IEEE Electrification - December 2022 - 78

stays within allowable temperature limits. A typical
BTMS consists of temperature sensors across the surface
of a battery pack and cooling and heating systems
that are activated based on the measured and predicted
temperature of the battery.
In this article, the cooling strategies of Li-ion battery
packs are reviewed, and their relevance and future prospects
are discussed. In particular, we
consider three widely adopted cooling
strategies [air cooling, liquid cooling,
and phase-change material
(PCM)-based cooling] and the potential
of nanomaterials to improve each
of them.
Air Cooling
Air cooling is the simplest form of
cooling and is adopted in several EV
models, such as the Toyota Prius
(2016-present), Nissan Leaf (2018-
present), and BYD E6 (2009-present).
Air cooling can be further classified as
forced and natural air cooling. In
forced-air cooling, fans are used to
induce the airflow, whereas in natural
air cooling, no fans are used. Air cooling has limitations
because of the low thermal conductivity of air; it can be
improved by modifying the channel design and cell
arrangement. Different airflow channels have also been
studied experimentally to improve the cooling efficiency.
Figure 1 shows the different types of cooling channel
arrangements used to analyze the heat transfer performance.
For example, in comparison to a simple channel
[see Figure 1(a)], cooling is effective in a wedge channel
Li-Ion Cell
Heat regulation
using PCMs does not
require any external
inputs-the heat
regulation happens
naturally because
of the property of
the PCM.
[see Figure 1(b)], where the area in the wedge channel is
gradually decreased from inlet to outlet, which results in
the batteries at the outlet receiving enough cooling. The
forced-air cooling strategy is shown in Figure 1(c).
It has also been found that the temperature uniformity
can be improved by the arrangement of cells in a
battery pack. Figure 2 shows three arrangements of Li-ion
cells in the battery pack. Aligned and
staggered arrangements were found
to be more prone to high-temperature
rise and nonuniformity in
Li-ion cells, whereas the trapezoidal
arrangement experienced better
temperature uniformity.
Despite all of the positive attributes
of an air-cooling system, such as a simple
design and low space usage, there
is still room to improve its efficiency.
There is a need to find an optimum
design of an air-cooling system that
can ensure temperature uniformity
among cells and also increase the cooling
performance under high-temperature
conditions. The heat dissipation
from a battery also depends on the
properties of the packaging material. It is desirable for battery
packaging materials to have good thermal properties,
such as high thermal conductivity and high heat capacity.
The use of nanomaterials is being studied to improve the
thermal properties of packaging materials.
Liquid Cooling
Liquids have better thermal conductivity than air. Liquid
cooling can be divided into the areas of direct and indirect
Inlet
Outlet
(a)
Inlet
(b)
Outlet
Inlet
Inlet
Outlet
(c)
Figure 1. Cooling channel arrangements. (a) Simple channel. (b) Wedge channel. (c) Simple channel with reciprocating cooling. (Source: Kumar
et al., 2020.)
78
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