A kind of viscous ceramic diaphragm and its preparation process

Abstract

The invention discloses a viscous ceramic diaphragm and a preparation process thereof, belonging to the technical field of lithium-ion batteries. The diaphragm comprises a base film and a ceramic coating, wherein the ceramic coating is obtained by coating a ceramic slurry on the base film and drying the ceramic slurry; the ceramic slurry comprises the following raw materials in parts by weight: 10-70 parts of inorganic ceramic particles, 0.5-20 parts of modified sodium carboxymethyl cellulose, 1-10 parts of a plasticizer, 0.5-2 parts of a dispersant, 0.5-1 parts of dopamine, and 10-90 parts of deionized water; boron trichloride, a solvent, dichloromethylsilane, and 1,3-bistrifluoropropyl-1,1,3,3-tetramethyldisilazane are reacted to obtain a mixed intermediate, which is then blended and modified with high-viscosity sodium carboxymethyl cellulose to obtain the modified sodium carboxymethyl cellulose. By introducing the modified sodium carboxymethyl cellulose into the ceramic coating, the ceramic coating and the base film have strong bonding at high temperatures and the ceramic diaphragm has good thermal stability, thereby meeting the requirements of lithium battery technology for the diaphragm.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a viscous ceramic diaphragm and a preparation process thereof. Background Art

[0002] Lithium-ion batteries are widely used in new energy vehicles, military applications, and other fields. As an essential component of lithium batteries, separators are subject to increasing safety requirements and expectations. As core components of electric vehicles, the majority of commercially available separators are polyolefin separators. Their primary function is to separate the positive and negative electrodes to prevent short circuits while providing a conductive path for lithium ions. However, due to their poor mechanical properties, they can also cause lithium dendrite penetration. Furthermore, separators experience severe thermal contraction in high-temperature environments, which can easily lead to battery short circuits and serious accidents.

[0003] In order to improve the performance of the diaphragm, many diaphragms have appeared in recent years that coat ceramic coatings containing inorganic fillers on polyolefins. However, due to insufficient adhesion between the ceramic coating and the base film at high temperatures, the battery performance is affected. Summary of the Invention

[0004] The object of the present invention is to provide a viscous ceramic diaphragm and a preparation process thereof to solve the existing problem of insufficient adhesion between the ceramic coating and the base film at high temperatures.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A viscous ceramic diaphragm comprises a base film and a ceramic coating, wherein the ceramic coating is obtained by coating a ceramic slurry on one or both sides of the base film and drying the ceramic slurry;

[0007] Preferably, the ceramic slurry is made of the following raw materials in parts by mass: 10-70 parts of inorganic ceramic particles, 0.5-20 parts of modified sodium carboxymethyl cellulose, 1-10 parts of plasticizer, 0.5-2 parts of dispersant, 0.5-1 part of dopamine, and 10-90 parts of deionized water.

[0008] Preferably, the inorganic ceramic particles include one or more of aluminum oxide, boehmite, silicon dioxide, and titanium dioxide.

[0009] Preferably, the plasticizer is polyethylene glycol.

[0010] Preferably, the dispersant is selected from one or more of N,N-dimethylaminopropylamine, polyethylene polyamine, and octadecylaminopropylamine.

[0011] Preferably, modified sodium carboxymethyl cellulose is prepared by the following steps:

[0012] Step 1. Under nitrogen, boron trichloride, solvent, and dichloromethylsilane are added to a flask, and 1,3-bis(trifluoropropyl)-1,1,3,3-tetramethyldisilazane is added dropwise. After the addition is complete, the mixture is stirred, evaporated, heated for polycondensation, and cooled to 25-35° C. to obtain a mixed intermediate.

[0013] Step 2: dissolving the high-viscosity sodium carboxymethyl cellulose and the mixed intermediate in deionized water, heating in a water bath, and drying to obtain modified sodium carboxymethyl cellulose.

[0014] Preferably, in step 1, the amount ratio of boron trichloride, solvent, dichloromethylsilane and 1,3-bistrifluoropropyl-1,1,3,3-tetramethyldisilazane is 4.6-5.8 g:10 mL:3-3.6 g:100-120 g.

[0015] Preferably, the solvent in step 1 comprises one or more of n-hexane, diethyl ether and benzene.

[0016] Preferably, in step 1, the stirring temperature is minus 20° C. to minus 10° C., and the stirring time is 30 to 90 minutes.

[0017] Preferably, the temperature of the heating polycondensation in step 1 is 250-350° C., and the time is 1-2 hours.

[0018] Preferably, in step 2, the mass ratio of high viscosity sodium carboxymethyl cellulose to the mixed intermediate is 1-1.4:1.

[0019] Preferably, in step 2, the water bath heating temperature is 80-85° C., and the water bath heating time is 3-6 h.

[0020] Preferably, high viscosity sodium carboxymethyl cellulose is prepared by the following steps:

[0021] The cotton pulp raw material is crushed by a plant fiber crusher, passed through 100-800 mesh, and put into isopropyl alcohol under a nitrogen atmosphere for stirring and mixing. A 25wt% sodium hydroxide solution is added for dehydration reaction, and then sodium monochloroacetate is added for substitution reaction. The raw material is cooled, the pH is adjusted to 6-8, washed, filtered, and vacuum dried at 60-95°C for 24-36 hours to obtain high-viscosity sodium carboxymethyl cellulose.

[0022] Preferably, the mass ratio of sodium hydroxide, cotton pulp, isopropyl alcohol and sodium monochloroacetate is 0.85-0.95:1:24-26:1.2-1.4; the dehydration reaction temperature is 32-38° C., and the reaction time is 1.5-2 h; the substitution reaction temperature is 50-60° C., and the reaction time is 2-3 h.

[0023] A process for preparing a viscous ceramic diaphragm comprises the following steps:

[0024] (1) Inorganic ceramic particles, modified sodium carboxymethyl cellulose, a plasticizer, a dispersant, and dopamine are sequentially added to deionized water, mixed, and stirred to obtain a ceramic slurry;

[0025] (2) The obtained ceramic slurry is coated on one side or both sides of the base film with a coating thickness of 2-5 μm, and dried to obtain a sticky ceramic diaphragm.

[0026] Preferably, the stirring speed is 300-500 r / min, and the stirring time is 2-6 h.

[0027] Preferably, the porosity of the base film is 40-65%, and the thickness of the base film is 3-20 μm.

[0028] Preferably, the coating method includes any one of gravure roller coating, wire rod coating, dip coating, and spray coating.

[0029] Preferably, the coating speed is 60-120 m / min, the drying temperature is 40-80° C., and the drying time is 6-18 h.

[0030] Beneficial effects of the present invention:

[0031] 1. The present invention provides a viscous ceramic diaphragm and its preparation process. Inorganic ceramic particles, modified sodium carboxymethyl cellulose, a plasticizer, a dispersant, dopamine, and deionized water are sequentially added to deionized water, mixed, and stirred to obtain a ceramic slurry. The ceramic slurry is then coated on a base film and dried to obtain a viscous ceramic diaphragm. The ceramic coating exhibits strong adhesion to the base film at high temperatures and good thermal stability, meeting the requirements of lithium battery process for diaphragms.

[0032] 2. The high-viscosity sodium carboxycellulose provided by the present invention uses cotton pulp as a raw material, reacts with a sodium hydroxide solution in an isopropyl alcohol solvent, and the hydroxyl groups in the raw material are replaced and dehydrated, and then a bimolecular nucleophilic substitution reaction occurs with sodium monochloroacetate. The obtained sodium carboxycellulose has high viscosity and high mechanical strength.

[0033] 3. In the modified sodium carboxycellulose provided by the present invention, boron trichloride, solvent, dichloromethylsilane, and 1,3-bistrifluoropropyl-1,1,3,3-tetramethyldisilazane are reacted, and a six-membered ring connected by boron-nitrogen bonds is formed by heating and polycondensation. Then, the nitrogen-hydrogen bonds and silicon-hydrogen bonds undergo dehydrogenation reactions to form a polymer unit with a trimethylsilyl group as the end group and a high-viscosity sodium carboxymethylcellulose blend modification; the skeleton structure containing silicon, nitrogen, and boron elements can improve the mechanical strength and thermal stability of the ceramic coating layer. At the same time, the product is accompanied by fluorine silicon groups and has hydrophobic properties, which helps to reduce the retention of water on the surface of the diaphragm. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] Example 1

[0036] This embodiment provides a high-viscosity sodium carboxymethyl cellulose, which is prepared by the following steps:

[0037] 20 g of cotton pulp raw material was crushed with a plant fiber crusher and passed through 100 mesh. Under a nitrogen atmosphere, the mixture was added into 480 g of isopropyl alcohol and stirred and mixed. 72 g of 25 wt% sodium hydroxide solution was added to cause a dehydration reaction at 32° C. for 1.5 h. 24 g of sodium monochloroacetate was then added to cause a substitution reaction at 50° C. for 2 h. The mixture was cooled, the pH was adjusted to 6, the mixture was washed, filtered, and vacuum dried at 60° C. for 24 h to obtain high-viscosity sodium carboxymethyl cellulose.

[0038] Example 2

[0039] This embodiment provides a high-viscosity sodium carboxymethyl cellulose, which is prepared by the following steps:

[0040] 20 g of cotton pulp raw material was crushed with a plant fiber crusher and passed through 800 mesh. The raw material was added into 520 g of isopropyl alcohol under a nitrogen atmosphere and stirred and mixed. 76 g of 25 wt% sodium hydroxide solution was added to cause a dehydration reaction at 38°C for 2 h. 28 g of sodium monochloroacetate was then added to cause a substitution reaction at 60°C for 3 h. The reaction was cooled, the pH was adjusted to 8, the mixture was washed, filtered, and vacuum dried at 95°C for 36 h to obtain high-viscosity sodium carboxymethyl cellulose.

[0041] Comparative Example 1

[0042] This comparative example provides a sodium carboxymethyl cellulose, which is prepared by the following steps:

[0043] On the basis of Example 2, the isopropyl alcohol in Example 2 was replaced by ethanol, and the remaining raw materials and preparation method were the same as in Example 2.

[0044] Example 3

[0045] This embodiment provides a modified sodium carboxymethyl cellulose, which is prepared by the following steps:

[0046] Step 1. Under nitrogen, 2.3 g of boron trichloride, 5 mL of n-hexane, and 1.5 g of dichloromethylsilane were added to a flask, and 50 g of 1,3-bis(trifluoropropyl)-1,1,3,3-tetramethyldisilazane was added dropwise. After the addition was complete, the mixture was stirred at a temperature of -20°C for 30-90 min, evaporated, and heated for polycondensation at a temperature of 250°C for 1 h, and cooled to 25-35°C to obtain a mixed intermediate.

[0047] Step 2: Dissolve 10 g of high-viscosity sodium carboxymethyl cellulose from Example 1 and 10 g of the mixed intermediate in 50 mL of deionized water, heat the mixture in a water bath at 80° C. for 3 h, and dry the mixture to obtain modified sodium carboxymethyl cellulose.

[0048] Example 4

[0049] This embodiment provides a modified sodium carboxymethyl cellulose, which is prepared by the following steps:

[0050] Step 1. Under nitrogen, 2.9 g of boron trichloride, 5 mL of n-hexane, and 1.8 g of dichloromethylsilane were added to a flask, and 60 g of 1,3-bis(trifluoropropyl)-1,1,3,3-tetramethyldisilazane was added dropwise. After the addition was complete, the mixture was stirred at a temperature of -10°C for 2 h, evaporated, and heated for polycondensation at a temperature of 350°C for 2 h, and cooled to 35°C to obtain a mixed intermediate.

[0051] Step 2: Dissolve 14 g of high-viscosity sodium carboxymethyl cellulose from Example 2 and 10 g of the mixed intermediate in 50 mL of deionized water, heat the mixture in a water bath at 85° C. for 6 h, and dry the mixture to obtain modified sodium carboxymethyl cellulose.

[0052] Comparative Example 2

[0053] This comparative example provides a modified sodium carboxymethyl cellulose, which is prepared by the following steps:

[0054] Step 1. Under nitrogen, 2.9 g of boron trichloride, 5 mL of n-hexane, and 1.8 g of dichloromethylsilane were added to a flask, and 60 g of 1,3-bis(trifluoropropyl)-1,1,3,3-tetramethyldisilazane was added dropwise. After the addition was complete, the mixture was stirred at a temperature of -10°C for 2 h, evaporated, and heated for polycondensation at a temperature of 350°C for 2 h, and cooled to 35°C to obtain a mixed intermediate.

[0055] Step 2: Dissolve 14 g of sodium carboxymethyl cellulose from Comparative Example 1 and 10 g of the mixed intermediate in 50 mL of deionized water, heat the mixture in a water bath at 85° C. for 6 h, and dry the mixture to obtain modified sodium carboxymethyl cellulose.

[0056] Example 5

[0057] This embodiment provides a process for preparing a viscous ceramic diaphragm, comprising the following steps:

[0058] (1) 20 g of silicon dioxide, 1 g of modified sodium carboxymethyl cellulose prepared in Example 4, 2 g of polyethylene glycol, 1 g of N,N-dimethylaminopropylamine, and 0.2 g of dopamine were sequentially added to 20 g of deionized water, stirred at a speed of 300 r / min for 2 h to obtain a ceramic slurry;

[0059] (2) The obtained ceramic slurry was coated on one side of a polyethylene microporous membrane with a porosity of 40% by gravure roller coating. The base membrane thickness was 3 μm, the coating speed was 60 m / min, the coating thickness was 2 μm, the drying temperature was 40°C, and the drying time was 6 h to obtain a sticky ceramic diaphragm.

[0060] Example 6

[0061] This embodiment provides a process for preparing a viscous ceramic diaphragm, comprising the following steps:

[0062] (1) 140 g of silicon dioxide, 40 g of modified sodium carboxymethyl cellulose prepared in Example 3, 20 g of polyethylene glycol, 4 g of N,N-dimethylaminopropylamine, and 2 g of dopamine were sequentially added to 180 g of deionized water and stirred at a speed of 500 r / min for 6 h to obtain a ceramic slurry;

[0063] (2) The obtained ceramic slurry was coated on one side of a polyethylene microporous membrane with a porosity of 65% by gravure roller coating. The base membrane thickness was 20 μm, the coating speed was 120 m / min, the coating thickness was 5 μm, the drying temperature was 80°C, and the drying time was 18 h to obtain a sticky ceramic diaphragm.

[0064] Example 7

[0065] This embodiment provides a process for preparing a viscous ceramic diaphragm, comprising the following steps:

[0066] (1) 40 g of silicon dioxide, 10 g of modified sodium carboxymethyl cellulose prepared in Example 4, 6 g of polyethylene glycol, 2 g of N,N-dimethylaminopropylamine, and 0.8 g of dopamine were sequentially added to 120 g of deionized water and stirred at a speed of 400 r / min for 5 h to obtain a ceramic slurry;

[0067] (2) The obtained ceramic slurry was coated on one side of a polyethylene microporous membrane with a porosity of 55% by gravure roller coating. The base membrane thickness was 13 μm, the coating speed was 80 m / min, the coating thickness was 4 μm, the drying temperature was 60°C, and the drying time was 16 h to obtain a sticky ceramic diaphragm.

[0068] Comparative Example 3

[0069] This comparative example provides a preparation process for a viscous ceramic diaphragm, comprising the following steps:

[0070] On the basis of Example 7, the modified sodium carboxymethyl cellulose in Example 7 was replaced by the high-viscosity sodium carboxymethyl cellulose in Example 2, and the remaining raw materials and preparation method were the same as in Example 7.

[0071] Comparative Example 4

[0072] This comparative example provides a preparation process for a viscous ceramic diaphragm, comprising the following steps:

[0073] On the basis of Example 7, the “modified sodium carboxymethyl cellulose of Example 4” in Example 7 was replaced with “modified sodium carboxymethyl cellulose of Comparative Example 2”.

[0074] The performance of the viscous ceramic diaphragms obtained by the preparation processes of the viscous ceramic diaphragms of Examples 5 to 7 and Comparative Examples 3 to 4 was tested.

[0075] 150°C shrinkage: A 100mm×100mm sample, with the long direction being the MD direction, is placed in an oven at 150°C for 30 minutes and then taken out. The sample length is L, and the thermal shrinkage rate = (100-L)%.

[0076] Puncture strength: Puncture strength is measured on sticky ceramic diaphragm samples according to GBT36363 / 2018 standard.

[0077] Moisture content: In an environment with a dew point less than -40°C, take 1.2g of composite membrane sample, bake at 120°C for 5 minutes, and test the moisture content in the composite membrane using the Karl Fischer method.

[0078] Peel strength: The ceramic diaphragm was cut into 10cm×10cm squares, clamped with glass plates, and tested using the 150° peel strength test method.

[0079] The results are shown in Table 1:

[0080] Table 1

[0081] project Example 5 Example 6 Example 7 Comparative Example 3 Comparative Example 4 150℃ shrinkage MD (%) 1.42 1.24 1.68 3.44 3.46 Moisture content (ppm) 476 524 506 568 513 Peel strength (N / m) 224 238 192 156 96 Puncture strength (gf) 783 724 796 632 612

[0082] As can be seen from Table 1, compared with Comparative Examples 3-4, the 150°C shrinkage MD in Examples 5-7 is maintained below 2%, and the modified sodium carboxymethyl cellulose has better stability at high temperatures; the peel strength in the examples is significantly higher than that in the comparative examples, indicating that the high-viscosity sodium carboxymethyl cellulose plays a promoting role at high temperatures after modification.

[0083] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0084] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A viscous ceramic diaphragm, characterized in that: It includes a base film and a ceramic coating, wherein the ceramic coating is obtained by coating a ceramic slurry on one or both sides of the base film and drying the ceramic slurry; The ceramic slurry is made of the following raw materials in parts by mass: 10-70 parts of inorganic ceramic particles, 0.5-20 parts of modified sodium carboxymethyl cellulose, 1-10 parts of plasticizer, 0.5-2 parts of dispersant, 0.5-1 parts of dopamine, and 10-90 parts of deionized water; Modified sodium carboxymethyl cellulose is prepared by the following steps: Step 1. Under nitrogen, boron trichloride, solvent, and dichloromethylsilane are added to a flask, and 1,3-bis(trifluoropropyl)-1,1,3,3-tetramethyldisilazane is added dropwise. After the addition is complete, the mixture is stirred at -20--10°C for 30-90 minutes, evaporated, and then heated for polycondensation at a temperature of 250-350°C for 1-2 hours. The mixture is cooled to obtain a mixed intermediate. Step 2: dissolving the high-viscosity sodium carboxymethyl cellulose and the mixed intermediate in deionized water, heating in a water bath, and drying to obtain modified sodium carboxymethyl cellulose; High viscosity sodium carboxymethyl cellulose is prepared by the following steps: The cotton pulp raw material is crushed by a plant fiber crusher, passed through 100-800 mesh, and added into isopropyl alcohol under a nitrogen atmosphere for stirring and mixing. A 25wt% sodium hydroxide solution is first added for dehydration reaction, and then sodium monochloroacetate is added for substitution reaction. The mixture is cooled, the pH is adjusted to 6-8, washed, filtered, and dried to obtain high-viscosity sodium carboxymethyl cellulose.

2. The viscous ceramic diaphragm according to claim 1, characterized in that: The inorganic ceramic particles include one or more of aluminum oxide, boehmite, silicon dioxide, and titanium dioxide.

3. The viscous ceramic diaphragm according to claim 1, characterized in that: The plasticizer is polyethylene glycol.

4. The viscous ceramic diaphragm according to claim 1, characterized in that: The dispersant is selected from one or more of N,N-dimethylaminopropylamine, polyethylene polyamine, and octadecylaminopropylamine.

5. The viscous ceramic diaphragm according to claim 1, characterized in that: In the step 1, the amount ratio of boron trichloride, solvent, dichloromethylsilane and 1,3-bistrifluoropropyl-1,1,3,3-tetramethyldisilazane is 4.6-5.8 g:10 mL:3-3.6 g:100-120 g.

6. The viscous ceramic diaphragm according to claim 1, characterized in that: In the step 2, the mass ratio of high viscosity sodium carboxymethyl cellulose to the mixed product is 1-1.4:

1.

7. The viscous ceramic diaphragm according to claim 1, characterized in that: The mass ratio of the sodium hydroxide, cotton pulp, isopropyl alcohol and sodium monochloroacetate is 0.85-0.95:1:24-26:1.2-1.4; the dehydration reaction temperature is 32-38° C., and the reaction time is 1.5-2 hours; the substitution reaction temperature is 50-60° C., and the reaction time is 2-3 hours.

8. The process for preparing a viscous ceramic diaphragm according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Inorganic ceramic particles, modified sodium carboxymethyl cellulose, plasticizer, dispersant, and dopamine are sequentially added to deionized water and mixed at a stirring speed of 300-500 r / min for 2-6 h to obtain a ceramic slurry; (2) The obtained ceramic slurry is coated on one side or both sides of the base film with a coating thickness of 2-5 μm, and dried to obtain a sticky ceramic diaphragm.