Bimetal oxide flame-retardant TPU (thermoplastic polyurethane) composite material, preparation method and application in blocking thermal runaway of battery

Abstract

The invention discloses a bimetallic oxide flame-retardant TPU (thermoplastic polyurethane) composite material, a preparation method and application of the composite material in blocking thermal runaway of a battery, and the composite material comprises the following components in percentage by mass: 94-98 wt% of TPU and 2-6 wt% of bimetallic oxide nano filler BN-CoMo. The preparation method comprises the following steps: 1, dispersing a bimetallic oxide filler BN-CoMo in an organic solvent, and ultrasonically stirring for 2-3 hours to obtain a primary mixed solution; step 2, dispersing TPU master batches in the mixed solution, keeping ultrasonic stirring for 4-6 hours to obtain a secondary mixed solution, dropwise adding the secondary mixed solution into water to obtain a precipitate, filtering the precipitate, and drying the precipitate at 70-100 DEG C for 48-96 hours to obtain a compound; and step 3, banburying the compound at 180-190 DEG C, and pressing to obtain the bimetallic oxide flame-retardant TPU composite material. The cobalt salt and the molybdenum salt are subjected to multiple mechanisms of catalytic char formation, heat absorption, toxic gas release inhibition, physical barrier and the like in the bimetallic oxide flame-retardant TPU composite material, so that the flame retardance and smoke suppression and toxicity reduction effects of the TPU composite material are remarkably improved, and a good barrier effect on thermal runaway of a battery is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame - retardant composite materials, and particularly relates to a double - metal - oxide flame - retardant TPU composite material, a preparation method, and an application for blocking thermal runaway of batteries. Background Art

[0002] Thermoplastic polyurethane elastomer (TPU) is a commonly used block copolymer with excellent mechanical properties, wear resistance, and acid - and alkali - resistance, and is widely used in fields such as wire and cable, transportation, and aerospace. However, TPU is mainly composed of carbon, hydrogen, and oxygen elements and is extremely flammable, releasing a large amount of heat and toxic gases (such as CO, HCN), which limits its application in fields with clear requirements for flame retardancy. Therefore, it is particularly important to improve the flame retardancy of TPU composite materials.

[0003] In the prior art, the flame - retardant performance of TPU can be improved by adding flame - retardant fillers, but the flame - retardant efficiency is low, and the inhibitory effect on toxic gases is average. For example, in patent CN201510686290.4, when adding 3wt% flame - retardant filler, the peak value of the heat release rate and the total heat release of the TPU composite material decreased by 26.0% and 7.8% respectively; in patent CN202210880761.5, when adding 9wt% flame - retardant filler, the limiting oxygen index increased to 30%. It can be seen that the existing flame - retardant fillers can reduce the heat release during the combustion of TPU composite materials, but the flame - retardant efficiency is low. At the same time, their inhibitory effect on toxic gases such as CO released during the combustion of TPU composite materials is average. Therefore, it is necessary to develop a high - efficiency flame - retardant filler that can suppress smoke and reduce toxicity.

[0004] Double - metal - oxide nano - fillers have excellent thermal stability and high specific heat capacity, can absorb heat, and prevent the spread of flames. At the same time, they can act as chemical catalysts and solid acids to promote the dehydrogenation, cross - linking, carbonization, and graphitization of polymers, forming more protective carbon layers, thereby enhancing the flame - retardant performance of polymers. Particularly noteworthy is that double - metal - oxide nano - fillers can inhibit the release of smoke and toxic gases through the Lewis - acid - catalyzed Friedel - Crafts mechanism. Summary of the Invention

[0005] The purpose of the present invention is to provide a double - metal - oxide flame - retardant TPU composite material, a preparation method, and an application for blocking thermal runaway of batteries to solve the above - mentioned technical problems.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A bimetallic oxide flame-retardant TPU composite material, calculated by mass percentage, TPU is 94-98 wt%, and the bimetallic oxide nano-filler BN-CoMo is 2-6 wt%.

[0008] Further optimization, the preparation method of the bimetallic oxide nano-filler BN-CoMo includes the following steps:

[0009] Step 1: Put boron nitride and a modifier into a high-energy ball mill for grinding, wash with water and dry in vacuum to obtain boron nitride nanosheets;

[0010] Step 2: Disperse the boron nitride nanosheets and polyethyleneimine in water and perform ultrasonic treatment to obtain a homogeneous solution;

[0011] Step 3: Add cobalt salt and molybdenum salt to the homogeneous solution and keep ultrasonic stirring;

[0012] Step 4: After adjusting the pH of the solution to 6.5-7.5 with ammonia water and nitric acid, perform hydrothermal reaction on the mixed solution for 10-14 hours; after the reaction is completed, wash with water and centrifuge to obtain the bimetallic oxide nano-filler BN-CoMo.

[0013] By preparing the bimetallic oxide nano-filler (BN-CoMo) through steps such as high-energy ball milling, ultrasonic dispersion and hydrothermal reaction, nano-fillers with high specific surface area and uniform dispersion can be prepared, significantly improving the catalytic activity and flame-retardant performance of the fillers.

[0014] Further optimization, the mass ratio of boron nitride to the modifier is 1:(10-15); the mass ratio of boron nitride nanosheets to polyethyleneimine is (2-3):1.

[0015] Further optimization, the boron nitride is one of hexagonal boron nitride, rhombohedral boron nitride, cubic boron nitride and wurtzite boron nitride;

[0016] The modifier is one or more of urea, melamine, potassium hydroxide;

[0017] The cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt acetate, cobalt sulfate;

[0018] The molybdate is one or more of sodium molybdate, potassium molybdate, ammonium molybdate.

[0019] Further optimization, the mass ratio of the boron nitride nanosheets, cobalt salt and molybdenum salt is 1:(1.4-4.4):(3.3-9.8).

[0020] This ratio optimization can ensure the uniform dispersion of the filler in the TPU matrix and improve its catalytic activity and flame-retardant performance. The optimized filler can effectively inhibit the release of toxic gases during the combustion process and significantly improve the flame-retardant performance of the composite material.

[0021] Preparation method of bimetallic oxide flame-retardant TPU composite material, comprising the following steps:

[0022] Step 1: Disperse bimetallic oxide filler BN-CoMo in an organic solvent, and ultrasonically stir for 2-3 hours to obtain a primary mixed solution;

[0023] Step 2: Disperse the TPU masterbatch in the above mixed solution, maintain ultrasonic stirring for 4-6 hours to obtain a secondary mixed solution; then drop the secondary mixed solution into water to obtain a precipitate, filter, and dry the solid at 70-100 °C for 48-96 hours to obtain a composite;

[0024] The above method can ensure the uniform distribution of the filler in the TPU matrix and improve the overall performance of the composite material. The experimental results show that the peak value of the heat release rate of the composite material decreases significantly, and the limiting oxygen index increases significantly, indicating its excellent flame retardant performance.

[0025] Step 3: Knead and press the above composite at 180-190 °C to obtain a bimetallic oxide flame-retardant TPU composite material.

[0026] Further optimization: The organic solvent is one or more of tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,4-dioxane.

[0027] Further optimization: The addition amount of the bimetallic oxide filler is 2-6 wt% of the total mass of the TPU composite material.

[0028] Application of bimetallic oxide flame-retardant TPU composite material, applied to blocking the thermal runaway of batteries. By arranging a separator made of TPU composite material between adjacent battery monomers in a battery pack, the transmission of battery thermal runaway can be well blocked.

[0029] In the bimetallic oxide flame-retardant TPU composite material, cobalt salt and molybdenum salt are used as key precursors to form bimetallic oxide (such as CoMoO 4 ) through a series of chemical reactions, which play an important role in improving the flame retardant performance and smoke suppression and toxicity reduction effect of the TPU composite material, specifically as follows:

[0030] 1. Catalytic charring effect: Cobalt salt and molybdenum salt can catalyze the dehydrogenation reaction of the TPU matrix during combustion, promote its crosslinking and carbonization. The carbon layer generated by the carbonization reaction can cover the surface of the material to form a protective layer, preventing the further transmission of heat and oxygen. At high temperatures, the carbon layer is further graphitized, improving its thermal stability and mechanical strength, and enhancing the flame retardant effect.

[0031] 2. Endothermic effect: The double metal oxide formed by cobalt salt and molybdenum salt has a high specific heat capacity, which can absorb a large amount of heat during the combustion process, thereby reducing the temperature of the material and delaying the combustion process. In addition, the high thermal stability of the double metal oxide enables it to maintain structural integrity at high temperatures and continuously play an endothermic role.

[0032] 3. Inhibiting the release of toxic gases: Metal ions in the double metal oxide can catalyze some chemical reactions during the combustion process to inhibit the generation of toxic gases. In addition, the active sites on the surface of the double metal oxide can adsorb toxic gases and reduce their release amount.

[0033] 4. Physical barrier effect: The double metal oxide nano-fillers formed by cobalt salt and molybdenum salt have a high specific surface area and can be evenly dispersed in the TPU matrix to form a dense physical barrier. Moreover, the filler particles can block the transfer of heat and oxygen, reducing the energy and oxygen supply required for combustion, thereby delaying the combustion process. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The double metal oxide flame retardant filler described in the present invention has higher flame retardant efficiency and smoke suppression and toxicity reduction effects. Cobalt salt and molybdenum salt significantly improve the flame retardant performance and smoke suppression and toxicity reduction effects of the TPU composite material through multiple mechanisms such as catalytic carbonization, endothermic, inhibiting the release of toxic gases, and physical barrier in the double metal oxide flame retardant TPU composite material. These mechanisms cooperate with each other, enabling the TPU composite material to more effectively block the transfer of heat and oxygen during the combustion process, form a protective carbon layer, absorb heat, and reduce the release of toxic gases, thereby significantly improving the flame retardant performance and safety of the material. This TPU composite material has a good effect in blocking the thermal runaway of the battery.

[0035] The experimental results show that: after adding 4wt% of the filler, the peak value of the smoke production rate and the peak value of the CO production rate of the double metal oxide flame retardant TPU composite material decrease by 76.7% and 66.7% respectively, which are better than the prior art. In addition, the limiting oxygen index (LOI) is significantly improved, indicating excellent flame retardant performance of the composite material. Description of the Drawings

[0036] Figure 1 SEM image of the double metal oxide nano-filler BN-CoMo-1 prepared in Example 1;

[0037] Figure 2 TEM image of the double metal oxide nano-filler BN-CoMo-1 prepared in Example 1;

[0038] Figure 3Comparison of the performance test results of commercially available TPU and the prepared flame-retardant TPU composite materials; among them, (a) is the heat release rate curve of commercially available TPU and the prepared flame-retardant TPU composite materials; (b) is the smoke production rate curve of commercially available TPU and the prepared flame-retardant TPU composite materials; (c) is the CO release rate curve of commercially available TPU and the prepared flame-retardant TPU composite materials.

[0039] Figure 4 Test results of commercially available TPU and the prepared flame-retardant TPU composite materials; among them, (a) is the intensity curve of aromatic compounds of commercially available TPU and the prepared flame-retardant TPU composite materials; (b) is the intensity curve of CO products of commercially available TPU and the prepared flame-retardant TPU composite materials.

[0040] Figure 5 Test results of the application of commercially available TPU and the prepared flame-retardant TPU composite materials in inhibiting the thermal runaway propagation of lithium-ion batteries; among them, (a) is the test result of TPU; (b) is the test result of the prepared flame-retardant TPU composite material. Detailed implementation manners

[0041] In order to further illustrate the technical solution of the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0042] At the same time, for the raw materials or reagents not detailed below, they are all commercially available products, and the process steps or methods not detailed are the process steps or methods known to those skilled in the art.

[0043] The sources of some raw materials and reagents involved in the following examples and test examples are as follows:

[0044] Boron nitride, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0045] Polyethyleneimine, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0046] Cobalt nitrate hexahydrate, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0047] Ammonium molybdate tetrahydrate, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0048] Ammonia water, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0049] Nitric acid, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0050] N,N-dimethylformamide, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0051] The TPU is polyester type 85E85, purchased from Baoding Bangtai New Polymer Materials Co., Ltd.

[0052] Example 1

[0053] Example 1 is a specific preparation process of the bimetallic oxide filler described in the present invention:

[0054] Step 1: Take 2.0 g of h-BN and manually grind it in 25 g of KOH mortar. Then transfer the mixture to a 250 mL zirconia jar filled with zirconia balls and ball-mill at a speed of 500 rpm for 22 h. After that, wash it with water multiple times to remove the excess KOH until the pH value of the suspension is close to 7. Centrifuge the suspension at 2500 rpm for 15 minutes to obtain the supernatant containing h-BN nanosheets. Filter and dry to obtain h-BN nanosheets.

[0055] Step 2: Take 1.0 g of h-BN nanosheets and 0.5 g of polyethyleneimine and place them in 400 ml of deionized water, and ultrasonicate for 4 h to obtain a homogeneous solution.

[0056] Step 3: Add 2.9 g of cobalt nitrate hexahydrate and 6.5 g of ammonium molybdate tetrahydrate to the homogeneous solution, and keep ultrasonically stirring for 3 h.

[0057] Step 4: Then adjust the pH of the mixture to 7 with ammonia water and nitric acid, and then hydrothermally react the mixture at 180 °C for 12 h. After the reaction is completed, centrifuge and wash with water to obtain BN-CoMo-1, and its scanning electron microscope image is as Figure 1 shown, and the transmission electron microscope image is as Figure 2 shown.

[0058] Example 2

[0059] The difference between Example 2 and Example 1 is only that: in Step 3, 4.4 g of cobalt nitrate hexahydrate and 9.8 g of ammonium molybdate tetrahydrate are added, and the obtained flame retardant is BN-CoMo-2.

[0060] Example 3

[0061] The difference between Example 3 and Example 1 is only that: in Step 3, 1.4 g of cobalt nitrate hexahydrate and 3.3 g of ammonium molybdate tetrahydrate are added, and the obtained flame retardant is BN-CoMo-3.

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is only that: in Step 3, 5.8 g of cobalt nitrate hexahydrate and 13 g of ammonium molybdate tetrahydrate are added, and the obtained flame retardant is BN-CoMo-4.

[0064] Comparative Example 2

[0065] The difference between Comparative Example 2 and Example 1 is only that: in Step 3, 0.725 g of cobalt nitrate hexahydrate and 1.625 g of ammonium molybdate tetrahydrate are added, and the obtained flame retardant is BN-CoMo-5.

[0066] The addition amounts of each component of the flame retardants in the above examples and comparative examples are shown in Table 1:

[0067] Table 1 Addition amounts of each component of the flame retardants in the above examples and comparative examples

[0068]

[0069] Example 4

[0070] The specific preparation method of the bimetallic oxide flame retardant TPU composite material includes:

[0071] Step 1, take 4 g of BN-CoMo-1 and ultrasonically stir and disperse it in 100 ml of N,N-dimethylformamide for 2 h, then add 96 g of polyurethane elastomer masterbatch, and continue to ultrasonically stir for 4 h until the polyurethane elastomer is completely dissolved. Then slowly drip the solution into water to obtain a precipitate, take out the precipitate and squeeze out the water. Dry the precipitate in an oven at 100 °C for 72 h to obtain a composite;

[0072] Step 2, use a press to press the composite into a shape of 100*100*3 mm to obtain a TPU composite material with a BN-CoMo-1 addition amount of 4 wt%.

[0073] Example 5

[0074] The difference between Example 5 and Example 4 is only that: BN-CoMo-2 prepared in Example 2 is used instead of BN-CoMo-1 prepared in Example 1 to obtain a TPU composite material.

[0075] Example 6

[0076] The difference between Example 6 and Example 4 is only that: BN-CoMo-3 prepared in Example 3 is used instead of BN-CoMo-1 prepared in Example 1 to obtain a TPU composite material.

[0077] Comparative Example 3

[0078] The difference between Comparative Example 3 and Example 4 is only that: BN-CoMo-4 prepared in Comparative Example 1 is used instead of BN-CoMo-1 prepared in Example 1 to obtain a TPU composite material.

[0079] Comparative Example 4

[0080] The difference between Comparative Example 4 and Example 4 is only that: BN-CoMo-5 prepared in Comparative Example 2 is used to replace BN-CoMo-1 prepared in Example 1 to obtain the TPU composite material.

[0081] Example 7

[0082] The difference between Example 7 and Example 4 is that: the addition amount of the flame retardant BN-CoMo-1 prepared in Example 1 is 2 wt% of the total mass of the TPU composite material.

[0083] Example 8

[0084] The difference between Example 8 and Example 4 is that: the addition amount of the flame retardant BN-CoMo-1 prepared in Example 1 is 6 wt% of the total mass of the TPU composite material.

[0085] Comparative Example 5

[0086] The difference between Comparative Example 5 and Example 4 is that: the addition amount of the flame retardant BN-CoMo-1 prepared in Example 1 is 1 wt% of the total mass of the TPU composite material.

[0087] Comparative Example 6

[0088] The difference between Comparative Example 6 and Example 4 is that: the addition amount of the flame retardant BN-CoMo-1 prepared in Example 1 is 8 wt% of the total mass of the TPU composite material.

[0089] Comparative Example 7

[0090] The difference between Comparative Example 7 and Example 4 is that: no flame retardant is added.

[0091] The component contents of the TPU composite materials in the above examples and comparative examples are shown in Table 2:

[0092] Table 2 Component contents of the TPU composite materials in the above examples and comparative examples

[0093]

[0094]

[0095] Test Example 1: Limiting oxygen index test

[0096] The specific test process is as follows: An oxygen index meter is used to conduct experiments on the samples. The specific samples are Examples 4 to 8 and Comparative Examples 3 to 7. The test results are shown in Table 3.

[0097] Table 3 Limiting oxygen index test results of the examples and comparative examples

[0098] Add flame retardant Addition amount Limiting oxygen index (LOI Example 4 BN-CoMo-1 4wt% 28.3％ Example 5 BN-CoMo-2 4wt% 27.5％ Example 6 BN-CoMo-3 4wt% 27.9％ Comparative example 3 BN-CoMo-4 4wt% 25.6％ Comparative example 4 BN-CoMo-5 4wt% 24.8％ Example 7 BN-CoMo-1 2wt% 27.8％ Example 8 BN-CoMo-1 6wt% 28.1％ Comparative example 5 BN-CoMo-1 1wt% 24.8％ Comparative example 6 BN-CoMo-1 8wt% 26.2％ Comparative example 7 None None 21.5％

[0099] As can be seen from Table 3, the flame retardants BN-CoMo-4 and BN-CoMo-5 result in relatively low limiting oxygen indices for the TPU composites. This is mainly because the double metal oxides can, on the one hand, play a catalytic degradation role on the TPU matrix, and on the other hand, play a catalytic charring role on the pyrolysis products. There is too much double metal oxide in BN-CoMo-4, leading to excessive catalytic degradation of the TPU matrix. While the addition amount of the double metal oxide in BN-CoMo-5 is too small, resulting in insufficient catalytic carbonization of the TPU volatiles. In contrast, BN-CoMo-1, BN-CoMo-2, and BN-CoMo-3 exhibit better flame retardant properties.

[0100] The addition amount of different flame retardants also has an impact on the flame retardant properties of the TPU composites. In contrast, when the addition amount of the flame retardant is 2 - 6 wt% of the total mass of the TPU composites, the composites exhibit relatively high LOI values. When the addition amount of the flame retardant is too low, the flame retardant effect is limited. When the addition amount of the flame retardant is too high, it may cause the flame retardant to be unable to disperse evenly in the TPU matrix, thus reducing the flame retardant effect. Test Example 2:

[0101] Cone calorimeter test of commercially available TPU and the flame retardant TPU composite prepared in Example 4

[0102] The specific test process is as follows: According to the ISO 5660 standard, a cone calorimeter (UK, Fire Testing Technology) is used to conduct a combustion test on the samples, and the sample specifications are 100×100×3 mm 3 , and it is ignited by an electric spark with a heat flux of 35 kW / m 2 .

[0103] Figure 3 For the comparison of the performance test results of commercially available TPU and the prepared flame retardant TPU composites; among them, (a) is the heat release rate curve of commercially available TPU and the prepared flame retardant TPU composites; (b) is the smoke production rate curve of commercially available TPU and the prepared flame retardant TPU composites; (c) is the CO release rate curve of commercially available TPU and the prepared flame retardant TPU composites.

[0104] From Figure 3 it can be seen that TPU is extremely easy to be ignited, releasing a large amount of heat and smoke, and the peak value of its heat release rate is 1236.8 kW / m 2 . While the peak value of the heat release rate of the TPU composite is 638.3 kW / m 2, which is a 48.4% decrease compared to pure TPU. At the same time, the peak value of the smoke production rate of the TPU composite material decreases by 76.7%. The release of the toxic gas CO is also a concern. Compared with pure TPU, the peak value of the CO production rate of the TPU composite material decreases by 66.7%. The TPU composite material exhibits excellent flame retardant properties, and at the same time, BN-CoMo-1 significantly inhibits the smoke toxicity during the combustion of TPU.

[0105] Test Example 3: Thermogravimetric Infrared TG-IR Test of Commercially Available TPU and Flame Retardant TPU Composite Material Prepared in Example 4

[0106] The specific test process is as follows: The TGIR results are obtained by using a Nicolet 6700 FTIR spectrophotometer in combination with a TGA Q5000 thermogravimetric analyzer. The test atmosphere is nitrogen, the heating rate is 20 °C / min, and the sampling mass is about 10 mg.

[0107] Figure 4 are the test results of commercially available TPU and the prepared flame retardant TPU composite material; among them, (a) is the intensity curve of aromatic compounds of commercially available TPU and the prepared flame retardant TPU composite material; (b) is the intensity curve of CO products of commercially available TPU and the prepared flame retardant TPU composite material.

[0108] From Figure 4 it can be seen that during the pyrolysis process of TPU, flammable substances such as aromatic compounds are released, which promotes the combustion of TPU. At the same time, CO gas is also released. On the one hand, CO will intensify the combustion, and on the other hand, it may cause human poisoning and loss of normal body functions. However, the release intensity of various pyrolysis products of the TPU composite material has decreased significantly. This indicates that the TPU composite material has more excellent flame retardant properties. Test Example 4: Application of Commercially Available TPU and Flame Retardant TPU Composite Material Prepared in Example 4 to Inhibit the Thermal Runaway Propagation Test of Lithium-Ion Batteries

[0109] The specific test process is as follows: The test uses a 103450 soft-pack lithium-ion battery (model: NCM 811, rated capacity: 2 Ah, rated voltage: 4.2 V, 100% SOC). The experimental bench is equipped with a fixed heating copper block, a separator prepared from the battery and the flame retardant TPU composite material, and a separator made of commercially available TPU.

[0110] Prepare two groups of experiments. Among them, the first group is to place a separator made of commercially available TPU between Battery-1 and Battery-2; the second group is to place a separator made of the TPU composite material between Battery-1 and Battery-2 to inhibit TRP.

[0111] During the test, heat was evenly transferred to Battery-1 through the copper block, triggering thermal runaway (TR) of Battery-1. Heat conduction initiated thermal runaway propagation (TRP), thus triggering TR of Battery-2. Thermocouples were placed at the centers of the copper block and the battery to measure the temperature on the surface of each component. Alligator clips for voltage data acquisition were firmly fixed on the tabs of the battery to monitor voltage changes during TRP.

[0112] The starting temperature of TR for Battery-1 was T 1 , and the corresponding time was t 1 . Similarly, the starting temperature of TR for Battery-2 was T 2 , and the corresponding time was t 2 . In addition, the time difference between t1 and t2 was Δt. The larger Δt was, the better the partition's inhibitory effect on TRP of lithium-ion batteries was, and the experimental results were as shown in Figure 5 . For the first group of experiments, as shown in (a) of Figure 5 , when TPU was used as the barrier material, Δt was 104 s. For the second group of experiments, as shown in (b) of Figure 5 , when TPU / 4.0BN-CoMo-1 was used as the barrier material, Δt was extended to 185 s. This indicates that the TPU composite material can inhibit the propagation of battery thermal runaway, mainly because of the excellent flame retardancy and heat insulation properties of TPU, which can inhibit heat transfer and thus delay the propagation of thermal runaway.

[0113] From the above performance test results, it can be seen that the double-metal oxide nano-fillers described in the present invention significantly improved the flame retardancy of the TPU composite material through mechanisms such as physical barrier effect, catalytic charring effect, endothermic effect, and inhibition of toxic gas release, and had good effects in blocking the propagation of battery thermal runaway.

[0114] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. Double metal oxide flame retardant TPU composite material, characterized in that: Calculated by mass percentage, TPU is 94~98wt% and the bimetallic oxide nanofiller BN-CoMo is 2~6 wt%.

2. The bimetallic oxide flame retardant TPU composite material according to claim 1, characterized in that: The preparation method of the bimetallic oxide nanofiller BN-CoMo comprises the following steps: Step 1: grinding boron nitride and a modifier in a high-energy ball mill, washing with water, and vacuum drying to obtain boron nitride nanosheets; Step 2: Dispersing boron nitride nanosheets and polyethyleneimine in water and ultrasonically treating to obtain a uniform solution; Step 3: Add cobalt salt and molybdenum salt to the homogeneous solution and keep ultrasonic stirring; Step 4: After adjusting the pH of the solution to 6.5-7.5 using ammonia water and nitric acid, the mixed solution is subjected to hydrothermal reaction for 10-14 hours; after the reaction, the bimetallic oxide nanofiller BN-CoMo is obtained by washing and centrifugation.

3. The bimetallic oxide flame retardant TPU composite material according to claim 2, characterized in that: The mass ratio of boron nitride to modifier is 1:(10~15); the mass ratio of boron nitride nanosheets to polyethyleneimine is (2~3):

1.

4. The bimetallic oxide flame-retardant TPU composite material according to claim 3, characterized in that: The boron nitride is one of hexagonal boron nitride, rhombohedral boron nitride, cubic boron nitride and wurtzite boron nitride; The modifier is one or more of urea, melamine and potassium hydroxide; The cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt sulfate; The molybdate is one or more of sodium molybdate, potassium molybdate and ammonium molybdate.

5. The bimetallic oxide flame retardant TPU composite material according to claim 4, characterized in that: The mass ratio of the boron nitride nanosheets, the cobalt salt and the molybdenum salt is 1:(1.4-4.4):(3.3-9.8).

6. A method for preparing a bimetallic oxide flame-retardant TPU composite material, characterized in that: The following steps are involved: Step 1: Disperse the bimetallic oxide filler BN-CoMo in an organic solvent and stir ultrasonically for 2 to 3 hours to obtain a primary mixed solution; Step 2: Disperse the TPU masterbatch in the above mixed solution, maintain ultrasonic stirring for 4 to 6 hours to obtain a secondary mixed solution; then drop the secondary mixed solution into water to obtain a precipitate, filter the solid and dry it at 70 to 100°C for 48 to 96 hours to obtain a composite; Step 3: The above-mentioned compound is kneaded at 180-190°C and pressed to obtain a bimetallic oxide flame-retardant TPU composite material.

7. The method for preparing the bimetallic oxide flame-retardant TPU composite material according to claim 6, characterized in that: The organic solvent is one or more of tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, and 1,4-dioxane.

8. The method for preparing the bimetallic oxide flame-retardant TPU composite material according to claim 7, characterized in that: The addition amount of the bimetallic oxide filler is 2-6 wt% of the total mass of the TPU composite material.

9. Application of bimetallic oxide flame retardant TPU composite material, characterized in that: Used to prevent battery thermal runaway.

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