VOL. 14, NO. 1, JANUARY 2019 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2019 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 265 THERMAL MANAGEMENT SYSTEMS FOR EV’S AND HEV’S Harit Bajaj and Chandrakant R. Kini Department of Aeronautical and Automobile Engineering, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal, Karnataka, India E-Mail: chandrakini@gmail.com ABSTRACT Seeing how electric vehicles are the future of automobiles in general, it has become crucial to manage heat properly, so as to maximize the efficiency and range of the vehicle. Most complex systems use Li-Ion batteries as there are several advantages to this, such as maximize range, minimize weight and space used by batteries. The high power density of Li-Ions batteries allows it to be a perfect candidate for electric vehicles given the current state of technology. One of the conditions that comes with such a battery pack is its optimum operating temperature which lies between 15 and 30 degrees Celsius. The battery must have a thermal management system, either passive or active, wherein it always stays within this range. This paper aims to answer the major questions which deal with how to most effectively manage heat in an EV or HEV by comparing multiple solutions. Keywords: battery cooling, BTMS, HVAC. 1. INTRODUCTION A battery has many varying characteristics based on many factors. Characteristics such as specific energy, specific tension, operating conditions, auto discharge rate, charge time, toxicity and C-rate (which is the charge/discharge rate). The definition of C-rate is the capacity in terms of Ah. The capacity is rated 1C when a fully charged battery can provide 1 amp for 1 hour. Life cycle, recycling and materials used are also of great concern for battery development. [1]. These characteristics vary on factors such as energy demand, load, operating temperature, ambient temperature and many more things. The variations occurring are different for different battery chemistries. Majority of the battery systems deployed in vehicles are: lead batteries, alkaline batteries, lithium batteries and sodium batteries. The main focus of this paper will be understanding and thermally managing Lithium Batteries. The paper will begin with understanding what the batteries are exactly and then proceed to the various solutions to deal with thermal management. 2. UNDERSTANDING LI-ION BATTERIES Li-Ion batteries are known for having high specific energy, high standby times (low auto-discharge), no memory effect and low maintenance requirements [2]. Memory effects of batteries are generally observed in Nickel-based batteries. It is when the battery appears to “remember” it’s lowered capacity after being charged from a state of being partially discharged. Though the battery poses problems such as overheating, explosion risks due to leakage and formation of crystalline structures between the electrodes. The biggest disadvantage is the cost per kilo-watt of energy and the requirement of a good thermal management system for maximum efficiency [3]. 2.1 Kinds of li-ion batteries Based on the kind of material used in the cathode, various kinds of batteries exist. The three kinds of main cathodes are as follows [1]. a) Cathodes based on metal dioxides. b) Batteries based on cathode spinel (Ex: Manganese oxide) c) Cathodes with transition metal phosphates The negative electrodes commonly tend to act as the “lithium sink” whereas the positive electrodes in the form of LiA z B y , acts as the “source of Li”. The first two kinds of cathodes are the ones that tend to be most commonly used [4]. 3. THERMAL BEHAVIOUR OF LI-ION BATTERIES There is an ideal temperature for Li-Ion batteries to function ideally. The reason this happens is that the battery can’t get too hot or too cold. If this happens, then the battery doesn’t perform as designed, and as a result, this could be detrimental to the overall performance and operation of the vehicle. If the battery is too cold then the battery capacity and autonomy is reduced, as well as its ability to operate. If the battery gets too hot then it destabilises, it ’s safety, power and life cycles are impacted. An example of the effect of temperature is shown in Figure-1. The graph in Figure-2 indicates the effects of temperature on the capacity of the battery. The capacity is an indicator of how much charge a battery can retain. As seen from both the graphs both extremely high or low temperatures are conducive for the battery performance. Hence an ideal temperature range is often prescribed by the manufacturer. Thermal management systems need to deal with this and dynamically adjust the operating conditions based on performance requirements.