Thermal Management for Batteries: From Basic Design to Advanced Simulation and Management Methods

By Hafiz Muhammad Ali

Thermal Management of Batteries presents a comprehensive examination of the various conventional and emerging technologies used for thermal management of batteries and electronics. With an emphasis on advanced nanofluids, the book provides step-by-step guidance on advanced techniques at the component and system level for both active and passive technologyStarting with an overview of the fundamentals, each chapter quickly builds into a comprehensive treatment of up-to-date technologies. The first part of the book discusses advanced battery technologies, while the second part addresses the design and performance optimization of battery thermal management systems. Power density and fast charging mechanisms of batteries are considered, as are role of thermal management systems on performance enhancement. The book discusses the design selection of various thermal management systems, parameters selection for different configurations, the operating conditions for different battery types, the setups used for experimentation and instrumentation, and the operation of thermal management systems. Advanced techniques such as heat pipes, phase change materials, nanofluids, novel heat sinks, and two phase flow loops are examined in detail.Presenting the fundamentals through to the latest developments alongside step-by-step guidance, mathematical models, schematic diagrams, and experimental data, Thermal Management of Batteries is an invaluable and comprehensive reference for graduates, researchers, and practicing engineers working in the field of battery thermal management, and offers valuable solutions to key thermal management problems that will be of interest to anyone working on energy and thermal heat systems.

• Critically examines the components of batteries systems and their thermal energy generation
• Analyzes system scale integration of battery components with optimization and better design impact
• Explores the modeling aspects and applications of nanofluid technology and PCMs, as well as the utilization of machine learning techniques
• Provides step-by-step guidance on techniques in each chapter that are supported by mathematical models, schematic diagrams, and experimental data

• Language: English
• Publisher: Academic Press
• Release date: Mar 15, 2024
• ISBN: 9780443190261

Book preview

1: Battery thermal management using phase-change material

Zhiyuan Jiang¹, Zhichao Li², and Zhiguo Qu²     ¹School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi, P.R. China     ²MOE Key Laboratory of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, P.R. China

Abstract

The implementation of phase-change materials (PCMs) provides battery thermal management system (BTMS) an excellent cooling solution that improves battery reliability, safety, lifespan, and performance. This chapter reviews the properties of common PCM, the utilization of it in BTMS, and thermal modeling of BTMS with PCM. First, the classification of PCM is introduced and thermal properties of different PCMs are reviewed. However, the poor cycle performance caused by leakage, low thermal conductivity, and fire safety concerns limit the usage of PCM. Therefore, methods for improving these shortcomings of PCM are completely discussed. Moreover, the utilization of PCM in BTMS is reviewed, and both the cooling and prewarming performances of batteries using PCM are discussed. Finally, two case studies of PCM-based battery cooling systems are discussed, along with their detailed modeling methods and simulation results. In Case-1, a transient 2D model was built for a square lithium-ion battery, which utilized paraffin infused with copper foam. The foam-PCM composite mode of thermal management significantly lowered the battery surface temperature to a safe level, unlike the air convection and adiabatic modes. In Case-2, the cooling structure that combines PCM and high thermal conductive heat pipe was simulated using a lumped numerical model. The model considers the heat generation by the batteries and dissipation through the PCM and heat pipe. The connection between the battery temperature and the PCM's melting process is explained.

Keywords

Battery; Battery cooling; Numerical modeling; Phase-change materials; Thermal management

Nomenclature

Ac   condensation section/fluid interface (m²)

Aco   condensation section/environment interface (m²)

Ae   evaporation section/fluid interface (m²)

Aeo   evaporation section/environment interface (m²)

As   specific interfacial area (m²)

asf   specific surface area of the metal foam (m²)

C   lithium-ion concentration (mol/cm³)

cp   specific heat capacity (J/(g Equation K))

dc   thickness of insulation cotton (m)

fl   liquid fraction in the pore

g   gravitational acceleration (cm/s²)

ΔH   latent heat (J/g)

Hc   contact hardness (Pa)

h   interfacial heat transfer coefficient (W/(cm² Equation K))

K   permeability (cm²)

k   thermal conductivity (W/(m Equation K))

M   mass (kg)

masp   slope of gap (m)

Nu   Nusselt number

P   pressure (Pa)

Pr   Prandtl number

R   thermal resistance (K/W)

Re   Reynold number

T   temperature (K)

t   time (s)

u,v   velocity in x and y direction (cm/s)

Uocv   open circuit potential (V)

Us   internal energy of vapor (J)

Y   mean plane distance (m)

Greeks

ρ   density (kg/cm³)

δ   liquid fraction (=εfl)

δt   thickness of wick (m)

β   thermal expansion coefficient (K−¹)

βt   thickness ratio of PCM layer and battery

σ   electronic conductivity of the solid electrode (m²/s)

κ   ion conductivity of the electrolyte (m²/s)

ε   porosity

μ   dynamic viscosity (N ⋅s/cm²)

φ   potential (V)

σasp   thickness of gap (m)

Acronyms

BTMS   battery thermal management system

CNTs   carbon nanotubes

CPCM   composite phase-change material

EG   expanded graphite

ER   epoxy resin

GS   graphene skeleton

HP   heat pipe

HRR   heat release rate

LOI   limiting oxygen index

PCM   phase-change material

PCR   phase-change ratio

PW   paraffin wax

Highlights

• Battery thermal management using PCM is emerging as an effective method.

• Enhancing structural stability, thermal conductivity, and flame retardancy is critical.

• The hybrid system using PCM is necessary for all climate temperature control.

• Case studies of PCM-based battery cooling systems are discussed.

1. Introduction

Phase-change materials (PCMs) show large latent heat undergoing a phase transition and maintain a relatively constant temperature during this period; using this property, energy storage and temperature control can be effectively achieved in a specific temperature range. Thermal management applications of PCM can be categorized into solid–liquid PCMs [1–3] and gas–liquid PCMs [4–6]. The use of PCMs in battery thermal management system (BTMS) was first proposed in yr. 2000, when Al-Hallaj's team observed that batteries wrapped in PCMs maintained a temperature 8°C lower than those cooled freely [7]. They compared the temperature control effects of multiple cooling methods, including phase-change cooling and natural convection. It was found that the battery heat dissipation using the structure of aluminum metal foam combined with PCMs can achieve a 50% temperature drop when comparing with that using natural convection. Subsequently, Kizilel et al. [1] applied phase-change paraffin wax (PW) to battery thermal management under extreme charge-discharge conditions. PCMs were found to maintain a low temperature level during the high-rate cycle, and the melting point control reduces the high temperature battery degradation significantly compared with the system without the PCM. Rao et al. [2] investigated the temperature control of square LiFePO4 cells using PCMs. It is found the most suitable PCM for keeping the cell temperature at 50°C had a melting point of 45°C. PCMs have several advantages over other cooling methods, such as no additional energy consumption, simple structure, good shape adaptability, high latent heat, and high temperature consistency. As a result, the use of PCMs in BTMS has gained increasing attention from researchers.

2. Classification and properties of PCM

2.1. Organic PCM

Organic PCMs are made primarily of carbon and hydrogen elements. These materials are characterized by low thermal conductivity and are commonly used at temperatures below 200°C, based on their melting points. To keep the best operating temperatures, organic PCMs can be applied in different areas and for different goals, for example, in solar energy systems and BTMS. Paraffins and nonparaffins are two main categories of organic PCMs. Table 1.1 illustrates the physical properties (solid state properties) of common organic PCMs.

Paraffins are primarily composed of straight-chain, saturated alkanes and can be represented by the chemical formula CnH2n+2, where the number of carbon atoms (n) falls between 20 and 40 [9]. During phase-change process, the molecular chain of the paraffin can release or absorb a significant amount of heat. Moreover, the total amount of latent heat released and PCM melting temperature increase with carbon atom number as the dipole attraction among the alkane chains grows stronger. Given the exorbitant cost of pure paraffin, technical grade paraffins are more commonly used. These modified versions possess desirable heat storage density and a controlled temperature range for phase transitions, as shown by studies. They have the ability to capture, hold, and release considerable amounts of heat during the conversion between solid and liquid states. As a result, paraffins with a lack of supercooling during freezing, good thermal stability, and low vapor pressure at melting hold great potential for practical applications. Nevertheless, paraffins also have certain drawbacks, including their low thermal conductivity and inability to be used with plastic containers.

The most abundant PCMs are the organic nonparaffins, including fatty acids and alcohols, which exhibit complex properties. In contrast, the properties of paraffins tend to be uniform. Despite the variations in properties among nonparaffins, they share many common features, including no supercooling phenomenon, high latent heat, and good thermal stability. However, they also possess certain disadvantages, such as mild toxicity, flammability, and low thermal conductivity. Among the nonparaffins organic PCMs, fatty acids have gained significant attention. These materials can be derived from both animal and plant sources and offer numerous benefits, including consistent melting point, good chemical stability, minimal volume expansion, noncorrosiveness, high energy density, and no supercooling. Given these advantages, fatty acids are considered to be the excellent materials for thermal management.

Table 1.1

2.2. Inorganic PCM

Inorganic PCMs generally contain salt hydrates and metallics. Different from organic PCMs, salt hydrates usually consist of multiple elements besides hydrogen and oxygen, while metallics contain only one element. What's more, thermal conductivity of inorganic PCMs can reach three times that of organic PCMs, which makes them have a wide application. The physical properties (solid state properties) of typical inorganic PCMs are shown in Table 1.2.

Salt hydrates are a type of inorganic PCM formed by the hydration of inorganic salts. They are composed of inorganic salts and water, typically represented as AB·nH2O [10]. Salt hydrates have a wide range of melting point which range from below 10°C to more than 100°C. At the melting point, salt hydrates will lose all or part of water molecules. This process is called dehydration, which is thermodynamically similar to melting. Compared to the paraffins, salt hydrates are less costly and their thermal conductivity is two times larger. Additionally, they usually have higher density, providing high enthalpy per volume. However, salt hydrates are prone to incongruent melting, resulting in the production of solid salts. These solid salts have a higher density than water, so they prefer to settle at the bottom, reducing the quality of the salt hydrates. Another challenge of using salt hydrates is supercooling, as they have poor nucleation ability, resulting in a slow rate of nucleation at the fusion temperature. To achieve an appropriate rate, the material must be supercooled. Salt hydrates are widely used in building energy conservation, such as providing better insulation performance than commercial foam insulation bricks by reducing indoor peak temperatures and creating hysteresis in the indoor temperature rise [11].

Table 1.2

Another category of inorganic PCMs is metallics which have high volumetric energy density, low vapor pressure, and good thermal stability [10]. Moreover, compared with other PCMs, metallics have much higher thermal conductivity, thereby improving their application effectiveness. In the 1970s, scholars had proposed the application of metallics as PCMs. However, metallic PCMs have not attracted attention for a long time due to its high melting point and weight. Currently, with the development of metallurgical technology, obtaining metallics with suitable melting points becomes possible. In this case, metallics will have a wider application.

2.3. Eutectics

Eutectics are compounds of two or more kinds of PCMs, which can be formed by melting and solidification of components during crystallization. Composites can take on various forms as mentioned earlier [12]. Eutectics exhibit a unique property of freezing to form an intimate mixture of crystals and both components liquefy simultaneously, reducing the risk of separation during the freezing or melting process [10]. Moreover, the melting points of eutectics are lower than those of either component. Thus, this property allows eutectics to obtain specific melting points and meet application requirements by adjusting the components. Eutectics have large heat storage density and can melt congruently. However, eutectics may tend to be more costly than other PCMs since they are usually used in specific applications. Moreover, thermal conductivity of eutectics is limited, so improvement measures for thermal conductivity are still needed. Compared with other PCMs, the most significant advantage of eutectics is that they can apply to given applications through adjusting their components. Thus, eutectics have a wider application in addition to thermal management, solar energy utilization, cold chain, and so on [13].

2.4. Measurement of PCM thermal properties

The properties, such as melting points (Tc), latent heat (ΔH), specific heat (cp), and thermal conductivity (k), are directly related to the use effect of PCMs. Thus, measuring these properties accurately is the key to selecting appropriate PCMs for given applications. At present, the most common methods to accurately measure Tc, ΔH, and cp are differential scanning calorimetry (DSC) and T-history [14]. In the DSC, the sample and a reference material are placed inside a specific instrument. Under the protection of N2, they are heated/cooled at a set rate. In this case, the temperature difference between sample and reference material is measured, and then it is converted into heat flow. The thermal properties can be obtained by analyzing the heat flows versus time plot (DSC curve). Even though this testing method has been widely used, there are still some limitations, such as the test efficiency is low; the result is influenced by the heating/cooling rate. Because of these limitations, T-history, which can measure the thermal properties of multiple samples simultaneously has been proposed. During the measurement, the samples and a reference material are heating/cooling simultaneously. Through comparing the temperature versus time plots of samples with that of reference material, the properties can be obtained. When it comes to the thermal conductivity measurement techniques, they include steady and transient methods [15]. In the steady method, the temperature difference is measured under steady-state heat flow through the sample, and then k is acquired by Fourier's law. However, in the transient method, k is obtained by measuring the transient temperature difference. And this method is based on the unsteady heat conduction equation.

3. Enhancement of PCM in battery thermal management

PCMs are considered as potential materials for battery thermal management. However, commercial feasibility considerations necessitate addressing the shortcomings of PCM in physical and chemical properties, such as low thermal conductivity, short cycling life, and fire safety concerns. This chapter provides a summary of commonly employed methods and measures to enhance the properties of PCM, including: (1) enhancing thermal conductivity for improved heat transfer; (2) improving material flexibility for a more versatile structural design; and (3) enhancing flame-retardant ability for improved safety.

3.1. Thermal conductivity enhancement

This section provides a comprehensive analysis of recent studies aiming at improving the thermal conductivity of PCM. At present, the primary way is to build the internal heat transfer path in PCM through the integration of high thermal conductivity materials. The following three strengthening methods are introduced successively: (1) incorporating carbon materials; (2) adding metal nanoparticles; and (3) incorporating a high thermal conductivity skeleton.

3.1.1. Adding carbon materials

Carbon materials refer to the materials which are mainly composed of carbon element without constant structure and property, such as the expanded graphite (EG), carbon fiber, and carbon nanotubes (CNTs). The carbon-based composite phase-change materials (CPCMs) are shown in Fig. 1.1.

EG is a form of flake graphite that has been expanded in the interlayer direction through a specialized process. It preserves the desirable qualities, such as high thermal conductivity and nontoxicity, but also exhibits properties such as adsorption, biocompatibility, and environmental compatibility. Researchers have combined EG with PW to create a plate-shaped composite and applied it in BTMS. The CPCM can achieve a remarkable increase in thermal conductivity through incorporating 30 wt.% of EG Ref. [18].

Carbon fiber is commonly used in the field of transportation, industrial buildings, and aerospace; it has high thermal conductivity (about 10–140 W/(m·K)), small proportion, high tension, high elasticity, and thermal expansion coefficient of the advantages. Hence, the thermal conductivity of PCMs can be increased by integrating carbon fiber. Previous researchers have combined various carbon materials with PCM [19–21]. For example, Noh et al. [21] have combined various carbon materials with PCM. By adding 20 wt.% carbon fiber, the bulk thermal conductivity and in-plane thermal conductivity of composite PCM are increased to 1.5 W/(m·K) and 4.9 W/(m·K), respectively. Carbon fiber is compatible with most PCMs, having strong corrosion resistance and small fiber diameter, which is conducive to uniform arrangement in materials. Babapoor et al. [19] conducted experiments and found that PCM containing 0.46% carbon fibers achieved the best thermal performance. This mixture was found to be highly effective in reducing the battery temperature increment by as much as 45%.

Figure 1.1  Carbon-based material for PCM enhancement. (a) Expanded graphite with organic PCM; (b) wax-filled composite of carbon-bonded carbon fiber. Panel (a) [16], Citation permission from Elsevier, Copyright 2019. Panel (b) [17], Citation permission from Elsevier, Copyright 2018.

Another material is CNTs, consisting mainly of carbon atoms arranged in a hexagonal shape to form a coaxial tube with several to dozens of layers. As a lightweight one-dimensional nanomaterial, CNTs possess exceptional mechanical, electrical, and chemical properties. In recent years, research on CNTs has deepened, revealing their broad application prospects. Some scholars have recently utilized CNTs to improve the performance of PCMs [22,23]. Compared to pure PCM, adding CNTs (5 wt%) improved the melting point and the thermal conductivity while keeping 90.7% of the latent heat [24].

3.1.2. Adding metal nanoparticles

Incorporating metal materials, which have higher thermal conductivity than normal substances in nature, is also an effective way to improve the thermal conductivity of PCM. Therefore, many researchers have investigated the effectiveness of adding nanoparticles of metals to PCM. The nanoparticles for PCM thermal conductivity enhancement include aluminum powder [25], copper powder [26], Ag nanoparticles [27], TiO2 nanoparticles [28], etc. The thermal conductivity of CPCM increases because the nanometal particles that are inserted alter the structure of the base phase, which improves the energy transfer process within the mixture. For example, TiO2 is a pretty choice due to its properties such as good dispersion, good chemical stability, nontoxic, and so on. Motahar et al. [28] dispersed spherical titanium dioxide nanoparticles (TiO2) into the PCM matrix. The thermal conductivity of the CPCM increases by approximately 230%.

However, with the ratio of nanoparticle content grows, the thermal conductivity of CPCM increases nonlinearly. Nabil et al. [29] dispersed copper oxide nanoparticles (CuO) in the matrix of epoxy PCM (Fig. 1.2). When the nanoparticle load increased to 5 wt.%, the thermal conductivity of CPCM increased, while if the load increases to 6.5 wt.%, that value of CPCM will decrease, which may be due to the stronger diffusion of nanoparticles at higher temperatures, such as Brownian diffusion and thermal swimming diffusion.

3.1.3. Adding high thermal conductivity skeleton

By adding skeletons to the PCM, a rapid heat transfer channel can be established inside the PCM. Moreover, the skeletons immersed in PCM can enhance the stability of PCM. As shown in Fig. 1.3, commonly used high thermal conductivity skeleton include: metal foam [30–32], steel fiber [33], chemical-treated carbon skeleton [34], etc. He et al. [31] presented a composite material was constructed with copper foam as thermal conduction skeleton, PW as PCM, and carbon material EG and epoxy resin (ER) added. Compared to the original basic PCM, the thermal conductivity has increased by 500%, reaching 2.9 W/(m·K). Meanwhile, the adsorption of EG and further encapsulation of ER effectively reduced the leakage of PCM. Furthermore, Lin et al. [35] presented a new method for preparing CPCM using a hydrothermal process. As shown in Fig. 1.3c, a three-dimensional spider structure graphene skeleton (GS) was used to impregnate paraffin in a vacuum environment. On the other hand, the CPCM showed higher transverse thermal conductivity with increasing filler. Moreover, when the filler volume is 2.25vol %, the transplane thermal conductivity of sw-GS/PW reaches 2.58 W/(m·K), which is increased by 1258% comparing with pure PW.

Figure 1.2  Photograph of composite samples of nanoparticle-enhanced PCM based on eicosane. [29], Citation permission from Elsevier, Copyright 2013.

Figure 1.3  Schematic illustration for incorporating high thermal conductivity skeleton in PCM. (a) Copper foam and foam-paraffin composite; (b) steel fiber and fiber-paraffin composite; (c) preparation of polymer composite, sw-GS/PW. Panel (a) [36], Citation permission from Elsevier, Copyright 2012. Panel (b) [33], Citation permission from Elsevier, Copyright 2013. Panel (c) [35], Citation permission under terms of CC BY-NC-ND license.

3.2. Mechanical stability

In addition to thermal conductivity issues, PCMs face challenges related to geometrical deformation, such as risk of leakage, assembly difficulties, and high contact thermal resistance. Addressing these challenges requires improvements to the mechanical properties of PCMs. One approach to achieving this is by enhancing the plasticity of PCMs through the addition of copolymer materials. This can be achieved by incorporating copolymer materials to form a supporting skeleton [37,38] or by evenly mixing copolymer materials with PCM to create flexible PCM materials that can prevent melting and leakage [39,40]. Moreover, the addition of viscoelastic polymers to PCMs through techniques such as dipping or physical blending can enhance thermal flexibility, resulting in a unique thermal response to morphological transformation, and improving the flexibility of PCMs while addressing their shortcomings in terms of easy leakage from melting.

To enhance the mechanical properties of PCMs, researchers have developed flexible CPCM materials. Huang et al. [37] presented a PW-based CPCM using organic compounds as a supporting skeleton, thermoplastic ester elastomer as the packaging material, with the addition of EG. The thermal conductivity of the resulting CPCM reached 1.2 W/(m·K) at room temperature and excellent elastic toughness. In addition to possessing a tensile strength of 0.09 MPa, the material is also capable of withstanding a 720° rotation at 60°C and stretching to twice its original length at 90°C. Fig. 1.4 shows the flexural resistance, tensile resistance, and morphological stability of CPCM. Moreover, Wu et al. [41] developed a CPCM with heat-induced flexibility and shape recovery abilities, which was applied to BTMS. By adding 5 wt.% EG and 16 wt.% octadecyl amine-modified boron nitride nanosheets into PW, a significant increase in thermal conductivity can be achieved. Furthermore, the CPCM showed different thermal interface properties in different phase states and excellent shape recovery characteristics.

3.3. Flame retardant

Under abused operating conditions, such as internal short circuit or external extrusion collisions, batteries may experience thermal runaway, leading to potentially catastrophic fire and explosion. As a result, it is imperative that the PCM applied to BTMS exhibit sufficient flame-retardant properties to improve the overall BTMS safety. The effectiveness of flame retardation is typically evaluated using two criteria. The first criterion is the limiting oxygen index (LOI), which is defined as the minimum proportion of oxygen required for a sample to begin burning in a nitrogen–oxygen mixture. The flame-retardant effect improves with the increase of the LOI value. The second criterion is the heat release rate (HRR) during combustion, which directly reflects the intensity of combustion exhibited by the sample.

Figure 1.4  Tensile state, bending resistance, and morphological stability of the CPCM. (a) Natural mobility; (b) tensile strength; (c) leakage of PCM. [37], Citation permission from American Chemical Society, Copyright 2021.

To prevent combustion, flame retardants can form a dense protective layer during combustion or release nonflammable gases to isolate oxygen. Mixing flame retardants with PCM can effectively enhance the fire retardancy of materials. Niu et al. [42] proposed a CPCM that had a low thermal conductivity and a flame-retardant coating. The preparation process of the CPCM and its working principle during battery thermal runaway are illustrated in Fig. 1.5. The base phase of the CPCM is PW, and when the silica aerogel content is 60 wt.%, the thermal conductivity of the CPCM drops to 0.051 W/(m·K). The LOI index of the coated CPCM reaches as high as 56.31%. The thermal runaway test shows that the faulty battery has a temperature of 700°C, while the neighboring battery has a much lower temperature of 182.6°C demonstrating the effectiveness of the CPCM in preventing thermal runaway propagation. Li et al. [43] investigated the preparation of a thermal runaway protection material using the synergistic effect of noncombustible PCM and flexible SiO2 nanofibers. When the thermal runaway is triggered, the silica sol inside the PCM will transform into silica aerogel nanoparticles, and the thermal conductivity drops from 0.36 to 0.026 W/(m·K), further inhibiting the thermal runaway.

Various flame retardants are used in practical engineering applications with different mechanisms to prevent combustion. For instance, Al(OH)3 is decomposed into water and Al2O3 when heated, where water vaporizes to absorb heat, while Al2O3 forms a film to obstruct the heat and mass transfer processes. Red phosphorus is another example that is decomposed by heat during thermal runaway, which achieves the flame-retardant effect by enhancing the dehydration and coking of the material to form a carbon layer. Given the flame-retardant mechanism, scholars continue to focus on discovering flame retardants with high effectiveness at a low proportion and minimizing the latent heat reduction resulting from the blending of PCM and flame retardants.

Figure 1.5  The preparation process of the CPCM with flame-retardant properties and the working principle of the battery under thermal runaway. [42], Citation permission from Elsevier, Copyright 2022.

4. PCM-based battery thermal management system

4.1. PCM cooling system

The cooling systems using PCMs typically comprise gas–liquid and solid–liquid PCMs. Gas–liquid PCMs, including water and some organic PCMs, such as propane, are commonly employed in internal cooling systems. Bandhauer and Garimella [44] have proposed a gas–liquid PCM cooling technique for a spirally wound battery, as presented in Fig. 1.6a. The liquid PCM passes through microchannels inside the battery, absorbs heat, and is then cooled externally. This technique efficiently reduces the temperature differential between the battery's internal and external components. In contrast, solid–liquid PCMs have a wider range of compositions, such as paraffins and salt hydrates [45]. In thermal management applications, PCMs are usually placed on the battery surface to directly absorb heat from the batteries [46]. Moreover, this arrangement can be easily combined with other heat dissipation methods. Khateeb et al. [3] added PCM to a battery pack with a 3S×6P configuration to examine the cooling performance, as depicted in Fig. 1.6b. The PCM significantly reduced the temperature of the batteries. However, during abusive battery operations, the low thermal conductivity can slow down the heat dissipation from the PCM to the surrounding environment, which can cause the PCM to melt completely.

4.2. Hybrid cooling system

Currently, the pure PCM cooling system is gradually becoming ineffective due to the lack of efficient methods for heat dissipation. Since the PCM in BTMS utilizes latent heat to control battery temperature, once the latent heat is exhausted, the BTMS fails, increasing the risk of battery overheating. Therefore, combining the PCM system with active cooling systems, such as air cooling, liquid cooling, and heat pipe (HP) cooling is an effective way to overcome that issue.

Figure 1.6  The structure of PCM cooling system. (a) Gas–liquid PCM; (b) solid–liquid PCM. Panel (a) [44], Citation permission from Elsevier, Copyright 2013. Panel (b) [3], Citation permission from Elsevier, Copyright 2005.

Figure 1.7  Hybrid PCM cooling system. (a) PCM/air cooling system; (b) PCM/liquid cooling system. Panel (a) [47], Citation permission from Elsevier, Copyright 2015. Panel (b) [48], Citation permission from Elsevier, Copyright 2018.

The PCM/air cooling system typically employs forced convection as the active cooling method. Ling et al. [47]. proposed a PCM/air cooling system composed of an exhaust fan, wind channel, and other accessories (Fig. 1.7a). Compared to the pure PCM cooling, this system improves the heat transfer effect as well as the stability of the PCM. The battery system can keep its temperature steady below 60°C, even under high discharge current. The PCM/air cooling system has low cost and minimal energy consumption. Moreover, it is easy to construct and is beneficial for maintaining the stability of the system. However, the temperature control ability of air cooling is still insufficient compared to other active cooling systems. The PCM/liquid cooling system is regarded as a more efficient technology due to the higher thermal conductivity of liquid. As shown in Fig. 1.7b, this system includes PCM, a water channel, and accessories such as a pump and cistern [48]. Compared to pure PCM cooling, this system can significantly reduce the battery heating rate and maximum battery temperature. Furthermore, this system is beneficial in maintaining the homogeneity of battery temperature. Moreover, the PCM/liquid cooling system has better cooling effect than the PCM/air cooling system, while the accessories usually require more space. Additionally, there is a risk of short circuit due to liquid leakage.

HP is a vacuum device designed to transfer heat efficiently through the evaporation of the internal liquid. As shown in Fig. 1.8, in the PCM/HP cooling system, the evaporating section of the HP is attached with PCM to absorb its heat through evaporation of liquid inside it, while the condensing section is exposed to other active cooling systems to dissipate the heat from PCM [49]. This cooling system offers excellent performance as the battery temperature remains below 50°C during 5C discharge. Additionally, the system benefits from a low cost, a long lifetime, and a compact structure, making the PCM/HP cooling system an increasingly popular solution for thermal management.

4.3. Battery warming up using PCM

Operating at low temperatures can cause several issues for lithium-ion batteries, including increased polarization, internal resistance, lithium plating, and reduced lifespan. Preheating the battery is thus considered an effective method to address these issues. PCMs can store and release heat, allowing it to transfer thermal energy to heat the battery in cold climate, which is a promising method. CPCMs are more stable and efficient than pure PCMs and have been developed for long-term battery heating in low-temperature environments. Specifically, as shown in Fig. 1.9a, Luo et al. [50] added EG to the PCM to increase its thermal and electrical conductivity, allowing the joule heat produced by the current flowing through it to be used to heat the battery. This could result in a heating rate of 13.4°C/min. Additionally, PCM's solidification process can be leveraged for battery warming. Undercooled PCM can release substantial heat during solidification, making it an effective method for battery preheating. As shown in Fig. 1.9b, Ling et al. [51] proposed a method that utilizing the heat from subcooled PCM to heat battery. In the heating process, a specially designed device can be used to control the solidification process, resulting in a heating rate of up to 7.5°C/min.

Figure 1.8  The structure of PCM/HP cooling system. [49], Citation permission from Elsevier, Copyright 2017.

Figure 1.9  The battery preheating utilizing PCM. (a) Joule heating with PCM/EG composite; (b) heating with subcooled PCM. Panel (a) [50], Citation permission from Elsevier, Copyright 2021. Panel (b) [51], Citation permission from Elsevier, Copyright 2021.

The preheating method using PCM is a form of passive heating that requires low energy consumption. This method can fully utilize the latent heat of PCM and keep the battery temperature uniform. However, in practical applications, the total amount of heat required to heat the battery to the appropriate temperature is usually much greater than the latent heat storage capacity of the PCM, especially for large-scale battery packs. Future development should focus on improving the heat transfer efficiency between PCM and the battery. Additionally, PCM can be used as an auxiliary method to preheat the battery and reduce the cooling rate, rather than being solely responsible for heating the battery.

5. Modeling of PCM-based battery thermal management

5.1. Case-1 battery cooling with copper foam saturated with PCM

5.1.1. Introduction of the Case-1

This section investigates the use of copper foam composite material saturated with PCM to cool high-power lithium-ion batteries under conditions of elevated current discharge. The numerical method is employed to examine variations in the battery surface temperature under different discharging rates. A numerical model of foam-PCM cooling based on an experimental module [52] and construct a two-dimensional coupling model for battery cycling and cooling performance with CPCM using a typical calculation domain is established, as illustrated in Fig. 1.10. The numerical modeling details are discussed in subsequent sections.

Figure 1.10  Experiment module and calculation domain for numerical model. [35], Citation permission from Elsevier, Copyright 2014.

5.1.2. Numerical model construction

5.1.2.1. Description of coupling model

Fig. 1.11 presents the two-dimensional physical model of a single lithium-ion battery, which contains two parts: the lithium-ion battery domain and the foam-PCM domain. The lengths in the x and y direction of this model are L and H, respectively. During charging and discharging, heat from the electrochemical reaction diffuses to the battery surface through internal thermal conduction. The foam-PCM composite absorbs this heat at the surface and transfers it to the material through convective diffusion. The PCM used in this study is paraffin. When the paraffin begins to melt, the solid–liquid interface moves in the positive x direction. Only the dimensions of the positive electrode (Lpe), negative electrode (Lne), and separator (Lsp) are considered in the calculation process since the negative electrode and positive current collector are much smaller than the other structures. The foam-PCM domain is metal foam filled with PCM. The length of this domain in the y direction is also H, and the length in the x direction is Lco. The left boundary of the foam-PCM composite is in contact with the positive electrode of the battery.

The establishment of a complete two-dimensional mathematical model for this problem involves addressing three main concerns, as described in the physical model. First, a complete solution to the coupling connection between the electrochemical parameters of the lithium-ion battery and the temperature needs to be established. Second, a solid–liquid phase transition model in metal foam needs to be developed, which fully considers the interfacial movement during paraffin melting, and the influence of natural convective heat transfer. Finally, a coupling correlation between the lithium-ion battery region and the porous medium region needs to be established.

Figure 1.11  Schematic of the single battery in passive thermal management system. [52], Citation permission from Elsevier, Copyright 2014.

To address these concerns, considering the conservation of electron charge, energy balance, and ion concentration, a complete thermo-electrochemical model is established in the lithium-ion battery domain. For the simulation of foam-PCM domain, a flow model of natural convection in the porous medium driven by buoyancy force is established, and the energy equations for PW and metal foam are derived, considering the local nonequilibrium thermal effect. The equation of natural flow driven by buoyancy in the foam region is established by Forchheimer extended Darcy model.

5.1.2.2. Governing equations

In the battery domain, the Doyle–Fuller–Newman type model is adopted to calculate the total amount of heat from battery region. The detailed lithium-ion battery thermal modeling can be found in Refs. [52,53]. The calculation formula of heat production is as follows