Paving the Road to Faster, Safer Batteries

Scanning electron microscope image shows an anode of asphalt, graphene nanoribbons, and lithium. This composite material holds promise for developing safer and faster-charging batteries.

Tour Group/Rice University; American Chemical Society

Rechargeable lithium ion batteries have been the overwhelming energy storage choice for portable electronic devices and electric-powered vehicles. However, one major shortcoming to increasing their speed and storage capacity is their potential to short-circuit and explode or catch fire. Chemist James M. Tour and his colleagues at Rice University have developed a process to build faster, safer batteries, using a surprisingly cheap material: asphalt.

When a lithium ion battery is charged and discharged, tiny mossy fibers called lithium dendrites can form on the battery’s negatively charged anode. If the lithium dendrites reach the battery’s positive cathode, the system can short-circuit, with dangerous repercussions. Tour’s team took gilsonite, a naturally occurring form of asphalt with ultrahigh surface porous area carbon, and added highly conductive graphene nanoribbons. When this new composite material was thinly coated with lithium metal, the lithium particles were evenly deposited across the porous asphalt matrix. This allowed it to withstand high currents and hundreds of charge-discharge cycles without forming the problematic lithium dendrites.

The researchers compared this composite material’s performance with anodes created from only the asphalt and lithium—without the crucial graphene nanoribbons. At low current levels, both versions showed stable and efficient performances, but at higher currents, dendrites began growing on the one without the nanoribbons, and efficiency dropped.

The real test came when Tour and his team used the new asphalt-graphene nanoribbon matrix to build a full lithium ion battery. The results were encouraging. The battery not only delivered high power and energy densities without forming dendrites, but it performed at speeds ten times faster than typical lithium ion batteries. “It charges superfast,” said Tour. “Think of charging your cell phone from empty to full in five minutes. A car could charge in less time than it takes to fill with gasoline, if the grid could deliver the current that fast.” In other words, adding a bit of asphalt to an electric car’s battery could help it hit the road even sooner. (ACS Nano)