Dutch silicon anodes inch closer to the gigafactory

Nanotextured silicon anodes perform even better than expected, boosting battery energy density to world-record levels, startup Leydenjar found. Now the Dutch company has set out to develop highthroughput deposition equipment to take its superior anodes into gigafactories.

Paul van Gerven

Leydenjar Technologies has developed a lithium-ion battery anode that’s made entirely from silicon. The spinout of applied research institute TNO has shown that swapping carbon for its silicon cousin results in batteries with up to 70 percent higher energy density. Preparations are underway to massively scale up the production of the anode.

Silicon is an excellent host for lithium ions but in itself, not a good anode material because of its propensity to crack under the stress of repeatedly taking in and letting go of guests. Leydenjar adopted a plasma-enhanced chemical vapor deposition (PECVD) process originally developed for thin-film solar cells to create nanotextured silicon that can comfortably accommodate the volume changes associated with lithium loading and unloading.

Last year, the Leiden-headquartered company proved that its process could make commercially relevant silicon anodes. Since then, it has been exploring the potential of its invention by making real batteries in various configurations. “The performance is well over what we thought was possible,” says Leydenjar CEO Christian Rood. “We assumed that swapping graphite for our silicon would result in a 50 percent increase in energy density, but it turns out we can reach 70 percent, achieving the highest energy for lithium-ion batteries in the world. Using the very best cathode materials available right now, we believe we can go even higher.”

Another advantage of the silicon anodes is that their single-step production is more efficient than making traditional graphite-based anodes. It requires less material and mining and processing graphite is rather energy intensive, as is the heating step that follows a slurry-based coating of

Credit: Leydenjar

the material. Leydenjar estimates that all things being equal, silicon anodes result in 62 percent less CO 2 emissions.

The right formula

The batteries, however, still feature a relatively short life span. “Currently, our cycle life is only appropriate for some specialty applications, such as e-flight, medical devices or robotics. In these markets, a life span of multiple years isn’t important. We recently started working with industry partners to work towards commercial solutions in these domains,” says Rood.

The comparatively limited life span isn’t surprising, as Leydenjar hasn’t spent much effort on improving it yet. Key will be identifying the right electrolyte composition – a delicate process that involves a bit of trial and error. Leydenjar recruited the help of German specialists to find the perfect formula.

Gigafactories

Meanwhile, Leydenjar has also been working on the manufacturing aspects of the anodes. This is actually the startup’s core business, as it won’t be selling anodes or batteries but deposition equipment along with the know-how. The in-house battery research is nonetheless a necessity because not a single sale would be made without proof that the anode enhances performance. Another hard requirement will be to seamlessly fit into current battery production processes, without adding cost.

Progress in the manufacturing department has been good too, Rood reveals. “We started building our pilot production line in Eindhoven last year. After installing and fine-tuning the machine originally used by TNO for the solar cell research, we now have a stable roll-to-roll deposition process (the silicon is deposited on copper foil, PvG). We’re getting sample orders from companies that want to test our technology. We’re also getting paid to make commercial prototypes.”

The next step will be to construct a modular deposition machine optimized for production. “We have the expertise to do that ourselves, though obviously, we’ll work with partners, both Dutch and German. Only when we’re ready to ramp up, will we likely outsource production.”

Though battery manufacturing is currently predominantly an Asian affair, Leydenjar’s strategy is mainly focused on Europe – and not just because the company received funding from the European Union. Determined not to miss out on another key technology, the EU has set ambitious battery plans in motion, which line up well with Leydenjar’s roadmap. Rood: “There are around 15 gigafactories planned in Europe over the next years, all of which will need a competitive edge. We’re convinced we can provide that, so this is an enormous opportunity for us.”