Sodium-ion battery thermal runaway flame-retardant coolant based on free radical annihilation-phase change phagocytosis and preparation method thereof

Abstract

The invention discloses a sodium ion battery thermal runaway flame-retardant cooling agent based on free radical annihilation-phase change phagocytosis. The sodium ion battery thermal runaway flame-retardant cooling agent is prepared from the following raw materials in percentage by mass: 35 to 40 percent of TEP, 18 to 22 percent of DMMP, 13 to 16 percent of DME, 10 to 15 percent of PMMA microcapsule ADP, 4 to 6 percent of perfluorohexanone, 3 to 5 percent of TEGDME, 2.5 to 3.5 percent of anticorrosive agent, 1.0 to 1.8 percent of perfluoropolyether surfactant, 0.8 to 1.2 percent of diethylene glycol monobutyl ether, 0.8 to 1.2 percent of nano SiO2, 0.3 to 0.7 percent of PIBSI and 0.01 percent of polyether modified silicone oil. The invention also provides a preparation method of the flame-retardant coolant. According to the flame-retardant coolant, the free radical concentration is reduced by more than 98% through low-pressure atomization spraying in the early stage of thermal runaway (130-160 DEG C), and meanwhile, temperature irreversible pressing is realized, so that combustion starting is blocked from the source.

Description

Technical Field

[0001] This invention relates to the field of new energy battery safety technology, and more specifically, to a sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change annihilation and its preparation method. It is particularly effective for early blocking of thermal runaway and rapid suppression of combustion and explosion in layered oxide cathode sodium-ion batteries, achieving triple protection of free radical quenching, heat absorption and cooling, and permanent barrier. Background Technology

[0002] With the rapid development of the new energy industry, lithium iron phosphate batteries are widely used in energy storage due to their advantages such as high safety and long cycle life. Sodium-ion batteries with layered oxide cathodes have developed rapidly in the energy storage field due to their cost advantage. However, their electrolytes are mainly ether solvents (such as ethylene glycol dimethyl ether). These solvents have low flash points (-20℃) and high volatility. When thermal runaway occurs, they are prone to forming flammable vapor clouds, posing an extremely high risk of deflagration.

[0003] Sodium-ion batteries (especially those using ether-based electrolytes) currently face two major safety challenges: Early stage of thermal runaway: At 130-160℃, ether solvents decompose to produce CH3 free radicals, which cannot be precisely quenched by existing flame retardants; Combustion and explosion period: At temperatures above 250℃, the deflagration energy density can reach as high as 250 MJ / m³. 3 Traditional fire extinguishing agents have difficulty penetrating flames and cannot suppress reignition.

[0004] Existing technologies suffer from several drawbacks: single-stage injection designs cannot adapt to both "blocking-extinguishing" and "fire suppression" scenarios; flame retardants and coolants have poor compatibility, and nozzles are prone to clogging at low temperatures; a dual-stage protection system of "early annihilation-explosive engulfment" has not been established, resulting in a lack of active suppression of exothermic side reactions and a secondary fire rate exceeding 20%. Therefore, there is an urgent need for a flame-retardant coolant based on a synergistic mechanism of free radical annihilation and phase change engulfment to fundamentally prevent irreversible thermal runaway. Summary of the Invention

[0005] To address the shortcomings of existing technologies, one of the objectives of this invention is to provide a sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change phagocytosis. In the early stage of thermal runaway (130-160℃), the free radical concentration is reduced by more than 98% through low-pressure atomization injection, while achieving irreversible temperature suppression (temperature drop ≥25℃ after triggering at 130℃, peak temperature ≤110℃), blocking the combustion initiation from the source. In the combustion and explosion stage (>250℃): the oxygen concentration drops to asphyxiation level (≤5%) within 3 seconds, and the permanent ceramic layer isolates the re-ignition path.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A flame-retardant coolant for sodium-ion batteries based on free radical annihilation-phase transition engulfment, comprising the following raw materials by mass percentage: triethyl phosphate (TEP) 35-40%, dimethyl methylphosphonate (DMMP) 18-22%, dimethyl ethylene glycol (DME) 13-16%, PMMA microcapsule ADP 10-15%, perfluorohexanone 4-6%, tetraethylene glycol dimethyl ether (TEGDME) 3-5%, corrosion inhibitor (benzotriazole) 2.5-3.5%, perfluoropolyether surfactant 1.0-1.8%, diethylene glycol monobutyl ether 0.8-1.2%, nano-SiO2 0.8-1.2%, polyisobutylene succinimide (PIBSI) 0.3-0.7%, and polyether-modified silicone oil 0.01%; wherein the perfluorohexanone is Novec 7100; the tetraethylene glycol dimethyl ether contains 0.1% nano-TiO2; and the corrosion inhibitor is benzotriazole.

[0007] The sodium-ion battery thermal runaway flame-retardant coolant provided by this invention reduces the free radical concentration by more than 98% in the early stage of thermal runaway (130-160℃) through low-pressure atomization injection, while achieving irreversible temperature suppression (temperature drop ≥25℃ after triggering at 130℃, peak value ≤110℃), blocking the combustion initiation from the source. In the combustion and explosion stage (>250℃): the oxygen concentration drops to the asphyxiation level (≤5%) within 3 seconds, and the permanent ceramic layer isolates the re-ignition path.

[0008] Preferably, the method for preparing the PMMA microcapsules ADP is as follows: (a) Pulverize ammonium dihydrogen phosphate (ADP) to D50=5μm, and dissolve PMMA resin in acetone to prepare a PMMA solution with a mass fraction of 15%. (b) ADP particles were coated with PMMA solution in a fluidized bed until the coating weight gain reached 300%; (c) After discharge, 1% nano SiO2 reinforcing agent is dry-mixed in to obtain PMMA microcapsules ADP with a particle size of 15±2μm (compressive strength ≥40MPa).

[0009] Preferably, in step (b), the inlet air temperature of the fluidized bed is set to 60℃±2℃, and the atomization pressure is set to 0.3MPa.

[0010] The second objective of this invention is to provide a method for preparing the above-mentioned sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change phagocytosis, comprising the following steps: (1) Raw material pretreatment: Ethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are dehydrated respectively, and the water content of ethylene glycol dimethyl ether is controlled to be ≤30ppm and the water content of tetraethylene glycol dimethyl ether is ≤20ppm. (2) Microemulsion preparation: According to the mass ratio, diethylene glycol monobutyl ether and dehydrated ethylene glycol dimethyl ether are added to the reactor. After stirring magnetically at 20-30℃ for 8-12 min, perfluoropolyether surfactant is added. Then, the mixture is stirred at a rate of 550-650 r / min for 25-35 min until the transmittance is ≥95%. Then, the mixture is initially ultrasonically emulsified at a power of 500W for 13-17 min (pulse mode). The particle size distribution of the micelles is detected by a laser particle size analyzer. Perfluorohexanone is added dropwise. The mixture is stirred at a rate of 550-650 r / min for 15-25 min. Then, the mixture is ultrasonically emulsified a second time at a power of 300W for 10-15 min. The particle size distribution of the mixture is detected by a laser particle size analyzer. (3) Preparation of flame retardant base liquid: Dissolve triethyl phosphate and polyisobutylene succinimide in a 40°C water bath according to the mass ratio, add dimethyl methylphosphonate and benzotriazole in sequence, purge the air in the reactor with high-purity nitrogen three times, and finally stir in an anchoring motion at a rate of 350-450 r / min for 15-25 min. Use dynamic light scattering to detect the particle size distribution of the mixture. (4) Add the prepared flame retardant base liquid and microemulsion to the reaction vessel and stir at a rate of 500-600 r / min for 10-15 min (temperature ≤30℃). Add the pretreated tetraethylene glycol dimethyl ether slowly at a rate of ≤5 g / min and stir at a rate of 250-350 r / min for 10-15 min. Then add PMMA microcapsules ADP in batches and stir at a rate of 200 r / min. Add nano SiO2 and circulate it using a pipeline high shear emulsification pump. At the same time, monitor the mixture using an online rotational viscometer to obtain a mixture with a viscosity of 5.0±0.5 mPa·s at 25℃. (5) Post-processing: Degas the mixture obtained in step (4) under a vacuum of -0.1MPa for 45 min (25℃) until the dissolved gas content is ≤0.05mL / L. Then add polyether modified silicone oil, stir at a rate of 250-350r / min for 2-3 min for initial dispersion, and then shear at a rate of 550-650r / min for 3-5 min to eliminate foam. Complete the filling in a nitrogen glove box and seal it with PTFE coated aluminum-plastic composite bags (corrosion resistance grade A).

[0011] Furthermore, the dehydration treatment method for the ethylene glycol dimethyl ether is as follows: the ethylene glycol dimethyl ether is statically dehydrated for 48 hours through a 4A molecular sieve with a particle size of 3-5 mm and the amount of molecular sieve used is 1 / 5 of the mass of DME. After dehydration, it is filtered under pressure through a 0.2 μm polyethersulfone filter membrane at a pressure of 0.3 MPa.

[0012] Furthermore, the dehydration treatment method for the tetraethylene glycol dimethyl ether is as follows: the tetraethylene glycol dimethyl ether is dehydrated with double the amount of 4A molecular sieve for 72 hours, the amount of molecular sieve being 2 / 5 of the mass of the tetraethylene glycol dimethyl ether. After dehydration, trace amounts of water are removed by molecular distillation at a temperature of 120°C. The mixture is then heated to 60°C, 0.1% nano-TiO2 crystal nucleus inhibitor is added, and the mixture is ultrasonically dispersed for 10 minutes. Finally, the mixture is cooled to 25°C for later use.

[0013] Further, in step (2), the laser particle size analyzer detects that the micelles after the first ultrasonic emulsification have a D90 ≤ 200 nm, and the laser particle size analyzer detects that the mixture after the second ultrasonic emulsification has a D90 ≤ 150 nm.

[0014] Furthermore, in step (3), the purity of the high-purity nitrogen gas is 99.999%, and the mixture D50 is ≤0.5μm detected by dynamic light scattering.

[0015] Furthermore, in step (4), the cyclic processing technique is as follows: shear rate 10 4 s -1 3 times × 5 minutes.

[0016] Furthermore, in step (5), the environment inside the nitrogen glove box is controlled as follows: O2≤1ppm, H2O≤10ppm.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. The free radical annihilation-phase change phagocytosis synergistic flame retardant coolant provided by this invention reduces the free radical concentration by more than 98% through low-pressure atomization injection in the early stage of thermal runaway (130-160℃), while achieving irreversible temperature suppression (temperature drop ≥25℃ after triggering at 130℃, peak value ≤110℃), blocking the combustion initiation from the source. In the combustion and explosion stage (>250℃): the oxygen concentration drops to the asphyxiation level (≤5%) within 3 seconds, and the permanent ceramic layer isolates the re-ignition path.

[0018] 2. This invention constructs a two-stage precision protection system, optimizes the rheological properties and spray adaptability of the agent, and achieves the early blocking stage by using 0.5MPa low-pressure atomization (particle size 5-10μm) to cover 90% of the battery surface within 3 seconds; and the explosion suppression stage by using 2MPa high-pressure injection (flow rate ≥15m / s) to reduce the oxygen concentration to below 5% within 3 seconds, and the flame suffocation time ≤0.5 seconds, completely eliminating the possibility of reignition.

[0019] 3. This invention solves the corrosion problem of the agent on the spraying device (corrosion rate ≤0.02mm / year) and the low-temperature blockage problem (viscosity ≤15mPa·s at -20℃, viscosity ≤105mPa·s at -40℃), overcomes the bottleneck of industrial application, and solves the compatibility problem between flame retardant and coolant. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfmentation according to the present invention. Figure 2 This is a schematic diagram illustrating the mechanism of action of the sodium-ion battery thermal runaway flame-retardant coolant of the present invention; Figure 3 This is a schematic diagram of the structure of the PMMA microcapsule ADP prepared in Example 1 of the present invention.

[0021] Explanation of the labels in the diagram: 1. PMMA wall material; 2. ADP core material; 3. Nano-SiO2. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available. For any specific techniques or conditions not specified in the examples, they can be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0024] A flame-retardant coolant for sodium-ion batteries based on free radical annihilation-phase transition phagocytosis thermal runaway comprises the following raw materials in weight percentages: triethyl phosphate (TEP) 35-40%, dimethyl methylphosphonate (DMMP) 18-22%, dimethyl ethylene glycol (DME) 13-16%, PMMA microcapsule ADP 10-15%, perfluorohexanone 4-6%, tetraethylene glycol dimethyl ether (TEGDME) 3-5%, corrosion inhibitor (benzotriazole) 2.5-3.5%, perfluoropolyether surfactant 1.0-1.8%, diethylene glycol monobutyl ether 0.8-1.2%, nano-SiO2 0.8-1.2%, polyisobutylene succinimide (PIBSI) 0.3-0.7%, and polyether-modified silicone oil 0.01%; wherein the perfluorohexanone is Novec. 7100; the tetraethylene glycol dimethyl ether contains 0.1% nano-TiO2; the corrosion inhibitor is benzotriazole.

[0025] Triethyl phosphate (TEP) is positioned as a core flame-retardant component in the early spraying stage. Its low viscosity (3.5 mPa·s at 25°C) ensures an atomized particle size of 5-10 μm under low pressure (0.5 MPa). It decomposes at 160°C to generate PO· radicals, which react with CH3· radicals at a rate of 8.5 × 10⁻⁶.8 L / (mol・s), rapidly reducing the concentration of active free radicals.

[0026] The functional role of dimethyl methylphosphonate (DMMP): the core of vapor phase flame retardancy during the explosion stage. Its high volatility (vapor pressure 2.6 kPa / 20℃) is suitable for high-pressure (2 MPa) injection, allowing the agent to penetrate the flame zone with a 15 m / s airflow. It decomposes at 250℃ to produce methylphosphonic anhydride and P2O5 aerosol (particle size 0.5-2 μm). Methylphosphonic anhydride captures ·O· free radicals (chain reaction terminator), and P2O5 aerosol physically isolates oxygen, forming a dual chemical and physical flame retardant barrier.

[0027] The functional positioning of dimethyl ethylene glycol (DME): to regulate injection flowability; microemulsion continuous phase, low viscosity (0.46 mPa·s / 25℃) to ensure that the agent can be pumped at -20℃.

[0028] Functional positioning of PMMA microcapsules containing ADP: Phase change endothermic material; at 160℃, the wall material cracks, and ADP decomposes (ADP decomposition: NH4H2PO4→HPO3+NH3↑+H2O↑), absorbing 198kJ / mol of heat and achieving a temperature drop of 35℃; Secondary flame retardant properties; the released NH3 reduces the oxygen concentration (↓5%), and HPO3 reacts with the positive electrode metal oxide (such as Co3O4) to generate a phosphate substrate framework, providing anchoring points for the crosslinking of PO· free radicals from TEP decomposition with TEGDME. At temperatures above 250℃, on the phosphate substrate, the PO· free radicals from TEP decomposition and TEGDME complete the three-dimensional ceramic network crosslinking, jointly forming an organic-inorganic hybrid ceramic layer.

[0029] The functional positioning of perfluorohexanone (Novec 7100): phase change consuming core, achieving microsecond-level vaporization at a boiling point of 34℃, absorbing 110kJ / kg vaporization heat dissipation, causing the flame zone temperature to drop sharply by 300℃; chemical asphyxiant, the decomposition product perfluoroalkanes dilute oxygen, and work with P2O5 to compress the oxygen concentration to the asphyxiation level (<6%).

[0030] The functional positioning of tetraethylene glycol dimethyl ether (TEGDME): a re-ignition barrier; its high boiling point (275℃) allows it to form a viscous ceramic precursor film (viscosity 250 mPa·s / 100℃) on the electrode surface after spraying, slowing the evaporation rate of the flame retardant by 40% and inhibiting re-ignition; the cross-linking of ether bond oxygen atoms with HPO3 enhances the toughness of the ceramic layer; a low-temperature stability core; nano-TiO2 locks in trace moisture (≤20ppm) through surface hydroxyl groups, blocking the nucleation path of low-temperature ice crystals, ensuring zero crystallization at -20℃; and it inhibits viscosity abrupt changes, with viscosity fluctuations ≤2% at -40℃ (fluctuations >30% without addition), ensuring spraying accuracy in extreme environments.

[0031] The function of the corrosion inhibitor (benzotriazole) is as a metal corrosion inhibitor to protect the spraying device. It forms an Al2O3-BTA composite film (5-8 nm thick) on the surface of the aluminum nozzle, reducing the corrosion rate from 0.12 mm / year to 0.02 mm / year, ensuring a spraying device lifespan of ≥5 years.

[0032] Functional positioning of perfluoropolyether surfactants: Microemulsion stabilization core, hydrophilic-perfluoroalkyl amphiphilic structure to form nano micelles (particle size ≤150nm), encapsulating Novec 7100, increasing its solubility in DME from 3.7% to 12.8%; Flame retardant enhancement: decomposes at high temperature to produce PF5 gas, diluting oxygen concentration.

[0033] Functional positioning of diethylene glycol monobutyl ether: microemulsion cosolvent, reducing oil / water interfacial tension to <5mN / m, stabilizing nano micelles; safe alternative, flash point 96℃ (compared to n-propanol 22℃), eliminating the risk of combustion and explosion during storage.

[0034] Functional role of nano-SiO2: Microencapsulation reinforcing agent, embedded in PMMA wall material (hydrogen bonding), increasing compressive strength from 18MPa to 42MPa; rheological regulation, forming a weak gel network to prevent microemulsion stratification. PMMA wall material (temperature resistance 180℃) + nano-SiO2 reinforcement (compressive strength increased by 230%) ensures storage stability.

[0035] Functional positioning of polyisobutylene succinimide (PIBSI): ensuring low-temperature flowability, adsorbing wax crystal nuclei with polar heads, and long alkyl chains (C 80 ~C 100 The microcapsules encapsulate the crystals, causing the viscosity at -40℃ to decrease from 300 mPa·s to 105 mPa·s; the microcapsule dispersant prevents the ADP microcapsules from settling (settling rate <0.05%).

[0036] The functional positioning of polyether modified silicone oil: the core of post-treatment defoaming, reducing surface tension to ≤22mN / m, eliminating microbubbles generated by vacuum degassing, and ensuring spraying accuracy.

[0037] Example 1: Preparation of a flame-retardant coolant for thermal runaway in sodium-ion batteries Step 1: Solvent dehydration and pretreatment ① Take 16 kg of ethylene glycol dimethyl ether (DME) and statically dehydrate it through a 4A molecular sieve (particle size 3-5 mm) for 48 h. After dehydration, filter it under pressure through a 0.2 μm polyethersulfone membrane at a pressure of 0.3 MPa to obtain DME with a water content ≤28 ppm. ② Take 4 kg of tetraethylene glycol dimethyl ether (TEGDME) and dehydrate it through a double amount of 4A molecular sieve for 72 h. After molecular distillation at 120℃ / 5Pa, a product with a water content of ≤18ppm is obtained. Then, add 4 g of nano TiO2 (0.1wt%) to it and ultrasonically disperse it at 60℃ for 10 min for later use.

[0038] Step 2: Preparation of ADP in PMMA microcapsules Crush ammonium dihydrogen phosphate (ADP) to D 50 =5μm; PMMA resin was dissolved in acetone to prepare a 15% (w / w) PMMA solution, which was then sprayed into a fluidized bed to coat ADP particles (inlet air 60℃±2℃, atomization pressure 0.3MPa) until the coating weight gain reached 300%; after discharge, 1.2kg of nano-SiO2 (accounting for 1% of the total microcapsule volume) was dry-mixed in to obtain microcapsules with a particle size of 15±2μm and a compressive strength of 42MPa. The structure is as follows. Figure 3 As shown.

[0039] PMMA microcapsule ADP functional timing: Stage 1 (Storage period): No crystallization at -20℃ (nano-TiO2 inhibits ice crystal nucleation).

[0040] Stage 2 (160℃ rupture): ADP decomposition is endothermic by 198kJ / mol, releasing NH; reducing oxygen concentration (15%), HPO3 reacts with positive electrode metal oxides (such as CO3O4) to generate a phosphate matrix framework, providing anchoring sites for the crosslinking of PO· free radicals from TEP decomposition with TEGDME.

[0041] Stage 3 (>250℃ for ceramic formation): On the phosphate substrate, PO· free radicals from TEP decomposition crosslink with TEGDME to form a ceramic layer (3D network structure).

[0042] Step 3: Microemulsion Pre-preparation 14.5 kg of dehydrated DME and 1 kg of diethylene glycol monobutyl ether were added to the reactor and magnetically stirred at 25 °C for 10 min. 1.5 kg of perfluoropolyether surfactant was added and stirred at 600 r / min for 30 min (transmittance 96%). Then, the mixture was initially ultrasonically emulsified at 500 W power for 15 min (pulse mode), and the micelles D90 was measured to be 180 nm by a laser particle size analyzer. 5 kg of perfluorohexanone (Novec 7100) was added dropwise, and the mixture was stirred at 600 r / min for 20 min. Then, it was ultrasonically emulsified a second time at 300 W power for 10 min, and the mixture D90 was measured to be 145 nm by a laser particle size analyzer.

[0043] Step 4: Preparation of flame retardant base liquid Dissolve 38 kg of triethyl phosphate (TEP) and 0.5 kg of polyisobutylene succinimide (PIBSI) in a 40°C water bath; then add 20 kg of dimethyl methylphosphonate (DMMP) and 3 kg of benzotriazole. Purge the air in the reactor three times with high-purity nitrogen (99.999%). Finally, stir at 400 r / min for 30 min. Dynamic light scattering analysis showed that the mixture's D50 was 0.45 μm.

[0044] Step 5: Final Mixing and Rheological Control The prepared flame-retardant base liquid and microemulsion were added to the reactor and stirred at 500 r / min for 10 min (stirring temperature ≤30℃); 4 kg of pretreated TEGDME was slowly added dropwise at a rate ≤5 g / min, and then stirred at 300 r / min for 10 min; then 12 kg of PMMA microcapsules ADP were added in batches and stirred at 200 r / min; 1 kg of nano-SiO2 was added, and the mixture was circulated using a pipeline high-shear emulsification pump (shear rate 10). 4 s -1 The mixture was tested 3 times for 5 minutes, and monitored using an online rotational viscometer to obtain a viscosity of 5.2 mPa·s at 25°C.

[0045] Step 6: Post-processing The mixture obtained in step 5 was degassed under a vacuum of -0.1 MPa for 45 min, with dissolved gas ≤0.04 mL / L; then 5 g of polyether modified silicone oil was added, and the mixture was first stirred at a rate of 300 r / min for 2 min for initial dispersion, and then sheared at a rate of 600 r / min for 3 min to eliminate foam; after defoaming, the mixture was filled in a nitrogen glove box (environmental control: O2 ≤1 ppm, H2O ≤10 ppm), and finally sealed in PTFE coated aluminum-plastic composite bags.

[0046] Comparative Examples

[0047] Comparative Example 1 (raw material without TEP): free radical concentration decreased by only 62% at 130℃ (above the critical value).

[0048] Comparative Example 2 (raw materials do not contain DMMP): at 250℃, the oxygen concentration only dropped to 11%, and the reignition rate was 100%.

[0049] Comparative Example 3 (raw material without ADP microcapsules): temperature drop of only 15℃ at 160℃, no ceramic layer formed.

[0050] Comparative Example 4 (raw materials do not contain perfluoropolyether surfactants): Novec 7100 precipitation rate reached 38%, clogging the nozzle.

[0051] Performance testing The sodium-ion battery thermal runaway flame-retardant coolant prepared in Example 1 was subjected to thermal runaway prevention test (50Ah layered oxide sodium battery module), and the results are shown in Table 1 and Table 2.

[0052] Table 1. Early blocking (triggered at 130℃)

[0053] Table 2 Explosion Suppression (Open Flame Triggering)

[0054] Mechanism of action of flame-retardant coolants for thermal runaway in sodium-ion batteries: I. Core Mechanism: Targeted blocking of key thermal runaway pathways across the entire chain 1. Early stage of thermal runaway (130-160℃): Free radical annihilation + phase transition extinguishes the "ignition source". ① Triggering conditions: Triggered when the temperature reaches 130℃ or the characteristic gas (methane ≥ 50ppm, acetaldehyde ≥ 30ppm).

[0055] ② Low-pressure injection: The micro pump sprays the flame-retardant coolant with free radical annihilation-phase change synergy from the multi-directional nozzle (0.8 mm orifice, distribution density 2 particles / dm²) at a pressure of 0.5 MPa (droplet size 5-10 μm), covering 90% of the battery surface in 3 seconds.

[0056] ③ Free radical annihilation: TEP decomposes to produce PO· free radicals, at a rate of 8.5 × 10⁻⁶. 8 The L / (mol·s) rate combines with the ·CH3 free radicals generated from the decomposition of ether solvents, reducing the free radical concentration by more than 98% (below the critical value of 5 × 10⁻⁶). 14 cm -3 ).

[0057] ④ Phase change engulfment: ADP microcapsules rupture and absorb heat at 160℃ (phase change enthalpy 198kJ / mol), which, combined with Novec 7100 vaporization and heat dissipation, achieves irreversible temperature suppression (temperature drop ≥35℃ after triggering at 160℃). ⑤ Oxygen dilution: Oxygen is diluted by NH3 produced from the decomposition of ADP (concentration ↓5%).

[0058] Initialization of ceramic formation: HPO3 released from the decomposition of ADP reacts with the electrode metal oxide to form a phosphate skeleton.

[0059] 2. Combustion and explosion stage (>250℃): Flame suffocation + permanent barrier extinguishes the "flame chain". ① Triggering conditions: Triggered when the flame sensor detects an open flame or the pressure sensor measures a sudden pressure increase > 0.5 MPa.

[0060] ② High-pressure injection: The plunger pump sprays the agent from the fan-shaped nozzle (injection angle 60°) at a pressure of 2MPa, penetrating the flame zone at a flow rate of 15m / s.

[0061] ③ Flame asphyxiation: Due to its high volatility, DMMP diffuses with the airflow and decomposes at high temperatures to produce methylphosphonic anhydride (capturing O free radicals) and P2O5 aerosol (physically isolating oxygen), which capture active free radicals and rapidly replace oxygen. Within 3 seconds, the oxygen concentration in the combustion zone is reduced from 21% to below 6%, and the flame asphyxiation time is ≤0.5 seconds.

[0062] ④ Phase change engulfment + oxygen dilution: Novec 7100 vaporizes and dissipates heat, which, together with the rupture of ADP microcapsules, absorbs heat, causing the temperature in the flame zone to drop sharply by 300°C; the decomposition product, perfluoroalkane, dilutes the oxygen.

[0063] ⑤ Permanent isolation: On the phosphate backbone, the PO· free radicals from TEP decomposition crosslink with TEGDME at high temperature to form a complete ceramic layer that adheres to the electrode surface. The hardness is >3 GPa and the oxygen permeability is as low as 2.8 × 10⁻⁶. -6 cm 3 / cm 2 •s, permanently isolates combustibles from oxygen, completely eliminating the possibility of reignition.

[0064] II. Collaborative Logic: Deep Coupling of Drug Properties and System Adaptability 1. Micro-nano carrier synergistic mechanism (two-phase loading structure, solving the compatibility problem between flame retardant and coolant) ① Hydrophobic core (perfluoropolyether): Encapsulated with Novec 7100 (increases solubility to 12.1g / 100g); ② Hydrophilic continuous phase (DME + diethylene glycol monobutyl ether): dissolves TEP / DMMP (interfacial tension < 5 mN / m) 2. Enhanced stability in extreme environments ① Low-temperature anti-crystallization: TEGDME contains 0.1% nano-TiO2 crystal nucleus inhibitor, ensuring zero crystallization at -20℃. ② Synergistic effect of pour point depressant: Low-temperature fluidity is achieved through PIBSI pour point depressant and nano-SiO2 weak gel network; viscosity ≤15mPa・s at -20℃ and ≤105mPa・s at -40℃, completely solving the low-temperature clogging problem and ensuring that the injection flow rate deviation is ≤2.1% at -40℃; ③ Corrosion protection: Benzotriazole forms a 5-8nm Al2O3-BTA protective film on the surface of the aluminum nozzle, suppressing the corrosion rate to 0.018mm / year.

[0065] In summary, the free radical annihilation-phase change phagocytosis synergistic flame retardant coolant provided by this invention reduces the free radical concentration by more than 98% in the early stage of thermal runaway (130-160℃) through low-pressure atomization injection, while achieving irreversible temperature suppression (temperature drop ≥25℃ after triggering at 130℃, peak temperature ≤110℃), thus blocking the combustion initiation from the source.

[0066] This invention constructs a two-stage precision protection system, optimizes the rheological properties and spray adaptability of the agent, and achieves the early blocking stage by using 0.5MPa low-pressure atomization (particle size 5-10μm) to cover 90% of the battery surface within 3 seconds; and the explosion suppression stage by using 2MPa high-pressure injection (flow rate ≥15m / s) to reduce the oxygen concentration to below 5% within 3 seconds, and the flame suffocation time ≤0.5 seconds, completely eliminating the possibility of reignition.

[0067] This invention solves the problems of corrosion of the spraying device by the agent (corrosion rate ≤0.02mm / year) and low-temperature blockage (viscosity ≤15mPa·s at -20℃, viscosity ≤105mPa·s at -40℃), overcomes the bottleneck of industrial application, and solves the compatibility problem between flame retardant and coolant.

[0068] The embodiments disclosed in this invention are preferred embodiments, but are not limited thereto. Those skilled in the art can easily understand the spirit of this invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of this invention, they are all within the protection scope of this invention.

Claims

1. A flame-retardant coolant for sodium-ion batteries based on free radical annihilation-phase transition phagocytosis, characterized in that, The raw materials include the following percentages by weight: triethyl phosphate 35-40%, dimethyl methylphosphonate 18-22%, ethylene glycol dimethyl ether 13-16%, PMMA microcapsule ADP 10-15%, perfluorohexanone 4-6%, tetraethylene glycol dimethyl ether 3-5%, corrosion inhibitor 2.5-3.5%, perfluoropolyether surfactant 1.0-1.8%, diethylene glycol monobutyl ether 0.8-1.2%, nano-SiO2 0.8-1.2%, polyisobutylene succinimide 0.3-0.7%, and polyether-modified silicone oil 0.01%; The perfluorohexanone is Novec 7100; The tetraethylene glycol dimethyl ether contains 0.1% nano-TiO2; The corrosion inhibitor is benzotriazole.

2. The sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfment according to claim 1, characterized in that, The method for preparing ADP from PMMA microcapsules includes the following steps: (a) Pulverize ADP to D50=5μm and dissolve PMMA resin in acetone to prepare a PMMA solution with a mass fraction of 15%. (b) PMMA solution was sprayed into a fluidized bed to coat ADP particles until the coating weight gain reached 300%; (c) After discharge, 1% of nano-SiO2 reinforcing agent is dry-mixed in to obtain PMMA microcapsules ADP with a particle size of 15±2μm.

3. The sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change phagocytosis according to claim 2, characterized in that: In step (b), the inlet air temperature of the fluidized bed is set to 60℃±2℃, and the atomization pressure is set to 0.3MPa.

4. A method for preparing a sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase transition engulfment as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Raw material pretreatment: Ethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are dehydrated respectively, and the water content of ethylene glycol dimethyl ether is controlled to be ≤30ppm and the water content of tetraethylene glycol dimethyl ether is ≤20ppm. (2) Microemulsion preparation: According to the mass ratio, diethylene glycol monobutyl ether and dehydrated ethylene glycol dimethyl ether are added to the reactor. After stirring magnetically at 20-30℃ for 8-12 min, perfluoropolyether surfactant is added. Then, the mixture is stirred at a rate of 550-650 r / min for 25-35 min until the transmittance is ≥95%. Then, the mixture is initially ultrasonically emulsified at a power of 500W for 13-17 min. The particle size distribution of micelles is detected by a laser particle size analyzer. Perfluorohexanone is added dropwise. The mixture is stirred at a rate of 550-650 r / min for 15-25 min. Then, the mixture is ultrasonically emulsified a second time at a power of 300W for 10-15 min. The particle size distribution of the mixture is detected by a laser particle size analyzer. (3) Preparation of flame retardant base liquid: Dissolve triethyl phosphate and polyisobutylene succinimide in a 40°C water bath according to the mass ratio, add dimethyl methylphosphonate and benzotriazole in sequence, purge the air in the reactor with high-purity nitrogen three times, and finally stir in an anchoring motion at a rate of 350-450 r / min for 15-25 min. Use dynamic light scattering to detect the particle size distribution of the mixture. (4) Add the prepared flame retardant base liquid and microemulsion to the reaction vessel, stir at a rate of 500-600 r / min for 10-15 min, slowly add the pretreated tetraethylene glycol dimethyl ether at a rate of ≤5 g / min, stir at a rate of 250-350 r / min for 10-15 min, then add PMMA microcapsules ADP in batches, stir at a rate of 200 r / min, add nano SiO2, use a pipeline high shear emulsification pump for circulation treatment, and use an online rotational viscometer for monitoring to obtain a mixture with a viscosity of 5.0±0.5 mPa·s at 25℃; (5) Post-processing: Degas the mixture obtained in step (4) under a vacuum of -0.1MPa for 45 minutes, then add polyether modified silicone oil, first stir at a rate of 250-350r / min for 2-3 minutes for preliminary dispersion, then shear at a rate of 550-650r / min for 3-5 minutes to eliminate foam, complete filling in a nitrogen glove box, and seal with PTFE coated aluminum-plastic composite bags.

5. The preparation method of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfmentation according to claim 4, characterized in that, The dehydration treatment method for ethylene glycol dimethyl ether is as follows: ethylene glycol dimethyl ether is statically dehydrated for 48 hours through a 4A molecular sieve with a particle size of 3-5 mm and the amount of molecular sieve used is 1 / 5 of the mass of DME. After dehydration, it is filtered under pressure through a 0.2 μm polyethersulfone filter membrane at a pressure of 0.3 MPa.

6. The preparation method of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfmentation according to claim 4, characterized in that, The dehydration treatment method of the tetraethylene glycol dimethyl ether is as follows: the tetraethylene glycol dimethyl ether is dehydrated with double the amount of 4A molecular sieve for 72 hours. The amount of molecular sieve used is 2 / 5 of the mass of the tetraethylene glycol dimethyl ether. After dehydration, trace water is removed by molecular distillation at 120°C. The mixture is heated to 60°C and 0.1% nano TiO2 crystal nucleus inhibitor is added. The mixture is then ultrasonically dispersed for 10 minutes and cooled to 25°C for later use.

7. The preparation method of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfment according to claim 4, characterized in that: In step (2), the micelles after the first ultrasonic emulsification are measured to have a D90 ≤ 200 nm, and the mixture after the second ultrasonic emulsification is measured to have a D90 ≤ 150 nm.

8. The preparation method of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfmentation according to claim 4, characterized in that: In step (3), the purity of the high-purity nitrogen gas is 99.999%, and the mixture D50 is ≤0.5μm when detected by dynamic light scattering.

9. The preparation method of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfmentation according to claim 4, characterized in that, In step (4), the cyclic processing technique is as follows: shear rate 10 4 s -1 3 times × 5 minutes.

10. The preparation method of the sodium-ion battery thermal runaway retardant coolant based on free radical annihilation-phase change engulfment according to claim 4, characterized in that, In step (5), the environment inside the nitrogen glove box is controlled as follows: O2≤1ppm, H2O≤10ppm.

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