Just about everyone has endured the frustration of their cell phone running out of power before they get a chance to recharge, and although electric cars are growing in popularity, they remain limited by how far they can drive before their battery runs out of juice. Indeed, the energy density of batteries—how much energy they pack in a given mass or volume—has been a major challenge for consumer electronics, electric vehicles, and renewable energy sources.

New advances at Caltech may go a long way toward improving things. Researchers working in the lab of Julia R. Greer have made a discovery that could lead to lithium-ion batteries that are both safer and more powerful. Their findings provide guidance for how lithium-ion batteries, one of the most common kinds of rechargeable batteries, can safely hold up to 50 percent more energy.

Conventional lithium-ion batteries use graphite to make up the anode, the electrode at which current enters a battery cell. Graphite has been the material of choice for this task for 30 years because it is light, stable, affordable, and can endure the rigors of countless battery cycles. But there are better materials for the job, says Greer, Caltech's Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering, and Fletcher Jones Foundation Director of the Kavli Nanoscience Institute—if only some technical challenges can be overcome.

"Every power-requiring application would benefit from batteries with lithium instead of graphite anodes because they can power so much more," she says. "Lithium is lightweight, it doesn't occupy much space, and it's tremendously energy dense."