Polyurethane foam and preparation method thereof, flame retardant thermal insulation pad and battery module

Abstract

The present invention relates to the field of battery manufacturing technology, and more particularly to a polyurethane foam, a preparation method thereof, a flame-retardant thermal insulation pad, and a battery module. The polyurethane foam comprises, by weight, 95-105 parts of a polyether polyol, 45-55 parts of an isocyanate, 0.008-0.012 parts of a tin catalyst, 5-15 parts of a carboxyl-containing short-chain aliphatic diol, 20-30 parts of a chain extender, 25-35 parts of a solvent, and 4-6 parts of triethylamine. The chain extender has the structural formula #imgabs0#. The present invention introduces a chain extender having the aforementioned structure into the polyurethane backbone to produce a polyurethane foam with excellent flame retardancy and heat absorption properties. The flame-retardant thermal insulation pad produced using this polyurethane foam improves the thermal safety of the battery module and increases the heat spread time.

Description

Technical Field

[0001] The present invention relates to the technical field of battery production and manufacturing, and in particular to a polyurethane foam and a preparation method thereof, a flame retardant heat insulating pad and a battery module. Background Art

[0002] With the country's vigorous promotion of new energy vehicles, new energy vehicles have ushered in a golden opportunity for development. The safety and stability of new energy vehicles have always been of primary concern. Therefore, improving the safety of new energy vehicles will be one of the key factors determining their rapid adoption. As the primary component of the battery pack in new energy vehicles, improving the safety of battery modules is a key approach to improving the safety of new energy vehicles.

[0003] A battery module typically includes multiple batteries, with the batteries facing each other. A module frame surrounds the batteries and provides a secure mounting mechanism for the module. Due to the electrical connection and mechanical contact between the batteries, the battery module can vibrate along with the electric vehicle during travel. At this point, the batteries in the module are squeezed together, making individual batteries susceptible to serious safety hazards such as wear, overheating, or fire. In particular, overheating of individual batteries can affect adjacent batteries, causing them to overheat and run away, leading to performance degradation and potentially safety hazards. To improve the safety of battery modules, thermal insulation is often added between the batteries to ensure that thermal runaway of a single battery does not affect adjacent batteries.

[0004] Currently, most thermal insulation devices used in battery modules only provide insulation. However, when a battery cell loses control, it generates a large amount of heat. This alone cannot guarantee the safety of adjacent cells. Therefore, it is necessary to develop a high-performance flame-retardant thermal insulation / heat absorption mat.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a polyurethane foam, in which a chain extender with a specific structure is introduced into the polyurethane main chain, thereby improving the flame retardant and heat absorption properties of the polyurethane foam.

[0007] The second object of the present invention is to provide a method for preparing the polyurethane foam as described above, which has simple steps.

[0008] The third purpose of the present invention is to provide a flame-retardant thermal insulation pad that can effectively improve the thermal safety of battery cells in a battery module, especially increase the heat spread time, and greatly reduce the probability of major accidents in the battery module.

[0009] A fourth object of the present invention is to provide a battery module comprising the flame retardant thermal insulation pad as described above.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] The present invention provides a polyurethane foam, wherein the raw materials thereof include, by weight: 95-105 parts of polyether polyol, 45-55 parts of isocyanate, 0.008-0.012 parts of tin catalyst, 5-15 parts of carboxyl-containing short-chain aliphatic diol, 20-30 parts of chain extender, 25-35 parts of solvent and 4-6 parts of triethylamine;

[0012] The structural formula of the chain extender is

[0013] Furthermore, the preparation method of the chain extender comprises the following steps:

[0014] p-Hydroxybenzaldehyde and N-[3-(trimethoxysilyl)propyl]ethylenediamine undergo a first reaction in an organic solvent to obtain a reaction liquid; and the reaction liquid undergoes a second reaction with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to obtain the chain extender.

[0015] Furthermore, the molar ratio of the hydroxybenzaldehyde, the N-[3-(trimethoxysilyl)propyl]ethylenediamine and the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1-1.2):(1-1.2).

[0016] Furthermore, the temperature of the first reaction is 55-65° C., and the time of the first reaction is 1.5-2.5 hours.

[0017] Furthermore, the temperature of the second reaction is 75-85° C., and the time of the second reaction is 5.5-6.5 hours.

[0018] Furthermore, the polyether polyol includes at least one of polytetramethylene glycol, polyethylene glycol and polypropylene glycol.

[0019] Preferably, the isocyanate includes at least one of 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate.

[0020] Preferably, the carboxyl-containing short-chain aliphatic diol includes at least one of dimethylolpropionic acid, dimethylolbutanoic acid and tartaric acid.

[0021] The present invention also provides a method for preparing the polyurethane foam as described above, comprising the following steps:

[0022] S1. Under an inert atmosphere, polyether polyol, isocyanate and tin catalyst react at 75-85° C. for 2-3 hours to obtain prepolymer I;

[0023] S2, reacting the prepolymer I, the carboxyl-containing short-chain aliphatic diol and the solvent at 75-85° C. for 2-3 hours to obtain a prepolymer II;

[0024] S3, reacting the prepolymer II, the chain extender and the solvent at 75-85° C. for 2-3 hours to obtain the prepolymer III;

[0025] S4. After the prepolymer III is mixed with triethylamine, it is dispersed in water under the action of shear force to obtain a foaming polyurethane emulsion, and the foaming polyurethane emulsion is placed in a mold to obtain the polyurethane foam.

[0026] The present invention also provides a flame retardant heat insulating pad, comprising a polyurethane foam layer and aerogel felt layers arranged on both sides of the polyurethane foam layer;

[0027] The polyurethane foam layer includes the polyurethane foam described above.

[0028] Furthermore, the thickness of the polyurethane foam layer is 1 to 2 mm.

[0029] Preferably, the thickness of the aerogel felt layer is 0.5-1 mm.

[0030] The present invention also provides a battery module comprising the flame retardant thermal insulation pad as described above.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention introduces a chain extender with a specific structure, namely a reactive flame-retardant and endothermic chain extender mainly synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (KH792), into a polyurethane main chain to obtain a flame-retardant and endothermic polyurethane foam. The polyurethane foam has excellent flame retardancy and endothermic properties, decomposes when heated, and can absorb a large amount of heat.

[0033] The flame-retardant thermal insulation mat of this invention, due to the introduction of KH792, contains silicon-oxygen bonds in the polyurethane foam layer, which can improve the adhesion between the polyurethane foam layer and the aerogel felt. When used in battery modules, this flame-retardant thermal insulation mat can effectively improve the thermal safety of the battery cells in the module, especially by increasing the heat propagation time, significantly reducing the probability of major battery module accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 Schematic diagram of the structure of the battery module of the present invention.

[0036] Reference numerals:

[0037] 1-battery cell; 2-flame retardant thermal insulation pad. DETAILED DESCRIPTION

[0038] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0039] The following is a detailed description of a polyurethane foam and a preparation method thereof, a flame retardant thermal insulation pad, and a battery module according to an embodiment of the present invention.

[0040] In some embodiments of the present invention, a polyurethane foam is provided, wherein the raw materials include, by weight: 95-105 parts of polyether polyol, 45-55 parts of isocyanate, 0.008-0.012 parts of tin catalyst, 5-15 parts of carboxyl-containing short-chain aliphatic diol, 20-30 parts of chain extender, 25-35 parts of solvent and 4-6 parts of triethylamine;

[0041] The structural formula of the chain extender is

[0042] The present invention introduces a chain extender with the above structure into the polyurethane main chain, and the obtained flame retardant and heat-absorbing polyurethane foam has excellent flame retardancy and heat absorption.

[0043] When the flame retardant and heat-absorbing polyurethane foam is heated, the chain extender decomposes into components containing phosphorus free radicals and nitrogen elements, which can absorb a large amount of heat during decomposition. The phosphorus and nitrogen coordinate the flame retardancy, giving it excellent flame retardant and heat-absorbing properties.

[0044] In some embodiments of the present invention, the polyurethane foam comprises, by weight, 100 parts of polyether polyol, 50 parts of isocyanate, 0.01 parts of a tin catalyst, 8 parts of a carboxyl-containing short-chain aliphatic diol, 20 parts of a chain extender, 30 parts of a solvent, and 5 parts of triethylamine. Using the above ratios of the raw materials can produce a polyurethane foam with even better performance.

[0045] In some embodiments of the present invention, the method for preparing a chain extender comprises the following steps:

[0046] p-Hydroxybenzaldehyde and N-[3-(trimethoxysilyl)propyl]ethylenediamine undergo a first reaction in an organic solvent to obtain a reaction liquid; and the reaction liquid undergoes a second reaction with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to obtain a chain extender.

[0047] The invention uses 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (KH792) to synthesize a reactive flame retardant endothermic chain extender, which is introduced into the polyurethane main chain to obtain a flame retardant endothermic polyurethane foam.

[0048] In some embodiments of the present invention, in the method for preparing the chain extender, the molar ratio of hydroxybenzaldehyde, N-(3-trimethoxysilylpropyl)ethylenediamine and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1-1.2):(1-1.2).

[0049] In some embodiments of the present invention, in the method for preparing the chain extender, the organic solvent includes ethanol.

[0050] In some embodiments of the present invention, in the method for preparing the chain extender, the temperature of the first reaction is 55 to 65° C., and the time of the first reaction is 1.5 to 2.5 hours.

[0051] In some embodiments of the present invention, in the method for preparing a chain extender, the temperature of the second reaction is 75 to 85° C., and the time of the second reaction is 5.5 to 6.5 hours.

[0052] In some embodiments of the present invention, in the method for preparing the chain extender, after the second reaction, the method further comprises filtering, washing and drying in sequence.

[0053] In some embodiments of the present invention, the polyether polyol includes at least one of polytetramethylene glycol, polyethylene glycol and polypropylene glycol; preferably, the molecular weight of the polyether polyol is 2000-4000.

[0054] In some embodiments of the present invention, the isocyanate comprises an aromatic or aliphatic diisocyanate.

[0055] In some embodiments of the present invention, the isocyanate includes at least one of 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0056] In some embodiments of the present invention, the tin-based catalyst includes dibutyltin laurate.

[0057] In some embodiments of the present invention, the carboxylic short-chain aliphatic diol includes at least one of dimethylol propionic acid, dimethylol butyric acid, and tartaric acid.

[0058] In some embodiments of the present invention, the solvent comprises N,N-dimethylformamide.

[0059] In some embodiments of the present invention, a method for preparing the polyurethane foam is also provided, comprising the following steps:

[0060] S1. Under an inert atmosphere, polyether polyol, isocyanate, and a tin catalyst react at 75-85° C. for 2-3 hours to obtain prepolymer I;

[0061] S2, prepolymer I, a short-chain aliphatic diol containing a carboxyl group, and a solvent are reacted at 75-85° C. for 2-3 hours to obtain prepolymer II;

[0062] S3, prepolymer II, chain extender and solvent are reacted at 75-85°C for 2-3h to obtain prepolymer III;

[0063] S4, prepolymer III and triethylamine are mixed and dispersed in water under the action of shear force to obtain a foaming polyurethane emulsion, which is placed in a mold to obtain polyurethane foam.

[0064] The prepolymer II of the present invention is a prepolymer with a block structure, the prepolymer III is a prepolymer terminated with -NCO and containing flame retardant components (DOPO and KH792), and the foaming polyurethane emulsion is a flame retardant water-based foaming polyurethane emulsion.

[0065] The invention introduces a reactive flame retardant and heat absorbing chain extender into a polyurethane main chain by chemical reaction, and then foams the polyurethane under the action of high shear force to prepare a flame retardant and heat absorbing polyurethane foam.

[0066] The present invention adopts water-based impregnated polyurethane to replace traditional solvent-based impregnated polyurethane, which greatly reduces VOCs emissions during the polyurethane preparation process and has outstanding green, environmentally friendly, healthy and safe characteristics.

[0067] In some specific embodiments of the present invention, the foamed polyurethane emulsion is placed in a polytetrafluoroethylene plate to form a film to obtain a polyurethane foam layer.

[0068] In some embodiments of the present invention, a flame retardant thermal insulation pad is further provided, comprising a polyurethane foam layer and aerogel felt layers arranged on both sides of the polyurethane foam layer; the polyurethane foam layer comprises the above-mentioned polyurethane foam.

[0069] In some embodiments of the present invention, the thickness of the polyurethane foam layer is 1 to 2 mm; typically but not limitatively, for example, the thickness of the polyurethane foam layer is 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm or a range consisting of any two thereof.

[0070] In some embodiments of the present invention, the thickness of the aerogel felt layer is 0.5-1 mm; typically but not limiting, for example, the thickness of the aerogel felt layer is 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm or a range consisting of any two thereof.

[0071] Due to the introduction of KH792 in the polyurethane foam layer of the present invention, silicon-oxygen bonds exist, which can improve the adhesion between the polyurethane foam layer and the aerogel felt.

[0072] The flame-retardant thermal insulation pad of the present invention has excellent flame retardancy, heat insulation and heat absorption properties; it can effectively improve the thermal safety of the battery cells in the module, especially it can increase the heat spread time, and greatly reduce the probability of major accidents in the liquid battery module.

[0073] In some embodiments of the present invention, a method for preparing the flame retardant thermal insulation pad is also provided, comprising the following steps:

[0074] The aerogel felt layer, the polyurethane foam layer and the aerogel felt layer are stacked in sequence and then hot-pressed to obtain a flame-retardant thermal insulation pad.

[0075] In some embodiments of the present invention, the temperature of hot pressing is 70-90° C., and the pressure of hot pressing is 0.8-1.2 MPa.

[0076] See also Figure 1 In some embodiments of the present invention, a battery module is also provided, comprising the flame retardant thermal insulation pad 2 mentioned above.

[0077] In some embodiments of the present invention, the battery module comprises a liquid battery module.

[0078] In some embodiments of the present invention, the battery module further includes a battery cell 1 ; preferably, flame retardant thermal insulation pads 2 are provided on both sides of the battery cell 1 .

[0079] Example 1

[0080] The preparation method of the chain extender provided in this embodiment is as follows:

[0081]

[0082] The specific steps include:

[0083] 24.4 g of p-hydroxybenzaldehyde was dissolved in 150 mL of ethanol, and then 44.5 g of N-[3-(trimethoxysilyl)propyl]ethylenediamine (KH792) was added dropwise, and the mixture was reacted at 60° C. for 2 h to obtain a reaction solution; then 43.2 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was added to the above reaction solution, and the mixture was reacted at 80° C. for 6 h. The filter cake was then filtered to obtain a chain extender.

[0084] The method for preparing the polyurethane foam layer provided in this embodiment comprises the following steps:

[0085] S1. Add 100 parts of polytetrahydrofuran diol, 50 parts of 2,4-toluene diisocyanate, and 0.01 parts of dibutyltin laurate as a catalyst into a reaction vessel, and heat to 85° C. under continuous stirring and nitrogen atmosphere protection, and react for 3 hours to obtain prepolymer I;

[0086] S2. Add 8 parts of dimethylolpropionic acid and 10 parts of N,N-dimethylformamide to the above prepolymer, and react at 85° C. for 3 hours to obtain prepolymer II;

[0087] S3. 20 parts of the chain extender prepared in this embodiment and 20 parts of N,N-dimethylformamide were added to prepolymer II, and the reaction was continued at 85° C. for 3 hours to obtain prepolymer III; 5 parts of triethylamine were used to neutralize prepolymer III, and under high shear force, prepolymer III was dispersed in deionized water to obtain a flame-retardant water-based foaming polyurethane emulsion, which was placed on a polytetrafluoroethylene plate and allowed to stand to form a film to obtain a polyurethane foam layer.

[0088] The method for preparing the flame retardant thermal insulation pad provided in this embodiment includes the following steps:

[0089] The aerogel felt layer, the polyurethane foam layer prepared in this embodiment, and the aerogel felt layer were stacked in sequence, and then hot pressed using a flat plate vulcanizer at a temperature of 80°C and a pressure of 1 MPa to obtain a flame retardant thermal insulation pad with a size of 30 cm × 30 cm; wherein the thickness of the aerogel felt layer is 0.5 mm, and the thickness of the polyurethane foam layer is 1 mm.

[0090] Example 2

[0091] The preparation method of the flame retardant thermal insulation pad provided in this embodiment refers to Example 1, with the only difference being that the thickness of the aerogel felt layer is 0.75 mm and the thickness of the polyurethane foam layer is 1.5 mm.

[0092] The preparation method of the chain extender and the polyurethane foam layer is the same as that in Example 1.

[0093] Example 3

[0094] The preparation method of the flame retardant thermal insulation pad provided in this embodiment refers to Example 1, with the only difference being that the thickness of the aerogel felt layer is 1 mm and the thickness of the polyurethane foam layer is 2 mm.

[0095] The preparation method of the chain extender and the polyurethane foam layer is the same as that in Example 1.

[0096] Example 4

[0097] The preparation method of the flame retardant thermal insulation pad provided in this embodiment refers to Example 1, with the only difference being that the polyurethane foam layer prepared in this embodiment is used.

[0098] The method for preparing the polyurethane foam layer provided in this embodiment comprises the following steps:

[0099] S1. Add 100 parts of polyethylene glycol, 50 parts of 4,4'-diphenylmethane diisocyanate, and 0.01 parts of dibutyltin laurate as a catalyst into a reaction vessel, and under continuous stirring and nitrogen atmosphere, heat to 85° C. and react for 3 hours to obtain prepolymer I;

[0100] S2. Add 8 parts of dimethylolbutyric acid and 10 parts of N,N-dimethylformamide to the above prepolymer, and react at 85° C. for 3 hours to obtain prepolymer II;

[0101] S3. 20 parts of the chain extender prepared in this embodiment and 20 parts of N,N-dimethylformamide were added to prepolymer II, and the reaction was continued at 85° C. for 3 hours to obtain prepolymer III; 5 parts of triethylamine were used to neutralize prepolymer III, and under high shear force, prepolymer III was dispersed in deionized water to obtain a flame-retardant water-based foaming polyurethane emulsion, which was placed on a polytetrafluoroethylene plate and allowed to stand to form a film to obtain a polyurethane foam layer.

[0102] The preparation method of the chain extender is the same as that in Example 1.

[0103] Example 5

[0104] The preparation method of the flame retardant thermal insulation pad provided in this embodiment refers to Example 1, with the only difference being that the polyurethane foam layer prepared in this embodiment is used.

[0105] The method for preparing the polyurethane foam layer provided in this embodiment comprises the following steps:

[0106] S1. Add 100 parts of polypropylene glycol, 50 parts of hexamethylene diisocyanate, and 0.01 parts of dibutyltin laurate as a catalyst into a reaction vessel. Under continuous stirring and nitrogen atmosphere, heat to 85° C. and react for 3 hours to obtain prepolymer I.

[0107] S2. Add 8 parts of tartaric acid and 10 parts of N,N-dimethylformamide to the above prepolymer, and react at 85° C. for 3 hours to obtain prepolymer II;

[0108] S3. 20 parts of the chain extender prepared in this embodiment and 20 parts of N,N-dimethylformamide were added to prepolymer II, and the reaction was continued at 85° C. for 3 hours to obtain prepolymer III; 5 parts of triethylamine were used to neutralize prepolymer III, and under high shear force, prepolymer III was dispersed in deionized water to obtain a flame-retardant water-based foaming polyurethane emulsion, which was placed on a polytetrafluoroethylene plate and allowed to stand to form a film to obtain a polyurethane foam layer.

[0109] The preparation method of the chain extender is the same as that in Example 1.

[0110] Comparative Example 1

[0111] The preparation method of the flame retardant thermal insulation pad provided in this comparative example refers to Example 1, the only difference being that the polyurethane foam layer prepared in this comparative example is used.

[0112] The preparation method of the polyurethane foam layer provided in this comparative example refers to Example 5, except that the chain extender is 1,4-butanediol.

[0113] Comparative Example 2

[0114] The flame retardant thermal insulation pad provided in this comparative example is an aerogel felt layer with a thickness of 1 mm.

[0115] Test Example 1

[0116] The limiting oxygen index and vertical burning test grade of the polyurethane foam layers prepared in Examples 1 to 5 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0117] The limiting oxygen index test standard is in accordance with GB / T2406.2-2009, Plastic Combustion Performance Test Method - Oxygen Index Method, and the vertical burning test is in accordance with UL-94 vertical burning test standard.

[0118] Table 1

[0119]

[0120]

[0121] As can be seen from Table 1, compared with 1,4-butanediol in Comparative Example 1, the reactive flame retardant endothermic chain extender synthesized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and N-[3-(trimethoxysilyl)propyl]ethylenediamine is introduced into the polyurethane main chain, which significantly improves the flame retardant properties of the polyurethane foam.

[0122] Test Example 2

[0123] Flame-retardant insulation pads are introduced into the battery module, and a heat spread test is carried out on the battery module (using the national standard GB38031-2020 Safety Requirements for Power Batteries for Electric Vehicles).

[0124] After the single battery cell is thermally induced to run away, the runaway time of adjacent battery cells in the battery modules using the flame retardant and thermal insulation pads of Examples 1 to 5 is greater than 10 minutes; the runaway time of adjacent battery cells in the battery module using the aerogel felt of Comparative Example 2 is 4 minutes.

[0125] It can be seen from the heat spread data that compared with the aerogel felt layer of Comparative Example 2, the flame retardant thermal insulation pad prepared by the present invention significantly improves the heat spread time, greatly improving the thermal safety performance of the battery cells in the entire package module.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polyurethane foam, characterized in that The raw materials include, by weight: 95-105 parts of polyether polyol, 45-55 parts of isocyanate, 0.008-0.012 parts of tin catalyst, 5-15 parts of carboxyl-containing short-chain aliphatic diol, 20-30 parts of chain extender, 25-35 parts of solvent and 4-6 parts of triethylamine; The structural formula of the chain extender is .

2. The polyurethane foam according to claim 1, characterized in that The preparation method of the chain extender comprises the following steps: p-Hydroxybenzaldehyde and N-[3-(trimethoxysilyl)propyl]ethylenediamine undergo a first reaction in an organic solvent to obtain a reaction liquid; and the reaction liquid undergoes a second reaction with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to obtain the chain extender.

3. The polyurethane foam according to claim 2, characterized in that The molar ratio of the hydroxybenzaldehyde, the N-[3-(trimethoxysilyl)propyl]ethylenediamine and the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1-1.2):(1-1.2).

4. The polyurethane foam according to claim 2, characterized in that The temperature of the first reaction is 55-65° C., and the time of the first reaction is 1.5-2.5 hours.

5. The polyurethane foam according to claim 2, characterized in that The temperature of the second reaction is 75-85° C., and the time of the second reaction is 5.5-6.5 hours.

6. The polyurethane foam according to claim 1, characterized in that The polyether polyol includes at least one of polytetramethylene glycol, polyethylene glycol and polypropylene glycol.

7. The polyurethane foam according to claim 1, characterized in that The isocyanate includes at least one of 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate.

8. The polyurethane foam according to claim 1, wherein The carboxyl-containing short-chain aliphatic diol includes at least one of dimethylol propionic acid, dimethylol butyric acid and tartaric acid.

9. The method for preparing the polyurethane foam according to any one of claims 1 to 8, characterized in that: The steps include: S1. Under an inert atmosphere, polyether polyol, isocyanate and tin catalyst react at 75-85° C. for 2-3 hours to obtain prepolymer I; S2, reacting the prepolymer I, a carboxyl-containing short-chain aliphatic diol, and a solvent at 75-85° C. for 2-3 hours to obtain a prepolymer II; S3, reacting the prepolymer II, the chain extender and the solvent at 75-85° C. for 2-3 hours to obtain a prepolymer III; S4. After the prepolymer III is mixed with triethylamine, it is dispersed in water under the action of shear force to obtain a foaming polyurethane emulsion, and the foaming polyurethane emulsion is placed in a mold to obtain the polyurethane foam.

10. A flame retardant heat insulation pad, characterized in that: It comprises a polyurethane foam layer and aerogel felt layers arranged on both sides of the polyurethane foam layer; The polyurethane foam layer comprises the polyurethane foam according to any one of claims 1 to 9.

11. The flame retardant heat insulation pad according to claim 10, characterized in that: The thickness of the polyurethane foam layer is 1-2 mm.

12. The flame retardant heat insulation pad according to claim 11, characterized in that: The thickness of the aerogel felt layer is 0.5-1 mm.

13. A battery module, characterized in that: Including the flame retardant thermal insulation pad according to any one of claims 10 to 12.

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