Expanding on Silicon - the material you should care about and an industry overview
part 1 of 2
Typically, cathodes get more attention as the ‘capacity limiting’ component of a lithium-ion battery. LIB cathodes typically have practical capacities in the range of 150-200 mAh/g and 350 mAh/g for graphite. However every gram matters and companies are targeting high performance and affordable batteries. To do that, they must also improve the capacity of the anode, and the material hitting the headlines lately is silicon.
Silicon provides a mixture of interesting material properties and engineering opportunities which has led to a wealth of companies to talk about. This article is part 1 of 2 sponsored by LeydenJar, who are a leading developer of silicon anodes based in the Netherlands. Issy digs into the background of silicon, and the different creative solutions on the market. Our last series on this was back in 2021 so it’s definitely time to revisit.
The fourteenth element in the periodic table, which is found everywhere from beach sand to granite, is powering the next generation of battery materials. Silicon is moving from a futuristic idea to being a source of power in many different flavours, some even made from pure sand itself. While lithium metal anodes are a tough nut to crack, with uneven plating and stripping causing dendrites, silicon is rightly getting lots of attention as a high capacity anode with perhaps lower technical hurdles to get to market.
The lowdown:
Silicon is abundant and with a more diverse supply chain than graphite
Next generation batteries aren’t just talking about technological advances anymore. Silicon is found all over the world, on beaches as SiO2 sand and rocks like granite. In fact, it’s the second most abundant element in the earth’s crust at 27%, after oxygen.
Elemental abundance is one thing; the geopolitics and supply chains are another. China produces 93% of the world’s anode grade graphite, while silicon, though still dominated by China, comes from a much more diverse supply chain - a key advantage as battery makers look for alternatives.
Silicon can store a lot of lithium
Silicon has a specific capacity around 10 times higher than graphite. Silicon anodes also have a low working potential (0.45 V vs Li/Li⁺) which contributes to having high gravimetric energy densities in batteries.
Unlike graphite, which relies on lithium intercalation and deintercalation between layers, silicon alloys with Li⁺ to form a series of alloys with different Li/Si ratios. Think of intercalation like finding your seats at a concert hall, filing in to find a designated gap, that will remain when you leave. Alloying is more like finding a space at a festival or stood up concert, where the crowd morphs into the space available and there are no pre-allocated spaces. You can file in, and find a space, but the crowd aren’t in rows and the structure of the whole space changes.
During lithiation:
During delithiation:
Silicon has expansion issues
The problem with being an alloy material is that during lithiation and delithiation the volume of silicon can expand and contract by up to 300%, leading to particle cracking and pulverisation.
The solid electrolyte interphase (SEI) which forms on the surface of the anode, prevents direct contact between electrolyte and the anode. However, when the particles expand the SEI is also broken and degraded. This exposes fresh anode surface, causing the SEI to repeatedly reform. Over time this creates a thick SEI layer that reduces capacity by consuming electrolyte whilst also increasing cell impedance.
The volume changes may also cause electrode delamination, leading to ‘isolated’ particles no longer connected to the electrode and therefore not able to store lithium or transfer electrons.
Who’s making silicon work and how?
In 2021, Whoop announced that its fourth-generation fitness tracker would use batteries incorporating silicon material from Sila Nanotechnologies., Meanwhile, Amprius makes cells with silicon anodes which are used by Airbus and BAE systems in stratospheric aircraft. These companies, and others, have mitigated the problem of volume expansion in different ways.
The focus here is predominantly European and American companies, however, don’t forget that there will be teams developing this technology in-house at CATL, LG Energy Solutions and many others in Asia. Whilst we’ve done our best to work out what each company does, there’s only so much you can determine from what’s out there, so a disclaimer that this may not be 100% accurate.
There are lots of ways to categorise the different trends seen in silicon companies. In this article, we’re going to group the approaches by a. starting material and b. desired architectures.
That gives us 4 categories:
Solid silicon oxides; mechanical fixes to expansion.
Solid silicon; composite structure or mechanical fixes.
Silane gas; composite structure.
Silane gas; pure structured silicon.
Each has different innovative ways to solve the challenges silicon presents. Let’s get into it!
Solid silicon oxides; mechanical fixes to expansion.
The first silicon products to make it into LIB were silicon oxide (SiOx) particles mixed into graphite anodes. Whilst SiOx materials store less lithium than pure silicon, they expand much less too, at around 100% compared to 300% for pure silicon. Silicon oxides can also form a more robust SEI, less prone to cracking and reforming.
Silicon oxide applications are simple and work well as a drop-in to existing industrial processes to give a small capacity boost. In practice, SiOx is incorporated at a low weight percentage (1-10%) with the graphite majority helping to mediate the volume expansion. However, particle additions to slurries can lead to faster degradation of the anode and cell.
The main SiOx suppliers are the Asian incumbents such as:
BTR New Material Group, China. Silicon monoxide powders.
Other companies are using pure silicon oxides without blending them with graphite:
Ionblox, US (formerly Zenlabs). Uses an elastic polymer binder to ensure contact with the current collector, and added pores to accommodate swelling. Used with prelithiation.
Nanograf, US. Metal-doped SiOx with a coating of graphene. Can also be used in blend with graphite.
Interestingly there is also a naturally occurring tubular ore of silicon called Halloysite. One company IonicMT is using this particular SiOx to synthesise nanotubular structured electrodes, bypassing the need for silane discussed in later sections.
Solid silicon; composite structure or mechanical fixes.
Silicon oxide can be reduced in the presence of carbon to create metallurgical-grade silicon (99% pure). This is also known as silicon metal, which is used to create silicon chips. Silicon chips are everywhere, in our portable electronics and devices, and as such there are diverse global supply chains for this material. Metallurgical silicon can then be directly used for anodes via mechanical routes like ball milling, which is cheap and simple. Some companies are attempting to mitigate the expansion using various approaches including:
Coreshell, US. Uses a coating which acts as artificial SEI and structural encapsulant.
Neo Battery Materials, Canada. Uses coatings to strengthen the surface.
E-Magy, Netherlands. Creating structured nano-porous silicon that allows expansion into pores of the structure.
Advano, US. Silicon nanoparticles dispersed within a porous carbon matrix, which can be mixed straight in with Graphite. More details here.
Enevate, US. The anode mix is formed and then the polymer pyrolysed to convert into conductive carbon. Only partially using the 70% silicon anode capacity, meaning the expansion is much lower and easier to mitigate, within an entirely conductive frame.
Talga, Sweden. A composite of graphite, graphene and ~50% silicon.
Silane gas; composite structure.
Metallurgical silicon can be reacted with HCl followed by H2 to get Silane (SiH4), a toxic gas which can be used as a silicon precursor in chemical vapour deposition to form different silicon products. This gas allows for the creation of different silicon-containing architectures not possible using simple blending or wet chemistry. While this route involves extra processing and cost, it can provide unparalleled control over silicon morphology.
The next big trend to watch for is silicon deposited within structured carbon hosts, made possible by silane gas diffusing through the solid framework. This can take various forms, from carbon matrices supporting silicon particles to graphite particles with silicon embedded directly on the surface. Group14, which relies on this type of technology, raised a $463 million series D round in August 2025, showing investors are serious about this. Approaches include:
OneD, US. Attaching silicon nanoparticles to graphite particle surfaces.
Group14, US. Silicon in structured carbon matrices with nanopores.
Zhide, China. Silicon nano-particles structured in a carbon matrix.
Sila Nanotechnologies, US. Silicon scaffolding that allows expansion into pores of the structure.
Nexeon, UK & Japan. Engineered porous nanostructure allowing for expansion.
Store-Dot, US. Metal-coated silicon embedded in conductive matrix.
This can also be combined with additional mechanical fixes, such as:
Enovix, US. Cell company purchasing pure silicon anodes, and using a mechanical stainless-steel constraint to ensure both stack pressure and limit swelling. Also uses prelithiation. In partnership with Group14.
Silane gas; pure structured silicon.
Using silane gas not only allows impregnation of carbon hosts but also control over pure silicon architecture. The silicon is deposited via Chemical Vapour Deposition (CVD) into the desired structure.
Silicon nanowires made from CVD were first published by Yi Cui’s group at Stanford in 2008. The nanowire approach did not swell as much as spherical nanoparticles, and the space between the wires allowed for the expansion. Cui then went on to found Amprius based on this technology.
Players in this space include:
LeydenJar, Netherlands. Anodes made of pure silicon, deposited into sponge-like microstructure of thin columns.
Amprius, US. Based on the silicon nanowire technology developed at Stanford.
Prelithiation
As well as improving the physical structure of the silicon, it is also possible to augment the electrochemical performance using prelithiation of the anode. One of the big limitations to silicon anodes is the continuous SEI formation, which reduces the charge carrying ions in the cell. Prelithiation gives an extra buffer of lithium to consume, which increases cycle life and energy density.
Prelithiation can be achieved through several approaches, including:
Direct contact. Lithium metal (powder or foil) is contacted with the anode, diffusing to form a prelithiated layer.
Electrochemical prelithiation. Passing a roll of anode material through a chemical bath with lithium salt and ‘charging’ a precise amount of lithium into the anode.
Sacrificial lithium additives. Lithium-containing compounds are incorporated into cathode or anode materials, releasing extra lithium ions during initial cycles.
Prelithiation can significantly enhance performance, but difficulties remain around safety, scalability and cost. This limits its adoption primarily to niche or high-performance applications for now. Companies currently utilizing prelithiation in their anodes include Enovix, Amprius, and IonBlox.
In the next article we will take a deeper dive into the technology and people behind LeydenJar’s anode technology, as they recently raised €13 million as well as €10 million in customer funding to build their new plant in the Netherlands.
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This is a very nice introductory-level summary of silicon anodes. You list the various companies and describe them very generally. I was not aware there were so many.
However, you miss on very important key points. First, you list niche applications, but give us no indication of timing and leaders on major commercialization. When will these show up in GWh applications, which applications (EV), and who leads in both cells and silicon? This is critical to such an article. Who holds the key patents and IP? For example, silane gas into structured substrates. There must be someone who first conceived and then patented this. Then, you didn’t even cover Amprius correctly. They are a leader (the leader?) on commercializing silicon. A year ago they introduced their SiCore technology. The nanowire stuff (SiMaxx), which you highlight with an important illustration, is being phased out. Tip: Only use figures on the most important points in a review article.