While President Bush spoke this week about a new kind of highly efficient hybrid vehicle, on a visit to battery-maker Johnson Controls in Milwaukee, WI, an article appeared in the current issue of Science describing the latest in a series of recent advances that could make hybrids, and even all-electric vehicles, practical.
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 has been that batteries based on this material could be charged and discharged only slowly, otherwise the amount of energy they could store would drop dramatically.
In the Science paper, researchers at MIT and the State University of New York (SUNY) in Stony Brook described 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 it was 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 – the potentially highly-efficient vehicle Bush spotlighted in his speech on Monday, saying these cars could eventually get 100 miles per gallon. The new technology could also help make all-electric vehicles practical.
President Bush came to Johnson Controls, which last fall announced a new center of excellence for developing lithium-ion batteries for hybrids, to talk up his Advanced Energy Initiative, first announced in this year’s State of the Union address. The Bush administration’s 2007 budget provides $31 million for battery technology research, compared with $150 million for research into deriving ethanol from biomass, and nearly twice that amount, $288 million, for hydrogen fuel-cell research.
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 reduce the weight of battery packs for plug-in hybrids by four to 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.
The MIT-SUNY research joins other recent advances in battery materials. Amine’s own work at Argonne has produced promising new lithium-ion electrodes, as has that of researchers at A123 Systems in Watertown, MA, and E-One Moli Energy in British Columbia. Meanwhile, Firefly Energy, Peoria, IL, is developing lighter lead-acid batteries that may work well for hybrids.
Developing battery packs using these new technologies and incorporating them into hybrids could take several years, as automakers perform further tests and integrate the technologies into their vehicle development cycles. Even then, the impact on fuel prices and energy consumption could take decades, as consumers gradually purchase the more efficient vehicles.
Because of this long time frame, some experts, including John Heywood at MIT, say that, to achieve shorter-term reductions in oil consumption and prices, people will have to buy cars available now that have better fuel economy. “The only things that work really fast are for people to change their buying and driving habits,” Heywood says. To encourage these changes, advocates have called for higher fuel-economy standards and tax breaks for purchasing higher fuel-economy vehicles.
Meanwhile, the MIT-SUNY computer model could help the field generally. 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.”
Home page image courtesy of Science journal.
Caption: Lithium (in green) moves from one octahedral site (in red) to another by passing through an intermediate tetrahedral site where it encounters strong repulsion from a nearby transition-metal cation (in blue).