Powering GM's Electric Vehicles

Recent advances in battery chemistry and systems design could lead to working prototypes by year's end.

General Motors (GM) recently announced that it is developing two types of plug-in hybrid vehicles, cars designed to run exclusively or almost exclusively on electricity for daily commutes. (See "GM's New Electric Vehicle" and "GM's Plug-In Hybrid.") But the announcements came with this caveat: the battery technology isn't ready, and production will have to wait. In reality, the battery technology is actually quite close to being ready.

A123 Systems has designed a new automotive-grade battery that may make General Motors’ plug-in hybrids possible. Credit: A123Systems

Indeed, GM's vehicle chief engineer, Nick Zielenski, says that individual batteries are already good enough. "We've got enough data at the cell level to feel that the technology is there," he says. What remains to be done is packaging the cells into large battery packs and testing them in actual vehicles. This will be a challenge, Zielenski says, since there is a big difference between using "a single cell and multiplying them all together to get the energy levels that we need for this type of vehicle." But according to development contracts GM recently signed with two groups of companies, such battery packs will be ready for testing in vehicles by the end of this year.

Making batteries for vehicles, especially plug-in hybrids, is very challenging. For accelerating and climbing hills, the battery pack has to deliver enough power to supply the electricity demand of several houses at once. The energy storage capacity required to give a vehicle a 40-mile range would be enough to power a laptop in continuous use for weeks. Yet the space on board for such a battery pack is limited. "What we need is a very reliable and long-lived battery that has also got quite high energy density so we can find a place for it in the car," says Peter Savagian, director of hybrid power-train systems at GM.

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Developers also need to make packs that can survive extremes in temperature and constant vibrations on the road, and still last the life of a vehicle. And they have to make the batteries safe. Last year millions of laptops were recalled because of the danger of their batteries bursting into flame. A plug-in hybrid would have the equivalent of hundreds of laptop battery packs bundled together.

Remarkably, at the level of individual cells, many of these problems have already been addressed. Lithium-ion batteries have much higher capacity than the lead acid batteries used in electric cars in the past, and even more than the nickel-metal hydride used in hybrids today. According to GM, its new Chevrolet Volt concept vehicle stores the same amount of energy as the company's EV-1 electric vehicle, but in just one-third the area. And while lead acid battery packs have to be replaced every couple of years, new lithium-ion batteries seem from lab tests to be able to last 10 years or more.