Chapter 9 - Evaluation of heat generation and application in liquid cooling of Li-ion battery packs

Abstract

Lithium-ion or Li-ion batteries are developing to be the major power source for electric vehicles (EVs). During the charging and discharging of these batteries, a large amount of heat is generated because of the existence of internal resistance. If the heat generated is not dissipated properly, excessive temperature and uneven temperature distribution in the battery pack would result, causing attenuation of battery capacity and cycle life, and even thermal runaway. To avert such issues it is necessary that Li-ion battery packs of EVs have battery thermal management systems (BTMS). Various thermal management techniques are available, but the liquid cooling thermal management has the advantage of high cooling performance and compact system structure. It is, therefore, not surprising that it has become one of the dominant thermal management techniques. At present, research on liquid cooling BTMS is mainly focused on the design of new system structures, optimization of cooling strategies, as well as coupling liquid cooling with other thermal management methods. The objectives of research efforts include enhancing cooling, as well as reducing the energy consumption, volume, weight, and cost of the BTMS. However, obtaining a coherent understanding through linking and integrating results from studies with different objectives is a major challenge in the design and optimization of BTMS. Therefore, a more intensive and fundamental approach to research on liquid cooling thermal management is essential. In this chapter, the heat generation mechanism and heat generation rate of Li-ion batteries will be analyzed. This is followed by a discussion on state of the art of liquid cooling thermal management. Finally, a case study to demonstrate the design and numerical simulation of a liquid cooling thermal management system for prismatic batteries will be given.