Since 2008, Silicon Valley startup Amprius has been working in a multi-pronged effort in next-generation energy storage technology — using silicon, rather than carbon, as a material for the electrodes within lithium-ion batteries.
The Stanford University spinout just announced a $30 million venture capital round aimed at supporting the first-generation batteries that Amprius has been producing at its Chinese facility since May, as well as continued development of the silicon nanowire technology behind the company’s founding.
Amprius’s new C round comes on top of a $25 million B round in 2011, bringing the Sunnyvale, Calif.-based company’s investment to date to at least $55 million, not counting its undisclosed Series A round and federal grants. Monday’s round was led by Asian private equity firm SAIF Partners and joined by previous investors Kleiner Perkins Caufield & Byers, Trident Capital, VantagePoint Capital Partners, IPV Capital, Chinergy Capital, and Innovation Endeavors, the investment firm founded by former Google CEO Eric Schmidt.
As for the company’s technology, it’s centered on using silicon to replace carbon in lithium-ion battery electrodes, and capture silicon’s much greater energy density potential — theoretically up to 10 times as much energy density. Stanford professor Li Cui, whose work on silicon nanotubes is at the core of Amprius’s intellectual property, has said that using anodes with this technology could increase the energy density of today’s lithium batteries by 40 percent.
Silicon-based electrodes have been a Holy Grail for battery makers and researchers for some time. But getting the advantages of silicon into real-world battery applications has proven difficult. The main challenge is that silicon, unlike carbon, expands by as much as 400 percent under lithium-ion insertion, and this expansion causes the silicon structures to fracture and degrade after only a handful of charging cycles.
Silicon nanowires can expand and contract without breaking, making them an ideal and practical battery material. But finding a cost-effective way to create these nanotube structures in commercial production is a significant challenge, as Amprius laid out in a 2010 document (PDF) describing a multi-million dollar R&D project it was undertaking in partnership with the National Institute of Standards and Technology: