A flame retardant composite phase change material and its preparation method and application

Abstract

This invention belongs to the field of phase change material technology, specifically relating to a flame-retardant composite phase change material, its preparation method, and its application. This invention provides a flame-retardant composite phase change material, comprising a phase change material, a polymer, a thermally conductive agent, and a flame retardant; the flame retardant includes a hydrated inorganic salt. The flame-retardant composite phase change material provided by this invention can undergo reversible cyclic heat absorption at 40~55℃ (i.e., thermal management and temperature control of the battery under normal operating conditions). Furthermore, it can absorb a large amount of heat generated by the battery before thermal runaway occurs, i.e., it can absorb a large amount of heat in the temperature range of 70~200℃, extending the time the battery is in the second stage of thermal runaway. Moreover, after thermal runaway occurs, this product, due to its high flame retardancy, can also prevent the spread of flames, thereby reducing the safety risks after thermal runaway.

Description

Technical Field

[0001] This invention belongs to the field of phase change material technology, specifically relating to a flame-retardant composite phase change material, its preparation method, and its application. Background Technology

[0002] With rapid economic development and continuous advancements in science and technology, concepts such as low-carbon economy and sustainable development are receiving increasing attention. Among these, replacing traditional gasoline-powered vehicles with green and environmentally friendly new energy electric vehicles is a crucial strategy for addressing energy depletion and environmental pollution. Although the development of new energy electric vehicles is booming, there is still significant market potential. One key factor affecting the further development of new energy electric vehicles is consumer concerns about their safety. Lithium-ion batteries, due to their high energy density, long cycle life, and rapid charge / discharge capabilities, are currently the primary energy carrier in new energy electric vehicles. The safety concerns of new energy electric vehicles mainly stem from the thermal safety issues of lithium-ion battery modules. During normal charging and discharging, the continuous electrochemical reaction generates a large amount of heat in lithium-ion batteries. When this accumulated heat is not effectively released, it can react against the lithium-ion battery itself, severely affecting its performance. In extreme cases, it can cause the lithium-ion battery to explode, resulting in personal injury and property damage.

[0003] Traditional battery thermal management methods mainly include forced air cooling and liquid cooling. Forced air cooling is not suitable for large-scale lithium-ion battery modules in new energy electric vehicles due to its low cooling efficiency and large temperature difference between the air inlet and outlet. Liquid cooling is more efficient for dissipating heat from lithium-ion battery modules, but its assembly system is complex, there is a risk of coolant leakage, and the overall system is difficult to maintain. In addition, since the liquid cooling pipes are generally located at the bottom of the battery module, the excessively concentrated heat dissipation area can further increase the temperature difference inside the battery.

[0004] Organic phase change materials (PCMs), as a novel battery thermal management method in recent years, have advantages such as low preparation cost, good temperature uniformity, and simple assembly. While the poor leakage resistance, low thermal conductivity, and poor mechanical properties of PCMs have been extensively studied, their flammability is often overlooked. Melamine, ammonium polyphosphate, silica, and other phosphorus-based, nitrogen-based, or silicon-based flame retardants are currently widely used to improve the flame retardant performance of PCMs. Although they avoid the toxicity issues of traditional halogen flame retardants, all types of flame retardants share a common problem: they can only act as flame arrestors after thermal runaway has occurred, but cannot inhibit or prolong the time before thermal runaway. Therefore, designing and preparing a novel flame-retardant PCM that can effectively manage battery thermal management under normal operating conditions, effectively suppress temperature rise before thermal runaway occurs, and effectively prevent flame spread after thermal runaway has occurred is one of the keys to the further development of PCM battery thermal management technology. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant composite phase change material, its preparation method, and its application.

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

[0007] This invention provides a flame-retardant composite phase change material, comprising a phase change material, a polymer, a thermally conductive agent, and a flame retardant;

[0008] The flame retardant comprises hydrated inorganic salts.

[0009] Preferably, by mass percentage, the flame-retardant composite phase change material comprises: 40-44% phase change material, 11-15% polymer, 1-2% thermal conductive agent and 44-47% flame retardant.

[0010] Preferably, the hydrated inorganic salt includes at least one of magnesium chloride hexahydrate, sodium tetraborate decahydrate, potassium aluminum sulfate octahydrate, zinc sulfate heptahydrate, and copper sulfate pentahydrate.

[0011] Preferably, the phase change material includes at least one of paraffin, polyethylene glycol, fatty alcohol, fatty acid, and fatty amine.

[0012] Preferably, the polymer comprises at least one of a single-component polymer and a two-component polymer;

[0013] The single-component polymer includes at least one of single-component epoxy resin and single-component polyurethane.

[0014] The two-component polymer includes at least one of two-component epoxy resin and two-component polyurethane.

[0015] Preferably, the thermal conductive agent includes a carbon-based thermal conductive agent, which includes at least one of expanded graphite, biochar, carbon black, carbon fiber, carbon nanotubes, and graphene.

[0016] This invention also provides a method for preparing the flame-retardant composite phase change material described in the above technical solution, comprising the following steps:

[0017] The flame-retardant composite phase change material is obtained by mixing the components included in the flame-retardant composite phase change material.

[0018] Preferably, when the polymer is a single-component polymer, the mixing includes:

[0019] Step 1: Mix the molten phase change material with the single-component polymer to obtain the first mixture;

[0020] Step 2: Mix the first mixture with the thermal conductive agent to obtain the second mixture;

[0021] Step 3: Mix the second mixture with the flame retardant and then cure it;

[0022] When the polymer is a two-component polymer, the mixing includes:

[0023] Step a: Mix the molten phase change material and polymer A to obtain mixture a;

[0024] Step b: Mix the mixture a with the thermal conductive agent to obtain mixture b;

[0025] Step c: Mix the mixture b with the flame retardant to obtain mixture c;

[0026] Step d: Mix the mixture c with the polymer B and then cure it.

[0027] Preferably, in steps 1 and a, the melting temperature is 60~80℃;

[0028] The mixing in step 1 and the mixing in step a are carried out independently under stirring conditions, and the stirring speed is 300~500 rpm;

[0029] The mixing in step 2 and the mixing in step b are carried out independently under stirring conditions, the stirring speed is 600~900 rpm, and the stirring time is 60~120 min;

[0030] The mixing in step 3 and the mixing in step c are carried out independently under stirring conditions, the stirring speed is 900~1200 rpm, and the stirring time is 30~60 min;

[0031] The mixing in step d is carried out under stirring conditions, with a stirring speed of 900~1200 rpm and a time of 2~3 min;

[0032] The curing temperatures in step 3 and step d are independently 25~40℃, and the curing times are independently 12~24h.

[0033] The present invention also provides the application of the flame-retardant composite phase change material described in the above technical solution or the flame-retardant composite phase change material prepared by the preparation method described in the above technical solution in battery thermal management.

[0034] This invention provides a flame-retardant composite phase change material, comprising a phase change material, a polymer, a thermally conductive agent, and a flame retardant; the flame retardant comprises a hydrated inorganic salt.

[0035] Compared to existing composite phase change materials applicable to battery thermal management and battery thermal runaway, the flame-retardant composite phase change material provided by this invention has the following advantages:

[0036] (1) The flame-retardant composite phase change material provided by the present invention can reversibly cycle and absorb heat at 40~55℃ (i.e., perform thermal management and temperature control of the battery under normal operating conditions). Secondly, it can also absorb a large amount of heat generated by the battery before the battery experiences thermal runaway, i.e., it can absorb a large amount of heat in the temperature range of 70~200℃, prolonging the time the battery is in the second stage of thermal runaway (other flame retardants such as melamine, ammonium polyphosphate, red phosphorus and other phosphorus and nitrogen flame retardants do not have the above effect). Furthermore, after the battery experiences thermal runaway, this product, due to its high flame retardancy, can also prevent the spread of flames, thereby reducing the safety risk after the battery experiences thermal runaway.

[0037] (2) This invention uses hydrated inorganic salts as flame retardants. Within a temperature range of 70~200℃, the flame retardant gradually loses water molecules upon heating, absorbing a large amount of heat in the process, thereby delaying thermal runaway of the battery. Simultaneously, as the temperature rises, the flame retardant decomposes into corresponding oxides. The generated oxides, together with the thermally conductive agent, form a dense barrier, blocking heat radiation and oxygen diffusion, thus achieving synergistic flame retardancy. The flame retardant provided by this invention is green and environmentally friendly, with widely available raw materials, low cost, and a simple preparation method, enabling industrial-scale production. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the battery module assembled in the test example;

[0039] Figure 2 The DSC curve of the composite material obtained in Example 1;

[0040] Figure 3 The DSC curve of the composite material obtained in Comparative Example 1 is shown.

[0041] Figure 4 Temperature curves of the battery module assembled from the composite material obtained in Example 1 during 1C charging and 1.5C discharging.

[0042] Figure 5 Temperature curves of the battery module assembled from the composite material obtained in Comparative Example 1 during 1C charging and 1.5C discharging.

[0043] Figure 6 The temperature curves of heating rods 1 to 9 of the battery module assembled from the composite material obtained in Example 1 during thermal runaway simulation;

[0044] Figure 7 Temperature curves of heating rods 1-9 during thermal runaway simulation of the battery module assembled from composite materials obtained in Comparative Example 1;

[0045] Figure 8 The temperature comparison of batteries 1 to 9 in the battery modules assembled from composite materials obtained in Example 1 and Comparative Example 1. Detailed Implementation

[0046] This invention provides a flame-retardant composite phase change material, comprising a phase change material, a polymer, a thermally conductive agent, and a flame retardant;

[0047] The flame retardant comprises hydrated inorganic salts.

[0048] In this invention, the flame-retardant composite phase change material preferably comprises, by mass percentage: 40-44% phase change material, 11-15% polymer, 1-2% thermal conductive agent and 44-47% flame retardant.

[0049] Based on mass percentage, the flame-retardant composite phase change material provided by this invention preferably comprises 40-44% phase change material, specifically 40%, 41%, 42%, 43%, or 44%. In this invention, the phase change material preferably comprises at least one of paraffin wax, polyethylene glycol, fatty alcohol, fatty acid, and fatty amine; the fatty alcohol preferably comprises at least one of tetradecyl alcohol and hexadecyl alcohol; the fatty acid preferably comprises at least one of tetradecanoic acid and hexadecanoic acid; the fatty amine preferably comprises at least one of tetradecylamine and hexadecylamine; the polyethylene glycol preferably comprises at least one of polyethylene glycol 1500 and polyethylene glycol 2000; and the paraffin wax preferably comprises at least one of paraffin wax No. 48 and paraffin wax No. 50. In this invention, the phase change temperature of the phase change material is preferably 48-52°C.

[0050] The flame-retardant composite phase change material provided by this invention preferably comprises 11-15% polymer by weight, specifically 11%, 12%, 13%, 14%, or 15%. In this invention, the polymer preferably comprises at least one of a single-component polymer and a two-component polymer; the single-component polymer preferably comprises at least one of a single-component epoxy resin and a single-component polyurethane; the two-component polymer preferably comprises at least one of a two-component epoxy resin and a two-component polyurethane. In a specific embodiment of this invention, the polymer is a two-component epoxy resin, specifically epoxy resin AB glue, specifically epoxy resin E-44. In this invention, the polymer provides adsorption for the phase change material during solid-liquid phase change, improving the overall thermal stability of the composite material and preventing leakage of the liquid phase change material.

[0051] The flame-retardant composite phase change material provided by this invention preferably includes 1-2% thermally conductive agent by weight percentage, specifically 1%, 1.5%, or 2%. In this invention, the thermally conductive agent preferably includes a carbon-based thermally conductive agent, which preferably includes at least one of expanded graphite, biochar, carbon black, carbon fiber, carbon nanotubes, and graphene; the biochar preferably includes at least one of wood-derived biochar, straw-derived biochar, and fruit shell-derived biochar. In this invention, the thermally conductive agent not only acts as a thermal conductivity enhancer but also synergistically enhances flame retardancy with the flame retardant. During product combustion, it acts as a carbon source and forms a dense carbon layer on its surface, thereby achieving a flame-retardant effect.

[0052] The flame-retardant composite phase change material provided by the present invention preferably comprises 44-47% flame retardant, specifically 44%, 45%, 46%, or 47% by mass percentage. In the present invention, the flame retardant comprises a hydrated inorganic salt, preferably at least one selected from magnesium chloride hexahydrate, sodium tetraborate decahydrate, potassium aluminum sulfate octadecahydrate, zinc sulfate heptahydrate, and copper sulfate pentahydrate.

[0053] This invention also provides a method for preparing the flame-retardant composite phase change material described in the above technical solution, comprising the following steps:

[0054] The flame-retardant composite phase change material is obtained by mixing the components included in the flame-retardant composite phase change material.

[0055] In this invention, when the polymer is a single-component polymer, the mixing preferably includes:

[0056] Step 1: Mix the molten phase change material with the single-component polymer to obtain the first mixture;

[0057] Step 2: Mix the first mixture with the thermal conductive agent to obtain the second mixture;

[0058] Step 3: Mix the second mixture with the flame retardant and then cure it.

[0059] In this invention, the melting temperature in step 1 is preferably 60-80°C. In this invention, the mixing is preferably carried out under stirring conditions, and the stirring speed is preferably 300-500 rpm.

[0060] In this invention, in step 2, the mixing order is preferably to slowly add the heat-conducting agent to the first mixture; the mixing is preferably carried out under stirring conditions, the stirring speed is preferably 600~900 rpm, and the stirring time after the heat-conducting agent is added is preferably 60~120 min.

[0061] In this invention, in step 3, the preferred mixing order is to slowly add the flame retardant to the second mixture; the mixing is preferably carried out under stirring conditions, the stirring speed is preferably 900~1200 rpm, and the stirring time after the flame retardant is added is preferably 30~60 min.

[0062] In this invention, prior to curing, it is preferable to place the obtained mixture in a suitable mold. In this invention, the curing temperature is preferably 25~40°C, and the curing time is preferably 12~24 hours.

[0063] In this invention, when the polymer is a two-component polymer, the mixing preferably includes:

[0064] Step a: Mix the molten phase change material and polymer A to obtain mixture a;

[0065] Step b: Mix the mixture a with the thermal conductive agent to obtain mixture b;

[0066] Step c: Mix the mixture b with the flame retardant to obtain mixture c;

[0067] Step d: Mix the mixture c with the polymer B and then cure it.

[0068] In this invention, the melting and mixing conditions in step a are preferably the same as those in step 1, and will not be repeated here.

[0069] In this invention, the mixing condition parameters in step b are preferably the same as those in step 2, and will not be repeated here.

[0070] In this invention, the mixing condition parameters in step c are preferably the same as those in step 3, and will not be repeated here.

[0071] In this invention, in step d, the mixing is preferably carried out under stirring conditions, the stirring speed is preferably 900~1200 rpm, and the stirring time is preferably 2~3 min. In this invention, the curing conditions in step d are preferably the same as in step 3, and will not be repeated here.

[0072] The present invention also provides the application of the flame-retardant composite phase change material described in the above technical solution or the flame-retardant composite phase change material prepared by the preparation method described in the above technical solution in battery thermal management.

[0073] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0074] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0075] Example 1

[0076] Weigh 44 parts of paraffin wax and place them in an oil bath at 65℃ for melting;

[0077] After the paraffin wax has completely melted, add 5.5 parts of epoxy resin A (specifically epoxy resin E-44) and mechanically stir at 300 rpm until the solution is homogeneous to obtain mixture a;

[0078] Next, one part of expanded graphite was slowly added to mixture a in batches. As the expanded graphite was added, the speed of the mechanical stirrer was gradually increased to 600 rpm. After the expanded graphite was completely added, the mixture was mechanically stirred at 600 rpm for 60 minutes to obtain mixture b.

[0079] 44 portions of magnesium chloride hexahydrate were slowly added to mixture b in batches, and the rotation speed was gradually increased to 900 rpm. After the magnesium chloride hexahydrate was completely added, the mixture was mechanically stirred at 900 rpm for 30 minutes to obtain mixture c.

[0080] Add 5.5 parts of epoxy resin B to the obtained mixture c, stir for 2 minutes, pour into the corresponding mold, and cure in an oven at 40°C for 24 hours to obtain the flame-retardant composite phase change material.

[0081] Example 2

[0082] Flame-retardant composite phase change materials were prepared according to the method in Example 1, except that paraffin was replaced with tetradecyl alcohol.

[0083] Example 3

[0084] Flame-retardant composite phase change materials were prepared according to the method in Example 1, except that magnesium chloride hexahydrate was replaced with sodium tetraborate decahydrate.

[0085] Example 4

[0086] Flame-retardant composite phase change materials were prepared according to the method in Example 1, except that the expanded graphite was 2 parts and the magnesium chloride hexahydrate was 43 parts.

[0087] Example 5

[0088] Flame-retardant composite phase change materials were prepared according to the method in Example 1, except that expanded graphite was replaced with Platycodon grandiflorum biochar.

[0089] Comparative Example 1

[0090] Flame-retardant composite phase change materials were prepared according to the method in Example 1, except that magnesium chloride hexahydrate was replaced with ammonium polyphosphate.

[0091] Performance testing

[0092] Test Example 1

[0093] The composite materials obtained in Example 1 and Comparative Example 1 were tested using differential scanning calorimetry, and the test results are as follows: Figure 2 and Figure 3 As shown, where Figure 2 The DSC curve of the composite material obtained in Example 1 is shown. Figure 3 The DSC curves of the composite material obtained in Comparative Example 1 are shown in Table 1. The specific test results are shown in Table 1.

[0094] Table 1. DSC curve results of the composite materials obtained in Example 1 and Comparative Example 1

[0095]

[0096] The test results above show that when the battery module is charged and discharged under normal operating conditions, the reversible latent heat of phase change (78.6 J / g) provided by paraffin can effectively control the temperature of the battery module, keeping the maximum temperature and maximum temperature difference of the battery module within the safe operating temperature range. When the battery module malfunctions and the temperature exceeds the safe operating temperature range, the decomposition heat provided by the inorganic hydrated salt in Example 1 can absorb a large amount of heat, delaying or even inhibiting the occurrence of thermal runaway.

[0097] Test Example 2

[0098] The composite materials obtained in the examples and comparative examples were used as test samples for battery thermal management simulation tests.

[0099] The composite material obtained in the examples and comparative examples is a module with dimensions of 90×90×65mm. Nine cylindrical holes with a diameter of 26mm are drilled at equal intervals using a drilling machine. Nine 26650 cylindrical batteries are embedded into the corresponding holes, assembling into a 3-series, 3-parallel battery module for charge-discharge testing. Thermocouples are used to monitor temperature changes during the charge-discharge process. A schematic diagram of the testing device is shown below. Figure 1 As shown.

[0100] Figure 4 Temperature curves of the battery module assembled from the composite material obtained in Example 1 during 1C charging and 1.5C discharging. Figure 5 The temperature curves of the battery module assembled from the composite material obtained in Comparative Example 1 during 1C charging and 1.5C discharging are shown in Table 2. Specific test results are also shown in Table 2.

[0101] Table 2. Temperature changes during charging and discharging of the composite material assembled batteries of Example 1 and Comparative Example 1.

[0102]

[0103] The above tests show that the battery module underwent 5 charge-discharge cycles at a charge-discharge rate of 1C to 1.5C. During this process, the highest temperature and the maximum temperature difference of the battery module were 50.49℃ and 2.45℃, respectively, both of which are within the safe operating temperature range of the battery. This proves that the composite phase change material of Example 1 has excellent temperature control effect on the battery module under normal operating conditions.

[0104] Test Example 3

[0105] Referring to Test Example 2, a 90×90×65mm module containing nine holes with a diameter of 26mm was also prepared. Nine heating rods with a diameter of 26mm were embedded in the corresponding holes for battery thermal runaway simulation testing. The specific test process is as follows: the central heating rod was heated by a DC power supply at a power of 30W, and the temperature changes of the heating rod and the surrounding heating rods were monitored by thermocouples.

[0106] Figure 6 The temperature curves of heating rods 1 to 9 of the battery module assembled from the composite material obtained in Example 1 during thermal runaway simulation; Figure 7 Temperature curves of heating rods 1-9 during thermal runaway simulation of the battery module assembled from composite materials obtained in Comparative Example 1; Figure 8 The temperature comparison of batteries 1 to 9 in the battery modules assembled from composite materials obtained in Example 1 and Comparative Example 1 is shown in Table 3.

[0107] Table 3 Temperature changes of the composite materials obtained in Example 1 and Comparative Example 1 in the battery module

[0108]

[0109] As can be seen from the above test results, the temperature of each heating rod in Example 1 is lower than that of the corresponding heating rod in Comparative Example 1. This is mainly due to the fact that inorganic hydrated salts can absorb a large amount of heat through the decomposition of water of crystallization at medium and high temperatures, thus inhibiting the rapid rise in battery temperature. This heat absorption capacity at medium and high temperatures is not possessed by traditional flame retardants such as ammonium polyphosphate.

[0110] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A flame-retardant composite phase change material, characterized in that, It is composed of phase change materials, polymers, thermal conductive agents, and flame retardants; The flame retardant is a hydrated inorganic salt; the hydrated inorganic salt is magnesium chloride hexahydrate; The phase change material is paraffin wax; the phase change temperature of the phase change material is 48~52℃. The polymer is epoxy resin A and epoxy resin B. The thermal conductive agent is expanded graphite; The flame-retardant composite phase change material contains, by weight percentage: 44% phase change material, 11% polymer, 1% thermal conductive agent and 44% flame retardant.

2. The preparation method of the flame-retardant composite phase change material according to claim 1, characterized in that, Includes the following steps: The flame-retardant composite phase change material is obtained by mixing the components included in the flame-retardant composite phase change material.

3. The preparation method according to claim 2, characterized in that, The mixture includes: Step a: Mix the molten phase change material with epoxy resin A to obtain mixture a; Step b: Mix the mixture a with the thermal conductive agent to obtain mixture b; Step c: Mix the mixture b with the flame retardant to obtain mixture c; Step d: Mix the mixture c with epoxy resin B and cure.

4. The preparation method according to claim 3, characterized in that, In step a, the melting temperature is 60~80℃; The mixing in step a is carried out under stirring conditions, and the stirring speed is 300~500 rpm; The mixing in step b is carried out under stirring conditions, the stirring speed is 600~900 rpm, and the stirring time is 60~120 min; The mixing in step c is carried out under stirring conditions, the stirring speed is 900~1200 rpm, and the stirring time is 30~60 min; The mixing in step d is carried out under stirring conditions, with a stirring speed of 900~1200 rpm and a time of 2~3 min; The curing temperature in step d is 25~40℃, and the time is 12~24h.

5. The application of the flame-retardant composite phase change material according to claim 1 or the flame-retardant composite phase change material prepared by the preparation method according to any one of claims 2 to 4 in battery thermal management.

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