A new silicon-anode battery offers the highest energy density yet
A novel lithium-ion battery that uses silicon in its anodes may have the highest energy density of any battery currently commercially available. Its manufacturer, Enovix, says it has shipped the new battery to a leading smartphone company for a debut in mobile phones later this year.
Many of the lithium-ion batteries that power everything from mobile devices to electric cars use graphite in their anodes. However, for decades, researchers have investigated silicon as a replacement for this graphite. In theory, silicon offers roughly 10 times the energy density of graphite in lithium-ion batteries.
“Basically, graphite holds onto lithium using holes in its structure,” says Raj Talluri, CEO of Enovix. “In contrast, with silicon in the anodes—usually a silicon oxide or a silicon carbide—lithium actually chemically combines with the silicon to form a new material. This lets a silicon-based anode hold onto much more lithium than graphite during charging. When the battery discharges, the silicon material goes back to its original state.”
One significant problem researchers have faced when using silicon in lithium-ion batteries is how it bulges during charging, breaking the batteries open. “If you put silicon in a small cellphone battery, stacking the anodes and cathodes like a deck of cards, the expansion that you would see from the silicon during charging would generate enough force to lift up a 2,000-pound truck,” Talluri says.
Enovix’s Energy Density
On 7 July, Enovix launched its AI-1 battery, which it says overcomes silicon’s major swelling problems. Its energy density, exceeding 900 watt-hours per liter in internal tests, is estimated to be roughly 50 percent greater than that of current major smartphone-model batteries, the company says.
The company also says the AI-1 battery, which is about 29.3 cubic centimeters large, possesses an energy capacity of 7,350 milliampere-hours, about 70 percent more than current major smartphone-model batteries. It also recharges quickly, reaching 20 percent charge in five minutes and 50 percent charge in 15 minutes.
The strategy that made this new battery possible was using microscopically thin silicon anode strips. “Then you stack the anodes in such a way that they only expand along their thin side,” Talluri says. “This way they only generate 200 pounds of force when they expand, which can be constrained just by holding them in a metal case.”
Improving a smartphone’s battery may improve other critical aspects of its performance. “I spent 25 years working on smartphones,” Talluri says. “One reason I moved to Enovix is that processors got faster and faster, and memories got bigger and bigger, but I found that you could not use either at their full performance because the battery would go down too fast. So by solving the battery problem, it can help everyone.”
A key application Enovix is targeting is use in AI-powered smartphones. “AI applications have become very prominent on phones, and they demand much more battery life, especially if they don’t want to process data on the cloud because of user privacy issues,” Talluri says. “Our goal is to have an all-day battery life on smartphones, despite them running the latest AI applications.”
Other potential applications for the new battery include Internet of Things (IoT) devices and augmented or virtual reality (AR or VR) glasses, Talluri says. Enovix is not currently manufacturing batteries for electric vehicles, but may license their technology to other companies in the market.
“We’re just at the beginning,” Talluri says. “We’re nowhere close to using the full potential of silicon.”