A phosphorus-silicon synergistic flame-retardant cooling liquid for immersion liquid cooling and a preparation method thereof

Abstract

This invention provides a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling and its preparation method, belonging to the field of thermal safety technology for energy storage batteries. The preparation method of the phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling includes adding diphenyl phosphate, allyl alcohol, a condensing agent, and an esterification catalyst to a reaction vessel under an inert atmosphere to carry out an esterification reaction, obtaining the intermediate allyl diphenyl phosphate; subsequently, adding 1,1,3,3-tetramethyldisiloxane and a platinum catalyst to the reaction system to carry out a hydrosilylation reaction; after the reaction, purification treatment is performed to obtain a siloxane-bridged phosphate; the obtained siloxane-bridged phosphate is added to a base mineral insulating oil, and a high-efficiency antioxidant is added, followed by uniform mixing to obtain the phosphorus-silicon synergistic flame-retardant coolant. This method can solve the problems of insufficient oxidation stability, easy increase in acid value, and difficulty in simultaneously achieving flame-retardant efficiency and long-term stability in existing coolants under long-term high-temperature operation.

Description

Technical Field

[0001] This invention belongs to the field of thermal safety technology for energy storage batteries. Specifically, it relates to a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling and its preparation method. Background Technology

[0002] As electrochemical energy storage systems based on lithium-ion and sodium-ion batteries rapidly develop towards higher energy density and large-scale clusters, thermal safety management has become a key bottleneck restricting the safe and sustainable development of the industry. Immersion liquid cooling technology, by directly immersing battery modules in an insulating cooling medium, leverages the medium's high specific heat capacity and direct contact heat exchange to achieve efficient and uniform thermal management. Furthermore, in the event of thermal runaway, physical isolation and rapid heat removal effectively suppress the spread of disaster, making it a revolutionary solution for improving the intrinsic safety of energy storage systems.

[0003] As the core functional material of this technology, the performance of the insulating coolant directly determines the system's heat dissipation efficiency and safety margin. Currently, mineral insulating oils or synthetic ester liquids are mainly used in engineering applications. While these media possess good insulation and heat transfer properties, they are themselves flammable organic compounds with flash points typically between 150 and 250°C. When a battery experiences severe thermal runaway, the released heat can cause the local coolant temperature to exceed its flash point or even ignition point, leading to coolant ignition and the release of chemical energy within the battery, escalating into a sustained oil pool fire with catastrophic consequences. Therefore, developing new coolants that combine excellent insulation and cooling performance with inherent flame-retardant properties is essential for the mature application of immersion liquid cooling technology.

[0004] Existing technologies have explored flame-retardant modification of insulating oils, primarily following the approach of adding functional flame retardants to the base oil. For example, Chinese patent application number CN201410309124.8 (authorization announcement number CN104130826B) discloses a "corrosion-inhibiting transformer oil with added red phosphorus flame retardant and its preparation method." This technical solution aims to simultaneously improve the flame retardancy and corrosion inhibition performance of copper windings by introducing microencapsulated red phosphorus into mineral insulating oil and compounding it with specific phosphate esters. However, this approach has significant limitations: First, the chemical stability of its core flame-retardant component, red phosphorus, faces challenges under long-term high-temperature (>80℃) operating conditions, and it may undergo slow oxidation or reaction, affecting the long-term electrical performance and acid value stability of the oil. Second, the research background and application scenarios of this technology are entirely based on the design of traditional static power transformers, without considering the long-term compatibility of flame-retardant additives with battery materials (such as positive and negative electrodes, current collectors, and leaked electrolytes) and the potential risks of side reactions in battery immersion liquid cooling systems with dynamic, intermittent charging and discharging and complex electrochemical environments.

[0005] Chinese patent application CN202511836892.3 (publication number CN121674132A) further discloses a wide-temperature flame-retardant coolant and its preparation method, an immersion energy storage device, a data center, and electrical equipment. This patent attempts to balance wide-temperature adaptability, thermal oxidation stability, and synergistic flame-retardant performance by introducing a phosphorus-containing modifier into the base oil. However, while the modifier in this design claims to improve antioxidant properties, its core flame-retardant mechanism still relies on the physical compounding of the added flame retardant and modifier, failing to achieve chemical bonding between the flame-retardant and stabilizing units at the single molecular scale. Under long-term high-temperature dynamic cycling conditions, this design still faces potential risks such as decreased compatibility between the flame-retardant components and the base oil, flame retardant migration and precipitation, and difficulty in ensuring the long-term oxidation stability of the system. Furthermore, this patent also fails to systematically examine its chemical stability and material compatibility under extreme conditions such as battery thermal runaway and electrolyte leakage.

[0006] In summary, existing flame-retardant coolant technologies largely focus on improving initial flame-retardant efficiency, but generally neglect the core challenge of the long-term chemical stability and compatibility of the flame-retardant additives themselves and the entire oil system under actual immersion liquid cooling operating conditions (long-term high temperature, dynamic circulation, complex electrochemical environment). Specifically, this manifests in the following ways: 1) Flame retardants are prone to chemical changes at high temperatures, leading to increased acid value, corrosion of metal components, and deterioration of insulation materials; 2) Physically added flame retardants pose a risk of phase separation, affecting long-term reliability; 3) There is a lack of systematic compatibility assessments for the special environment of battery immersion.

[0007] Therefore, developing a novel coolant additive that integrates flame retardant function and stable structure at the molecular scale, maintains excellent oxidation stability (low acid value) and superior flame retardant efficiency during long-term high-temperature operation, and has good compatibility with battery systems and mineral oil-based liquids has become an urgent need in this field to overcome technical bottlenecks and ensure the long-term safe operation of energy storage systems. Summary of the Invention

[0008] In view of this, the present invention provides a phosphorus-silicon synergistic flame retardant coolant for immersion liquid cooling and its preparation method, which can solve the problems of insufficient oxidation stability, easy increase of acid value, and difficulty in balancing flame retardant efficiency and long-term stability of existing flame retardant coolants under long-term high-temperature operation.

[0009] This invention is implemented as follows:

[0010] The first aspect of this invention provides a method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling, comprising the following specific steps:

[0011] S10: Synthesis of siloxane-bridged phosphate esters; Under an inert atmosphere, diphenyl phosphate, allyl alcohol, anhydrous organic solvent, condensing agent, and esterification catalyst were added to a three-necked round-bottom flask. The esterification reaction was carried out under ice-water bath cooling conditions, with the reaction temperature controlled not to exceed 10°C, to obtain the intermediate allyl diphenyl phosphate. After the reaction, the intermediate was filtered, washed, dried, and distilled under reduced pressure to obtain the purified intermediate. The intermediate was dissolved in an anhydrous organic solvent with 1,1,3,3-tetramethyldisiloxane and transferred to a three-necked round-bottom flask. The mixture was heated to 70-90°C under an inert atmosphere, and then a platinum catalyst was added to the reaction system. The mixture was stirred for 6-12 hours to carry out a hydrosilylation reaction. After the reaction, the mixture was cooled to room temperature, filtered through a silica gel short column to remove catalyst residue, and distilled under reduced pressure to remove solvent, to obtain siloxane-bridged phosphate esters.

[0012] S20: Preparation of flame-retardant coolant; the obtained siloxane-bridged phosphate ester is added to the base mineral insulating oil, and a high-efficiency antioxidant is added. The mixture is stirred for 1 to 3 hours under water bath heating conditions to obtain the phosphorus-silicon synergistic flame-retardant coolant.

[0013] The three-necked round-bottom flask is a reaction vessel equipped with a mechanical stirrer and a reflux condenser.

[0014] Diphenyl phosphate: As a phosphorus source, it provides the phosphate ester skeleton structure, and the two phenoxy groups it contains can give the product good thermal stability and compatibility with mineral oil;

[0015] Allyl alcohol: as a reactant, it provides a terminal allyl (-CH2-CH=CH2) functional group for constructing unsaturated bonds that can participate in hydrosilylation reactions;

[0016] Condensing agent (N,N-dicyclohexylcarbodiimide): As a dehydrating agent, it activates the hydroxyl groups in diphenyl phosphate, promotes its esterification reaction with allyl alcohol, and improves the reaction efficiency.

[0017] Esterification catalyst (4-dimethylaminopyridine): As an acylation catalyst, it accelerates the esterification reaction rate and shortens the reaction time;

[0018] 1,1,3,3-Tetramethyldisiloxane: As a silicon source, it provides Si-H bonds and is connected to allyl double bonds through a hydrosilylation reaction, introducing organosilicon segments into the molecular structure;

[0019] Platinum catalysts (Karstedt catalysts): As catalysts for the hydrosilylation reaction, they efficiently catalyze the addition reaction of Si-H bonds to carbon-carbon double bonds, and have the characteristics of mild reaction conditions and high selectivity.

[0020] Purification process: This includes steps such as filtration, washing, drying, vacuum distillation, and column chromatography, used to remove unreacted raw materials, byproducts, and catalyst residues to obtain high-purity target products;

[0021] Siloxane-bridged phosphate esters: As flame retardant additives, they exert a dual effect of gas-phase flame retardancy and condensed-phase flame retardancy through intramolecular phosphorus-silicon synergistic effect.

[0022] High-efficiency antioxidant: As an oxidation inhibitor, it inhibits the increase in acid value and darkening of color of coolant under long-term high-temperature operation by capturing free radicals to terminate chain oxidation reaction, thus extending service life;

[0023] Uniform mixing: Heating and stirring are used to form a uniform and stable dispersion system of additives and antioxidants in the base oil, ensuring product consistency and long-term storage stability.

[0024] Based on the above technical solution, the preparation method of the phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling of the present invention can be further improved as follows:

[0025] The molar ratio of diphenyl phosphate to allyl alcohol is 1:1 to 1.2.

[0026] Furthermore, the condensing agent is N,N-dicyclohexylcarbodiimide (22.0 g, 0.106 mol), and the esterification catalyst is 4-dimethylaminopyridine (1.2 g, 0.01 mol).

[0027] Furthermore, the molar ratio of the intermediate allyl phosphate diphenyl ester to 1,1,3,3-tetramethyldisiloxane is 2:1 to 2.2:1.

[0028] Furthermore, the platinum catalyst is a Karstedt catalyst, and its amount, calculated as platinum, is 0.01% to 0.1% of the molar amount of Si-H bonds in the reaction system; the temperature of the hydrosilylation reaction is 70 to 90°C, and the reaction time is 6 to 12 hours.

[0029] The Karstedt catalyst is a platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex.

[0030] Furthermore, the mass percentage of the siloxane-bridged phosphate added to the coolant is 1% to 10%.

[0031] Furthermore, the mass percentage of the siloxane-bridged phosphate added to the coolant is 3% to 6%.

[0032] Furthermore, the highly effective antioxidant is a hindered phenolic antioxidant, and its mass percentage added to the coolant is 0.1% to 0.5%.

[0033] Furthermore, the base mineral insulating oil is a naphthenic or paraffinic mineral insulating oil.

[0034] A second aspect of the present invention provides a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling, wherein the phosphorus-silicon synergistic flame-retardant coolant is prepared by the above-described preparation method, and the coolant is used in an immersion liquid cooling system for energy storage batteries.

[0035] Compared with existing technologies, the beneficial effects of the phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling and its preparation method provided by the present invention are as follows:

[0036] (1) This invention innovatively designs and synthesizes siloxane-bridged phosphate as a flame retardant additive. This molecular structure connects phosphorus-based flame retardant units (diphenyl phosphate) through flexible siloxane chains, forming an intramolecular phosphorus-silicon synergistic flame retardant system. During combustion, phosphorus plays a role in capturing gaseous free radicals, while silicon tends to migrate to the surface to form a dense, heat-resistant Si-OC protective char layer, producing an excellent condensed phase barrier effect, thereby significantly improving the flame retardant efficiency of the coolant.

[0037] (2) The flame-retardant coolant prepared by this invention has outstanding thermal oxidation stability. The combination of flexible siloxane segments and stable aryl phosphate ester structure endows the additive molecules with excellent thermal stability. More importantly, the organosilicon component itself has extremely strong resistance to hydrolysis and oxidation, which can essentially inhibit the increase of acid value of coolant under long-term high temperature (such as 100°C) operating environment, solving the key problem that traditional phosphate ester flame retardants are prone to causing oil deterioration.

[0038] (3) The additive synthesis process of the present invention is mature, the product is liquid, and it has excellent compatibility with mineral insulating oil. It can maintain a uniform and stable solution state in a wide temperature range (-40℃~100℃) without the risk of precipitation, and fully meets the stringent requirements of immersion liquid cooling system for coolant fluidity and stability. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the preparation method of a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling.

[0040] Figure 2 A comparison chart showing the acid value changes of coolant samples from Comparative Example 1 (base oil), Comparative Example 2 (base oil + 4% triphenyl phosphate), and Example 1 (base oil + 4% additive of the present invention) after accelerated aging at 120°C for 500 hours.

[0041] Figure 3 Comparative images of the flame morphology of the coolant samples from Comparative Example 1, Comparative Example 2, and Example 1 are shown.

[0042] Figure 4 A comparison graph showing the flame temperatures of the coolant samples from Comparative Example 1, Comparative Example 2, and Example 1 during combustion tests;

[0043] Figure 5 This is a comparison chart showing the mass changes of the coolant samples in the combustion test of Comparative Example 1, Comparative Example 2, and Example 1. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0045] like Figure 1 The image shows a first embodiment of a method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling provided by the present invention. This embodiment includes the following specific steps:

[0046] S10: Synthesis of siloxane-bridged phosphate esters; Under an inert atmosphere, diphenyl phosphate, allyl alcohol, anhydrous organic solvent, condensing agent, and esterification catalyst were added to a three-necked round-bottom flask. The esterification reaction was carried out under ice-water bath cooling conditions, with the reaction temperature controlled not to exceed 10°C, to obtain the intermediate allyl diphenyl phosphate. After the reaction, the intermediate was filtered, washed, dried, and distilled under reduced pressure to obtain the purified intermediate. The intermediate was dissolved in an anhydrous organic solvent with 1,1,3,3-tetramethyldisiloxane and transferred to a three-necked round-bottom flask. The mixture was heated to 70-90°C under an inert atmosphere, and then a platinum catalyst was added to the reaction system. The mixture was stirred for 6-12 hours to carry out a hydrosilylation reaction. After the reaction, the mixture was cooled to room temperature, filtered through a silica gel short column to remove catalyst residue, and distilled under reduced pressure to remove solvent, to obtain siloxane-bridged phosphate esters.

[0047] S20: Preparation of flame-retardant coolant; the obtained siloxane-bridged phosphate ester is added to the base mineral insulating oil, and a high-efficiency antioxidant is added. The mixture is stirred for 1 to 3 hours under water bath heating conditions to obtain the phosphorus-silicon synergistic flame-retardant coolant.

[0048] In the above technical solution, the molar ratio of diphenyl phosphate to allyl alcohol is 1:1 to 1.2.

[0049] Furthermore, in the above technical solution, the condensing agent is N,N-dicyclohexylcarbodiimide (22.0 g, 0.106 mol), and the esterification catalyst is 4-dimethylaminopyridine (1.2 g, 0.01 mol).

[0050] Furthermore, in the above technical solution, the molar ratio of the intermediate allyl phosphate diphenyl ester to 1,1,3,3-tetramethyldisiloxane is 2:1 to 2.2:1.

[0051] Furthermore, in the above technical solution, the platinum catalyst is a Karstedt catalyst, and its amount, calculated as platinum, is 0.01% to 0.1% of the molar amount of Si-H bonds in the reaction system; the temperature of the hydrosilylation reaction is 70 to 90°C, and the reaction time is 6 to 12 hours.

[0052] Furthermore, in the above technical solution, the mass percentage of siloxane-bridged phosphate added to the coolant is 1% to 10%.

[0053] Furthermore, in the above technical solution, the mass percentage of siloxane-bridged phosphate added to the coolant is 3% to 6%.

[0054] Furthermore, in the above technical solution, the high-efficiency antioxidant is a hindered phenolic antioxidant, and its mass percentage added to the coolant is 0.1%~0.5%.

[0055] Furthermore, in the above technical solution, the base mineral insulating oil is a naphthenic or paraffinic mineral insulating oil.

[0056] The present invention provides a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling, which is prepared by the above preparation method and is used in an immersion liquid cooling system for energy storage batteries.

[0057] The specific reaction process of the first embodiment provided by the present invention is as follows:

[0058] (1) Synthesis of siloxane-bridged phosphate esters:

[0059] Under nitrogen protection, diphenyl phosphate (25.0 g, 0.1 mol), allyl alcohol (6.0 g, 0.103 mol), and 250 mL of anhydrous tetrahydrofuran were added to a dry 500 mL three-necked flask. After stirring and dissolving, 4-dimethylaminopyridine (1.2 g, 0.01 mol) was added, and the mixture was cooled in an ice-water bath. N,N-dicyclohexylcarbodiimide (22.0 g, 0.106 mol) was slowly added with stirring, and the mixture was reacted at 0–5 °C for 1 hour, then at room temperature for another 12 hours. After the reaction was complete, the mixture was filtered, and the filtrate was concentrated, washed, dried, and subjected to column chromatography to obtain the allyl diphenyl phosphate intermediate.

[0060] The above intermediate (15.0 g, 0.05 mol) and 1,1,3,3-tetramethyldisiloxane (3.9 g, 0.026 mol) were dissolved in 30 mL of anhydrous toluene and heated to 80 °C under nitrogen protection. A Karstedt catalyst solution (approximately 2 mg Pt) was added, and the reaction was stirred at this temperature for 10 hours. The reaction endpoint was determined by the disappearance of the characteristic peak of the Si-H bond (2150 cm⁻¹) monitored by infrared spectroscopy. The reaction solution was filtered through a short silica gel column to remove the catalyst, and the solvent was removed by rotary evaporation. The product, siloxane-bridged phosphate (approximately 16.2 g), was obtained as a colorless, transparent, viscous liquid with a yield of 82.1%.

[0061] (2) Preparation of flame-retardant coolant:

[0062] Take 4.0 g of the synthesized siloxane-bridged phosphate ester and add it to 96.0 g of 25# cycloalkyl mineral insulating oil, along with 0.3 g of hindered phenolic antioxidant Irganox L135. Stir the mixture magnetically in a 60°C water bath for 2 hours and then sonicate it for 30 minutes to obtain a uniform and transparent phosphorus-silicon synergistic flame-retardant coolant.

[0063] The specific reaction process of the second embodiment provided by the present invention is as follows:

[0064] (1) Synthesis of siloxane-bridged phosphate esters:

[0065] Under nitrogen protection, diphenyl phosphate (25.0 g, 0.1 mol), allyl alcohol (6.0 g, 0.103 mol), and 250 mL of anhydrous tetrahydrofuran were added to a dry 500 mL three-necked flask. After stirring and dissolving, 4-dimethylaminopyridine (1.2 g, 0.01 mol) was added, and the mixture was cooled in an ice-water bath. N,N-dicyclohexylcarbodiimide (22.0 g, 0.106 mol) was slowly added with stirring, and the mixture was reacted at 0–5 °C for 1 hour, then at room temperature for another 12 hours. After the reaction was complete, the mixture was filtered, and the filtrate was concentrated, washed, dried, and subjected to column chromatography to obtain the allyl diphenyl phosphate intermediate.

[0066] The above intermediate (15.0 g, 0.05 mol) and 1,1,3,3-tetramethyldisiloxane (4.3 g, 0.023 mol) were dissolved in 30 mL of anhydrous toluene and heated to 80 °C under nitrogen protection. A Karstedt catalyst solution (approximately 2 mg Pt) was added, and the reaction was stirred at this temperature for 10 hours. The reaction endpoint was determined by the disappearance of the characteristic peak of the Si-H bond (2150 cm⁻¹) monitored by infrared spectroscopy. The reaction solution was filtered through a silica gel short column to remove the catalyst, and the solvent was removed by rotary evaporation. The product, siloxane-bridged phosphate (approximately 15.1 g), was obtained as a colorless, transparent, viscous liquid with a yield of 76.8%.

[0067] The difference from Example 1 is that the molar ratio of the intermediate allyl phosphate diphenyl ester to 1,1,3,3-tetramethyldisiloxane was adjusted to 2.2:1, while the remaining steps were the same as in Example 1. Approximately 15.1 g of the target product was obtained, with a yield of 76.8%.

[0068] (2) Preparation of flame-retardant coolant:

[0069] Take 4.0 g of the synthesized siloxane-bridged phosphate ester and add it to 96.0 g of 25# cycloalkyl mineral insulating oil, along with 0.3 g of hindered phenolic antioxidant Irganox L135. Stir the mixture magnetically in a 60°C water bath for 2 hours and then sonicate it for 30 minutes to obtain a uniform and transparent phosphorus-silicon synergistic flame-retardant coolant.

[0070] The specific reaction process of the third embodiment provided by the present invention is as follows:

[0071] (1) Synthesis of siloxane-bridged phosphate esters:

[0072] Under nitrogen protection, diphenyl phosphate (25.0 g, 0.1 mol), allyl alcohol (6.0 g, 0.103 mol), and 250 mL of anhydrous tetrahydrofuran were added to a dry 500 mL three-necked flask. After stirring and dissolving, 4-dimethylaminopyridine (1.2 g, 0.01 mol) was added, and the mixture was cooled in an ice-water bath. N,N-dicyclohexylcarbodiimide (22.0 g, 0.106 mol) was slowly added with stirring, and the mixture was reacted at 0–5 °C for 1 hour, then at room temperature for another 12 hours. After the reaction was complete, the mixture was filtered, and the filtrate was concentrated, washed, dried, and subjected to column chromatography to obtain the allyl diphenyl phosphate intermediate.

[0073] The above intermediate (15.0 g, 0.05 mol) and 1,1,3,3-tetramethyldisiloxane (3.9 g, 0.026 mol) were dissolved in 30 mL of anhydrous toluene and heated to 70 °C under nitrogen protection. A Karstedt catalyst solution (approximately 2 mg Pt) was added, and the reaction was stirred at this temperature for 12 hours. The reaction endpoint was determined by the disappearance of the characteristic peak of the Si-H bond (2150 cm⁻¹) monitored by infrared spectroscopy. The reaction solution was filtered through a silica gel short column to remove the catalyst, and the solvent was removed by rotary evaporation. The product, siloxane-bridged phosphate (approximately 14.8 g), was obtained as a colorless, transparent, viscous liquid with a yield of 75.2%.

[0074] The difference from Example 1 is that the hydrosilylation reaction temperature was adjusted to 70°C and the reaction time was 12 hours, while the remaining steps were the same as in Example 1. Approximately 14.8 g of the target product was obtained, with a yield of 75.2%.

[0075] (2) Preparation of flame-retardant coolant:

[0076] Take 4.0 g of the synthesized siloxane-bridged phosphate ester and add it to 96.0 g of 25# cycloalkyl mineral insulating oil, along with 0.3 g of hindered phenolic antioxidant Irganox L135. Stir the mixture magnetically in a 60°C water bath for 2 hours and then sonicate it for 30 minutes to obtain a uniform and transparent phosphorus-silicon synergistic flame-retardant coolant.

[0077] The specific reaction process of the fourth embodiment provided by the present invention is as follows:

[0078] (1) Synthesis of siloxane-bridged phosphate esters:

[0079] Under nitrogen protection, diphenyl phosphate (25.0 g, 0.1 mol), allyl alcohol (6.0 g, 0.103 mol), and 250 mL of anhydrous tetrahydrofuran were added to a dry 500 mL three-necked flask. After stirring and dissolving, 4-dimethylaminopyridine (1.2 g, 0.01 mol) was added, and the mixture was cooled in an ice-water bath. N,N-dicyclohexylcarbodiimide (22.0 g, 0.106 mol) was slowly added with stirring, and the mixture was reacted at 0–5 °C for 1 hour, then at room temperature for another 12 hours. After the reaction was complete, the mixture was filtered, and the filtrate was concentrated, washed, dried, and subjected to column chromatography to obtain the allyl diphenyl phosphate intermediate.

[0080] The above intermediate (15.0 g, 0.05 mol) and 1,1,3,3-tetramethyldisiloxane (3.9 g, 0.026 mol) were dissolved in 30 mL of anhydrous toluene and heated to 90 °C under nitrogen protection. A Karstedt catalyst solution (approximately 2 mg Pt) was added, and the reaction was stirred at this temperature for 8 hours. The reaction endpoint was determined by the disappearance of the characteristic peak of the Si-H bond (2150 cm⁻¹) monitored by infrared spectroscopy. The reaction solution was filtered through a silica gel short column to remove the catalyst, and the solvent was removed by rotary evaporation. After high-vacuum drying, the target product, siloxane-bridged phosphate (approximately 16.0 g), was obtained, with a yield of 81.2%.

[0081] The difference from Example 1 is that the hydrosilylation reaction temperature was adjusted to 90°C and the reaction time was 8 hours, while the remaining steps were the same as in Example 1. Approximately 16.0 g of the target product was obtained, with a yield of 81.2%.

[0082] (2) Preparation of flame-retardant coolant:

[0083] 4.0 g of the synthesized siloxane-bridged phosphate ester was added to 96.0 g of 25# cycloalkyl mineral insulating oil, along with 0.3 g of hindered phenolic antioxidant Irganox L135. The mixture was magnetically stirred in a 60°C water bath for 2 hours and then sonicated for 30 minutes to obtain a uniform and transparent phosphorus-silicon synergistic flame-retardant coolant. Table 1 shows that the optimized conditions of Example 1 (molar ratio 2.0:1, reaction temperature 80°C) yielded the highest yield (82.1%), and the product exhibited suitable viscosity and a low pour point, demonstrating optimal compatibility with mineral oil.

[0084] The different reaction conditions and the corresponding key physical properties of the products in the above four embodiments are shown in Table 1:

[0085] Table 1 Key physical properties of the products under different synthesis conditions

[0086]

[0087] In addition, two comparative examples are also set up.

[0088] Comparative Example 1: Pure base oil: 100 g 25# naphthenic mineral insulating oil.

[0089] Comparative Example 2: Conventional flame-retardant coolant: Take 4.0 g of triphenyl phosphate (TPP), add 96.0 g of 25# cycloalkyl mineral insulating oil and 0.3 g of Irganox L135, and mix well.

[0090] The properties of the coolant obtained in Example 1 and the materials in the comparative example were tested, and the specific physicochemical properties are shown in Table 2.

[0091] Table 2. Effects of flame retardant addition on the physicochemical properties and safety of mineral insulating oil:

[0092]

[0093] By comparing the data from the comparative examples and the actual examples, the addition of flame retardant significantly affected the overall performance of the mineral insulating oil. Regarding basic physicochemical properties, the viscosity of Example 1 increased (10.4 mPa·s, between 9.7 for Comparative Example 1 and 11.6 for Comparative Example 2), while the thermal conductivity (0.174 W / m·K) and dielectric loss (0.141%) remained at levels comparable to those without flame retardant, indicating that its basic electrical and thermal properties were not significantly impaired. However, the effect of the flame retardant was extremely prominent in key safety indicators: the flash point and ignition point of Example 1 reached 219°C and 222°C, respectively, significantly exceeding those of the two comparative examples (flash points of 188°C and 201°C, and ignition points of 207°C and 218°C, respectively). This change clearly demonstrates that the addition of flame retardant effectively improved the thermal stability and flame resistance of the insulating oil, significantly enhancing its safety under high-temperature or fault conditions while maintaining its original functional characteristics.

[0094] like Figures 2-5 As shown, the properties of the coolant obtained in the above embodiments and the materials in the comparative examples were tested for thermal oxidation stability and immersion flame retardancy. The results are as follows:

[0095] Thermal oxidation stability test: such as Figure 2 As shown, oil samples from Example 1, Comparative Example 1, and Comparative Example 2 were placed in a 100°C forced convection oven for accelerated aging, and acid values ​​were measured periodically. The results are as follows: Figure 2 As shown, after aging for 500 hours, the acid value of Comparative Example 2 (TPP system) increased from 0.0033 mg KOH / g to 0.0368 mg KOH / g, while the base oil of Comparative Example 1 increased to 0.0151 mg KOH / g. The acid value of the coolant in Example 1 of this invention only increased slightly to 0.0178 mg KOH / g compared to the base oil, exhibiting extremely excellent thermal oxidation stability. The acidity changes of the coolant samples from the above four examples and two comparative examples were measured after accelerated aging at 100°C, and the results are shown in Table 3.

[0096] Table 3 Comparison of acid value changes of different coolant samples after accelerated aging at 100℃ for 500 hours

[0097]

[0098] Immersion flame retardant test: such as Figures 3-5As shown, a small-scale immersion combustion apparatus was constructed. 300 ml of each oil sample was added to an oil pan with a diameter of 20 cm, and 10 ml of igniter (n-heptane) was added simultaneously. The oil pan was moved to an electronic balance, and a thermocouple was placed 10 cm above the oil pan. The oil sample was ignited using an igniter, and the temperature and mass changes of the oil sample during combustion were recorded. Comparison revealed that the coolant sample of Example 1 (with the addition of the siloxane-bridged phosphate ester prepared according to this invention) exhibited a rapid flame shrinkage after ignition, a significantly reduced mass loss rate, a significantly lower combustion temperature than Comparative Example 1 (pure base oil), and a prolonged combustion duration, demonstrating excellent flame retardant effects. In contrast, while Comparative Example 2 (with the addition of triphenyl phosphate) showed some flame retardant effect, its mass loss rate and temperature curve were still significantly higher than those of Example 1. This indicates that the phosphorus-silicon synergistic flame-retardant coolant described in this invention has a faster and more thorough flame suppression capability in real combustion scenarios, effectively delaying or blocking the combustion chain reaction, and providing more reliable thermal safety protection for immersion liquid cooling systems. The coolant samples from the above four embodiments and two comparative examples were subjected to immersion flame retardancy tests, and the results are shown in Table 4.

[0099] Table 4 Comparison of flame retardant test results for immersion in different coolants

[0100]

[0101] Specifically, the principle of this invention is as follows: In use, under an inert atmosphere, diphenyl phosphate, allyl alcohol, anhydrous organic solvent, a condensing agent, and an esterification catalyst are added to a three-necked round-bottom flask. The esterification reaction is carried out under ice-water bath cooling conditions, with the reaction temperature controlled not to exceed 10°C, to obtain the intermediate allyl diphenyl phosphate. After the reaction, the intermediate is filtered, washed, dried, and distilled under reduced pressure to obtain a purified intermediate. The intermediate is then dissolved in an anhydrous organic solvent with 1,1,3,3-tetramethyldisiloxane and transferred... The mixture is heated to 70-90°C in a three-necked round-bottom flask under an inert atmosphere. Platinum catalyst is then added to the reaction system, and the mixture is stirred for 6-12 hours to carry out the hydrosilylation reaction. After the reaction is completed, the mixture is cooled to room temperature, filtered through a silica gel short column to remove catalyst residue, and the solvent is removed by vacuum distillation to obtain siloxane-bridged phosphate. The obtained siloxane-bridged phosphate is added to a base mineral insulating oil, along with a high-efficiency antioxidant. The mixture is stirred for 1-3 hours under water bath heating to obtain the phosphorus-silicon synergistic flame-retardant coolant.

[0102] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling, characterized in that, The specific steps include the following: S10: Synthesis of siloxane-bridged phosphate esters; Under an inert atmosphere, diphenyl phosphate, allyl alcohol, anhydrous organic solvent, condensing agent, and esterification catalyst were added to a three-necked round-bottom flask. The esterification reaction was carried out under ice-water bath cooling conditions, with the reaction temperature controlled not to exceed 10°C, to obtain the intermediate allyl diphenyl phosphate. After the reaction, the intermediate was filtered, washed, dried, and distilled under reduced pressure to obtain the purified intermediate. The intermediate was dissolved in an anhydrous organic solvent with 1,1,3,3-tetramethyldisiloxane and transferred to a three-necked round-bottom flask. The mixture was heated to 70-90°C under an inert atmosphere, and then a platinum catalyst was added to the reaction system. The mixture was stirred for 6-12 hours to carry out a hydrosilylation reaction. After the reaction, the mixture was cooled to room temperature, filtered through a silica gel short column to remove catalyst residue, and distilled under reduced pressure to remove solvent, to obtain siloxane-bridged phosphate esters. S20: Preparation of flame-retardant coolant; the obtained siloxane-bridged phosphate ester is added to the base mineral insulating oil, and a high-efficiency antioxidant is added. The mixture is stirred for 1 to 3 hours under water bath heating conditions to obtain the phosphorus-silicon synergistic flame-retardant coolant.

2. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 1, characterized in that, The molar ratio of diphenyl phosphate to allyl alcohol is 1:1 to 1.

2.

3. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 2, characterized in that, The condensing agent is N,N-dicyclohexylcarbodiimide, and the esterification catalyst is 4-dimethylaminopyridine.

4. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 3, characterized in that, The molar ratio of the intermediate allyl phosphate diphenyl ester to 1,1,3,3-tetramethyldisiloxane is 2:1 to 2.2:

1.

5. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 4, characterized in that, The platinum catalyst is a Karstedt catalyst, and its amount, calculated as platinum, is 0.01% to 0.1% of the molar amount of Si-H bonds in the reaction system; the temperature of the hydrosilylation reaction is 70 to 90°C, and the reaction time is 6 to 12 hours.

6. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 5, characterized in that, The siloxane-bridged phosphate ester is added to the coolant at a mass percentage of 1% to 10%.

7. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 6, characterized in that, The siloxane-bridged phosphate ester is added to the coolant at a mass percentage of 3% to 6%.

8. The method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 7, characterized in that, The high-efficiency antioxidant is a hindered phenolic antioxidant, and its mass percentage added to the coolant is 0.1%~0.5%.

9. A method for preparing a phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to claim 8, characterized in that, The base mineral insulating oil is a naphthenic or paraffinic mineral insulating oil.

10. A phosphorus-silicon synergistic flame-retardant coolant for immersion liquid cooling according to any one of claims 1 to 9, characterized in that, The phosphorus-silicon synergistic flame-retardant coolant is prepared by the above preparation method, and the coolant is used in the immersion liquid cooling system of energy storage battery.

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