousands of cycles, but its energy density is far too low to make it practical as an EV drive system. You'd need four times the weight of a battery to deliver a comparable range to what lithium can deliver.

And this, says Pohlmann, was never what it was designed for.

What's the Skeleton Superbattery useful for, if not EV powertrains?

For Pohlmann, it all comes down to discharge event times. "The Superbattery is a new cell-level development which allows you to fill the energy/power gap that exists in the energy storage market today," he says. "Lithium-ion batteries normally have an issue with high-powered charge/discharge events that last shorter than 5-10 minutes.

"Ultracapacitors, on the other hand, are high power storage devices, but they don't make any sense if you have charge or discharge events longer than 60 seconds – you'd need to pay too much for your system, you'd be better off paying more for your lithium-ion system and oversizing it. So that gap between 60 seconds and 10-15 minutes is filled by overscaled lithium batteries, but rather poorly."

One area where he expects the Superbattery to make a quick impact is in the 12-volt "board net" electrical systems that still run the air con, the windows, the stereo, the infotainment, the heating and all the other bits of a car that need power outside the powertrain itself. In most cars – indeed, amusingly even in Teslas – this role is filled by a lead-acid battery, and when those fail, which most certainly happens, the car stops working altogether.

"If you check the Tesla forums for complaints," says Pohlmann, "you'll find a lot of complaints about these lead-acid batteries. It's a classic problem that's not going away. It's less often an issue in electric cars, but it's still an issue. So we see this as a valuable replacement technology for lead-acid batteries."

Upcoming environmentally-focused EU regulations, says Pohlmann, will likely soon start putting pressure on automakers to find alternatives to lead-acid batteries, and the Superbattery is designed to fit that niche perfectly.

It will also play a part, says Pohlmann, in the next-generation 48-volt board net and starter/generator systems that are starting to crop up in cars now. These things can apply enough torque to the motor to act as mild hybrids, reducing fuel consumption and emissions as much as 20% without requiring people to pay for the large battery packs associated with plug-in hybrids.

In these applications, says Pohlmann, "you don't want a big battery, you don't have a requirement for long, drawn-out battery use. You need an energy storage device that can quickly react to the application it's powering." The Superbattery is tailor-made to suit the job.

What's more, hydrogen fuel cells are no good at quickly regulating how much power they're putting out, so fuel cell vehicles always need a buffer battery between the hydrogen system and the powertrain.

"Again, you don't need it for range, it's just for power peaks," says Pohlmann. "And in that situation, the Superbattery is able to do the job better, because you can cover loads from a couple of seconds up to 15 minutes, which covers all your uphill driving, braking, acceleration, recuperation of braking energy, and use of power applications in the vehicle. The fuel cell can run in its preferred static mode." The benefits of the Superbattery will be even greater, he says, for fuel cell trucks and buses.

The automotive segment, he says, is where Skeleton is getting the most interest, because automakers are feeling the biggest pain. But it'll find its niches elsewhere too: "You can imagine a lot of other stationary applications. When you think of how industrial customers are billed for power, they pay for the highest power peak in every 15-minute interval. That's how the billing often works in Europe, anyway. So if you can shave off the peaks, you can bring your power bill down significantly. For that, the Superbattery would be quite the perfect system."

What's Skeleton's timeline?

"For the Superbattery," Pohlmann says, "we're currently bringing this into industrialization. Bringing it from pilot cells in the lab to industrial cells. We have signed a 1 billion dollar LOI with a large OEM, and we're working together with them and with other high level customers in order to bring this into product development. The technology is all there, it's all fixed. Now it's product development, processes, building up the supply chain for this technology. We're looking at start of production towards the end of 2023. The start of production aligns with our customers' project timelines."

So there you have it. I warned you this story would get geeky. Skeleton's Superbattery might not be the killer technology that gives your new EV super-fast charging times and a near-infinite lifespan, but it looks like it'll be a significant step forward in the less-glamorous niche of board net and peak smoothing applications, where it can deliver some impressive advantages. And that multi-billion dollar nook still seems like an excellent opportunity.

The space in between the ultracapacitor and the lithium battery is hotly contested at the moment. Notable competitors we've covered in the last few months include France's Nawa Technologies, which claims it can cheaply produce the "world's fastest electrodes" using vertically aligned carbon nanotubes, thus taking more or less any battery chemistry and delivering up to 3x the energy density, 10x the power, vastly faster charging and battery lifespans up to five times as long.

Another worth watching is China's Shenzhen Toomen New Energy, which is manufacturing a "power capacitor" design that's claimed to be capable of giving energy densities very comparable to lithium-ion packs and huge charge/discharge rates well within the capacitor range.

Thanks to Dr. Sebastian Pohlmann and Arnaud Castaignet at Skeleton, and also to Dr. Cameron Shearer, Research Fellow at the School of Chemical and Physical Sciences at Flinders University, South Australia and an independent expert on battery technologies, who consulted on this story.

Source: Skeleton Technologies