A microencapsulated composite fire extinguishing medium and its preparation method and application

Abstract

This invention belongs to the technical field of road traffic fire extinguishing agents, specifically relating to a microencapsulated composite fire extinguishing medium, its preparation method, and its application. This medium comprises an NH4H2PO4 solution and aluminum hydroxide as the core layer, and a gelatin-sodium alginate cross-linked wall material as the shell layer. It triggers controlled release through high temperature, achieving a synergistic effect of chemical inhibition and physical cooling. Its preparation method includes emulsification, coagulation, and cross-linking curing. The product exhibits high fire extinguishing efficacy (extinguishing time <7 seconds), strong re-ignition resistance (re-ignition probability <5%), and excellent storage stability (core material loss rate 6% over 30 days), making it suitable for fighting fires involving lithium batteries in new energy vehicles and hazardous chemicals.

Description

Technical Field

[0001] The present invention belongs to the technical field of road traffic fire extinguishing agents, and in particular relates to a microencapsulated composite fire extinguishing medium and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] With the accelerating pace of global urbanization, modern transportation networks have become a vital lifeline for maintaining social functioning. However, amidst the surge in transportation volume, road fires are becoming increasingly frequent, particularly those caused by hazardous chemical transport accidents and spontaneous combustion of new energy vehicles, which have become a major public safety threat. Currently, road traffic fire prevention and control faces two technical challenges: First, the complex hazards associated with hazardous chemical transport accidents are often accompanied by the violent energy release of flammable and explosive materials, creating a multi-dimensional hazard field characterized by thermal radiation (peak temperatures exceeding 1200°C), shock waves (peak pressure exceeding 0.3 MPa), and toxic diffusion (VOC concentrations exceeding 1000 ppm); second, thermal runaway hazards stem from the combustion of new energy vehicle power batteries, whose combustion process exhibits significant three-dimensional heat transfer characteristics (longitudinal propagation speeds of up to 0.5 m / s) and carries a re-ignition probability of up to 63%. In traffic congestion, the response effectiveness of traditional firefighting equipment is significantly reduced, making the suitability of fire extinguishing media within the golden rescue time window (typically less than 5 minutes) a critical factor in disaster control effectiveness. Based on this, it is imperative to develop a fire extinguishing agent that can effectively suppress road transport fires.

[0004] Existing fire extinguishing technologies have the following limitations:

[0005] (1) Water mist fire extinguishing agent: It relies on physical cooling (cooling rate of up to 50℃ / s), but has low momentum transfer efficiency (droplet velocity <10 m / s), resulting in insufficient coverage of flowing fire (<60%), and cannot effectively suppress the chain exothermic reaction of thermal runaway of lithium batteries;

[0006] (2) Powder fire extinguishing agent: Although it has rapid chemical suppression capability (extinguishing time <15 s), its specific heat capacity is low (<1.5 kJ / (kg·K)), its cooling capacity is insufficient, and the probability of re-ignition is as high as >60%. In addition, powder is easily affected by air flow disturbances and is difficult to provide stable coverage in complex fire environments.

[0007] (3) Foam fire extinguishing agent: The covering layer is easily damaged by impact, the chemical inhibition efficiency is low (fire extinguishing time > 30 s), and the tolerance to high temperature fire is poor (decomposition temperature < 150 °C).

[0008] Therefore, in road fire scenarios, traditional technologies are difficult to meet the following core requirements:

[0009] (1) Rapid response and precise release: The golden rescue time window is usually less than 5 minutes, and the deployment efficiency of fixed water mist systems is reduced by about 70% in congested scenarios;

[0010] (2) Synergistic fire extinguishing mechanism: It is necessary to simultaneously achieve multiple functions of chemical inhibition (free radical scavenging), physical cooling (specific heat capacity > 2.0 kJ / (kg·K)) and dynamic isolation (oxygen concentration ≤ 14.5%);

[0011] (3) Anti-reignition and long-term protection: Existing technologies are difficult to block the secondary exothermic reaction of thermal runaway of lithium batteries (reignition probability > 40%), and lack the ability to adsorb and treat toxic smoke (smoke elimination efficiency < 65%).

[0012] In summary, the existing technical system has significant shortcomings when dealing with complex road fires. A single fire extinguishing medium cannot meet the above requirements, and there is an urgent need to develop a composite material system. Summary of the Invention

[0013] To address the above-mentioned technical problems, the present invention aims to provide a microencapsulated composite fire-extinguishing medium, its preparation method, and its application. This invention utilizes microencapsulation technology to integrate chemical inhibitors and physical cooling materials into a core-shell structure. The specific structure is as follows: the core layer encapsulates a highly active ammonium dihydrogen phosphate solution (chemical inhibition) and a trace amount of Al(OH)3 (efficiency enhancement), enhancing fire-extinguishing efficiency and environmental friendliness; the shell layer utilizes intelligently responsive materials (such as pH / temperature-sensitive wall materials). This structure enables precise release in response to fire conditions, transcending the functional limitations of traditional technologies and resolving the conflict between storage stability and release efficiency. This composite powder-based fire-extinguishing medium will demonstrate enhanced applicability and effectiveness in road traffic fires, particularly those involving hazardous chemicals and new energy vehicles, providing a novel solution for firefighting.

[0014] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0015] In a first aspect of the present invention, a microencapsulated composite fire extinguishing medium is provided, comprising a core layer and a shell layer, wherein the core layer is composed of an NH4H2PO4 solution and Al(OH)3, and the shell layer is a pH-responsive wall material formed by cross-linking gelatin and sodium alginate; wherein the mass ratio of the NH4H2PO4 solution to Al(OH)3 is 10-12:1; the mass ratio of the gelatin to sodium alginate is 7-8:4-6; and the mass ratio of the NH4H2PO4 solution in the core layer to the shell layer is 3-4:1.

[0016] Preferably, the thickness of the shell layer is 50-150 nm, and the trigger release temperature is >125°C.

[0017] Preferably, the mass ratio of NH4H2PO4 to Al(OH)3 is 11:1; the mass ratio of gelatin to sodium alginate is 7:5; and the mass ratio of the NH4H2PO4 solution of the core layer to the shell layer is 4:1.

[0018] The second aspect of the present invention provides a method for preparing the above-mentioned microencapsulated composite fire extinguishing medium, comprising the following steps:

[0019] S1, mixing gelatin solution, sodium alginate solution, NH4H2PO4 solution, Al(OH)3 modifier and emulsifier to emulsify and react to obtain a stable emulsion;

[0020] S2, adding glacial acetic acid solution to the emulsion to adjust the pH and perform a coagulation reaction;

[0021] S3. Add a curing agent to the reaction mixture obtained in step S2, adjust the pH, perform a curing reaction, and perform post-processing to obtain a microencapsulated ammonium phosphate salt solution composite fire extinguishing medium.

[0022] Preferably, in step S1, the concentration of the gelatin solution is 7-8 wt%, the concentration of the sodium alginate solution is 4-6 wt%, and the concentration of the emulsifier is 1-2 wt%.

[0023] Preferably, in step S1, the emulsifier is selected from one or more of sodium dodecylbenzenesulfonate, OP-10, FSN-100, and Span-80.

[0024] Preferably, in step S1, the temperature of the emulsification reaction is 24-26° C., the time is 10-15 min, and the emulsification speed is 750-850 rpm.

[0025] Preferably, in step S2, the concentration of the glacial acetic acid solution is 8-12 wt%, and the pH adjustment range is 3.8-4.0; the temperature of the coagulation reaction is 40-45° C., and the time is 10-20 min.

[0026] Preferably, in step S3, the curing agent is selected from one or more of ethylenediamine, glutaraldehyde, diethylenetriamine, and dicyandiamide, the concentration of the curing agent is 23-26 wt%, and the pH adjustment range is 7-10.

[0027] Preferably, in step S3, the post-treatment includes filtering, washing and drying the microcapsule precipitate obtained by the curing reaction in sequence.

[0028] A third aspect of the present invention provides a use of the microencapsulated composite fire extinguishing medium described in the first aspect in suppressing thermal runaway of lithium batteries or fires of hazardous chemicals.

[0029] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0030] (1) The present invention uses a composite emulsification-interfacial polymerization method to construct a core-shell structure system wrapped with gelatin / sodium alginate (GE / SA) wall material to achieve precise encapsulation of fire extinguishing functional components. Among them:

[0031] Core layer: Contains 27 wt% ammonium phosphate (NH4H2PO4) solution as a chemical inhibitor, combined with Al(OH)3 modifier to enhance dilution and product adsorption, increasing flue gas treatment efficiency to 89% ± 2.5% (ISO 5923 standard test);

[0032] Shell: Through glutaraldehyde cross-linking, a smart wall material (thickness 50-150 nm) with pH-responsive properties is formed, which triggers controlled release at high temperatures (>125°C) in the fire scene, achieving a dual-stage effect of the fire extinguishing agent: initial rapid rupture of the capsule to release the powder for chemical inhibition (response time <5 s), and later continuous release of the hydrated gel to exert physical cooling (phase change enthalpy value reaches 215 J / g).

[0033] (2) The present invention realizes the innovation of multifunctional coordinated fire extinguishing mechanism, including:

[0034] Chemical-physical synergistic inhibition: NH4H2PO4 solution rapidly extinguishes flames through a free radical capture mechanism (·OH removal rate >95%). The water vapor produced by the decomposition of Al(OH)3 dilutes the concentration of oxygen and combustibles. At the same time, the hydrated gel phase transition process produces a steam expansion effect, forming a physical isolation layer (oxygen concentration drops below 14.5%).

[0035] Dynamic protection against re-ignition: The formed ammonium phosphate film effectively blocks the release of pyrolysis gases from combustibles. Alumina particles produced by the decomposition of Al(OH)3 further fill and enhance the film's stability, providing continuous protection against re-ignition. Simultaneously, the residual gel layer continuously releases water vapor to maintain local humidity and lower the temperature of the combustibles.

[0036] (3) This invention addresses the key technical bottlenecks in the field of road fire prevention and control, namely, the common defects of existing fire extinguishing agents, such as insufficient chemical inhibition efficiency (fire extinguishing time > 30s), limited smoke treatment capacity (smoke elimination efficiency < 65%), lack of thermal management (temperature drop rate < 10°C / s), and failure of combustible gas barrier (reignition probability > 40%). It innovatively proposes a core-shell structure composite fire extinguishing medium design strategy based on microencapsulation technology. By constructing a "powder-water mist phase change" synergistic fire extinguishing system, a new microencapsulated ammonium phosphate salt solution composite fire extinguishing agent was successfully developed. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the synthesis route of the GE-SA / NH4H2PO4 core-shell structure composite fire extinguishing medium prepared in Example 1 of the present invention;

[0038] Figure 2 TG curve of GE-SA / NH4H2PO4 microcapsules and their shells prepared in Example 1 of the present invention;

[0039] Figure 3 These are storage stability test graphs of the GE-SA / NH4H2PO4 microcapsules prepared in Example 1 of the present invention, wherein (a) is a graph showing the mass loss rate of the GE-SA / NH4H2PO4 microcapsules after 30 days of storage, (b) is a thermogravimetric analysis graph of the GE-SA / NH4H2PO4 microcapsules after storage for 1 day and 30 days, (c) is a SEM image of the GE-SA / NH4H2PO4 microcapsules after storage for 1 day, and (d) is a SEM image of the GE-SA / NH4H2PO4 microcapsules after storage for 30 days;

[0040] Figure 4 Microscopic images of GE-SA / NH4H2PO4 microcapsules prepared at different core-shell mass ratios of the present invention;

[0041] Figure 5 Microscopic images of GE-SA / NH4H2PO4 microcapsules prepared at different GE concentrations according to the present invention;

[0042] Figure 6 Microscopic images of GE-SA / NH4H2PO4 microcapsules prepared at different coagulation pH values ​​according to the present invention;

[0043] Figure 7 Microscope images of GE-SA / NH4H2PO4 microcapsules prepared at different Al(OH)3 concentrations according to the present invention;

[0044] Figure 8 Schematic diagram of the fire extinguishing test platform involved in Test Example 2 of the present invention;

[0045] Figure 9This is the thermal runaway combustion of the battery without adding fire extinguishing agent in Test Example 3 of the present invention;

[0046] Figure 10 This is the fire extinguishing process of the battery thermal runaway flame by the GE-SA / NH4H2PO4 microcapsule fire extinguishing agent in Test Example 3 of the present invention;

[0047] Figure 11 This is a temperature change curve of the lithium battery surface during the process of suppressing the lithium battery flame using the GE-SA / NH4H2PO4 core-shell structure composite fire extinguishing medium prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0049] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0050] Example 1:

[0051] This embodiment provides a microencapsulated composite fire extinguishing medium and a preparation method thereof:

[0052] (1) Preparation of GE solution: Place 7 g of GE in a beaker and add 93 g of deionized water. Place the beaker in a water bath and stir at room temperature for 25 min to allow the GE to fully absorb water and swell. Then, heat to 50°C and stir slowly for 30 min to form a transparent GE solution for use.

[0053] (2) Preparation of SA solution: Place 5 g of SA in a beaker, add 95 g of deionized water, and stir slowly in a 60°C water bath for 60 min to completely dissolve the SA.

[0054] (3) Preparation of other solutions: Prepare 25 wt% glutaraldehyde solution, 10 wt% glacial acetic acid solution, and 10 wt% NaOH solution in sequence through dissolving, stirring, heating, and other steps for later use.

[0055] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then injected into 120 g of a saturated (approximately 27 wt%) NH4H2PO4 core material solution, followed by 2.95 g of Al(OH)3 powder (the mass ratio of NH4H2PO4 to Al(OH)3 was 11:1), and finally 2 mL of 1.5 wt% Span-80 emulsifier was added. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0056] (5) Coagulation step: Slowly add 3 mL of 10 wt% glacial acetic acid solution to the above emulsion to adjust the pH of the emulsion to 3.8. Heat the water bath to 45°C and continue stirring for 15 min.

[0057] (6) Cross-linking and curing step: First, the reaction mixture was naturally cooled to room temperature. Then, it was stirred in an ice-water bath at about 8°C for 5 minutes. Subsequently, 2 mL of 25 wt% glutaraldehyde solution was added dropwise to the reaction system. The pH was adjusted to about 8.5 with 5 mL of 10 wt% NaOH solution. The mixture was stirred for 30 minutes to obtain a microcapsule precipitate.

[0058] (7) Filtration and drying: Filter the microcapsule precipitate, wash it with deionized water at least three times, and then place it in a blast oven to dry naturally to obtain the final microcapsules. The specific synthesis route is as follows: Figure 1 shown.

[0059] Comparative Example 1:

[0060] The difference between this comparative example and Example 1 is that the SA concentration in the shell material is 7%, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation methods in steps (2) and (4) are as follows:

[0061] (2) Preparation of SA solution: Place 7 g of SA in a beaker, add 93 g of deionized water, and stir slowly in a 60°C water bath for 60 min to completely dissolve the SA.

[0062] (4) Emulsification step: Equal volumes of 7 wt% GE and 7 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then added, followed by 120 g of saturated (approximately 27 wt%) NH4H2PO4 core material solution, 2.95 g of Al(OH)3 powder, and finally 2 mL of 1.5 wt% Span-80 emulsifier. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0063] Comparative Example 2:

[0064] The difference between this comparative example and Example 1 is that the SA concentration in the shell material is 3%, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation methods in steps (2) and (4) are as follows:

[0065] (2) Preparation of SA solution: Place 3 g of SA in a beaker, add 97 g of deionized water, and stir slowly in a 60°C water bath for 60 min to completely dissolve the SA.

[0066] (4) Emulsification step: Equal volumes of 7 wt% GE and 3 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then added, followed by 120 g of saturated (approximately 27 wt%) NH4H2PO4 core material solution, 2.95 g of Al(OH)3 powder, and finally 2 mL of 1.5 wt% Span-80 emulsifier. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0067] Comparative Example 3:

[0068] The difference between this comparative example and Example 1 is that the core-shell mass ratio is 3:1, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation method in step (4) is as follows:

[0069] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then added, followed by 90 g of saturated (approximately 27 wt%) NH4H2PO4 core material solution, 2.21 g of Al(OH)3 powder, and finally 2 mL of 1.5 wt% Span-80 emulsifier. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0070] Comparative Example 4:

[0071] The difference between this comparative example and Example 1 is that the core-shell mass ratio is 5:1, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation method in step (4) is as follows:

[0072] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then added, followed by 150 g of saturated (approximately 27 wt%) NH4H2PO4 core material solution, 3.68 g of Al(OH)3 powder, and finally 2 mL of 1.5 wt% Span-80 emulsifier. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0073] Comparative Example 5:

[0074] The difference between this comparative example and Example 1 is that the mass ratio of NH4H2PO4 to Al(OH)3 is 9:1, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation method in step (4) is as follows:

[0075] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then injected into 120 g of saturated (approximately 27 wt%) NH4H2PO4 core material solution, followed by 3.60 g of Al(OH)3 powder (the mass ratio of NH4H2PO4 to Al(OH)3 was 9:1). Finally, 2 mL of 1.5 wt% Span-80 emulsifier was added. The mixture was emulsified with high-speed stirring for 10 min until a stable milky white emulsion was formed.

[0076] Comparative Example 6:

[0077] The difference between this comparative example and Example 1 is that the mass ratio of NH4H2PO4 to Al(OH)3 is 13:1, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation method in step (4) is as follows:

[0078] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then injected into 120 g of a saturated (approximately 27 wt%) NH4H2PO4 core material solution, followed by 2.49 g of Al(OH)3 powder (the mass ratio of NH4H2PO4 to Al(OH)3 was 13:1). Finally, 2 mL of 1.5 wt% Span-80 emulsifier was added. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0079] Comparative Example 7:

[0080] The difference between this comparative example and Example 1 is that the GE concentration in the shell material is 9%, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation methods in steps (1) and (4) are as follows:

[0081] (1) Preparation of GE solution: Place 9 g of GE in a beaker and add 91 g of deionized water. Place the beaker in a water bath and stir at room temperature for 25 min to allow the GE to fully absorb water and swell. Then, heat to 50°C and stir slowly for 30 min to form a transparent GE solution for later use.

[0082] (4) Emulsification step: Equal volumes of 9 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then injected into 120 g of a saturated (approximately 27 wt%) NH4H2PO4 core material solution, followed by 2.95 g of Al(OH)3 powder (the mass ratio of NH4H2PO4 to Al(OH)3 was 11:1). Finally, 2 mL of 1.5 wt% Span-80 emulsifier was added. The mixture was stirred at high speed for 10 min until a stable milky white emulsion was formed.

[0083] Comparative Example 8:

[0084] The difference between this comparative example and Example 1 is that the GE concentration in the shell material is 6%, and the other components, contents and preparation methods are exactly the same as those in Example 1. The specific preparation methods in steps (1) and (4) are as follows:

[0085] (1) Preparation of GE solution: 6 g of GE was placed in a beaker, and 94 g of deionized water was added. The beaker was then placed in a water bath and stirred at room temperature for 25 min to allow the GE to fully absorb water and swell. The temperature was then raised to 50°C and stirred slowly for 30 min to form a transparent GE solution for later use.

[0086] (4) Emulsification step: Equal volumes of 6 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then injected into 120 g of a saturated (approximately 27 wt%) NH4H2PO4 core material solution, followed by 2.95 g of Al(OH)3 powder (the mass ratio of NH4H2PO4 to Al(OH)3 was 11:1). Finally, 2 mL of 1.5 wt% Span-80 emulsifier was added. The mixture was emulsified with high-speed stirring for 10 min until a stable milky white emulsion was formed.

[0087] Comparative Example 9:

[0088] This embodiment provides a GE-SA composite fire extinguishing medium and its preparation method:

[0089] (1) Preparation of GE solution: Place 7 g of GE in a beaker and add 93 g of deionized water. Place the beaker in a water bath and stir at room temperature for 25 min to allow the GE to fully absorb water and swell. Then, heat to 50°C and stir slowly for 30 min to form a transparent GE solution for use.

[0090] (2) Preparation of SA solution: Place 5 g of SA in a beaker, add 95 g of deionized water, and stir slowly in a 60°C water bath for 60 min to completely dissolve the SA.

[0091] (3) Preparation of other solutions: Prepare 25 wt% glutaraldehyde solution, 10 wt% glacial acetic acid solution, and 10 wt% NaOH solution in sequence through dissolving, stirring, heating, and other steps for later use.

[0092] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 2 mL of 1.5 wt% Span-80 emulsifier was added, and the mixture was emulsified with high-speed stirring for 10 min until a stable milky white emulsion was formed.

[0093] (5) Coagulation step: Slowly add 3 mL of 10 wt% glacial acetic acid solution to the above emulsion to adjust the pH of the emulsion to 3.8. Heat the water bath to 45°C and continue stirring for 15 min.

[0094] (6) Cross-linking and curing step: First, the reaction mixture was naturally cooled to room temperature. Then, it was stirred in an ice-water bath at about 8°C for 5 minutes. Subsequently, 2 mL of 25 wt% glutaraldehyde solution was added dropwise to the reaction system. The pH was adjusted to about 8.5 with 5 mL of 10 wt% NaOH solution. The mixture was stirred for 30 minutes to obtain a microcapsule precipitate.

[0095] (7) Filtration and drying: The microcapsule precipitate is filtered out, washed with deionized water at least three times, and then placed in a forced air oven for natural drying to obtain the final microcapsules.

[0096] Comparative Example 10:

[0097] This embodiment provides a fire extinguishing agent containing NH4H2PO4 solution of Al(OH)3 and a preparation method thereof:

[0098] (1) Preparation of NH4H2PO4 solution: Place 27 g of NH4H2PO4 in a beaker, add 73 g of deionized water, and then place the beaker in a water bath and stir at room temperature for 2 min to completely dissolve it.

[0099] (2) Preparation of mixed solution: Add Al(OH)3 powder to 27 wt% NH4H2PO4 solution in a mass ratio of 11:1.

[0100] Comparative Example 11:

[0101] This embodiment provides a microencapsulated composite fire extinguishing medium (without Al(OH)3 solution) and its preparation method:

[0102] (1) Preparation of GE solution: Place 7 g of GE in a beaker and add 93 g of deionized water. Place the beaker in a water bath and stir at room temperature for 25 min to allow the GE to fully absorb water and swell. Then, heat to 50°C and stir slowly for 30 min to form a transparent GE solution for later use.

[0103] (2) Preparation of SA solution: Place 5 g of SA in a beaker, add 95 g of deionized water, and stir slowly in a 60°C water bath for 60 min to completely dissolve the SA.

[0104] (3) Preparation of other solutions: 25 wt% glutaraldehyde solution, 10 wt% glacial acetic acid solution, and 10 wt% NaOH solution were prepared in sequence through dissolving, stirring, heating, and other steps.

[0105] (4) Emulsification step: Equal volumes of 7 wt% GE and 5 wt% SA solutions (15 mL each) were injected into a 250 mL three-necked flask, placed in a constant temperature water bath (25 ± 1°C) and equipped with a mechanical stirrer (800 rpm). 30 g of the above mixed solution was then added, followed by 120 g of a saturated (approximately 27 wt%) NH4H2PO4 core material solution. Finally, 2 mL of 1.5 wt% Span-80 emulsifier was added. The mixture was emulsified with high-speed stirring for 10 min until a stable milky white emulsion was formed.

[0106] (5) Coagulation step: Slowly add 3 mL of 10 wt% glacial acetic acid solution to the above emulsion to adjust the pH of the emulsion to 3.8. Heat the water bath to 45°C and continue stirring for 15 min.

[0107] (6) Cross-linking and curing step: First, the reaction mixture was naturally cooled to room temperature. Then, it was stirred in an ice-water bath at about 8°C for 5 minutes. Subsequently, 2 mL of 25 wt% glutaraldehyde solution was added dropwise to the reaction system. The pH was adjusted to about 8.5 with 5 mL of 10 wt% NaOH solution. The mixture was stirred for 30 minutes to obtain a microcapsule precipitate.

[0108] (7) Filtration and drying: The microcapsule precipitate is filtered out, washed with deionized water at least three times, and then placed in a forced air oven for natural drying to obtain the final microcapsules.

[0109] Comparative Example 12:

[0110] The difference between this comparative example and Example 1 is that in step (5), the pH value is 4.2.

[0111] Comparative Example 13:

[0112] The difference between this comparative example and Example 1 is that in step (5), the pH value is 3.6.

[0113] Experimental Example 1:

[0114] In this experimental example, thermogravimetric testing (TG) was performed on the fire extinguishing media prepared in Example 1 and Comparative Example 9.

[0115] Under the optimal coagulation reaction conditions of 40°C coagulation temperature, 3.8 coagulation pH, 7% shell material concentration, and 4:1 core-shell mass ratio (Example 1), GE-SA / NH4H2PO4 microcapsules were optimized and prepared, and TG analysis was performed on the dried GE-SA / NH4H2PO4 microcapsules and their pure shell structures.

[0116] like Figure 2As shown in the figure, the TG curves of GE-SA / NH4H2PO4 microcapsules and GE-SA shells from 30℃ to 600℃ are different, which indirectly confirms that NH4H2PO4 is effectively encapsulated in the GE-SA shell. Compared with the TG curve of the GE-SA shell, the thermal gravimetric loss of GE-SA / NH4H2PO4 microcapsules goes through four different stages.

[0117] In the first stage, the temperature range is 30~75℃, at which time the quality of GE-SA / NH4H2PO4 microcapsules decreases slightly, which may be caused by the volatilization of bound water in the GE-SA shell or the evaporation of NH4H2PO4 on the microcapsule surface;

[0118] The second stage, within the temperature range of 75-125°C, saw a brief plateau in the TG curve. The GE-SA / NH4H2PO4 microcapsules showed no weight loss as the temperature increased. Normally, NH4H2PO4 evaporates at 49.2°C, but the encapsulation of the shell increased the NH4H2PO4's operating temperature to 125°C. This suggests that the GE-SA shell provides a degree of protection for NH4H2PO4, enhancing its stability.

[0119] In the third stage, within the temperature range of 125–400°C, the weight of the GE-SA / NH₄H₂PO₄ microcapsules decreased by 58.6%. This was attributed to the combined effects of thermal release of NH₄H₂PO₄ and thermal decomposition of the GE-SA shell. The TG curve during this stage was not smooth due to the structural complexity of the GE-SA shell and the uneven release of NH₄H₂PO₄. The final stage, primarily driven by the continued thermal decomposition of the residual GE-SA shell, ultimately entered a stable plateau.

[0120] The total weight loss of the GE-SA / NH4H2PO4 microcapsules was 90.6%, while the weight loss of the GE-SA shell was 63.4%. Calculations show that the encapsulation efficiency of the GE-SA / NH4H2PO4 microcapsules under the optimal preparation conditions was 27.2%. In summary, the GE-SA shell, composed of GE and SA, effectively encapsulated NH4H2PO4, and the GE-SA / NH4H2PO4 microcapsules exhibited excellent thermal stability.

[0121] Experimental Example 2:

[0122] In this experimental example, the storage stability of the microencapsulated composite fire extinguishing medium prepared in Example 1 was tested.

[0123] Microencapsulation technology can slow down the loss of core materials and achieve controlled release of core materials. Storage stability is a key indicator of microencapsulation products and is crucial for their application and promotion. Therefore, GE-SA / NH4H2PO4 microcapsules were stored at room temperature for 30 days, and their storage stability was studied by observing the mass loss and changes in appearance. Figure 3 shown.

[0124] from Figure 3 As shown in (a), after 30 days of storage, the mass loss of the GE-SA / NH4H2PO4 microcapsules reached approximately 6%, with the rate of mass loss gradually decreasing over time. Freshly prepared GE-SA / NH4H2PO4 microcapsules contain a high concentration of core material and are relatively full, resulting in a rapid mass loss. The rate of mass loss slows with extended storage (e.g., after 10 days) because the protective GE-SA shell reduces the contact area between the NH4H2PO4 and the outside world, slowing further volatilization of the NH4H2PO4.

[0125] from Figure 3 As can be seen in (b), compared with the freshly prepared GE-SA / NH4H2PO4 microcapsules, the encapsulation efficiency of the microcapsules decreased by 6% after 30 days of storage, and the initial release temperature decreased from 125℃ to 110℃. These phenomena can be seen from Figure 3 The morphology of the microcapsules in (c) shows that the freshly prepared GE-SA / NH4H2PO4 microcapsules have a smooth surface with no cracks or micropores. However, after 30 days of storage, the GE-SA / NH4H2PO4 microcapsules have not cracked, but have developed micropores. These tiny micropores may be due to the GE-SA shell absorbing moisture from the air, resulting in a localized decrease in shell density and localized wrinkling or cracking.

[0126] In summary, the GE-SA / NH4H2PO4 microcapsules prepared by complex coacervation using GE and SA as shell materials exhibited moderate storage stability and a high core material retention rate. However, the hygroscopicity of the GE-SA shell can cause micropores, and the storage performance of the microcapsules will slowly decline over time.

[0127] Test Example 1:

[0128] This test example conducted structural tests on the fire extinguishing media prepared in Example 1 and Comparative Examples 1 to 13.

[0129] (1) When changing the concentration of SA in the shell material:

[0130] The amount of sodium alginate (SA) significantly affects microcapsule performance; either too much or too little can degrade key properties. Low SA content can lead to structural defects in the shell due to insufficient crosslinking density and increased permeability. Furthermore, because SA forms a synergistic chemical extinguishing effect with the core material during fire extinguishing, a low SA content can also reduce the microcapsule's fire-extinguishing effectiveness. High SA content can increase viscosity and reduce coverage, while an overly dense crosslinking network can also reduce the core material's diffusion rate. Considering the morphology, encapsulation efficiency, and fire-extinguishing performance of the GE-SA / NH4H2PO4 microcapsules, a 5% SA concentration in the shell material in Example 1 was the optimal parameter for preparing the GE-SA / NH4H2PO4 microcapsules.

[0131] (2) When changing the core-shell volume ratio:

[0132] from Figure 4 As can be seen, when the core-shell mass ratio is 2:1, the structure appears as empty shell microcapsules. As the core-shell mass ratio increases (3:1-4:1), the number of GE-SA / NH4H2PO4 microcapsules gradually increases, and their shapes become more rounded. When the core-shell mass ratio increases to 5:1-6:1, the GE-SA / NH4H2PO4 microcapsules gradually adhere to each other and vary in size. Considering the morphology and encapsulation efficiency of the GE-SA / NH4H2PO4 microcapsules, the core-shell mass ratio of 4:1 in Example 1 is the optimal parameter for preparing GE-SA / NH4H2PO4 microcapsules.

[0133] (3) When the concentration of GE in the shell material is changed:

[0134] Depend on Figure 5 It can be seen that the shell material concentration has a significant impact on the microcapsule morphology. When the shell material concentration is 9%, the GE-SA / NH4H2PO4 microcapsules adhere to each other. As the concentration decreases, the GE-SA / NH4H2PO4 microcapsules gradually disperse and become more regular in shape. However, when the concentration drops to 3%, the shell layer of the GE-SA / NH4H2PO4 microcapsules is too thin due to the low shell material concentration. At this time, SA and GE cannot form a stable shell to cover the NH4H2PO4 solution. Therefore, when the shell material concentration is 7%, the microcapsules have high encapsulation efficiency and regular microcapsule morphology.

[0135] (4) When changing the coagulation pH setting:

[0136] from Figure 6Microscopic images of the microcapsules show that at a pH of 4.2, the number of GE-SA / NH4H2PO4 microcapsules is sparse and the distribution is dispersed. As the pH continues to decrease, the GE-SA / NH4H2PO4 microcapsules gradually increase in size, the shell thickens, and the outer shell and core material are clearly visible. When the pH drops to 4.0 and 3.8, the GE-SA / NH4H2PO4 microcapsules have a regular, rounded shape, are densely distributed, and are numerous. As the pH continues to decrease to 3.6 and 3.4, the shell becomes thinner, the volume decreases, and they begin to disperse. This is because pH has a significant influence on the electrostatic binding ability of SA and GE during the coagulation process. When the pH is too high, it approaches the isoelectric point of GE itself, which easily leads to coagulation and precipitation of GE itself, causing adhesion and other phenomena. When the pH is too low, it is far away from the positive and negative charge equilibrium point between SA and GE, resulting in a poor coagulation effect, dissociation between microcapsules, and a decrease in number.

[0137] (5) When changing the mass ratio of NH4H2PO4 to Al(OH)3:

[0138] The effect of Al(OH)3 content on encapsulation efficiency is nonlinear. The Al(OH)3 produced by dissolution 3+ It can enhance the electrostatic attraction between the positive charge of the core material and the negatively charged sodium alginate (Zeta≈−45 mV), promote the cohesion of the core and shell, and when the Al 3+ When the viscosity of the core material increases continuously, the isoelectric point of gelatin will become unstable, and the core material will flocculate and aggregate, eventually leading to core-shell phase separation and uneven coating. Figure 7 It can be seen that the mass ratio of 11:1 in Example 1 is the optimal parameter for preparing GE-SA / NH4H2PO4 microcapsules.

[0139] Test Example 2:

[0140] In this test example, the fire extinguishing media prepared in Example 1 and Comparative Examples 1 to 13 were subjected to a Cup-burner fire extinguishing test.

[0141] (1) This test case takes into account that the combustion and fire hazard of lithium batteries after thermal runaway are mainly determined by their gas products. Therefore, only the gas composition of the thermal runaway products will be considered and used as fuel. A diffusion flame cup burner (Cup-burner) is used to simulate the flame characteristics. The non-premixed flame produced by the cup burner is highly similar to the actual fire diffusion flame and has better flame stability and anti-interference ability. This enhanced stability characteristic results in the need to apply a higher dose of fire extinguishing agent in the fire extinguishing experiment, making the obtained fire extinguishing efficiency parameters closer to the actual fire working conditions.

[0142] This device has been widely adopted in the fire protection engineering field, and its test data has been incorporated into several industry standard technical manuals, such as the shipbuilding industry standard CB / T 4222-2013, "Marine Rotary Cup Burners," which replaced CB / T 1050-2001 and explicitly requires the use of a cup-burner to determine the critical concentration of fire extinguishing agents for diesel / heavy fuel oil flames, as a basis for the design of ship engine room fire extinguishing systems. The International Maritime Organization (IMO) "Fire Safety Systems Code" (FSS Code) cites cup-burner data to specify the minimum spray intensity of marine water mist systems. NFPA 750, "Standard for Water Mist Fire Extinguishing Systems," a data center and building fire protection standard, uses cup-burner-determined critical concentrations (e.g., for CH4 flames) to guide the design parameters of high-pressure water mist systems in confined spaces such as data centers. GB 50898-2013, "Data Center Design Code," cites actual fire test data (including cup-burner results) to verify the effectiveness of high-pressure water mist systems. The ISO 50898-2013 standard for the evaluation of alternative halon fire extinguishing agents is also available. 14520, "Gas Fire Extinguishing Systems," lists the Cup-burner as a standard test method for comparing the effectiveness of clean agents like HFC-227ea and FK-5-1-12 with traditional halons (for example, ultrafine ammonium dihydrogen phosphate is 2–4 times more effective than halon 1211). In the past two years, the inventors have used this equipment to publish numerous papers in top SCI journals, including the International Journal of Hydrogen Energy and Case Studies in Thermal Engineering. These papers include "Study on the suppression mechanism of NH4H2PO4 inhibiting gas flame of red pine pyrolysis," "Study on the development of aerial fire extinguishing munition for forest fires and fire extinguishing tests," and "Study on the suppression of pyrolytic gas flames in red pine wood by water mist."

[0143] In order to better observe the effectiveness of the GE-SA / NH4H2PO4 microcapsules prepared in the examples of the present invention in suppressing thermal runaway gas flames, this test example selected CO2, N2, perfluorohexanone, NH4H2PO4 powder, saturated NH4H2PO4 solution, shell material and other comparative examples as control group experiments. When conducting the perfluorohexanone and NH4H2PO4 solution and core material fire extinguishing experiments, the powder feeding and conveying system needs to be replaced with a 9306 atomizer (oxidant flow rate 40 L / min).

[0144] Each set of experiments was repeated ten times, and the minimum fire extinguishing concentration of each type of fire extinguishing agent was obtained by taking the average, as shown in Table 1 below.

[0145] Table 1 Minimum extinguishing concentrations of various fire extinguishing agents for thermal runaway gas flames of lithium iron phosphate

[0146]

[0147] Comparative experiments show that the minimum fire extinguishing concentration of traditional inert gases (N2, CO2) and shell materials (Comparative Example 9) is significantly higher than that of the perfluorohexanone and ammonium dihydrogen phosphate system. Although NH4H2PO4 powder has better fire extinguishing performance than saturated NH4H2PO4 solution, it lacks cooling capacity and cannot effectively suppress lithium battery thermal runaway fires. The GE-SA / NH4H2PO4 microcapsules formed by compounding NH4H2PO4 solution with shell materials have a higher fire extinguishing efficiency than perfluorohexanone due to their synergistic fire extinguishing effect. A comparison of Example 1 with Comparative Examples 1-13 reveals the following:

[0148] Comparative Examples 1 and 2 have insufficient crosslinking density, increased permeability or increased viscosity due to too low or too high SA content, resulting in defects in the shell structure, which in turn leads to low core material coverage or affects the diffusion rate of the core material, ultimately resulting in reduced fire extinguishing efficiency.

[0149] Comparative Examples 3 and 4: the former is because a large number of empty shell microcapsules appear in the formed microcapsules, thus affecting the fire extinguishing efficiency; the latter is because the microcapsules adhere to each other and are of different sizes, thus affecting the fire extinguishing efficiency.

[0150] Comparative Examples 5 and 6, the former is because Al 3+ Continuous increase will cause the viscosity of the core material to increase exponentially, the isoelectric point of gelatin to become unstable, the core material to flocculate, and eventually lead to core-shell phase separation, thus affecting the fire extinguishing efficiency; the latter is because Al 3+ The content is relatively low, so the fire extinguishing efficiency is slightly insufficient compared to Example 1.

[0151] In Comparative Examples 7 and 8, the former is because the excessively high GE content causes the microcapsules to stick together. The stuck microcapsules cannot evenly and effectively cover the flame root, thus affecting its fire extinguishing effect. The latter is because the low GE content causes the microcapsule shell to be too thin and easily ruptured. During the fire extinguishing process, the core material may be released due to various factors before it comes into contact with the core material at the flame root, thus affecting the fire extinguishing efficiency.

[0152] Comparative Example 9 is equivalent to an empty shell microcapsule without a core material. Due to the lack of a core fire extinguishing agent and the lack of NH4H2PO4 in the core material, sodium alginate cannot react with polyphosphoric acid to form sodium pyrophosphate at high temperature, thereby catalyzing the dehydration of the organic electrolyte and the polymer diaphragm into carbon, thereby blocking the chain exothermic reaction.

[0153] Comparative Example 10, compared with Example 1, lacks sodium alginate in the shell material, so that it lacks the synergistic inhibition network of P / Na multi-radicals formed together with the sodium-containing intermediates, greatly reducing the fire extinguishing efficiency. On the other hand, due to the lack of a microcapsule structure, it loses the functions of intelligent sustained release and directional transport, greatly weakening its role in lithium battery vehicle fire safety.

[0154] Comparative Example 11, on the one hand, Al(OH)3 dissolution produced Al 3+ This can enhance the electrostatic attraction between the core material's positive charge and the negatively charged sodium alginate (zeta ≈ −45 mV), promoting core-shell cohesion and increasing the microcapsule formation rate. Furthermore, Al(OH)3 reduces heat and suppresses smoke, enhancing fire extinguishing efficiency. Therefore, the fire extinguishing efficiency of Comparative Example 11 is slightly inferior to that of Example 1.

[0155] Comparative Examples 12 and 13, when the pH value is too high, gelatin is negatively charged above the isoelectric point, and electrostatic repulsion with sodium alginate causes shell delamination, and the core material leakage rate will greatly increase, thereby affecting the fire extinguishing efficiency; when the pH value is too low, it will promote the Al in the core material to 3+ Dissolution, and the -COO of sodium alginate - Pre-crosslinking occurs, resulting in droplet aggregation. At the same time, the positive charge of gelatin increases below the isoelectric point, and the positively charged Al 3+ It generates electrostatic repulsion, destroys the interface stability, reduces the forming rate, and thus affects the fire extinguishing efficiency.

[0156] Test Example 3:

[0157] In this test example, the fire extinguishing media prepared in Example 1 and Comparative Examples 1 to 13 were subjected to engineering fire extinguishing experimental tests.

[0158] (1) Analysis of open flame extinguishing: In order to establish a fire extinguishing efficiency evaluation system with more engineering guidance value, this study constructed an empirical research platform for battery boxes, as shown in the schematic diagram. Figure 8. According to the dynamic characteristics of thermal runaway process of lithium iron phosphate battery, Figure 9 The experiment demonstrated the typical evolution of combustion behavior without the application of a fire extinguishing agent. The experiment showed that when the heating plate continuously applied to the battery, heat accumulation triggered an internal exothermic chain reaction, leading to continuous vaporization of the electrolyte. Under the action of thermodynamic coupling, the battery's aluminum shell underwent plastic deformation and formed a localized bulge. The tab was ruptured by gas, and high-temperature combustible gas and electrolyte inside the battery spewed out from the breach. Upon contact with the ambient air, they deflagrated under the influence of the battery's high temperature. The aluminum-plastic film on the side of the battery was also torn, and jet flames were generated around the battery. About 25 seconds after the fire started, jet flames also appeared on the negative electrode side. Subsequently, the jet flames of combustible gas and electrolyte gradually weakened, leaving only a relatively stable flame on the upper surface of the battery. The entire combustion phase lasted about 52 seconds.

[0159] Figure 10 The effectiveness of a fire extinguishing agent (the material prepared in Example 1) in suppressing thermal runaway and combustion in lithium iron phosphate batteries was demonstrated. Experimental data showed that under continuous heat loading from the heating plate, heat accumulation within the battery triggered electrolyte vaporization, ultimately leading to safety valve failure and the release of highly concentrated flammable gases. Ignition of the flammable gases triggered intense combustion. At this point, the high-pressure gas system precisely released microencapsulated ammonium dihydrogen phosphate fire extinguishing agent, pushing the flames toward or beneath the battery, where they gradually diminished and ultimately extinguished. The flames were rapidly extinguished within 5 seconds. Continuous monitoring showed no rekindling within 10 minutes of extinguishing the fire.

[0160] Repeated experiments demonstrate that the fire extinguishing medium prepared in Example 1 of the present invention exhibits stable effectiveness, capable of suppressing flames within 5-7 seconds. Notably, the micron-sized droplets formed by the extinguishing agent create a physical barrier in the gas phase, effectively blocking the cascade reaction pathway leading to thermal runaway through a dual mechanism of heat absorption, cooling, and chemical free radical chain termination.

[0161] (2) Analysis of cooling effect: Temperature is a key thermodynamic parameter that characterizes the evolution of thermal runaway in lithium-ion batteries and the effectiveness of fire extinguishing agents. Its dynamic changes directly affect the assessment of heat spread risk and re-ignition probability. This experiment uses a thermocouple array (Tc1) arranged on the battery surface to monitor the evolution of the temperature field in real time, revealing the important role of the cooling performance of the fire extinguishing agent in suppressing secondary thermal runaway. The specific tests are shown in Table 2:

[0162] Table 2

[0163]

[0164] Taking Example 1 as an example for specific analysis, the monitoring data shows (such as Figure 11As shown in Figure 3, the battery surface temperature exhibited a multi-stage transition due to the coupling of external heating and internal exothermic reactions. Without the addition of a fire extinguishing agent, the thermal runaway phase reached a peak temperature of 394°C. However, the introduction of the GE-SA / NH₄H₂PO₄ microencapsulated fire extinguishing agent, through its unique physicochemical synergy, caused the temperature to plummet to 50°C, near room temperature, during the flame suppression phase. After the thermal runaway ceased, all dosage groups (0.25 kg, 0.50 kg, and 0.75 kg) accelerated system cooling.

[0165] Experiments confirm that the fire extinguishing agent prepared in this embodiment of the present invention possesses dual control advantages: during the gas-phase combustion phase, its high latent heat of vaporization enables rapid cooling and extinguishing of fires; during the solid-phase reaction phase, decomposition products form an isolation layer, inhibiting chain reactions. Dose-response analysis shows that for every 0.25 kg increase in extinguishing agent loading, the peak temperature decreases by 55-60°C, demonstrating a significant dose-response effect. Compared to traditional halogenated hydrocarbon fire extinguishing agents, this system demonstrates superior engineering applicability in blocking heat spread and preventing re-ignition.

[0166] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A microencapsulated composite fire extinguishing medium, characterized in that: The microencapsulated composite fire extinguishing medium includes a core layer and a shell layer, wherein the core layer is composed of an NH4H2PO4 solution and Al(OH)3, and the shell layer is a pH-responsive wall material formed by cross-linking gelatin and sodium alginate; wherein the mass ratio of the NH4H2PO4 solution to Al(OH)3 is 10-12:1; the mass ratio of the gelatin to sodium alginate is 7-8:4-6; and the mass ratio of the NH4H2PO4 solution in the core layer to the shell layer is 3-4:

1.

2. The microencapsulated composite fire extinguishing medium according to claim 1, characterized in that: The thickness of the shell layer is 50-150 nm, and the trigger release temperature is >125°C.

3. The microencapsulated composite fire extinguishing medium according to claim 1, wherein: The mass ratio of the NH4H2PO4 solution of the core layer to the wall material of the shell layer is 4:

1.

4. A method for preparing the microencapsulated composite fire extinguishing medium according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, mixing gelatin solution, sodium alginate solution, NH4H2PO4 solution, Al(OH)3 modifier and emulsifier to emulsify and react to obtain a stable emulsion; S2, adding glacial acetic acid solution to the emulsion to adjust the pH and perform a coagulation reaction; S3. Add a curing agent to the reaction mixture obtained in step S2, adjust the pH, perform a curing reaction, and perform post-processing to obtain a microencapsulated ammonium phosphate salt solution composite fire extinguishing medium.

5. The preparation method according to claim 4, wherein In step S1, the concentration of the gelatin solution is 7-8 wt %, the concentration of the sodium alginate solution is 4-6 wt %, and the concentration of the emulsifier is 1-2 wt %.

6. The preparation method according to claim 4, wherein In step S1, the emulsifier is selected from one or more of sodium dodecylbenzenesulfonate, OP-10, FSN-100, and Span-80; The emulsification reaction temperature is 24-26° C., the time is 10-15 min, and the emulsification speed is 750-850 rpm.

7. The preparation method according to claim 4, wherein In step S2, the concentration of the glacial acetic acid solution is 8-12 wt%, and the pH is adjusted in the range of 3.8-4.0; the temperature of the coagulation reaction is 40-45° C., and the time is 10-20 min.

8. The preparation method according to claim 4, wherein In step S3, the curing agent is selected from one or more of ethylenediamine, glutaraldehyde, diethylenetriamine, and dicyandiamide, the concentration of the curing agent is 23-26 wt%, and the pH is adjusted in the range of 7-10.

9. The preparation method according to claim 4, wherein In step S3, the post-treatment includes filtering, washing and drying the microcapsule precipitate obtained by the curing reaction in sequence.

10. Use of the microencapsulated composite fire extinguishing medium according to any one of claims 1 to 3 in suppressing thermal runaway of lithium batteries or fires of hazardous chemicals.

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