Data Points

Apr 1, 2008 12:00 PM

Battery Tests Suggest Li-Ion is Tough Enough to Rule Automotive Jungle

Researchers in the Power Sources R&D group at Sandia National Laboratories have been driving nails into batteries, heating them to extreme temperatures, overcharging them and putting them into some of the most adverse conditions possible to see how much abuse they can take before they blow up. And for certain types of Li-ion batteries, the answer is a lot.

The research is part of the U.S. Department of Energy (DOE)-funded FreedomCAR program, which is looking at Li-ion batteries to be part of hybrid electric vehicles and eventually plug-in hybrid electric vehicles (PHEVs).

Current hybrid vehicles run on gasoline and use nickel-metal hydride (NiMH) batteries as the energy-storage device for the electric motor. The intent of the battery portion of the FreedomCAR program is to replace the older-type batteries with safe Li-ion batteries that have six times the energy density of lead-acid batteries and two to three times the energy density of NiMH batteries.

“Lithium-ion batteries, generally found in laptop computers and power tools, have greatly improved over the past few years,” says Peter Roth, lead researcher for Sandia's FreedomCAR battery efforts. “In fact, they have improved so much that we expect to see them in hybrids later this year and possibly even in short-range plug-in hybrids within two years.”

Roth notes that the battery industry has made great strides in manufacturing safe, long-lasting, affordable batteries. Sandia has played a role in assuring that the Li-ion batteries are indeed safe and can operate for long periods of time. One way Sandia researchers have helped determine how safe and long-lasting batteries are is by testing them in adverse situations to determine when and how they can fail or leak their electrolyte.

The Sandia research group obtains batteries and battery materials from research laboratories, such as Argonne National Laboratory, and companies that manufacture and sell batteries. Sandia researchers then study the stability of the materials, their flame-retardant performance, the high-temperature integrity of separators between the cathode and anode, and general thermophysical properties.

“We look at fundamental chemistry, wanting to discover the kinds of gasses 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.”

Roth says that some of the newer batteries, like the new lithium/iron-phosphate batteries used in handheld power tools, are extremely resilient and less reactive when subjected to extreme conditions, unlike other types of batteries.

These are the type of batteries the FreedomCAR program is seeking, particularly for PHEVs. A PHEV is a regular hybrid that operates on both gas and battery power, but with an extension cord that allows recharging of the vehicle's batteries from an ac outlet. PHEVs make it essential that batteries be completely safe since they will be recharging in people's garages.

Industry experts predict that PHEVs that can run 10 miles purely on electric energy are two to three years away, while PHEVs that can run 40 miles on all electric are three to four years away.

Li-ion batteries that will go into vehicles will be similar to computer laptop batteries. One main difference is there will be “a lot of them,” Roth says.

The first hybrids using Li-ion batteries are expected on the market later this year. Mercedes-Benz soon will launch the S400 BlueHybrid. After that, it will launch the S300 Bluetec Hybrid, a diesel car that is combined with a Li-ion battery. Also, General Motors plans to introduce a 40-mile PHEV with Li-ion batteries in 2010.

Ford, which is also working with Southern California Edison (SCE; Rosemead, Calif.), is said to be the first automotive manufacturer to partner with the utility industry to facilitate advancing PHEVs. The EPRI-Ford program will build on the ongoing Ford-SCE partnership and help determine regional differences in how the operation of PHEVs will impact the grid.

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