Anti-reburning lithium battery fire extinguishing agent and preparation method thereof

Abstract

This invention discloses a fire extinguishing agent for lithium batteries that prevents reignition and its preparation method, belonging to the field of fire extinguishing agent technology. The fire extinguishing agent uses a modified cyclotriphosphazene flame retardant as its core component. Through molecular structure design, polyethylene glycol hydrophilic penetration units, hydroxyphosphonate anchoring units, and hindered amine radical capturing units are covalently grafted onto the hexachlorocyclotriphosphazene matrix, achieving multifunctional integration of deep penetration, active site anchoring, and chain reaction blocking. The fire extinguishing agent of this invention can not only quickly extinguish open flames but also penetrate deep into the battery cell to terminate thermal runaway reactions, forming a high-temperature resistant passivation film in situ on the electrode surface, effectively inhibiting reignition and chain thermal spread. Furthermore, it is fluorine-free and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of fire extinguishing agent technology, and in particular to a lithium battery fire extinguishing agent with anti-reignition properties and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their core advantages such as high energy density, long cycle life, low self-discharge rate, and wide operating temperature range, have become core energy storage devices in new energy vehicles, electrochemical energy storage power stations, portable consumer electronics, aerospace, and other fields, with their market size and application scenarios continuing to expand rapidly. However, the electrochemical system of lithium-ion batteries inherently determines their inherent safety risks. The battery contains highly active ternary cathode materials, flammable carbonate-based organic electrolytes, and lithium-intercalated anodes, making them highly susceptible to internal thermal runaway under abuse scenarios such as overcharging, over-discharging, external short circuits, puncture, compression, and high temperatures. This can release large amounts of heat and flammable gases in a short time, leading to violent combustion or even explosion. Lithium-ion battery thermal runaway fires are characterized by rapid temperature rise, self-sustaining oxygen release from the cathode material, strong concealment of deep-seated fire sources, self-sustaining free radical chain reactions, extremely high risk of reignition, and a tendency to trigger a chain reaction of thermal spread between cells. Traditional fire extinguishing agents and control technologies are insufficient for effective handling, making this a key bottleneck restricting the safe development of the lithium-ion battery industry.

[0003] Currently, various fire extinguishing agent technologies have been developed in the industry for the prevention and control of lithium battery fires. Among them, the most widely used are fluorinated fire extinguishing agents, conventional water-based fire extinguishing agents, dry powder fire extinguishing agents, and various modified compound fire extinguishing agents. Fluorinated fire extinguishing agents, represented by perfluorohexanone and perfluoropolyether systems, have found some application in extinguishing fires in energized scenarios due to their excellent electrical insulation properties and gas-phase chemical inhibition capabilities. Conventional water-based fire extinguishing agents rely on the high specific heat capacity of water to achieve strong physical cooling and are the most commonly used type of fire extinguishing agent in the fire protection field. The industry has also carried out a lot of modification research on them, optimizing their adaptability in lithium battery fire scenarios by adding surfactants, flame retardants, thickeners, and microencapsulation components. In addition, environmentally friendly flame retardant systems based on phosphorus and nitrogen flame retardants are gradually becoming a research hotspot for lithium battery fire extinguishing agents. Among them, cyclotriphosphazene derivatives have become an important research direction for flame retardant modification due to their excellent phosphorus and nitrogen synergistic flame retardant effect. However, existing lithium battery fire extinguishing technologies all have insurmountable technical flaws and cannot fundamentally solve the problem of lithium battery fire prevention and control. Although fluorinated fire extinguishing agents have good insulation and extinguishing speed, they can only extinguish gaseous flames and cannot achieve deep cooling and termination of thermal runaway inside the battery cell. The reignition rate after extinguishing is extremely high. At the same time, fluorinated compounds belong to the PFAS class of "permanent chemicals," which have serious environmental persistence and bioaccumulation. Under high temperature combustion, they will also decompose to produce highly toxic and corrosive gases such as hydrogen fluoride, causing serious secondary disasters. Policies have been gradually introduced worldwide to restrict their application. While conventional water-based fire extinguishing agents excel in cooling capabilities, they suffer from inherent defects such as high surface tension and weak wetting and penetration. They cannot penetrate the micro-gaps in the battery cell casing and the internal electrode structure, making it difficult to reach deep-seated fire sources within the cell. They can only extinguish surface flames and cannot stop the self-sustaining thermal runaway within the cell. Furthermore, conventionally added small-molecule flame retardants lack active site anchoring capabilities and are easily lost through electrolyte flow and high-temperature gas evaporation, failing to achieve long-term flame retardancy and thus struggling to address the problem of reignition. Existing modified compound water-based agents mostly compensate for the shortcomings of single-function agents through multi-component physical compounding, but they cannot solve the core problems of asynchronous functions between different components and the contradiction between penetration and retention. Technologies such as thermosensitive thickening and microencapsulation can only optimize the surface adhesion performance of the agent and cannot overcome the technical bottleneck of deep penetration. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing an anti-reignition lithium battery fire extinguishing agent and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a lithium battery fire extinguishing agent with anti-reignition properties, comprising the following components by weight: modified triphosphazene flame retardant: 12-30 parts, deionized water: 80-100 parts, dispersant: 0.1-1 parts, preservative: 0.1-0.5 parts, thickener: 0.005-0.03 parts.

[0006] Preferably, the modified cyclotriphosphazene flame retardant is prepared as follows: (1) Under nitrogen protection and an anhydrous and oxygen-free environment, hexachlorocyclotriphosphazene and triethylamine are added to an anhydrous organic solvent, heated to 25-30℃ with stirring, stirred for 10-20 min, polymerization inhibitor 701 is added, and the mixture is kept warm and stirred for 3-5 h. Then, hydroxyphosphonate is added dropwise over 20-30 min. After the addition is complete, the mixture is kept warm and stirred for 1.5-2.5 h. Finally, polyethylene glycol monomethyl ether is added, the temperature is raised to 40-60℃, and the mixture is stirred for 6-10 h. (2) After the reaction is completed, cool to room temperature, filter, remove the solvent from the filtrate by rotary evaporation, dissolve the crude product in dichloromethane, wash the organic phase three times with deionized water, dry the washed organic phase with anhydrous sodium sulfate, remove the solvent by rotary evaporation, add the concentrated product to dichloromethane to just dissolve it completely, and then add it dropwise to cold petroleum ether at 0℃. The product precipitates immediately. After the addition is complete, let it stand for 30-60 minutes, filter and collect the precipitated solid, wash it twice with cold petroleum ether at 0℃, and dry it to obtain the modified cyclotriphosphazene flame retardant.

[0007] Preferably, the dispersant refers to polyether-modified polysiloxane.

[0008] More preferably, the dispersant refers to either BYK-349 or TEGO Wet 280.

[0009] Preferably, the preservative is one of sodium benzoate or potassium sorbate.

[0010] Preferably, the thickener is either xanthan gum or sodium carboxymethyl cellulose.

[0011] Preferably, the anhydrous organic solvent in (1) refers to one of anhydrous 1,4-dioxane, anhydrous tetrahydrofuran, or anhydrous acetonitrile.

[0012] More preferably, the anhydrous organic solvent in (1) refers to anhydrous 1,4-dioxane.

[0013] Preferably, the molar ratio of hexachlorocyclotriphosphazene, triethylamine, polymerization inhibitor 701, hydroxyphosphonate and polyethylene glycol monomethyl ether in (1) is 1:6-6.5:2-2.5:1.8-2.2:1.5-2.5.

[0014] Preferably, in (1), the weight ratio of hexachlorocyclotriphosphazene and anhydrous organic solvent is 1:5-10.

[0015] Preferably, the ratio of the total molar number of polymerization inhibitor 701, hydroxyphosphonate and polyethylene glycol monomethyl ether to the molar number of hexachlorocyclotriphosphazene in (1) is ≥6.

[0016] Preferably, the hydroxyphosphonate in (1) refers to dimethyl 2-hydroxyethylphosphonate or diethyl 3-hydroxypropylphosphonate.

[0017] Preferably, the number-average molecular weight of the polyethylene glycol monomethyl ether in (1) is 200-500 g / mol.

[0018] More preferably, the number-average molecular weight of the polyethylene glycol monomethyl ether in (1) is 350 g / mol.

[0019] Furthermore, the present invention also provides a method for preparing a lithium battery fire extinguishing agent that prevents reignition, comprising the following steps: Deionized water was added to a stirred tank, and modified triphosphazene flame retardant was added at room temperature. The mixture was stirred at 300-500 rpm for 15-30 minutes. Then, dispersant, preservative and thickener were added and stirred evenly. The pH of the system was adjusted to 7.5-8.5 with triethanolamine. After filtration through a 0.45μm microporous membrane, the anti-reignition lithium battery fire extinguishing agent was obtained.

[0020] Preferably, the mechanism of action of the anti-reignition lithium battery fire extinguishing agent of the present invention is explained as follows: This invention addresses the core characteristics of lithium battery thermal runaway fires: rapid temperature rise, strong oxygen release, concealed deep ignition sources, self-sustaining chain reactions, and high risk of reignition. It uses a modified cyclotriphosphazene flame retardant as its core component, combined with the rapid cooling characteristics of a water-based system and performance optimization through trace amounts of functional additives. This achieves rapid fire extinguishing and long-term anti-reignition effects from the root cause of thermal runaway. The specific mechanism of action is as follows: The core component of this invention is a modified cyclotriphosphazene flame retardant that achieves multifunctional integration through covalent bonding. It uses a six-membered phosphorus-nitrogen heterocycle as its parent material, grafted with a polyethylene glycol monomethyl ether hydrophilic permeation unit, a hydroxyphosphonate anchoring unit, and a hindered amine free radical capture unit. These three functional units form an integrated molecular structure with the phosphorus-nitrogen heterocycle parent material, solving the inherent defects of traditional multi-component compound agents such as "asynchronous functions and contradictory penetration and retention." When fire extinguishing agents act on thermally runaway lithium batteries through a spray system, they first rely on the high specific heat capacity of the water-based system to achieve rapid surface cooling. Simultaneously, under the synergistic effect of polyethylene glycol monomethyl ether units and dispersants, the surface tension of the agent system is reduced, breaking down the interfacial barriers between the lithium battery casing, electrode gaps, and separator. This allows flame retardant molecules to quickly penetrate the micro-gaps in the battery casing, the gaps in the electrode structure, and even pass through the separator to reach the thermal runaway region inside the battery cell. At the same time, the modified triphosphazene molecules, with their amphiphilic properties due to the polyether side chains and phosphonate groups, can quickly become miscible with the flammable carbonate organic electrolyte inside the battery cell, achieving full coverage of the electrolyte combustion reaction zone and the thermal runaway reaction zone of the positive and negative electrode active materials. This solves the problem that traditional agents can only act on the battery surface and cannot reach deep-seated fire sources. After the flame retardant molecules penetrate into the core region of thermal runaway, the hydroxyphosphonate units in the molecular structure can play a targeted anchoring role. The phosphonate groups contained therein can form stable coordination bonds with nickel, cobalt, and manganese transition metal ions in the high-nickel ternary cathode material. At the same time, they can react with active lithium on the negative electrode surface and lithium dendrites generated during thermal runaway to generate irreversible Li-OP covalent chemical bonds. This firmly fixes the entire flame retardant molecule at the most intense positive and negative electrode active sites of thermal runaway, avoiding the loss of flame retardant components caused by the flow of electrolyte and volatilization of high-temperature airflow in traditional small-molecule flame retardants. It achieves the effect of "targeted arrival and permanent retention", laying the structural foundation for subsequent chain reaction blocking and long-term protection, and spatially locking the range of flame retardancy and anti-reignition action. While anchoring the active sites, the modified cyclotriphosphazene molecules can block the chain reaction of lithium battery thermal runaway and combustion through multi-dimensional chemical action, achieving rapid fire extinguishing and termination of thermal runaway.On the one hand, the hindered amine radical scavenging unit (polymer inhibitor 701) grafted into the molecule carries stable nitroxide radicals, which can irreversibly capture highly reactive free radicals such as ·OH, H·, and R· released during thermal runaway from electrolyte pyrolysis and cathode material decomposition within a wide temperature range from room temperature to 800℃, converting them into stable inactive products and fundamentally interrupting the free radical chain reaction of combustion and pyrolysis. On the other hand, the phosphorus-nitrogen heterocyclic structure of the cyclotriphosphazene parent compound will cleave at high temperatures, releasing phosphorus-containing oxygen-active free radicals. This invention can simultaneously capture active free radicals in gas-phase combustion, achieving synergistic flame retardancy in both gas and liquid phases. Simultaneously, the inert nitrogen-containing gas generated by pyrolysis can dilute the oxygen and combustible gas concentrations in the combustion zone, aiding in suffocation fire suppression. Furthermore, the phosphonate groups decompose at high temperatures to generate acidic species such as polymetaphosphoric acid, which can catalyze the dehydration and carbonization of the organic phase, reducing the release of small combustible molecules and further inhibiting the continued pyrolysis and combustion reactions. This differs from traditional fire extinguishing agents, which can only extinguish surface flames and cannot terminate the self-sustaining thermal runaway within the battery cell. After the thermal runaway reaction is suppressed, the agent of this invention can achieve long-term prevention of reignition and suppression of thermal spread through in-situ film formation and interface passivation effects. Under high-temperature conditions, the pyrolysis products of the cyclotriphosphazene parent compound and the decomposition products of the phosphonate unit work synergistically to form a dense, high-temperature resistant phosphorus-nitrogen-carbon hybrid ceramic passivation film on the pre-anchored positive and negative electrode active sites through in-situ cross-linking. The thermal decomposition temperature of this passivation film far exceeds the peak temperature of lithium-ion battery thermal runaway. It not only completely isolates oxygen from the electrolyte, blocking the material basis for combustion reactions, but also forms a highly efficient thermal barrier, inhibiting heat transfer within the cell and secondary decomposition of active materials. Simultaneously, trace amounts of thickener in the system optimize the adhesion of the agent to the battery pack and cell surfaces, further isolating external oxygen and heat backflow in conjunction with the passivation film. The weakly alkaline environment of the system, along with the auxiliary effects of corrosion inhibitors and metal passivators, ensures the stability of the agent during long-term storage and prevents corrosion of the battery pack's metal structure and fire-fighting equipment. This enables rapid extinguishing of lithium-ion battery fires and permanent prevention of reignition, while effectively inhibiting the chain reaction of thermal spread between cells.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses hexachlorocyclotriphosphazene as the parent compound and covalently integrates three major functional units—hydrophilic penetration, targeted anchoring, and free radical capture—within the parent molecule. This solves the inherent defects of traditional multi-component compound agents, such as asynchronous functions and contradictory penetration and retention. It achieves full-chain synergy of deep penetration, site anchoring, and chain reaction blocking, fundamentally terminating the self-sustaining thermal runaway inside the battery cell and overcoming the industry pain point of high re-ignition rate in lithium battery fires.

[0022] 2. The modified cyclotriphosphazene flame retardant of this invention is fluorine-free, completely avoiding the PFAS environmental compliance risks of fluorine-containing fire extinguishing agents and the secondary disaster problem of producing highly toxic hydrogen fluoride gas during high-temperature decomposition. Relying on the synergistic flame retardant effect of phosphorus and nitrogen from the cyclotriphosphazene parent compound, combined with the synergistic effect of multiple functional groups, excellent fire extinguishing and anti-reignition effects can be achieved at low addition levels. The entire process of production, use, and subsequent disposal is green and environmentally friendly, conforming to the global trend of upgrading environmental regulations.

[0023] 3. The fire extinguishing agent prepared by this invention exhibits excellent comprehensive performance. Under high-temperature conditions of thermal runaway, it can form a dense, high-temperature-resistant phosphorus-nitrogen-carbon hybrid ceramic passivation film. This film not only isolates oxygen from contact with the flammable electrolyte but also forms a highly efficient thermal insulation barrier, blocking heat transfer and secondary decomposition of active materials. It can not only quickly extinguish open flames but also effectively inhibit the chain-reaction thermal spread between battery cells, achieving one-time treatment and long-term protection, significantly improving the safety and thoroughness of lithium battery fire prevention and control. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Preparation Example 1: The preparation method of modified cyclotriphosphazene flame retardant is as follows: (1) Under nitrogen protection and an anhydrous and oxygen-free environment, 1 mol (344.64 g) of hexachlorocyclotriphosphazene and 6 mol of triethylamine were added to 1723.2 g of anhydrous 1,4-dioxane. The mixture was heated to 25-30 °C with stirring and stirred for 10 min. Then, 2 mol of polymerization inhibitor 701 was added and the mixture was kept warm and stirred for 3 h. Then, 1.8 mol of dimethyl 2-hydroxyethylphosphonate was added dropwise over 20 min. After the addition was completed, the mixture was kept warm and stirred for 1.5 h. Finally, 2.5 mol of polyethylene glycol monomethyl ether (PEG-350) was added and the mixture was heated to 40 °C and stirred for 6 h. (2) After the reaction is completed, the mixture is cooled to room temperature, filtered, and the solvent is removed by rotary evaporation of the filtrate. The crude product is dissolved in dichloromethane, and the organic phase is washed three times with deionized water. After washing, the organic phase is dried with anhydrous sodium sulfate and the solvent is removed by rotary evaporation. The concentrated product is added to dichloromethane until it is completely dissolved, and then added dropwise to cold petroleum ether at 0°C. The product precipitates immediately. After the addition is complete, the mixture is allowed to stand for 30 minutes, filtered, and the precipitated solid is collected. The solid is washed twice with cold petroleum ether at 0°C and dried to obtain the modified cyclotriphosphazene flame retardant.

[0026] Preparation Example 2: The preparation method of modified cyclotriphosphazene flame retardant is as follows: (1) Under nitrogen protection and an anhydrous and oxygen-free environment, 1 mol (344.64 g) of hexachlorocyclotriphosphazene and 6.2 mol of triethylamine were added to 2.7 kg of anhydrous 1,4-dioxane. The mixture was heated to 25-30 °C with stirring and stirred for 15 min. Then, 2.2 mol of polymerization inhibitor 701 was added and the mixture was kept warm and stirred for 4 h. Then, 2 mol of dimethyl 2-hydroxyethylphosphonate was added dropwise over 25 min. After the addition was completed, the mixture was kept warm and stirred for 2 h. Finally, 2 mol of polyethylene glycol monomethyl ether (PEG-350) was added, the mixture was heated to 50 °C, and stirred for 8 h. (2) After the reaction is completed, the mixture is cooled to room temperature, filtered, and the solvent is removed by rotary evaporation of the filtrate. The crude product is dissolved in dichloromethane, and the organic phase is washed three times with deionized water. The washed organic phase is dried with anhydrous sodium sulfate and the solvent is removed by rotary evaporation. The concentrated product is added to dichloromethane until it is completely dissolved, and then added dropwise to cold petroleum ether at 0°C. The product precipitates immediately. After the addition is complete, the mixture is allowed to stand for 45 minutes, filtered, and the precipitated solid is collected. The solid is washed twice with cold petroleum ether at 0°C and dried to obtain the modified cyclotriphosphazene flame retardant.

[0027] Preparation Example 3: The preparation method of the modified cyclotriphosphazene flame retardant is as follows: (1) Under nitrogen protection and an anhydrous and oxygen-free environment, 1 mol (344.64 g) of hexachlorocyclotriphosphazene and 6.5 mol of triethylamine were added to 3446.4 g of anhydrous 1,4-dioxane. The mixture was heated to 25-30 °C with stirring and stirred for 20 min. Then, 2.5 mol of polymerization inhibitor 701 was added and the mixture was kept warm and stirred for 5 h. Then, 2.2 mol of dimethyl 2-hydroxyethylphosphonate was added dropwise over 30 min. After the addition was completed, the mixture was kept warm and stirred for 2.5 h. Finally, 1.5 mol of polyethylene glycol monomethyl ether (PEG-350) was added, the mixture was heated to 60 °C, and stirred for 10 h. (2) After the reaction is completed, the mixture is cooled to room temperature, filtered, and the solvent is removed by rotary evaporation of the filtrate. The crude product is dissolved in dichloromethane, and the organic phase is washed three times with deionized water. The washed organic phase is dried with anhydrous sodium sulfate and the solvent is removed by rotary evaporation. The concentrated product is added to dichloromethane until it is completely dissolved, and then added dropwise to cold petroleum ether at 0°C. The product precipitates immediately. After the addition is complete, the mixture is allowed to stand for 60 minutes, filtered, and the precipitated solid is collected. The solid is washed twice with cold petroleum ether at 0°C and dried to obtain the modified cyclotriphosphazene flame retardant.

[0028] Preparation Example 4: The difference between Preparation Example 4 and Preparation Example 2 is that 2-hydroxyethylphosphonic acid dimethyl ester is replaced with an equimolar amount of 3-hydroxypropylphosphonic acid diethyl ester.

[0029] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 2 is that no polymerization inhibitor 701 is added, the molar ratio of 2-hydroxyethylphosphonic acid dimethyl ester and PEG-350 is 1:1, and the ratio of the total molar amount of the two to the molar amount of hexachlorocyclotriphosphazene is 6:1.

[0030] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 2 is that 2-hydroxyethylphosphonic acid dimethyl ester is not added, the molar ratio of polymerization inhibitor 701 and PEG-350 is 1:1, and the ratio of the total molar amount of the two to the molar amount of hexachlorocyclotriphosphazene is 6:1.

[0031] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 2 is that PEG-350 is not added, the molar ratio of polymerization inhibitor 701 and dimethyl 2-hydroxyethylphosphonate is 1:1, and the ratio of the total molar amount of the two to the molar amount of hexachlorocyclotriphosphazene is 6:1.

[0032] Example 1: A specific preparation method of a lithium battery fire extinguishing agent that prevents reignition, comprising the following steps: Add 8 kg of deionized water to a stirred tank, add 1.2 kg of the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 1 at room temperature, stir at 300 rpm for 15 min, then add 10 g of dispersant (BYK-349), 10 g of preservative (sodium benzoate) and 0.5 g of thickener (xanthan gum), stir evenly, adjust the pH of the system to 7.5-8.5 with triethanolamine, and filter through a 0.45 μm microporous membrane to obtain the lithium battery fire extinguishing agent that prevents reignition.

[0033] Example 2: A specific preparation method of a lithium battery fire extinguishing agent with anti-reignition properties, comprising the following steps: Add 9 kg of deionized water to a stirred tank, add 2.2 kg of the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 2 at room temperature, stir at 400 rpm for 20 min, then add 50 g of dispersant (BYK-349), 25 g of preservative (potassium sorbate) and 1.5 g of thickener (sodium carboxymethyl cellulose), stir evenly, adjust the pH of the system to 7.5-8.5 with triethanolamine, and filter through a 0.45 μm microporous membrane to obtain the anti-reignition lithium battery fire extinguishing agent.

[0034] Example 3: A specific preparation method of a lithium battery fire extinguishing agent with anti-reignition properties, comprising the following steps: 10 kg of deionized water was added to a stirred tank, and 3 kg of the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 3 was added at room temperature. The mixture was stirred at 500 rpm for 30 min, and then 100 g of dispersant (TEGO Wet 280), 50 g of preservative (sodium benzoate) and 3 g of thickener (sodium carboxymethyl cellulose) were added. After stirring evenly, the pH of the system was adjusted to 7.5-8.5 using triethanolamine. After filtration through a 0.45 μm microporous membrane, the anti-reignition lithium battery fire extinguishing agent was obtained.

[0035] Example 4: The difference between Example 4 and Example 2 is that the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 2 is replaced with the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 4.

[0036] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 2 is replaced with the modified cyclotriphosphazene flame retardant prepared according to Comparative Preparation Example 1.

[0037] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 2 is replaced with the modified cyclotriphosphazene flame retardant prepared according to Comparative Preparation Example 2.

[0038] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the modified cyclotriphosphazene flame retardant prepared according to Preparation Example 2 is replaced with the modified cyclotriphosphazene flame retardant prepared according to Comparative Preparation Example 3.

[0039] Performance testing: 1. Fire extinguishing and anti-reignition performance test: A fully charged 18650 type NCM811 high-nickel ternary lithium battery (rated capacity 2000mAh, nominal voltage 3.6V) was selected. In an explosion-proof test chamber in a fume hood, thermal runaway was triggered by vertical needle penetration. A fixed spray device was used to spray the fire extinguishing agents prepared in Examples 1-4 and Comparative Examples 1-3 onto the burning battery cell. The time for the open flame to be completely extinguished was recorded as the extinguishing time. After the open flame was extinguished, the internal and surface temperatures of the battery cell were continuously monitored for 24 hours. The temperature change of the battery cell was recorded throughout the process. If the temperature of the battery cell exceeded 200℃ again and secondary combustion occurred, it was determined to be reignition. The experimental results are shown in Table 1.

[0040] 2. Thermal runaway internal blocking performance test: A fully charged 18650 NCM811 ternary lithium battery of the same specifications as the fire extinguishing test was used. Armored thermocouples were pre-embedded at the positive electrode, negative electrode, and core of the battery cell. Thermal runaway was triggered by needle penetration. A fixed spray device was used to spray the fire extinguishing agents prepared in Examples 1-4 and Comparative Examples 1-3. The temperature changes in the core of the battery cell and the positive and negative electrodes were continuously monitored, and the time t it took for the core temperature to drop from its peak value to below 50°C was recorded. 降The experimental results, including whether a temperature rebound occurred, are shown in Table 1.

[0041] 3. Thermal propagation suppression performance test: A module was composed of three fully charged 18650 NCM811 ternary lithium batteries connected in series. The cells were tightly packed without additional insulation layers. A thermocouple was embedded inside each cell. A needle puncture was used to trigger thermal runaway in the middle cell of the module. Simultaneously with the needle puncture, fire extinguishing agents prepared in Examples 1-4 and Comparative Examples 1-3 were sprayed into the module according to fixed spraying conditions. The temperature changes of the three cells were continuously monitored, and the highest temperature T of adjacent cells was recorded. max We observed whether a chain reaction of thermal runaway occurred, and the experimental results are shown in Table 1.

[0042] Table 1 Performance Test Results

[0043] Data Analysis: As can be seen from the experimental data in Table 1, the lithium battery fire extinguishing agents prepared using the technical solution of the present invention in Examples 1-4 all exhibit excellent fire extinguishing efficiency, thermal runaway blocking ability, and thermal spread suppression effect. They can quickly extinguish open flames in lithium batteries and completely terminate the self-sustaining thermal runaway inside the cell. There is no reignition phenomenon within 24 hours. At the same time, they completely avoid the chain thermal runaway between cells. Their overall performance is better than that of the comparative sample; among them, Example 2 has the best overall performance.

[0044] In terms of fire extinguishing and anti-reignition performance, Example 2 has a faster fire extinguishing speed and can achieve 24 hours without reignition. The reason may be that its modified cyclotriphosphazene flame retardant integrates the hindered amine free radical capturing unit, phosphonate anchoring unit and polyether permeation unit in a single molecule through covalent bonding. The three types of functional units work together to solve the inherent defect of asynchronous function of traditional agents. When the agent acts on the burning battery cell, the polyether unit and the dispersant work together to reduce the surface tension of the system, allowing the flame retardant molecules to quickly reach the combustion reaction zone. The hindered amine unit can irreversibly capture the active free radicals generated by pyrolysis and combustion over a wide temperature range, interrupting the combustion chain reaction at its source. Combined with the rapid cooling effect of the water-based system, the flame extinguishing time is significantly shortened. Meanwhile, the phosphonate unit can firmly anchor the flame retardant molecules to the positive and negative electrode active sites, preventing the flame retardant components from being lost with the electrolyte flow and high-temperature volatilization. Combined with the high-temperature passivation film formed by the cyclotriphosphazene matrix and the phosphonate unit, the continuous occurrence of thermal runaway reaction is blocked for a long time, fundamentally eliminating the risk of secondary reignition.

[0045] From the perspective of thermal runaway prevention performance, Example 2 can reduce the core temperature of the battery cell to a safe range more quickly without temperature rebound. This may be because the polyether permeation unit in its molecular structure gives the flame retardant excellent deep penetration ability, allowing it to penetrate the gap between the battery cell shell and the electrode structure and reach the core area of ​​thermal runaway inside the battery cell, rather than just acting on the battery surface. At the same time, the flame retardant molecules anchored on the active sites can directly terminate the self-sustaining pyrolysis and exothermic reaction inside the battery cell through multiple actions such as free radical capture, catalytic carbonization, and in-situ film formation, rather than relying solely on the physical cooling effect of water to temporarily suppress the temperature. Therefore, it can achieve a rapid decrease in the internal temperature of the battery cell without temperature rebound caused by the restart of the thermal runaway reaction.

[0046] From the perspective of thermal propagation suppression performance, Example 2 can effectively suppress the chain thermal runaway between cells and significantly reduce the maximum temperature of adjacent cells. This may be because it can quickly terminate the exothermic reaction inside the cell that triggers thermal runaway, greatly reducing the generation and transfer of heat. At the same time, the ceramic passivation film formed on the surface of the active site has excellent heat insulation effect, further blocking the conduction of heat to adjacent cells and preventing adjacent cells from triggering thermal runaway due to thermal shock. Ultimately, it achieves effective prevention and control of chain combustion of battery modules.

[0047] The overall performance of each comparative sample was significantly worse than that of Example 2. This is because their flame retardant molecular structures have functional defects, preventing them from achieving the synergistic effect of the present invention. Specifically, the flame retardant in Comparative Example 1 lacks a hindered amine radical scavenging unit, relying solely on the limited flame retardant effect of the cyclotriphosphazene matrix and the cooling effect of water to extinguish the fire. It cannot quickly interrupt the combustion chain reaction, resulting in a significantly prolonged extinguishing time. Furthermore, it cannot fundamentally terminate the thermal runaway chain reaction within the battery cell. Even if the open flame is temporarily extinguished, the exothermic reaction within the battery cell continues, eventually leading to a temperature rebound and secondary reignition. The continuously released heat can also trigger a chain reaction of thermal runaway in adjacent battery cells. The flame retardant in Comparative Example 2 lacks a phosphonate anchoring unit. Although it retains radical scavenging and penetration capabilities, the flame retardant molecules cannot remain at the active sites for a long time after entering the battery cell. They are easily lost rapidly with electrolyte spraying and high-temperature airflow, failing to achieve long-term blocking of the thermal runaway reaction. Therefore, its extinguishing speed is slower than that of Example 2, and it cannot avoid subsequent reignition and chain reaction of thermal runaway. The flame retardant in Comparative Example 3 lacks a polyether hydrophilic permeation unit, which makes it impossible for the flame retardant to dissolve in the water-based system and penetrate into the cell with the water phase. It can only act on the battery surface to achieve physical cooling and has almost no inhibitory effect on the violent thermal runaway reaction inside the cell. Therefore, the time for extinguishing the open flame is greatly extended, the temperature inside the cell continues to rise, and the reignition and chain thermal runaway phenomena cannot be controlled, which completely fails to meet the prevention and control requirements of lithium battery fires.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lithium battery fire extinguishing agent with anti-reignition properties, characterized in that, It comprises the following components by weight: modified triphosphazene flame retardant: 12-30 parts, deionized water: 80-100 parts, dispersant: 0.1-1 parts, preservative: 0.1-0.5 parts, thickener: 0.005-0.03 parts; The preparation method of the modified cyclotriphosphazene flame retardant is as follows: (1) Under nitrogen protection and an anhydrous and oxygen-free environment, hexachlorocyclotriphosphazene and triethylamine are added to an anhydrous organic solvent, heated to 25-30℃ with stirring, stirred for 10-20 min, polymerization inhibitor 701 is added, and the mixture is kept warm and stirred for 3-5 h. Then, hydroxyphosphonate is added dropwise over 20-30 min. After the addition is complete, the mixture is kept warm and stirred for 1.5-2.5 h. Finally, polyethylene glycol monomethyl ether is added, the temperature is raised to 40-60℃, and the mixture is stirred for 6-10 h. (2) After the reaction is completed, cool to room temperature, filter, remove the solvent from the filtrate by rotary evaporation, dissolve the crude product in dichloromethane, wash the organic phase three times with deionized water, dry the washed organic phase with anhydrous sodium sulfate, remove the solvent by rotary evaporation, add the concentrated product to dichloromethane to just dissolve it completely, and then add it dropwise to cold petroleum ether at 0℃. The product precipitates immediately. After the addition is complete, let it stand for 30-60 minutes, filter and collect the precipitated solid, wash it twice with cold petroleum ether at 0℃, and dry it to obtain the modified cyclotriphosphazene flame retardant.

2. The lithium battery fire extinguishing agent for preventing reignition according to claim 1, characterized in that, The dispersant refers to polyether-modified polysiloxane.

3. The lithium battery fire extinguishing agent for preventing reignition as described in claim 1, characterized in that, The preservative refers to either sodium benzoate or potassium sorbate.

4. The lithium battery fire extinguishing agent for preventing reignition as described in claim 1, characterized in that, The thickener is either xanthan gum or sodium carboxymethyl cellulose.

5. The lithium battery fire extinguishing agent for preventing reignition according to claim 1, characterized in that, The anhydrous organic solvent in (1) refers to one of anhydrous 1,4-dioxane, anhydrous tetrahydrofuran, or anhydrous acetonitrile.

6. The lithium battery fire extinguishing agent for preventing reignition according to claim 1, characterized in that, In (1), the molar ratio of hexachlorocyclotriphosphazene, triethylamine, polymerization inhibitor 701, hydroxyphosphonate and polyethylene glycol monomethyl ether is 1:6-6.5:2-2.5:1.8-2.2:1.5-2.5; the weight ratio of hexachlorocyclotriphosphazene and anhydrous organic solvent is 1:5-10.

7. The lithium battery fire extinguishing agent for preventing reignition according to claim 1, characterized in that, The ratio of the total molar number of polymerization inhibitor 701, hydroxyphosphonate and polyethylene glycol monomethyl ether to the molar number of hexachlorocyclotriphosphazene in (1) is ≥6.

8. The lithium battery fire extinguishing agent for preventing reignition according to claim 1, characterized in that, The hydroxyphosphonate in (1) refers to dimethyl 2-hydroxyethylphosphonate or diethyl 3-hydroxypropylphosphonate.

9. The lithium battery fire extinguishing agent for preventing reignition according to claim 1, characterized in that, The number average molecular weight of the polyethylene glycol monomethyl ether in (1) is 200-500 g / mol.

10. The method for preparing the anti-reignition lithium battery fire extinguishing agent according to any one of claims 1-9, characterized in that, Includes the following steps: Deionized water was added to a stirred tank, and modified triphosphazene flame retardant was added at room temperature. The mixture was stirred at 300-500 rpm for 15-30 minutes. Then, dispersant, preservative and thickener were added and stirred evenly. The pH of the system was adjusted to 7.5-8.5 with triethanolamine. After filtration through a 0.45μm microporous membrane, the anti-reignition lithium battery fire extinguishing agent was obtained.

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