Progress in design and development of battery thermal management system for electric vehicles

Abstract

Reversible electrochemical batteries having reasonable cyclic charging and discharging capabilities are commonly employed in portable applications. The battery technology has improved on various aspects such as high specific energy density, high nominal voltage (up to 3.7 V), long cycle life and low self-discharge, and reached to a level, where it can be incorporated in large-scale applications, e.g. Electric Vehicles (EVs). Lithium-ion (Li-ion) batteries are commonly used in light and heavy-duty vehicles nowadays due to its superior performance, long life, and high energy density. The battery is the most critical component in an EV, and its effectiveness decides the success of the vehicle. In terms of economics, the battery pack represents a significant portion of the overall cost of an EV. Therefore, not only optimum design but also operation and maintenance of the battery pack is considered crucial. In this regard, both high and low temperatures have a significant impact on the performance of the Li-ion battery. Temperature non-uniformity also leads to capacity differences among individual cells, ultimately affecting the overall performance of the battery pack. To enhance electrochemical performance, prolong battery life, and maintain optimal power performance, it is crucial to develop a Battery Thermal Management System (BTMS) that can effectively and reasonably regulate its temperature. Most of the electrical automobile industries have adopted active cooling systems, including both air and liquid cooling. Air cooling systems are simple and low maintenance. However, due to the low heat transfer coefficient, the core part of the battery generally reaches high temperatures, leading to high thermal non-uniformity. Liquid cooling, on the other hand, has a higher heat transfer coefficient, which helps in creating a more effective cooling system. However, liquid cooling requires an external cooling system and a very effective leak-proofing, making it generally costlier. The energy provided to the active system is extracted from the battery pack, compromising the vehicle’s range. Passive cooling systems come into play as they are capable of eliminating or reducing these issues. However, passive techniques alone cannot provide effective cooling during high discharge and charging conditions. It is recommended to use a combination of passive and active techniques in BTMS to achieve the desired maximum temperature and thermal uniformity.