Preparation method of phase change thermal metamaterial applied to thermal management of power battery pack

Abstract

The application relates to the field of new energy electric vehicle lithium battery safety technology, in particular to a phase change thermal metamaterial applied to power battery pack thermal management and a preparation method thereof. The thermal metamaterial is prepared by adopting topological optimization design of a thermal super phase change composite material, the temperature of the overall battery pack is effectively reduced, the temperature difference between the battery packs is reduced, and the problems of unbalanced battery pack temperature and excessively high local temperature in the middle are solved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery safety technology for new energy electric vehicles, specifically to a phase change thermal metamaterial for thermal management of power battery packs and its preparation method. Background Technology

[0002] In recent years, new energy electric vehicles have been developing rapidly, and lithium batteries, as their main power source, have been widely used due to their excellent power density. Research shows that the capacity, cycle life, and safety of power batteries are all heavily dependent on temperature. Excessively low temperatures can lead to a significant reduction in battery capacity, while high temperatures can accelerate side reactions and degradation. In practical applications, the charging and discharging process of lithium batteries generates chemical reaction heat and polarization heat, accompanied by a certain amount of side reaction heat. If this heat cannot be dissipated effectively and in a timely manner, the local temperature of the battery will rise rapidly, causing a series of complex chemical reactions inside the battery, ultimately leading to thermal runaway and serious accidents such as fires and explosions. Furthermore, excessive temperature differences within the battery pack can also cause some batteries to overheat and experience rapid degradation. Therefore, designing a thermal management system for the battery pack based on the effects of temperature is crucial for maintaining the battery temperature within an appropriate range and reducing temperature differences between batteries.

[0003] Battery thermal management systems typically employ three methods: air cooling, liquid cooling, and phase change material (PCM) cooling. Air cooling offers advantages such as simple structure and light weight, but it has a low heat transfer coefficient and requires sophisticated airflow design, potentially leading to excessive temperature differences between individual battery cells. Liquid cooling boasts a high heat transfer coefficient and can be integrated with vehicle cooling systems, but its design is more complex, its weight is relatively large, and it carries the risk of leakage. Phase change materials (PCMs) can convert absorbed heat into latent heat of phase change during battery heating, storing heat as potential energy within the material while maintaining a constant temperature. This buffers against rapid temperature increases and provides some insulation in low-temperature environments. However, because PCMs themselves have relatively low thermal conductivity, their cooling often requires integration with other heat dissipation systems.

[0004] Currently, most battery thermal management systems for phase change materials use uniform phase change composite materials, which cannot effectively dissipate heat. This results in excessively high local temperatures in the middle of the battery pack, poor temperature uniformity between battery packs, and overall unevenness. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and solve the problems of poor temperature uniformity and excessively high temperature in some parts of the battery pack mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a phase change composite material, the phase change composite material comprising a common phase change material and a high thermal conductivity filler, characterized in that the method comprises: S1, establishing an initial geometric model based on the geometrical physical parameters of a battery pack and the positional relationship between the battery pack and the phase change composite material; S2, assigning corresponding thermal conductivity properties to the initial geometric model, the thermal conductivity properties including density, specific heat capacity, thermal conductivity, and a distribution function of the high thermal conductivity filler based on a solid isotropic material penalty model; S3, setting optimization objectives and constraints to establish a topology optimization model, the constraints being the content of the high thermal conductivity filler; S4, calculating the distribution of the high thermal conductivity filler based on the topology optimization model; S5, preparing the phase change composite material based on the distribution of the high thermal conductivity filler.

[0008] In some embodiments, the optimization objective in step S3 is the lowest overall battery pack temperature, the highest overall battery pack temperature, or the lowest battery pack temperature difference.

[0009] In some embodiments, the content of the high thermal conductivity filler in step S3 is 20-30%.

[0010] In some embodiments, step S4 includes: calculating the distribution of the high thermal conductivity filler using the moving asymptote method.

[0011] In some embodiments, the number of calculation iterations in step S4 is 1-2 times.

[0012] A second aspect of the present invention provides a system for preparing a phase change composite material, the phase change composite material comprising a conventional phase change material and a high thermal conductivity filler, characterized in that the system comprises: an initial setting module for establishing an initial geometric model based on the geometrical physical parameters of a battery pack and the positional relationship between the battery pack and the phase change composite material; a setting module for assigning corresponding thermal conductivity properties to the initial geometric model, the thermal conductivity properties including density, specific heat capacity, thermal conductivity, and a distribution function of the high thermal conductivity filler based on a solid isotropic material penalty model; a construction module for setting optimization objectives and constraints to establish a topology optimization model, the constraints being the content of the high thermal conductivity filler; a calculation module for calculating the distribution of the high thermal conductivity filler based on the topology optimization model; and a preparation module for preparing the phase change composite material based on the distribution of the high thermal conductivity filler.

[0013] A third aspect of the present invention provides a phase change composite material for thermal management of a battery pack, the phase change composite material comprising a common phase change material and a high thermal conductivity filler, characterized in that the phase change composite material is prepared by a method for preparing phase change composite materials.

[0014] In some embodiments, the high thermal conductivity filler is distributed at the locations where single-cell heat accumulation is determined by topology optimization.

[0015] A fourth aspect of the present invention provides a computer device including a memory and a processor, the memory storing a computer program, characterized in that the processor executes the computer program to implement the steps of a method for preparing a phase change composite material.

[0016] A fifth aspect of the present invention provides a computer program product comprising a computer program that, when executed by a processor, implements the steps of a method for preparing a phase change composite material.

[0017] Compared with the prior art, the beneficial effect of the present invention is that by optimizing the distribution of high thermal conductivity fillers in the phase change composite material through topology optimization, a thermal super phase change composite material for wrapping the power battery cell is designed. This material converts the heat absorbed during the battery heating process into latent heat of phase change, and by timely removing the heat, the temperature of the overall battery pack is reduced, making the temperature between individual cells more uniform. This solves the problems of uneven battery pack temperature and excessively high local temperature in the middle, and also reduces the thermal management cost of the power battery. Attached Figure Description

[0018] Figure 1 Flowchart for the optimized design of phase change thermal metamaterials for thermal management of power battery packs;

[0019] Figure 2 This is a schematic diagram of the geometric and physical model of the battery pack;

[0020] Figure 3 This is a distribution diagram of high thermal conductivity fillers within a phase change material thin film.

[0021] Figure 4 A graph showing the temperature variation of the battery pack during topology optimization iteration calculations;

[0022] Figure 5 Temperature distribution diagrams for topology-optimized phase change material thin-film battery packs and ordinary phase change material thin-film battery packs. Detailed Implementation

[0023] The technical solution of this patent will be further described in detail below with reference to specific embodiments. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0024] Topology optimization is a mathematical method that optimizes the distribution of materials within a given design region based on given load conditions, constraints, and performance indicators, thereby maximizing material utilization.

[0025] Metamaterials are combinations of materials and structures that can achieve properties unknown in nature. They possess special properties that natural materials do not have, and these properties mainly come from special artificial structures. The thermal metamaterials involved in this invention are a type of metamaterial with special thermal properties.

[0026] This invention describes its specific implementation using the lowest overall battery pack temperature as an example. However, it should be understood that the target parameters for topology optimization can also be adjusted to achieve the highest overall battery pack temperature, the lowest average temperature difference, etc. Therefore, this should not be used as a limitation on the present invention.

[0027] Example 1

[0028] like Figure 1 As shown, this embodiment establishes two sets of three-dimensional transient battery pack thermal conduction models using COMSOL multiphysics simulation software. One set adds a common phase change material thin film model around the battery pack, and the other adds a topology-optimized phase change composite material thin film model around the battery pack. Corresponding geometric and thermal conduction parameters are assigned to both sets of models. Then, with a constant high thermal conductivity filler content, the overall battery pack temperature is controlled to be minimized by adjusting the distribution of the high thermal conductivity filler in the phase change composite material, as detailed below:

[0029] (1) Two identical three-dimensional transient battery pack thermal conduction models were established using COMSOL multiphysics simulation software. Each battery pack consists of 10 individual cells. The specific geometric parameters and material properties of the individual cells are shown in Table 1. The geometric and physical model of the battery pack is as follows: Figure 2 As shown.

[0030] Table 1 Geometric parameters and material properties of a single cell

[0031]

[0032] (2) Construct thin film models of ordinary phase change materials and phase change composite materials outside the two sets of battery packs for comparison. Specifically, a 2mm thick phase change material is attached tightly around each single cell to facilitate surface heat dissipation through the thin film.

[0033] (3) Assign material properties to the corresponding regions. The phase change composite material is composed of ordinary phase change material and high thermal conductivity filler material. The specific material properties are shown in Table 2.

[0034] Table 2 Performance of Common Phase Change Materials and High Thermal Conductivity Fillers

[0035] name ordinary phase change materials High thermal conductivity filler material <![CDATA[Density ρ (kg / m 3 )]]> 1000 3000 Thermal conductivity κ (W / (m·K)) 1.3 {110,20,110} <![CDATA[Specific heat capacity C before phase change ρ1 (J / (kg·K))]]> 3000 978 <![CDATA[Specific heat capacity C after phase change ρ2 (J / (kg·K))]]> 23000 - <![CDATA[Latent heat of phase change L 1→2 (J / kg)]]> 140000 - Phase transition initiation temperature (K) 310.15 -

[0036] Apart from the initial physical properties, the physical properties of ordinary phase change materials and phase change composite materials during the phase change process satisfy the following equation, where ρ solid Let θ1 and θ2 be the density of the solid, and α be the phase variable distribution values. m This represents the enthalpy distribution value of the phase transition.

[0037] ρ=ρ solid

[0038]

[0039]

[0040] k=θ1κ1+θ2κ2

[0041] θ1+θ2=1

[0042] The distribution of the high thermal conductivity filler was calculated using the topology optimization method of the Solid Isotropic Material with Penalization (SIMP) model. ρ min The minimum relative density is set as ρ. min =0.001, ρ e ρ is the relative density of the element, which reflects the filler content. p is the penalty factor, set to p=3.

[0043]

[0044] 0≤ρ e ≤1

[0045] The thermal conductivity, specific heat capacity, and density of the phase change composite material, based on a specific high thermal conductivity filler distribution, are as follows:

[0046]

[0047]

[0048]

[0049] (4) Set initial and boundary conditions. After inputting the above material parameters and functions into the corresponding parameter areas of the COMSOL phase change material module, set the heat transfer type to solid heat transfer model, consider temperature optimization during the charging process, and the overall model satisfies the heat conduction equation that changes with time, where T is temperature, t is time, ρ is density, and C is the temperature. eq It is the effective specific heat capacity, κ eq Q is the effective thermal conductivity, and Q is the heat source.

[0050]

[0051] Considering that the heat source of the battery pack comes from the active battery material region, the heat generated during its charging process is set to 160,000 W / m. 3 Furthermore, heat transfer occurs between the battery pack and the surface heat dissipation film material via solid-state heat transfer, while the surface heat dissipation film undergoes convective heat dissipation with the outside air. Its convective heat transfer coefficient is 10 W / (m²). 2 ·K).

[0052] (5) Mesh generation. Select the physical control mesh and set the cell size to normal to meet the requirements of calculation accuracy.

[0053] (6) Set topology optimization parameters. Using the average temperature of the battery pack as the optimization objective, the Method of Moving Asymptotes (MMA) algorithm is selected for calculation to find the optimal solution that minimizes the average temperature of the battery pack by changing the distribution of the high thermal conductivity filler material. The tolerance is set to 0.001. Considering the large overall computational load of the battery pack, the maximum number of model evaluations is set to 20 to shorten the computation time.

[0054] (7) Perform topology optimization calculations. Since the material undergoes a phase transition during heating, a transient solution is selected. To shorten the calculation time, the heating time is set to 480 seconds, with a time period of (0, 240, 480).

[0055] Figure 3 The distribution of high thermal conductivity filler within the phase change material thin film is shown. When the filler content is 20-30%, the average temperature of the battery pack is minimized under the distribution shown in the figure. It can be seen that the high thermal conductivity filler is mainly concentrated in the active battery material region, with less distribution in the battery shell and electrode regions. Furthermore, considering economic costs, this scheme sets the high thermal conductivity filler content at 20-30%, achieving an effective reduction in the overall temperature of the battery pack at a lower cost.

[0056] like Figure 4 As shown, compared with ordinary phase change material films, phase change composite material films effectively reduced the average temperature, maximum temperature and minimum temperature of the battery pack after one iteration of optimization calculation. Figure 5 The temperature distribution of the two materials is shown in the comparison. It can be found that after heating for 480 seconds, the phase change composite material film reduces the temperature of various parts of the battery by 1-3K compared with ordinary phase change material film. Therefore, it shows advantages such as lower average temperature and smaller temperature difference in battery pack in terms of battery heat dissipation.

[0057] This invention prepares a phase change thermal metamaterial for power battery thermal management by optimizing the distribution of high thermal conductivity fillers through topology optimization. It converts the heat released by the battery during heating into latent heat of phase change and promptly removes the heat from the battery pack, thereby reducing the overall temperature of the battery pack and making the temperature between batteries more uniform. This solves the problems of uneven battery pack temperature and excessively high local temperature in the middle.

[0058] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a phase change composite material applied to thermal management of a power battery pack, the phase change composite material comprising a common phase change material and a high thermal conductivity filler, characterized in that, The method includes: S1. Based on the geometric and physical parameters of the battery pack and the positional relationship between each individual cell in the battery pack and the phase change composite material, establish an initial geometric model of the active battery material region and the battery can shell containing each individual cell. S2. Assign corresponding thermal conductivity properties to the initial geometric model, including density, specific heat capacity, thermal conductivity, and a distribution function of high thermal conductivity filler based on a solid isotropic material penalty model; the density, specific heat capacity, and thermal conductivity satisfy the property relationship as a function of phase change during the phase transition. S3. Set optimization objectives and constraints, and establish a topology optimization model. The optimization objective is to minimize the overall temperature of the battery pack or the temperature difference of the battery pack. The constraint is the content of the high thermal conductivity filler. S4. Based on the topology optimization model, perform transient calculations to determine the distribution of the high thermal conductivity filler in the initial geometric model; S5. Based on the calculated distribution of the high thermal conductivity filler, prepare a phase change composite film that is tightly attached to the periphery of each single cell.

2. The method of claim 1, wherein, The content of the high thermal conductivity filler in step S3 is 20-30%.

3. The method of claim 2, wherein, Step S4 includes: calculating the distribution of the high thermal conductivity filler using the moving asymptote method.

4. The method according to claim 3, characterized in that, The number of calculation iterations in step S4 is 1-2 times.

5. A system for preparing a phase change composite material, used to implement the method as described in any one of claims 1-4, wherein the phase change composite material comprises a common phase change material and a high thermal conductivity filler, characterized in that, The system includes: The initial setup module is used to establish an initial geometric model based on the battery pack's geometric and physical parameters and the positional relationship between the battery pack and the phase change composite material. A setting module is used to assign corresponding thermal conductivity properties to the initial geometric model. The thermal conductivity properties include density, specific heat capacity, thermal conductivity, and a high thermal conductivity filler distribution function based on a solid isotropic material penalty model. The construction module is used to set optimization objectives and constraints to establish a topology optimization model, wherein the constraint is the content of the high thermal conductivity filler. The calculation module is used to calculate the distribution of the high thermal conductivity filler according to the topology optimization model; The preparation module is used to prepare phase change composite materials according to the distribution of the high thermal conductivity filler.

6. A phase change composite material for thermal management of a battery pack, the phase change composite material comprising a conventional phase change material and a high thermal conductivity filler, characterized in that, The phase change composite material is prepared by the method described in any one of claims 1-4.

7. The phase change composite material for battery pack thermal management according to claim 6, characterized in that, The high thermal conductivity filler is distributed at the heat accumulation points of the single cell, as determined by topology optimization.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1-4.

9. A computer program product comprising a computer program that, when executed by a processor, implements the steps of the method according to any one of claims 1-4.

Images