Silicon anode battery companies get a major boost

Start-ups hoping to commercialize silicon materials for battery anodes raised nearly half a billion dollars in the final quarter of 2022. The money is intended to help them build factories and incorporate their materials into mass-market electric vehicles in the next few years.

Nearly all lithium-ion batteries use graphite materials in their anodes, the negatively charged ends of batteries that store lithium ions flowing from the positively charged cathodes during charging.

Materials containing silicon metal can improve a battery’s energy density because they store more lithium ions than the same amount of graphite. However, silicon has proven difficult to incorporate into commercial batteries because it swells during charging, potentially causing a damaging reaction with the battery’s electrolyte.

The bulk of the recent funding came in mid-October when the US Department of Energy announced $250 million in combined funding to help Amprius Technologies, Group14 Technologies, and Sila Nanotechnologies build factories for silicon anode materials.

In December, Group14 followed that grant with an additional $214 million in private investment. The company plans to build a 20 GW US factory capable of producing enough silicon material for 400,000 electric vehicle batteries.

Group14 currently runs a pilot-scale plant in Washington state and has nearly completed construction on a 10 GW plant in South Korea, built in partnership with SK Materials. None of the large-scale facilities are operational yet, but Chief Technology Officer Rick Costantino says the company still aims to have its materials in an electric vehicle in 2023 or 2024.

Sila has similar plans. The company is using the DOE grant to build a 20 GW plant in Washington and hopes to incorporate its materials into Mercedes-Benz’s G-Wagon SUV by the middle of the decade.

Sila has already started selling material produced in a California factory to a company that makes fitness trackers. Serving the consumer electronics market from that plant will ease the way to serving the auto market from the new Washington facility, says CEO Gene Berdichevsky. “Our mission is to power the world’s transition to clean energy. We are focused on that as a north star,” he says. “But you have to be pragmatic.”

Both Group14 and Sila both use miniature scaffolds to house silicon molecules as a way to control swelling. Berdichevsky says the scaffolding leaves enough space for silicon to expand at the molecular level, reducing swelling at the anode level.

Amprius and another firm, OneD Battery Sciences, take a different approach. They grow silicon nanowires that they claim are less prone to swelling than spherical silicon particles. Earlier this year, Amprius raised $87 million by merging with a special purpose acquisition company, and OneD closed a $25 million funding round led by General Motors’ venture capital arm.

While Amprius is pursuing a pure silicon anode, OneD hopes to increase battery energy density by infusing silicon nanowires into graphite powder. CEO Vincent Pluvinage says the approach allows customers to make more, and better, batteries with the same amount of graphite. “You have a lighter, smaller battery,” he says.

The anodes in many current lithium-ion batteries already include 5–7% silicon oxide, but adding more of this material results in too much swelling.

In November, NanoGraf received a $10 million grant from the US Department of Defense to build a factory that will produce 35 metric tons per year of a second-generation silicon oxide. CEO Francis Wang says the company pre-swells its material so that it’s more stable, allowing customers to use more per anode. That could help soldiers carry smaller batteries on the battlefield.

“You get the same amount of radio call time for less weight,” Wang says. Similar to Sila, NanoGraf hopes that selling materials for smaller batteries will help the company jump to the larger volumes needed for cars.

Berdichevsky argues that the latest wave of funding is evidence that silicon will be the next step in battery technology. Other companies are trying to improve battery performance by developing solid-state batteries with lithium anodes, but progress has been slow. While targets for commercializing solid-state batteries are consistently pushed back, Berdichevsky says, “silicon is now.”