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A comprehensive review of battery thermal
management systems for electric vehicles
I
rfan Çetin
1
, Ekrem Sezici
1
, Mustafa Karabulut
1
,
Emre Avci
2
and Fikret Polat
1
Abstract
Trying to prevent and mitigate carbon emissions and air pollution is one of the biggest challenges for the technological
development of the automobile industry. In addition, the automobile industry has stepped up research and field applica-
tions of electric vehicles as the European Union encourages the restriction of the use of conventional fuel-powered
vehicles such as diesel and gasoline vehicles. However, the cycle life, environmental adaptability, driving range, and char-
ging time of the battery currently used in electric vehicles are far beyond comparison with internal combustion engines.
Therefore, studies have focused on batteries, and battery thermal management systems (BTMSs) have been developed.
Battery performance is highly dependent on temperature and the purpose of an effective BTMS is to ensure that the
battery pack operates within an appropriate temperature range. Ensuring that the battery operates in the appropriate
temperature range is vital for both efficiency and safety. To determine the best convenient BTMS for several types of
battery packs attached to many factors such as volumetric constraints, installation costs, and working efficiency. The max-
imum temperature rise and the maximum temperature difference are the basic parameters to analyze the efficiency of the
BTMS. Most of the research about thermal management has focused on especially air cooling, liquid cooling, and phase
change material (PCM) cooling methods. In this study, different BTMSs (air cooling, liquid cooling, PCM cooling, etc.) were
examined and their advantages and disadvantages were compared, usage restrictions in today’s technology, requirements,
and studies on this subject were reported.
Keywords
Battery thermal management, air cooling, liquid cooling, phase change material cooling, electrical vehicle
Date received: 12 April 2022; accepted: 27 July 2022
Introduction
In today’s world, most countries meet their energy needs
mainly from fossil-based fuels, especially in the transpor-
tation sector. However, the fact that fossil fuel reserves are
in danger of being depleted in parallel with their
unplanned and irregular use has caused alarming environ-
mental and economic problems for countries. In addition,
global warming and climate change are showing their
effects more and more every day, and it is an undoubted
fact that the use of fossil fuels is largely responsible for
this situation.
1–8
In order to prevent the worst scenarios
that will occur as a result of this, the carbon released
into the atmosphere had to be brought under control
with certain control mechanisms all over the world. In
this context, the first step was taken with the United
Nations Framework Convention on Climate Change;
this agreement was expanded with the Kyoto Protocol
and took its final form with the Paris Climate
Agreement. With these mechanisms, it is aimed to
reduce global warming by 2°C as a result of reducing
the use of fossil fuels and reducing carbon emissions.
Both these situations and global competition have
accelerated the transition of countries from fossil
sources to renewable energy sources.
9,10
Along with
technological developments, the most concrete example
of the studies carried out for this purpose in the transpor-
tation sector is electric vehicles (EVs). EVs are increasing
in popularity day by day due to their environmental
friendliness and high energy efficiency.
11–13
EVs have four main distinguishing features:
•Reduce urban pollution and carbon emissions.
14
•More fuel-efficient than diesel or gasoline vehicles.
15
•Easy to use, similar to automated tools.
16
•Reduce dependency on fuel importing countries.
17
1
Department of Mechanical Engineering, Faculty of Engineering, Düzce
University, Düzce, Turkey
2
Department of Electrical and Electronics Engineering, Faculty of
Engineering, Düzce University, Düzce, Turkey
Corresponding author:
Fikret Polat, Department of Mechanical Engineering, Faculty of
Engineering, Düzce University, 81620, Düzce, Turkey.
Email: fikretpolat@duzce.edu.tr
Review article
Proc IMechE Part E:
J Process Mechanical Engineering
1–16
© IMechE 2022
Article reuse guidelines:
sagepub.com/journals-permissions
DOI: 10.1177/09544089221123975
journals.sagepub.com/home/pie
Thanks to the distinguishing features mentioned above, in
order for EVs to compete with vehicles using internal
combustion engine (ICE) technology, low cost and high
range criteria need to be improved, as stated in many
studies.
1,18–20
One of the most important components of
EVs is their batteries. Because the performance of the
EV mostly depends on the performance of the battery.
Therefore, studies on EVs mostly focus on batteries.
The most important criteria for users, such as how long
the battery will charge, the life of the battery cells, and
the maximum range that can be reached on a full
charge, are directly related to the battery system. The
energy required for the movement of the EV is provided
by the energy stored in the battery. In order for the
battery to work reliably and at maximum performance,
the batteries are managed by systems called battery man-
agement systems (BMSs).
21–26
BMSs have undertaken three basic tasks: calculation,
data monitoring, and protection, and they perform these
tasks with the help of various algorithms.
27,28
Data mon-
itoring algorithms monitor the battery’s current, voltage,
and temperatures. The calculation algorithm of the BMS
interprets the instantaneous values in the monitored data
and calculates values such as battery health, battery
charge rate, maximum and minimum charge/discharge
current, maximum and minimum voltage, operating
time, and the number of cycles. The values obtained
from the first two algorithms are used on the protection
side of the BMS. The protection algorithm prevents
high current drawn from cells and battery packs during
charge/discharge, formation of high/low voltages,
leakage current, and high/low-temperature formation.
29
During the use of battery packs, the charging and dischar-
ging processes of the cells occur with the formation of
various chemical and electrochemical reactions, most of
which are exothermic.
30
As it can be understood from
here, the temperature that will occur during use will also
directly affect the performance of the battery pack. This
has allowed the creation of a concept called battery
thermal management systems (BTMSs) as well as BMSs.
Battery thermal management systems
Global problems such as energy scarcity and environmen-
tal pollution have directed the automotive industry to EVs
and hybrid EVs (HEVs) that can be used with alternative
energies. EVs and HEVs are considered the most sustain-
able solutions that can replace traditional ICEs. When it
comes to electric motors, the first thing that comes to
mind is battery systems.
31
However, the source of the
range problem also, which is the most discussed disadvan-
tage of EVs, is the batteries they have. Batteries are con-
sidered the heart of EVs and also the features sought for
batteries can be summarized as high power and energy
density, fast charging–discharging, and long life.
32
Lithium-ion (Li-ion) batteries are widely preferred in
EVs due to their high energy density and long service
life. Lithium battery packs, like other batteries, have a
high sensitivity to temperature. The imbalance in tem-
perature distribution inside the battery pack can cause dif-
ferent electrochemical behaviors, electrically unstable
cells, and chemical deteriorations that may occur in
battery cells significantly affect battery performance.
The optimum operating temperature for Li-ion batteries
is in the range of 15°C to 35°C. Normally, the
maximum temperature difference (MTD) between the
cells should be kept at 5°C. At operating temperatures
below the optimum range, a decrease in the power and
energy of the batteries was observed. In addition to poor
performance, the aging rate of batteries increases, espe-
cially at temperatures below 0°C. At operating tempera-
tures above the optimum range, depending on the
overheating of the batteries, serious problems such as
decreases in capacity and performance and self-discharge
occur. A strong and effective cooling and heat dissipation
system is necessary for the design of the battery pack for
lithium cells. For this reason, BTMSs are needed to keep
the temperature of the battery pack in the optimum range,
to ensure the battery pack’s thermal uniformity, and to
balance the charge/discharge state.
32–35
The BTMS plays a crucial role in the high efficiency,
reliability, and safety of batteries under various operating
conditions. Basically, BTMSs can be classified into dif-
ferent types such as active or passive, series or parallel,
heating or cooling, internal or external, air or liquid or
phase change material (PCM), or hybrid strategy combin-
ing multiple methods.
31
All around the world, lots of
researchers have conducted several studies about
BTMSs. In conclusion, BTMS technologies can also be
classified as shown in Figure 1.
30
Figure 1. Classification of different battery thermal manage-
ment techniques
30
.
2Proc IMechE Part E: J Process Mechanical Engineering 0(0)
The principle of an air cooling system is natural con-
vection such as directly using the wind around when the
car is in motion or forced convection such as by creating
airflow with the help of a fan. In an air cooling system,
natural convection provides convenience and low cost,
but it has poor heat dissipation capacity due to the uncon-
trollable wind. Forced convection is more reliable and
more comfortable to maintain than natural convection,
therefore forced convection is a more common system
compared with natural convection. However, the tempera-
ture non-uniformity between cells is a big problem that
waiting to solve for forced convection.
36–39
The liquid cooling system basically consists of direct
and indirect systems. In direct cooling, which is also
called the immersion method, by immersing the battery
cells in the coolant liquid, a direct contact is ensured
between all surfaces of the battery cells and the coolant
liquid.
40–42
It should be a dielectric coolant that has low
viscosity and high thermal conductivity and thermal cap-
acity. In indirect liquid cooling, the contact of the batteries
with the coolant is basically provided by three different
systems that were created to regulate the liquid flow
around the cells: cold plates, liquid channels (jacket),
and heat pipes. In these indirect liquid cooling systems,
as a fluid, a water–glycol mixture is generally used.
Indirect BTMSs are widely preferred in EVs due to
their practicality, reliability, and stability compared to
direct BTMSs.
43–46
A PCM cooling method is a passive cooling method in
which PCMs are included. During melting, PCMs absorb
the heat released from the batteries until they reach their
latent heat value and ensure that the temperature
remains constant for a while. In addition, in case of
thermal leakage between cells, they directly absorb the
leakage heat within themselves and prevent another
battery cell from splashing. Besides, PCMs also allow
the battery pack to be lightened due to their low-density
values.
47–50
To determine the best convenient BTMS many factors
such as volumetric constraints, installation costs, and
working efficiency are attached to several types of
battery packs. The maximum temperature rise and the
MTD are the basic parameters to analyze the efficiency
of the BTMS.
41
Most of the research about thermal man-
agement has focused on especially air cooling, liquid
cooling, and PCM cooling.
28,41,51–53
This study is a comprehensive review article that
focused especially on recent and up-to-date studies
about battery thermal management technologies. In this
study, lots of different battery thermal management tech-
nologies and systems have been investigated. In the
reviewed studies, information is given clearly about the
methods used by the researchers in the studies they pre-
sented and basically their contents. Apart from applied
studies, review articles also were examined and clear
information about the focal points of those articles is
given. In this way, a researcher who gets this study will
have the opportunity to reach a wide range of information
on the subject. Further, researchers will have the
advantage of knowing which studies have been done in
recent years for the BTMS they want to focus on. Since
this article is a detailed study, it offers its readers a
broad perspective on BTMS. It presents comparisons of
the advantages and disadvantages of the studies described
throughout the research in the Discussion section. This
comparison will be beneficial for researchers who are
incipient with the subject, in order to decide on the most
appropriate system.
Air cooling systems
In many scientific studies, some problems and solutions of
BTMSs have been examined and necessary information
has been sought to find a suitable design. The air
cooling system is divided into two: active cooling and
passive cooling. In the passive system, the air is taken dir-
ectly from the atmosphere. The system in which air is
taken from the air conditioning system and the evaporator
is an active cooling system. In addition, these two systems
provide heating and cooling processes.
54
Li-ion battery exhibits high sensitivity to temperature.
The thermal management system has a significant impact
on the efficiency and safety of batteries. To obtain suffi-
cient power and energy, the battery cells are connected
to form a package. Pressure, temperature, and vibration
are considered sensitive for this application. Operating
temperature and storage greatly affect the performance
of batteries. Temperature imbalance inside the battery
pack causes the battery cells to behave differently. In
general, low temperature reduces the power of the batter-
ies. However, batteries may face the problem of capacity
reduction due to the non-uniformity of the solid electro-
lyte interface layer and high-temperature electrolyte
decomposition. Also, batteries are vulnerable to extreme
heat. Therefore, it is important to develop a heating and
cooling system for EVs and HEVs to keep the battery
temperature at an optimum level.
31
All batteries heat up during charge/discharge. The
cooling system is more needed in the battery pack. A
lot of work has been done on the cooling system. Some
of them are as follows: Lu et al. numerically investigated
the air cooling system for the battery pack. The advan-
tages of the battery pack are making the most of the
space of the battery pack and providing higher power to
meet the requirements of EVs operating conditions. In
the study, air cooling capacity on temperature uniformity
and reduction of hot spots in the battery pack subject to
different flow paths (uneven air-refrigerant transitions),
and airflow rates were investigated. Using FLUENT
14.5, the airflow and temperature distributions of the com-
puting unit are simulated numerically. Due to the low flow
rate and short characteristic lengths, the cooling airflow is
assumed to be constant, incompressible, and laminar
(Reynolds number <2300). Considering the heat flow,
the surfaces of all batteries are fixed according to the
heat produced by the batteries at different charge/dis-
charge rates. All wall boundaries are modeled using the
non-slip boundary condition. The solution method is as
Çetin et al. 3
follows: Green-Gaussian-based node is adopted to make
the diffusion terms discrete. A quadratic wind direction
scheme was used for numerical diffusion reduction and
convective terms. Combined velocity–pressure terms
were solved using the semi-implicit method for pressure
linked equations (SIMPLE) algorithm. The cooling
process of the battery pack was investigated by numerical
simulation to determine the temperature uniformity and
air cooling capacity under different flow paths and
airflow rates. Based on this simulation, the temperature
decreased as the cooling channel size increased; the
greater the number of vents, the greater the heat transfer
area between the cooling air and the battery surfaces,
therefore the better the cooling process.
55
In 1991, the
Li-ion battery was first commercialized. Although it cost
more than lead-acid and NiMH batteries, it had the
highest performance. Tesla used 2976 Li-ion battery
cells for the Model 3 Standard Range Version. Honda
introduced Li-ion battery products for the E Urban EV.
The company that implemented the ternary Li-ion
battery with BTMS in its model, the Emgrand EV, is
Gelly Auto of China. Renault, which has a 25% EV
market share in Europe, has equipped its latest model
ZOE with Li-ion batteries. Hyundai has installed a 64
kWh Li-ion battery module in the 2019 EV Kona
Electric Elite. The Fiat Chrysler Automobiles group,
one of the auto giants, has started to move from ICE to
EV and plans to invest 9 billion Euros in this business.
56
Wu et al. focused their review on liquid-based BTMS
systems and battery modeling methods and thermal man-
agement strategies. They studied different cooling techni-
ques for batteries used in EVs and other applications. A
comprehensive review of air-cooled BTMSs for EVs
and HEVs has yet to be done. Air-cooled BTMS is one
of the main cooling techniques that make EVs and
HEVs more efficient and safer. It is popular in some com-
mercial EV and HEV BTMS applications due to its simple
structure and low cost.
31
Akinlabi et al. examined passive
and active air cooling methods. They designed parameter
optimization methods to improve BTMS performance.
They reported that the forced air cooling system would
not be able to provide adequate cooling for
high-energy-density battery systems. First, they explored
the battery heat generation mechanisms and their effects
on the powertrain in EVs and HEVs (e.g. thermal aging,
thermal runaway, and fire accident). Then, after reviewing
the air-cooled BTMS design, new designs were developed
to explore the benefits and challenges of using the air-
cooled system. It consists of new design techniques,
battery-pack layout, cooling channel, inlet and outlet loca-
tions, new thermally conductive materials, and improve-
ments on secondary cooling channels. The advantages,
potentials, and challenges of implementing air-cooled
systems in EVs and HEVs are explored.
57
The temperature and flow fields of the battery pack
were analyzed by the computational fluid dynamics
(CFD) method. Parallel plates were placed between the
battery cells in the battery pack. These plates are also par-
allel to the airflow. Instead of working on a single design,
the idea of improving the flow pattern can also be a refer-
ence for other air cooling systems. Minor changes to the
original design can also contribute to cooling efficiency.
Wang et al. investigated the effect of parallel plates on
the cooling process. The findings they observed in this
study for cooling the battery pack are as follows:
•The inlet and outlet positions of the airflow have a great
effect on the cooling process.
•The temperature fluctuated according to the number of
parallel plates. The number of plates that need to be
checked when power is lost.
58
The use of EVs and HEVs is expected to become wide-
spread in the near future. Li-ion batteries are used in
storage technology in EVs due to their superior perform-
ance and durability. The effect of temperature is great
during storage and use. A BTMS is required to keep the
battery temperature within the optimum performance
range and to cool or heat the battery pack. The purpose
of BTMS is to reduce the maximum temperature of the
battery pack and to provide temperature homogeneity.
Some of the research on this subject is as follows:
effects of airflow mode (active and passive), airflow direc-
tion (unidirectional airflow (UDAF) and reciprocal
airflow (RAF)), module design, cell arrangement, and
spacing between cells. The method used in the compari-
son is by looking at the input temperature difference.
Since there is no heat generation data for different struc-
tures in the literature on this subject, a comparison is
made by looking at the ambient temperature. The com-
parison parameters made in terms of the maximum tem-
perature and temperature difference in the battery pack
are used in the active cooling system. Various studies
have been carried out on the effect of airflow direction
in an air-cooled system. RAF and UDAF are some of
these studies. Compared to the system with one-way
airflow, temperature homogeneity is better in the system
with RAF. The reason for this was thought to be due to
the redistribution and deterioration of the boundary
layers by the reversal of the airflow.
53,59
Having a simple structure without the need for cooling
cycles and being easier to pack are the biggest advantages
of the air cooling system. The maintenance cost is low and
there is no leakage of liquid into the electronics. Among
the cooling systems, the air cooling system is the least
energy-consuming and the lightest. To get the best per-
formance, Toyota used an air-cooled system for the
Ni-MH battery pack in 2010 and a Li-ion battery pack
in 2014. Volkswagen has decided to replace the liquid
cooling system in the battery pack with an air cooling
system on some models. An air-cooled system was used
in the EV, which won the Pikes Peak International Hill
Climb held in Colorado Springs in 2018. Lexus’first
EV model, the UX300e, used air-cooled BTMS for its
54.3 kWh Li-ion battery pack. Nissan has successfully
used the active air cooling system in the e-NV200
model. In its latest model, the Marvel X, Roewe has
returned to the air-cooled BTMS for the battery pack. In
4Proc IMechE Part E: J Process Mechanical Engineering 0(0)
the SAIC-GM Wuling Hongguang model, China adopted
air-cooled BTMS for cooling both the battery pack and
the engine. In 2020, EV sales volume in China exceeded
Tesla Model 3 in 3 months.
56,60
The air cooling system is
the system commonly used for battery packs. Some of the
processes used for solution in air cooling systems are heat
transfer structure, use of more thermally conductive
material, airflow optimization, and temperature monitor-
ing. Figure 2 shows the passive air-cooled system.
While the vehicle moves, outside air enters the battery
pack and flows through the space between the battery
cells. Air is discharged from the outlet on the other side
of the battery pack. In this way, the heat generated in
the battery pack is carried by the airflow. The passive
cooling system may not be sufficient when the vehicle
is moving slowly or when the weather is hot. In this
case, the cooling process should be improved with the
active cooling system by using a blower to increase the
airflow. The battery pack, cooling channels, inlets, and
outlets, cooling fan make up the passive cooling system.
Figure 3 shows the active cooling system. In the active
cooling system, blowers at the inlet or outlet are used to
dissipate excess heat and provide better temperature dis-
tribution. Although it has a few disadvantages such as
noise and extra energy consumption, the active air
cooling system is preferred in most battery packs due to
its performance and reliability. Park et al. designed the
conventional air-cooled system to achieve a better per-
formance cooling system. They achieved a good balance
between fuel economy, comfortable travel, and produc-
tion cost. Wang et al. investigated the behavior of the
uncooled battery pack and the air-cooled battery pack.
An active air-cooled system is not needed when the
ambient temperature is below 20°C and the discharge
rate is below 3°C. On the other hand, when the ambient
temperature rises above 35°C, the active cooling system
may lose its effectiveness, and more blowing power is
required for the cooling process.
61–64
Using the air cooling system prolongs the cost and life
of the battery pack. It directly affects the performance,
cost, and longevity of EVs and HEVs. For this reason,
all parameters affecting the battery pack should be consid-
ered and optimized to achieve the highest performance of
the vehicle. The design of the battery pack, the cooling
channel, the inlet and outlet of the airflow, and the prefer-
ence for materials with better thermal conductivity are the
parameters to be considered in the improvement of the air-
cooled system.
56
Pesaran et al. analyzed the two-dimensional (2D)
thermal properties of the air cooling method using the
analysis program ANSYS. They examined two types of
cooling methods, series-ventilated and parallel-vented. It
was determined that the temperature difference is less in
the parallel ventilated cooling system. In other words,
the parallel ventilated cooling system is more efficient
than the series ventilated cooling system. In order to
achieve the best performance in cooling the battery
pack, in the parallel ventilated cooling system, some
Figure 2. Schematic diagram of passive air cooling.
56
Figure 3. Schematic diagram of active air cooling.
56
Çetin et al. 5
scientists changed the spacing of the gaps between the
battery cells. Instead of providing the airflow straight to
the inlet and outlet of the battery pack, the inlet and
outlet angles are conical. It has been observed that the
temperature homogeneity of the model with a conical
inlet and outlet is better than the parallel air inlet and
outlet. It was also observed that it was effective in the
cooling process according to the arrangement of the
battery cells. Fan et al. compared one-sided and two-sided
cooling systems. They observed that the one-sided
cooling system had a more homogeneous temperature dis-
tribution than the two-sided cooling system. It was
observed that the cooling performance improved when
the porous structure was added to the air-cooled battery
pack. It was observed that the cooling performance
improved when the porous structure was added to the air-
cooled battery pack.
65
Mohammadian et al. added a
porous structure to the airflow channel to improve
cooling efficiency. They investigated the effect of porous
structure on air permeability and the effect of porous struc-
ture on cooling performance. In this study, it was seen that
the most efficient structure in the cooling process was the
model with a porous structure added to the cooling
channel. In this finding obtained from the porous structure
applied to 70% of the airflow channel, the permeability of
the porous medium and the degree of porosity are two
important parameters. In order to provide better heat
flow, some scientists made some changes in the shape of
the air duct. Corrugated and wavy heat sinks can increase
efficiency in the cooling system.
66
Liquid cooling system
The liquid cooling system is based on reducing the tem-
perature and provides uniform heat dissipation in the
battery packs by contacting the battery directly or indir-
ectly. The refrigerant fluids used in this system can be
categorized into two groups: dielectric fluids (mineral
oils) that have direct contact with battery modules and
indirect fluids (ethylene glycol water mixture) that have
indirect contact with battery modules. Direct liquid
cooling can achieve better thermal efficiency. Whereas,
considering its disadvantages, particularly the liquid
leakage problem, indirect liquid cooling was more suit-
able for practical applications. The diagram of active
and passive liquid cooling systems is shown in Figures
4to6.
67
Compared to other cooling systems, a liquid
cooling system has higher thermal conductivity and spe-
cific heat capacity. Liquid cooling has become the more
preferred system for EVs thanks to its excellent thermal
management performance. Even if there are lots of
studies about different types of cooling systems, liquid-
cooled BTMS is the most widely used system for the
current EV market. However, for a liquid-cooled
system, there must be some energy-consuming compo-
nents to ensure fluid circulation. This state negatively
affects the overall efficiency of the EV.
31,68–71
On the
other hand, this system has some shortcomings and dis-
cussed aspects. Especially, its compact structure and
high weight, which is crucial to the specific energy of
the battery pack, have drawn attention.
Lai et al. developed a thermally conductive structure
(TCS) to cool cylindrical lithium battery cells. They pro-
posed the most suitable design parameters to reduce the
weight of TCS with numerical analysis. In conclusion,
when comparing the design parameters of TCS, the
order of importance for lightweight is as follows: inner
diameter, contact surface height, and contact surface
angle. The designed TCS can control maximum tempera-
ture under 313 K with a temperature difference of 4.137
K. Owing to the designed TCS, pressure drop, tempera-
ture difference, and weight are, respectively, reduced by
80%, 14%, and 46%, compared to the original TCS.
72
Studies of BTMS aim to provide an efficient cooling
and uniform heat dissipation medium in the battery
pack. Therefore every type of cooling system should be
designed as much possible as to protect temperature uni-
formity. The focused point of much research is the peak
temperature of battery packs. Although uniformity of
heat dissipation is significant for the performance and
life of the lithium battery system, there is little study
about temperature uniformity. In order to solve this
issue, Xu et al. analyzed two different types of cooling
channels, serpentine-type and U-type for the liquid-
cooled system with thermal simulation. As a result of
this comparison, they proposed a serpentine-type
cooling channel, which has a better cooling effect. The
main purpose of this study is to minimize the MTD
value thanks to the optimization framework. In conclusion
of the optimization studies, the MTD is reduced by 7.49%
compared with the initial state and it reached a more
uniform temperature distribution for the lithium battery
Figure 4. Passive cooling-liquid circulation.
Figure 5. Active moderate cooling/heating –liquid circulation.
6Proc IMechE Part E: J Process Mechanical Engineering 0(0)
pack.
68
Li et al. also analyzed the U-type and serpentine-
type liquid cooling systems. Their research showed that
two different schemes exhibit results so close to each
other about cooling effects. However, they found that
the u-type channel, unlike the serpentine-type channel,
can reduce the pressure drop remarkably. The U-shaped
channel is modeled with the Gaussian process model,
which is a machine learning method. With the optimiza-
tion process, cooling water decreases by 26.67%, and
pressure drop decreases by 24.18% compared with the
initial scheme. As it is seen that after the optimized solu-
tion, the pressure drop is greatly reduced. In a research
study, Lui et al. investigated the thermal effects of the
basic fluids and nanofluids as coolants in the liquid
cooling system on the mini-channel cooling system for
high-power prismatic lithium battery thermal manage-
ment. They designed a battery pack model and conducted
numerical simulations in the computer environment.
Water is the most preferred coolant in liquid cooling
applications owing to its different advantages especially
thermal conductivity provided more successful thermal
performance than ethylene glycol and engine oil. On the
other hand, with the addition of nanoparticles, the
cooling effect of other fluids, which have lower conduct-
ivity, particularly engine oil, became more impressive.
Furthermore, the maximum temperature of cells can be
decreased by adding nanoparticles but it does not show
the same effect on temperature uniformity. Effective
factors on the mini channel cooling performance and the
enhancement of nanoparticles rate are comprehensively
investigated in this research. In conclusion, it was
reached that all of these examined parameters have con-
siderable impacts on the thermal performance of mini
channel cooling.
73
Chung et al. worked on the structural
design for the battery pack. They presented a pouch
battery pack with liquid cooling to investigate the
thermal uniformity and thermal effectiveness of different
types of batteries and they compared them with a typical
battery pack with a fin-cooling structure that is a reference
type in this study. According to the numerical simulation
reports, poor heat conductivity between the bottom of the
cell stack and the cooling plate has caused significant
negative impacts on the thermal behavior of the battery
pack. A structural design is proposed that aims to
improve the thermal performance and temperature uni-
formity of the large-scale battery by minimizing system
volume, weight, and pressure drop.
74
In another study,
to provide essential thermal behaviors with a liquid
cooling system, Zhou et al. proposed a new structural
design that is based on the half-helical duct and examined
the effects of inlet mass flow rate, pitch, number of helical
ducts, fluid flow direction, and diameter of the helical duct
on the thermal performance. After analyzing the results, it
was observed that the half-helical duct liquid cooling
method might provide better and more efficient thermal
management when compared with the jacket liquid
cooling method.
75
Wiriyasart et al. also presented a
liquid cooling system design based on a corrugated mini-
channel in the battery module. The main purpose of this
work is to propose a new approach with a presentation
of a mathematical model, experimentations, and numer-
ical analysis about temperature uniformity and pressure
drop using nanofluids as a coolant for EV battery packs.
In this study, it was used an EV battery pack which con-
sists of 444 battery cells of type 18650. It examined the
effects of the flow direction of coolant, mass flow rate,
and coolant types on the proposed three models based
on mini channels. In conclusion, among all of the
models, model 2 that was used nanofluids as coolants
has the best cooling performance. However, it was
observed that the pressure drop increased due to a nega-
tive situation.
76
Wang et al. presented a study of cooling
performance based on a practical modular structure. This
proposed novel modular liquid cooling system provided
research opportunities about the effect of the coolant flow
rate and cooling modes (serial and parallel) on the
thermal behavior of the battery module with numerical
simulation and experiments.
77
Chen et al. worked about
to develop the fast-charging process in their studies. They
designed a thermal management system that has mini-
liquid channels. And they proposed a neural network-based
regression model. The best suitable fast-charging–cooling
schedule for thermal effectiveness was selected with the
results of datasets and experimental sets.
78
Zhao et al. con-
ducted a numerical examination to analyze the effective-
ness of cooling channels, and serpentine channels on
Figure 6. Active cooling- and heating-liquid circulation.
Çetin et al. 7
temperature uniformity and to provide zero or near-zero
thermal non-uniformity in Li-ion battery packs. In that ana-
lysis, some specific approaches are proposed and their per-
formance and applicability are evaluated with numerical
simulations. The application of the thermal model is
made on a battery module of 71 18650-type nickel–manga-
nese–cobalt batteries. They reported which proposed
approach is better and more effective for reducing the
pack thermal non-uniformity.
79
Heat pipes liquid cooling systems. Gan et al. presented a
new BTMS based on heat pipes. They aimed to provide
the connection between the batteries and the heat pipes
and enhance the contact area between them by using alu-
minum sheaths that are surrounding cylindrical cells. In
that investigation study, they researched the effects of
some parameters on the thermal performance of the
system. The parameters are, respectively, the coolant
flow rate, the length of the heat pipe condenser section,
and the height of the aluminum sheaths. In conclusion,
among these parameters, the coolant flow rate is the
most effective in terms of maximum temperature. They
proposed a coolant flow rate of 0.5 L⋅min
−1
when the
battery pack is discharged at 2°C. Increasing the values
of the other two parameters can improve the maximum
temperature and temperature uniformity for the battery
pack.
80
In an analysis study, Smith et al. proposed a
new design for a high-capacity battery pack consisting
of eight prismatic cells and tested it for heat load up to
400 W. The first part of the proposed system is cooling
plates that consist of heat pipes to remove heat from
cells and another part is heat pipes that remote heat trans-
fer to carry the heat from the module to liquid-cooled cold
plates positioned at a certain distance. As a result of the
tests implemented on the mentioned parts of the system,
the final design for the whole system was determined.
According to this study, the two-part heat pipe thermal
management system like the proposed system will
ensure more efficiency in temperature uniformity, ease
of design, and system safety.
81
Zhang et al. presented
an experiment and analysis study to improve temperature
uniformity in the BTMS. This study designed a battery
model that includes 5 prismatic LiFePO4batteries and
flat heat pipes passing through between batteries.
Thanks to temperature uniformity, it is aimed to achieve
better results in terms of battery performance, longevity,
and safety. They compared this system with air natural
convection and aluminum plate cooling in terms of
battery temperature fields by using simulation analyses.
In conclusion, a flat heat pipes system is better than
others in reducing maximum temperature rates and the
temperature difference, and also ıt is more economical
in terms of energy cost.
82
In another design and experi-
mental study, Mbulu et al. investigated the performance
of BTMS under high input power for cooling Li-ion bat-
teries by using heat pipes, which are L-type and I-type. In
the experimental setup, aluminum prismatic blocks repre-
sented the batteries that have a close thermal conductivity
value with Li-ion cells. The blocks were wrapped like a
sandwich shape with L-type and I-type heat pipes and it
is heated at different values between 30 and 60 W. The
heat pipes consist of two sections: the condenser part
and the evaporator part. Water was used as a coolant
liquid and experiments were carried out with different
flow rates. The results of experiments show that at high
input powers, the system maintains the maximum tempera-
ture below 55°C.
83
Jouhara et al. developed a test setup to
investigate the performance of a heat pipe-based BTMS
on a battery module prototype that consists of 16 prismatic
lithium–titanate cells. As a result of the experiments, it has
been proven that the heat pipe system significantly reduces
the maximum cell temperature and the temperature homo-
geneity is better than the batteries without a thermal manage-
ment system.
84
Jang et al. proposed three different liquid
cooling designs for the thermal management system, mini-
channel, A-type heat pipe, and B-type heat pipe, and ana-
lyzed the effects of these systems on Li-ion batteries under
various conditions. They analyzed the cooling performances
of these three different designs with the thermo-fluid simula-
tion they developed. Consequently, they determined that the
B-type heat pipe cooling system, which is one of the heat
pipe systems they recommended, performs better than the
liquid cooling system with the mini channel that is com-
monly used, thanks to its large heat transfer area.
85
Liquid cooling with cold plates. In a study to improve tem-
perature uniformity and management, Sheng et al. pro-
posed a novel serpentine-channel liquid cooling plate
with double inlets and outlets. They applied numerical
analysis on the software of FloEFD for cell modules. In
that analysis, they examined the effects of flow parameters
and channel widths of the cooling plate on the temperature
performance of cells.
86
In another investigation, Qian
et al. analyzed the thermal performance of a lithium
battery pack using mini-channel cooling cold plates that
are sandwiched by two rectangular battery cells. For this
analysis, they proposed two different three-dimensional
(3D) numerical model designs. The influences of some
parameters, such as channel and flow properties, on the
thermal attitudes of the battery pack were evaluated for
two proposed design models. In conclusion, the outputs
of the analyses are as follows: the mini-channel cold-plate
thermal management system has effective cooling per-
formance in controlling the battery temperature at 5C dis-
charge, it was a sufficient 5-channel cold plate, and the
temperature could be reduced when the inlet mass flow
rate was increased. Moreover, the temperature difference
and maximum temperature values were reduced by 13.3%
and 43.3%, respectively, when compared to design 2,
which has three cold plates, with design 1, which has
two cold plates, and design 2 provided much better tem-
perature uniformity.
87
Guo et al. presented a system in
which pin fins combined with the cold plates thermal
management system. In this study, different arrangements
of pin fins have been proposed for insertion into mini-
channel cold plates. The heat transfer properties, pressure
loss, and flow structure of the BTMS were examined with
a 3D numerical model. The performance of BTMS was
8Proc IMechE Part E: J Process Mechanical Engineering 0(0)
evaluated according to an efficiency index consisting of
heat transfer performance and pressure loss. The results
showed that pin fins in mini-channel cold plates have a
significant positive effect on the thermal management per-
formance of the battery in general.
88
In a study to reduce
the temperature difference in large battery packs for EVs
with a BTMS, Chen et al. presented a bidirectional sym-
metrical parallel mini-channel cold plate (PMCP).
Numerical analysis was performed to evaluate the per-
formance of the proposed design. The results were also
supported by the experiments. As a result, the proposed
PMCP has importantly increased system efficiency.
89
In
almost all of the studies about cold plate BTMSs, cold
plates have a structure with straight mini channels in
them. However, Kong et al. presented a new cold plate
design that has a divergent channel shape to reduce the
maximum temperature and pressure loss. This proposed
cold plate shows high heat dissipation and low frictional
resistance for battery packs. They worked to make local
resistance even less by adding an extra inlet to the cold
plate that they designed with divergent-shaped. Due to
this new design for cold plates, they obtained a more influ-
ential battery cooling system.
90
In another cold plate
study, Jiang et al. used the mini V-shaped rips. Their
purpose of using them is to prevent the increase of the
pump power consumption while increasing the heat trans-
fer. The flow and heat transfer properties of V-shaped rips
models with different cross-sectional shapes were investi-
gated. It has been concluded that this designed system
outperforms conventional cold plate systems after experi-
ments and analysis.
91
PCM cooling system
The working principle of this system is based on the phase
change of the PCMs used by absorbing or releasing the
excess heat in the battery. As it is known, the most important
problem in the batteries used in EVsistheheatingproblem.
Although it varies according to the operating conditions of
the EV, the excess heat produced by the battery is absorbed
by the PCMs close to the battery pack, and when the tempera-
ture of the battery reaches the melting temperature of the
PCM, the heat is stored in the form of latent heat and the tem-
perature rise in the battery pack is tried to be kept at reason-
able levels. Thus, the operating temperature of the batteries in
the PCM cooling system remains within a relatively constant
temperature range. This cooling system does not require a
pump or blower and is, therefore, more cost-effective and
simpler in design and construction than other cooling
systems.
23,47,50,92–96
Figure 7 shows a schematic diagram
of the PCM cooling system.
Also, this method is one of the subjects that are fre-
quently studied because it does not require additional
energy use and therefore does not reduce the efficiency
of thermal management and battery.
94,98–101
Talluri
et al. used PCMs (Rubitherm15, Rubitherm31,
Expanded Graphite5, and Expanded Graphite26) with dif-
ferent thermal properties in the BTMS and wanted to
observe the effects of these PCMs on the thermal
performance of the Li-ion battery. For this purpose, a
6 kW battery pack design and simulation were made
and compared with previous experimental studies. In con-
clusion, the experiment and simulation results showed
that expanded graphite PCM is the most suitable PCM
among the four PCMs due to its superior thermal proper-
ties such as thermal conductivity, heat energy storage cap-
acity, and fluid leakage to control the battery temperature
at safe operating temperatures.
98
In their optimization
study to minimize the PCM mass, Li et al. used four
types of BTMSs, single, double, triple, and quadruple
cell, and examined the effects of cell radius, spacing
between neighboring cells, heat generation rate, and
upper and lower PCM thickness on the minimum PCM
mass.
102
In a study investigating the effects of PCM thick-
nesses (3, 6, 9, and 12 mm) around battery cells on per-
formance, Javani et al. stated that the maximum
temperature and temperature deviation in the cell was
reduced when a PCM was used. They also observed
that by using a 3 mm thick PCM for the Li-ion battery
cell, the temperature distribution became approximately
10% smoother.
103
In another study investigating the
effects of PCM’s thicknesses (3, 7, 9, and 12 mm) on per-
formance, Verma et al. used capric acid as PCM. Analyses
were made at 294 K and 323 K ambient conditions, and
the results were compared with conventionally used par-
affin. They reported that among the four different thick-
nesses, the 3 mm thick PCM layer was more optimal
and could reduce the maximum temperature in the cells
up to 305 K.
94
In another study, researchers tried to
observe the effects of PCM thickness, melting point,
and thermal conductivity of PCMs on cooling perform-
ance. For this reason, they conducted analyses by design-
ing modules in the computer environment. In conclusion,
they reported that the maximum temperature and
maximum temperature deviation decreased when the
spacing between modules and the thermal conductivity
of the PCMs increased. They also stated that as the
Figure 7. Schematic illustration of phase change material
(PCM) cooling method
97
.
Çetin et al. 9
melting point of PCMs increases, the maximum tempera-
ture increases, and the maximum temperature deviation
decreases.
104
In their study where they numerically exam-
ined the effects of PCM types, fin thickness, fin spacing,
and PCM thickness on the cooling performance of the
battery pack, Ping et al. proposed a new PCM and blade
structure for the thermal management system of the
LiFePO4battery module to reduce the maximum tempera-
ture and improve temperature uniformity in a high-
temperature environment (40°C). As a result, they stated
that the PCM-fin structured thermal management system
with optimized design exhibits good thermal performance
by keeping the maximum temperature of the battery
surface below 51°C. In addition, they emphasized that
increasing the PCM thickness appropriately improves
thermal performance and is more efficient than other
factors, but the critical value for PCM thickness is 10
mm, and it does not increase efficiency after this
value.
97
Huang et al. wanted to investigate the thermal
performance of a battery module with 25 parallel 18650
Li-ion batteries numerically and experimentally by apply-
ing phase change cooling with PCM. For this, they investi-
gated the effects of thermophysical parameters of PCMs
such as thermal conductivity, latent heat, and porosity. The
results indicate that higher thermal conductivity and latent
heat lead to better thermal management performance when
the maximum temperature and temperature uniformity of
the lithium-ion battery (LIB) module are taken into
account comprehensively.
105
In another study, Jiang et al.
designed a sandwich-structured thermal management
system consisting of a battery, PCM, and heat pipe. The vari-
ation of the battery temperature was determined experimen-
tally with three discharge and charge cycles. As a result, they
stated that the melting point of the PCM should be at least 3°
C higher than the ambient temperature in order to guarantee
safe battery temperature, low energy consumption, and suf-
ficient energy density in the long-term cycle.
106
Hybrid cooling systems
Hybrid BTMSs are generated by a combination of two or
more basic BTMSs. Each of the different BTMSs has
advantages and disadvantages. Hybrid BTMSs combine
the advantages of these systems. It achieves higher
thermal performance. In this way, it achieves higher
thermal performance and efficiency. However, hybrid
BTMSs may include some volume, weight, and energy
consumption problems. Basic hybrid BTMS types are
listed in Table 1.
In an experimental study, Ling et al. showed that insuf-
ficient cooling of air natural convection caused heat accu-
mulation that leads to some problems in thermal
management systems in PCMs. In this study, a battery
pack that has a thermal management system with a
PCM is operated continuously with a discharge rate of
1.5C and 2C, and the temperature in the battery pack
exceeds the maximum operating range of 60°C after
two cycles. In order to solve this problem, they proposed
the integration of the air-forced convection system into
the PCM system. In the experiments with this hybrid
system, the maximum battery pack temperature was
kept at 50°C. Experiments show that the thermophysical
properties of PCMs affect the maximum temperature
rise and temperature homogeneity for the battery pack.
Forced air convection is crucial for recovering the
thermal energy storage capacity of PCMs.
107
In another
numerical and experimental study, Qin et al. proposed a
BTMS that is a combination of air-forced convection
and PCM. They compared the thermal performance of
the system with passive and active strategies. As a result
of the experiments, the MTD is reduced to 1.2°C and
the maximum temperature is 16°C under the 3C rate in
the active strategy. The active mode presented a very
good performance compared to the passive mode.
108
Yue et al. developed a new hybrid BTMS for EVs
under dynamic working conditions. Their hybrid system
consists of micro heat pipe arrays, convective air,and
intermittent spray water. In this project, the heat pipes
remove the accumulated heat in the battery pack from
the pack, convective air dissipates accumulated heat in
the packs of the EVs under normal operating conditions,
and more cooling is provided by intermittent water spray-
ing at high power operations. They conducted experi-
ments on a 75 Ah Li-ion battery pack under dynamic
operating conditions. The proposed hybrid system
reduces the maximum temperature to 29.6°C and the
Table 1. Types of hybrid BTMS.
93
Type Hybrid BTMS
1 Heat pipe +air/liquid active cooling Heat Pipe Air
Heat Pipe Liquid
2 PCM +heat pipe passive cooling PCM Heat Pipe
PCM Heat Pipe Air
PCM Heat Pipe Liquid
3 PCM +air/liquid active cooling PCM Air
PCM Liquid
4 Others +thermoelectric cooling Thermoelectric Cooling Air Liquid
Thermoelectric Cooling PCM
5 Liquid +air cooling active cooling Liquid Air
BTMS: battery thermal management system; PCM: phase change material.
10 Proc IMechE Part E: J Process Mechanical Engineering 0(0)
temperature non-uniformity to 1.6°C. These values are
lower at 21% and 57%, respectively, compared to
systems without water spraying functions.
109
Wang
et al. proposed a new hybrid system by integrating
liquid cold plates into the PCM BTMS. For experimenta-
tion setup, PCM thickness and cooling plate size were
used from the other researchers’previous studies,
110, 111
and three different locations related to the placement of
the cooling plates around the battery were determined,
respectively, bottom, two sides, and one side. They used
a 3D thermal model for the proposed system’s numerical
simulation. The thermal performance of the proposed
hybrid cooling system was analyzed considering the var-
iations from cell to cell of a 168-cell battery pack. In con-
clusion, a hybrid cooling system with two-sided cold
plates is more effective than a bottom and one-sided
system in reducing the temperature. Experimentation
data shows that for a 53 Ah Li-ion battery under a 5C dis-
charge rate, the maximum temperature in the battery pack
was decreased from 64°C to 46.3°C due to the hybrid
cooling system with two-sided cold plates.
112
Song
et al. proposed a hybrid thermal management system
design consisting of a combination of liquid cooling and
PCMs. The presented system package layers consist of
a heat spreading plate, thermal column, insulation layer
cold plate, and PCM. A total of 106 cylindrical batteries
were used in this study. Further 3D numerical models’
simulations were made in the computer environment for
a hybrid cooling system and battery module and they
examined the aforementioned layers’geometric para-
meters of the hybrid system. Results show that the
battery temperature ramp-up rate and the steady-state
battery temperature are importantly decreased by the
hybrid cooling system. In this study, experimental
studies and numerical simulation results support signifi-
cantly each other.
92
Chen et al. worked on a system
using liquid cooling and PCM. In this study, it was
observed that the maximum temperature level and the
temperature difference decreased with the increase of
the cell spacing and the diameter of the fluid channel. In
order to investigate the effects of the PCM placement
on the length distribution and the structural parameters
of the battery pack and the cooling method, the battery
pack in the discharged state at 277 K was investigated
using CFD at an ambient temperature of 308 K. When
the third of the segmented settlements of 110, 120,
and 120 mm, respectively, are compared to the first, it is
observed that the maximum temperature and temperature
difference decrease by 30% and 40%.
113
One-dimensional
electrochemical and 2D thermal models were used to simu-
late the temperature of 16 cylindrical LiFePO
4
Li-ion battery
cells in one of the studies, considering the cooling perform-
ance, thermal conditions, and lifetimes of the battery cells
when the PCM and active air cooling system are used
together. Using the realistic current profile of the HEV,
Chen et al. simulated the changes in the temperature of the
PCM and the inlet velocities of the air cooling at different
ambient temperatures. In conclusion, the hybrid system
with active air cooling is more efficient than the cooling
process using just PCM in this study. It was also determined
as a disadvantage that the temperature distribution was more
irregular in cases where the air inlet velocity was low. When
the cyclical cost of these two cooling methods used is com-
pared, the cyclical cost of air cooling is lower. The cyclical
cost first decreases as the air intake velocity is increased,
then shows an increasing trend.
114
One of the works done
to increase the heat conduction between the cooling tubes
and the curved surfaces of the cylindrical lithium battery
cells is silica gel, to which graphene oxide is added, and is
filled into the space between the battery cells and the
liquid cooling channel. Graphene oxide used to increase
thermal conductivity provides superior performance for
cooling the battery pack. Test results show that the tempera-
ture value was reduced by 4°C to 5°C.
115
Considering the
performance of the system made by using PCM and heat
pipe, it is a very useful system since cooling is done
without power consumption. It has been determined that in
systems used actively/passively, hybrid systems are more
efficient than systems using a single cooling method.
When the statistical maximum cell temperature and tempera-
ture distribution were reviewed, it contributed to the devel-
opment of the most suitable cooling system for limited
power consumption, weight, and volume restrictions.
116
In
addition to the ducted cooling system in the mini structure,
the effects of the flow rate of the coolant, the cooling tube,
the amount of channel and the direction of the coolant
flow on the performance of the Li-ion battery cell were
investigated. It has been determined that the temperature
decreases when the flow rate of the liquid fluid is increased.
When the flow rate is 3 ×10−4kg ·s−1, the cooling per-
formance improves when the channel amount is increased.
It was observed that when the temperature decreased, the
temperature difference was reduced by up to 80% in
cooling with air at a speed of 4 m ·s−1.
117
In order to
prevent the heat that occurs in fast charging and dischar-
ging situations, a flat designed mini-channel layer is
placed between the battery cells in the sequential struc-
ture and the cooling liquid is allowed to pass through
this layer. Electrochemical and thermal events are exam-
ined by considering the channel width and amount, the
properties of the liquid used for cooling, the flow rate
and the temperature of the liquid. As the number of chan-
nels increases, there is a pressure drop due to the flow
resistance. When the flow rate is increased, the average
temperature and pressure drop, and the power consump-
tion increase. With five channels of 6 mm width, a flow
rate of 3 ×10−3kg ·s−1and a liquid inlet at a tempera-
ture of 298 K, the LiFePO4battery pack with a capacity
of 20 Ah can be used in any climatic conditions in the
range of 298 to 313 K.
118
Discussion
Temperature variation and operating temperature range
affect battery performance. Climate, season, and region
determine the outside temperature. In general, the
outside temperature is 35°C to 50°C. The factors on
which battery temperature depends are heat generation,
Çetin et al. 11
heat transfer, and heat dissipation. Other causes that cause
differences between cells are thermal boundary conditions
and battery incompatibility. These problems make BTMS
mandatory. The BTMS is critical to achieving optimum
performance and extending the life of the battery under
different climatic conditions. Battery life, performance,
operating temperature, and ambient temperature directly
affect the performance of EVs and HEVs.
Mismanagement of the thermal management system in
the battery pack can result in shortened battery life,
reduced battery capacity, and many other issues. The
cost and performance of the BTMS are important consid-
erations for EV and HEV manufacturers. So the cost of
EV or HEV has a big impact on sales volume. EVs are
more expensive than ICE vehicles. Battery packs
account for almost half of the EV manufacturing cost.
Efforts to reduce costs have provided manufacturers
with the opportunity to make more profits. Although the
operating temperature range of the Li-ion battery is
between 25°C and 40°C, the actual operating tempera-
tures are between −30°C and 60°C.
119
In BTMS, design
is important to keep battery cell temperatures at
optimum levels during charging and discharging. Many
studies have been carried out on this subject. Air, liquid,
and PCMs are the three most common cooling methods
for BTMS. The production cost of air-cooled BTMS is
generally lower than liquid-cooled BTMS. The major dis-
advantage of most solid-liquid PCMs is their low thermal
conductivity, which leads to excessive heat build-up
during charging and discharging. The pros and cons of
air, liquid, and PCM cooling methods are listed in
Table 2.
Conclusions
In this study, different BTMSs (air cooling, liquid
cooling, PCM cooling, etc.) were examined and their
advantages and disadvantages were compared, usage
restrictions in today’s technology, requirements, and
studies on this subject were reported. As a result of the
detailed literature review, the following conclusions
were reached:
•The development of EVs is directly proportional to the
development of battery technologies, and today many
studies are aimed at increasing the service life, stability,
and efficiency of batteries. In other words, the most
important part, which is the heart of EVs and HEVs,
is the battery pack. Battery life, performance, operating
temperature, and ambient temperature directly affect
the performance of EVs and HEVs. Mismanagement
of the thermal management system in the battery pack
can result in shortened battery life, reduced battery cap-
acity, and many other issues. The cost and performance
of the BTMS are important considerations for EV and
HEV manufacturers. So the cost of EV or HEV has a
big impact on sales volume. EVs are more expensive
than ICE vehicles. Battery packs account for almost
half of the cost of EV manufacturing. Efforts to
reduce costs have provided producers with an oppor-
tunity to make more profits. In this context, the first
thing to do is to develop the operating temperature
range of the batteries.
•In order for EVs not to lose efficiency and power while
operating under different climatic conditions, it is
necessary to develop BTMSs and to determine and
use a thermal management system suitable for the
climate structure of the region where it will be used.
•In general, in the air cooling method, air ducts must be
used to direct the air, and fans and other fasteners must
be used to provide this movement. Compared to other
methods, it is relatively large and the heat transfer effi-
ciency is lower.
•In the liquid cooling method, there is no need for a fan
and air duct as in air cooling, but instead, pipes are
needed to transport the fluid, and pumps are needed
to provide this movement. Although the use of liquid
increases heat transfer efficiency, it should not be for-
gotten that possible liquid leakage carries a great risk.
•Although it has been shown in previous studies that the
use of PCM significantly improves the thermal man-
agement performance of batteries, it is not very
common in commercial terms today due to problems
such as volume expansion during phase change, the
risk of leakage after the material is melted, and that
they are relatively heavier. However, many studies
are carried out on a laboratory scale.
In future works, investigation of the effect of adding dif-
ferent types and different sizes of nanoparticles on cooling
performance in PCM cooling and liquid cooling methods
is seen as a suitable option for researchers who want to
conduct new studies in this field. It would also be appro-
priate to design more BMSs and optimize them using
CFD to increase cooling performance. Not all EVs have
the same battery usage requirements, and these
Table 2. Comparison of air, liquid, and PCM cooling BTMS.
119
Thermal
conductivity
Structure
complexity Compactness Weight
Uniform temperature
distribution
Coolant
viscosity Cost Maintenance
Air cooling M L H L L L L L
Liquid cooling H M L H M M M M
PCM based cooling L H L H H H H H
PCM: phase change material; BTMS: battery thermal management system.
*L stands for low, M stands for medium, and H stands for high.
12 Proc IMechE Part E: J Process Mechanical Engineering 0(0)
requirements may vary from model to model, depending
on the vehicle’s intended use. It is a fact that EVs
should have the lowest possible weight in order to
travel long distances with the same energy. This shows
that in the future, efforts to increase the energy density
of Li-ion batteries will be carried out as well as weight
reduction studies. On the other hand, these studies will
bring with them abnormal heat formations and serious
thermal difficulties. For this reason, studies that will
increase the advantages and reduce the disadvantages of
each cooling system should be given importance, and
studies on hybrid cooling systems should be intensified.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) disclosed receipt of the following financial
support for the research, authorship, and/or publication of
this article: This present work is being funded by Düzce
University Scientific Research Projects Coordination Unit
with the project number “2022.06.05.1296”. The authors
thank “Düzce University”for its financial support.
ORCID iD
Fikret Polat https://orcid.org/0000-0003-3767-3156
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Appendix 1
Nomenclature
°C degree celsius
BMS battery management systems
BTMS battery thermal management system
CFD computational fluid dynamics
EV electric vehicle
HEV hybrid electric vehicle
ICE internal combustion engine
K Kelvin
kWh kilowatt hour
L liter
Li-ion lithium-ion
MTD maximum temperature difference
NiMH nickel–metal hydride
PCM phase change material
PMCP parallel mini-channel cold plate
RAF reciprocal airflow
TCS thermally conductive structure
UDAF unidirectional airflow
W Watt
16 Proc IMechE Part E: J Process Mechanical Engineering 0(0)