Preparation method of fire extremely-early warning coating for lithium battery thermal runaway

Abstract

The invention discloses a preparation method of a fire extremely early warning coating for lithium battery thermal runaway, and relates to the technical field of lithium battery fire safety, in particular to the preparation method of the fire extremely early warning coating for lithium battery thermal runaway. Comprising the following steps: step 1, adding oily polyurethane and N, N-dimethylformamide into a reaction container provided with a thermometer and a stirrer; step 2, adding a flame retardant on the basis of the polyurethane ester matrix prepared in the step 1; step 3, adding nano particles into the reaction liquid obtained in the step 2, and uniformly stirring and mixing to obtain an early-warning coating material; based on the adjustable 20 nm silicon dioxide aerogel proportion, accurate control over the thermal collapse temperature of the coating material is achieved. The lower the thermal collapse temperature of the early warning coating material is, the potential fire risk can be detected earlier by the pyrolysis particle detector, so that the lithium battery fire risk can be early warned at an extremely early stage.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery fire safety, and particularly to a preparation method of a fire very early warning coating for lithium battery thermal runaway. Background Art

[0002] Under the background of the rapid development of lithium battery technology, its safety issue is particularly prominent. Lithium batteries are widely used in new energy vehicles and energy storage fields due to their high energy density and long cycle life. In applications, lithium batteries are connected by means such as series and parallel connections. During the long-term use of lithium batteries, poor contact may occur at the connections of series and parallel lithium batteries, resulting in an increase in contact resistance. When current passes through, heat is generated, and the temperature rises to a certain level, posing a fire hazard. The continuous increase in temperature will cause the pressure protection valve of the lithium battery to open, spraying out combustible gases and solid particles. For aspirating pyrolysis particle fire detectors, since they detect fire warnings by capturing nano-scale pyrolysis particles in the air, they often detect pyrolysis particles after the lithium battery has been heating for some time, that is, after the pressure valve has opened. In order for this type of aspirating pyrolysis particle fire detector to detect the heating and fire hazards of lithium batteries before the safety valve opens, obviously a pyrolysis particle coating capable of achieving very early fire warning is required. Developing such a coating material that can give early warning of lithium battery thermal runaway is of great significance for new energy safety.

[0003] With the development of functional coatings, the function of releasing fire symptom signals through coatings has always been concerned by scholars. Spraying a fire warning coating on the metal shell, electrodes of lithium batteries, and the exposed parts of the wires connected to the electrodes is considered an effective method to solve the above problems. Polyurethane is a unique polymer material with various forms and properties. Different application requirements can be achieved by adjusting the conditions of the polymerization reaction and the material composition. Polyurethane coatings have excellent properties such as low film-forming temperature, strong adhesion, and chemical resistance, and are one of the main varieties that occupy a very important position in the coating industry.

[0004] For aspirating pyrolysis particle fire detectors, the premise of achieving early warning is to monitor the pyrolysis particles released when substances are thermally decomposed by heat. Pyrolysis particles are nano-sized invisible particles to the naked eye caused by temperature changes in substances, with a diameter of about 2nm - 300nm. Pyrolysis particle detectors adopt a light-shielding technology based on the cloud chamber principle. When pyrolysis particles pass through the cloud chamber, the condensation characteristics of water droplets contain these invisible sub-micron particles in the center of small water droplets with a diameter of about 20μm. By measuring the light-shielding surface and light transmittance formed by this huge fog-like water droplet, the number of pyrolysis particles contained in the air can be measured, thereby judging the very early state of a fire.

[0005] By combining a fire warning coating with an aspirating pyrolysis particle fire detector, it is possible to accurately identify the hidden heat generation hazard of lithium battery thermal runaway before visible smoke is produced. When the temperature of the lithium battery housing or the electrode terminal exceeds the thermal breakdown point of the coating material, pyrolysis particles are released. When the pyrolysis particle detector detects the pyrolysis particles, an alarm is issued, and the fire hazard can be detected at the very early stage of thermal runaway. It can be seen that such a fire warning coating that can undergo thermal breakdown at a relatively low temperature and stably release pyrolysis particles is the key to realizing the very early fire warning of lithium battery thermal runaway. For this reason, the present invention proposes a preparation method for a fire very early warning coating for lithium battery thermal runaway. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a preparation method for a fire very early warning coating for lithium battery thermal runaway. This coating can adjust the thermal breakdown temperature, uses polyurethane as the base material, N,N-dimethylformamide as the solvent, and adds nanoparticles to enhance the porosity and heat transfer rate of the coating to form a warning coating material. The warning coating material is sprayed onto the metal shell, electrodes of the lithium battery, and the exposed parts of the wires connected to the electrodes. When the internal temperature of the lithium battery rises abnormally and conducts heat to the metal shell, electrodes, and exposed parts of the wires of the lithium battery, the warning coating material undergoes thermal breakdown, and pyrolysis particles are released through the pyrolysis of the warning coating material. At the same time, the pyrolysis particle detector detects the pyrolysis particles and issues a warning to achieve fire safety.

[0007] To achieve the above object, the present invention provides the following technical solution: A preparation method for a fire very early warning coating for lithium battery thermal runaway, comprising the following steps:

[0008] Step 1: Add oil-based polyurethane and N,N-dimethylformamide into a reaction vessel equipped with a thermometer and a stirrer;

[0009] Step 2: After the polyurethane matrix prepared in Step 1 meets the requirements, add a flame retardant;

[0010] Step 3: Based on the reaction solution obtained in Step 2, add nanoparticles, stir and mix evenly to obtain a warning coating material;

[0011] Step 4: Spray the warning coating material onto the metal shell, electrodes of the lithium battery, and the exposed parts of the wires connected to the electrodes, with the coating thickness being 30μm - 80μm, and let it stand until the coating is completely solidified. Install a pyrolysis particle detector near the warning coating. When the internal temperature of the lithium battery rises abnormally and conducts heat to the metal shell, electrodes, and the exposed parts connected to the electrodes of the lithium battery, the warning coating is heated to release pyrolysis particles, and the pyrolysis particle detector detects the pyrolysis particles and issues a warning.

[0012] Further, in the step 1, the mass ratio of the oil-based polyurethane and N,N-dimethylformamide added is 1:1;

[0013] Further, in the step 1, the temperature of the reaction vessel equipped with a thermometer and a stirrer is raised to 50 °C;

[0014] Further, in the step 1, the oil-based polyurethane and N,N-dimethylformamide are stirred at 300 r / min for 10 min - 30 min at a temperature of 50 °C;

[0015] Further, in the step 2, the flame retardants added are decabromodiphenylethane and antimony trioxide;

[0016] Further, in the step 2, the mass fraction of the decabromodiphenylethane and antimony trioxide added is 10%;

[0017] Further, in the step 2, the ratio of the decabromodiphenylethane and antimony trioxide added is 3:1;

[0018] Further, in the step 2, after adding the decabromodiphenylethane and antimony trioxide, the temperature is raised to 80 °C

[0019] Further, in the step 2, after raising the temperature to 80 °C, stirring is continued at a rotation speed of 300 r / min for 30 min - 1 h;

[0020] Further, in the step 3, 20 nm silica aerogel nanoparticles are added;

[0021] Further, in the step 3, after adding the 20 nm silica aerogel, stirring is continued at a temperature of 80 °C for 30 min.

[0022] The substantial effect of the present invention: Based on the adjustable proportion of 20 nm silica aerogel, precise control of the thermal collapse temperature of the coating material is achieved. Different substances have different thermal collapse temperatures. The lower the thermal collapse temperature of the coating, the earlier the pyrolysis particle detector can detect potential fire risks, thus realizing the very early warning of fires. The present invention solves the applicability problem of aspirating pyrolysis particle type fire detectors to the thermal runaway and fire warning of new energy lithium batteries, and avoids the drawback that pressure needs to be opened when the lithium battery reaches the edge of thermal runaway for application. The present invention has the advantage of earlier warning through the pyrolysis particles generated during the thermal collapse of the fire warning coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a process schematic diagram of the present invention

[0024] Figure 2 is a thermal collapse temperature test bench of the present invention

[0025] Figure 3 Schematic diagram of the pyrolysis particle detector for detecting pyrolysis particles

[0026] Figure 4 Pyrolysis particle concentration diagram of the present invention Detailed implementation manners

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, those of ordinary skill in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

[0028] The raw materials, instruments and other supplies used in the present invention can be obtained through conventional channels if not otherwise specified.

[0029] Example 1

[0030] A preparation method of a fire early warning coating for thermal runaway of lithium batteries, the coating is composed of a base material, a solvent, a flame retardant and a nano-particle additive.

[0031] Step 1: Add oil-based polyurethane and N,N-dimethylformamide into a reaction vessel equipped with a thermometer and a stirrer in a mass ratio of 1:1;

[0032] Step 2: After adding the oil-based polyurethane and N,N-dimethylformamide, raise the temperature of the reaction vessel to 50 °C, and stir at a speed of 300 r / min for 10 min at a temperature of 50 °C;

[0033] Step 3: Add 10% by mass of decabromodiphenylethane and antimony trioxide to the reaction solution prepared in Step 2, and the addition ratio of decabromodiphenylethane and antimony trioxide is 3:1;

[0034] Step 4: After adding decabromodiphenylethane and antimony trioxide in Step 3, raise the temperature of the reaction vessel to 80 °C, and continue to stir at a speed of 300 r / min for 30 min at a temperature of 80 °C;

[0035] Step 5: Add 5% by mass of 20 nm silica aerogel nanoparticles and continue to stir at a speed of 300 r / min for 30 min to obtain the warning coating material, and name the obtained coating Q1;

[0036] Step 6: Spray the warning coating material onto the metal shell, electrodes of the lithium battery, and the exposed parts of the wires connected to the electrodes. The coating thickness is 30 μm, and let it stand until the coating is completely solidified. Install a pyrolysis particle detector near the warning coating. When the internal temperature of the lithium battery rises abnormally and conducts heat to the metal shell, electrodes of the lithium battery, and the exposed parts of the wires connected to the electrodes, the warning coating releases pyrolysis particles when heated, and the pyrolysis particle detector detects the pyrolysis particles and issues a warning.

[0037] Example 2

[0038] A preparation method of a fire ultra-early warning coating for thermal runaway of lithium batteries, which is different from Example 1 in that: add 20 nm silica aerogel nanoparticles with a mass fraction of 10% and continue to stir at a speed of 300 r / min for 40 min to obtain a coating, and name the obtained coating Q2.

[0039] Other parts not mentioned are the same as in Example 1.

[0040] Example 3

[0041] A preparation method of a fire ultra-early warning coating for thermal runaway of lithium batteries, which is different from Example 1 in that: add 12% by mass of decabromodiphenylethane and antimony trioxide, and stir at a speed of 300 r / min at a temperature of 80 °C for 1 h. Next, add 20 nm silica aerogel nanoparticles with a mass fraction of 15% and continue to stir at a speed of 300 r / min for 30 min to obtain a coating, and name the obtained coating Q3.

[0042] Other parts not mentioned are the same as in Example 1.

[0043] Testing method

[0044] To avoid external influence, use a transparent acrylic board to build a test space. Set the temperature of the intelligent constant temperature heating table to 80 °C - 120 °C. Place the metal test sample sprayed with the warning coating on the heating table. Place the intake pipe of the ZW-FGS ultra-early aspirating pyrolysis particle detector at the position centered downward at the top of the acrylic. Attach a K-type thermocouple to the back of the test sample, record the temperature of the K-type thermocouple when the pyrolysis particle detector alarms, and this temperature is the thermal breakdown temperature of the warning coating. Record the changes in the thermal breakdown temperature test bench and pyrolysis particle concentration within 5 min.

[0045] The performance test results of the warning coating samples obtained in Examples 1 - 3 are shown in Table 1.

[0046] Table 1 Test results of pyrolysis particles and thermal breakdown temperature

[0047]

[0048] From the test data of Examples 1 to 3 in Table 1, it can be seen that the warning coatings prepared by adding different proportions of 20nm silica aerogel have different thermal collapse temperatures, and pyrolysis particles can be stably released at different thermal collapse temperatures. With the increase of the proportion of 20nm silica, more inorganic substances are dispersed in the organic polymer material. Under continuous heating, physical heat transfer and chemical reactions occur between the 20nm silica aerogel and the coating base material, reducing the critical temperature that the coating can withstand and causing thermal collapse at a lower temperature. When the addition amount of 20nm silica aerogel in the warning coating is 15%, the thermal collapse temperature drops the most, and the concentration of pyrolysis particles released at the thermal collapse temperature is the highest at this time. At this time, the warning coating is more easily detected by the pyrolysis particle detector, thus realizing the very early warning of battery thermal runaway.

Claims

1. A preparation method of a fire very early warning coating for lithium battery thermal runaway, characterized in that It includes the following steps: Step 1: Add oil-based polyurethane and N,N-dimethylformamide into a reaction vessel equipped with a thermometer and a stirrer; Step 2: After the polyurethane matrix prepared in Step 1 meets the requirements, add a flame retardant; Step 3: Based on the reaction solution obtained in Step 2, add nanoparticles, stir and mix evenly to obtain a warning coating; Step 4: Spray the warning coating onto the metal shell and electrode connection of the lithium battery, with the coating thickness being 30μm - 80μm, and let it stand until the coating is completely solidified. Install an aspirating pyrolysis particle fire detector near the lithium battery. When the internal temperature of the lithium battery rises abnormally and conducts heat to the metal shell, electrode and the exposed part of the wire connected to the electrode of the lithium battery, the warning coating decomposes by heat and releases pyrolysis particles into the air. The pyrolysis particle fire detector detects the pyrolysis particles and issues a fire warning.

2. The preparation method of a very early warning coating for lithium battery thermal runaway according to claim 1, characterized in that, The mass ratio of the oil-based polyurethane and N,N-dimethylformamide added in Step 1 is 1:

1.

3. The preparation method of a fire very early warning coating for lithium battery thermal runaway according to claim 1, characterized in that The oil-based polyurethane and N,N-dimethylformamide added in Step 1 should be stirred at 300r / min for 10min - 30min at a temperature of 50°C.

4. The preparation method of a fire very early warning coating for lithium battery thermal runaway according to claim 1, characterized in that, The flame retardant added in Step 1 is decabromodiphenylethane and antimony trioxide.

5. The preparation method of a very early fire warning coating for lithium battery thermal runaway according to claim 1, characterized in that, The mass fraction of decabromodiphenylethane and antimony trioxide added in Step 2 is 10%.

6. The preparation method of a very early fire warning coating for lithium battery thermal runaway according to claim 1, characterized in that, The ratio of decabromodiphenylethane and antimony trioxide added in Step 2 is 3:

1.

7. The preparation method of a very early fire warning coating for lithium battery thermal runaway according to claim 1, characterized in that, After adding decabromodiphenylethane and antimony trioxide in Step 2, raise the temperature of the reaction vessel to 80°C and continue to stir at 300r / min for 30min - 1h.

8. The preparation method of a very early warning coating for lithium battery thermal runaway according to claim 1, characterized in that The heat insulation agent added in Step 3 is 20nm silica aerogel.

9. The preparation method of a very early fire warning coating for lithium battery thermal runaway according to claim 1, characterized in that, After adding 20nm silica aerogel in Step 3, maintain the temperature of the reaction vessel at 80°C and continue to stir at a speed of 300r / min for 30min.

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