Explosion-proof cooling liquid for lithium ion battery and explosion-proof performance testing method

Abstract

The application discloses a kind of explosion-proof cooling liquid for lithium ion battery and explosion-proof performance test method, the explosion-proof cooling liquid is with glycol, boric acid and deionized water constitute base fluid, high activity phosphate, benzotriazole, o-phenylenediacetic acid, defoaming agent and flame retardant are added in base fluid.The cooling liquid of the application has excellent explosion-proof, anticorrosion performance.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals, and more particularly to a coolant for lithium-ion batteries, especially an explosion-proof coolant for lithium-ion batteries with excellent antifreeze, explosion-proof, and corrosion-resistant properties. Background Technology

[0002] Developing new energy vehicles is the only way for my country to move from a major automobile producer to a leading automobile power. Currently, my country's new energy vehicles account for 68% of the global market. In pure electric vehicles and plug-in hybrid electric vehicles, the voltage of a single lithium battery cell is generally around 4V, and the output voltage of a lithium battery pack is generally 500V-700V. Therefore, in a battery pack, hundreds of cells need to be connected and fed through copper busbars. Current solutions for interconnecting cells mostly use flexible connections on the busbars. The temperature control fluid used by mainstream new energy vehicle manufacturers can cause short circuits when the battery ruptures due to physical impact, potentially leading to combustion and explosion. This poses a significant risk.

[0003] Currently, lithium-ion battery coolants generally use a basic combination of deionized water and ethylene glycol, with additives added to impart various properties to adapt to different application requirements under various operating conditions. Chinese patent CN107768766A discloses a coolant for power batteries and its preparation method, whose main components are bis(hydroxymethyl)imidazolidinyl urea, nano-barium sulfate, propylene glycol, graphite tailings, sodium o-nitrophenolate, chloroplatinic acid, and water. Its main effects are: accelerating heat release from the battery module and effectively reducing the battery's operating temperature. Chinese patent CN114686182A discloses a method for preparing an environmentally friendly coolant for new energy vehicles, whose main components are ethylene glycol, boric acid, glycerol, and various aliphatic amines including N,N-dimethylethanolamine. Its main effects are high specific heat capacity and thermal conductivity, along with advantages such as low freezing point and high flash point. Both of these patents use ethylene glycol and propylene glycol as antifreeze agents, effectively solving the antifreeze problem of lithium-ion batteries during operation. However, during the use of lithium-ion batteries, coolant leakage frequently occurs, leading to contact between the coolant and the battery plates. Currently, the conductivity of existing lithium-ion battery coolants is generally above 2000 μS / cm. Once a leak occurs, the high conductivity of the coolant can easily short-circuit the battery plates, causing a rapid rise in battery temperature and potentially resulting in explosions or other safety accidents. Furthermore, some existing lithium-ion battery coolants are highly corrosive to metal containers, also posing a safety hazard. GB 38031-2020, "Safety Requirements for Power Batteries for Electric Vehicles," clearly stipulates that after a single battery cell experiences thermal runaway, the battery system should not catch fire or explode within 5 minutes.

[0004] In response to existing problems, lithium-ion batteries have placed more stringent requirements on coolants, especially the need for a new cooling medium that can reduce the conductivity of the coolant to solve the problem of overheating and explosion caused by coolant leakage, while ensuring the corrosion resistance of the coolant. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-performance lithium-ion battery coolant with low conductivity and strong corrosion resistance.

[0006] To achieve its objectives, the present invention employs the following technical solution:

[0007] An explosion-proof coolant for lithium-ion batteries is characterized in that: the explosion-proof coolant is based on ethylene glycol, boric acid, and deionized water, and contains highly active phosphate ester, benzotriazole, phthalic acid, defoamer, and flame retardant. Specifically, the composition of each raw material by weight is as follows: ethylene glycol 20-30 parts, boric acid 10-20 parts, deionized water 50-60 parts, highly active phosphate ester 0.2-0.8 parts, benzotriazole 0.25-0.55 parts, phthalic acid 0.1-1 parts, defoamer 0.03-0.06 parts, and flame retardant 0.03-0.1 parts.

[0008] Furthermore, the defoamer is at least one of BASF's nonionic surfactant Plurafac LF401, BASF's low-foaming isomeric alcohol surfactant glass cleaner Profen LF403, BASF surfactant PE-6200, and BASF's low-foaming surfactant Pluronic PE6400.

[0009] Furthermore, the flame retardant is at least one selected from triphenyl phosphate, decabromodiphenyl ethane, and ammonium polyphosphate.

[0010] Furthermore, the resistivity of the deionized water used is above 16 MΩ·cm.

[0011] Furthermore, the conductivity of the explosion-proof coolant is no greater than 500 μS / cm.

[0012] In the formulation system of this invention: the boric acid acts as a corrosion inhibitor, improving the anti-corrosion performance of the coolant and also has a certain flame-retardant effect. The highly active phosphate ester acts as a surfactant, optimizing the dispersion effect and also has a certain flame-retardant effect. The benzotriazole acts as an antioxidant and anti-scaling agent, and has an anti-corrosion effect on some metal materials. The phthalic acid increases the specific heat and thermal conductivity of the coolant, enhancing heat transfer efficiency. Coolants prepared by mixing ethylene glycol, boric acid, and deionized water in different proportions have different freezing points and flash points.

[0013] This invention also provides a method for testing the explosion-proof performance of explosion-proof coolant for lithium-ion batteries. The method simulates the working condition when the coolant leaks in the battery and tests the explosion-proof performance as follows: two copper busbars are immersed in the coolant, and a DC voltage is applied to the two copper busbars as the positive and negative electrodes, respectively. The time without explosion or fire is recorded. If the time exceeds 5 minutes, it is considered qualified.

[0014] Furthermore, the DC voltage is 600V, the copper busbar has dimensions of 70mm in length, 52mm in width, and 3mm in thickness, and the two copper busbars are spaced 150mm apart and immersed in the coolant.

[0015] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0016] The explosion-proof coolant for lithium-ion batteries of the present invention has excellent cooling performance and explosion-proof performance, which can reduce the safety hazards when battery coolant leaks. At the same time, it has excellent anti-corrosion performance and has a good corrosion inhibition effect on a variety of metals such as copper, brass, steel (304), aluminum (3003) and cast aluminum. Detailed Implementation

[0017] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention; unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the materials, reagents, etc. used in the following examples are commercially available.

[0018] The resistivity of the deionized water used in the following examples is all above 16 MΩ·cm.

[0019] Example 1

[0020] The coolant in this embodiment is prepared by mixing 20 kg of ethylene glycol, 12 kg of boric acid, 51.5 kg of deionized water, 0.25 kg of highly active phosphate ester, 0.3 kg of benzotriazole, 0.5 kg of phthalic acid, 0.03 kg of LF401, and 0.05 kg of decabromodiphenyl ethane.

[0021] Example 2

[0022] The coolant in this embodiment is prepared by mixing 25.5 kg of ethylene glycol, 13 kg of boric acid, 55.5 kg of deionized water, 0.37 kg of highly active phosphate ester, 0.34 kg of benzotriazole, 0.59 kg of phthalic acid, 0.03 kg of LF401, and 0.04 kg of ammonium polyphosphate.

[0023] Example 3

[0024] The coolant in this embodiment is prepared by mixing 22 kg of ethylene glycol, 11 kg of boric acid, 56 kg of deionized water, 0.33 kg of highly active phosphate ester, 0.30 kg of benzotriazole, 0.87 kg of phthalic acid, 0.03 kg of PE-6200, and 0.035 kg of ammonium polyphosphate.

[0025] Example 4

[0026] The coolant in this embodiment is prepared by mixing 28 kg of ethylene glycol, 16.6 kg of boric acid, 51 kg of deionized water, 0.76 kg of highly active phosphate ester, 0.55 kg of benzotriazole, 0.32 kg of phthalic acid, 0.03 kg of PE-6200, and 0.04 kg of triphenyl phosphate.

[0027] Example 5

[0028] The coolant in this embodiment is prepared by mixing 26 kg of ethylene glycol, 19 kg of boric acid, 55 kg of deionized water, 0.74 kg of highly active phosphate ester, 0.49 kg of benzotriazole, 0.12 kg of phthalic acid, 0.03 kg of PE6400, and 0.08 kg of decabromodiphenyl ethane.

[0029] Example 6

[0030] The coolant in this embodiment is prepared by mixing 27.8 kg of ethylene glycol, 13.4 kg of boric acid, 55 kg of deionized water, 0.68 kg of highly active phosphate ester, 0.49 kg of benzotriazole, 0.66 kg of phthalic acid, 0.03 kg of LF402, and 0.06 kg of ammonium polyphosphate.

[0031] Example 7

[0032] The coolant of this embodiment is prepared by mixing 21.9 kg of ethylene glycol, 10 kg of boric acid, 52.2 kg of deionized water, 0.54 kg of highly active phosphate ester, 0.38 kg of benzotriazole, 0.58 kg of phthalic acid, 0.03 kg of LF402, and 0.05 kg of triphenyl phosphate.

[0033] Comparative Example 1

[0034] This comparative example provides a battery coolant, the composition of which, by weight, includes: 20 kg of ethylene glycol and 50 kg of deionized water.

[0035] Comparative Example 2

[0036] This comparative example provides a battery coolant, the composition of which, by weight, includes: 20 kg of ethylene glycol, 50 kg of deionized water, and 10 kg of boric acid.

[0037] Comparative Example 3

[0038] This comparative example provides a battery coolant with the same composition as Example 2, except that the amount of highly active phosphate ester added is 0.

[0039] Comparative Example 4

[0040] This comparative example provides a battery coolant with the same composition as in Example 4, except that the amount of triphenyl phosphate added is 0.

[0041] Conductivity and thermal conductivity were tested on the lithium-ion battery coolants prepared in Examples 1-7 and the coolants prepared in Comparative Examples 1-4. The electrical conductivity was determined according to GB / T 6682 "Specifications and Test Methods for Water Used in Analytical Laboratories", and the thermal conductivity was determined according to ASTM D7896-19 "Standard Test Method for Determination of Thermal Conductivity, Thermal Diffusivity and Volumetric Heat Capacity of Engine Coolants and Related Liquids by Transient Hot-Wire Liquid Thermal Conductivity Method". The results are shown in Table 1.

[0042] The explosion-proof performance of the lithium-ion battery coolant prepared in Examples 1-7 and the coolant prepared in Comparative Examples 1-4 was tested. The test method is as follows: two copper busbars (70 mm long, 52 mm wide, and 3 mm thick) were immersed in the coolant at a distance of 150 mm. The two copper busbars were used as the positive and negative electrodes, respectively, and a DC voltage of 600 V was applied to the two copper busbars. The ignition time of the sample was recorded from the moment the power was applied. The results are shown in Table 1.

[0043] Table 1

[0044] Inspection items Time of ignition (s) Electrical conductivity (25℃) / (μS / cm) Thermal conductivity (20℃) / (W / m·K) Example 1 655 494 0.663 Example 2 991 450 0.656 Example 3 635 433 0.609 Example 4 679 462 0.571 Example 5 720 481 0.589 Example 6 695 475 0.627 Example 7 989 441 0.696 Comparative Example 1 95 2498 0.494 Comparative Example 2 82 2514 0.537 Comparative Example 3 251 2721 0.418 Comparative Example 4 176 2311 0.589

[0045] As shown in Table 1, the ignition times of the samples, arranged from longest to shortest, are: Example 7, Example 2, Example 5, Example 6, Example 4, Example 1, Example 3, Comparative Example 3, Comparative Example 4, Comparative Example 1, and Comparative Example 2. Examples 1-7 show a significant increase in ignition time compared to Comparative Examples 1-4, indicating that Examples 1-7 possess superior fire and explosion-proof performance compared to Comparative Examples 1-4. The safety of the coolant has been greatly improved.

[0046] The corrosion resistance of the lithium-ion battery coolants prepared in Examples 1-7 and the coolants prepared in Comparative Examples 1-4 was tested according to SH / T0085 "Engine Coolant Corrosion Determination Method (Glassware Method)". The test method is as follows: Copper, brass, steel, cast aluminum, 6-series aluminum, 3-series aluminum, and 4-series aluminum were weighed and connected into a bundle of test pieces, with polytetrafluoroethylene (PTFE) used for insulation. The bundles were then completely immersed in 750 mL of coolant with an air flow rate of 100 mL / min and tested at 88°C for 336 h. The copper, brass, steel, cast aluminum, 6-series aluminum, 3-series aluminum, and 4-series aluminum test pieces were all standard test pieces specified in standard NB / SH / T 6047 "Electric Vehicle Coolant". After the test, the test pieces were removed, cleaned, and weighed again. The weight changes of the test pieces before and after the test were compared, and the results are shown in Tables 2 and 3. The units of the data in the tables are mg / test piece.

[0047] Table 2

[0048] project Quality Indicators Example 1 Example 2 Example 3 Example 4 Example 5 Copper ±5 -4.7 -5.9 -1.1 -4.1 -5.7 brass ±5 -1.9 -1.0 -2.8 -4.8 -3.4 steel ±5 +3.3 +3.7 +3.1 +3.8 +4.9 Cast aluminum ±10 -2.1 -5.5 -2.8 -4.4 -4.2 6-series aluminum ±10 -6.6 -7.4 -6.6 -8.4 -6.3 3-series aluminum ±10 +10.9 +8.1 +9.4 +9.2 +12.9 4-series aluminum ±10 -8.8 -7.8 -10.0 -9.8 -8.1

[0049] Table 3

[0050]

[0051]

[0052] As shown in Tables 2 and 3, the absolute values ​​of the weight changes of the seven test pieces in Examples 1-7 are generally smaller than the absolute values ​​of the weight changes in Comparative Examples 1-4. Specifically, the absolute values ​​of the weight changes of the copper sheet in the above 11 coolants, from largest to smallest, are: Example 2, Comparative Example 2, Example 5, Comparative Example 3, Comparative Example 4, Example 1, Comparative Example 1, Example 4, Example 7, Example 6, Example 3. The absolute values ​​of the weight changes of the brass sheet in the above 11 coolants, from largest to smallest, are: Comparative Example 2, Comparative Example 3, Comparative Example 1, Example 6, Example 4, Comparative Example 4, Example 5, Example 3, Example 7, Example 1, Example 2. The absolute values ​​of the weight changes of the steel in the above 11 coolants, from largest to smallest, are: Example 6, Comparative Example 2, Comparative Example 3, Comparative Example 1, Example 5, Example 7, Comparative Example 4, Example 4, Example 2, Example 1, Example 3. The absolute values ​​of the weight changes of cast aluminum in the above 11 coolants, from largest to smallest, are: Comparative Example 3, Comparative Example 4, Comparative Example 1, Example 2, Comparative Example 2, Example 4, Example 5, Example 6, Example 7, Example 3, Example 1. The absolute values ​​of the weight changes of 6-series aluminum in the above 11 coolants, from largest to smallest, are: Comparative Example 1, Comparative Example 2, Example 4, Example 2, Comparative Example 4, Example 7, Comparative Example 3, Example 1, Example 3, Example 6, Example 5. The absolute values ​​of the weight changes of 3-series aluminum in the above 11 coolants, from largest to smallest, are: Example 5, Comparative Example 2, Example 6, Comparative Example 3, Example 1, Comparative Example 4, Example 3, Example 4, Example 7, Comparative Example 1, Example 2. The absolute values ​​of the weight changes of 4-series aluminum in the above 11 coolants, from largest to smallest, are: Comparative Example 2, Example 6, Comparative Example 3, Example 3, Comparative Example 1, Example 4, Comparative Example 4, Example 1, Example 5, Example 2, Example 7.

[0053] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. An explosion-proof coolant for lithium-ion batteries, characterized in that: The explosion-proof coolant is based on ethylene glycol, boric acid, and deionized water. Highly active phosphate ester, benzotriazole, phthalic acid, defoamer, and flame retardant are added to the base liquid. The composition of each raw material by weight is as follows: ethylene glycol 20-30 parts, boric acid 10-20 parts, deionized water 50-60 parts, highly active phosphate ester 0.2-0.8 parts, benzotriazole 0.25-0.55 parts, phthalic acid 0.1-1 parts, defoamer 0.03-0.06 parts, and flame retardant 0.03-0.1 parts. The flame retardant is at least one selected from triphenyl phosphate, decabromodiphenyl ethane, and ammonium polyphosphate.

2. The explosion-proof coolant for lithium-ion batteries according to claim 1, characterized in that: The defoamer is at least one of BASF's nonionic surfactant Plurafac LF401, BASF's low-foaming isomeric alcohol surfactant glass cleaner Profen LF403, BASF surfactant PE-6200, and BASF's low-foaming surfactant Pluronic PE6400.

3. The explosion-proof coolant for lithium-ion batteries according to claim 1, characterized in that: The resistivity of the deionized water used is above 16 MΩ·cm.

4. The explosion-proof coolant for lithium-ion batteries according to claim 1, characterized in that: The conductivity of the explosion-proof coolant is no greater than 500 μS / cm.

5. The application of the explosion-proof coolant according to any one of claims 1 to 4 in a lithium-ion battery temperature control system.

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