A meta-aramid coating slurry, its preparation method, and a battery separator

Abstract

This invention discloses a meta-aramid coating slurry, its preparation method, and a battery separator. Hydrogenated nitrile butadiene rubber (NBR) is used as a binder. During the synthesis of meta-aramid, m-phenylenediamine and NBR are first prepared into a mixed solution, and then meta-aramid is prepared. The amide bonds in the meta-aramid form hydrogen bonds with the NBR, allowing the meta-aramid and NBR to bond well together without intermolecular repulsion. When used in a separator coating, the non-repulsive aramid and NBR not only retain the temperature resistance of the meta-aramid but, more importantly, enable the coated separator and the electrode to exhibit extremely high adhesion under hot-pressing conditions. Applying this coated separator to lithium batteries can significantly improve battery safety.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and in particular to a meta-aramid coating slurry, its preparation method, and a battery separator. Background Technology

[0002] Meta-aramid coated separators possess high temperature resistance and wettability. However, they also have a significant drawback in battery applications: during hot pressing, they exhibit almost no adhesion to the electrodes. When used in lithium-ion batteries, this can lead to a looser overall structure within the battery cell, making it susceptible to electrode misalignment and short circuits when subjected to impacts or violent shaking. Current technologies address this issue by adding binders to the aramid slurry. However, directly adding binders like PVDF to the aramid slurry results in mutual repulsion due to their different molecular compositions. This not only significantly diminishes the temperature resistance of the meta-aramid but also reduces the adhesion of PVDF to the electrodes. Summary of the Invention

[0003] The purpose of this invention is to address the technical deficiencies in the prior art by providing a method for preparing meta-aramid coating slurry.

[0004] Another object of the present invention is to provide a meta-aramid coating slurry based on a preparation method.

[0005] Another object of the present invention is to provide a battery separator based on the meta-aramid coating slurry.

[0006] Another object of the present invention is to provide a battery including the battery separator.

[0007] The technical solution adopted to achieve the purpose of this invention is:

[0008] A method for preparing a meta-aramid coating slurry includes the following steps:

[0009] Step 1: Dissolve hydrogenated nitrile butadiene rubber in dimethylacetamide to obtain a hydrogenated nitrile butadiene rubber solution. Under a protective gas, add m-phenylenediamine at 20 ℃~10 ℃ with stirring. Lower the temperature again to 0 ℃~5 ℃, add isophthaloyl chloride and stir. Raise the temperature to 75~85 ℃ and stir until the reaction is complete. Add calcium hydroxide to obtain a meta-aramid slurry of composite hydrogenated nitrile butadiene rubber.

[0010] Step 2: Stir and disperse the ceramic powder in an organic solvent, and then mill it to obtain a ceramic powder solution;

[0011] Step 3: Under stirring, dimethyl carbonate solution and ceramic powder solution described in step 2 are added sequentially to the meta-aramid slurry of composite hydrogenated nitrile rubber prepared in step 1 to obtain meta-aramid coating slurry.

[0012] In the above technical solution, the mass fraction of hydrogenated nitrile rubber in step 1 is 1-5 parts, the mass fraction of dimethylacetamide is 73-87 parts, the mass fraction of m-phenylenediamine and isophthaloyl chloride is 7-12 parts, wherein the molar ratio of m-phenylenediamine to phthaloyl chloride is 1:1, the mass fraction of calcium hydroxide is 5-10 parts, the stirring and dissolution time of hydrogenated nitrile rubber is 24-26 h, the stirring time after adding isophthaloyl chloride is 20-40 min, and the heating rate is 0.9-1 ℃ / min.

[0013] In the above technical solution, the ceramic powder in step 2 is 30-45 parts by mass, and the organic solvent is 55-70 parts by mass. The organic solvent is selected from one or two of dimethylacetamide or tripropylene glycol.

[0014] In the above technical solution, in step 3, the mass fraction of the meta-aramid slurry of the composite hydrogenated nitrile rubber is 50-60 parts, the mass fraction of the dimethyl carbonate solution is 5-15 parts, and the mass fraction of the ceramic powder solution is 25-45 parts.

[0015] Another aspect of the present invention includes a meta-aramid coating slurry prepared by the preparation method described above.

[0016] Another aspect of the present invention includes a meta-aramid slurry-coated diaphragm, wherein the coating layer of the diaphragm comprises meta-aramid and hydrogenated nitrile rubber.

[0017] Another aspect of the present invention includes a method for preparing a meta-aramid slurry-coated diaphragm, comprising the following steps:

[0018] Step 1: Prepare meta-aramid coating slurry according to the method described above;

[0019] Step 2: Coat the meta-aramid coating slurry obtained in Step 1 onto the base film;

[0020] Step 3: Extraction to obtain a diaphragm coated with meta-aramid slurry.

[0021] In the above technical solution, during extraction in step 3, the diaphragm passes through ten extraction tanks. The extract in the first three extraction tanks is an extract of deionized water and dimethylacetamide mixed in different mass ratios to form a coagulation bath. The mass ratio of dimethylacetamide to water in the first extraction tank is 3:2, the mass ratio of dimethylacetamide to water in the second extraction tank is 1:1, the mass ratio of dimethylacetamide to water in the third extraction tank is 2:3, and the remaining extraction tanks contain deionized water.

[0022] Another aspect of the present invention includes the application of the meta-aramid slurry-coated separator in lithium-ion batteries.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention uses hydrogenated nitrile rubber as a binder. In the process of synthesizing meta-aramid, m-phenylenediamine and hydrogenated nitrile rubber are first prepared into a mixed solution. Hydrogenated nitrile rubber is a highly viscous molecule with strong adsorption. Since hydrogenated nitrile rubber is a saturated polymer, it will adsorb m-phenylenediamine. After being adsorbed by nitrile rubber, m-phenylenediamine can better adhere to aramid molecules when participating in the polymerization reaction of aramid.

[0025] 2. Meta-aramid is prepared by polymerizing hydrogenated nitrile butadiene rubber with isophthaloyl chloride using m-phenylenediamine. The amide bonds in the aramid form hydrogen bonds with the hydrogenated nitrile butadiene rubber, which allows the meta-aramid and the hydrogenated nitrile butadiene rubber to bond together well without intermolecular repulsion.

[0026] 3. The use of aramid and hydrogenated nitrile rubber, which do not exhibit repulsion, in the separator coating not only does not lose the temperature resistance of meta-aramid, but more importantly, it can generate extremely high adhesion between the coated separator and the electrode under hot pressing conditions. Applying this coated separator to lithium batteries can greatly increase the safety performance of the battery.

[0027] 4. Because the coating slurry contains hydrogenated nitrile butadiene rubber, when the electrolyte is added to the battery, the electrolyte, being a polar solution, will cause the hydrogenated nitrile butadiene rubber to swell upon contact. The swollen hydrogenated nitrile butadiene rubber will absorb the electrolyte, causing it to gel. This gel state will make the electrolyte adhere better to the separator, increasing the battery's cycle efficiency. Attached Figure Description

[0028] Figure 1 The image shows a scanning electron microscope (SEM) image of the surface of Example 1.

[0029] Figure 2 This is a scanning electron microscope image of Comparative Example 1. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0031] In the embodiments of this application, the coating extraction of the diaphragm is carried out according to the following steps:

[0032] The extraction tank is divided into 10 smaller tanks, each 1 m deep. The first three tanks contain an extract solution of deionized water and dimethylacetamide mixed in different mass ratios to form a coagulation bath. In the first tank, the mass ratio of dimethylacetamide to water is 3:2, in the second tank it is 1:1, and in the third tank it is 2:3. The remaining tanks contain deionized water. The diaphragm passes through each tank and is extracted sequentially through three different concentrations of coagulation bath and deionized water.

[0033] Example 1

[0034] A method for preparing a meta-aramid coating slurry includes the following steps:

[0035] Step 1: Add 1% by mass of hydrogenated nitrile butadiene rubber to 87% by mass of dimethylacetamide and stir for 24 h until dissolved. Then, purge the reaction vessel with nitrogen and add the dissolved hydrogenated nitrile butadiene rubber solution to the nitrogen-protected reaction vessel. Purge the reaction vessel jacket with cold water and cool to 20 ℃. Then add m-phenylenediamine and stir for 20 min. Remove the cold water and purge with chilled water. Then cool to 0 ℃ and add isophthaloyl chloride. Stir for 20 min. The mass fraction of m-phenylenediamine and isophthaloyl chloride is 7% and the molar mass ratio is 1:1. Remove the chilled water and gradually heat and stir to 80 ℃. The heating process takes about 80 min. Add 5% by mass of calcium hydroxide and stir for 30 min to obtain the meta-aramid slurry of composite hydrogenated nitrile butadiene rubber.

[0036] Step 2: Add 30% by mass of ceramic powder to a 70% by mass of dimethylacetamide solution, stir for 25 min, and then grind it for 15 min using a pin mill at a speed of 500 r / min to obtain a ceramic powder solution.

[0037] Step 3: Add dimethyl carbonate solution to 50% by mass of meta-aramid slurry of composite hydrogenated nitrile butadiene rubber, stir for 30 min, then add 45% by mass of ceramic powder solution, stir for 30 min to obtain meta-aramid coating slurry;

[0038] The diaphragm was coated and extracted using the meta-aramid coating slurry prepared by the above method.

[0039] Example 2

[0040] A method for preparing a meta-aramid coating slurry includes the following steps:

[0041] Step 1: Add 3% by mass hydrogenated nitrile rubber to 80% by mass dimethylacetamide and stir for 30 h until dissolved. Then, purge the reaction vessel with nitrogen and add the dissolved hydrogenated nitrile rubber solution to the nitrogen-protected reaction vessel. Purge the reaction vessel jacket with cold water and cool to 15 ℃. Then add m-phenylenediamine and stir for 30 min. Remove the cold water and purge with chilled water. Then cool to 3 ℃ and add isophthaloyl chloride. Stir for 30 min. The mass fraction of m-phenylenediamine and isophthaloyl chloride is 10% and the molar mass ratio is 1:1. Remove the chilled water and gradually heat and stir to 80 ℃. The heating process takes about 80 min. Add 7% by mass calcium hydroxide and stir for 30 min.

[0042] Step 2: Add 40% by mass of ceramic powder to a 60% by mass of dimethylacetamide solution, stir for 25 min, and then grind for 20 min using a pin mill at a speed of 700 r / min to obtain a ceramic powder solution.

[0043] Step 3: Add dimethyl carbonate solution to 55% by mass of meta-aramid slurry of composite hydrogenated nitrile butadiene rubber, stir for 40 min, then add 10% by mass of ceramic powder solution, stir for 40 min to obtain meta-aramid coating slurry.

[0044] The diaphragm was coated and extracted using the above-mentioned meta-aramid coating slurry.

[0045] Example 3

[0046] A method for preparing a meta-aramid coating slurry includes the following steps:

[0047] Step 1: Add 5% by mass hydrogenated nitrile rubber to 73% by mass dimethylacetamide and stir for 36 h until dissolved. Then, purge the reaction vessel with nitrogen and add the dissolved hydrogenated nitrile rubber solution to the nitrogen-protected reaction vessel. Purge the reaction vessel jacket with cold water and cool to 10 °C. Then add m-phenylenediamine and stir for 40 min. Remove the cold water and purge with chilled water. Then cool to 5 °C and add isophthaloyl chloride. Stir for 40 min. The mass fraction of m-phenylenediamine and isophthaloyl chloride is 12% and the molar mass ratio is 1:1. Remove the chilled water and gradually heat and stir to 80 °C for about 80 min. Add 10% by mass calcium hydroxide and stir for 30 min.

[0048] Step 2: Add 45% ceramic powder to a 55% dimethylacetamide solution, stir for 25 min, and then grind for 30 min using a pin mill at a speed of 800 r / min to obtain a ceramic powder solution.

[0049] Step 3: Add dimethyl carbonate solution to the meta-aramid slurry with a mass fraction of 60% composite hydrogenated nitrile rubber, stir for 45 min, then add 15% of the solution from step 2, stir for 45 min, and obtain the meta-aramid coating slurry.

[0050] The diaphragm was coated and extracted using the above-mentioned meta-aramid coating slurry.

[0051] Comparative Example 1

[0052] Unlike Example 1, hydrogenated nitrile rubber is added after the synthesis of aramid in step 1. Step 1 is as follows:

[0053] Nitrogen gas was introduced into the reaction vessel for protection. Then, 73% by mass of dimethylacetamide was added to the nitrogen-protected reaction vessel. Cold water was circulated through the jacket of the reaction vessel to lower the temperature to 20℃~10℃. Then, m-phenylenediamine was added and stirred for 20~40 minutes. The cold water was removed, and chilled water was introduced. The temperature was then lowered to 0℃~5℃. Isophthalyl chloride was added and stirred for 20~40 minutes. The chilled water was removed, and the temperature was gradually increased and stirred to 80℃ over approximately 80 minutes. The mass fraction of m-phenylenediamine and isophthalyl chloride was 12%, and the molar mass ratio of m-phenylenediamine to phthalyl chloride was 1:1. Then, 10% by mass of calcium hydroxide was added and stirred for 30 minutes. Finally, hydrogenated nitrile rubber was added and stirred until dissolved.

[0054] The remaining steps are the same as in Example 1.

[0055] Figure 1 and Figure 2 The scanning electron microscope (SEM) images of Example 1 and Comparative Example 1 are shown below. Figure 1 As can be seen, the aramid mesh and hydrogenated nitrile rubber are tightly bonded with no obvious repulsion, and the pore size is relatively three-dimensional; from Figure 2 As can be seen, hydrogenated nitrile rubber and aramid exhibit severe delamination, with significant repulsion.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that the adhesive is PVDF, but the rest is the same as in Example 1.

[0058] Example 1

[0059] The basic properties of the diaphragms prepared in Examples 1-3 and Comparative Examples 1-2, such as thickness, air permeability, and shrinkage rate at 150°C for 1 hour, were tested. The specific data are shown in Table 1.

[0060] Table 1. Comparison of diaphragm-based data provided in Examples 1-3 and Comparative Examples 1-2

[0061]

[0062] The diaphragm has a porous structure and will shrink severely at high temperatures. One of the standards for measuring the temperature resistance of the diaphragm is to test the shrinkage rate of the diaphragm at high temperatures. As can be clearly seen from the test data in Table 1, the aramid and hydrogenated nitrile rubber are tightly bonded together, which gives the diaphragm higher temperature resistance.

[0063] Example 2

[0064] The adhesion strength between the separators prepared in Examples 1-3 and Comparative Examples 1-2 and the battery electrodes was tested. The method for testing the adhesion strength of the battery electrodes is as follows:

[0065] The electrode and separator were cut into shapes with a width of 12 mm and a length of 100 mm, then stacked together and tested using a battery electrode press. The test sample was prepared under the conditions of pressure of 0.8 MPa, temperature of 70℃ and time of 20 s. Then, the force required to tear the electrode and separator was tested using a tensile tester. The results are shown in Table 2.

[0066] Table 2 Comparison of diaphragm adhesion data provided in Examples 1-3 and Comparative Examples 1-2

[0067]

[0068] The data above shows that the method of combining hydrogenated nitrile rubber and aramid in this invention can generate a high electrode adhesion force in the diaphragm.

[0069] Example 3

[0070] The ionic conductivity of the membranes prepared in Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in Table 3.

[0071] Table 3 Ionic conductivity of the membrane

[0072]

[0073] Ionic conductivity mainly tests the rate at which ions shuttle through the separator. The detection of ionic conductivity can test the efficiency of the separator in enabling lithium ions to shuttle through the battery. As can be seen from the above test, after aramid and hydrogenated nitrile rubber are fully combined and coated onto the separator to form an internal network, lithium ions shuttle through the separator more smoothly.

[0074] Example of effect 4

[0075] The liquid absorption saturation rate of the membranes prepared in Examples 1-3 and Comparative Examples 1-2 was tested using the following methods:

[0076] Liquid absorption rate test method: The prepared coated diaphragm is cut into pieces 30 mm wide and 100 mm long, weighed and recorded as the mass before soaking, and then soaked in lithium hexafluorophosphate electrolyte for 30 min. After soaking, it is removed and weighed and recorded as the mass after soaking. The liquid absorption rate is calculated (liquid absorption rate = (mass after soaking - mass before soaking) / mass before soaking).

[0077] Liquid retention rate test method: The coated diaphragm is immersed in lithium hexafluorophosphate electrolyte for 30 min, removed and suspended for 30 min. Then, the excess electrolyte on the surface is gently absorbed with non-woven fabric and weighed to record the liquid retention diaphragm mass. The liquid retention rate is calculated as follows: (liquid retention rate = (liquid retention diaphragm mass - mass before immersion) / mass before immersion).

[0078] Table 4. Test of diaphragm saturation rate

[0079]

[0080] The data above shows that after aramid and hydrogenated nitrile rubber are fully combined and coated onto the diaphragm, it is more beneficial to improve the liquid absorption rate and saturation rate of the diaphragm.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a meta-aramid coating slurry, characterized by, Includes the following steps: Step 1: Dissolve hydrogenated nitrile rubber in dimethylacetamide to obtain a hydrogenated nitrile rubber solution. Under a protective gas, cool the solution to 10 ℃~20 ℃, add m-phenylenediamine while stirring, lower the temperature to 0 ℃~5 ℃ again, add isophthaloyl chloride and stir, heat the solution to 75~85 ℃ and stir for 20-40 min, add calcium hydroxide to obtain a meta-aramid slurry of composite hydrogenated nitrile rubber. Step 2: Stir and disperse the ceramic powder in an organic solvent, and then mill it to obtain a ceramic powder solution; Step 3: Under stirring, dimethyl carbonate solution and ceramic powder solution described in step 2 are added sequentially to the meta-aramid slurry of composite hydrogenated nitrile rubber prepared in step 1 to obtain meta-aramid coating slurry.

2. The method of making a meta-aramid coating slurry of claim 1, wherein, In step 1, the mass fraction of hydrogenated nitrile rubber is 1-5 parts, the mass fraction of dimethylacetamide is 73-87 parts, the mass fraction of m-phenylenediamine and isophthaloyl chloride is 7-12 parts, wherein the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:1, and the mass fraction of calcium hydroxide is 5-10 parts.

3. The method of making a meta-aramid coating slurry of claim 1, wherein, In step 1, the hydrogenated nitrile rubber is stirred and dissolved for 24-26 hours, and the heating rate is 0.9-1 °C / min.

4. The method of making a meta-aramid coating slurry of claim 1, wherein, In step 2, the ceramic powder is 30-45 parts by mass and the organic solvent is 55-70 parts by mass.

5. The method of making a meta-aramid coating slurry of claim 1, wherein, In step 2, the organic solvent is selected from one or both of dimethylacetamide and tripropylene glycol.

6. The method of making a meta-aramid coating slurry of claim 1, wherein, In step 3, the mass fraction of the meta-aramid slurry of the composite hydrogenated nitrile rubber is 50-60 parts, the mass fraction of the dimethyl carbonate solution is 5-15 parts, and the mass fraction of the ceramic powder solution is 25-45 parts.

7. A meta-aramid coating slurry prepared by the preparation method as described in claim 1.

8. A diaphragm obtained by coating with the meta-aramid coating slurry as described in claim 7, characterized in that, The coating of the diaphragm includes meta-aramid and hydrogenated nitrile rubber.

9. A method for preparing a diaphragm, characterized in that, Includes the following steps: Step 1: Prepare meta-aramid coating slurry according to the method for preparing meta-aramid coating slurry as described in claim 1; Step 2: Coat the meta-aramid coating slurry obtained in Step 1 onto the base film; Step 3: Extraction to obtain a diaphragm coated with meta-aramid slurry.

10. The application of the separator as described in claim 8 in a lithium-ion battery.

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