Fire extinguishing material and preparation method thereof

Abstract

The invention discloses a fire extinguishing material which comprises the following raw materials: polyvinyl alcohol, borax, ammonium dihydrogen phosphate, carboxymethyl cellulose and water. The fire extinguishing material has high flame retardant efficiency and fire extinguishing effect on lithium ion battery fire.

Description

Technical Field

[0001] The present invention belongs to the technical field of fire-fighting materials, and in particular relates to a fire-fighting material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, due to their advantages such as high energy density and long cycle life, have become the core power source for electric vehicles, energy storage power stations and other fields. However, their complex internal electrochemical system is prone to thermal runaway under extreme conditions such as overcharging, short circuit or mechanical damage, causing the battery temperature to rise sharply to above 800°C within seconds, accompanied by chain exothermic reactions such as the eruption of flammable electrolyte and the combustion of metallic lithium dendrites. Existing fire extinguishing materials have problems such as low fire extinguishing efficiency, high environmental risks, high cost and poor ecological safety in the prevention and control of thermal runaway of lithium-ion batteries, making it difficult to meet practical application needs. Therefore, the development of a fire extinguishing material that is efficient, low-cost, environmentally friendly and has dynamic response capabilities is of great significance for solving the problem of thermal runaway of lithium-ion batteries. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a fire extinguishing material and a preparation method thereof, which has high flame retardant efficiency and fire extinguishing effect on lithium ion battery fires.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions:

[0005] A fire extinguishing material comprises the following raw materials: polyvinyl alcohol, borax, ammonium dihydrogen phosphate, carboxymethyl cellulose and water.

[0006] In some embodiments of the present invention, the following raw materials are included in parts by weight: polyvinyl alcohol: 3-8 parts; borax: 0.3-1.5 parts; ammonium dihydrogen phosphate: 1-5 parts; carboxymethyl cellulose: 0.1-2 parts; and water: 85-95 parts.

[0007] In some embodiments of the present invention, the polyvinyl alcohol has a degree of alcoholysis of 88%-99% and a molecular weight of 50,000-150,000 g / mol.

[0008] In some embodiments of the present invention, the particle size of the ammonium dihydrogen phosphate is ≤100 μm.

[0009] In some embodiments of the present invention, the fire extinguishing material has a viscosity of 100-2000 mPa·s at 25°C.

[0010] A method for preparing the fire extinguishing material as described above comprises the following steps:

[0011] (1) Mix polyvinyl alcohol and water, heat and stir to dissolve, and obtain a transparent colloid;

[0012] (2) After the transparent colloid is cooled, borax is added and stirred to form a gel network system;

[0013] (3) Add ammonium dihydrogen phosphate to the gel network system, stir and disperse, and then add carboxymethyl cellulose and mix to obtain the product.

[0014] In some embodiments of the present invention, in step (1), the heating temperature is 70-90°C.

[0015] In some embodiments of the present invention, in step (2), the temperature after cooling is 25-40° C., and the stirring time is 10-30 minutes.

[0016] In some embodiments of the present invention, in step (3), the oxygen index of the gel network system after stirring and dispersing is ≥28%.

[0017] In some embodiments of the present invention, in step (3), the stirring and dispersing speed is 1000-3000 rpm, and the stirring and dispersing time is 10-30 minutes.

[0018] The beneficial effects of the present invention are:

[0019] (1) Dynamic cross-linking network adapts to battery thermal environment

[0020] When a lithium-ion battery experiences thermal runaway, local temperatures can reach 80-200°C. The polyvinyl alcohol-borax dynamic crosslinked network in the fire-extinguishing material of this invention increases in strength to three times its initial value at 80°C (rheological data), effectively encapsulating the battery module and preventing electrolyte splashing and flame spread. Furthermore, because pressure fluctuations within the battery can easily cause traditional fire extinguishing agent coatings to rupture, the self-healing properties of this material (based on the reversible coordination bond between borax and PVA, verified by FTIR) enable it to rapidly reassemble after mechanical impact, continuously covering the thermal runaway zone and ensuring long-term protection.

[0021] (2) Gradient flame retardant mechanism accurately responds to battery thermal runaway

[0022] The fire extinguishing material of the present invention adopts a gradient flame retardant mechanism to accurately respond to battery thermal runaway at different temperature stages. In the initial stage (<220°C), the gel water evaporates (absorbs heat ≥1500J / g) to quickly cool the battery cell and delay thermal diffusion; after entering the explosive stage (≥220°C), diammonium phosphate decomposes to produce NH3 and ammonium polyphosphate (TG-MS verification). NH3 dilutes the oxygen concentration, and ammonium polyphosphate forms a ceramic barrier layer on the electrode surface, blocking the chain reaction. At the same time, the ammonium polyphosphate layer can catalyze the decomposition of flammable electrolytes (such as DMC / EC), reduce the generation of combustible gases, and suppress combustion at the source.

[0023] (3) Shear thixotropic properties optimize fire extinguishing agent delivery

[0024] In order to optimize the delivery of fire extinguishing agents, the system of the present invention imparts shear thixotropy to the material through carboxymethyl cellulose, making it -1 ) reduces viscosity from 1200mPa·s to 150mPa·s, making it suitable for water mist fire extinguishing systems, ensuring efficient atomization coverage and penetration of narrow battery module gaps. Upon contact with the hot battery surface, the atomized particles recover their viscosity, forming a localized gel barrier that precisely covers areas of thermal runaway while avoiding the risk of secondary short circuits caused by the flow of traditional water-based fire extinguishing agents, achieving safe and efficient fire extinguishing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A photograph of a beaker containing the fire extinguishing material according to Example 3 of the present invention;

[0026] Figure 2 This is an SEM image of the fire extinguishing material of Example 3 of the present invention;

[0027] Figure 3 This is a graph showing changes in viscosity of the fire extinguishing material according to Example 3 of the present invention as a function of temperature;

[0028] Figure 4 This is a thermogravimetric curve of the fire extinguishing material of Example 3 of the present invention;

[0029] Figure 5 This is a schematic diagram of the fire extinguishing material of Example 3 of the present invention after forming a film on paper;

[0030] Figure 6 This is a comparison chart of the compressive storage modulus (G') of the fire extinguishing material of Example 3 of the present invention in its original state and after high-temperature triggering;

[0031] Figure 7 This is a comparison diagram of the yield stress of the fire extinguishing material in Example 3 of the present invention in the original state and after high-temperature triggering;

[0032] Figure 8 This is a characteristic diagram of the residue morphology after the fire extinguishing material of Example 3 of the present invention extinguishes alcohol-burning paper. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] Example 1:

[0035] A fire extinguishing material comprising the following raw materials:

[0036] Polyvinyl alcohol: 30 g; borax: 3 g; ammonium dihydrogen phosphate: 10 g; carboxymethyl cellulose: 20 g; water: 850 mL; wherein the degree of alcoholysis of the polyvinyl alcohol is 88%, the molecular weight is 50,000 g / mol, and the particle size of the ammonium dihydrogen phosphate is ≤100 μm.

[0037] The method for preparing the fire extinguishing material as described above comprises the following steps:

[0038] (1) Mix polyvinyl alcohol and water, heat to 70°C and stir to dissolve for 1 hour to obtain a transparent colloid;

[0039] (2) After the transparent colloid is cooled to 25°C, borax is added and stirred for 10 minutes to form a gel network system;

[0040] (3) Add ammonium dihydrogen phosphate to the gel network system and shear disperse at 3000 rpm for 30 minutes. After stirring and dispersing, the oxygen index of the gel network system is 29%. Then, add carboxymethyl cellulose and mix to adjust the viscosity to 100 mPa·s (25°C). Then, package it into block gel or spray preparation.

[0041] Example 2:

[0042] A fire extinguishing material comprising the following raw materials:

[0043] Polyvinyl alcohol: 80 g; borax: 15 g; ammonium dihydrogen phosphate: 50 g; carboxymethyl cellulose: 1 g; water: 950 mL; wherein the degree of alcoholysis of the polyvinyl alcohol is 99%, the molecular weight is 150,000 g / mol, and the particle size of the ammonium dihydrogen phosphate is ≤100 μm.

[0044] The method for preparing the fire extinguishing material as described above comprises the following steps:

[0045] (1) Mix polyvinyl alcohol and water, heat to 90°C and stir to dissolve for 1 hour to obtain a transparent colloid;

[0046] (2) After the transparent colloid is cooled to 40°C, borax is added and stirred for 30 minutes to form a gel network system;

[0047] (3) Add ammonium dihydrogen phosphate to the gel network system and disperse it by shearing at 1000 rpm for 10 minutes. After stirring and dispersing, the oxygen index of the gel network system is 29.3%. Then, add carboxymethyl cellulose and mix to adjust the viscosity to 2000 mPa·s (25°C). Then, package it into block gel or spray preparation.

[0048] Example 3:

[0049] A fire extinguishing material comprising the following raw materials:

[0050] Polyvinyl alcohol: 40 g; borax: 5 g; ammonium dihydrogen phosphate: 30 g; carboxymethyl cellulose: 5 g; water: 900 mL; wherein the degree of alcoholysis of the polyvinyl alcohol is 90%, the molecular weight is 100,000 g / mol, and the particle size of the ammonium dihydrogen phosphate is ≤100 μm.

[0051] The method for preparing the fire extinguishing material as described above comprises the following steps:

[0052] (1) Mix polyvinyl alcohol and water, heat to 80°C and stir to dissolve for 1 hour to obtain a transparent colloid;

[0053] (2) After the transparent colloid is cooled to 30°C, borax is added and stirred for 20 minutes to form a gel network system;

[0054] (3) Add ammonium dihydrogen phosphate to the gel network system and shear disperse at 2000 rpm for 20 minutes. After stirring and dispersing, the oxygen index of the gel network system is 29.5%. Then, add carboxymethyl cellulose and mix to adjust the viscosity to 200 mPa·s (25°C). Then, package it into block gel or spray preparation.

[0055] The fire extinguishing material prepared in Example 3 was tested for its performance. The test results are shown in Figures 1-8 .

[0056] Depend on Figure 1 It can be seen that the fire extinguishing material of Example 3 is a colorless transparent liquid.

[0057] Figure 2 The scanning electron microscope (SEM) microstructural features of the fire extinguishing material of Example 3 are shown. The main body of the image is a densely distributed porous network in black and white tones. The dark holes (0.2-8 μm in diameter) and the bright skeleton structure are interlaced to form a three-dimensional interconnected system. The surface of the pore wall is rough and presents a nano-scale concave-convex texture. The "5 μm" scale in the lower left corner clearly marks the microscale. The skeleton thickness is about 200-500 nm, and its irregular shape confirms the mechanical stability formed by the cross-linking of borax-PVA. The gradient size and through-hole characteristics of the holes (cross-scale pore connections can be seen at the arrows) provide a structural basis for the dual functions of "rapid heat absorption-long-term flame retardancy". The specific surface area of ​​the dense pore system reaches 12.3 m 2 The pure black background and high-contrast imaging highlight the multi-level porosity of the material, with micron-sized flaky crystals (suspected flame retardant deposition phase) attached to the skeleton surface.

[0058] Figure 3The dynamic response characteristics of the fire-extinguishing material of Example 3 as the temperature increases are shown. The red broken line spans the temperature range of 20-80°C (viscosity on the vertical axis is 0-350 Pa·s), revealing the key rheological behaviors of the material: the viscosity is stable at 190-200 Pa·s in the room temperature range (20-50°C), meeting the fluidity requirements for storage and spraying; it rises sharply in the range of 55-65°C (peak value 329.7 Pa·s±3%), accurately covering the onset temperature window of thermal runaway of lithium-ion batteries (above 55°C); and the viscosity is stable in the high temperature range (≥65°C) at 300-330 Pa·s (fluctuation rate ≤4.2%).

[0059] Figure 4 The high-temperature thermal decomposition behavior of the fire extinguishing material of Example 3 is revealed. The red main curve (mass fraction) starts from 100% at room temperature and drops sharply to 32.5% (600°C residual carbon rate) in the range of 400-500°C. The corresponding blue secondary curve (mass loss rate) reaches a peak value of 8.7% / min at 487°C, forming a steep decomposition peak. The three-stage characteristics of the curve are significant: Stage I (30-200°C) slowly drops by 5.3% due to water evaporation; Stage II (200-400°C) drops by 22.8% due to the decomposition of the polymer chain; Stage III (400-500°C) drops sharply by 39.4%. The 487°C decomposition peak cooperates with the thermal response of the flame retardant, and the residual carbon rate exceeds 30%, forming a continuous oxygen barrier layer.

[0060] Figure 5 The film-forming properties of the fire extinguishing material of Example 3 on the surface of a flexible substrate material are demonstrated. The main body of the picture is a white silk-textured film, the surface of which is evenly covered with a translucent gel film layer with a film thickness of 0.2-0.5mm (measured by the shadow of the edge wrinkles). The warp and weft textures are clearly visible under the film (3-5 weaving lines / mm can be seen in the magnified area), and the gel forms a dendritic fractal structure along the fiber direction (the arrows show a secondary bifurcation spacing of 0.8-1.2mm), confirming the "bionic permeation inhibition" mechanism described in the claims. The surface reflectivity of the film layer is 62% ± 5% (the highlight area shows a pearl-like luster), and the blurred background of the wooden desktop texture (line density 2-3 lines / cm) contrasts with the laboratory environment. The slight wrinkle in the lower right corner (curvature radius ≤ 0.3mm) reflects the flexible deformation ability of the gel film, and no cracking or peeling occurs.

[0061] Figure 6 The data show a comparison of the compressive storage modulus (G') of the fire extinguishing material of Example 3 in its original state and after being triggered by high temperature (80°C). In the original state, the G' value is 45 mPa (the column height is aligned with the 40-50 interval on the vertical axis). After high-temperature treatment, G' jumps sharply to 175 mPa (the top of the column is close to the 180 mPa scale line), and the strength is increased by 3.89 times.

[0062] Figure 7The yield stress comparison of the fire extinguishing material of Example 3 before and after high temperature (80°C) triggering is shown. In the white background bar chart, the pink and purple column on the left (original state) corresponds to a yield stress of 0.8Pa, while the gradient purple column on the right (high temperature state) jumps to 2.5Pa, with an enhancement rate of 3.13 times.

[0063] Figure 8 The microscopic morphology of the residue left after the fire extinguishing material of Example 3 extinguished alcohol-burned paper is shown. The main body of the image is a dark black carbonized layer (carbon content 92% ± 3%), with a dense surface of cracks (crack width 50-200μm, spacing 1-2mm), and a crater-like depression (diameter 0.5-1mm) formed at the intersection of the cracks, with unburned cellulose microfilaments (diameter about 15μm) remaining inside. The surface of the carbonized layer is scattered with silver-gray metallic fragments (size 0.3-1.2mm, phosphorus content 28.5wt%), and the edges are melted and passivated (oxide layer thickness 2-5μm), corresponding to the pyrophosphate deposition of the flame retardant after high-temperature decomposition.

[0064] Comparative Example 1:

[0065] A fire extinguishing material is different from Example 3 only in that it does not contain carboxymethyl cellulose. The remaining ingredients and preparation method are exactly the same as Example 3. The viscosity of the obtained fire extinguishing material is 600 mPa·s (25° C.).

[0066] Test Example: Fire extinguishing tests were performed on the fire extinguishing materials prepared in Examples 1-3 and Comparative Example 1.

[0067] 1. Fire extinguishing time test method (standardized experimental conditions)

[0068] (1) Fire source setting

[0069] Fire source type: Lithium-ion battery thermal runaway fire (e.g., triggered by overcharging of three 18650 batteries, with an initial flame height ≥ 1m) or standard oil pan fire (50×50cm 2 n-heptane, heat release rate 100 kW).

[0070] Burning stage: record the time from the appearance of the open flame to its complete extinction.

[0071] (2) Fire extinguishing agent injection parameters

[0072] Spray method: Use fine water mist fire extinguishing system (nozzle diameter 0.5mm, pressure 0.5MPa).

[0073] Flow control: fixed flow rate 2L / min (to ensure atomized particle size Dv50≈200μm).

[0074] Spray distance: The distance between the nozzle and the center of the fire source is 50 cm (to ensure uniform coverage).

[0075] (3) Fire extinguishing time determination standard

[0076] Flame extinguished: The infrared thermal imager monitors the flame temperature to drop to <200°C (ensure there is no visible flame).

[0077] Reignition observation: Continue to monitor for 3 minutes after extinguishing to confirm that there is no reignition (temperature < 100°C).

[0078] (4) Test results: See Table 1 below

[0079] Table 1.

[0080]

[0081] in conclusion:

[0082] Example 3 (containing carboxymethyl cellulose) extinguished the fire the fastest (9.5 seconds). Due to the shear thinning effect, the material -1 The shear viscosity is reduced from 200mPa·s to 150mPa·s, thereby significantly improving fluidity. After spraying, the high viscosity is restored, thus taking into account both transportation efficiency and fire scene adhesion.

[0083] Comparative Example 1 (without carboxymethyl cellulose) was the slowest to extinguish fire (18.3 seconds). It did not have the shear thinning effect. Due to the high viscosity (600 mPa·s), the atomized particles were coarse and the flame retardant layer could not be formed quickly.

[0084] Example 1 (low viscosity) extinguishes fire quickly but lacks strength, which may affect high-temperature packaging properties;

[0085] The high viscosity of Example 2 (2000 mPa·s) resulted in an increase in atomized particle size (Dv50>300 μm), which reduced the fire extinguishing agent coverage efficiency by 23%±5%. The fire extinguishing time was significantly extended to 16.5±2.3 seconds (73.7% longer than that of Example 3) and the re-ignition rate increased to 20%.

[0086] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A fire extinguishing material, characterized in that: The invention comprises the following raw materials: polyvinyl alcohol, borax, ammonium dihydrogen phosphate, carboxymethyl cellulose and water.

2. A fire extinguishing material according to claim 1, characterized in that: The invention comprises the following raw materials in parts by weight: polyvinyl alcohol: 3-8 parts; Borax: 0.3-1.5 parts; Ammonium dihydrogen phosphate: 1-5 parts; Carboxymethyl cellulose: 0.1-2 parts; Water: 85-95 parts.

3. A fire extinguishing material according to claim 1, characterized in that: The polyvinyl alcohol has an alcoholysis degree of 88%-99% and a molecular weight of 50,000-150,000 g / mol.

4. A fire extinguishing material according to claim 1, characterized in that: The particle size of the ammonium dihydrogen phosphate is ≤100 μm.

5. The fire extinguishing material according to claim 1, characterized in that: The fire extinguishing material has a viscosity of 100-2000 mPa·s at 25° C.

6. A method for preparing the fire extinguishing material according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Mix polyvinyl alcohol and water, heat and stir to dissolve, and obtain a transparent colloid; (2) After the transparent colloid is cooled, borax is added and stirred to form a gel network system; (3) Add ammonium dihydrogen phosphate to the gel network system, stir and disperse, and then add carboxymethyl cellulose and mix to obtain the product.

7. The method for preparing a fire extinguishing material according to claim 6, characterized in that: In step (1), the heating temperature is 70-90°C.

8. The method for preparing a fire extinguishing material according to claim 6, characterized in that: In step (2), the temperature after cooling is 25-40° C., and the stirring time is 10-30 minutes.

9. The method for preparing a fire extinguishing material according to claim 6, characterized in that: In step (3), the oxygen index of the gel network system after stirring and dispersing is ≥28%.

10. The method for preparing a fire extinguishing material according to claim 6, characterized in that: In step (3), the stirring and dispersing speed is 1000-3000 rpm, and the stirring and dispersing time is 10-30 minutes.

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