From your drill to your car

By Chris Burroughs

Lithium-ion batteries like those that power your drill and your nail gun could someday power your car.

Lithium batteries have six times the energy density of lead-acid batteries and two to three times the energy density of nickel-metal hydride batteries. But before they can replace the nickelmetal-hydride batteries that power current model hybrid cars and trucks, lithium batteries must be proven safe for the task.

"The lithium-ion batteries that will go into vehicles will be similar to computer laptop batteries," says Peter Roth, lead researcher of Sandia's FreedomCAR battery efforts. "One main difference is there will be a lot of them."

The FreedomCAR program at Sandia tests lithium-ion batteries like those used with power tools for safety and strength. Researchers in Sandia's Power Sources R&D group drive nails into batteries, heat them to extreme temperatures, overcharge them, and put them into some of the most adverse conditions possible to discover how much they can endure before failure.

The Sandia research group studies the stability of battery materials, their flame-retardance, high-temperature integrity of separators between the cathode and anode, and general thermophysical properties. Sandia's work helps confirm that lithium-ion batteries are indeed safe and can operate for long periods of time.

Researchers test batteries in adverse situations to also determine when and how they fail or leak their electrolyte.

"We look at fundamental chemistry, wanting to discover the kinds of gases they emit when they are heated and explode," Roth says. "We also build smaller prototype batteries that, once we get the chemistry right, may eventually be built full size to go into vehicles." Some types of lithium-ion batteries can take a lot of abuse.

"The new lithium/iron phosphate batteries used in handheld power tools are hardier and less reactive when subjected to extreme conditions", says Roth.

Safe, dense batteries will be particularly impor-tant for plug-in hybrid electric vehicles (PHEV). PHEVs operate both on gas and a battery, but they also have an extension cord, so it can be filled with gas at the gas station or plugged into any home 120-volt outlet for all-electric driving. "The battery industry has made great strides in manufacturing safe, long-lasting, and afford-able batteries,” Roth says. "We expect to see lithium/iron phosphate batteries in hybrids later this year and possibly even in short-range PHEVs within two years."

Industry experts predict that plug-ins that can run 10 miles on all electric are two to three years away while plug-ins that can run 40 miles on all electric are three to four years away. The first hybrids using lithium-ion batteries will be on the market later this year.