Silicon Battery Technologies Explained

Electric vehicles are the key pathway to meeting the world's climate goals. Mass adoption of EVs is the clearest path to eliminate fossil fuel use, reduce greenhouse gasses, and expand the planet’s clean energy infrastructure.

Consumer adoption of EVs however, is still struggling to make the leap from early niche adoption to mainstream market acceptance. After years of steep sales growth, global carmakers have begun to see drops in consumer interest in vehicles that are often more expensive than gasoline-fueled cars, take long periods to recharge, and don’t have sufficient range. Batteries in many EVs account for as much as 40 percent of the price of the vehicle which has made EVs cost-prohibitive to many consumers, and in many cases, money-losing to car manufacturers. 

Battery innovation can overcome these obstacles and promote faster EV consumer adoption. But not all batteries are the same in composition, production, and cost. This is why we must prioritize the strongest and most efficient battery chemistry that can be deployed quickly, cost-effectively, and at mass scale.

Several emerging technologies meet some of these needs. Lithium metal batteries that replace typical lithium-ion graphite anodes with a much lighter pure lithium metal anode offer increased energy density and range. However, lithium metal anodes are difficult and expensive to produce and so far there is a major shortage of high-quality lithium metal for batteries and no significant producers at volume production quantity and quality. In addition, lithium metal batteries are more explosive than their counterpart lithium-ion batteries and therefore also necessitate a solid electrolyte safety barrier. But this solid-state technology requires a reinvention of the entire battery, along with disruptions to current battery manufacturing systems and supply chains to reach mass production and adoption. In short, the road to commercialization for both lithium-metal and solid state is too long to meet the world’s immediate needs. 
‍

Silicon as the long term solution

Silicon-based batteries can solve many of these challenges, and in the nearer term. Silicon is a widely accessible metal. It’s the second most prevalent element in the earth’s crust after oxygen and is currently mined in large volume from mines in the western world, particularly in West Virginia and Alabama. It can also hold more than 10 times more energy per kilogram than graphite. As a low-cost and drop-in technology to existing manufacturing, silicon-based batteries can be deployed quickly to meet the world’s growing needs for EVs.

Silicon batteries come in different varieties and do not all offer the same accelerated path to production and adoption. One of silicon’s primary liabilities is its electrochemical property of volumetrically expanding during charging, which creates mechanical and electrical challenges in a vehicle that may be charged hundreds or thousands of times. Three primary silicon battery technologies attempt to overcome this problem of volume expansion with different battery compositions and different value tradeoffs.

‍

Synthetic Silicon, sometimes referred to as Composite Silicon, uses silicon-based anodes that have been engineered to meet the challenges of commercialization for electric vehicles. Synthetic silicon takes the form of silicon nanoparticles or nanowires, which are far less likely to fracture during charge-discharge cycling. However, silicon nanoparticles are predominantly made from silane, and silane is expensive, highly flammable, and highly toxic. These problems can be mitigated, but at a cost. Like premium gasoline, synthetic pure silicon offers high performance at a high price, which makes it unsuited for affordability and adoption by the broader market.

Silicon Monoxide, often called Si Oxide, attempts broader market appeal with a more accessible type of silicon that also reduces swelling, although not as much as synthetic pure silicon. This is a compromise approach: It can be half the cost of higher-end silicon batteries, but also offers half the energy density, and thus half the performance. Si Oxide also has low first-cycle coulombic efficiency, which eats into its energy density benefits. What’s more, Si Oxide requires an additional manufacturing step called pre-lithiation in which more lithium is added into a battery to offset inefficiencies. Lithium can be added directly to Si Oxide, which makes the material more expensive, or it can be added in the battery manufacturing process, which increases production timelines and costs. Like synthetic silicon, Si Oxide also has no significant existing supply-chain.

As a result of shortfalls with synthetic pure silicon and Si Oxide, the only way to significantly drive down cost per kilowatt hour compared to graphite batteries while maintaining high performance is to harness the lowest cost form of pure silicon.

Metallurgical Silicon (MG-Si) is low-processed, natural silicon from silica quartz rock. Batteries built with metallurgical silicon have shown early promise in offering a balanced value proposition to manufacturers and consumers. Metallurgical silicon requires the least processing and is the most abundantly produced form of silicon, making it a building block that can be scaled easily and quickly. Unlike current graphite anodes which are almost entirely sourced from China, the US and Europe have several existing quartz mines and metallurgical silicon production facilities. This makes metallurgical silicon the best chance to de-risk anode material supply chains from complete reliance on a single source. 

In 2020, Tesla began experimenting with metallurgical silicon batteries to improve battery density and performance. In their 2020 Battery Day presentation they reiterated the belief to shareholders and the broader public that metallurgical silicon offered the most promising approach to tomorrow’s batteries that can be made and sold widely and cost-efficiently.

In 2023 Coreshell Technologies was the first to publicly release performance data at the International Battery Seminar demonstrating that metallurgical silicon has the potential to meet the industry’s growing and diverse needs by replacing Graphite as the majority anode material (Coreshell IBS Presentation).

Metallurgical silicon offers the EV automotive OEMs the best pathway to becoming a resilient and profitable industry. We believe that, instead of reinventing and producing expensive top-heavy technologies, companies that return to basics and build from the ground-up with low-cost materials will be the leaders of a crucial and transformative new era of battery innovation.