1. Introduction

Due to their outstanding properties regarding high energy density, power density, high service life, low self-discharge and rare pollution, the use of lithium ion batteries for battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs) shows excellent promise [1]. Battery charging and discharging are strongly coupled to the operating temperature with a higher temperature increasing the number of undesired reactions, that is, the decomposition of the

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

electrolyte, thickening of the solid electrolyte interface (SEI) film, and so on, which have the effect of degrading the battery capacity [2–4]. Lithium-ion battery cells are also highly sensitive to low temperatures. For example, at below 10C, it has been shown that batteries' performance deteriorates considerably [5, 6]. Safety is also an issue in that at high temperatures, lithium-ion batteries are prone to uncontrollable temperature build-up (thermal runaway) [7]. In addition, a battery pack is usually composed of up to hundreds of single cells connected in series and/or in parallel to produce output voltage and power/energy capacity to achieve the BEVs' or HEVs' operating needs. This contributes to the accumulation of heat and uneven temperature distributions across the battery pack so degrading performance. To counteract these serious problems, it is necessary to cool a battery pack effectively and uniformly.

block, for a lithium ion battery module. A thermal model is developed for the battery module where electrochemical equations are solved to provide boundary conditions for a computational fluid dynamics code in which the energy and fluid flow conservation equations are solved. Variation of parameters such as the velocity of water within the tube and the number of turns

Effectiveness of a Helix Tube to Water Cool a Battery Module

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The mathematical model for a single lithium-ion battery developed here is based on the work of Doyle et al. [26]. The battery cells used are cylindrical with a central mandrel, with thin layers of anode, cathode, current collector and separator rolling up on the mandrel and with protection provided by a battery can. The anode is made of graphite derivatives and the cathode material is a metallic oxide such as LiFePO4 and LiM2O4. A schematic of a lithium

Generally, a lithium ion battery consists of the current collector, the positive electrode, the separator and the negative electrode. A lithiated organic solution fills the porous components and serves as the electrolyte. Several assumptions are needed, that is, the active electrode material is composed of spherical particles with uniform radius and the winding zone of the battery is a lumped model with homogeneous electrochemical properties. The material balance for the Li ions in an active solid material particle is governed by Fick's second law, here

used for the helix were investigated.

2.1. Modelling within a single cell

2. Mathematical model

ion cell is shown in Figure 1.

expressed in spherical coordinates

Figure 1. Schematic of a lithium ion battery.

Important to the development of a realistic thermal model of a battery module is good knowledge of heat generation either from the battery module as a whole or from individual cells within the module. The battery heat generation rate can be estimated by direct measurement [8], by indirect measurement, for example by measuring equilibrium voltage [9], measuring internal electrical resistance [10] or using the electrochemical mechanism [11, 12]. For direct measurement, the results apply to only a few operating points, and for indirect measurements, accuracy is a problem as the heat generation rate is a nonlinear function of the state of charge (SOC), current and operating temperature [13]. Work on single cell thermalelectrochemical modelling has already been done [13–16], and it is the view here that an essential component for the modelling of battery modules and eventually battery packs is to start with accurate calculations of heat generation within a given single cell.

There are a number of ways of cooling battery modules with the major division being between air cooling and liquid cooling. There are advantages and disadvantages associated with each choice. For liquid cooling systems, a disadvantage is that they have the potential to leak, which could cause an electrical short. Also when liquid is used, maintenance and repair can be more costly and more complicated, and generally liquid cooled systems are more heavy and require more components. However, a design can be used, as in the present application where the battery module and liquid can be separated by aluminium. Air cooling systems are generally less effective at maintaining a uniform temperature within and between cells in a battery module, and they cannot carry as much heat away from the battery as quickly as a liquid-based system. Air convection (natural or forced) quite often is insufficient for effective heat dissipation from batteries under abuse conditions leading often to nonuniform temperature distributions within battery packs [17, 18]. Although air cooling systems are lighter, have a lower cost and generally a longer life, water cooling is favoured for this work due to its much superior cooling effect. There are many investigations of cooling systems reported in the literature with the majority of the work focusing on lumped parameter models [19]. The effectiveness of passive air cooling using phase change materials (PCMs) combined with forced cooling has been investigated [17], as has different single cell spacing arrangements [11, 20, 21]. It has been stated and demonstrated in the literature that indirect liquid cooling of battery packs (both passive and active) can prove an efficient method for dissipation or addition of heat [22–25].

This chapter presents an investigation of the thermal performance of indirect water cooling, using the proposed design prototype of a thin copper helix tube contained within an aluminium block, for a lithium ion battery module. A thermal model is developed for the battery module where electrochemical equations are solved to provide boundary conditions for a computational fluid dynamics code in which the energy and fluid flow conservation equations are solved. Variation of parameters such as the velocity of water within the tube and the number of turns used for the helix were investigated.
