How can lithium-ion batteries improve hybrids?

Image Gallery: Hybrid Cars An assembly line for General Motors lithium-ion battery for the Chevrolet Volt is seen at the Brownstown Battery Pack Assembly in Brownstown Township, Mich., on Jan. 7, 2010. See pictures of hybrid cars.
AP Photo/Carlos Osorio

It seems like lithium-ion batteries are everywhere these days, in the tiniest portable electronics and the biggest electric cars. These rechargeable powerhouses will soon be installed in hybrid vehicles, too, replacing the nickel metal hydride (NiMH) batteries used most often in the hybrids of the past decade.

Though lithium-ion (Li-ion) batteries have been expensive in the past, as more of them are made, they become less expensive to manufacture. In the long run, as more and more lithium-ion cells are created, automakers can lower the cost of hybrid cars until the prices are closer to that of conventional gasoline-powered cars [source: HybridCars].

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The biggest advantage in lithium-ion technology is its ability to be rapidly recharged, which is exactly what's required in hybrid driving. The power stored in the batteries is easily tapped and readily available, and when technology like regenerative braking is factored into the equation, the cells can be recharged rather quickly.

With lithium-ion technology so frequently in the news, it's easy to forget that these batteries aren't being used much in vehicles -- not yet, anyway. The latest generation of hybrids, like the Chevy Volt and Fisker Karma, use Li-ion battery cells. But the hybrids we've come to know and love over the years, including the Toyota Prius, Honda CR-Z and Ford Escape, still use NiMH battery packs.

Keep reading to find out how these types of batteries stack up against each other.

Lithium-ion vs. Nickel Metal Hydride Batteries

General Motors Chairman and CEO Ed Whitacre addresses the media next to the first lithium-ion battery off the assembly line for the Chevrolet Volt at the Brownstown Battery Pack Assembly in Brownstown Township, Mich., on Jan. 7, 2010.
General Motors Chairman and CEO Ed Whitacre addresses the media next to the first lithium-ion battery off the assembly line for the Chevrolet Volt at the Brownstown Battery Pack Assembly in Brownstown Township, Mich., on Jan. 7, 2010.
AP Photo/Carlos Osorio

The most obvious difference between Li-ion and NiMH batteries is the material used to store power. Lithium-ion batteries are made of carbon and highly reactive lithium, which can store a lot of energy. Nickel metal hydride batteries use hydrogen to store energy, with nickel and another metal (such as titanium) keeping a lid on the hydrogen ions.

With these different structures there are, of course, several practical differences, too:

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Cost: Nickel metal hydride batteries are, right now, the less-expensive technology. As production of lithium-ion cells ramps up, though, economies of scale come into play and the cost of Li-ion cells should drop. When more vehicles require more batteries, each individual battery becomes less expensive to manufacture.

Weight: NiMH batteries are larger and heavier than Li-ion batteries. Weight matters in hybrid cars, since the battery power will have to overcome the vehicle's inertia (without any help from the gasoline engine) for maximum mileage. Lighter battery packs with higher energy density make it easier to get the car going.

Power: Li-ion and NiMH batteries can actually hold a similar amount of power, but the lithium-ion cells can be charged and discharged more rapidly. Li-ion also doesn't have as much of a "memory effect," which occurs when a battery is recharged before it is fully empty. This can diminish a battery's capacity. Lithium-ion batteries are less affected by memory effect than NiMH batteries are [source: Hitachi].

Durability: While both types of batteries are durable and both have been in use for years in various applications, this is the one area where NiMH has an advantage. Some Li-ion batteries don't last as long in extreme temperatures, particularly in very hot climates. But manufacturers are working to improve the chemistry to make the Li-ion batteries last as long as the vehicles they power.

For more information about hybrid cars, batteries and other related topics, follow the links on the next page.

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Sources

  • Hitachi. "Lithium-Ion Batteries for Hybrid Electric Vehicles." December 2009. (Dec. 10, 2010) http://www.hitachi.com/environment/showcase/solution/mobility/lithiumion.html
  • HybridCars.com. "Expert: Lithium Ion Batteries Will Help Hybrids More Than Electric Cars" Dec. 14, 2009. (Dec. 10, 2010) http://www.hybridcars.com/components/expert-lithium-ion-batteries-will-help-hybrids-more-electric-cars-26284.html
  • HybridCars.com. "Lithium Ion Hybrid Batteries." April 3, 2006. (Dec. 10, 2010) http://www.hybridcars.com/technology-stories/lithium-ion-batteries.html
  • McGuigan, Brendan, "What Are NiMH Batteries?" WiseGeek. Sept. 9, 2010. (Dec. 8, 2010) http://www.wisegeek.com/what-are-nimh-batteries.htm
  • Siuru, Bill. "Toyota to Unveil Lithium-Ion Powered Prius Plug-In Hybrid." GreenCar.com. Sept. 11, 2009. (Dec. 8, 2010) http://www.greencar.com/articles/toyota-unveil-lithium-ion-powered-prius-plug-hybrid.php