With average U.S.
gasoline prices approaching $4 a gallon, drivers and automakers are thinking
electric. Previously steered in this direction by concerns about pollution and
dependence on foreign oil, consumer interest in electric-drive cars continues
to surge. But before Americans are able to flip the switch from gasoline to
electricity, automakers need batteries for the next generation of electric
vehicles that can deliver the range, performance, reliability, and safety
drivers expect.
The Large-Volume Battery Calorimeter (LVBC) is a crucial tool to help put
these new automobiles on the road. Unveiled last year by the U.S. Department of
Energy’s National Renewable Energy Laboratory (NREL), the LVBC is designed to
measure the heat generated by batteries for electric-drive vehicles, analyze
temperature’s effects on systems, and help pinpoint the ways to manage battery
temperatures for the best performance and maximum life. The Vehicle
Technologies Program at the Department of Energy supported the development and
fabrication of the LVBC for advancing battery technologies for advanced
vehicles.
To make electric-drive vehicles that are attractive to consumers, the
batteries that power those cars need to be affordable, high-performing,
long-lasting, and operate at maximum efficiency in a wide range of driving
conditions and climates. The next generation of electric-drive cars and light
trucks will be required to travel farther on electric power alone, placing
greater energy demands on the vehicles’ battery packs. As the packs get larger,
regulating battery temperatures become even more important in helping improve performance,
lifespan, safety, and affordability.
“NREL’s large-volume battery calorimeter is the first system large enough
and accurate enough to test the whole battery systems for electric
vehicles,” says Dr. Said Al-Hallaj, chairman and CEO of AllCell, a major
battery integrator. “We strongly believe that this leading-edge instrument
is critical in developing the battery management system of the next generation
of electric vehicles.”
“Larger and more advanced versions of the lithium ion battery
technology that powers laptops are the next wave in energy storage for plug-in
hybrid and all-electric vehicles. High temperatures shorten the life of lithium
ion batteries, while cold temperatures diminish lithium ion batteries’ power
capabilities and hurt overall vehicle performance. NREL’s LVBC is the only
calorimeter capable of accurately quantifying the heat generation and efficiency
of these lithium ion batteries,” said NREL Principal Engineer Ahmad
Pesaran, who leads the vehicle Energy Storage projects.
Greatest volume and accuracy
The LVBC can determine the exact amount of heat generated by battery cells,
modules, sub-packs, and even some full-size packs as they are charged and
discharged. It combines a high volume test chamber and wide temperature range
options thermal isolation and control, current load capabilities, and precision
measurement.
In addition, the LVBC is the only calorimeter designed to test the
liquid-cooled batteries found in the Ford Electric Focus, the Chevy Volt, and
the Tesla Roadster. GM used an earlier NREL calorimeter to help create the Volt
battery.
“We knew there was a need for this technology. Testing cells and
smaller modules in lower-capacity calorimeters was only giving us—and car and
battery manufacturers—part of the picture,” said NREL Senior Engineer
Matthew Keyser, who developed the LVBC.
Despite the LVBC’s large size, its heat-flux measurements are extremely
precise, recording heat rates as low as 15 milliwatts and heat inputs as low as
15 Joules. Achieving this degree of sensitivity in such a large volume required
a number of design innovations, including superior thermal isolation and the
ability to test batteries under realistic driving conditions. The instrument is
able to determine heat levels and energy efficiency within plus or minus 2% of
actual values.
Troubleshooting before cars hit the road
Members of the U.S. Advanced Battery Consortium, which includes Chrysler,
Ford, and GM, realize that in-depth analysis of battery heat management issues
can help automakers troubleshoot thermal issues and engineer systems capable of
maintaining batteries within the ideal temperature range. The comprehensive and
accurate information that the LVBC provides will be critical to the automotive
and battery industry as new advanced batteries and thermal management systems
are optimized for the next generation of electric-drive vehicles. NREL is
testing batteries from a number of battery developers including A123Systems,
LGChem-CPI, and Johnson Control Saft in the LVBC.
By addressing thermal management issues in the design stage, before these
vehicles hit American roadways, carmakers are more likely to offer consumers
affordable, high-performance options to gasoline-powered automobiles—and relief
from high prices at the pump.