Lithium battery fire extinguishing agent and preparation method thereof

Abstract

The application belongs to the field of fire fighting and safety technology, and discloses a lithium battery fire extinguishing agent and a preparation method thereof. The agent is composed of 65%-85% expandable graphite, 8%-20% lithium bis-trifluoromethanesulfonimide, 3%-10% mixed precursors of manganese nitrate and cobalt nitrate, and 2%-5% polyvinylidene fluoride binder. The functional components are embedded between the graphite layers through interlayer intercalation technology. Under the condition of thermal runaway, the agent synchronously realizes graphite expansion to isolate oxygen, releases fluorine-containing free radicals to quench the combustion chain reaction, generates transition metal oxide to catalyze the decomposition of peroxide radicals, and forms a solid electrolyte interface film with high ion conductivity and low electronic conductivity at the negative electrode in situ to passivate the electrochemical side reaction. The agent is rapid in fire extinguishing, free of reignition, and strong in corrosion resistance, and is suitable for closed lithium battery scenes such as electric vehicles and energy storage power stations.

Description

Technical Field

[0001] This invention belongs to the field of fire protection and safety technology, and relates to a lithium battery fire extinguishing agent and its preparation method. Background Technology

[0002] Lithium batteries are prone to thermal runaway under abnormal operating conditions such as overcharging, mechanical damage, or internal short circuits, leading to fires or even explosions. Their combustion is characterized by high temperature, rapid spread, and a high re-ignition rate, rendering traditional fire extinguishing methods ineffective. Aerosol fire suppression technology, due to its advantages such as not requiring pressurized containers, rapid response, and applicability to confined spaces, is gradually becoming an important option for lithium battery fire prevention and control. Among these, potassium-based K-type aerosol extinguishing agents are the mainstream solution.

[0003] K-type aerosols, upon electro-initiation, generate a large number of micron-sized potassium salt particles (such as potassium carbonate and potassium acetate) and inert gases, interrupting the free radical chain reaction in the flame zone, thus achieving rapid fire extinguishing. Although potassium salt-based aerosols can achieve instantaneous fire extinguishing, their residues are highly hygroscopic and alkaline, easily forming conductive liquid films in humid environments. This not only severely corrodes precision electronic components but may also induce secondary short circuits.

[0004] Meanwhile, such fire extinguishing agents only act on the outside of the flame and cannot intervene in the ongoing electrochemical side reactions inside the battery—especially the internal short circuit process caused by lithium dendrites piercing the separator. They lack a long-term suppression mechanism for the root cause of thermal runaway. In addition, the high temperature (up to 1000°C or more) that accompanies the instantaneous aerosol spray may also cause thermal shock to nearby undamaged batteries, exacerbating the risk of system-wide cascading failures. Summary of the Invention

[0005] To achieve the aforementioned objectives, this invention provides a lithium battery fire extinguishing agent and its preparation method. The fire extinguishing agent is based on a synergistic mechanism of inorganic mineral expansion and free radical quenching. It uses lithium salt-doped expandable graphite as a core carrier and introduces specific functional components through interlayer intercalation technology. Under high-temperature thermal runaway conditions, it simultaneously achieves a triple fire extinguishing effect of physical isolation, gas-phase chemical inhibition, and electrochemical interface passivation. This fundamentally solves the technical defects of existing potassium salt-based aerosol fire extinguishing agents, such as strong corrosiveness, inability to inhibit reignition, and lack of ability to intervene in the internal electrochemical processes of the battery.

[0006] The lithium battery fire extinguishing agent of the present invention is composed of the following components in mass percentage: 65% to 85% expandable graphite, 8% to 20% lithium salt, 3% to 10% transition metal oxide precursor, and 2% to 5% binder. The expandable graphite has an initial expansion temperature of 180℃ to 220℃, an expansion ratio greater than 300 times at 900℃, an initial particle size of 50μm to 200μm, and a carbon content greater than 99%. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide with a melting point of 236℃, undergoing thermal decomposition above 250℃, releasing fluorine-containing free radicals (·CF3, ·SO2F) and inert gases (N2, CO2). The transition metal oxide precursor is a mixture of manganese nitrate and cobalt nitrate, with a molar ratio of manganese to cobalt of 2:1. This precursor decomposes within the 300℃ to 400℃ range to generate a spinel-structured Mn3O4 and Co3O4 composite oxide with a specific surface area of ​​40m². 2 / g to 80m 2 / g, exhibiting catalytic decomposition activity against peroxy free radicals (ROO·); the binder is polyvinylidene fluoride with a molecular weight of 500,000 to 1,000,000, added in the form of an N-methylpyrrolidone solution with a solid content of 10%, used to maintain the integrity of the particle structure during the formulation process.

[0007] The lithium salt and transition metal oxide precursors of the lithium battery fire extinguishing agent are uniformly embedded in the interlayer lattice gaps of expandable graphite through ion exchange and interlayer intercalation processes, increasing the interlayer spacing from the original 0.335 nm to 0.7 nm to 1.2 nm. This structure ensures that, in the initial stage of heating, the intercalated material preferentially decomposes and releases the active components, while simultaneously inducing the graphite layer to expand dramatically along the c-axis, forming a worm-like porous carbon skeleton. The expanded graphite worms are loaded with nanoscale transition metal oxide particles with a particle size of 10 nm to 50 nm, uniformly distributed on the outer surface of the carbon layer and the inner wall of the pores, constituting a highly efficient gas-solid phase catalytic interface.

[0008] In a preferred embodiment of the present invention, the lithium battery fire extinguishing agent is prepared by the following steps: First, expandable graphite is placed in deionized water and ultrasonically dispersed for 30 minutes to form a suspension with a concentration of 50 g / L; then, under stirring, a measured amount of lithium bis(trifluoromethanesulfonyl)imide mixed solution with manganese nitrate and cobalt nitrate is added sequentially, controlling the pH of the reaction system to be 5.5 to 6.5 and the temperature to be 60°C, and stirring is continued for 4 hours to allow lithium ions and transition metal ions to enter the graphite interlayer through electrostatic interaction and coordination bonding; next, the obtained slurry is filtered and washed until the conductivity of the filtrate is lower than 50 μS / cm, and then vacuum dried at 80°C for 12 hours to obtain an intercalated composite precursor; finally, the precursor is mixed with an N-methylpyrrolidone solution of polyvinylidene fluoride in a certain proportion, homogenized by ball milling, and pressed into cylindrical explosive columns with a diameter of 10 mm and a thickness of 5 mm, and cured in a vacuum environment at 60°C for 24 hours to obtain the finished fire extinguishing agent.

[0009] In another preferred embodiment of the present invention, the extinguishing agent is directly packaged in powder form within the reaction chamber of a non-pressurized fire extinguishing device, without the need for additional molding. This powder is obtained by freeze-drying the aforementioned intercalated composite precursor and then pulverizing it to a particle size of 100 μm to 300 μm, with a loose packing density of 0.3 g / cm³. 3 up to 0.5 g / cm 3 Its flowability meets the requirement of Hall effect flowmeter readings of less than 15 seconds / 50g, making it suitable for fast-response systems triggered by electrothermal or laser.

[0010] The working mechanism of the fire extinguishing agent described in this invention is as follows: When a lithium battery experiences thermal runaway and the local temperature rises above 200°C, the agent is activated. First, the intercalated lithium bis(trifluoromethanesulfonyl)imide undergoes thermal decomposition, as shown in the following reaction formula: 2LiTFSI→2LiF+(CF3SO2)2N - →·CF3+·SO2F+N2+CO2+other inert gases.

[0011] The released ·CF3 and ·SO2F free radicals rapidly capture ·H and ·OH free radicals in the flame zone, interrupting the combustion chain reaction. Simultaneously, the LiF produced by decomposition and the incompletely decomposed lithium salt residue migrate to the damaged battery surface at high temperatures. At the same time, expandable graphite expands perpendicular to the basal plane due to a sudden increase in interlayer gas pressure, rapidly increasing in volume by more than 300 times, forming a low-density, high-porosity (porosity greater than 95%) worm-like carbon network covering the surface of the battery cells, isolating oxygen and blocking heat radiation from being transferred to adjacent cells. During this process, the Mn3O4-Co3O4 composite oxide generated by the simultaneous decomposition of transition metal oxide precursors is loaded onto the surface of the expanded graphite, where surface oxygen vacancies and variable valence metal centers (Mn3O4-Co ... 2+ / Mn3+ Co 2+ / Co 3+ It continuously catalyzes the decomposition of peroxy free radicals in the gas phase (ROO·→RO·+1 / 2O2), thus prolonging the duration of chemical inhibition.

[0012] This invention achieves an electrochemical passivation effect on thermal runaway batteries. When fire extinguishing agents cover battery areas with electrolyte leakage or separator damage, the residual lithium salts and expanded graphite work together to form a layer rich in LiF and Li on the exposed lithium metal or graphite surface of the negative electrode in situ. x PO y F z A composite solid electrolyte interface membrane of organic lithium salts was developed. This membrane exhibits high ionic conductivity and low electronic conductivity, preventing electrons from crossing the interface and initiating continuous side reactions, while simultaneously inhibiting the further growth and penetration of lithium dendrites.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention, by constructing a novel composite carrier system of lithium salt-doped expandable graphite, integrates for the first time three major functions—physical expansion isolation, gas-phase free radical quenching, and electrochemical interface repair—into a single agent. This achieves a shift in the fire extinguishing process from external flame suppression to internal electrochemical steady-state reconstruction, solving the problems of strong corrosiveness and high reignition rate of traditional aerosol fire extinguishing agents. Through an in-situ solid electrolyte interface film repair mechanism, it provides a new safety pathway after lithium battery fires. The agent's preparation process is mature, raw materials are widely available, and costs are controllable, making it promising for large-scale engineering applications. Detailed Implementation

[0014] This invention provides a lithium battery fire extinguishing agent and its preparation method. Based on the synergistic mechanism of inorganic mineral expansion and free radical quenching, this technical solution uses lithium salt-doped expandable graphite as the core carrier and introduces specific functional components through interlayer intercalation technology. Under high-temperature thermal runaway conditions, it simultaneously achieves a triple fire extinguishing effect of physical isolation, gas-phase chemical inhibition, and electrochemical interface passivation. This fundamentally solves the technical defects of existing potassium salt-based aerosol fire extinguishing agents, such as strong corrosiveness, inability to inhibit reignition, and lack of ability to intervene in the internal electrochemical processes of the battery.

[0015] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0016] Example 1 The lithium battery fire extinguishing agent is composed of the following components by mass percentage: 75% expandable graphite, 15% lithium bis(trifluoromethanesulfonyl)imide, 6% manganese nitrate + cobalt nitrate, and 4% polyvinylidene fluoride. Mn:Co molar ratio = 2:1; Expansion initiation temperature: 200℃; The expansion ratio at 900℃ is 320 times; Intercalation reaction at 60℃ for 4 hours, press into Φ10mm×5mm propellant columns, and vacuum cure at 60℃ for 24 hours; Preparation steps: S1: Expandable graphite is ultrasonically dispersed into a 50 g / L suspension; S2: Lithium bis(trifluoromethanesulfonyl)imide and metal salt solution were added at 60℃ and pH 6.0, and the mixture was intercalated for 4 hours. S3: Filter and wash until conductivity <50μS / cm, then vacuum dry at 80℃ for 12h; S4: Mix with polyvinylidene fluoride, ball mill, mold, and vacuum cure to obtain a drug cartridge.

[0017] Example 2 The lithium battery fire extinguishing agent is composed of the following components by mass percentage: 65% expandable graphite, 20% lithium bis(trifluoromethanesulfonyl)imide, 10% metal precursor, and 5% polyvinylidene fluoride; the rest is the same as in Example 1. Preparation steps: Same as in Example 1.

[0018] Example 3: The lithium battery fire extinguishing agent is composed of the following components by mass percentage: 85% expandable graphite, 8% lithium bis(trifluoromethanesulfonyl)imide, 5% metal precursor, and 2% polyvinylidene fluoride; the remainder is the same as in Example 1. Preparation steps: Same as in Example 1.

[0019] Example 4 The lithium battery fire extinguishing agent is composed of the following components by mass percentage: lithium bis(trifluoromethanesulfonyl)imide 8%, expandable graphite 82%, metal precursor 7%, polyvinylidene fluoride 3%; the remainder is the same as in Example 1. Preparation steps: Same as in Example 1.

[0020] Example 5 The lithium battery fire extinguishing agent is composed of the following components by mass percentage: lithium bis(trifluoromethanesulfonyl)imide 20%, expandable graphite 68%, metal precursor 8%, polyvinylidene fluoride 4%; the rest is the same as in Example 1. Preparation steps: Same as in Example 1.

[0021] Example 6 The composition is as follows: 3% metal precursor, 79% expandable graphite, 15% lithium bis(trifluoromethanesulfonyl)imide, 3% polyvinylidene fluoride; the remainder is the same as in Example 1. Preparation steps: Same as in Example 1.

[0022] Example 7: The composition of the lithium battery fire extinguishing agent is the same as in Example 1; The process was changed to freeze drying + air jet milling, with a particle size of 100-300μm; the preparation steps are: freeze drying of the intercalation precursor, air jet milling and sieving to obtain powdered drug.

[0023] Example 8 The lithium battery fire extinguishing agent is composed of the following components by mass percentage: 5% polyvinylidene fluoride, 74% expandable graphite, 15% lithium bis(trifluoromethanesulfonyl)imide, and 6% metal precursor; the rest is the same as in Example 1. Preparation steps: Same as in Example 1.

[0024] Comparative Example 1 Potassium-based aerosol, free of expanded graphite, lithium bis(trifluoromethanesulfonyl)imide, and transition metal components; Preparation steps: Traditional aerosol ignition powder production process.

[0025] Comparative Example 2 The components are the same as in Example 1, and are directly physically mixed without interlayer intercalation. Preparation steps: simple ball milling and mixing, without intercalation or interlayer diameter expansion.

[0026] Test method: Extinguishing time: 10kW lithium iron phosphate fire, 50g / m³ of fire extinguishing agent 3 Record the time it takes for the flame to extinguish; Reignition status: Observe for 30 minutes after extinguishing the fire and record whether reignition occurs; Expansion ratio: The number of times a volume expands at 900℃; Corrosion rate: FR-4 copper plate accelerated corrosion test 72h; Residual current decay rate: the percentage decrease in short-circuit current 5 minutes after fire extinguishing; pH value: pH value of the aqueous extract of the residue.

[0027] The test data comparisons are shown in Table 1 and Table 2.

[0028] Table 1. Comparison of Extinguishing Time, 30-Minute Reignition, and Expansion Ratio Table 2 Comparison of Corrosion Rate, Residual Current Decay Rate, and Residue pH Examples 1 to 8 exhibited extinguishing times of 5-9 seconds, no reignition within 30 minutes, expansion ratios ≥305 times, corrosion rates ≤1.4 μm / year, current decay rates ≥90%, and residue pH of 6.8-7.1, demonstrating comprehensive performance far superior to the comparative examples. Comparative example 1, with its traditional potassium salt exhibiting strong corrosion, easy reignition, and lack of electrochemical passivation, and comparative example 2 lacking intercalation structure, exhibiting poor expansion and dispersion, slow extinguishing, and easy reignition, confirming that the intercalation composite system is the core technology.

[0029] Increased lithium bis(trifluoromethanesulfonyl)imide content (Examples 4 → 1 → 5) results in stronger free radical quenching, faster fire extinguishing, and higher current decay; increased expandable graphite content (Examples 2 → 1 → 3) provides better physical isolation and lower corrosion; the powder (Example 7) has performance comparable to the propellant column and is suitable for different devices; physical mixing (Comparative Example 2) results in uneven composition and a significant decrease in efficiency.

[0030] This invention achieves rapid fire extinguishing, no reignition, low corrosion, and high safety through a four-layer synergistic mechanism: physical oxygen isolation by expanded graphite, chain scission of fluorine-containing free radicals released by lithium bis(trifluoromethanesulfonyl)imide, catalytic decomposition of peroxy free radicals by Mn3O4-Co3O4, and passivation of electrochemical side reactions by in-situ formation of a solid electrolyte interface film. It completely replaces traditional potassium salt aerosols and is suitable for fire protection of lithium batteries in power batteries and energy storage power stations.

[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium battery fire extinguishing agent, characterized in that, Composed of the following components by mass percentage: Expandable graphite contains 65% to 85%; Lithium salts: 8% to 20%; Transition metal oxide precursors 3% to 10%; Adhesive 2% to 5%.

2. The lithium battery fire extinguishing agent according to claim 1, characterized in that, The lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

3. The lithium battery fire extinguishing agent according to claim 1, characterized in that, The transition metal oxide precursor is a mixture of manganese nitrate and cobalt nitrate, wherein the molar ratio of manganese to cobalt is 2:

1.

4. The lithium battery fire extinguishing agent according to claim 1, characterized in that, The adhesive is polyvinylidene fluoride with a molecular weight of 500,000 to 1,000,000.

5. The lithium battery fire extinguishing agent according to claim 1, characterized in that, The expandable graphite, after being expanded at high temperature, forms a worm-like porous carbon skeleton with a porosity greater than 95% and an expansion ratio greater than 300 times.

6. The lithium battery fire extinguishing agent according to claim 5, characterized in that, The worm-like porous carbon skeleton has Mn3O4-Co3O4 composite oxide nanoparticles loaded on its surface and the inner walls of its pores, forming a gas-solid phase catalytic interface.

7. The lithium battery fire extinguishing agent according to claim 1, characterized in that, The agent is in the form of a cylindrical drug column with a diameter of 10 mm, a thickness of 5 mm, and a compressive strength greater than 8 MPa.

8. The lithium battery fire extinguishing agent according to claim 7, characterized in that, The cylindrical propellant grains are prepared by ball milling, homogenizing, molding, and vacuum curing at 60°C for 24 hours using an intercalated composite precursor and a polyvinylidene fluoride binder.

9. The lithium battery fire extinguishing agent according to claim 1, characterized in that, The pharmaceutical agent exists in powder form and is prepared by freeze-drying and air-jet milling of an intercalated composite precursor, with a specific surface area of ​​100 m². 2 / g to 140m 2 / g.

10. A method for preparing a lithium battery fire extinguishing agent as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Expandable graphite was ultrasonically dispersed in deionized water to form a 50 g / L suspension. Add lithium bis(trifluoromethanesulfonylimide) solution and mixed solution of manganese nitrate and cobalt nitrate in sequence, and stir to complete the intercalation; Filter and wash until the conductivity of the filtrate is below 50 μS / cm; Vacuum drying yields intercalated composite precursors; It is then mixed with polyvinylidene fluoride binder, and after ball milling, pressing and molding and vacuum curing, a cylindrical drug cartridge is obtained.

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