Composite phase change material with variable heat conductivity coefficient for lithium battery module and preparation method of composite phase change material
The variable thermal conductivity composite phase change material is prepared through a directional freezing process. The graphite sheets are arranged in an orderly manner to form an efficient heat conduction path, and the expanded microspheres cut off heat conduction, solving the problem of thermal runaway propagation in lithium battery modules and achieving the dual effects of safety and thermal management.
Patent Information
- Application Number
- CN202510888473.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-30
- Publication Date
- 2025-10-10
AI Technical Summary
When a lithium battery module experiences thermal runaway, heat is rapidly transferred to adjacent batteries, causing chain thermal runaway and posing a risk of fire and explosion. Existing technologies make it difficult to effectively prevent the spread of thermal runaway.
A composite phase change material with variable thermal conductivity is used. The graphite sheets are arranged in an orderly manner through a directional freezing process to form an efficient heat conduction path. In the event of thermal runaway, the heat conduction path is cut off by expandable microspheres and converted to a heat-insulating state. The material is composed of polymers, expandable microspheres, graphite sheets and phase change materials.
It provides efficient thermal management during normal operation and quickly switches to an insulating state when the battery experiences thermal runaway, preventing the spread of thermal runaway and significantly improving battery safety. It is low-cost and applicable to batteries of different specifications.
Smart Images
Figure CN120758232A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of composite phase change materials, and in particular to a composite phase change material with variable thermal conductivity for a lithium battery module. Background Art
[0002] Lithium batteries are widely used in aerospace, energy storage power stations, electric vehicles and other fields due to their advantages such as high energy density, long cycle life and no memory effect. However, the chemical substances inside lithium batteries are extremely active. Under extreme conditions such as thermal abuse and mechanical abuse, violent exothermic reactions are prone to occur inside, triggering thermal runaway, releasing large amounts of heat and flammable gases, which can easily lead to fires or even explosions, seriously threatening the safety of life and property. In actual applications, lithium batteries are often used in groups in the form of battery clusters. If a battery experiences thermal runaway, the high temperature and heat it generates will quickly transfer to adjacent batteries, triggering a chain reaction of thermal runaway, expanding the scale and risk of the accident. This chain reaction seriously restricts the promotion and application of lithium batteries in areas with high safety requirements. Therefore, there is a need for a new composite phase change material with variable thermal conductivity that is particularly suitable for lithium battery modules. Summary of the Invention
[0003] In order to achieve thermal management of lithium battery modules and effectively prevent the propagation of thermal runaway when thermal runaway occurs in the battery, the present invention provides a composite phase change material with variable thermal conductivity for lithium battery modules, and at the same time, a preparation method of the composite phase change material with variable thermal conductivity for lithium battery modules.
[0004] A composite phase change material with variable thermal conductivity for lithium battery modules includes the following raw materials by mass fraction: 0.3%-1.8% polymer, 2.7%-8.8% expandable microspheres, 6.4%-17.6% graphite sheets, 0.6%-1.8% surfactant, and 70%-90% phase change material;
[0005] The polymer is one or more of sodium carboxymethyl cellulose, sodium alginate, and polyvinyl pyrrolidone, and is added in the form of a polymer solution;
[0006] The expandable microspheres are made of a core-shell polymer material with an initial expansion temperature of 100-130°C and a peak expansion temperature of 140-180°C.
[0007] The surfactant is an anionic surfactant;
[0008] The phase change material is an inorganic phase change material, and the phase change mode is solid-liquid phase change, and the phase change temperature is 30-35°C;
[0009] The variable thermal conductivity composite phase change material has a thermal conductivity of 7.2 W·m at room temperature. -1 K-1, the phase change enthalpy is 190 J / g; when the temperature is higher than 130 ° C, its thermal conductivity drops rapidly to 0.046 W·m-1 K-1 thermal insulation status.
[0010] Further technical solutions are as follows:
[0011] The polymer solution is prepared by uniformly mixing 0.5%-1.5% of polymer and 98.5%-99.5% of deionized water.
[0012] The expandable microspheres are composed of a thermoplastic polymer shell and an internal low-boiling point liquid alkane foaming agent, with an average particle size of 5-50 μm; the thermoplastic polymer is acrylonitrile-methyl methacrylate copolymer, and the low-boiling point liquid alkane foaming agent is n-butane or isobutane.
[0013] The graphite sheet has a size of 10-50 μm and a sheet thickness of less than 150 nm.
[0014] The anionic surfactant is sodium dodecylbenzenesulfonate.
[0015] The inorganic phase change material is sodium hydrogen phosphate dodecahydrate.
[0016] The preparation steps of a composite phase change material with variable thermal conductivity for lithium battery modules include preparing a polymer solution, mixing and dispersing, freeze drying, impregnating the phase change material, and packaging. The improvement lies in that a directional freezing step is added before the freeze drying step.
[0017] The directional freezing device consists of an insulated container, a polytetrafluoroethylene mold, and a copper block, and uses liquid nitrogen as a cold source. The specific directional freezing operation is as follows:
[0018] Before the start of directional freezing, a polytetrafluoroethylene mold is placed on a copper block, and the mixed solution obtained by mixing and dispersing is added to the polytetrafluoroethylene mold; the polytetrafluoroethylene mold and the copper block are then placed in an insulated container; finally, liquid nitrogen is injected to completely submerge the copper block; the entire freezing process lasts 5-8 minutes; the cold source is transferred from the copper block to the mixed solution, and ice crystals will grow from the bottom of the copper block to the top, forming an ordered ice crystal structure inside the mixed solution, thereby guiding the expandable microspheres and graphite sheets to achieve orderly arrangement during the freezing process.
[0019] Compared with the prior art, the beneficial technical effects of the present invention are embodied in the following aspects:
[0020] 1. The thermal conductivity of the variable thermal conductivity composite phase change material of the present invention is 7.2W·m at room temperature. -1 K-1, the phase change enthalpy is 190 J / g; when the temperature is higher than 130 ° C, its thermal conductivity drops rapidly to 0.046 W·m -1 K-1. Conventional graphite sheet-composite phase change material has a thermal conductivity of only 1.03W·m -1K-1; compared with the traditional composite phase change material, the composite phase change material of the application not only has excellent thermal conductivity, but also has excellent heat insulation effect. It can not only meet the heat management needs of the battery in normal operation, but also provide reliable heat insulation protection after the battery thermal runaway, effectively guaranteeing the safe operation and use of the battery.
[0021] Compared with traditional materials, the graphite sheet selected by the application is easy to obtain, and its cost is only one percent of that of graphene. Other raw materials also have a wide source. The application not only has a simple processing technology, but also can flexibly adjust the shape and size of the composite phase change material according to actual needs, and is suitable for different specifications of lithium battery thermal runaway protection, which significantly reduces the cost of battery thermal safety protection, and greatly improves the universality of the material.
[0022] 2, the conventional graphite sheet-composite phase change material is mixed uniformly at room temperature, and the thermal conductivity is only 1.03W·m -1 K-1. The application makes the graphite sheet orderly arranged along the ice crystal growth direction by directional freezing process, forms a heat conduction path, and makes the thermal conductivity of the composite phase change material with variable thermal conductivity significantly increase to 7.2W·m -1 K-1, and realizes more efficient heat exchange with the battery. At the same time, the expandable microspheres embedded in the graphite sheet can expand when the temperature is higher than 130℃, cutting off the heat conduction path, and rapidly reducing the thermal conductivity of the composite phase change material from 7.2W·m -1 K-1 to 0.46W·m -1 K-1. The thermoplastic polymer in the expandable microspheres is acrylonitrile-methyl methacrylate copolymer, which has good airtightness and thermal responsiveness, and the inside is packaged with low-boiling alkane foaming agent such as n-butane and / or isobutane. When heated to 100-130℃, the shell softens, and the low-boiling alkane foaming agent in the core rapidly vaporizes, pushing the microspheres to expand, and the volume can reach 80 times of the original. The orderly arranged graphite sheet and the expandable microspheres realize the switching function of the thermal conductivity of the composite phase change material at the preset temperature. In the process of normal cycle use of the battery, the composite phase change material of the application realizes effective thermal management of the lithium battery module by virtue of high thermal conductivity and excellent heat absorption capacity; and when the battery occurs thermal runaway, the composite phase change material of the application will change from the heat conduction state to the heat insulation state, thereby effectively preventing the spread of thermal runaway and significantly improving the safety of the battery module. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1 is a scanning electron microscope image of the three-dimensional structure of the graphite sheet formed after directional freezing without adding expandable microspheres;
[0024] Figure 2 is a scanning electron microscope image of the graphite sheet;
[0025] Figure 3 is a scanning electron microscope image of the graphite sheet-microsphere structure obtained in Example 2;
[0026] Figure 4 yes Figure 3 A partial enlarged view of
[0027] Figure 5 This is a physical picture of the variable thermal conductivity phase change material after aluminum foil packaging. DETAILED DESCRIPTION
[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below.
[0029] Example 1
[0030] A variable thermal conductivity composite phase change material for a lithium battery module comprises the following raw materials by mass: 1.18% polymer, 5.88% expandable microspheres, 11.76% graphite sheets, 1.18% surfactant, and 80% phase change material.
[0031] The polymer is sodium carboxymethyl cellulose and is added in the form of a polymer solution. The polymer solution includes the following raw materials in mass fractions: 0.5% sodium carboxymethyl cellulose and 99.5% deionized water.
[0032] The expandable microspheres are core-shell polymer materials, consisting of a thermoplastic polymer shell and a low-boiling-point liquid alkane interior, with an average particle size of 36-44 μm. The thermoplastic polymer is acrylonitrile-methyl methacrylate copolymer, and the low-boiling-point liquid alkane is n-butane.
[0033] The initial expansion temperature of the expandable microspheres is 110-130°C, the peak expansion temperature is 160-180°C, the particle size after expansion exceeds 150μm, and the volume expands more than 80 times.
[0034] The graphite sheet size is 10-50 μm, and the sheet thickness is less than 150 nm.
[0035] The surfactant is an anionic surfactant, specifically sodium dodecylbenzenesulfonate.
[0036] The phase change material is an inorganic phase change material, specifically sodium hydrogen phosphate dodecahydrate, and the phase change mode is solid-liquid phase change, and the phase change temperature is about 35°C.
[0037] The preparation steps of the variable thermal conductivity composite phase change material for lithium battery modules are as follows:
[0038] S1. Preparation of polymer solution
[0039] The polymer and deionized water were accurately weighed according to the raw material ratio, and stirred at room temperature for 24 h until fully mixed to obtain a uniform polymer solution.
[0040] S2, Mixing and Dispersion
[0041] Accurately weigh expandable microspheres, graphite flakes, and surfactant according to the raw material ratio and sequentially add them to the polymer solution prepared in S1. Disperse the mixed solution using an ultrasonic dispersing device at a power of 150W for 3 hours to ensure that all components are evenly dispersed in the polymer solution, forming a uniform mixed solution.
[0042] S3, directional freezing
[0043] The directional freezing device consists of an insulated container, a polytetrafluoroethylene mold, and a copper block, and uses liquid nitrogen as a cooling source. The specific operation is as follows:
[0044] Before the start of directional freezing, a polytetrafluoroethylene mold is placed on a copper block, and the mixed solution obtained by mixing and dispersing is added to the polytetrafluoroethylene mold; the polytetrafluoroethylene mold and the copper block are then placed in an insulated container; finally, liquid nitrogen is injected to completely submerge the copper block; the entire freezing process lasts for 7 minutes; the cold source is transferred from the copper block to the mixed solution, and ice crystals will grow from the bottom of the copper block to the top, forming an ordered ice crystal structure inside the mixed solution, thereby guiding the expandable microspheres and graphite sheets to achieve orderly arrangement during the freezing process.
[0045] S4. Freeze drying
[0046] The polytetrafluoroethylene mold is quickly transferred to a freeze-drying device and freeze-dried under a vacuum degree of less than 10 Pa to remove moisture after the ice crystals sublime, and finally a porous material with a three-dimensional support structure of graphite sheets and microspheres is obtained.
[0047] S5. Impregnation of phase change materials and packaging
[0048] The pre-melted phase-change material is poured into the porous material of the three-dimensional support structure in a specific ratio, allowing the phase-change material to fully penetrate and fill the pores of the three-dimensional support structure. The material is then cooled and solidified at room temperature to ensure a tight bond between the phase-change material and the three-dimensional support structure. Aluminum foil is cut to an appropriate size, and the solidified composite phase-change material is encapsulated in the foil using a heat sealer.
[0049] The thermal conductivity of the composite phase change material with variable thermal conductivity prepared in Example 1 is 2.73 W·m at room temperature. -1 K-1, the phase change enthalpy is 190 J / g; when the temperature is higher than 130 ° C, its thermal conductivity drops rapidly to 0.038 W·m -1 In the heat-insulating state of K-1, the heat switching ratio (times) is 60.5.
[0050] Example 2
[0051] A variable thermal conductivity composite phase change material for lithium battery modules comprises the following raw materials by weight: 0.51% polymer, 2.56% expandable microspheres, 15.38% graphite flakes, 1.54% surfactant, and 80% phase change material. The polymer is added in the form of a polymer solution comprising the following raw materials by weight: 0.5% polymer and 99.5% deionized water.
[0052] The polymer, expandable microspheres, graphite sheets, surfactant and phase change material used are the same as those in Example 1.
[0053] The preparation steps are the same as those in Example 1.
[0054] The thermal conductivity of the composite phase change material with variable thermal conductivity prepared in Example 2 is 7.2 W·m at room temperature. -1 K-1, when the temperature is higher than 130℃, its thermal conductivity drops rapidly to 0.046W·m -1 In the heat-insulating state of K-1, the heat switching ratio (times) is 156.4.
[0055] Example 3
[0056] A variable thermal conductivity composite phase change material for lithium battery modules comprises the following raw materials by weight: 0.33% polymer, 1.64% expandable microspheres, 16.39% graphite flakes, 1.64% surfactant, and 80% phase change material. The polymer is added in the form of a polymer solution comprising the following raw materials by weight: 0.5% polymer and 99.5% deionized water.
[0057] The polymer, expandable microspheres, graphite sheets, surfactant and phase change material used are the same as those in Example 1.
[0058] The preparation steps are the same as those in Example 1.
[0059] The thermal conductivity of the composite phase change material with variable thermal conductivity prepared in Example 3 is 3.6 W·m at room temperature. -1 K-1, when the temperature is higher than 130℃, its thermal conductivity drops rapidly to 0.052W·m -1 In the heat-insulating state of K-1, the heat switching ratio (times) is 69.2.
[0060] See also Figure 1 When expandable microspheres are not added, the graphite sheets formed after directional freezing are arranged neatly to form a multi-layer structure, which serves as a heat conduction path for subsequent phase change materials.
[0061] See also Figure 2 The graphite sheets used are relatively thick and do not belong to graphene, which is enough to prove its low cost.
[0062] See also Figure 3 After adding the expanded microspheres, the directional freezing process results in the expanded microspheres being evenly embedded in the graphite sheets, forming a good foundation for subsequent expansion and cutting paths. Figure 4 , it can be seen that the particle size of the expanded microspheres embedded in the graphite sheets.
[0063] See also Figure 5 The surface of the variable thermal conductivity composite phase change material after aluminum foil packaging is smooth, can have good contact with the battery, and is conducive to heat exchange.
[0064] The properties of the variable thermal conductivity composite phase change materials prepared in Examples 1-3 are shown in the following table:
[0065] Main parameters Example 1 Example 2 Example 3 <![CDATA[室温下导热系数(W·m -1 ·K -1 )]]> 2.73 7.2 3.6 <![CDATA[高温后导热系数(W·m -1 ·K -1 )]]> 0.038 0.046 0.052 Hot switching ratio (times) 60.5 156.4 69.2
[0066] As can be seen from the data in the table above, the present invention achieves excellent performance in the variable thermal conductivity composite phase-change materials prepared in Examples 1-3 through precise selection and optimization of the component ratios and improved preparation processes. During normal battery cycling, the high thermal conductivity of the phase-change material within the battery provides thermal management, extending the battery's service life. In the event of thermal runaway, the variable thermal conductivity composite phase-change material rapidly switches its thermal conductivity, acting as an insulator, severing the heat conduction path between cells and suppressing the propagation of thermal runaway.
Claims
1. A composite phase change material with variable thermal conductivity for lithium battery modules, characterized by: The variable thermal conductivity composite phase change material comprises the following raw materials by mass fraction: 0.3%-1.8% polymer, 2.7%-8.8% expandable microspheres, 6.4%-17.6% graphite flakes, 0.6%-1.8% surfactant and 70%-90% phase change material; The polymer is one or more of sodium carboxymethyl cellulose, sodium alginate, and polyvinyl pyrrolidone, and is added in the form of a polymer solution; The expandable microspheres are made of a core-shell polymer material with an initial expansion temperature of 100-130°C and a peak expansion temperature of 140-180°C. The surfactant is an anionic surfactant; The phase change material is an inorganic phase change material, and the phase change mode is solid-liquid phase change, and the phase change temperature is 30-35°C; The variable thermal conductivity composite phase change material has a thermal conductivity of 7.2 W·m at room temperature. -1 K-1, the phase change enthalpy is 190 J / g; when the temperature is higher than 130 ° C, its thermal conductivity drops rapidly to 0.046 W·m -1 K-1 thermal insulation status.
2. The variable thermal conductivity composite phase change material for lithium battery modules according to claim 1, characterized in that: The polymer solution is prepared by uniformly mixing 0.5%-1.5% of polymer and 98.5%-99.5% of deionized water.
3. The variable thermal conductivity composite phase change material for lithium battery modules according to claim 1, characterized in that: The expandable microspheres are composed of a thermoplastic polymer shell and an internal low-boiling point liquid alkane foaming agent, and have an average particle size of 5-50 μm; The thermoplastic polymer is acrylonitrile-methyl methacrylate copolymer, and the low-boiling-point liquid alkane foaming agent is n-butane or isobutane.
4. The variable thermal conductivity composite phase change material for lithium battery modules according to claim 1, characterized in that: The graphite sheet has a size of 10-50 μm and a sheet thickness of less than 150 nm.
5. The variable thermal conductivity composite phase change material for lithium battery modules according to claim 1, characterized in that: The anionic surfactant is sodium dodecylbenzenesulfonate.
6. The variable thermal conductivity composite phase change material for lithium battery modules according to claim 1, characterized in that: The inorganic phase change material is sodium hydrogen phosphate dodecahydrate.
7. The method for preparing a composite phase change material with variable thermal conductivity according to any one of claims 1 to 6, comprising preparing a polymer solution, mixing and dispersing, freeze-drying, impregnating the phase change material, and encapsulating, wherein: A directional freezing operation step is added before the freeze-drying operation step; The directional freezing device consists of an insulated container, a polytetrafluoroethylene mold, and a copper block, and uses liquid nitrogen as a cold source. The specific directional freezing operation is as follows: Before directional freezing begins, a polytetrafluoroethylene mold is placed on a copper block. The mixed solution obtained by mixing and dispersing is added to the polytetrafluoroethylene mold. The polytetrafluoroethylene mold and the copper block are then placed together in an insulated container. Finally, liquid nitrogen is injected to completely submerge the copper block. The entire freezing process lasts 5-8 minutes. The cold source is transferred from the copper block to the mixed solution, and ice crystals will grow from the copper block from bottom to top, forming an ordered ice crystal structure inside the mixed solution, thereby guiding the expandable microspheres and graphite sheets to achieve orderly arrangement during the freezing process.