Battery Breakthrough

A new high-capacity battery material could lead to super-efficient hybrid cars and electric vehicles, helping to slash U.S. gas consumption.

Researchers have long known that a material based on lithium, nickel, and manganese could be used to make lithium-ion batteries that store large amounts of energy. The problem is that batteries based on this material could be charged and discharged only slowly, otherwise the amount of energy they could store would drop dramatically.

Now researchers at MIT and the State University of New York in Stony Brook have shown a way around the problem. The breakthrough came last summer, when Kisuk Kang, a materials science graduate student at MIT, created a computer model that showed that when under conditions of high power, disorder in the lithium-nickel-manganese material caused it to compress and trap the lithium ions that allow electricity to flow. The researchers then synthesized a version of this material without this disorder, freeing the ions to move quickly.

The newly structured material might be a candidate for replacing the batteries used in today's hybrids cars. But its real value could come in taking advantage of both its power and high energy storage capacity in a different kind of hybrid, known as a plug-in hybrid, or else in all-electric vehicles.

Unlike today's hybrids, which ultimately depend on gasoline for power, but run efficiently by storing extra energy in batteries, a plug-in hybrid would use energy from the outlet in a garage, charging overnight, and would run completely on electricity for distances typical in a daily commute. The gasoline-powered engine would only kick in for long trips, after the batteries were depleted. This type of hybrid could save significant amounts of gasoline, since something like 75 percent of daily driving is for short trips, says Gerbrand Ceder, the materials science professor at MIT who led the effort to develop the new material.

Ceder says the new material could cut down on the weight of battery packs for plug-in hybrids by four or five times. The higher rate capability should also make for speedier charging, allowing top-offs between trips that extend the distance a vehicle could go between overnight recharges.

Other attractive features of batteries based on the new material, according to Ceder, are improved safety over other lithium-ion batteries and lower cost. Lower cost, lighter weight, and faster charging might make the batteries attractive for electric vehicles as well.

The material still needs to go through extensive testing, to find out if it will have the longevity and performance capability needed for demanding automotive applications, says Khalil Amine, group leader for battery research at Argonne National Laboratory. He says the relatively high voltages described in the paper may cause batteries to deteriorate quickly, although Ceder says their tests so far have not shown this to be the case. Amine also points to the need for testing charging rates.

Stanley Whittingham, professor of chemistry at SUNY, whose work led to the first commercialized lithium-ion batteries (and who was not involved with the current project), says the computer model, by showing how disorder affects materials, will help other researchers to develop new high-performance batteries. As for the new material, "In the end, to really determine whether this is a critical material, what we need is some extended cycling," he says. "But the rate capability looks great. It looks really promising."