Paul van Gerven
6 March

The Leiden and Eindhoven-based battery specialist Leydenjar is leasing a former Philips production hall to ramp up silicon anode production.

With the acquisition of an empty factory shell at Eindhoven Strijp-T, Leydenjar is taking the next step toward large-scale application of silicon anodes in lithium-ion batteries. According to CEO Christian Rood, it’s the final test for the technology developed in Leiden and Eindhoven to pass. If anode foils with the promised specifications and at the expected cost are churned out from 2026 onward, the sky will be the limit for the startup.

Silicon is an attractive alternative to standard graphite anodes because it accommodates up to 10 times more lithium ions per unit volume. Unfortunately, the material swells and shrinks during charging and discharging to such an extent that it tends to crack, resulting in catastrophic battery failure.

Leydenjar has developed a porous silicon nanostructure that accommodates the volume changes during charging and discharging. This enables batteries that can retain up to 70 percent more energy than the equivalent with graphite. In addition, they can (dis)charge faster and require less energy to produce.

After years of development in its Leiden laboratory and pilot plant in Eindhoven, Leydenjar is now ready to start thinking about actual production. “Two things have come together recently. We’ve demonstrated that we’re able to manufacture silicon anodes on a copper foil that’s interchangeable with the graphite foil that battery manufacturers already employ. And we now know for sure that we can build a machine that can produce this foil at the right price,” Rood explains.

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Leydenjar Strijp T
Remodeling is about to start. Credit: Leydenjar

Plasma chemistry

Leydenjar is focusing on the foils, not just the equipment to produce them, because of the technology’s revolutionary nature. “We could offer manufacturing equipment, but battery manufacturers wouldn’t know what to do with it. By offering a foil similar to what they’re already using, our product will be more quickly accepted,” Rood says. “Additionally, it’s easier to copy a piece of equipment than it is to figure out how to manufacture well-performing silicon anodes.”

The tool that Leydenjar will install in the former Philips production hall in Eindhoven will be a descendant of a plasma-enhanced vapor deposition system (PECVD) from PV research center ECN (later TNO). At one time, nanostructured PECVD’ed silicon was theorized to produce more efficient thin-film solar cells. That didn’t pan out as expected, but one alert researcher realized years later that the material might be ideally suited for storing more energy in batteries.

That turned out to be the case, but the discovery was still far removed from a commercially viable product. On the one hand, a high-performance battery system had to be developed around the anode. “Our customers want to see what our technology has to offer. So we had to find a combination of silicon anode, electrolyte and cathode that not only results in maximum energy density but also meets lifetime requirements, for example.”

On the other hand, nanosilicon deposits rather slowly on copper, a shortcoming that Leydenjar solved partly by tinkering with the plasma chemistry and partly by designing a machine that achieves a large number of deposition steps in succession. “The more serial deposition steps, the higher the throughput.”


Christened PlantOne, Leydenjar’s first full-fledged production facility will produce about 70 megawatt-hours worth of anode foils per year. That’s enough to make four million smartphone batteries that don’t need to be recharged as often as the ones currently in use.

Leydenjar will have to focus on this characteristic for the time being because competing with graphite anodes on cost isn’t yet viable. “This is mainly the result of scale effects. We won’t be able to match the manufacturing capacity of our competition anytime soon, but we do have a product that’s worth a premium.” It’s not only about having to recharge less often. “Better batteries enable functionality that would otherwise drain the battery. For example, AI also requires considerably more power-hungry computing power on the device side.”