the anisotropy in the structure of the battery. This
model, then, can therefore simulate a localized fail-
ure, space-dependent heat transfer, and the conse-
quences to the thermal management of a battery.”
Tatsuya Yamaue, a member in the Engineering
Mechanics Div., of Kobelco Research Institute,
Kobe, Japan, has modeled the thermal runaway of
Li-ion batteries using Multiphysics software and
successfully compared those results to the testing
of actual systems in his laboratory. Kobelco is a
contract testing and research firm that focuses on
automotive, battery, iron and steel, semiconduc-
tor, and medical industries. He initially validated
his thermal runaway models with results mea-
sured on actual devices with accelerating rate
calorimeters. “We have since made various modifications of modeling heat
generation in Li-ion batteries and thermal runaway situations in short-
circuit testing, for example, voltage drop and discharge heat generation
considering the structure of electrodes,” says Yamaue.
In addition to modeling thermal runaway situations, Yamaue has modeled charge and discharge cycles, ionic transport within the battery electrodes, and nanosimulations of electrode surface reactions. These models
were created using Multiphysics software and several other applications
relating to molecular dynamics and ab intio molecular dynamics.
“Multiphysics is a good platform for studying advanced technology batteries such as Li-ion systems, which requires the analysis of complex physical phenomena on different scales. This includes such studies as the modification of chemical reaction model formulae, the application of integral
boundary conditions for current distribution analysis, and the analysis of
different physical phenomena for each domain,” says Yamaue.
Li-ion battery modeling is a good application for Multiphysics software
because the whole system consists of multiphysics applications. A Li-ion battery model is not just a CAD program utilizing structural mechanics and
computational fluid dynamics (or thermal analysis) modules. A good battery
model includes electrochemical reactions involving the transfer of electrons
through current collectors and electrodes matrices. Materials balances also
need to be calculated for the transport of chemical species through diffusion,
migration, and convection to and from the electrode surfaces, as well as any
possible chemical reactions that might occur in the electrolytic solution.
In one of his studies, Yamaue simulated a failure resulting from an
internal short circuit in a Li-ion battery. Temperatures within the cell
over a period of time during a thermal runaway event were shown on the
model along with the isosurfaces of reacted ratios of the negative electrode
at 20-W and 100-W heat sources from the short circuit. For several tens of
seconds, a wide reaction zone was observed to move from the vicinity of
the short circuit toward the end of the battery.
Multiphysics modeling of 3-D temperature
streamlines around lithium-ion batteries provide
battery designers indicators of the performance
characteristics they can expect. Source: Comsol
“You can learn a lot more from an accurate
Multiphysics model and such models can also be
used over a much wider range of operating conditions, and conditions that more often resemble
real operating conditions,” says Fontes. This leads
to a better design and cost savings in the search
for better products.
John Newman, the Charles Tobias Chair
of Electrochemistry in the Dept. of Chemical
Researchers at the University of Illinois, Urbana-Champaign, recent-
ly announced a new Li-ion battery design that is up to 2,000 times more
powerful and recharges up to 1,000 times faster than current devices.
These huge advances come from a new cathode and anode structure.
Conventional Li-ion batteries have a solid, 2-D anode made of graphite
and a cathode made of a lithium salt. The new Li-ion battery, however, has
a porous 3-D anode and cathode. To create this new electrode structure,
the UI researchers built up a structure of polystyrene on a glass substrate,
electro-deposited nickel onto the polystyrene and then electro-deposited
nickel-tin onto the anode and manganese dioxide onto the cathode. This
results in porous electrodes with a massive surface area, allowing for more
chemical reactions to take place in a given space and resulting in a mas-
sive boost to discharge speed, or power output, and charging. The initial
prototypes are relatively small, with an energy density that is slightly lower
than conventional systems, but with a 2,000 times greater power density.
“Multiphysics models in automotive applications are infinite in number,”
says Comsol’s Fontes. “I don’t think that regulatory agencies have researched
the modeling area to any large extent, especially compared to its future
potential as a complement to physical testing.” Automotive manufacturers
don’t really have much of a choice in terms of accepting or not accepting
models and model results, according to Fontes. They have to keep themselves updated to the highest level possible.
Researchers at the Fiat Research Center in Orbassano, Italy, also make use
of Comsol’s Multiphysics software for managing the thermal loads generated in Li-ion battery packs used in their company’s electric and hybrid
vehicles. For their designs, they chose to employ convection air cooling
for the battery packs, while keeping the packs as small and as light as possible. If one cell out of 100 doesn’t work well due to problems with heat, it
has a negative impact on the entire pack. Their design limit was to keep all
cells within a 5 C maximum differential. With the Multiphysics model, the
researchers were able to reduce the physical cooling channels between cells,
thereby reducing overall space requirements, reducing the frame size, and
increasing the ability to replace the battery pack. The researchers calculated
that the model reduced their overall system design time by 70%, or a net
reduction of 700 man-hr needed to design the battery pack.