We saw a real gap in the marketplace for accurate testing of the larger battery systems. It was obvious that NREL’s technology, missing in the marketplace, could provide improved information on battery performance and safe system integration key for success in these growing application areas.

—Dr. Gilles Widawski, President of NETZSCH North America, LLC

With better measurement of the heat signatures for LFLIBs, researchers can better understand how to enhance the chemistry to improve battery performance, life-time and to make them inherently safer using improved materials and chemistries.

Automakers can use these data to predict battery performance and design thermal management systems capable of maintaining a battery pack within the desired temperature range. Regulating the operating temperature of a battery pack is essential because it affects performance (power and capacity), charge acceptance (during regenerative braking), lifespan, safety, and vehicle operating and maintenance expenses.

Under funding from the DOE’s Office of Energy Efficiency and Renewable Energy, NREL has been working on battery thermal testing and calorimetry for more than 15 years, developing numerous instruments and measuring heat generation from batteries for clients around the world.

NREL presented its initial calorimeter—initially fabricated by Calorimetry Sciences Corporation and later improved upon by NREL—at the Long Beach Battery Conference in January 1998. Since then, NREL has developed a number of isothermal calorimeter systems, including the Large-Volume Battery Calorimeter, and a new Isothermal Cell Calorimeter, for which NREL signed a Cooperative Research and Development Agreement (CRADA) and license agreement with NETZSCH to commercialize the design.

Isothermal Cell Calorimeter. The new single chamber conduction, isothermal calorimeter at NREL has a testing chamber measuring 15 cm x 10 cm x 6 cm; the test chamber is submerged under an isothermal bath. Heat detection limit is 1 mW and 10 J, and initial testing shows excellent baseline stability and an error of less than ±1.6%.

Large-Volume Battery Calorimeter (LVBC). The Large-Volume Battery Calorimeter in NREL’s lab has a calorimeter chamber measuring 40 cm x 60 cm x 40 cm—the largest of its kind in the world for battery applications—and has the ability to test cells, modules, sub-packs, and some full-size battery packs. The calorimeter is also uniquely able to test liquid-cooled batteries, such as those found in the Ford Electric Focus, the Chevy Volt, and the Tesla Roadster.

The Large-Volume Battery Calorimeter differentiates between the heat generated from the cells in a module, the inter-connects between cells, the battery management system, the thermal management system, and the connection points to the vehicle.

NREL’s Large-Volume Battery Calorimeter is designed to:

• Obtain accurate heat generation data for modules developed by battery manufacturers under different modes of system operation, battery power profiles and operating temperatures. Accuracy is better than 3%.

• Measure round-trip energy efficiency (i.e., to distinguish energy stored from waste heat generated) for use in estimating vehicle energy consumption.

• Compile data to validate and refine thermal models developed by researchers, battery developers and vehicle manufacturers.

• Generate a performance history to evaluate the effects of aging and cycling.

• Evaluate physical and electrochemical design changes that could lead to better battery modules and improved performance.

• Understand the heat lost due to inefficient interconnects within a module or pack, as well as those from the energy storage cells.

• Evaluate the efficacy of liquid-cooled energy storage systems.

NREL received a CO-Labs award for development of the LVBC in October 2012 from Colorado Governor John Hickenlooper.

It was clear from our success working with researchers and engineers involved in all aspects of Li-Ion battery development and their use, and feedback from the USABC battery developers that we had a first-rate calorimeter technology. We felt that this technology could be useful in the hand of scientists and engineers in many organizations and just needed a path to go from our laboratory prototypes to a commercial product.

NETZSCH has a proven track record of developing and commercializing calorimeters and thermal analysis tools to demand requirements. When NETZSCH approached us for collaboration, we felt it was a natural fit for our technology as they already offer battery testing systems in the market.

—Dr. Ahmad Pesaran, Manager of the Battery and Energy Storage Research Group at NREL

The new calorimeter is currently under a rapid development and verification process and is expected to be released in the beginning of summer 2013. Based on initial testing done on the NREL prototype, this instrument is expected to provide data which is currently unavailable.

Resources

• Ahmad Pesaran, Matt Keyser, Gi‐Heon Kim, Shriram Santhanagopalan, Kandler Smith (2013) Tools for Designing Thermal Management of Batteries in Electric Drive Vehicles (presented at AABC 2013)