Inorganic slurry and its preparation method and application

Abstract

The present invention discloses an inorganic slurry and a preparation method and application thereof. The inorganic slurry comprises: a dispersant, a wetting agent, a ceramic powder, a thickener and a binder. The inorganic slurry of the present invention can better meet the requirements of tension and centrifugal force when a dot coating roller transfers the slurry during the dot coating process by selecting the binder and adjusting the ratio of the binder. The deformation is effectively controlled during the slurry transfer process. When the inorganic slurry is coated on a base film, the hemispherical droplets formed have a better wrapping effect and the shape of the coating point is closer to a circle.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators, and in particular relates to an inorganic slurry and a preparation method and application thereof. Background Art

[0002] With the rapid advancement of electronic products and the rapid expansion of new energy electric vehicles in the market, lithium batteries, as a key energy storage device with high energy density and long life, are attracting increasing attention from manufacturers and users. A core component of lithium batteries is the separator, which effectively separates the positive and negative electrodes, preventing short circuits and electrolyte immersion, thereby ensuring the safety and performance stability of lithium batteries. Compared to PP or PE-based films, coating films offer better high-temperature stability, chemical stability, and higher mechanical strength and toughness. Therefore, the lithium battery separator coating process is crucial to the performance and lifespan of lithium batteries.

[0003] The commonly used diaphragm coating processes at present include roller coating, spray coating, scraper coating and rotary spray coating. Due to process limitations, a single diaphragm coating process cannot meet the needs of all coating materials. Among them, roller coating can be applied to most coating materials due to its relatively simple process, stable coating effect and easy operation.

[0004] Taking inorganic coating fluids as an example, most are based on inorganic compounds such as alumina and boehmite, which contain large particles or impurities. Due to their large particles, high specific gravity, and high hardness, they are prone to scratches and coating leaks. While roller coating poses no major issues, spraying can easily clog the nozzle due to the large particles. Rotary spraying, due to its high specific gravity, can easily cause solid-liquid separation during the rotary spraying process. When the inorganic coating fluid is applied to 100% of the membrane surface, excessive coating thickness or high coating fluid density can affect the air permeability of the finished membrane, thereby hindering ion penetration.

[0005] Spot coating, a new contact-based partial coating method, eliminates the clogging and solid-liquid separation issues of spray coating, nor does it worry about missed coating or scratches caused by large particles in the coating solution. Furthermore, because spot coating systematically applies controlled coverage to the diaphragm, it eliminates concerns about air permeability caused by coating thickness and coating solution density. Furthermore, the finished product exhibits the same characteristics as roller coating in testing and use, further enhancing its advantages.

[0006] However, the principles of transfer slurry between spot coating and conventional roller coating are different. The main material of slurry currently used in spot coating is mostly PVDF. Because PVDF particles are lighter than ceramic particles in the same volume, the slurry has a lower specific gravity, and it has good adhesion. When applied to the spot coating process, it can overcome the centrifugal force of the plate roller, so that the slurry does not undergo large deformation during the transfer process. However, compared with ceramic slurry, PVDF has lower hardness, higher price, and is not as environmentally friendly as ceramic. Therefore, the development of ceramic spot coating slurry is also very important to meet different needs. However, conventional ceramic slurry (inorganic slurry) has no adhesion between powders due to its high specific gravity and cannot adapt to the spot coating process. Therefore, it is necessary to prepare an inorganic slurry that can meet the requirements of the spot coating process. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide an inorganic slurry.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned inorganic slurry.

[0009] Another object of the present invention is to provide an application of the above-mentioned inorganic slurry in spot coating.

[0010] The purpose of the present invention is achieved through the following technical solutions.

[0011] An inorganic slurry comprises: a dispersant, a wetting agent, a ceramic powder, a thickener and a binder. Calculated by mass, the ratio of the dispersant, the wetting agent, the ceramic powder, the thickener and the binder is (0.5-1.0): (2.0-2.5): (15-20): (15-18): (15-25).

[0012] The above technical solution further comprises: water, and the ratio of the ceramic powder to water is (15-20): (45-55) by mass.

[0013] In the above technical solution, the binder is one or a mixture of methyl methacrylate copolymer, acrylate copolymer and styrene-butyl methacrylate.

[0014] In the above technical solution, the dispersant is ammonium polyacrylate.

[0015] In the above technical solution, the ceramic powder is an inorganic substance with thermal stability and chemical inertness.

[0016] In the above technical solution, the ceramic powder is a metal oxide, hydroxide, nitride, hydrated oxide or inorganic polymer.

[0017] In the above technical solution, the metal oxide is aluminum oxide, silicon oxide, zirconium oxide or titanium oxide; the hydroxide is magnesium hydroxide; the nitride is aluminum nitride; the hydrated oxide is boehmite; and the inorganic polymer is nano-silicon.

[0018] In the above technical solution, the wetting agent is an inorganic wetting agent.

[0019] In the above technical solution, the inorganic wetting agent is sodium tripolyphosphate.

[0020] In the above technical solution, the thickener is hydroxymethyl cellulose.

[0021] In the above technical solution, the viscosity of the inorganic slurry is 100-200 cp.

[0022] A method for preparing an inorganic slurry comprises: mixing ceramic powder, water and a dispersant until uniform, sand-grinding to obtain a first solution, mixing the first solution, a thickener, a binder and a wetting agent, stirring until uniform, to obtain an inorganic slurry, wherein the ratio of the dispersant, wetting agent, ceramic powder, thickener, binder and water is (0.5-1.0): (2.0-2.5): (15-20): (15-18): (15-25): (45-55) by mass.

[0023] In the above technical solution, the method for uniformly mixing ceramic powder, water and dispersant is: stirring the ceramic powder, water and dispersant at a rotation speed of 1800-2200 r / min and a revolution speed of 30-50 r / min for 60-70 minutes.

[0024] In the above technical solution, the sanding time is 12 to 30 minutes.

[0025] Application of inorganic slurry in spot coating.

[0026] In the above technical solution, the inorganic slurry is coated on the base film by spot coating and then dried to obtain a battery separator.

[0027] In the above technical solution, the drying time is 1 to 3 minutes, and the drying temperature is 45 to 60°C.

[0028] In the above technical solution, the coating speed is 50 to 150 m / min.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The inorganic slurry of the present invention can better meet the requirements of tension and centrifugal force when the dot coating roller transfers the slurry during the dot coating process by selecting and adjusting the binder ratio. It effectively controls deformation during the slurry transfer process and can also make the hemispherical droplets formed when the inorganic slurry is applied to the base film have a better wrapping effect, and the shape of the coating point is closer to a circle;

[0031] 2. The inorganic slurry of the present invention is applied to the spot coating process to solve the problem that roller coating cannot achieve controllable coverage and spray coating cannot apply inorganic slurry, and can also improve the problem of high air permeability of roller coating inorganic slurry;

[0032] 3. The inorganic slurry of the present invention can be applied to the spot coating process to improve the appearance of the battery separator, effectively avoiding the defects of missing coating, scratches and large spots caused by the presence of large particles in the slurry;

[0033] 4. Spot coating is not a full-surface coating. Compared with roller coating, it can save slurry and reduce costs. Compared with roller coating, spot coating leaves much less slurry on the base film, making the water content of the diaphragm relatively low, reducing the amount of water and lithium reacting, reducing the gas generated, and reducing the risk of explosion due to high internal gas pressure of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a cross-sectional view of a battery separator obtained by spot coating;

[0035] Figure 2 This is a photo of the battery separator obtained by spot coating in Example 2;

[0036] Figure 3 This is a photograph of the battery separator obtained by roller coating in Example 2;

[0037] Figure 4 This is a photograph of the battery separator obtained by roller coating in Example 2;

[0038] Figure 5 Schematic diagram of the coverage measurement method;

[0039] Figure 6 This is the OM appearance of the battery separator in Example 5. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below with reference to specific embodiments.

[0041] The raw material information involved in the following examples is as follows:

[0042] Sodium tripolyphosphate: It is an amorphous water-soluble linear polyphosphate with the chemical formula Na5P3O 10, is an inorganic compound. It is a white powdery crystal with good fluidity, easily soluble in water, and its aqueous solution is alkaline.

[0043] Alumina: An inorganic substance with the chemical formula Al2O3, it possesses properties such as a high melting point, high thermal conductivity, and high corrosion resistance. It has a melting point of 2054°C and a boiling point of 2980°C. It ionizes at high temperatures and is an ionic crystal. It appears as a white, amorphous powder and is insoluble in water, but soluble in strong alkalis and acids.

[0044] Acrylate copolymers are a general term for polymers produced through the copolymerization of acrylic esters (primarily methyl, ethyl, butyl, and methyl methacrylate). Acrylates have active double bonds and readily self-polymerize and copolymerize. The comonomers can be one or more; they can be other acrylic compounds or other unsaturated compounds with double bonds (primarily styrene, acrylonitrile, vinyl acetate, vinyl chloride, etc.).

[0045] Friction powder loss: Take a battery separator with a size of 30*250mm, weigh it and record it as a (mg), place the battery separator in a powder loss rate tester, use the pressure measurement method, the test time is 30s, after the test is completed, weigh it and record it as b (mg), the friction powder loss c = (ab).

[0046] Air permeability value added: battery separator air permeability value - base film air permeability value.

[0047] Ionic conductivity: The test temperature is 25±5℃ and the relative humidity is 60%RH.

[0048] In the following examples, the base film has a thickness of 9 μm and a width of 1000 mm.

[0049] Example 1

[0050] A method for preparing an inorganic slurry comprises: mixing ceramic powder, pure water, and a dispersant; stirring the mixture in a planetary stirring device at a rotation speed of 2000 r / min and a revolution speed of 35 r / min for 60 minutes until the mixture is uniform; and sand milling the mixture for 15 minutes to obtain a first solution; mixing the first solution, a thickener, a binder, and a wetting agent; and stirring the mixture in a planetary stirring device at a rotation speed of 1500 r / min and a revolution speed of 20 r / min for 10 minutes until the mixture is uniform to obtain an inorganic slurry. The viscosity of the inorganic slurry is 100 cp; the ratio of the dispersant, the wetting agent, the ceramic powder, the thickener, the binder, and the pure water is 0.7:2.3:15:15:21:46 in parts by mass; the binder is an acrylate copolymer; the dispersant is polyacrylate ammonium salt; the ceramic powder is alumina; the wetting agent is sodium tripolyphosphate; and the thickener is hydroxymethyl cellulose.

[0051] Example 2

[0052] The inorganic slurry of Example 1 was applied to a single surface of a 3000 m long base film at a speed of 120 m / min. The inorganic slurry formed a coating on the base film, which was then dried at 50°C for 2 min to obtain a battery separator. The coating was performed by either spot coating or roller coating, with a coating thickness of 2 μm and an effective coating width of 800 mm. The spot coating coverage was controlled at 20±5%.

[0053] Before coating, two barrels (200 kg per barrel) of the inorganic slurry in Example 1 were prepared, one barrel each for roller coating and spot coating. After roller coating was completed, 55.6 kg of inorganic slurry remained, and after spot coating was completed, 171.2 kg of inorganic slurry remained.

[0054] Ten points were randomly selected on each of the spot-coated and roller-coated battery separators, and the thickness, air permeability, coating weight, adhesion, ionic conductivity, and frictional powder loss of the battery separators at each point were measured. The thickness increment was calculated based on the thickness of the battery separator. The thickness increment and coating weight are shown in Table 1. The average values ​​of the thickness, thickness increment, air permeability increment, coating weight, adhesion, ionic conductivity, and frictional powder loss of the battery separators at 10 points of the spot-coated / roller-coated battery separators are shown in Table 2.

[0055] Table 1

[0056]

[0057] As shown in Table 1, in terms of coating thickness and uniformity, spot coating is slightly better than roller coating, and in terms of coating amount, spot coating is much less than roller coating.

[0058] Table 2

[0059]

[0060]

[0061] As can be seen from Table 2, for the same coating thickness, the coating amount of spot coating is much smaller than that of roller coating, which saves a lot of inorganic slurry and thus reduces costs; and the battery separator obtained by spot coating has better air permeability, adhesion and friction powder loss than the battery separator obtained by roller coating.

[0062] Observe the appearance of the battery separator obtained by spot coating and the battery separator obtained by roller coating: it is found that there are two places where the battery separator obtained by roller coating has missed coating: one is that the bottom film is uneven (such as Figure 3 As shown), one is the large particles in the inorganic slurry (as Figure 4There was also one spot of material (caused by impurities in the coating liquid). The battery separator obtained by spot coating did not show such defects, indicating that spot coating has relatively low requirements for the coating base film (base film), and it can avoid large particles that may be present in the inorganic slurry without affecting the coating.

[0063] Example 3

[0064] The inorganic slurry of Example 1 was applied to a single surface of a 3000 m long base film at a speed of 120 m / min. The inorganic slurry formed a coating on the base film, which was then dried at 50°C for 2 min to obtain a battery separator. The coating was performed by either spot coating or roller coating, with a coating thickness of 4 μm and an effective coating width of 800 mm. The spot coating coverage was controlled at 20±5%.

[0065] 10 points were randomly selected on the battery separator obtained by spot coating and the battery separator obtained by roller coating, and the thickness and permeability of the battery separator at each point were measured. The thickness value-added was obtained by calculating the thickness of the battery separator, and the permeability value-added was obtained by calculating the permeability value of the battery separator. The thickness value-added and the permeability value-added are shown in Table 3.

[0066] Table 3

[0067]

[0068] It can be seen from Table 3 that when the thickness increase is about 4 μm, the air permeability increase of the battery separator coated by point coating is much smaller than that of roller coating, which is more conducive to ion penetration.

[0069] The present invention adopts the method of spot coating to apply inorganic slurry, forming a cylindrical inorganic support (such as Figure 1 ), the material of the contact electrode is a ceramic powder with high hardness, and the base film in the area not coated with inorganic slurry has no contact with the electrode, so that it can effectively prevent the lithium dendrites formed during long-term battery cycling from piercing the diaphragm and causing a short circuit (the same effect as ceramic roller coating). Because there is a large area of ​​gap between the base film and the electrode, the liquid retention and wettability of the battery diaphragm are greatly increased, thereby extending the cycle life of the lithium battery.

[0070] The inorganic slurry of the present invention can meet the needs of transferring the slurry to the surface of the base film by the point coating process, replacing the roller coating (roller coating is applied to the surface of the base film), and forming a Figure 2 The dot shape is neatly arranged in a matrix, and the dot area is controllable, that is, the coverage of the inorganic slurry on the base film is controllable. The coverage is measured as follows: Figure 5As shown, under a low magnification microscope (e.g., 50X), the area of ​​the rectangle in the microscope field of view, a1, and the areas of the nine coating points in the rectangle are measured using the "area mode." The sum of the areas of the nine coating points is a2, and the coverage is a2 / a1. The inorganic slurry combined with the spot coating process of the present invention solves the problem that inorganic slurry cannot be applied due to the equipment and coating method of spray coating, and solves the problem that roller coating cannot achieve partial coating.

[0071] Example 4 (for comparison)

[0072] A conventional ceramic slurry uses alumina as a main material. The preparation process is as follows: ceramic powder, pure water and a dispersant are mixed, and the mixture is stirred in a planetary stirring device at a rotation speed of 2000 r / min and a revolution speed of 40 r / min for 60 minutes until uniformity is achieved, and the mixture is sand-milled for 15 minutes to obtain a first solution. The first solution, a thickener and a binder are mixed, and the mixture is stirred in a planetary stirring device at a rotation speed of 1200 r / min and a revolution speed of 20 r / min for 10 minutes until uniformity is achieved to obtain an inorganic slurry. The viscosity of the inorganic slurry is 60 cp. The ratio of the dispersant, ceramic powder, thickener, binder and pure water is 3.0:17:13:20:47 in parts by mass. The binder is methyl methacrylate copolymer, the dispersant is polyacrylate ammonium salt, the ceramic powder is alumina, and the thickener is hydroxymethyl cellulose.

[0073] The conventional ceramic slurry from Example 4 was applied to a 3000 m long base film on one side at a speed of 120 m / min. The coating method was spot-coated and dried at 50°C for 2 minutes. The coating thickness was 2 μm, and the spot coating coverage was controlled at 20 ± 5%. During the coating process, the anilox roller was properly loaded with liquid, but the conventional ceramic slurry could not be properly transferred to the plate roller, and therefore could not be applied to the base film.

[0074] Example 5

[0075] A method for preparing an inorganic slurry is basically the same as the “method for preparing an inorganic slurry” in Example 1, with the only difference being that “the ratio of dispersant, wetting agent, ceramic powder, thickener, binder and pure water is 0.7:2.3:15:15:21:46 in parts by mass” is replaced by “the ratio of dispersant, wetting agent, ceramic powder, thickener, binder and pure water is 0.7:2.3:19:15:14:49 in parts by mass”.

[0076] The inorganic slurry in Example 5 was coated on one side of a 3000 m long base film at a speed of 120 m / min. The coating method was point coating. The inorganic slurry formed a coating on the base film and dried at 50°C for 2 minutes to obtain a battery separator. The coating thickness was 2 μm and the coverage of the point coating was controlled at 20±5%. The battery separator was observed under a microscope. The morphology was as follows: Figure 6 As shown, the coating point is irregular and does not meet the requirements of the diaphragm.

[0077] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A battery separator, characterized in that: The invention comprises a base film and coating points covering the base film, wherein each coating point is formed by dot coating of an inorganic slurry, wherein the inorganic slurry comprises: a dispersant, a wetting agent, a ceramic powder, a thickener and a binder, and the ratio of the dispersant, the wetting agent, the ceramic powder, the thickener and the binder is (0.5-1.0): (2.0-2.5): (15-20): (15-18): (15-25) by mass, wherein the wetting agent is sodium tripolyphosphate, the dispersant is ammonium polyacrylate, and the binder is a mixture of one or more of methyl methacrylate copolymer, acrylate copolymer and styrene-butyl methacrylate.

2. The battery separator according to claim 1, characterized in that The inorganic slurry also includes water. The ratio of the ceramic powder to water is (15-20): (45-55) by mass.

3. The battery separator according to claim 1, characterized in that The ceramic powder is metal oxide, hydroxide, nitride, hydrated oxide or inorganic polymer.

4. The battery separator according to claim 1, characterized in that The thickener is hydroxymethyl cellulose.

5. The battery separator according to claim 1, characterized in that The preparation method of the inorganic slurry includes: mixing ceramic powder, water and a dispersant until uniform, sand grinding to obtain a first solution, mixing the first solution, a thickener, a binder and a wetting agent, stirring until uniform, to obtain an inorganic slurry, wherein the ratio of the dispersant, wetting agent, ceramic powder, thickener, binder and water is (0.5~1.0): (2.0~2.5): (15~20): (15~18): (15~25): (45~55) by mass.

6. The method for preparing a battery separator according to claim 1, wherein: The inorganic slurry is coated on the base film by spot coating and dried to obtain a battery separator.

Images