Dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries and its preparation method

Abstract

This invention discloses a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, and its preparation method, relating to the field of battery fire prevention and extinguishing technology. The method includes: firstly, adding phytic acid solution to an ammonium polyphosphate suspension for reaction; then, centrifuging, washing, and vacuum drying the resulting reaction solution to obtain an ammonium polyphosphate-phytic acid polymer; next, adding N,N′-methylenebisacrylamide and azobisisobutyronitrile to an N-isopropylacrylamide solution, reacting the resulting mixture to form a transparent gel, and post-processing to obtain powdered polyN-isopropylacrylamide; adding nano-silica, the ammonium polyphosphate-phytic acid polymer, and polyN-isopropylacrylamide to a methylcellulose solution to obtain a mixed solution; finally, adding sodium polyacrylate and magnesium chloride hexahydrate, and stirring at room temperature to obtain the final product. The dual-network temperature-sensitive nanohydrogel prepared by this invention exhibits high thermal stability.

Description

Technical Field

[0001] This invention relates to the field of battery fire prevention and extinguishing technology, specifically to a dual-network temperature-sensitive nanohydrogel for fire extinguishing and preventing reignition in lithium iron phosphate batteries and its preparation method. Background Technology

[0002] With the miniaturization of electronic devices, the widespread adoption of electric vehicles, and the development of large-scale energy storage systems, lithium-ion batteries, with their advantages of high energy density, long cycle life, and low self-discharge rate, have become one of the most promising energy storage devices today. From everyday electronic devices like smartphones and laptops to high-end fields such as new energy vehicles and aerospace, lithium-ion batteries are ubiquitous. However, lithium battery energy storage systems face the risks of thermal runaway and fire throughout their entire lifecycle. Compared to traditional fires, the main challenges in extinguishing these fires are: firstly, lithium battery fires are gas-liquid composite combustions that spread rapidly, and the high power of the fire source in megawatt-hour systems makes rapid extinguishing difficult; secondly, lithium battery thermal runaway is an electrochemical reaction that can spontaneously continue, making it difficult to prevent reignition after extinguishing. Therefore, efficient fire extinguishing technology for lithium battery energy storage systems has become a research hotspot for scholars both domestically and internationally in recent years.

[0003] Currently, fire extinguishing materials for lithium-ion batteries mainly include water-based fire extinguishing agents, gaseous fire extinguishing agents, and dry powder fire extinguishing agents. Among them, water-based fire extinguishing agents are the most widely used because water has a high specific heat capacity, can quickly absorb a large amount of heat, has the best cooling capacity, and can effectively inhibit further temperature rise of the battery. Furthermore, some water-based fire extinguishing agents are environmentally friendly and non-toxic. However, water has poor insulation properties, which can cause short circuits in the battery module, leading to secondary disasters, and its fire extinguishing efficiency is hindered by obstacles. Gaseous fire extinguishing agents, such as perfluorohexanone, mainly extinguish fires through an endothermic mechanism, resulting in high fire extinguishing efficiency, but they are expensive and produce toxic byproducts (HF) at high temperatures, posing a danger to human health and equipment safety. Dry powder fire extinguishing agents can quickly extinguish open flames, are inexpensive, and have a wide range of applications, but they cannot lower the internal temperature of lithium batteries, and their use causes serious pollution, damaging normal batteries and requiring timely cleanup. Therefore, developing a fire extinguishing material with high fire extinguishing efficiency and preventing reignition is crucial. Hydrogels, as a highly hydrophilic three-dimensional network structure, are generally divided into synthetic polymer hydrogels and natural polymer hydrogels. As a type of water-based fire extinguishing agent, it has strong water absorption and water-binding properties, which can prolong the residence time of water, rapidly cool down the temperature, and has the functions of oxygen isolation and sealing, which can effectively improve the utilization rate of water and the fire extinguishing effect.

[0004] However, existing hydrogel technologies still suffer from poor high-temperature stability. For example, hydrogels have poor high-temperature resistance. When lithium iron phosphate batteries experience thermal runaway, the temperature becomes extremely high, exceeding the hydrogel's tolerance limit. The hydrogel decomposes and loses moisture at high temperatures, thus affecting its ability to extinguish fires and prevent reignition.

[0005] Therefore, the high-temperature resistance of hydrogels in the existing technology still needs to be further improved. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, which has high thermal stability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, comprising the following steps:

[0009] a. Add phytic acid solution to ammonium polyphosphate suspension, adjust pH to 4, stir at a certain temperature, collect the precipitate by centrifugation, and obtain powdered ammonium polyphosphate-phytic acid polymer after washing, vacuum drying and grinding.

[0010] b. Add N,N′-methylenebisacrylamide and azobisisobutyronitrile to the N-isopropylacrylamide solution respectively, react the resulting mixture at a certain temperature to form a transparent gel, cut it into pieces, freeze-dry it, and grind it to obtain poly-N-isopropylacrylamide in powder form.

[0011] c. Simultaneously add nano-silica and ammonium polyphosphate-phytic acid polymer to the methylcellulose solution, then add the aforementioned polyN-isopropylacrylamide to the resulting mixed solution, and stir at room temperature; in the methylcellulose solution, the mass-to-volume ratio of methylcellulose to water is 0.012 g / mL; the mass ratio of methylcellulose to nano-silica is 27:1; the mass ratio of methylcellulose to ammonium polyphosphate-phytic acid polymer is 0.2:1; and the mass ratio of methylcellulose to polyN-isopropylacrylamide is 0.28:1.

[0012] d. Add sodium polyacrylate and magnesium chloride hexahydrate to the mixed solution obtained in step c, and stir at room temperature to obtain a double-grid thermosensitive nanohydrogel.

[0013] The above-mentioned method for preparing a dual-grid temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, in step a, the preparation step of the ammonium polyphosphate suspension is as follows: ammonium polyphosphate is dispersed in deionized water and ultrasonically treated at 50-70℃ for 30 min to obtain the ammonium polyphosphate suspension; the mass-volume ratio of ammonium polyphosphate to deionized water is 0.05 g / mL.

[0014] In the preparation method of the above-mentioned dual-grid temperature-sensitive nanohydrogel for fire extinguishing and re-ignition prevention in lithium iron phosphate batteries, in step a, the phytic acid solution is obtained by diluting 2g of phytic acid with 50mL of deionized water; stirring in a constant temperature water bath at 50-70℃ for 3-5h; centrifuging for 10min; and washing the precipitate with ethanol to remove unreacted phytic acid.

[0015] In the preparation method of the above-mentioned dual-grid temperature-sensitive nanohydrogel for fire extinguishing and re-ignition prevention in lithium iron phosphate batteries, in step a, the vacuum drying temperature is 50-70℃, the vacuum drying time is 24h, and the material is ground through a 200-mesh sieve.

[0016] In the preparation method of the above-mentioned dual-grid temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, in step b, the N-isopropylacrylamide solution is prepared by dissolving 5g of N-isopropylacrylamide in 100mL of deionized water and purging with nitrogen for 10-20min to remove oxygen.

[0017] The preparation method of the above-mentioned dual-grid temperature-sensitive nanohydrogel for fire extinguishing and re-ignition prevention in lithium iron phosphate batteries is characterized by: adding 0.05g of N,N′-methylenebisacrylamide and 0.1g of azobisisobutyronitrile to an N-isopropylacrylamide solution, and reacting the resulting mixture in a water bath at 50-70°C for 2-4 hours to form a transparent gel.

[0018] In the preparation method of the above-mentioned dual-network temperature-sensitive nanohydrogel for fire extinguishing and re-ignition prevention in lithium iron phosphate batteries, in step d, 1.1g of sodium polyacrylate and 6g of magnesium chloride hexahydrate are added to the mixed solution obtained in step c, and stirred at room temperature for 1-3h.

[0019] Another objective of this invention is to provide a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries.

[0020] Another objective of this invention is to provide the application of the aforementioned dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries. When a lithium iron phosphate battery catches fire, the fire extinguishing process of the dual-network temperature-sensitive nanohydrogel is divided into three stages: the first stage: the evaporation of water and the transformation from sol to gel absorb heat and dissipate some of the heat generated by thermal runaway; the second stage: the decomposition of ammonium polyphosphate at high temperature to produce ammonia gas, which dilutes some of the flammable gas generated by thermal runaway and reduces the fire intensity; the third stage: magnesium chloride catalyzes the formation of a char layer by the L-glucan in methylcellulose, preventing reignition.

[0021] The fire extinguishing mechanism of the dual-network temperature-sensitive nano-hydrogel of this invention is as follows:

[0022] Based on the synergistic effect of multiple components: At the free radical level, the polyphosphoric acid produced by the high-temperature decomposition of polyphosphoric acid can effectively capture free radicals (such as ·OH, ·H) in the combustion chain reaction, inhibiting the spread of fire; at the same time, the ammonia (NH3) released by the decomposition of APP acts as an inert gas to dilute the combustible gases (such as H2, CO) produced by the decomposition of the electrolyte, reducing the combustion intensity. In terms of cooling, the temperature-sensitive poly(N-isopropylacrylamide) network undergoes a phase change at 60–80℃, rapidly releasing moisture, and significantly reducing the battery temperature through evaporative cooling (20.5% lower than pure water). Regarding the electrolyte, phytic acid can react with lithium salts (such as LiPF6) in the lithium iron phosphate battery electrolyte to form a stable lithium phosphate layer, blocking the continuous decomposition of the electrolyte. Furthermore, Mg... 2+ Catalyzing the dehydration and crosslinking of methylcellulose, it synergistically forms a dense char layer (char residue >35%) with APP / PA, achieving long-term anti-reignition by physically isolating oxygen and blocking heat transfer. This multi-synergistic mechanism of "free radical capture - gas dilution - evaporative cooling - electrolyte stabilization - high char barrier" effectively solves the dual challenges of rapid fire extinguishing and long-term protection in lithium iron phosphate battery fires.

[0023] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0024] This invention provides a dual-network temperature-sensitive nano-hydrogel for lithium-ion battery fires, aiming to avoid economic damage and protect personnel safety in such fires. The fire-extinguishing hydrogel uses N-isopropylacrylamide as a monomer and methylcellulose (MC) and sodium polyacrylate (PAAS) as matrices. The MC molecular chain has numerous hydroxyl groups, while the PAAS molecular chain has carboxyl groups and carboxyl anions resulting from carboxyl dissociation. The hydroxyl groups can form hydrogen bonds with the carboxyl groups or carboxyl anions, causing the molecular chains of methylcellulose and sodium polyacrylate to approach and entangle, initially constructing the basic framework of a three-dimensional network. This hydrogen bonding enhances the interaction between the two polymers, providing stability and flexibility for the hydrogel formation. Magnesium chloride acts as a bridge between methylcellulose and sodium polyacrylate. Magnesium ions bind to the hydroxyl groups of methylcellulose through coordination and to the carboxyl anions of sodium polyacrylate through ionic bonds, thus connecting the networks of methylcellulose and sodium polyacrylate to form a more complex, complete, and stable three-dimensional network structure, greatly enhancing the overall performance of the hydrogel. Nano-SiO2 is uniformly dispersed in the structure and forms a composite hydrogel through physical cross-linking. The ammonium polyphosphate (APP) and phytic acid (PA) composite mainly plays a flame-retardant role. In the event of a lithium-ion battery fire, the working mechanism of the fire-extinguishing hydrogel mainly consists of three stages: First, the evaporation of water and the transition from sol to gel absorb heat, carrying away some of the heat generated during the heating process and thermal runaway; second, the decomposition of ammonium polyphosphate at high temperature produces ammonia gas, diluting some of the flammable gases generated by thermal runaway and reducing the fire intensity; third, magnesium chloride catalyzes the formation of a char layer from the L-glucan in methylcellulose, preventing reignition. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings:

[0026] Figure 1 This is a flowchart illustrating the preparation process of the dual-grid temperature-sensitive nanohydrogel of the present invention.

[0027] Figure 2 This is a diagram of the fire extinguishing test apparatus used in this invention;

[0028] Figure 3 (a) is a scanning electron microscope image of the thermosensitive nanohydrogel of the present invention, and (b) is a magnified view of (a).

[0029] Figure 4 This is the thermogravimetric curve of the temperature-sensitive nanohydrogel of the present invention;

[0030] Figure 5 , Figure 6 HRR and mass change curves for thermosensitive nanohydrogel samples with different contents;

[0031] Figure 7 The THR variation curves of thermosensitive nanohydrogel samples with different contents are shown.

[0032] Figure 8 EHC variation curves for thermosensitive nanohydrogel samples with different contents;

[0033] Figure 9 The CO release rate curves of thermosensitive nanohydrogel samples with different contents are shown.

[0034] Figure 10 The CO2 release rate curves of thermosensitive nanohydrogel samples with different contents are shown.

[0035] Figure 11 Temperature change curve of lithium-ion battery body when extinguishing fire with pure aqueous solution;

[0036] Figure 12 Temperature change curve of the battery body when using nano-hydrogel solution to extinguish lithium-ion battery fire;

[0037] Figure 13 This is a diagram illustrating the fire extinguishing mechanism of the temperature-sensitive nano-hydrogel of this invention. Detailed Implementation

[0038] This invention proposes a dual-network temperature-sensitive nano-hydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries and its preparation method. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be further described below with reference to specific embodiments.

[0039] All the raw materials mentioned in this invention can be purchased through commercial channels.

[0040] Example 1:

[0041] like Figure 1 As shown, a method for preparing a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries includes the following steps:

[0042] Step 1: Disperse 10g of ammonium polyphosphate in 200mL of deionized water and sonicate at 60℃ for 30min to obtain an ammonium polyphosphate suspension. Dilute 2g of phytic acid with 50mL of deionized water and slowly add it dropwise to the ammonium polyphosphate suspension. Adjust the pH to 4 and stir in a constant temperature water bath at 60℃ for 4h. Centrifuge the resulting reaction solution at 8000rpm for 10min, discard the supernatant, wash the precipitate three times with anhydrous ethanol to remove unreacted phytic acid, and then vacuum dry at 60℃ for 24h. Grind the precipitate through a 200-mesh sieve to obtain a light yellow powder of ammonium polyphosphate-phytic acid polymer.

[0043] Step 2: Dissolve 5g of N-isopropylacrylamide in 100mL of deionized water, purge with nitrogen for 15min to remove oxygen, obtaining an N-isopropylacrylamide solution. Add 0.05g of N,N′-methylenebisacrylamide and 0.1g of azobisisobutyronitrile to the N-isopropylacrylamide solution, and react the resulting mixture in a 60℃ water bath for 3h to form a transparent gel. Cut the gel into pieces, freeze-dry, and grind to obtain poly-N-isopropylacrylamide in powder form.

[0044] Step 3: Add 0.0442g of nano-silica and 6g of ammonium polyphosphate-phytic acid polymer to the methylcellulose solution at the same time. Add 4.25g of poly-N-isopropylacrylamide to the resulting mixed solution and stir thoroughly on a magnetic stirrer for 30 minutes at room temperature.

[0045] Step 4: Add 1.1g of sodium polyacrylate and 6g of magnesium chloride hexahydrate to the mixed solution obtained in Step 3, and stir thoroughly on a magnetic stirrer at room temperature for 2 hours to obtain a dual-network thermosensitive nanohydrogel.

[0046] Figure 3 Image (a) is a scanning electron microscope (SEM) image of the thermosensitive nanohydrogel in this embodiment, and image (b) is a magnified view of a portion of image (a). The matrix of the dual-network thermosensitive nanohydrogel prepared in this embodiment is methylcellulose and sodium polyacrylate, and the monomer is N-isopropylacrylamide. The poly(N-isopropylacrylamide) network is combined with the methylcellulose / sodium polyacrylate network to form a dynamically responsive dual-network structure. Mg 2+ Simultaneously with PAAS's -COO - Phytic acid coordinates with the -OH group of MC to form an ionic cross-linked network, which interpenetrates with the chemical cross-linked network of poly(N-isopropylacrylamide), significantly improving mechanical strength. In addition, phytic acid and ammonium polyphosphate are bonded through phosphate groups to form an ammonium polyphosphate-phytic acid complex, increasing the thermal decomposition temperature of the hydrogel. Multiple phosphate groups of phytic acid interact with Mg... 2+ Synergistically, it promotes the cross-linking of L-glucan during combustion, thereby increasing the char residue.

[0047] Example 2:

[0048] A method for preparing a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, comprising the following steps:

[0049] Step 1: Disperse 10g of ammonium polyphosphate in 200mL of deionized water and sonicate at 50℃ for 30min to obtain an ammonium polyphosphate suspension. Dilute 2g of phytic acid with 50mL of deionized water and slowly add it dropwise to the ammonium polyphosphate suspension. Adjust the pH to 4 and stir in a constant temperature water bath at 50℃ for 3h. Centrifuge the resulting reaction solution at 8000rpm for 10min, discard the supernatant, wash the precipitate three times with anhydrous ethanol to remove unreacted phytic acid, and then vacuum dry at 50℃ for 24h. Grind the precipitate through a 200-mesh sieve to obtain a light yellow powder of ammonium polyphosphate-phytic acid polymer.

[0050] Step 2: Dissolve 5g of N-isopropylacrylamide in 100mL of deionized water, purge with nitrogen for 15min to remove oxygen, obtaining an N-isopropylacrylamide solution. Add 0.05g of N,N′-methylenebisacrylamide and 0.1g of azobisisobutyronitrile to the N-isopropylacrylamide solution, and react the resulting mixture in a 60℃ water bath for 3h to form a transparent gel. Cut the gel into pieces, freeze-dry, and grind to obtain poly-N-isopropylacrylamide in powder form.

[0051] Step 3: Add 0.0442g of nano-silica and 6g of ammonium polyphosphate-phytic acid polymer to the methylcellulose solution at the same time. Add 4.25g of poly-N-isopropylacrylamide to the resulting mixed solution and stir thoroughly on a magnetic stirrer for 30 minutes at room temperature.

[0052] Step 4: Add 1.1g of sodium polyacrylate and 6g of magnesium chloride hexahydrate to the mixed solution obtained in Step 3, and stir thoroughly on a magnetic stirrer at room temperature for 1 hour to obtain a dual-network thermosensitive nanohydrogel.

[0053] Example 3:

[0054] A method for preparing a dual-network temperature-sensitive nanohydrogel for fire extinguishing and reignition prevention in lithium iron phosphate batteries, comprising the following steps:

[0055] Step 1: Disperse 10g of ammonium polyphosphate in 200mL of deionized water and sonicate at 70℃ for 30min to obtain an ammonium polyphosphate suspension. Dilute 2g of phytic acid with 50mL of deionized water and slowly add it dropwise to the ammonium polyphosphate suspension. Adjust the pH to 4 and stir in a constant temperature water bath at 70℃ for 4h. Centrifuge the resulting reaction solution at 8000rpm for 10min, discard the supernatant, wash the precipitate three times with anhydrous ethanol to remove unreacted phytic acid, and then vacuum dry at 70℃ for 24h. Grind the precipitate through a 200-mesh sieve to obtain a light yellow powder of ammonium polyphosphate-phytic acid polymer.

[0056] Step 2: Dissolve 5g of N-isopropylacrylamide in 100mL of deionized water, purge with nitrogen for 15min to remove oxygen, obtaining an N-isopropylacrylamide solution. Add 0.05g of N,N′-methylenebisacrylamide and 0.1g of azobisisobutyronitrile to the N-isopropylacrylamide solution, and react the resulting mixture in a 60℃ water bath for 3h to form a transparent gel. Cut the gel into pieces, freeze-dry, and grind to obtain poly-N-isopropylacrylamide in powder form.

[0057] Step 3: Add 0.0442g of nano-silica and 6g of ammonium polyphosphate-phytic acid polymer to the methylcellulose solution at the same time. Add 4.25g of poly-N-isopropylacrylamide to the resulting mixed solution and stir thoroughly on a magnetic stirrer for 30 minutes at room temperature.

[0058] Step 4: Add 1.1g of sodium polyacrylate and 6g of magnesium chloride hexahydrate to the mixed solution obtained in Step 3, and stir thoroughly on a magnetic stirrer at room temperature for 3 hours to obtain a dual-network thermosensitive nanohydrogel.

[0059] The dual-network thermosensitive nanohydrogel prepared in Example 1 was subjected to scanning electron microscopy and thermogravimetric analysis. Its application in lithium iron phosphate batteries is then described, specifically... Figure 2 Fire extinguishing test apparatus.

[0060] First, scanning electron microscopy test

[0061] The hydrogel powder was observed using a SEM (SU8200, Japan) to determine the structure of the hydrogel.

[0062] Second, thermogravimetric testing

[0063] The thermal stability of the prepared temperature-sensitive nanohydrogel was studied using thermogravimetric analysis (TG). The final product was dried in a vacuum drying oven, and 9 mg of solid powder was weighed. The sample was then placed in a high-temperature TG analyzer (TGA11600HT) to analyze the thermal stability of the material under a nitrogen atmosphere. The heating rate was set to 10 °C / min, and the temperature range was 30–300 °C to measure the weight loss and thermal stability of the sample. The DTG curve of the final product showed that the main decomposition temperatures of the hydrogel were 20 °C and 54 °C. Combined with the TG curve, the decomposition of the hydrogel sample showed two main stages. The first stage, from 20–54 °C, involved a mass loss of approximately 45.08%, due to the disappearance of water of crystallization and the structural destruction of small molecule products. The second stage, from 54 °C to 300 °C, involved a smaller loss than the initial mass loss. In this stage, polymer chains began to rearrange and degrade at higher temperatures, leading to the collapse of the gel structure and further mass loss. The thermogravimetric curve shows that the composite hydrogel retains 11.22% of its molecular weight even after heating to 300℃, which easily indicates that the gel has high thermal stability and that high temperatures will not affect its practical application.

[0064] Third, flame retardant performance test

[0065] from Figure 4 It can be seen that the addition of ammonium polyphosphate / phytic acid polymer can significantly improve the flame retardant properties of the hydrogel, with the heat release rate increasing from 51.79 KW / m³. 2 It dropped to 37.37 KW / m 2 The combustion time was shortened from 90s to 80s, mass loss was reduced by 6.48%, total heat release decreased by 65.79%, and the effective combustion heat peak time was delayed by 13.7%. This is because APP is a highly efficient phosphorus-based non-halogenated smoke suppressant and flame retardant. When heated at high temperatures, it decomposes to generate NH3 and very stable polyphosphoric acid. Polyphosphoric acid can not only generate many free radicals to block the chain reaction of combustion, but also act as a strong dehydrating agent to dehydrate the carbon-forming substances in the flame retardant system to form a single-element carbon layer. Then, through the action of non-flammable gases generated by the gas source, an expanded carbon layer is formed, which plays a role in isolating air and blocking the fire source.

[0066] Fourth, fire extinguishing experiment

[0067] Figure 5 , Figure 6 The figures show the HRR and mass change curves for thermosensitive nanohydrogel samples with different contents. The hydrogel without ammonium polyphosphate / phytic acid polymer started burning at 20 s. Due to the evaporation of water in the hydrogel structure, the small molecule combustibles in the hydrogel began to decompose thermally as the temperature continued to rise. The burning duration was 90 s, and the peak HRR was 51.79 KW / m. 2In contrast, the hydrogel containing ammonium polyphosphate / phytic acid polymers only began to burn after 25 seconds, with a burning duration of 80 seconds and a peak HRR of 37.37 kW / m³. 2 The addition of ammonium polyphosphate / phytic acid polymer reduced the peak HRR of the final product by 27.84% and the mass loss rate by 6.48%. This indicates that the content of flammable components released from the APP-containing hydrogel is reduced, and the flame retardant properties and thermal stability are significantly improved. Figure 7 The THR curves for thermosensitive nanohydrogel samples with different contents are shown. Compared with hydrogel samples with ammonium polyphosphate / phytic acid polymer contents of 0 g / L and 12 g / L, the THR increased by 65.79%. Figure 8 The EHC curves for thermosensitive nanohydrogel samples with different contents are shown. The times to reach the EHC peak were 315s and 365s, respectively, a delay of 13.7%. Due to the addition of ammonium polyphosphate / phytic acid polymer, the polyphosphate / phytic acid polymer particles undergo thermal cracking during combustion or under strong heat, forming a multilayered carbon silicate layer on the polymer surface. This layer acts as an excellent insulation and mass transfer barrier, improving the flame retardant properties of the material and delaying the release of volatile products generated during thermal decomposition. Therefore, the time to reach the peak EHC curve for the hydrogel sample containing APP was extended by 45s, thus improving the flame retardant properties of the hydrogel sample. Figure 9 The CO release rate curves of thermosensitive nanohydrogel samples with different contents are shown. Figure 10 The figures show the CO2 release rate curves for thermosensitive nanohydrogel samples with different contents. The addition of ammonium polyphosphate / phytic acid polymer significantly reduced the amount of harmful gases produced by the hydrogel samples. This material exhibits good thermal stability and environmental friendliness. Figure 11 Temperature change curve of lithium-ion battery body when extinguishing fire with pure aqueous solution; Figure 12 The graph shows the temperature change of the lithium-ion battery body after using a nano-hydrogel solution to extinguish a fire. With pure water, the highest temperature the battery could reach was 150.2℃, while after applying the hydrogel solution, the battery temperature was only 119.4℃, a decrease of 20.5% compared to pure water. Furthermore, reignition occurred with pure water, but not with the hydrogel solution. This indicates that the hydrogel solution fire extinguishing agent has a certain cooling effect on lithium-ion batteries experiencing thermal runaway; it not only has a good cooling effect but also effectively prevents reignition. Figure 13 This is a diagram illustrating the fire extinguishing mechanism of the temperature-sensitive nano-hydrogel of this invention.

[0068] This temperature-sensitive nano-hydrogel achieves efficient fire extinguishing and reignition prevention through the synergistic effect of multiple components: In the initial stage (60-80℃), the poly-N-isopropylacrylamide temperature-sensitive network undergoes a phase transition and shrinks, rapidly releasing a large amount of water and quickly cooling down through evaporation and heat absorption; in the middle stage (80-150℃), phytic acid-modified ammonium polyphosphate (APP-PA) decomposes to produce polyphosphoric acid and NH3, the former catalyzing the dehydration of the material into char, and the latter diluting the combustible gas to achieve chemical flame retardancy; in the later stage (>150℃), Mg... 2+ Cross-linked methylcellulose / sodium polyacrylate network catalyzes the formation of a dense char layer, which, combined with the physical barrier effect of nano-silica, effectively isolates oxygen and heat transfer. The entire process exhibits a three-stage synergistic protection mechanism of "moisture evaporation and cooling - chemical flame retardancy and explosion suppression - physical isolation by the char layer," in which phytic acid and Mg... 2+ The coordination effect significantly improves the quality and thermal stability of the carbon layer (the residual carbon content reaches more than 35%), thereby completely blocking the reignition path and solving the dual problem of rapid fire extinguishing and long-term protection in lithium battery fires.

[0069] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0070] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of protection claimed in this application.

Claims

1. A method for the preparation of a dual network temperature sensitive nanohydrogel for fire extinguishing and anti-reignition in lithium iron phosphate batteries, characterized by, Comprise the following steps in turn: a. Add phytic acid solution to ammonium polyphosphate suspension, adjust pH to 4, stir at a certain temperature, collect the precipitate by centrifugal treatment, wash, vacuum dry, and grind to obtain powder-like ammonium polyphosphate-phytic acid polymer; b. Add N,N'-methylenebisacrylamide and azobis isobutyronitrile to N-isopropyl acrylamide solution, react the obtained mixture at a certain temperature to form transparent gel, cut, freeze-dry, and grind to obtain powder-like poly N-isopropyl acrylamide; c. Add nano-silicon dioxide and ammonium polyphosphate-phytic acid polymer to methyl cellulose solution, add the poly N-isopropyl acrylamide to the obtained mixture, and stir at room temperature; in the methyl cellulose solution, the mass / volume ratio of methyl cellulose to water is 0.012 g / mL; the mass ratio of methyl cellulose to nano-silicon dioxide is 27:1; the mass ratio of methyl cellulose to ammonium polyphosphate-phytic acid polymer is 0.2:1; and the mass ratio of methyl cellulose to poly N-isopropyl acrylamide is 0.28:1; d. Add sodium polyacrylate and magnesium chloride hexahydrate to the mixture obtained in step c, and stir at room temperature to obtain the double-network temperature-sensitive nanohydrogel.

2. A process for the preparation of a dual network temperature sensitive nanohydrogel for fire extinguishing and anti-reignition in lithium iron phosphate batteries as claimed in claim 1, wherein: In step a, the preparation of ammonium polyphosphate suspension is as follows: disperse ammonium polyphosphate in deionized water, ultrasonic treatment at 50-70℃ for 30 min to obtain ammonium polyphosphate suspension; the mass / volume ratio of ammonium polyphosphate to deionized water is 0.05 g / mL.

3. The method for preparing a dual-network temperature-sensitive nanohydrogel for extinguishing and preventing reignition in a lithium iron phosphate battery according to claim 1, characterized in that: In step a, the phytic acid solution is obtained by diluting 2 g of phytic acid with 50 mL of deionized water; stir in a constant-temperature water bath at 50-70℃ for 3-5 h; centrifugal treatment for 10 min, and use ethanol to wash the precipitate to remove unreacted phytic acid.

4. The method of claim 1, wherein the method is characterized by: In step a, the vacuum drying temperature is 50-70℃, the vacuum drying time is 24 h, and the grinding is through a 200-mesh sieve.

5. The process for the preparation of a dual network temperature sensitive nanohydrogel for fire extinguishing and anti-reignition in lithium iron phosphate batteries according to claim 1, characterized by the fact that: In step b, the N-isopropyl acrylamide solution is prepared by dissolving 5 g of N-isopropyl acrylamide in 100 mL of deionized water, and removing oxygen by nitrogen for 10-20 min.

6. The process for the preparation of a dual network temperature sensitive nanohydrogel for fire extinguishing and anti-reignition in lithium iron phosphate batteries according to claim 5, characterized by the fact that: Add 0.05 g of N,N'-methylenebisacrylamide and 0.1 g of azobis isobutyronitrile to the N-isopropyl acrylamide solution, and react the obtained mixture in a 50-70℃ water bath for 2-4 h to form transparent gel.

7. The process for the preparation of a dual network temperature sensitive nanohydrogel for fire extinguishing and anti-reignition in lithium iron phosphate batteries as claimed in claim 1, wherein: In step d, add 1.1 g of sodium polyacrylate and 6 g of magnesium chloride hexahydrate to the mixture obtained in step c, and stir at room temperature for 1-3 h.

8. A dual network temperature sensitive nanohydrogel for fire extinguishing and anti-reignition in lithium iron phosphate battery characterized in that, It is prepared by the preparation method of any one of claims 1-7.

9. The use of a dual-network temperature-sensitive nanohydrogel for extinguishing and preventing reignition in lithium iron phosphate batteries according to claim 8, characterized by the fact that it is used in the form of a gel. When the lithium iron phosphate battery catches fire, the fire extinguishing process of the double-network temperature-sensitive nanohydrogel includes three stages: the first stage: water evaporation, heat absorption of the sol-gel transition, and part of the heat generated by thermal runaway; the second stage: ammonium polyphosphate decomposes to produce ammonia gas, which dilutes part of the flammable gas generated by thermal runaway and reduces the fire; the third stage: magnesium chloride catalyzes the formation of a carbon layer on the left-handed dextran in the methyl cellulose, preventing rekindling.

Images