Energy storage battery thermal management liquid prepared from coal-based base oil and preparation method thereof

Abstract

The application discloses a coal-based base oil preparation energy storage battery thermal management liquid and a preparation method thereof, and particularly relates to the technical field of energy storage system thermal management. The thermal management liquid is composed of a composite base oil and a functional composite agent. The composite base oil is composed of Fischer-Tropsch synthesis isomerized alkanes CTL III+ base oil and poly-alpha-olefin PAO base oil. The functional composite agent is composed of an antioxidant, a metal deactivator, an organic phosphorus flame retardant, a viscosity index improver and a surface tension regulator. The preparation method comprises base oil compounding, additive premixing, blending and homogenizing, viscosity adjustment and filtering and packaging. The application has excellent low-temperature fluidity, thermal insulation and active thermal runaway inhibition capacity, is good in compatibility, low in cost, environmentally friendly, and can meet the needs of energy storage battery immersion cooling.

Description

Technical Field

[0001] This invention relates to the field of thermal management technology for energy storage systems, and more specifically, to thermal management fluids for energy storage batteries prepared from coal-based base oils and their preparation methods. Background Technology

[0002] With the rapid development of technologies such as 5G communication, artificial intelligence, and big data, the scale of data centers and energy storage systems continues to expand, and their energy consumption and safe operation issues are receiving increasing attention. As the core component of energy storage systems, lithium-ion batteries are extremely sensitive to operating temperature. The optimal operating temperature range is 15℃-35℃. Too low a temperature will lead to reduced electrolyte activity, slower ion diffusion, and decreased battery performance, and may even cause lithium plating and lithium dendrite growth. Lithium dendrites can pierce the separator and cause internal short circuits. Too high a temperature will accelerate battery aging, reduce cycle life, and in severe cases may lead to thermal runaway, causing fire and explosion accidents. Therefore, an efficient and reliable thermal management system is crucial to ensuring the safe operation of energy storage batteries.

[0003] Currently, the main cooling methods for energy storage batteries include air cooling, cold plate liquid cooling, and immersion liquid cooling. Among them, immersion liquid cooling, which directly immerses the battery in the coolant, has advantages such as high heat exchange efficiency, good temperature uniformity, and low energy consumption, and has become an important development direction for high-density energy storage scenarios. Immersion coolants are mainly divided into three categories: fluorinated liquids, silicone oils, and hydrocarbon oils. Fluorinated liquids, such as 3M's Novec and Fluorinert series, have excellent insulation and chemical inertness, but they have problems such as high price and high global warming potential (GWP). Although silicone oils have good insulation and high flash point, they have poor low-temperature fluidity, making it difficult to meet the needs of cold-region applications. Hydrocarbon oils, such as Shell S5 X, have relatively low cost, but existing products still need to be improved in terms of low-temperature performance and thermal runaway suppression capabilities, and there is a lack of dedicated additive systems designed for the characteristics of coal-based base oils.

[0004] On the other hand, my country possesses abundant coal-to-oil resources. Fischer-Tropsch isoparaffin CTL III+ base oil and polyalphaolefin (PAO) base oil have advantages such as high viscosity index, low pour point, and good oxidation resistance, making them ideal raw materials for preparing high-performance thermal management fluids. However, how to develop an immersion thermal management fluid with excellent low-temperature fluidity, high thermal conductivity and insulation, active thermal runaway suppression capability, and good material compatibility through the synergistic design of base oil compounding and additive systems to meet the safe operation requirements of energy storage batteries under extreme conditions remains a technical challenge that urgently needs to be solved in this field. In view of this, the present invention provides a thermal management fluid for energy storage batteries prepared from coal-based base oil and its preparation method. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide thermal management fluid for energy storage batteries prepared from coal-based base oil and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a thermal management fluid for energy storage batteries prepared from coal-based base oil, which is composed of the following components by weight percentage: The complex base oil comprises 89.9%-97.99% isoparaffinic CTL III+ base oil and polyalphaolefin (PAO) base oil, wherein the CTL III+ base oil accounts for 60%-80% of the total weight of the complex base oil, and the PAO base oil accounts for 20%-40% of the total weight of the complex base oil. The functional composite agent comprises 2.01%-10.1% of the total weight of the heat management fluid, and the functional composite agent is composed of the following components, which are respectively percentages of the total weight of the heat management fluid: Antioxidant 0.5%-3%; Metal deactivating agent 0.1%-0.5%; Organophosphorus flame retardants 1%-5%; Viscosity index improver: 0.4%-1.5%; Surface tension modifier 0.01%-0.1%.

[0007] Preferably, the PAO base oil is at least one of PAO 2, PAO 4, and PAO 6.

[0008] Preferably, the antioxidant is a mixture of alkylated diphenylamine and hindered phenolic antioxidant, with a weight ratio of 1:0.2 to 1:0.5.

[0009] Preferably, the metal deactivator is at least one of a benzotriazole derivative or a thiadiazole derivative.

[0010] Preferably, the organophosphorus flame retardant is a phosphate ester, which is selected from one or more of tricresyl phosphate, triphenyl phosphate, and tributyl phosphate.

[0011] Preferably, the viscosity index improver is a hydrogenated styrene-diene copolymer.

[0012] Preferably, the surface tension modifier is at least one of a fluorinated surfactant or a polysiloxane surfactant.

[0013] On the other hand, the present invention also provides a method for preparing a thermal management fluid for energy storage batteries made from coal-based base oil, which includes the following steps: S1. Base oil compounding: Add CTL III+ base oil and PAO base oil to the blending tank according to the ratio, heat to 50℃-70℃, and stir for 30-60 minutes under nitrogen protection to obtain a homogeneous compound base oil. S2. Additive premixing: Mix antioxidants, metal deactivators, organophosphorus flame retardants and surface tension modifiers according to the formula, stir at room temperature for 10-20 minutes to obtain a premixed additive package; S3. Blending and homogenization: Slowly add the premixed additive package obtained in step S2 to the composite base oil in step S1, keep the temperature at 50℃-70℃, and stir for 60-120 minutes. S4. Viscosity adjustment: Add the specified amount of viscosity index improver to the mixture from step S3, and continue stirring for 30-60 minutes to make the system homogeneous and transparent. S5. Filtration and Packaging: The mixture obtained in step S4 is filtered through a precision filter with a diameter of ≤10μm to obtain the finished thermal management fluid.

[0014] Preferably, in step S1, the compounding ratio of CTL III+ base oil to PAO base oil is 70:30, the blending temperature is 60°C, and the stirring time is 45 min.

[0015] Preferably, the stirring time in step S3 is 90 min, and the filter accuracy in step S5 is 5 μm.

[0016] The technical effects and advantages of this invention are as follows: This invention achieves a synergistic improvement in low-temperature fluidity, thermal conductivity and insulation, and active safety protection by compounding Fischer-Tropsch isoparaffinic CTL III+ base oil and polyalphaolefin PAO base oil in a specific ratio and adding a five-element functional composite agent containing organophosphorus flame retardants. Through the synergistic combination of CTL III+ base oil and PAO base oil, the thermal management fluid has excellent low-temperature fluidity, which can meet the year-round operation requirements of cold region energy storage systems. It solves the problem of insufficient low-temperature fluidity of existing hydrocarbon coolants, while controlling the kinematic viscosity within a suitable range, taking into account both heat transfer efficiency and pump sealing performance. This invention introduces organophosphorus flame retardants into a coal-based submerged thermal management fluid system, endowing the thermal management fluid with active thermal runaway suppression capabilities. This represents a breakthrough from a passive heat transfer medium to an active safety barrier. Under the high-temperature conditions of battery thermal runaway, organophosphorus flame retardants can decompose and absorb heat, capture free radicals, and form a heat-insulating carbon layer, effectively blocking the propagation of thermal runaway between battery modules and significantly improving the operational safety of the energy storage system. This function is not available in existing ordinary hydrocarbon coolants. This invention significantly improves the overall performance and long-term stability of the thermal management fluid through the synergistic formulation of five functional composite agents. The synergistic effect of antioxidants and metal deactivators can effectively inhibit the oxidative deterioration of the thermal management fluid during use and extend its service life. The surface tension regulator ensures that the thermal management fluid fully wets the surface of the battery cell and structural components and quickly removes entrained air bubbles during cyclic use, avoiding local dry burning and a decrease in insulation performance. The synergistic effect of each component gives the thermal management fluid excellent thermal conductivity, electrical insulation performance and material compatibility. It will not cause significant corrosion, swelling or mechanical performance degradation when in long-term contact with metal and non-metal materials in the battery pack, ensuring the long-term safe operation of the energy storage system. This invention uses coal-based base oil as the main raw material, which is abundant and inexpensive. It has a significant cost advantage over fluorinated thermal management fluids and has an extremely low GWP value, making it environmentally friendly and possessing both significant economic and environmental benefits. Attached Figure Description

[0017] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Example 1

[0019] This embodiment provides a thermal management fluid for energy storage batteries prepared from coal-based base oil. In this embodiment, all parts are by weight, and the sum of the weight parts of all components is 100 parts. Specifically, it includes the following components: Complex base oils: 70 parts CTL III+ base oil, 23 parts PAO 4 base oil, totaling 93 parts; Functional composite agent: 1.2 parts alkylated diphenylamine, 0.4 parts hindered phenolic antioxidant, 0.3 parts benzotriazole derivative, 4 parts tricresyl phosphate, 1 part hydrogenated styrene-diene copolymer, 0.1 parts polysiloxane surfactant, totaling 7 parts; This embodiment also provides a method for preparing a thermal management fluid for energy storage batteries made from coal-based base oil, which includes the following steps: S1. Base oil compounding: CTL III+ base oil and PAO 4 base oil are added to the blending kettle according to the ratio, heated to 60°C, and stirred for 45 minutes under nitrogen protection to obtain a homogeneous compound base oil. S2. Additive premixing: Alkylated diphenylamine, hindered phenol, benzotriazole derivative, tricresyl phosphate and polysiloxane surfactant are mixed and stirred at room temperature for 15 minutes according to the formula to obtain a premixed additive package. S3. Blending and homogenization: Slowly add the premixed additive package obtained in step S2 to the composite base oil in step S1, and stir at 60°C for 90 minutes. S4. Viscosity adjustment: Add the prescribed amount of hydrogenated styrene-diene copolymer to the mixture from step S3, and continue stirring for 45 minutes to make the system uniform and transparent. S5. Filtration and Packaging: The mixture obtained in step S4 is filtered through a 5μm precision filter to obtain the finished thermal management fluid. Example 2

[0020] The difference between this embodiment and Embodiment 1 is that: Complex base oils: 70 parts CTL III+ base oil, 19 parts PAO 2 base oil, 5 parts PAO 6 base oil, totaling 94 parts; Functional compounding agent: 1 part alkylated diphenylamine, 0.5 parts hindered phenolic antioxidant, 0.4 parts thiadiazole derivative, 3 parts triphenyl phosphate, 1 part hydrogenated styrene-diene copolymer, 0.1 parts fluorinated surfactant, totaling 6 parts.

[0021] The preparation method is the same as in Example 1. Example 3

[0022] The difference between this embodiment and Embodiment 1 is that: Complex base oils: 61.45 parts of CTL III+ base oil, 30 parts of PAO 6 base oil, totaling 91.45 parts; Functional compounding agent: 1.5 parts alkylated diphenylamine, 0.5 parts hindered phenolic antioxidant, 0.2 parts benzotriazole derivative, 5 parts tributyl phosphate, 1.3 parts hydrogenated styrene-diene copolymer, 0.05 parts polysiloxane surfactant, totaling 8.55 parts.

[0023] The preparation method is the same as in Example 1.

[0024] Comparative Example 1: Single base oil, without functional additives It uses only 100 parts of CTL III+ base oil, without any additives, and is used directly as a heat management fluid.

[0025] Comparative Example 2: Contains no organophosphorus flame retardants Complex base oils: 74.2 parts of CTL III+ base oil, 22 parts of PAO 4 base oil, totaling 96.2 parts; Functional composite agent: 1.5 parts alkylated diphenylamine, 0.6 parts hindered phenolic antioxidant, 0.4 parts benzotriazole derivative, 1.2 parts hydrogenated styrene-diene copolymer, 0.1 parts polysiloxane surfactant, totaling 3.8 parts, without organophosphorus flame retardants; The preparation method is the same as in Example 1.

[0026] It is worth noting that the above raw material components come from the following sources: CTL III+ base oil: produced by Shanxi Lu'an Taihang Lubrication Technology Co., Ltd., Fischer-Tropsch isoparaffin, viscosity index >140, typical pour point <-30℃; PAO base oils: commercially available, PAO 2, PAO 4, PAO 6 (ExxonMobil or similar products); Alkylated diphenylamine: Commercially available, such as Irganox L57; Hindered phenolic antioxidants: commercially available, such as Irganox L135; Benzotriazole derivatives: commercially available, such as T551; Thiadiazole derivatives: commercially available, such as T561; Trimethylbenzene phosphate, triphenyl phosphate, tributyl phosphate: Commercially available, industrial grade; Hydrogenated styrene-diene copolymers: commercially available, such as viscosity index improver OCP; Fluorinated surfactants: commercially available, such as perfluoropolyether surfactants; Polysiloxane surfactants: commercially available, such as polyether-modified silicone oil.

[0027] The performance of Examples 1-3 and Comparative Examples 1-2 were tested respectively, and the testing methods are as follows: Kinematic viscosity: determined according to GB / T 265; Pour point: determined according to GB / T 3535; Flash point (open cup): determined according to GB / T 3536; Thermal conductivity: determined according to ASTM D7896; Dielectric strength: determined according to GB / T 507; Volume resistivity: determined according to GB / T 5654; Copper strip corrosion: determined according to GB / T 5096, 100℃, 3h; Material compatibility: Immerse EPDM in thermal management fluid and place at 80°C for 1000 hours, then test the rate of mass change. Thermal runaway suppression experiment: Using a 280Ah lithium iron phosphate energy storage battery, the battery module was immersed in thermal management fluid, and thermal runaway of a single cell was triggered by needle puncture. The highest temperature of adjacent cells and whether thermal runaway propagation occurred were recorded.

[0028] The final test results are shown in the table below: Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Kinematic viscosity at 40℃ (mm² / s) 9.8 10.2 8.5 32.5 9.9 Pour point (°C) -52 -48 -55 -28 -51 Flash point (open aperture, °C) 212 208 218 224 210 Thermal conductivity (W / m·K) 0.138 0.141 0.135 0.125 0.137 Dielectric strength (kV) 52 50 55 48 51 Volume resistivity (Ω·cm) <![CDATA[1.2×10¹ 4 ]]> <![CDATA[1.1×10¹ 4 ]]> <![CDATA[1.5×10¹ 4 ]]> 8×10¹³ <![CDATA[1×10¹ 4 ]]> Copper sheet corrosion (100℃, 3h) 1a 1a 1a 1b 1a EPDM quality change rate (%) +0.8 +0.7 +0.9 +3.2 +0.8 Thermal runaway suppression effect (highest temperature of adjacent cells in °C / whether it propagates) 68 / Not Spread 72 / Not Spread 65 / Not Spread >200 / Spread 156 / Thermal runaway occurred but did not immediately spread to the entire module. As can be seen from the table above: The pour points of Examples 1-3 are all below -48°C, indicating that the thermal management fluid of the present invention has excellent low-temperature fluidity and can meet the needs of energy storage systems in cold regions. The thermal conductivity, dielectric strength, and volume resistivity of Examples 1-3 are all better than those of Comparative Example 1, and no additives were used, indicating that the addition of the functional composite agent improves the heat transfer and insulation performance of the thermal management fluid. The copper sheet corrosion grade of Examples 1-3 is 1a, and the EPDM mass change rate is less than 1%, indicating good compatibility with both metallic and non-metallic materials. In the thermal runaway suppression experiment, Comparative Example 1, without additives, experienced thermal runaway propagation after needle puncture, with the temperature of adjacent batteries rapidly exceeding 200°C; Comparative Example 2, without flame retardants, had a maximum temperature of 156°C for adjacent batteries, and thermal runaway occurred but did not immediately spread to the entire module; while the temperatures of adjacent batteries in Examples 1-3 were all below 80°C, effectively suppressing the propagation of thermal runaway. This indicates that the presence of organophosphorus flame retardants plays a key role in suppressing thermal runaway.

[0029] This invention combines CTL III+ base oil and PAO base oil in a specific ratio, and adds a five-element functional composite agent containing antioxidants, metal deactivators, organophosphorus flame retardants, viscosity index improvers and surface tension modifiers. The resulting thermal management fluid has excellent low-temperature fluidity, thermal conductivity, electrical insulation, material compatibility and active thermal runaway suppression capabilities. Its comprehensive performance is outstanding and can meet the application requirements of immersion cooling for energy storage batteries.

[0030] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermal management fluid for energy storage batteries prepared from coal-based base oil, characterized in that: Composed of the following components by weight percentage: The complex base oil comprises 89.9%-97.99% isoparaffinic CTL III+ base oil and polyalphaolefin (PAO) base oil, wherein the CTL III+ base oil accounts for 60%-80% of the total weight of the complex base oil, and the PAO base oil accounts for 20%-40% of the total weight of the complex base oil. The functional composite agent comprises 2.01%-10.1% of the total weight of the heat management fluid, and the functional composite agent is composed of the following components, which are respectively percentages of the total weight of the heat management fluid: Antioxidant 0.5%-3%; Metal deactivating agent 0.1%-0.5%; Organophosphorus flame retardants 1%-5%; Viscosity index improver: 0.4%-1.5%; Surface tension modifier 0.01%-0.1%.

2. The thermal management fluid for energy storage batteries prepared from coal-based base oil according to claim 1, characterized in that: The PAO base oil is at least one of PAO 2, PAO 4 and PAO 6.

3. The thermal management fluid for energy storage batteries prepared from coal-based base oil according to claim 1, characterized in that: The antioxidant is a mixture of alkylated diphenylamine and hindered phenolic antioxidant, with a weight ratio of 1:0.2 to 1:0.

5.

4. The thermal management fluid for energy storage batteries prepared from coal-based base oil according to claim 1, characterized in that: The metal deactivator is at least one of a benzotriazole derivative or a thiadiazole derivative.

5. The thermal management fluid for energy storage batteries prepared from coal-based base oil according to claim 1, characterized in that: The organophosphorus flame retardant is a phosphate ester, which is selected from one or more of tricresyl phosphate, triphenyl phosphate, and tributyl phosphate.

6. The thermal management fluid for energy storage batteries prepared from coal-based base oil according to claim 1, characterized in that: The viscosity index improver is a hydrogenated styrene-diene copolymer.

7. The thermal management fluid for energy storage batteries prepared from coal-based base oil according to claim 1, characterized in that: The surface tension modifier is at least one of a fluorinated surfactant or a polysiloxane surfactant.

8. A method for preparing thermal management fluid for energy storage batteries based on coal-based base oil, used to prepare the thermal management fluid for energy storage batteries based on coal-based base oil as described in any one of claims 1-7, characterized in that: Includes the following steps: S1. Base oil compounding: Add CTL III+ base oil and PAO base oil to the blending tank according to the ratio, heat to 50℃-70℃, and stir for 30-60 minutes under nitrogen protection to obtain a homogeneous compound base oil. S2. Additive premixing: Mix antioxidants, metal deactivators, organophosphorus flame retardants and surface tension modifiers according to the formula at room temperature and stir for 10-20 minutes to obtain a premixed additive package. S3. Blending and homogenization: Slowly add the premixed additive package obtained in step S2 to the composite base oil in step S1, keep the temperature at 50℃-70℃, and stir for 60-120 minutes. S4. Viscosity adjustment: Add the specified amount of viscosity index improver to the mixture from step S3, and continue stirring for 30-60 minutes to make the system homogeneous and transparent. S5. Filtration and Packaging: The mixture obtained in step S4 is filtered through a precision filter with a diameter of ≤10μm to obtain the finished thermal management fluid.

9. The method for preparing thermal management fluid for energy storage batteries based on coal-based base oil according to claim 8, characterized in that: In step S1, the blending ratio of CTL III+ base oil to PAO base oil is 70:30, the blending temperature is 60℃, and the stirring time is 45min.

10. The method for preparing thermal management fluid for energy storage batteries based on coal-based base oil according to claim 8, characterized in that: The stirring time in step S3 is 90 min, and the filter accuracy in step S5 is 5 μm.

Images