Building a Better Battery

A newly engineered battery material could allow quick charging of portable devices.

State-of-the-art lithium rechargeable batteries have very high energy densities, that is, they are good at storing large amounts of charge. The downside is they are sluggish at recharging and discharging that energy.

Such batteries in modern electric cars, for example, have a lot of energy, so you can drive at 55 miles an hour for a long time, but you can't accelerate quickly.

So what’s the problem? Scientists have thought the lithium ions responsible, along with electrons, for carrying charge across the battery simply move too slowly through the material. But about 5 years ago, Gerbrand Ceder, a professor of materials science and engineering the Massachusetts Institute of Technology, and his colleagues made computer calculations of the commonly used battery material lithium iron phosphate, which predicted that the lithium ions should actually be moving extremely quickly.

"If transport of the lithium ions was so fast, something else had to be the problem," Ceder said.

Now, he and his coworkers have re-engineered a well-known battery material to allow electrical energy to pass rapidly through it, which could usher in smaller, lighter batteries that allow cell phones and other devices to recharge almost instantly.

"The ability to charge and discharge batteries in a matter of seconds rather than hours may open up new technological applications and induce lifestyle changes," Ceder and graduate student Byoungwoo Kang conclude in a recent report on the process.

It turns out lithium ions can indeed move very quickly in battery material but only through tunnels accessed from the surface. If a lithium ion at the surface is directly in front of a tunnel entrance, there's no problem: it proceeds efficiently into the tunnel. But if the ion isn't directly in front, it can’t move to access the tunnel entrance.

So, Ceder and Kang devised a way around the problem by creating a new surface structure that allows the lithium ions to move quickly around the outside of the material, much like a beltway around a city. When an ion traveling along the beltway reaches a tunnel, it is instantly diverted into it.

Using their new processing technique, the two went on to make a small battery that could be fully charged or discharged in 10 to 20 seconds (it takes 6 minutes to fully charge or discharge a cell made from the unprocessed material). And, Ceder says further tests showed the new material does not degrade as much other battery materials when repeatedly charged and recharged. That could lead to smaller, lighter batteries, because less material is needed for the same result, he said.

Ceder believes the work could make it into the marketplace within two to three years.

The work, which was reported in the March 12 issue of the journal Nature, was supported by the National Science Foundation through the Materials Research Science and Engineering Centers program and the Batteries for Advanced Transportation Program of the U.S. Department of Energy.

—By Leslie Fink/NSF from material provided by MIT.