Thermal Management of Electric Vehicle Battery Packs

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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