X-CAP: the sprinter and the marathon runner winning the energy race
It's one of the Europe's biggest greener energy success stories you've never heard of. Skeleton Technologies did what no-one thought was possible and combined the best of batteries and capacitors to create a whole new product field—SuperBatteries—that are set to power everything from mining trucks to AI data centres.
The initiative to document and share successful stories from projects within DeepSync, funded by the European Innovation Council (EIC), offers a unique opportunity to connect with fellow members and innovators by showcasing each project's journey, including both successes and challenges. By highlighting the key moments and insights that have shaped the path, these stories contribute to a richer collective knowledge base. This effort aims to raise visibility, foster a deeper understanding, and enhance the sharing of knowledge across the community.
The sprinter wins the short race, the long-distance runner triumphs in the marathon. A combined athlete with performance in them both would surely win nearly every race. And now in the battery market, European scientists have made a hybrid product charging first to the finish line across the modern industrial energy centre, powering up everything from mining trucks to electricity-hungry AI data centres. Welcome to the world of the SuperBattery.
"There was a moment where our founder together with our chief technical chemist, were sitting together and just on a napkin, drawing ideas of like: how could this work if we had like a hybrid between a supercapacitor and a battery?" recalls former political scientist turned project manager Patricia Godel of Skeleton Technologies, the company that used EU funding to merge two of the contrasting powerhouses of the portable energy world into the product the future was asking for.
Forget your cute little triple AAA powering a child's toy. Skeleton Tech's SuperBatteries can give 30 minutes of driving in 90 seconds of charging and are good for 50,000 charging lifecycles—10 times more than lithium-ion batteries. They are about the size of a soda can, weigh 800g, and are no juvenile fantasy. Today, they are used in everything from urban buses to 500+tonne industrial mining trucks; they can replace secondary diesel generators on shipping freight-carrying ships displacing 150,000 tonnes of water. Realistic ambitions are on the table to scale up SuperBatteries to power buildings, remote villages and AI data centres.
It's one of the EU's great energy innovation success stories: Skeleton Tech now employs one of the largest SuperBattery development teams in the world of over 40 chemists and physicists, as well as chemical, electrical and mechanical engineers, and hundreds of skilled support staff. But because of the COVID pandemic, it almost never happened at all.
Crisis cured by collaboration
As the idea of mixing the best of both worlds from batteries and capacitors gained traction in the office, the company realised the pathway to success was a EIC Accelerator grant to develop innovative, potentially game-changing products that use deep tech to create new markets or disrupt existing ones. But just as it was secured, the COVID virus swept across Europe nixing the travel and academic mixing needed to make it all happen.
"Because of COVID safety restrictions we couldn't host enough people in the lab, pure and simple, and originally we had foreseen to do this entirely in Germany," recalls Godel. The solution was to step up pan-European collaboration and bring in colleagues based in Estonia, where employees worked in modules more suited to restrictions at the time, which also varied from country to country. "We had to tell the guys in Estonia 'hey, we need you to drop some stuff and start doing simulations in XCAP right now," says Godel, adding the project name was born from CAP for capacitor, and X to represent the unknown.
And this project had many unknowns. Too many for Skeleton Tech's investors who shied away from funding a high-risk project based on unproven tech that simply did not exist. The EIC Accelerator grant team had faith and bridged the gap. But could it be bridged? No one had ever tried to synergise a battery and a capacitor in this way before.
Batteries vs. capacitors
At this point it's worth revisiting the differences, advantages and drawbacks of each. Batteries are the long-distance runners of the race, powered by chemistry converted to electricity that produces energy to power devices over a longer time—hours, days or weeks at best. Capacitors are essentially physics devices that can store energy in an electrostatic field and can release it, like the sprinter, much faster for short bursts like powering the flash on a camera or changing channels on TV; but they lack the energy density to play the long game.
"One does physics and the other chemistry, which is why it's so tricky to combine them," says Godel. Her company role as Head of Grant Financing and Risk was heavily intertwined with the project, especially if it failed. After just over a year's testing, the engineers nailed it: it's about adding just the right amount of lithium—less than 5%.
Sadly, for this story, for intellectual property reasons Godel isn't revealing the exact 'sweet spot' amount, but teases at how the typical team overcame such a challenge. "You have to change something about the cathode, and the anode… and the electrolyte! All this stuff needs to be changed," she says. "And while there's a lot of company expertise in the battery field we could draw from, it's something nobody had ever done before."
It didn't work first time. The team had to solve myriad problems from the cells leaking, to something being amiss with the laser welding, to the units catching fire during safety testing. Godel is frank about how difficult it was, but batteries are batteries, experimental ones are going to catch fire, it happens, you carry on. You have failure mode processes where you bring the team together and thrash it out, you work weekends, you huddle together, support each other, and make it work.
Powering the future
The SuperBatteries don't use cobalt, nickel, graphite or copper, enhancing again their environmental credentials. As the world graduates to greener energy solutions, deep-tech projects using pan-European collaboration can drive the capacity for societies to make the change at scale, to fill the gap where other power sources come up short.
Now in 2025 there's a refitted factory in Finland making 250,000 SuperBatteries a year (the marketing people came in and made them change the name) and a new production facility in France underway. The overall ambition is to make millions of units a year to power the AI grids, the hospitals, transport platforms and buildings of the future. "The end of the grant it was very nearly mass producible," says Godel. "And that's right down to the EIC. We could not have paid for the research to make it work." And with Europe's competitors churning out gigawatt factories by the month, Godel's last word is that you can't wait 5, 10, 15 years to do this research anymore.
Contacts:
Project coordinator:
APRE
Stefania De Santi
Communication Team:
Fondazione ICONS
Cesar Giovanni Crisosto
Caterina Falcinelli
Project website: https://deepsync.eu
LinkedIn: DEEPSYNC
Provided by iCube Programme
