IEEE Electrification Magazine - March 2017 - 52

Accurate SOC
estimation is very
important, especially
for BEV, to enable
the driver to have
the maximum range
available.

generate much larger quantities of heat because of the
significantly wider SOC window that the batteries need to
be operated, usually require more efficient method such
as liquid cooling.
The Volt and Tesla thermal systems, which were developed to address two different cell foot-prints, are archetypes of direct liquid-cooled batteries that are able to keep
the temperature variation within and between cells to a
minimum, sometimes less than 1 °C. In these systems,
the coolant, usually a mixture of glycol and water, flows
through either tubes, which is used in the Tesla system, or
through fins, which is used in the Volt system (Figure 7).
There is a trend to switch to simpler cooling systems
such as indirect liquid cooling. In this system, heat generated from the cell surface is transported, typically through
conduction, to a heat sink that removes the heat energy to
the fluid usually via aluminum cooling fins that are in
direct contact with the cell surface. There is typically a
thermal interface material between the cooling fins and
the heat sink to minimize contact resistance (Figure 8).
However, the temperature variation between cells is larger
with this system design, approximately 3-5 °C maximum.
The indirect cooling system design requires lower coolant
temperatures to achieve similar performance to the direct
system. It is also potentially a simpler and less costly system with fewer components.
Lastly, an alternative indirect cooling strategy leverages
the existing heating, ventilation, and air conditioning system of the vehicle and flows the refrigerant through tubes
upon which the cells are positioned, and the BMW i3 uses
such a system.

current and planned launches of future xEVs. Long-range
BEVs, higher-end PHEVs, and microhybrids appear to be
the vehicle platforms currently receiving the most attention from OEMs. Li-ion batteries mostly using the layered
cathodes and graphite anodes meet the key requirements
of the batteries that are used in these vehicles. A number
of different thermal and electrical BMSs that are critical to
ensure the safe and long-life operation of these batteries
are currently available.
At this time, there are several battery systems currently being developed that potentially have higher energy density and lower cost. But based on the present
status of battery systems research and development, it is
apparent that the next generation of batteries for automotive application will still be based on advanced Li-ion
batteries with improved chemistries, more efficient
BMSs, and lower cost.

For Further reading
T. Waldmann, B.-I. Hogg, M. Kasper, S. Grolleau, C. G. Couceiro,
K. Trad, B. P. Matadi, and M. Wohlfahrt-Mehrens, "Interplay of
operational parameters on lithium deposition in lithium-ion
cells: Systematic measurements with reconstructed 3-electrode
pouch full cells," J. Electrochem. Soc., vol. 163, pp. A1232-A1238, 2016.
K. M. Abraham, "Prospects and limits of energy storage in
Batteries," J. Phys. Chem. Lett., vol. 6, pp. 830-844, 2015.
M. H. Braga, N. S. Grundish, A. J. Murchison, and J. B. Goodenough, "Alternative strategy for a safe rechargeable battery,"
Energy Environ. Sci., 2017. doi: 10.1039/C6EE02888H.
C. Restropo, A. Salazar, H. Schweitzer, and A. Ginart, "Residential battery storage: Is the timing right?" IEEE Electrific.
Mag., vol. 3, no. 3, p. 14, Sept. 2015.

Biography

conclusions

Mohamed Alamgir (alamgir@lgchem.com) is with LG

Vehicle electrification around the globe has now gained
significant momentum, as reflected by the number of

Chem Power, Troy, Michigan.

I E E E E l e c t r i f i c ati o n M agaz ine / march 2017

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2017