Electric Vehicle Battery Thermal Management Techniques Report

This report analyzes and quantifies the thermal management needs of electric vehicle battery packs, focusing on lithium-ion batteries and their heat-related issues. It explores various battery thermal management systems (BTMS) such as air cooling, liquid cooling, direct refrigerant cooling, and phase change materials (PCM). The report details the working principles of lithium-ion batteries, their operating temperature ranges, and the importance of maintaining optimal temperatures to prevent thermal runaway and performance degradation. A combined liquid cooling system with PCM is proposed as an appropriate thermal management solution to enhance battery life and performance. This document is available on Desklib, a platform offering a range of study tools and resources for students.

To analyze & quantify the thermal (Heat) management needs of Electric Vehicle battery packs &
apply appropriate thermal management techniques
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Abstract
Electric vehicles are becoming more and more popular because they used electricity as the
source of energy, which does not emit any hydrocarbons or greenhouse gas. They are
efficient, fast to meet the requirements of the masses. However, there are certain factors that
limits their development. Some of them are cost, safety and life of the battery. Therefore, the
study of this management needed in order to accomplish the maximum power improving the
performance under any condition.
The battery thermal management system (BTMS) plays a very important role to regulate the
heat exchange in the batteries. Some of the BTMS technologies are, air cooling system, liquid
cooling system, director refrigerant cooling system and phase change material (PCM). This
evaluated on the basis of their size, cost, reliability and many other factors and based on that
a combined solution is evolved that could solve the issues of thermal management and
increasing the performance to a great level compared to the before systems.
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Acknowledgment
The support from my teachers needs to be acknowledged because without their support it
would not have been possible for me to finish this project. They guided me throughout the
project which was precious. Apart from them I would also like to acknowledge staff members
and my friends who encouraged me to take this project as a challenge that would help me to
learn and grow.
A special thanks to me parents who helped me in my research for the sources. They have
always inspired me. Last but never the least I would like to acknowledge god almighty who
have always filled me with positive energy, not just in this project but throughout my life.
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Table of Contents
Abstract.......................................................................................................................................i
Acknowledgment.......................................................................................................................ii
Table of Contents......................................................................................................................iii
1 Introduction.........................................................................................................................1
1.1 Background..................................................................................................................1
1.2 Objectives....................................................................................................................1
1.3 Overview.....................................................................................................................1
2 Lithium-ion Batteries..........................................................................................................2
2.1 Working.......................................................................................................................2
2.2 Heat problems..............................................................................................................4
2.3 Operating range...........................................................................................................5
3 Battery Thermal Management Systems (BTMS)...............................................................7
3.1 Needs...........................................................................................................................7
3.2 Some of the cooling techniques...................................................................................7
3.2.1 Air systems...........................................................................................................7
3.3 Liquid systems.............................................................................................................9
3.4 Direct refrigerant systems..........................................................................................11
3.5 Phase Change Materials............................................................................................12
4 Appropriate Thermal Management Solution...................................................................14
4.1 Combined liquid cooling system (CLS) + PCM.......................................................15
5 Conclusion........................................................................................................................19
References.................................................................................................................................iv
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1 Introduction
1.1 Background
As the time is changing, the technology is also changing. The electric vehicles are becoming
more and more advanced. Different types of batteries are employed for the purpose is to
optimise everything. The batteries operate by generating energy through electrochemical
reactions which are highly temperature dependent. In order to maintain proper working
environment of temperature, a battery thermal management system is employed. Therefore
the correct knowledge of the system, its application and implementation is very much
required. Also note that as the time is changing everything is become compact, and so is the
battery but as the batteries are becoming smaller and smaller, its capacity and power
requirements are increasing. Therefore the energy consumption is another important aspect in
BTMS. Thus increasing the life of the battery.
1.2 Objectives
The goal of this report propose a model for balancing the temperature of a battery so that its
performance is increased. For this every aspect of a battery is discussed starting from the
basic model of a lithium-ion battery. Many systems for heating and cooling are discussed in
detail and at last a combined solution is provided that includes the best systems, ideal for
implementing in the electric vehicles today.
1.3 Overview
This report discusses some acceptable and popular techniques to manage the temperature and
heat. The correct balancing between them is discussed in order to increase the performance.
At first the basic working of a lithium-ion batteries discussed because the fundamentals play
an important role in understanding the whole scenario. The temperature dependency is
discussed in a lithium-ion battery along with the operating temperature range required. Next
some of the common BTMS solutions are discussed. The mechanism, functions, advantages
and disadvantages are discussed. At last a new method is proposed combining the already
discussed models in order to increase the performance.
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2 Lithium-ion Batteries
2.1 Working
A lithium-ion battery is very popular among the electric vehicles (EVs) as well as the hybrid
electric vehicles (HEVs). It constitutes two electrodes, electrolyte and the separator as shown
in figure 1. The anode is made up of graphite or carbon, the cathode is made up of lithium
metal oxide and electrolyte is an organic solvent in which the thieves also dissolved. During
discharging, the goal of the anode is to throw the electrons out to the external circuit. Thus,
the anode undergoes oxidation. Whereas, the cathode receives all the electrons from the
external circuit that are thrown away by the anode (Techopedia, n.d.). Thus, a cathode
undergoes reduction process. An electrolyte is a substance that contains both the electrodes
debris inside it and it makes it possible to exchange irons between cathode and anode. The
separator helps to act as a boundary between the two electrodes and hence preventing their
short circuit. The solid electrolyte interface (SEI) is formed outside the anode during the first.
It decreases the rate of the reaction and hence the current (Woodford, 2018). One of the
biggest advantage with the lithium-ion batteries is that it can be charged again and again. This
means that the electrochemical reactions can be reversed (Poole, n.d.). The lithium ions travel
from the negative electrode to the positive electrode during discharging while, it travels from
the positive electrode to the negative electrode (Troiano, 2013). The reaction for the lithium-
cobalt batt is given as,
Figure 1 (Electropaedia, n.d.)
Reaction at cathode is shown in the figure 2:
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Figure 2 (Electropaedia, n.d.)
Reaction at anode is shown in the figure 3:
Figure 3 (Electropaedia, n.d.)
There are a variety of lithium batteries available in the market which varies in terms of the
material used as the cathode. For example Lithium Cobalt Oxide, Lithium Manganese Oxide,
Lithium Iron Phosphate and many more. In the table 1, many types of cathode substances
along with its description is mentioned.
Chemical name Material Short form Description
Lithium Cobalt
Oxide
LiCoO2 Li-cobalt The capacity is large
and ideal for cell
phone, camera and
laptop batteries.
Lithium Manganese
Oxide
LiMn2O4 Li-manganese Very safe, although
there capacity is low
as compared to the
lithium cobalt oxide
but the power is
specific and runs
longer. There are
used in electric bikes,
medical apparatus
and EV.
Lithium Iron
Phosphate
LiFePO4 Li-phosphate
Lithium Nickel
Manganese Cobalt
Oxide
LiNiMnCoO2 NMC
Lithium Nickel
Cobalt Aluminium
Oxide
LiNiCoAlO2 NCA There are becoming
popular in electrical
power trains and
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grids.Lithium titanate Li4Ti5O12 Li-titanate
Table 1 (Battery University, 2018)
As per the table 1, three cathode materials are best suited for EVs, li-phosphate, li-manganese
and NMC (Evans, n.d.), (Energy Storage Association, n.d.).
2.2 Heat problems
The performance of the lithium ion batteries are dependent on the operating voltage and the
temperature. If it doesn’t operate within the range than it can be damaged permanently. First
of all we analyse in terms of operating voltage. If the battery is charged at a voltage higher
than the acceptable voltage, then the amount of current increases in the circuit. It creates two
issues, when the currents are high, more number of lithium ions are deposited at the anode as
lithium. This process is called as lithium plating. Due to this process the number of free
lithium irons decreases also there is a loss of the capacity of the battery. There are two kinds
of lithium plating, heterogeneous and homogeneously lithium plating. It occurs in the form of
branch that is the layers of lithium increases subsequently over time and ultimately if the
overvoltage situation persists then a time comes when both electrodes gets short-circuited. In
the case of under voltage during discharging, the copper current collector of the anode breaks
down. The rate of discharge is increased and so the voltage of the battery. The copyrights that
are broken down gets deposited as copper metal (Electropaedia, n.d.). This was is not
reversible. If the control the situation persists longer, time comes when both electrodes gets
short-circuited. It damages the battery permanently as well as it is dangerous. Another plus is
also happens. The metallic oxide, either cobalt oxide or manganese oxide, gets reduced by
depleting oxygen. This results in further loss of capacity.
The temperature also plays a very important role. The rate of the reaction is linearly
dependent upon the temperature. The capacity is directly proportional to the reaction rate. In
the case of low temperature, the reaction rate is decreased and therefore the current carrying
ions also decreases. In the case of higher operating temperature, the temperature of the
battery is increased. The rate of dissipation is less than the heat generated. Hence, the overall
temperature is high and hence it will damage the battery in the long run. The resultant in a
thermal runaway. Thermal runaway constitutes many stages such that each would make the
situation worse.
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Around 80° the SEI layer dissolves in the electrolyte. Due to this and exothermic reaction
occurs between the anode and the electrolyte. This increases the temperature further. Now, at
around 110°C the organic solvents begins to disintegrate in this release is hydrocarbon gases.
The pressure increases inside the battery due to the gas but they do not burn because there is
insufficient oxygen to enable conversion. At this point the temperature is so much that the
separator also gets dissolved and the anode and cathode gets short-circuited. The temperature
happens to be around 135°C. Finally around 200°C, the metal oxide also gets disintegrated.
This releases oxygen which allows the hydrocarbon gas to burn. This process is also
exothermic and increases the temperature as well as the pressure further.
Another problem is the unequal distribution of temperature in the battery. This is due to the
huge temperature, fluctuating current, positioning of positive and negative terminals and
many more. It results in thermal runaway and hence the life of the battery decreases.
2.3 Operating range
In order to avoid the issues mentioned above, the temperature of the battery should be
maintained in the optimum range of operation. This would not only increase the life of the
battery but also increase its performance and energy consumption which is highly needed in
an EV. The temperature distribution should be even. Thus, the battery thermal management
system is very important for a battery.
Figure 4 shows a graph between the operating temperature and the power. When the
temperature of the battery is between 20° and 40°, it attains the maximum power. The cycle
life of the battery drops below 10°C due to the lithium plating. Also it drops after 60° because
of the breakdown of the materials of electrodes as shown in the figure 5. Thus, the operating
temperature of the battery should be controlled in such a manner that it lies between 20° and
40° so that the maximum power and performance is achieved. The even destruction of the
temperature can be controlled under 5K in order to ensure safety and increase the life of the
battery. The ventilation of the battery should be proper so that heat is dissipated properly.
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Figure 4 (Electropaedia, n.d.)
Figure 5 (Electropaedia, n.d.)
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3 Battery Thermal Management Systems (BTMS)
3.1 Needs
The safety of the battery pack along with its performance in terms of power and capacity has
to be ensured. The electric vehicles have a limited power supply therefore it should be stored
and controlled in such a way that the thermal runaway is prevented thus increasing its life.
The BPMS has to accomplish the following functionality is in order to enhance the battery
usability.
1. Cooling: during the operation of the battery, heat is generated. This heat is in the form
of an energy loss which cannot be prevented but it can be minimised by taking proper
measures. When the temperature of the battery increases beyond the optimal range, it
should be managed to bring it back to the required temperature range. A cooling
system can serve this purpose in BTMS.
2. Heating: the temperature of the battery may become less than the optimum range if it
is operating in a cold climate. Therefore, to bring it back to the optimal range, IET
mechanism can be employed such as a PTC heater quickly.
3. Insulation: there occurs a wide range of temperature difference between the outside
and inside environment of the battery when it is either kept too hot or too cold
conditions. This difference is not like when it is kept under normal conditions and
therefore the temperature of the battery falls arises very quickly outside the optimum
range. This is a major issue that affects the performance of the battery and to avoid
this proper insulation should be ensured.
4. Ventilation: ventilation is very much important in order to exhaust all those gases
which are harmful. These are generated due to the electrochemical reactions of the
battery. This function is combined with the cooling and heating functions in case of
certain BTMS systems.
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3.2 Some of the cooling techniques
3.2.1 Air systems
Air is used as a medium to transfer the heat around the battery system. The air that is taken in
for cooling and heating purpose can be either atmospheric or from a system that could be a
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