According to Moore's Law, the speed of computer chips grows at an exponential rate. Sadly, there is no such rule regarding battery capacity. So while computer chips trip over themselves getting faster, the batteries that power them—in laptops, cell phones and other chip-driven devices—lag behind, constrained by chemistry. However, thanks to a breakthrough by Stanford researcher Yi Cui, the lithium-ion batteries that power most of these devices may soon be able to hold 10 times as much power as the ones powering today's gadgets.

Lithium-ion batteries work by transferring lithium ions from an anode, typically made from carbon, to a metal-oxide cathode. Carbon anodes can only hold 1 ion per 6 carbon atoms. A silicon anode, by comparison, can hold a much greater charge—4.4 lithium ions per single silicon atom. But because silicon swells to four times its volume when charged, using it in a battery causes the anode to break apart, rendering standard silicon useless for power. The breakthrough is in the discovery that, while 100-nanometer-wide silicon nanowires expand, they do not break. This phenomenon is a mystery. Maybe it’s their small size or shape that keeps them from breaking, or perhaps they are just fundamentally different. "But," Cui says, "the results are exciting."

A paper published this week in the journal Nature Nanotechnology gives the results of 30 charge-and-discharge cycles. But since submitting his paper six months ago, Cui claims to have pushed his battery through 1000 cycles. The results? An energy storage capacity of more than 4200 milliampere hours per gram, or 10 times that of a standard lithium-ion battery.

Imagine a laptop that could run for nearly two days or an electric car with the power to motor from New York to Chicago on a single charge. In fact, improvements in battery energy capacity could positively impact nearly everyone, extending the life—and shrinking the size—of cellphones, iPods and portable computers, and maybe even giving plug-in cars the edge they need to catch on.

And while modern lithium-ion batteries are, for the most part, safe and stable, a couple of highly-publicized laptop explosions in recent years means that a new power source's basic safety can not be overlooked. "We have fundamental reasons to believe a silicon nanowire anode is going to be safer," Cui says. Battery safety, he says, depends on "volume expansion and the surface chemistry of the electrode." His nanowires can handle the volume expansion. And he says tests show that the surface chemistry is more stable than in batteries with carbon anodes. "Of course to prove something to be safe, you've got to accumulate lots of data. We hope to do that."

"Usually people want low surface area to make batteries safe," says Mark Obrovac, senior scientist at the 3M Lithium Ion Battery Laboratory. "The surface area of a nanowire electrode must be astronomical." Adds Obrovac: "It's a great thing he's done making silicon cycle, but it will require a lot of work before we'll see this in a commercial application."