Energy-Dense Silicon Batteries Get $3M

The National Institute of Standards and Technology has awarded $3 million in funding to start-up Amprius, which is developing silicon-nanowire battery anodes. The Menlo Park, CA company, spun out of Stanford University, will use the money to develop manufacturing processes. We’ve covered the Stanford research on silicon battery materials, and in November we wrote about the company’s launch. Here’s some more on the technology from that story:

Amprius’ lithium-ion anodes are made of silicon nanowires, which can store 10 times more charge than graphite, the material used for today’s lithium-ion battery anodes. According to the company, electric vehicles that run 200 miles between charges could go 380 miles on its batteries, and laptops that have four hours of run time could last for seven hours between charges.

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When lithium-ion batteries are charged, lithium ions move from the cathode to the anode, while electrons flow in through an external electrical circuit; the process is reversed during discharge. Silicon has shown promise as an anode material because it can take up much more lithium than the carbon materials now used. Indeed, the theoretical maximum energy density of silicon is 10 times greater than carbon’s. But silicon is fragile and tends to swell and crack after just one charge cycle.

However, battery anodes made from silicon nanowires can be cycled over and over again without damage. This fall, Yi Cui, Amprius founder and assistant professor of materials science and engineering at Stanford, demonstrated nanostructured silicon anodes that meet silicon’s theoretical charge storage capacity without breaking. Mats of long, thin nanowires are pliable, which relieves the strain when the battery is charged and discharged. And collections of nanowires have a very high surface area, which means more sites for interacting with lithium.