New Batteries Readied for GM's ElectricVehicle
The technologies behind the battery packs for the GMVolt are being tested and could be ready within ayear.
By Kevin Bullis
Electrifyingdevelopment:General Motors' electric-vehicle platform useselectric motors powered by batteries to propel the car. In theconfiguration shown here, a large battery pack down the center ofthe vehicle provides 40 miles of range before an onboard generator(at the front of the car) kicks in to extend the range by 600miles.
Credit: General Motors
This week, GeneralMotors (GM) announced its selection ofbattery makers to develop and test battery packs for use in itsproposed electric vehicles. The selected battery makers,Compact Power, based in Troy,MI, and Continental AutomotiveSystems, based in Germany, say that they'veovercome the performance and cost limitations that have been anobstacle to electric vehicles in the past.
Over the next 12 months, researchers from, CompactPower, Continental Automotive Systems and GM will be testing thebattery-pack designs in the lab and in vehicles to confirm that thepacks can work for the life of the car--at least 10 years,says Denise Gray,director of hybrid energy storage devices at GM. Initial tests ofindividual battery cells, along with projections about theperformance of battery packs that can contain hundreds of thesecells, have Gray optimistic that her company will have proven packsby June 2008.
If the packs perform well, they are slated for usein the proposed Chevrolet Volt, an electric concept car announcedby GM in January. The Volt marks a change in emphasis for GM, whichpreviously focused on more distant plans to bringhydrogen-fuel-cell-powered cars to market. The Volt could be readywithin a few years. Until now, however, it has been unclear whowould develop its advanced batteries.
There are a number of design variations for theVolt, but they will all be propelled by electric motors. In oneversion, the battery pack, which can be recharged by plugging itin, will provide 40 miles of range. Then an onboard gasoline- orethanol-powered generator will kick in to recharge the battery,providing an additional 600 miles of range. A proposedhydrogen-fuel-cell version would have a smaller battery pack and noonboard generator.
To make batteries that are up to GM'sspecifications, battery makers have had to redesign the chemistryof lithium-ion batteries, a type of battery widely used in mobilephones and laptops. While lithium-ion batteries are light andcompact, the type of lithium-ion battery typically used inelectronic devices relies heavily on cobalt, an expensive metal.The cobalt oxide used in one of the battery's electrodes isn'tthermally stable, making the batteries prone to bursting into flameif damaged or poorly manufactured--a shortcoming that led to themassive recall of millions of laptop computer batteries last year.(See "Safer Lithium-IonBatteries.") This could be a problem invehicle battery packs, which would be much larger than those inportable electronics, so an accident could be moredangerous.
One alternative is to replace cobalt with manganese.Mohamed Alamgir, director of research at Compact Power, says thatmanganese-oxide electrodes are significantly more thermally stablethan cobalt oxide, and less expensive. The battery maker has alsodeveloped a new material for keeping the electrodes separate: thematerial remains stable at higher temperatures than conventionalmaterials, further guarding against the runaway heating that causesbatteries to catch fire. What's more, the company makes thebatteries in a flat shape rather than in the typical cylindricaldesign. Alamgir says this flat shape prevents heat from building upat the center of the cell, making it easier to keep the battery atan even, cool temperature.