Ryan Kottenstette, Amprius' director of business development, says the company has made a number of improvements in the nanowire growth process to make it compatible with large-scale manufacturing. The nanowires are grown from a gas on a metal substrate coated with a catalyst. The company would not detail how the anodes are made, but it has developed a process that uses a more conductive substrate and a cheaper catalyst. "The anodes can be grown on a large scale at a fast speed in large areas on foil and with lower materials costs," says Cui.

Amprius is in talks with vehicle and electronics manufacturers, and raised its first round of venture funding in March. The company hopes to raise more funds next summer to build a pilot manufacturing line.

No matter how good the anode is, the overall charge capacity of a battery depends on the cathode, too. The performance of today's lithium-ion cathodes isn't as good as that of the anodes Amprius is developing. The company's initial battery designs make up for this mismatch by pairing a thin anode with a thick cathode. Compared to a conventional lithium-ion battery of equal size, this design stores 40 percent more charge. In order to further increase the energy density, however, the company will need new cathode materials.