Rolling Out Silicon with LeydenJar
Ultra-thin smartphones, all-day health monitoring and comfortable augmented reality glasses: our everyday electronic devices demand increasing amounts of energy whilst getting smaller and smaller. Analysts predict that the AI-wearable market will grow 20% each year to 2030, so squeezing more watt-hours into tiny cells is becoming pivotal for the consumer tech industry. Silicon anodes can enable higher energy density lithium-ion batteries, so have received increasing interest in recent years.
This article is part 2 of 2 sponsored by LeydenJar, who are a leading developer of silicon anodes based in the Netherlands. If you missed part 1, you can find it here.
Recap from the last newsletter: silicon’s promise and its headaches
With a capacity of 3000-3600 mAh/g - roughly ten times that of graphite - silicon stores far more lithium while operating at a low potential (~0.4 V vs Li/Li⁺). This is great for energy density. Yet silicon alloying with lithium causes ~300 % volume expansion; particles crack, contacts break, surface chemistry keeps reacting and consuming lithium. Many solutions also suffer a low initial coulombic efficiency (ICE), losing up to 30 % capacity on the first cycle. Some lab designs even require high external pressures applied via metal clamps to keep swelling in check, a non-starter for slim consumer cells.
Silicon materials for anodes available from various companies today are typically supplied in the form of powders, e.g. finely milled silicon or engineered silicon-carbon composites. These powders can be blended in low amounts (e.g. 1-20%) with graphite, mixed with binder and solvent to form a slurry, which is then coated onto copper foil. This approach fits existing electrode lines but limits the energy density gain and retains the multi-step coating, drying and calendaring processes typical of graphite anodes.
Some companies using silicon have developed unconventional cell designs or cell manufacturing processes, to mitigate silicon expansion.
There is another option: ready-to-go pure silicon anode rolls.
LeydenJar’s roll-to-roll foil
LeydenJar, the silicon anode innovator in the Netherlands, uses a plasma-enhanced chemical vapor deposition (PECVD) technique adapted from solar and semiconductors to produce pure silicon anodes. Silane gas (SiH4) is decomposed within a plasma, growing a ~12 µm layer of nano-porous silicon columns directly on copper foil in one step without the use of any solvents. This approach gives LeydenJar precise control over the silicon layer’s thickness, porosity, and morphology by adjusting the parameters of the PECVD process. Expansion of the silicon is mitigated in the unique material structure. The columnar “sponge” lets silicon expand into internal voids, while the extremely strong interfacial bond between the copper and silicon prevents delamination.
This technological revolution is happening in the fifth largest city in the Netherlands, called Eindhoven. It is known as ‘City of Light’ because of Philips, the lightbulb company and still a household name today, and also hosts semiconductor companies like ASML and NXP.
We checked in with LeydenJar’s team to further discover the story behind its silicon material and production process:
Majid Hussain (Production Line Manager)
In the factory hall in Eindhoven, Majid oversees LeydenJar’s PECVD production line, which turns silane gas into pure silicon anodes. “It’s not a batch tool,” he explains, “it runs continuously. The beauty of this process is that it’s dry and direct. No slurry, no binder, no solvent recovery. Just silane gas, plasma, and copper moving through the chamber.”
Inside the reactor, a plasma grows a sponge-like layer of nano-porous silicon columns about twelve microns thick onto the copper foil. The result is Silyte, a continuous roll of pure-silicon anode foil flexible enough to wind, cut, and integrate into cells on automated battery lines. The columnar structure grown by PECVD absorbs silicon’s swelling internally, keeping the layer intact through hundreds of cycles. “I have been running this continuous process for four years now, and you see how small changes in the process affect the battery performance.” Majid adds. “Producing here in the Netherlands helps us keep control and deliver foil that behaves the same in every cell.”
The material is shipped as SilyteTM, a ready-to-go anode roll designed for the consumer electronics industry. The foil can be slit, punched and stacked using conventional equipment, while sparing cell manufacturers the work of slurry coating, solvent drying and calendering. LeydenJar’s cells with LCO and NMC cathodes show up to 1350 Wh/L nominal stack energy density, 0–80 % charge in 12 minutes, and 500 cycles at 80 % retention with zero external pressure.
Pieter Swarts (Senior Application Engineer)
Further east, in China, Pieter, one of LeydenJar’s application engineers, is working closely with Highpower, a major cell manufacturer that supplies leading consumer electronics brands. His team’s role is to make sure LeydenJar’s silicon anode foil behaves flawlessly in Highpower’s mass-production environment.
Pieter explains: “We deliver rolls that slot directly into Highpower’s electrode lines. The processing is very similar to traditional graphite electrodes, slitting, punching, lamination, stacking, and so on. Only now, the cells come out with much higher energy density.”
LeydenJar announced a major partnership with Highpower earlier this month. The large cell maker is already producing thousands of pouch cells using LeydenJar’s silicon anode. Over the coming years, this volume will scale up through customer validation projects, ultimately expecting to reach millions of cells by 2027.
The collaboration focuses on pouch cells for wearables, maximizing energy into a battery size you can comfortably keep close to your body. With LeydenJar’s silicon foil, Highpower can build cells that deliver up to 50 % more energy in the same volume. “For a smartwatch or smartphone, that’s the difference between one-day use and multi-day operation.” Pieter says. “Our customers are designing smaller and lighter devices with heavy energy demands, they need compact batteries that can keep up with the latest innovations in AI and sensing.”
Elizabeth Couves: Project Manager PlantOne
Back in the Netherlands, Elizabeth Couves, project manager for PlantOne, oversees every fine detail of what will become LeydenJar’s first large-scale anode production facility. LeydenJar recently raised €13 million of equity funding and an additional €10 million from a major US-based tech company. This will enable them to scale their new plant and produce reams of Silyte.
This is a pivotal milestone in a journey that began almost a decade ago. “LeydenJar started producing silicon anodes with PECVD in 2016,” Elizabeth explains. “By 2023, we had broken ground on PlantOne. Now, we’re getting ready to complete the facility, installing our latest generation PECVD equipment and reaching mass scale process speeds. By 2027, a steady stream of anode rolls will be leaving Eindhoven every week.”
PlantOne is designed to service LeydenJar’s customers in the consumer electronics market. 70 MWh per year capacity is sufficient to supply enough anode for about five million smartphones. “PlantOne is just the beginning,” Elizabeth promises, standing amid the construction site’s rising frame. “We’ll take everything we’ve learned to build PlantTwo by the end of this decade. That’s where we’ll scale up yet again, and see truckloads of pure silicon anode foil rolling out regularly.”
Remaining challenges and the road ahead
LeydenJar continues to refine its in-house equipment, aiming to raise throughput while lowering production costs. At the same time, the team is working closely with partners to improve material integration in full cells. The performance of pre-production cells has been promising and attracted market attention, and now this will be transferred into consistent, manufacturable batteries. These developments will define the next stage of LeydenJar’s growth as the company prepares for full-scale operation at PlantOne. Establishing silicon anode production in Eindhoven shows that Europe’s strength in battery materials research is now extending into component manufacturing, a crucial step toward giving the region a stronger position in the global battery supply chain.
Wearables as the first large-scale market for pure silicon
Consumer electronics, from phones and tablets to watches and glasses, are one of the most demanding battery applications, and therefore the driving industry behind battery innovations. Their limited volume and high energy requirements make every micron of electrode design matter. Pure silicon anodes offer a route to longer runtimes and slimmer product designs.
As validation expands through partnerships with cell manufacturers and OEMs, LeydenJar welcomes collaboration with companies exploring next-generation batteries for consumer electronics and beyond. Soon, batteries that started as a gas in a warehouse in the Netherlands will be powering devices worn by people all over the world.
www.leyden-jar.com • info@leyden-jar.com
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Great writeup. Am I understanding it correctly when they say the technology is rated for 500 cycles?