Environmental Energy Technologies Division Newsletter, Fall 2007,Vol.4, No. 4) Page: 4 of 28
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combustion engines still out-perform all other power sources, but battery researchers
are confident that they can improve the profile of lithium-ion batteries substantially.
The map's horizontal axis is power, and represents acceleration; for acceleration comparable to internal
combustion engines, electric cars need to be able to ramp up power quickly. The map's vertical axis is
energy, representing the amount of energy a battery can store. It's a measure of range-the more energy
the battery stores, the farther the car can travel.
Different types of batteries are represented on the map by curved lines, which show the decrease in stored
energy as power increases. All batteries show a big decline in energy-that is, range-as they achieve
more and more power, or acceleration.
A star on the lower right of the map represents the U.S. Department of Energy's goal for hybrid electric
vehicles. Some lithium-ion batteries on the market today already meet the goal established for hybrid
vehicles; these batteries provide sufficient acceleration but not much range. Nickel metal hydride batteries
fall just short, and lead acid batteries, the oldest of all technologies, trail the pack.
The upper star on the map represents DOE's range and acceleration goal for future electric vehicles.
Internal combustion engines sit high on the performance curve, but no battery technology currently meets
the goal, although lithium-ion batteries come closest. According to some claims, fuel cells could
theoretically come close to the range and acceleration needs of electric vehicles, but this technology is still
From Real Batteries to Models and Back Again
Srinivasan models lithium-ion materials sent to Berkeley Lab from many groups throughout the world
who are developing these materials. A model's output for a specific material might be a plot of how its
voltage and capacity changes with increasing power, for example.
Srinivasan and other Berkeley Lab researchers perform lab tests on the materials, and similar battery
chemistries from different sources are compared. Srinivasan's model can tell whether differences in
performance are caused by a battery's design or by something intrinsic to the material itself. Anything
from electrode thickness, to porosity, to particle size, to the parameters of the battery's chemical reactions
can affect the results.
The basic model that Srinivasan starts with was developed by John Newman, head of the Electrochemical
Technologies Group at Berkeley Lab and a professor of chemical engineering at UC Berkeley. Newman's
group has been modeling batteries since the 1970s, and their approach is widely used throughout the field.
Fitting the model to the specific chemistry he's working with allows Srinivasan to get close to a battery's
"This is what I love about batteries," he says. "Each one has its own idiosyncrasies; there's something a
little different about each battery chemistry. To get the right physics, you have to keep adding more
Srinivasan has graphically summarized some of the materials he has modeled recently, again plotting their
energy against their power. Materials come from all over the world-from Berkeley Lab's own groups,
from MIT, from a researcher in Slovenia, and from the Canadian power company Hydro-Quebec, which
sent a commercial prototype. So far no material has come close to the theoretical maximum performance,
which Srinivasan represents by a curve labeled "ideal." The ideal battery material would have the particle
size of the MIT sample and the conductivity of the Hydro-Quebec sample, so there is still a lot of room
for improvement in this particular set of chemical combinations. Particularly promising are compounds of
lithium iron phosphate with graphite, an electrically conductive form of carbon.
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Chen, Allan (Editor). Environmental Energy Technologies Division Newsletter, Fall 2007,Vol.4, No. 4), periodical, December 14, 2007; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc901682/m1/4/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.