Effect analysis on thermal behavior enhancement of lithium–ion battery pack with different cooling structures

Highlights

• Research and optimization strategies for different mini-channel cooling plate structures are proposed.

• The effect of different cooling structure schemes on heat dissipation performance is obtained by single-factor analysis.

• Different cooling structures and mass flow rate obviously affect the temperature uniformity of the battery pack.

• The optimal combination is achieved by combining orthogonal analysis with a comprehensive analysis.

Abstract

Thermal management plays a vital role in ensuring that each single cell in the battery pack works within a reasonable temperature range while maintaining the temperature uniformity among the cells and battery modules in the pack as much as possible. In this study, an electrochemical–thermal model coupled to conjugate heat transfer and fluid dynamics simulations is utilized to accurately evaluate the thermal behavior of the battery pack. The effect of different cooling structures, the number of mini-channels, and the inlet mass flow rate on the temperature indexes of the battery pack are investigated by single-factor analysis method. Then, the simple and efficient orthogonal analysis and comprehensive analysis are used to obtain the optimal factor combination. Results show that the cooling structure design significantly affects the area where the highest temperature occurs in the battery pack. Meanwhile, case D can obviously improve the temperature indexes of the battery pack. The maximum temperature of the battery pack decreases as the number of mini-channels increases, but the downward trend decreases. On the basis of aforementioned work, the optimal combination can control the maximum temperature below 302 K and reduce the maximum temperature difference to 3.52 K. The research and optimization strategies in this paper can provide promising optimization solutions for battery thermal management systems.

Introduction

In recent years, great attention has been paid to energy and environmental issues, and this situation has led to new vigor in the development of electric vehicles [1]. The pros and cons of power batteries, which are the main source of power for electric vehicles, determine the mileage, safety, and service life of electric vehicles [2], [3]. However, temperature significantly affects the performance of the battery pack [4], [5]. Failure to take corresponding heat dissipation measures for battery packs will result in the battery charge and discharge performance degradation, accelerated aging, and even thermal runaway or explosion [6], [7], [8], [9]. Therefore, research on the optimization design of the battery thermal management system (BTMS) is important to ameliorate the useful life of the power battery and enable the maximum power of the battery at a safe temperature [10], [11], [12], [13]. The BTMS is used to ensure that the battery operates within a reasonable temperature range to prevent thermal runaway [14], [15]. The ideal temperature range for battery operation is between 20°C and 40°C, and the temperature difference within the battery pack should be less than 5°C [16], [17], [18], [19]. The BTMS is divided into four main ways, namely, air cooling, liquid cooling, heat pipe cooling, and phase change materials (PCMs), according to the heat transfer medium. Air cooling is widely used at a lower cost, but the heat exchange capacity of air is limited [20], [21]. The difficulty of packaging and volume changes of PCMs limits their application in the engineering field [22]. Heat pipe, which is an efficient cooling device, is costly and often affected by local gravity [23], [24]. Liquid cooling is mainly due to the high thermal conductivity and heat capacity (higher than air) of the liquid coolant, which has played an effective role and has the advantages of compact structure and convenient arrangement [25], [26].

Liquid cooling is the best among the mainstream cooling methods [27]. Moreover, it can develop different designs of cooling methods. In recent years, an increasing attention has been paid to this method of battery cooling. Rao et al. [28] proposed a new liquid-cooled thermal management system for lithium–ion battery modules. The effects of three contact surface variations on the maximum temperature and the temperature difference of the battery pack were studied. The results demonstrated that the linear change method can effectively improve the temperature uniformity of the battery module. Tang et al. [29] investigated and optimized the mini-channel liquid-cooled battery pack and developed three different water-cooling strategies. The results showed that the bottom and sides of the battery module have cold plate structures to achieve the best cooling performance. Huang et al. [30] designed and optimized the cooling plate with streamlined channels inside to investigate the influence of the design of the mini-channels in the cooling plate on the cooling performance of the battery thermal management, and the flow resistance is proven to be the smallest. The results revealed that the streamlined cooling plate heat transfer efficiency can be enhanced by 44.5%, and the temperature uniformity can be effectively improved. A new serpentine channel liquid cooling plate with dual inlets and dual outlets was developed by Sheng et al. [31]. The effects of flow direction, flow rate, and channel width on the temperature distribution of the cooling plate were researched. The effects of different parameters on the heat dissipation performance are fully discussed, but the improvement of the thermal performance of the BTMS is insufficiently effective.

Most researchers focus on the structural parameters or thermal management parameters of a specific cooling structure as the research objects. Qian [32] comprehensively designed the liquid-cooled BTMS and studied the effect of the changes in five parameters on the battery temperature. The optimal value of the first parameter is selected as the basis for the analysis of the next optimal parameter. In this way, the optimal design of the five parameters is obtained in turn. Wang et al. [33] developed a liquid cooling optimization strategy for cylindrical batteries. The orthogonal test was used to obtain the influence rank of the affecting factors of the thermal performance of the battery pack, which provided guidance for the optimization of the cooling plate design. E et al. [34] established an orthogonal test table of four factors and four levels to optimize the heat dissipation performance of the mini-channel liquid-cooled battery pack. Four factors include channel width, channel height, the number of channels, and the coolant flow rate. The results showed that the number of channels has the greatest effect on the heat dissipation of the system, and the number of channels and the coolant flow velocity have similar effects on the temperature difference. However, the previously reported thermal management methods only consider the research and comparison of specific cooling structures. The single factor analysis method to select the optimal parameters not only requires a lot of time, but also ignores the effect of multiple parameters on the heat dissipation performance of the liquid cooling system. Faced with the development and challenges of liquid cooling technology, it is necessary to further develop the influence of different cooling structures on the thermal performance of lithium-ion battery packs. In short, the heat dissipation effect of the combination of different cooling structure designs and thermal management parameters will be a major issue for future research and discussion. Therefore, this study aims to analyze and optimize different cooling structure schemes to achieve efficient heat dissipation and temperature uniformity.

In this work, a combination of single-factor analysis and orthogonal analysis is used to investigate and optimize the heat dissipation effects of different cooling structures. First, under the 2C constant discharge rate, the influence of single-factor variables (different cooling structures, the number of mini-channels, and the inlet mass flow rate) on the maximum temperature and temperature difference of the battery pack is analyzed. Next, the different cooling structure schemes are used as a factor of the orthogonal experiment, which has never been used in published articles. A simple and efficient orthogonal experiment design method is used to study the best combination of the factors and quantitatively investigate the different influence ranks of the factors. Finally, the influence rank of the factors and the manufacturing difficulty of the channel are comprehensively considered to obtain the best combination of the factors for meeting the thermal management requirements. As highlighted here, this work reveals the research and optimization strategies for different cooling structures in addition to providing different influence ranks of the factors for the thermal management system. It also provides guidance for the thermal management of mini-channel liquid-cooled battery packs.