Electric vehicles (EVs) are critical for reducing fossil fuel dependency and greenhouse gas emissions. Yet, while EV sales have risen in recent years, challenges remain. EVs are typically more expensive than gasoline-powered cars, charging times can be slow, and driving ranges often fall short of consumer expectations.
Figure 1. Researchers are exploring silicon materials to advance EV batteries, aiming for greater range and efficiency.
Since batteries account for up to 40% of an EV’s cost, they’re a crucial area for innovation, potentially making EVs more affordable and financially viable in the long run.
To avoid relying on foreign countries for innovation and production, cost-effective, scalable, and rapidly deployable battery improvements are crucial to accelerating widespread EV adoption in the United States. EV battery makers are exploring silicon as a potential replacement for graphite in lithium-ion battery anodes. Silicon can store up to ten times more energy than graphite, potentially boosting driving range by 30%.
However, this advantage is offset by challenges like degradation, which reduces the range over time. Fortunately, there is good news. A type of silicon made from earth-abundant materials, known as metallurgical-grade silicon, has shown significant promise (Figure 1). It offers a high energy storage capacity, a lower price point, and compatibility with existing manufacturing processes, making it a potential game-changer for the EV industry.
Before discussing the advantages of metallurgical silicon, it’s important to understand why silicon outperforms graphite despite certain drawbacks.
Silicon versus graphite
Figure 2. Graphite has been valued for its stability in lithium-ion anodes, but silicon’s advancements are redefining the performance standards.
For the past decade, graphite anodes have been the standard in lithium-ion batteries due to their stability (Figure 2). In contrast, silicon anodes can store over ten times more energy but face a significant challenge: they can swell up to three times their size during charging.
This expansion can cause silicon anodes to crack and degrade over time, dramatically shortening the battery’s lifespan.
To address this, the battery industry is exploring various types of silicon anodes and technologies, each offering distinct approaches to mitigate swelling while balancing trade-offs in cost, energy density, and scalability.
The problem with swelling
Synthetic silicon, typically produced using silane, reduces swelling in anodes while maintaining energy density. However, the high material and production costs and safety concerns due to silane’s toxicity and flammability make it costly.
Applying synthetic silicon via chemical vapor deposition (CVD), a process in which gaseous reactants form a solid material on a substrate, is energy-intensive and inefficient since this process is only about 30% effective in silicon deposited compared to silane used and accounts for the significant expense of using the material. While synthetic silicon offers premium performance, its high cost makes it unsuitable for mass-market EV adoption.
The silicon oxide alternative
Silicon oxide (SiO) anodes provide a middle-ground solution, appealing to broader markets due to their lower cost than synthetic silicon. While they help reduce swelling, they fail to achieve the same level of expansion control. This compromise for cost impacts performance, as SiO batteries deliver about half the energy density of higher-end silicon options — meaning they store less charge and provide reduced power per unit.
Additionally, silicon oxide anodes suffer from low-capacity retention and low first-cycle coulombic efficiency, limiting their ability to convert and retain energy, which can shorten battery life and decrease energy density benefits.
To address these inefficiencies, silicon oxide requires a pre-lithiation step — an extra manufacturing stage where additional lithium is incorporated into the electrodes to enhance performance. This can be done by adding lithium directly to the SiO base material or by integrating the extra lithium during battery cell production, which increases the manufacturing complexity and cost.
The metallurgical-grade silicon difference
Figure 3. Metallurgical-grade silicon is being explored as a promising material to enhance EV battery efficiency and scalability.
Metallurgical-grade silicon, derived directly from silica quartz, is the most scalable and cost-effective solution for EV batteries (Figure 3). Unlike synthetic silicon, it requires minimal refinement and is an abundant material, making it ideal for widespread adoption and scalability.
As the lowest-cost form of silicon, it has attracted major OEMs, including Tesla, which in 2020 highlighted its potential for improving battery density and performance at a lower cost.
The swelling and fracturing of metallurgical-grade silicon have previously limited its use, but that’s changing. Recently, a thin polymer nano-coating has been developed to stabilize silicon particles, prevent electrode fragmentation, and enhance battery life by forming a durable solid electrolyte interphase (SEI) — a protective layer that forms between the electrode and electrolyte.
This advancement is positioning metallurgical-grade silicon anodes as a key material for next-generation, affordable, high-performance EV batteries.
The future of silicon-based batteries
Silicon anode technology offers a promising pathway to lower EV battery costs and diversify material sourcing, with many regions able to use silicon domestically. As research and development progress, batteries using metallurgical silicon could address affordability challenges while boosting performance. Advancing this technology could lead to long-range, fast-charging, and more affordable EVs, supporting the industry’s broader sustainability goals.
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