GM has lithium-ion batteries for hybrids figured out

— -- General Motors will begin mass production in 2010 of hybrid vehicles that use lithium-ion batteries and, in many cases, turbocharged small-displacement gasoline engines. The combination will let GM use the hybrid system on any size vehicle it produces.

The announcement, made at the Geneva auto show on Tuesday, follows a Mercedes announcement last week that its S-Class sedans will come in a hybrid version next year that uses a lithium-ion battery. Toyota tm has also said it will roll out low-emission vehicles using lithium-ion batteries in the near future.

It's a sign that lithium-ion batteries, now common in laptops and cellphones, may finally be ready for prime time in vehicles. Automakers have been striving to develop the battery, because it is better-suited to power hybrids — and eventually fully electric vehicles — than the current nickel-metal-hydride batteries.

Lithium-ion batteries are "starting to turn the corner," says Prabhakar Patil, CEO of Compact Power, one of the companies chosen by GM gm to help develop a lithium-ion battery for the fully electric Chevrolet Volt expected to go on sale in 2010. "For the first time with the lithium ion, we see a battery that can make the technology work."

Lithium-ion batteries have some drawbacks. They don't work well in very cold weather; they generate heat and need a way to be cooled; and they cost more than other batteries. But they are lighter and smaller for their power, so carmakers like them because they don't have to waste a lot of space on a huge battery.

The lithium-ion battery GM will use in its second generation of hybrids is a quarter the size of the nickel-metal-hydride batteries it now is using.

"We need a battery that is very compact and is very light," says Stephen Poulos, global chief engineer of GM's hybrid systems. "Lithium ion is a great enabler for that."

GM isn't the first to use lithium-ion batteries — they are already used in pilot projects as automakers work on developing hybrids and hydrogen fuel-cell vehicles. Honda is using them in its FCX Clarity hydrogen fuel-cell vehicle, but fewer than 100 will be made and will be leased to customers in California this year. Prototype plug-in versions of the Toyota Prius and Ford Escape f also use lithium-ion batteries.

Tesla Motors, a specialty company in California, is to begin production this month of a fully electric sports car using a package of nearly 7,000 laptop computer batteries with a catacomb of cooling channels.

As the automakers continue developing the batteries, cooling them will remain one of the biggest challenges. Patil says the Volt may use a liquid cooling system to reduce battery temperature.