Coating slurry, ceramic coating diaphragm and preparation method thereof

Abstract

The present invention provides a coating slurry, a ceramic coated diaphragm, and a preparation method thereof. The coating slurry comprises ceramic powder, additives, and water; the additives include an adhesive, a thickener, a water reducer, and a wetting agent; and the coating slurry has a solids content of 50% to 62%. By adding a water reducer and controlling the ratio of the thickener and water reducer within a certain range, the coating slurry solids content is increased. Furthermore, the coating slurry can be completely dried under high-speed coating without increasing the oven temperature of the coating machine. The resulting ceramic coated diaphragm has a moisture content of less than 600 ppm and a peel strength of more than 100 N / mm.

Description

Technical Field

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

[0002] The common coating production process for lithium-ion battery ceramic separators typically involves preparing a slurry: ceramic powder and a water-based adhesive are mixed in a specific ratio to create a water-based ceramic slurry. This slurry is then transferred to a polyolefin-based base film through a refined coating process and cured. However, traditional ceramic slurries cannot be applied at high speeds without increasing drying temperatures and wind frequency. This results in low separator moisture content and peel strength, resulting in low product yields and hindering the widespread application of ceramic separators in lithium-ion batteries. Summary of the Invention

[0003] The object of the present invention is to provide a coating slurry, a ceramic coating diaphragm and a preparation method thereof. By adding a water reducer and increasing the solid content of the coating slurry, the coating slurry can be completely dried under high-speed coating without increasing the oven temperature of the coater, thereby ensuring qualified product performance.

[0004] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a coating slurry, the coating slurry comprising ceramic powder, an additive and water;

[0006] The auxiliary agents include adhesives, thickeners, water reducers and wetting agents;

[0007] The solid content of the coating slurry is 50%-62%, for example, it can be 50%, 52%, 54%, 56%, 58%, 60% or 62%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0008] The coating slurry of the present invention utilizes the characteristics of the water reducer to reduce the amount of water used. The water reducer and the thickener are used in combination to increase the solid content of the slurry while ensuring the stability of the slurry. The drying temperature of the coating slurry under high-speed coating is also reduced, saving energy consumption.

[0009] The solid content of the coating slurry of the present invention is the mass fraction of the powder in the entire slurry system, and the powder mainly comprises ceramic powder and adhesive.

[0010] In the present invention, when the solid content of the coating slurry is lower than 50%, the water content of the coating slurry is high and the peeling strength is low. When the solid content of the coating slurry is higher than 62%, the slurry feeding system is easily blocked and lines begin to appear on the roller surface.

[0011] As a preferred technical solution of the present invention, the mass of the ceramic powder is 30%-60% of the total mass of the coating slurry, for example, it can be 30%, 35%, 40%, 45%, 50%, 55% or 60%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0012] Preferably, the ceramic powder includes any one or a combination of at least two of aluminum oxide, boehmite, silicon oxide, titanium oxide, calcium carbonate, barium sulfate or magnesium oxide. Typical but non-limiting examples of the combination include: a combination of aluminum oxide and boehmite, a combination of silicon oxide and titanium oxide, or a combination of calcium carbonate and barium sulfate.

[0013] Preferably, the specific surface area of ​​the ceramic powder is 2-5m 2 , for example it can be 2m 2 , 2.5m 2 , 3m 2 , 3.5m 2 , 4m 2 , 4.5m 2 or 5m 2 The present invention is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0014] In the present invention, when the specific surface area of ​​the ceramic powder is less than 2m 2 When the particle size of the coating slurry is too large and the membrane surface particles are too many, the micro-concave roller is prone to wear during long-term continuous production, resulting in a high thickness of the coated diaphragm and a low surface density; when the specific surface area of ​​the ceramic powder is higher than 5m 2 When the coating slurry is not coated, it will agglomerate, the slurry will easily settle, the shelf life will be short, the feeding system will be easily clogged during the coating process, and the surface density of the coated diaphragm will be low.

[0015] Preferably, the mass of the water is 30%-50% of the total mass of the coating slurry, for example, it can be 30%, 34%, 38%, 40%, 44%, 48% or 50%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] As a preferred technical solution of the present invention, the mass of the water-reducing agent is 0.2%-2% of the total mass of the coating slurry, for example, it can be 0.2%, 0.5%, 0.7%, 1%, 1.4%, 1.8% or 2%, etc., but is not limited to the values ​​listed above. Other values ​​not listed within the numerical range are also applicable. It should be understood that the proportion of the water-reducing agent in the total mass of the coating slurry mentioned in the present invention refers to the mass proportion of the water-reducing agent solution or emulsion in the entire slurry system.

[0017] Preferably, the water reducer comprises any one of a melamine-based water reducer, a sulfamate-based water reducer or a polycarboxylate-based water reducer, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of a melamine-based water reducer and a sulfamate-based water reducer, a combination of a sulfamate-based water reducer and a polycarboxylate-based water reducer, or a combination of a melamine-based water reducer, a sulfamate-based water reducer and a polycarboxylate-based water reducer.

[0018] As a preferred technical solution of the present invention, the mass ratio of the thickener and the water reducer is (2-5):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. The mass of the thickener is determined according to the mass of the water reducer and the ratio of the water reducer to the thickener, for example, it can be 3%, 4%, 5%, 6%, 7% or 8%, etc., but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. It can be understood that the proportion of the thickener in the total mass of the coating slurry mentioned in the present invention refers to the mass proportion of the thickener solution or emulsion in the entire slurry system.

[0019] The present invention prevents the coating slurry from agglomerating and improves the stability of the coating slurry by controlling the water reducer and the thickener to be used in combination within a certain ratio.

[0020] Preferably, the thickener comprises any one of hydroxypropyl methylcellulose solution, sodium carboxymethylcellulose solution, methylcellulose solution or layered silicate solution, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of hydroxypropyl methylcellulose solution and sodium carboxymethylcellulose solution, a combination of methylcellulose solution and sodium carboxymethylcellulose solution, or a combination of methylcellulose solution and layered silicate solution.

[0021] In the present invention, the thickener is an aqueous solution or emulsion with a mass fraction of 8%-12%.

[0022] As a preferred technical solution of the present invention, the mass of the adhesive is 4%-6% of the total mass of the coating slurry, for example, it can be 4%, 4.4%, 4.8%, 5%, 5.4%, 5.8% or 6%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the adhesive is a water-based adhesive, and the adhesive includes any one or a combination of at least two of acrylic acid, polyvinylidene fluoride-hexafluoropropylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol or polyvinyl acetate.

[0024] In the present invention, the adhesive is an emulsion with a solid content of 30%-70%, for example, 30%, 40%, 50%, 60% or 70%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] As a preferred technical solution of the present invention, the mass of the wetting agent is 1%-3% of the total mass of the coating slurry, for example, it can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the wetting agent comprises any one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether or polyether-modified polysiloxane, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of alkylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether, a combination of fatty acid polyoxyethylene ether and polyether-modified polysiloxane, or a combination of fatty alcohol polyoxyethylene ether and polyether-modified polysiloxane.

[0027] In the present invention, the coating slurry further includes a dispersant.

[0028] In the present invention, the mass of the dispersant is 0%-2% of the total mass of the coating slurry, for example, it can be 0, 0.4%, 0.8%, 1%, 1.4%, 1.8% or 2%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In the present invention, the dispersant includes any one of sodium polyacrylate, ammonium polyacrylate, carboxylate or sulfonate, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of sodium polyacrylate and ammonium polyacrylate, a combination of ammonium polyacrylate and carboxylate, or a combination of carboxylate and sulfonate.

[0030] In a second aspect, the present invention provides a method for preparing a ceramic coated diaphragm, the preparation method comprising the following steps:

[0031] (1) providing a basement membrane;

[0032] (2) preparing a slurry: using the coating slurry described in the first aspect;

[0033] (3) coating: coating the slurry prepared in step (2) on the base film in step (1);

[0034] (4) drying;

[0035] There is no restriction on the order of steps (1) and (2).

[0036] As a preferred technical solution of the present invention, the coating speed in step (3) is 150-250 m / min, for example, it can be 150 m / min, 170 m / min, 200 m / min, 220 m / min, 240 m / min or 250 m / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, the drying temperature in step (4) is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] In the present invention, the method for preparing the slurry in step (2) is: mixing and dispersing ceramic powder and water to obtain ceramic slurry; and sequentially mixing and dispersing an adhesive, a thickener, a water reducer, and a wetting agent with the ceramic slurry to obtain slurry.

[0039] The coating slurry prepared in the present invention can be coated under a high-speed coating machine and the slurry can be completely dried without increasing the oven temperature of the coating machine, thereby improving the problems of the existing slurry such as difficulty in drying under high-speed coating, low peeling force, and high moisture content.

[0040] In the present invention, each time a raw material is added, dispersion stirring is performed for 30 minutes, the dispersion speed is 700-1700 rpm, and the stirring speed is 20-80 rpm.

[0041] In a third aspect, the present invention further provides a ceramic coated diaphragm, wherein the ceramic coated diaphragm is prepared by the preparation method described in the second aspect;

[0042] The ceramic-coated diaphragm includes a base film and a ceramic coating layer coated on at least one surface of the base film.

[0043] As a preferred technical solution of the present invention, the base film includes a polyolefin microporous film.

[0044] Preferably, the thickness of the ceramic coating is 1-5 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the moisture content of the ceramic coated diaphragm is less than 600 ppm, for example, it can be 200 ppm, 300 ppm, 400 ppm, 500 ppm or 550 ppm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the peel strength of the ceramic coated diaphragm is greater than 100 N / mm, for example, it can be 105 N / mm, 110 N / mm, 112 N / mm, 114 N / mm, 118 N / mm or 120 N / mm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The coating slurry of the present invention reduces water consumption by adding a water reducer and controlling the thickener and water reducer within a certain range, thereby increasing the solid content of the slurry while ensuring the dispersibility of the slurry. The obtained coating slurry has moderate viscosity and good stability.

[0050] (2) The coating slurry prepared by the present invention can be applied by a high-speed coating machine under drying at 60-80°C, thereby improving the problems of the existing slurry such as difficulty in drying under high-speed coating, low peeling force, and high moisture content;

[0051] (3) The coating slurry of the present invention has low raw material cost, simple preparation method and is suitable for large-scale production. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0053] In the following examples and comparative examples, the ceramic powder is alumina ceramic powder; the adhesive is a water-based adhesive containing acrylic acid ester, and the solid content of the adhesive emulsion is 50%; the thickener is a 10% sodium carboxymethyl cellulose aqueous solution; the wetting agent is alkylphenol polyoxyethylene ether; and the dispersant is sodium polyacrylate. The ceramic powder, adhesive, thickener, wetting agent, and dispersant may be other materials described in the specification to achieve the same effect.

[0054] Except that the water reducer in Example 2 is a polycarboxylate-based water reducer and the water reducer in Example 3 is a sulfamate-based water reducer, the water reducers in other examples and comparative examples are all melamine-based water reducers.

[0055] Example 1

[0056] This embodiment provides a method for preparing a coating slurry, the preparation method comprising the following steps:

[0057] (1) 45kg specific surface area is 3m 2 The ceramic powder was mixed with 42 kg of ultrapure water and dispersed at a speed of 1200 rpm to prepare a ceramic slurry;

[0058] (2) 5 kg of adhesive, 5 kg of 10% sodium carboxymethyl cellulose aqueous solution, 1 kg of melamine-based water-reducing agent, and 2 kg of wetting agent were sequentially mixed and dispersed with the ceramic slurry described in step (1). Each time a raw material was added, the dispersion and stirring were performed for 30 minutes at a dispersion speed of 1200 rpm and a stirring speed of 50 rpm to obtain a coating slurry with a solid content of 50%.

[0059] Examples 2-11, Example 14 and Comparative Examples 1-5

[0060] The specific raw material contents of the coating slurry in the above examples and comparative examples are shown in Table 1, and other conditions are the same as in Example 1.

[0061] Example 12

[0062] This embodiment provides a method for preparing a coating slurry, except that step (1) uses a specific surface area of ​​5m 2 The other formulas and conditions are the same as those in Example 1.

[0063] Example 13

[0064] This embodiment provides a method for preparing a coating slurry, except that step (1) uses a specific surface area of ​​10m 2 The other formulas and conditions are the same as those in Example 1.

[0065] Table 1

[0066]

[0067]

[0068] The coating slurries prepared in the above examples and comparative examples were used to prepare ceramic coated diaphragms for lithium-ion batteries. The preparation method of the ceramic coated diaphragm included: coating the coating slurry on one side of a polyethylene microporous membrane with a thickness of 12 μm and a porosity of 40-50% at a speed of 200 m / min, wherein the thickness of the ceramic coating was 4 μm, and drying the membrane at 80°C to obtain a ceramic coated diaphragm; and performing peel strength and moisture content performance tests on the obtained ceramic coated diaphragm. The results are shown in Table 2.

[0069] Table 2

[0070]

[0071]

[0072] The following points can be drawn from Table 2:

[0073] (1) The coating slurries provided in Examples 1-6 of the present invention improve the solid content of the slurry while ensuring the dispersibility of the slurry. The resulting ceramic coated diaphragms have excellent performance, with a moisture content of <600 ppm and a peel strength of >100 N / mm.

[0074] (2) Based on Example 1 and Examples 7-10, it can be seen that when the ratio of the thickener to the water reducer is too high, flocculation occurs due to the excess thickener, causing the coating slurry to easily agglomerate. When the ratio of the thickener to the water reducer is too low, saturated adsorption is likely to occur, resulting in poor stability of the coating slurry. Therefore, properly controlling the ratio of the thickener to the water reducer can reduce the difficulty of the production process and improve the yield of the coating product.

[0075] (3) From Example 1 and Examples 10-11, it can be seen that when the amount of water reducer is less than 0.2%, the dispersion effect of the coating slurry is reduced, the ceramic particles are agglomerated, the particle size is large, and the slurry viscosity is high, resulting in particles on the membrane surface of the ceramic coating diaphragm, and the battery is prone to short circuit. When the amount of water reducer is higher than 2%, supersaturated adsorption occurs, and the excess water reducer molecules bridge each other to form a network structure, which restricts the movement of the particles, thereby deteriorating the fluidity of the slurry and making it easy to precipitate. The slurry stability is reduced, which may cause large-area leakage of the ceramic coating diaphragm and make it unusable.

[0076] (4) Based on Example 1 and Example 13, it can be seen that when the specific surface area of ​​the ceramic powder is higher than 5m 2 When the coating slurry is too large, it will cause the coating slurry to agglomerate, the slurry is easy to settle, there are more slurry particles on the coating membrane surface, the membrane surface has light and dark lines, and the micro-concave roller is prone to wear during long-term continuous production. The feeding system is easy to be blocked during the coating process. Therefore, the specific surface area of ​​the ceramic powder is controlled at 5m 2 The following is beneficial to improve the yield of coated products;

[0077] (5) Based on Example 1 and Example 14, it can be seen that when a water reducer and a dispersant are added to the coating slurry at the same time, the membrane surface of the obtained ceramic coated diaphragm has no obvious abnormality, but its moisture content and peel strength are slightly inferior to those of Example 1;

[0078] (6) Based on Example 1 and Comparative Example 2, it can be seen that when the solid content of the coating slurry is too low, it is impossible to achieve drying at 60-80°C under high-speed coating, resulting in unqualified performance of the ceramic coated diaphragm and the diaphragm being scrapped;

[0079] (7) Based on Example 1 and Comparative Examples 3-5, it can be seen that when a dispersant is used instead of a water reducer, the slurry particles on the membrane surface are prone to agglomeration, and the peel strength of the ceramic coated diaphragm is lower than 100N / mm, and the moisture content is greater than 600ppm. Due to the serious agglomeration of ceramic particles in the slurry, not only the feeding system is prone to clogging during the coating process, the coating micro-concave roller is severely worn, and the thickness consistency is poor, but also there are many defects on the membrane surface (missing coating, slurry particle foreign matter, etc.), making it impossible to carry out high-speed continuous coating production.

[0080] The applicant declares that the present invention is intended to illustrate the detailed structural features of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed structural features. This does not mean that the present invention must rely on the above-described detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific embodiments, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A diaphragm coating slurry, characterized in that: The diaphragm coating slurry includes ceramic powder, additives and water; The auxiliary agents include adhesives, thickeners, water reducers and wetting agents; The water reducer includes any one of melamine-based water reducers, aminosulfonate-based water reducers, or polycarboxylate-based water reducers, or a combination of at least two thereof; The mass of the water reducer is 0.2%-2% of the total mass of the coating slurry; The mass ratio of the thickener to the water reducer is (2-5):1; The solid content of the coating slurry is 50%-62%.

2. The diaphragm coating slurry according to claim 1, characterized in that The mass of the ceramic powder is 30%-60% of the total mass of the coating slurry.

3. The diaphragm coating slurry according to claim 1, characterized in that The ceramic powder includes any one of aluminum oxide, boehmite, silicon oxide, titanium oxide, calcium carbonate, barium sulfate or magnesium oxide, or a combination of at least two of them.

4. The diaphragm coating slurry according to claim 1, characterized in that The specific surface area of ​​the ceramic powder is 2-5m 2 / g.

5. The diaphragm coating slurry according to claim 1, characterized in that: The mass of the water is 30%-50% of the total mass of the diaphragm coating slurry.

6. The diaphragm coating slurry according to claim 1, characterized in that: The thickener includes any one of hydroxypropyl methylcellulose solution, sodium carboxymethylcellulose solution, methylcellulose solution or layered silicate solution, or a combination of at least two of them.

7. The diaphragm coating slurry according to claim 1, characterized in that The mass of the adhesive is 4%-6% of the total mass of the coating slurry.

8. The diaphragm coating slurry according to claim 1, characterized in that: The adhesive is a water-based adhesive.

9. The diaphragm coating slurry according to claim 1, characterized in that: The mass of the wetting agent is 1%-3% of the total mass of the coating slurry.

10. The diaphragm coating slurry according to claim 1, characterized in that: The wetting agent includes any one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether or polyether-modified polysiloxane, or a combination of at least two thereof.

11. A method for preparing a ceramic coated diaphragm, characterized in that: The preparation method comprises the following steps: (1) Providing a basement membrane; (2) Preparing a slurry: using the diaphragm coating slurry according to any one of claims 1 to 10; (3) coating: coating the slurry prepared in step (2) on the base film in step (1); (4) Drying; There is no restriction on the order of steps (1) and (2).

12. The method for preparing a ceramic coated diaphragm according to claim 11, wherein: The coating speed in step (3) is 150-250 m / min.

13. The method for preparing a ceramic coated diaphragm according to claim 11, wherein: The drying temperature in step (4) is 60-80°C.

14. A ceramic coated diaphragm, characterized in that: The ceramic coated diaphragm is prepared by the preparation method according to any one of claims 11 to 13; The ceramic-coated diaphragm includes a base film and a ceramic coating layer coated on at least one surface of the base film.

15. The ceramic coated diaphragm according to claim 14, characterized in that The base film includes a polyolefin microporous film.

16. The ceramic coated diaphragm according to claim 14, characterized in that The thickness of the ceramic coating is 1-5 μm.

17. The ceramic coated diaphragm according to claim 14, characterized in that The moisture content of the ceramic coated diaphragm is less than 600 ppm.

18. The ceramic coated diaphragm according to claim 14, characterized in that The peel strength of the ceramic coated separator is greater than 100 N / mm.

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