A fire-retardant immersion type cooling liquid for high-rate lithium iron phosphate battery pack and a preparation method thereof

Abstract

The application provides a fire-retardant immersion type cooling liquid for high-multiplicity lithium iron phosphate battery packs and a preparation method thereof, raw materials of the fire-retardant immersion type cooling liquid include, in percentage by weight, 85-95% fluorine compound base carrier, 5-15% phosphorus-nitrogen composite fire retardant; the fluorine compound base carrier contains low-boiling-point hydrofluoroether, branched-chain perfluoropolyether and h-BN nanosheet, and the fire retardant is a microencapsulated ammonium polyphosphate and melamine cyanurate compound system. The preparation is completed through carrier mixing, nanosheet composite dispersion, fire retardant compounding and vacuum degassing. The application realizes high heat dissipation, high insulation, UL94 V-0 level halogen-free fire retardancy and more than 6 months of stable performance, solves problems such as high viscosity, slow heat dissipation, poor fire retardancy, environmental protection hidden danger and insufficient stability of traditional cooling liquids, and adapts to the safety cooling demand of high-multiplicity lithium iron phosphate battery packs.

Description

Technical Field

[0001] This invention relates to the field of battery cooling technology, specifically to a flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage power stations, and other fields, high-rate lithium iron phosphate batteries have been widely used due to their advantages such as high energy density and long cycle life. However, high-rate lithium iron phosphate batteries generate a large amount of heat in a short period of time during fast charging and high-power discharging. If the heat cannot be dissipated in time, the battery temperature will rise sharply, leading to the risk of thermal runaway and seriously affecting the safety and service life of the battery pack.

[0003] Immersion cooling technology, because the coolant is in direct contact with the battery, has a much higher heat exchange efficiency than traditional air-cooling and liquid-cooling (indirect contact) technologies, making it one of the core directions for solving the heat dissipation problem of high-rate batteries. Currently available immersion coolants mainly include synthetic esters, mineral oils, and traditional fluoride-based coolants, but they have the following significant drawbacks or shortcomings in practical applications: Synthetic ester coolants: high viscosity (typically ≥10 mPa at 25°C) Its poor fluidity results in a slow heat dissipation rate and a low basic thermal conductivity (typically ≤0.18W / (m²)). K)) cannot meet the rapid heat dissipation requirements of high-rate batteries; Mineral oil-based coolants have extremely poor flame retardancy and require the addition of halogenated flame retardants to achieve basic flame retardant effects. However, halogenated flame retardants release toxic and harmful gases (such as hydrogen chloride and hydrogen bromide) when burning at high temperatures, polluting the environment and endangering human health. At the same time, traditional flame retardants (such as unmodified ammonium polyphosphate) have poor compatibility with mineral oil carriers and are prone to sedimentation and moisture absorption, resulting in poor long-term stability of the coolant. Traditional fluoride-based coolants, while possessing good insulation and thermal stability, have limited basic thermal conductivity (typically ≤0.20 W / (m²)). K)) is difficult to match the heat dissipation requirements of high-rate batteries when used alone, and the existing flame retardant system has poor compatibility with fluoride carriers, which can easily lead to problems such as delamination and performance degradation.

[0004] The aforementioned shortcomings of existing technologies prevent current submersible coolants from simultaneously achieving a synergistic balance of "high heat dissipation efficiency, reliable insulation, environmentally friendly flame retardancy, and long-term stability," thus limiting the safe application and performance improvement of high-rate lithium iron phosphate battery packs. Therefore, developing a submersible coolant that combines high heat dissipation, high insulation, environmentally friendly flame retardancy, and long-term stability is of significant practical importance. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide an immersion coolant that integrates a nanofluid-enhanced heat transfer carrier and a microencapsulated stable flame-retardant system, as well as its preparation method. The aim is to overcome existing technical bottlenecks through material selection and structural innovation, achieving synergistic breakthroughs in heat dissipation efficiency, reliable insulation, flame retardancy, environmental friendliness, and long-term stability. This solves problems such as high viscosity, slow heat dissipation, poor flame retardancy, lack of environmental friendliness, easy sedimentation of flame retardants, and poor compatibility with the carrier in existing coolants, thus meeting the safe cooling requirements of high-rate lithium iron phosphate battery packs.

[0006] The technical solution of the present invention: The present invention discloses a flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs, wherein the raw materials of the flame-retardant immersion coolant, by weight percentage, include: 85-95% fluorine compound base carrier and 5-15% phosphorus-nitrogen composite flame retardant.

[0007] In a further embodiment of this example, the raw materials for preparing the fluorinated compound base carrier include a composite carrier and a nano-reinforcing phase. The composite carrier is a mixture of low-boiling-point hydrofluoroether and branched perfluoropolyether; the nano-reinforcing phase is h-BN nanosheets.

[0008] In a further embodiment of this example, the phosphorus-nitrogen composite flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate in a mass ratio of 2:1 to 4:1. The microencapsulated ammonium polyphosphate is coated with urea-formaldehyde resin or silicone resin to form spherical microcapsules with a particle size of 5-15 μm.

[0009] In a further embodiment of this example, the low-boiling-point hydrofluoroether has a boiling point of 50-80°C and is selected from at least one of HFE-347 or HFE-449.

[0010] In a further embodiment of this example, the number average molecular weight of the branched perfluoropolyether is 1000-3000.

[0011] In a further embodiment of this example, the h-BN nanosheets have a particle size of 50-200 nm and a thickness of 5-20 nm.

[0012] In a further embodiment of this example, the preparation of the fluorinated compound base support includes the following steps: S1: Weigh low-boiling-point hydrofluoroether and branched perfluoropolyether according to the proportion, add them to a temperature-controlled stirred reactor, and stir for 30-60 minutes at 30-50℃ and 300-500rpm to obtain the composite carrier. S2: Add h-BN nanosheets to the composite support in proportion, first disperse by ultrasonication at 100-200W for 30-60min, then mechanically stir at 500-800rpm for 60-120min to obtain the fluorinated compound basic support.

[0013] In a further embodiment of this example, the amount of h-BN nanosheets added is 0.5%-3% of the total mass of the composite carrier.

[0014] In a further embodiment of this example, the mass ratio of the low-boiling-point hydrofluoroether to the branched perfluoropolyether is 20-40:60-80.

[0015] This invention provides a method for preparing a flame-retardant submersible coolant for high-rate lithium iron phosphate battery packs, characterized by comprising the following steps: (1) Slowly add the phosphorus-nitrogen composite flame retardant to the fluorinated compound base carrier and stir for 60-90 min at 40-60℃ and 400-600 rpm to obtain a mixture; (2) Transfer the above mixture into a vacuum degassing device and degas for 30-60 minutes at a vacuum of -0.08 to -0.09 MPa and 40-50℃ to remove bubbles and obtain a flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs.

[0016] Beneficial effects: This invention provides a beneficial effect of a flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs: 1. Significantly improved heat dissipation efficiency: Hydrofluoroethers result in low viscosity (≤5mPa at 25℃). (s) and latent heat of phase change ensure efficient heat transfer; branched perfluoropolyether forms a stable matrix; h-BN nanosheets form continuous thermal conductivity pathways, improving thermal conductivity by 15%-30% compared to traditional fluoride carriers (reaching 0.23-0.26 W / (m²)). K)) solves the problems of high viscosity and slow heat dissipation of synthetic esters, and adapts to the heat dissipation requirements of high-rate batteries.

[0017] 2. Excellent insulation reliability: The branched perfluoropolyether has a breakdown voltage of ≥60kV / mm, and the h-BN nanosheets are inorganic insulating materials that do not affect the insulation performance of the coolant (breakdown voltage ≥50kV / mm), eliminating the risk of electrical short circuits and ensuring the safety of the battery system.

[0018] 3. Flame retardant, environmentally friendly and efficient: Microencapsulated ammonium polyphosphate and melamine cyanurate react synergistically when heated to release non-flammable gases and form an expanded char layer, achieving UL94V-0 flame retardancy; the microcapsule shell improves compatibility and prevents flame retardant sedimentation, and the halogen-free system eliminates the release of harmful gases, taking into account both flame retardancy and environmental protection.

[0019] 4. Excellent long-term stability: The fluorinated compound carrier has an operating temperature range of -40~120℃ and excellent thermal stability; the microencapsulated flame retardant is uniformly dispersed and shows no sedimentation or stratification after more than 6 months of storage, ensuring stable performance of the coolant throughout its entire life cycle. Detailed Implementation

[0020] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0021] Emulsifier OP-10 was purchased from Jinan Yuanlian Chemical Co., Ltd., model OP-10; h-BN nanosheets were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., model XFBN06; branched perfluoropolyether was purchased from Shanghai Yuanye Biotechnology Co., Ltd., item number Y41833; synthetic ester coolant was purchased from Shanghai Enlaibao Trading Co., Ltd., model: MIDEL 7131; unless otherwise specified, all chemical reagents used in this invention are commercially available analytical grade.

[0022] Preparation of microencapsulated ammonium polyphosphate: S1: Weigh 20g of melamine, 0.6g of emulsifier OP-10 and 120mL of deionized water and add them to a flask. Stir at 800rpm for 30 minutes to obtain a uniform melamine dispersion. S2: Add 12g of methyltrimethoxysilane, adjust the pH to 9.5 with ammonia, heat to 60℃, and stir at 600rpm for 4 hours. S3: After the reaction was completed, the mixture was centrifuged and washed three times, dried under vacuum at 60°C for 12 hours, and then sieved to obtain 10 μm microencapsulated ammonium polyphosphate.

[0023] Example 1 Preparation of fluorine compound-based supports: S1: Weigh 30 parts of hydrofluoroether (HFE-347) (parts by weight, the same below) and 70 parts of branched perfluoropolyether (number average molecular weight 2000), add them to a temperature-controlled stirred reactor, stir at 40℃ and 400rpm for 45min to obtain a composite carrier. S2: Add 1.5 parts of h-BN nanosheets (particle size 100nm, thickness 10nm) to the composite support, disperse by ultrasonication at 150W for 45min, and then mechanically stir at 600rpm for 90min to obtain the fluorine compound basic support.

[0024] Preparation of coolant: (1) Add 15 parts of microencapsulated ammonium polyphosphate and 5 parts of melamine cyanurate to 180 parts of fluorinated compound base carrier, and stir at 50°C and 500 rpm for 75 min to obtain a mixture; (2) The above mixture is transferred to a vacuum degassing device and degassed at a vacuum of -0.085MPa and 45℃ for 45 minutes to obtain a flame-retardant immersion coolant.

[0025] Example 2 Preparation of fluorine compound-based supports: S1: Weigh 25 parts of hydrofluoroether (HFE-449) and 75 parts of branched perfluoropolyether (number average molecular weight 1500), add them to a temperature-controlled stirred reactor, stir at 35°C and 350 rpm for 50 min to obtain a composite carrier. S2: Add 2 parts of h-BN nanosheets (particle size 80nm, thickness 8nm), ultrasonically disperse at 180W for 35min, and mechanically stir at 700rpm for 80min to obtain the fluorine compound basic support.

[0026] Preparation of coolant: (1) Add 12 parts of microencapsulated ammonium polyphosphate and 4 parts of melamine cyanurate to 184 parts of fluorinated compound base carrier, and stir at 45°C and 550 rpm for 80 min to obtain a mixture; (2) The above mixture is transferred to a vacuum degassing device and degassed at a vacuum of -0.085MPa and 45℃ for 45 minutes to obtain a flame-retardant immersion coolant.

[0027] Example 3 Preparation of fluorine compound-based supports: S1: Weigh 35 parts of hydrofluoroether (HFE-347 and HFE-449 mixed in a mass ratio of 1:1) and 70 parts of branched perfluoropolyether (number average molecular weight 2500), add them to a temperature-controlled stirred reactor, stir at 40°C and 400 rpm for 45 min to obtain the composite carrier. S2: Add 2.5 parts of h-BN nanosheets (particle size 100nm, thickness 10nm) to the composite support, disperse by ultrasonication at 160W for 45min, and then mechanically stir at 600rpm for 10min to obtain the fluorine compound basic support.

[0028] Preparation of coolant: (1) Add 18 parts of microencapsulated ammonium polyphosphate and 6 parts of melamine cyanurate to 176 parts of the above-mentioned fluorinated compound base carrier, and stir at 45°C and 550 rpm for 80 min to obtain a mixture; (2) The above mixture is transferred to a vacuum degassing device and degassed at a vacuum of -0.085MPa and 45℃ for 45 minutes to obtain a flame-retardant immersion coolant.

[0029] Comparative Example 1 Commercially available synthetic ester coolant was used, without the addition of any flame retardants, compound carriers, or nano-reinforcing phases.

[0030] Comparative Example 2 The difference between this preparation example and Example 1 is that: Preparation of coolant: (1) Mix 180 parts of mineral oil and 20 parts of decabromodiphenyl ether at 40°C and 500 rpm for 60 min to obtain a mixture; (2) The above mixture is transferred to a vacuum degassing device and degassed at a vacuum of -0.08MPa and 45℃ for 40 minutes to obtain a flame-retardant immersion coolant.

[0031] Comparative Example 3 The difference between this preparation example and Example 1 is that: Preparation of fluorine compound-based supports: S1: Weigh 30 parts of hydrofluoroether (HFE-347) and 70 parts of branched perfluoropolyether (number average molecular weight 2000), add them to a temperature-controlled stirred reactor, stir at 40℃ and 400rpm for 45min to obtain a composite carrier. S2: Add 1.5 parts of h-BN nanosheets (particle size 100nm, thickness 10nm) to the composite support, disperse by ultrasonication at 150W for 45min, and then mechanically stir at 600rpm for 90min to obtain the fluorine compound basic support.

[0032] Preparation of coolant: (1) The fluorinated compound base carrier is transferred into a vacuum degassing device and degassed at a vacuum of -0.085MPa and 45℃ for 45 minutes to obtain a flame-retardant immersion coolant.

[0033] Comparative Example 4 Preparation of fluorine compound-based supports: S1: Weigh 30 parts of hydrofluoroether (HFE-347) (by weight, the same below) and 70 parts of branched perfluoropolyether (number average molecular weight 2000), add them to a temperature-controlled stirred reactor, stir at 40℃ and 400rpm for 45min to obtain the composite carrier, which is the fluorinated compound basic carrier. Preparation of coolant: (1) Add 15 parts of microencapsulated ammonium polyphosphate and 5 parts of melamine cyanurate to 180 parts of fluorinated compound base carrier, and stir at 50°C and 500 rpm for 75 min to obtain a mixture; (2) The above mixture is transferred to a vacuum degassing device and degassed at a vacuum of -0.085MPa and 45℃ for 45 minutes to obtain a flame-retardant immersion coolant.

[0034] The flame-retardant immersion coolants for high-rate lithium iron phosphate battery packs prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to the following tests: 1. Thermal conductivity test: According to GB / T22588-2008, the thermal conductivity was measured using a hot-wire method at a constant temperature of 25℃ (accuracy ±0.01W / (m)). K)) test, five parallel measurements are taken and the average value is taken, which should reach 0.23-0.26 W / (m) K).

[0035] 2. Viscosity Test: According to GB / T10247-2008, the viscosity shall be tested at a constant temperature of 25℃ using a rotational viscometer (NDJ-8S, rotor No. 1, 60 r / min). Three parallel measurements shall be taken, and the average value shall be ≤5 mPa. s.

[0036] 3. Breakdown voltage test: According to GB / T1408.1-2016, an oil-immersed high-voltage breakdown tester is used, with an electrode spacing of 2mm and a voltage rise rate of 2kV / s. Three samples are tested at 25℃, and the minimum value is taken. The voltage must be ≥50kV / mm.

[0037] 4. Flame retardancy rating test: According to UL94-2013, a 127mm×12.7mm×3.2mm sample was prepared and tested with a vertical burning tester to determine whether it reached the V-0 rating.

[0038] 5. Long-term stability test: According to SH / T0069-2005, the coolant is placed in a 50℃ constant temperature chamber and left to stand for 6 months. The flame retardant is observed to see if it separates or settles. The settlement rate is calculated to be ≤0.3%.

[0039] 6. Flame retardancy and environmental protection test: According to GB / T20284-2006, the sample is burned using a cone calorimeter, and harmful gases such as hydrogen halides are detected by GC-MS. It must be halogen-free and have no release of harmful gases.

[0040] Table 1: Test Results Table

[0041] As shown in Table 1, the flame-retardant immersion coolant used in Examples 1-3 for high-rate lithium iron phosphate battery packs exhibits outstanding heat dissipation efficiency. Its low viscosity design ensures rapid flow and heat exchange, while its high thermal conductivity meets the heat dissipation requirements of high-rate batteries. It also demonstrates strong insulation reliability, effectively avoiding the risk of electrical short circuits. Furthermore, it meets flame-retardant standards, is halogen-free and environmentally friendly, and releases no harmful gases. It exhibits good long-term stability, with no sedimentation or stratification issues. All core performance indicators meet the standards and are significantly superior to existing technologies, fully satisfying the safety cooling requirements of high-rate lithium iron phosphate battery packs. Specifically: Comparative Example 1 (commercially available synthetic ester coolant): Without the addition of nano-reinforcing phase and flame retardant system, its core shortcomings lie in heat dissipation efficiency and basic performance compatibility. Its high viscosity and low thermal conductivity fail to meet the core requirement of rapid heat dissipation in high-rate batteries, and its lack of flame retardant function results in insufficient safety protection, highlighting the performance limitations of traditional synthetic ester coolants in high-rate battery cooling scenarios and underscoring the necessity of the low-viscosity, high-thermal-conductivity formulation design of this invention. Comparative Example 2 (mineral oil + halogenated flame retardant system): This system suffers from two key defects: firstly, environmental concerns, as halogenated flame retardants release toxic and harmful gases upon combustion, failing to meet environmental requirements; secondly, insufficient stability, as traditional flame retardants have poor compatibility with mineral oil carriers, leading to flame retardant sedimentation with long-term use, affecting cooling and flame retardant effects. This comparative example verifies the core advantages of the halogen-free microencapsulated flame retardant system of this invention in balancing environmental friendliness, compatibility, and long-term stability. Comparative Example 3 (without phosphorus-nitrogen composite flame retardant): Due to the lack of core flame-retardant components, it completely lacks flame-retardant properties and cannot cope with the risk of battery thermal runaway. This directly proves that the microencapsulated ammonium polyphosphate and melamine cyanurate composite system is the key to achieving UL94V-0 flame-retardant performance in the coolant, confirming the irreplaceable role of the phosphorus-nitrogen synergistic flame-retardant design in ensuring battery pack safety. Comparative Example 4 (without h-BN nanosheets): Without the addition of a nano-reinforcing phase, the thermal conductivity significantly decreases, resulting in insufficient heat dissipation efficiency and an inability to meet the rapid heat dissipation requirements of high-rate batteries. This result highlights the core role of h-BN nanosheets in constructing continuous thermal conduction pathways and enhancing heat transfer, demonstrating the key value of the nanofluidic carrier design of this invention in improving heat dissipation performance.

[0042] This invention can also be implemented in various other ways. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs, characterized in that, The raw materials of the flame-retardant immersion coolant, by weight percentage, include: 85-95% fluorine compound base carrier and 5-15% phosphorus-nitrogen composite flame retardant.

2. The flame-retardant submersible coolant for high-rate lithium iron phosphate battery packs according to claim 1, characterized in that, The raw materials for preparing the fluorinated compound base carrier include a composite carrier and a nano-reinforcing phase. The composite carrier is a mixture of low-boiling-point hydrofluoroether and branched perfluoropolyether. The nano-reinforcing phase is h-BN nanosheets.

3. The flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs according to claim 1, characterized in that, The phosphorus-nitrogen composite flame retardant is composed of microencapsulated ammonium polyphosphate and melamine cyanurate in a mass ratio of 2:1 to 4:

1. The microencapsulated ammonium polyphosphate is coated with urea-formaldehyde resin or silicone resin to form spherical microcapsules with a particle size of 5-15 μm.

4. The flame-retardant submersible coolant for high-rate lithium iron phosphate battery packs according to claim 2, characterized in that, The low-boiling-point hydrofluoroether has a boiling point of 50-80°C and is selected from at least one of HFE-347 or HFE-449.

5. The flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs according to claim 2, characterized in that, The branched perfluoropolyether has a number average molecular weight of 1000-3000.

6. The flame-retardant submersible coolant for high-rate lithium iron phosphate battery packs according to claim 1, characterized in that, The h-BN nanosheets have a particle size of 50-200 nm and a thickness of 5-20 nm.

7. The flame-retardant submersible coolant for high-rate lithium iron phosphate battery packs according to claim 1, characterized in that, The preparation of the fluorine compound-based support includes the following steps: S1: Weigh low-boiling-point hydrofluoroether and branched perfluoropolyether according to the proportion, add them to a temperature-controlled stirred reactor, and stir for 30-60 minutes at 30-50℃ and 300-500rpm to obtain the composite carrier. S2: Add h-BN nanosheets to the composite support in proportion, first disperse by ultrasonication at 100-200W for 30-60min, then mechanically stir at 500-800rpm for 60-120min to obtain the fluorinated compound basic support.

8. The flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs according to claim 7, characterized in that, The amount of h-BN nanosheets added is 0.5%-3% of the total mass of the composite carrier.

9. The flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs according to claim 7, characterized in that, The mass ratio of the low-boiling-point hydrofluoroether to the branched perfluoropolyether is 20-40:60-80.

10. The method for preparing the flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs according to any one of claims 1-9, characterized in that, Includes the following steps: (1) Slowly add the phosphorus-nitrogen composite flame retardant to the fluorinated compound base carrier and stir for 60-90 min at 40-60℃ and 400-600 rpm to obtain a mixture; (2) Transfer the above mixture into a vacuum degassing device and degas for 30-60 minutes at a vacuum of -0.08 to -0.09 MPa and 40-50℃ to remove bubbles and obtain a flame-retardant immersion coolant for high-rate lithium iron phosphate battery packs.

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