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NREL Battery Testing Capabilities Get a Boost

February 5, 2010

Photo of a Test engineer standing next to a camera showing a thermal image of a battery being tested. Enlarge image

Engineer Dirk Long uses thermal imaging equipment to capture a battery's infrared fingerprint to diagnose its behavior. NREL soon will be ramping up testing as the battery industry uses stimulus funding to enhance batteries used in advanced vehicles.
Credit: Pat Corkery

Batteries are the heart of today's advanced electric drive vehicles and many manufacturers have their own preference for specific battery geometry and chemistry including their choice of materials for cathodes and anodes. However, all of the manufacturers are concerned about the performance, life, safety and cost of lithium ion batteries even though their designs are varied. The U.S Department of Energy (DOE) is looking to help the U.S. battery industry with a simple goal — to mass produce better batteries domestically while addressing safety, affordability, life, and performance.

As a result of DOE's support, more work and funding for battery research is coming to NREL via both indirect and direct avenues thanks to the American Recovery and Reinvestment Act (ARRA). In March, President Obama announced $2.4 billion to help drive the development of the next generation of electric drive vehicles in the United States. As part of that announcement, DOE released a competitive solicitation for up to $1.5 billion in federal funding for manufacturing advanced batteries and related drive components.

The funding will spur faster development of batteries for cars with electric powertrains, including hybrid electric, plug-in hybrid electric, all-electric and fuel-cell vehicles. Battery thermal management is crucial in optimizing the performance and reducing the life-cycle costs for these types of batteries. Once manufacturers start cranking out new and more efficient prototypes, they'll turn to NREL for thermal testing and validation.

"Right now, we already have a back-log of batteries for thermal testing," NREL Principle Engineer and Energy Storage Task Leader Ahmad Pesaran said. "We know that in one or two years, when the battery companies start producing new batteries to evaluate, we wouldn't have been able to keep up without the new investment in equipment."

NREL Garners Big Bucks for Battery Lab Improvements

Photo of three men standing in front of various battery components in a laboratory. Enlarge image

Senior Engineer and Battery Lab Manager Matt Keyser, Principal Engineer Ahmad Pesaran and Engineer Dirk Long discuss projects in NREL's Thermal and Life Test facility, which recently received $2 million in ARRA funding to enhance battery testing equipment and facilities.
Credit: Pat Corkery

This fall, DOE recognized that NREL would be a key laboratory in the development of these advanced vehicle batteries. So, the lab was awarded $2 million from ARRA for the Battery Thermal and Life Test Facility.

"ARRA has already funded the battery industry to design and build new batteries. DOE also recognized that they needed to equip the national labs to test the new batteries that will be manufactured as a result of the ARRA investments," Pesaran said.

The $2 million dollars coming to NREL will be used to upgrade and enhance the capabilities of the lab with new testing and analysis equipment. Some of the money will also be used to upgrade the utilities and facilities where the researchers perform the testing.

NREL will be purchasing up to 20 new battery testers, which will nearly triple the lab's ability to test batteries. NREL will also purchase two new calorimeters to measure the heat and the efficiency of small and medium sized cells; augmenting NREL's two existing larger calorimeters.

"The team is very excited," Pesaran said. "There have been times where we haven't been able to accomplish all the technical studies that we wanted to do because of lack of equipment. This is going to help resolve that issue."

Pesaran noted that U.S. testing equipment manufacturers also will benefit from NREL's ARRA award because the new testing equipment will be ordered from U.S. suppliers.

Why Better Batteries are Needed

"The longer a battery lasts the better the cost efficiency and consumer satisfaction," Pesaran said. "For cars, it is expected that batteries will last 15 years compared with current lifetimes of only 5-10 years, mainly due to thermal issues."

Batteries are the centerpiece for advanced electric-drive vehicles. Making cars more energy efficient means using less fuel, which helps reduce oil consumption and the nation's dependence on foreign oil. Furthermore, they allow vehicles to drive on electricity, adding diversity to the fuel supply and increasing national energy security.

NREL researchers seek to improve the thermal performance of batteries by studying how heat affects the performance and life of batteries. NREL experts analyze fluid flow (liquid or air) through different types of battery packs to determine how the flow affects the pack's performance and life-cycle costs. Researchers measure and analyze the heat generation, efficiency, and specific heat of battery modules under specified charge/discharge cycles using the state-of-the-art calorimeters in NREL's energy storage laboratory. Incorporating thermal imaging (still and time-lapse video) helps researchers determine temperature distributions and identify potential hot spots in battery modules and packs.

"Measuring heat generated from a battery tells you how efficiently the battery is operating," Pesaran said. "The data on the heat generation is used by battery companies to determine how much cooling is needed to keep the battery at optimal temperatures because higher temperatures cause the battery to degrade faster.

"It's then up to the battery company to make some decisions. Can they reduce the amount of heat by changing the cell or material design? Or, will they design a cooling system to keep the battery at an optimal temperature. Cooling is easier; but because of the battery size, you need to make the cooling system as small and as efficient as possible without adding weight to the car."

In the end, the goal at NREL is to help industry develop better batteries. And, NREL has lots of companies lined up for future testing, many of which, according to Pesaran, wrote strong letters of support for NREL's ARRA funding application.

NREL Has its Own Testing Planned

Photo of a man holding large rectangular box with battery cells inside. Enlarge image

Dirk Long holds a liquid-cooled battery module consisting of 12 cylindrical lithium ion cells. The unit was tested for Saft America as part of a DOE/FreedomCAR project.
Credit: Pat Corkery

The battery research team will also spend time generating data to be used for validating battery thermal and electrochemical models. Modeling and simulating advanced energy storage systems in vehicles will help designers and researchers accelerate finding solutions for innovative battery designs and best ways to enhance overall vehicle performance.

Pesaran noted that NREL "has leading edge computer models of thermal and electro-chemical battery performance." NREL's team evaluates energy storage devices, such as batteries and ultracapacitors by constructing computerized representations of energy storage devices and vehicles which simulate real world driving conditions and environments including temperature changes and driving styles. Researchers then look at the data to determine how much heat was generated under various driving conditions.

"The data that we generate is going to help us validate the battery models that we have developed," Pesaran said. "This is really important because NREL has developed a number of models that are being used for industry, but in some cases we haven't had sufficient data to validate them. So, new equipment is essential to generate the data to validate the models so that industry can use them with greater confidence."

Learn more about NREL's energy storage group and battery R&D.

— Heather Lammers