Researchers at the Stanford University Department
'It's not a small improvement,' researcher Yi Cui said. 'It's a revolutionary development.' Traditional lithium ion batteries use graphite as the anode, or the part of the battery that positive current flows into. Scientists have long known that a much higher theoretical charge could be achieved with a silicon anode, but due to a quirk of silicon's nature, until now such anodes have been impossible. Silicon expands when charged with lithium ions, and then contracts again as the charge flows out. Typically, one such charge-discharge cycle causes the silicon to be pulverized, making it ineffective for future cycles. Cui and his fellow researchers overcame the problem by growing a cluster of silicon nanowires directly onto the stainless steel that serves as the battery's current collector. While these nanowires, originally on thousandth the thickness of a sheet of paper, swell to about four times their size when charged with lithium, they do not fracture when they shrink back down. On the first charge cycle, the anode attained silicon's maximum theoretical charge. Subsequent cycles achieved 75 percent of that charge and maintained it even over many charge-discharge cycles. Cui expressed optimism that the technology could be commercialized within 'several years.' 'We are working on scaling up and evaluating the cost of our technology,' he said. Cui has filed a patent for the technology and says that he is considering either starting his own company or forming a partnership with an existing battery company to further develop and market it.