Insights provided by the team at Coreshell. To learn more, check out the full essay on the Coreshell website.
Metallurgical Silicon: The Key to Low-Cost, High-Performance Batteries
Currently, almost all lithium-ion batteries utilize graphite materials in their anodes. Since graphite was first incorporated into lithium-ion batteries in the early 1990s, it has remained the de facto anode material. As one of the largest single materials in a battery cell, it heavily influences the overall performance and cost of the final product.
To enhance battery performance while reducing costs, technologists have been exploring alternative anode materials. Silicon has emerged as a promising candidate due to its superior specific capacity—10 times that of graphite—and its abundance as the second most prevalent element in the Earth’s crust. In contrast, graphite production is geographically constrained, with China alone accounting for over 90% of global output. These factors make silicon an attractive material for next-generation batteries. However, its historical challenges in charge and discharge cycling have hindered widespread adoption. These challenges have now been addressed through Coreshell’s advanced cell technology, enabling the production of the lowest-cost, high-performance batteries.
Understanding the Different Grades of Elemental Silicon
Silicon materials exist in various forms and grades, each with distinct properties and applications. In its elemental form, silicon is produced in three main grades:
- Metallurgical-Grade Silicon (MG-Si): With a purity level of 98-99.9% (3N), MG-Si is the foundational form of elemental silicon. It is primarily used as an alloying agent in aluminum, steel, and copper production. Additionally, it serves as the precursor for higher-purity silicon grades.
- Solar-Grade Silicon (SoG-Si): At approximately 99.9999% (6N) purity, SoG-Si is used in solar energy applications, particularly in manufacturing solar cells, where high purity is essential for efficiency.
- Electronic-Grade Silicon (EG-Si): This is the highest purity grade (99.9999999% or 9N) and is used in semiconductor and integrated circuit production, where extreme purity ensures optimal device performance.
Understanding the Different Forms of Silicon in Batteries
Beyond elemental silicon grades, specialized silicon forms are used in battery anode production, including:
- Silicon Oxide (SiO): With 99.99% purity, SiO is more stable in battery applications but requires additional pre-lithiation to address poor first-cycle efficiency.
- Silane Gas (SiH4): Produced at 99.9999% purity, silane is commonly used in chemical vapor deposition (CVD) to create thin silicon coatings or nano-deposits, often onto carbon matrices to form composite silicon.
While these forms offer some advantages, they require complex and expensive production methods, making them costlier than MG-Si.
Metallurgical-Grade Silicon: Production and Applications
How Metallurgical Silicon is Produced
MG-Si production begins with quartz or silica sand (both forms of silicon dioxide). Quartz, being the second most abundant mineral in the Earth’s crust, is widely mined. Due to its high purity and consistency, quartz is often preferred for MG-Si production.
The production process is straightforward:
- Quartz is smelted in a furnace with carbon.
- A chemical reaction occurs, forming silicon and carbon dioxide:
- The silicon solidifies into MG-Si upon cooling.
Due to the abundance of quartz and the simplicity of the process, MG-Si is both inexpensive and widely available.
Key Producers of Metallurgical Silicon
Unlike graphite, where over 90% of global supply is controlled by China, MG-Si is produced worldwide, including in the U.S., France, Norway, Brazil, and Russia. Key silicon metal producers include:
- Ferroglobe
- Dow
- Elkem ASA
- Anyang Huatuo Metallurgy Co.
- Hoshine Silicon Industry Co.
- Mississippi Silicon
This broad production base reduces supply chain risks and allows for localized MG-Si production—an advantage graphite and other emerging battery materials lack.
MG-Si in Battery Production: How It Compares to Other Silicon Technologies
Other battery-grade silicons, such as SiO and silane-derived silicon, require additional processing:
- SiO: Produced by co-evaporating MG-Si with SiO₂, offering stability but necessitating pre-lithiation to improve efficiency.
- Silane-Derived Silicon: Created through chlorination and high-temperature reduction, silane gas is used in CVD to produce nano-sized silicon deposits. This method is highly energy-intensive and costly.
These processes make SiO and silane-derived silicon more expensive than MG-Si while only replacing a minority portion of graphite in the anode.
Potential Benefits and Challenges of MG-Si in Batteries
Advantages:
- Higher Specific Capacity: MG-Si stores 10x more lithium than graphite.
- Lower Cost: Cheaper than both graphite and other silicon technologies.
- Scalability: Produced in vast quantities annually, MG-Si can support rapid industry expansion without requiring significant new infrastructure.
Challenges:
- Volume Expansion: Silicon expands and contracts during lithium-ion cycling, causing stress, cracking, and degradation.
- Solid Electrolyte Interphase (SEI) Instability: Capacity loss over time due to unstable SEI formation.
- Limited Past Success: Historically, these challenges have prevented MG-Si from replacing graphite in anodes.
Breakthrough in MG-Si for Batteries
To fully unlock the potential of metallurgical silicon, Coreshell has developed a revolutionary solution-phase deposition process that overcomes these historical challenges. This technology allows for the direct use of 100% MG-Si in the anode—without additional refining steps or expensive manufacturing modifications.
Key advancements include:
- Use of Mechanically-Milled, Micron-Sized, and Non-Uniform Silicon Particles: Reduces costs and enhances scalability.
- Innovative Electrolyte and Binder Formulations: Ensures compatibility with MG-Si while stabilizing battery cycling.
Results and Industry Impact
Coreshell has successfully demonstrated:
- The first commercial-scale 60 Ah battery cells using 100% domestically sourced MG-Si.
- 30% more capacity while reducing costs by up to 25%.
- A breakthrough that dramatically lowers battery production costs and enhances supply chain security.
By leveraging domestically produced MG-Si, Coreshell has created a transformative solution that could significantly accelerate electrification by making batteries cheaper and more accessible. With these advancements, widespread adoption of next-generation lithium-ion batteries is not just possible—it is inevitable.
Conclusion
Metallurgical-grade silicon presents an unparalleled opportunity to reshape the lithium-ion battery industry. With its abundance, low cost, and high energy capacity, MG-Si could replace graphite as the dominant anode material—provided its historical challenges are addressed. Thanks to Coreshell’s breakthrough technology, MG-Si is now a viable and scalable solution for high-performance, low-cost batteries. As this innovation gains traction, it has the potential to accelerate electrification and make sustainable energy storage more affordable than ever before.
