Battery separator having high heat-resistant ceramic coating, and manufacturing method therefor

Abstract

A battery separator having a high-heat-resistance ceramic coating (1), said separator comprising a base film (2) and a ceramic coating (1) coated on the base film (2); the ceramic coating (1) comprises a ceramic powder (12) and a binder, and the binder bonds the ceramic powder (12) onto the base film (2); the ceramic powder (12) further comprises at least one inorganic substance A (11) having a density of 5-15 g / cm3. When the base film (2) is coated with a layer of the ceramic coating (1) containing at least one high-density inorganic substance A (11), because of the large gravity of the inorganic substance A (11), a "pillar" effect can be achieved in the three-dimensional structure of the separator, forming a more stable rigid structure; this allows the separator to avoid large surface area shrinkage resulting from stress release that is caused by molecular chain movement in the separator in a high-temperature environment.

Description

A battery separator with high heat-resistant ceramic coating and preparation method thereof Technical Field

[0001] The present invention relates to the field of battery manufacturing technology, and in particular to a battery separator with a high heat-resistant ceramic coating and a preparation method thereof, so as to improve the electrochemical performance and safety performance of lithium batteries. Background Art

[0002] With the widespread adoption of power batteries and energy storage batteries, their safety is receiving increasing attention. As a key material influencing battery safety, the safety requirements and expectations for separators are also continuously increasing. Furthermore, battery companies both domestically and internationally are seeking separators that maintain dimensional stability in temperatures between 220°C and 300°C.

[0003] Currently, the market primarily uses alumina or boehmite coated polyolefin microporous membranes to improve their heat resistance. However, with the increasing demand for heat resistance in high-power, high-energy-density electronic products, these membranes struggle to meet market demand. Therefore, there is an urgent need to develop high-temperature resistant membranes that exhibit thermal stability at temperatures as low as 220°C, for example. Summary of the Invention

[0004] The present invention aims to address the high-temperature thermal stability of the separator. Existing production technologies lack sufficient heat resistance, which can easily lead to safety issues. This invention improves the thermal stability of the separator, thereby enhancing safety. Specifically, the base film, which is stretched during its preparation, exhibits internal stress. Under high-temperature conditions, the molecular chains within the separator release this stress, leading to large-scale shrinkage. Another object of the present invention is to provide a method for preparing a highly heat-resistant ceramic-coated battery separator.

[0005] To achieve the above object, the present invention provides a battery separator with a high heat-resistant ceramic coating, characterized in that the battery separator comprises a base film and a ceramic coating coated thereon, wherein the ceramic coating comprises ceramic powder and a binder, and the binder bonds the ceramic powder to the base film; the ceramic powder further comprises at least one inorganic substance A, and its density is 5-15 g / cm 3 .

[0006] Preferably, the ceramic powder further comprises at least one having a density of 0.1-5 g / cm 3 The inorganic particles make the average density of the ceramic powder be 1-15g / cm 3 , wherein the density of the inorganic substance A is greater than that of the inorganic particles.

[0007] Preferably, the inorganic particles include titanium oxide, aluminum hydroxide, magnesium hydroxide, aluminum oxide, boehmite, magnesium oxide, calcium oxide, beryllium oxide, or any combination thereof.

[0008] Preferably, the inorganic substance A includes barium titanate, cerium oxide, zirconium dioxide, yttrium oxide, or any combination thereof.

[0009] Preferably, the ceramic coating is coated on one side or both sides of the base film, and the ceramic powder and the binder contained in each ceramic coating are the same or different in proportion.

[0010] Preferably, the ceramic powder has a D50 particle size of 0.05 μm to 2 μm and a specific surface area of ​​1 to 200 m 2 / g.

[0011] Preferably, the inorganic material A has a particle size of 0.05 μm to 2 μm and a specific surface area of ​​1 to 200 m 2 / g.

[0012] Preferably, the mass ratio of the inorganic substance A to the ceramic powder is 1:(1-100).

[0013] A method for preparing a battery separator with a high heat-resistant ceramic coating, characterized by comprising the following steps:

[0014] S1: Add the dispersant to deionized water and stir thoroughly to obtain a dispersant solution.

[0015] S2: adding ceramic powder containing at least one inorganic substance A into a dispersant solution and continuing to stir, and then adding the powder into a grinder for dispersion.

[0016] S3: adding a thickener, a binder, and a wetting agent to the mixture ground in step S2 in sequence and stirring the mixture evenly, and then performing demagnetization filtration to obtain a coating slurry.

[0017] S4: coating the coating slurry obtained in step S3 on the base film, and then drying it to obtain a diaphragm with a coating layer.

[0018] Preferably, the mass ratio of the inorganic substance A to the ceramic powder is 1:(1-100).

[0019] Preferably, the particle size of the ceramic powder D50 is 0.05 μm-2 μm; and the particle size of the inorganic substance A is 0.05 μm-2 μm.

[0020] The present invention provides a battery separator with a highly heat-resistant ceramic coating and a method for preparing the same. This beneficial effect stems from the distribution of the ceramic material within the separator's three-dimensional structure, forming a rigid framework. This rigid support effectively prevents the separator from shrinking and melting under thermal runaway conditions. When a ceramic coating containing at least one high-density inorganic substance A is applied to the base membrane, its high gravity acts as a "pillar" within the separator's three-dimensional structure, creating a more stable and rigid structure. This resists the stress release caused by molecular chain motion within the separator, which can lead to large-scale shrinkage under high-temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a schematic diagram illustrating the state of the ceramic coating and base film after being exposed to high temperature.

[0022] FIG2 is a flow chart illustrating the preparation process of the present invention. DETAILED DESCRIPTION

[0023] To make the above and / or other purposes, effects, and features of the present invention more clearly understood, preferred embodiments are described in detail below:

[0024] Referring to FIG1 , the present invention provides a battery separator with a high heat-resistant ceramic coating, which comprises a base film (2) and a ceramic coating (1); the ceramic coating (1) comprises ceramic powder (12) and a binder, wherein the binder bonds the ceramic powder (12) to the base film (2); the ceramic powder (12) further comprises at least one inorganic substance A (11) having a density of 5-15 g / cm 3 .

[0025] In some embodiments, the inorganic material A (11) comprises barium titanate, cerium oxide, zirconium dioxide, yttrium oxide, or any combination thereof; the particle size is 0.05 μm-2 μm, preferably 0.1-1 μm; the density is 5-15 g / cm 3 , preferably a density of 5-10g / cm 3 ;Specific surface area is 1-200m 2 / g, preferably 1-100m 2 / g.

[0026] In some embodiments, the ceramic powder (12) further comprises at least one material having a density of 0.1-5 g / cm 3 The inorganic particles make the ceramic powder (12) have an average density of 1-15 g / cm 3 , wherein the density of the inorganic substance A is greater than that of the inorganic particles.

[0027] In some embodiments, the inorganic particles include titanium oxide, aluminum hydroxide, magnesium hydroxide, aluminum oxide, boehmite, magnesium oxide, calcium oxide, beryllium oxide, or any combination thereof. The total mass ratio of the ceramic powder (12) to deionized water is 1: (1.25-10), i.e., 10% to 80%; the D50 particle size of the ceramic powder (12) is 0.05 μm-2 μm, preferably 0.1-1 μm; the average density of the ceramic powder (12) is 1-15 g / cm 3 , preferably 2-10g / cm 3 The average specific surface area of ​​the ceramic powder (12) is 1 to 200 m 2 / g, preferably 1-100m 2 / g.

[0028] In some embodiments, the ceramic coating (1) is coated on one side or both sides of the base film (2), and each ceramic coating (1) contains the same or different ceramic powder (12) and binder.

[0029] In some embodiments, the base film (2) used includes a polyethylene microporous film, a polypropylene microporous film or a polypropylene / polyethylene composite microporous film, and the base film (2) has a thickness of 3 to 20 μm, preferably 5 to 14 μm, and an air permeability of 30 to 300 s / 100 cc.

[0030] In some embodiments, the coating has a thickness of 0.5 μm to 7 μm, preferably 0.5-4 μm.

[0031] In some embodiments, the total mass ratio of the inorganic substance A (11) to the ceramic powder (12) is 1:(1-100), that is, the inorganic substance A (11) accounts for 1% to 100% of the mass of the ceramic powder (12), preferably 50% to 100%.

[0032] Preparation method

[0033] A method for preparing a high-heat-resistant ceramic coating (1) battery separator, the preparation method comprising the following steps: S1: adding a dispersant to deionized water and stirring thoroughly to obtain a dispersant solution; S2: adding at least one of a density of 5-15 g / cm 3 The ceramic powder (12) of the inorganic substance A (11) is added to the dispersant solution and continued to be stirred, and then added to the grinder for dispersion; S3: the thickener, binder, and wetting agent are added to the mixture after grinding in step S2 in sequence, stirred evenly, and then demagnetized and filtered to obtain a coating slurry; S4: the coating slurry obtained in step S3 is applied to the base film (2), and then dried to obtain a diaphragm with a coating layer; the coating is performed using a wire rod, a groove roller, etc.

[0034] In some embodiments, in step S1, the dispersant is at least one of polyethylene glycol, sodium polyacrylate, polypropylene, polyethylene, polyvinylpyrrolidone, ammonium polyacrylate, and sodium hexametaphosphate; and the total mass ratio of the dispersant to the ceramic powder (12) is 1:(50-2000).

[0035] In some embodiments, in step S2, the ceramic powder (12) further comprises at least one material with a density of 0.5-15 g / cm 3 The inorganic particles make the ceramic powder (12) have an average density of 1-15 g / cm 3 , preferably 2-10g / cm 3 , wherein the density of the inorganic substance A is greater than that of the inorganic particles.

[0036] In some embodiments, in step S3, the binder includes polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylic acid, polyacrylonitrile and polyacrylate, polyacrylamide, melamine, styrene-butadiene rubber, phosphates, silicates, lignin, polyimide, or any combination thereof; the total mass ratio of the binder to the ceramic powder (12) is 1: (5-100).

[0037] In some embodiments, in step S3, the thickener includes sodium carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, carbomer resin, or any combination thereof; the total mass ratio of the thickener to the ceramic powder (12) is (0.1-2):100.

[0038] In some embodiments, in step S3, the wetting agent comprises organic modified silicon oxides, polyols, fatty alcohol ethers, or any combination thereof, and the ratio of the wetting agent to the total mass of the ceramic powder (12) is (0.01-2):100.

[0039] In some embodiments, in step S4, the coating method is one of gravure printing, doctor blade coating, extrusion coating or wire rod coating; the coating location is any one side or both sides of the base film (2).

[0040] In some embodiments, in step S4, the base film (2) coated with the coating slurry is dried. The drying method is preferably oven drying. The drying temperature is 40 to 150° C. and the drying time is 0.01 to 0.5 hours.

[0041] The slurry preparation methods provided in this application are all implemented at room temperature, are simple to operate, and are easy to scale up.

[0042] Example 1

[0043] A method for preparing a high-heat-resistant ceramic coating battery separator, the preparation method is as follows:

[0044] Step 1: Weigh 0.5 g of sodium polyacrylate and dissolve it in 100 g of deionized water. Use an overhung stirrer to stir at 1000 rpm for 1 hour to form a dispersant aqueous solution.

[0045] Step 2: Place 10g of barium titanate (density 6g / cm 3 , the specific surface area is 3.4m 2 / g) was added to the dispersant aqueous solution and stirred at 2000r / min using an overhung stirrer for 1h. Then 90g of alumina (density 4g / cm 3 , the specific surface area is 7.5m 2 / g) was added to the dispersant aqueous solution, stirred at 2000 r / min using an overhead stirrer for 1 h, and then ground.

[0046] Step 3: Add 3g of sodium carboxymethyl cellulose aqueous solution, stir for 30 minutes, then add 10g of acrylate emulsion, stir for 1 hour using a cantilever stirrer at 300r / min, and after uniform dispersion, add 0.05g of silicone surface additive, and stir for 1 hour using a cantilever stirrer at 300r / min to obtain a uniform slurry.

[0047] Step 4: Use a coating machine to apply the slurry to one side of a 9μm-thick polyethylene film and dry it in a 60°C oven for 3 minutes. After drying, the coating thickness is 2μm, resulting in a single-sided coated separator. Then, use a coating machine to apply the slurry to the other side of the polyethylene film and dry it in a 60°C oven for 3 minutes. After drying, the coating thickness is 2μm, resulting in a double-sided 4μm-thick separator.

[0048] Example 2

[0049] This embodiment provides a method for preparing a high-heat-resistant ceramic coated battery separator. The difference between Example 2 and Example 1 is that in step 2, the amount of barium titanate powder added is 30 g, and the amount of aluminum oxide added is 70 g.

[0050] Example 3

[0051] This embodiment provides a method for preparing a high-heat-resistant ceramic coating battery separator. The difference between Example 3 and Example 1 is that in step 2, the amount of barium titanate powder added is 50 g, and the amount of aluminum oxide added is 50 g.

[0052] Example 4

[0053] This embodiment provides a method for preparing a high-heat-resistant ceramic coating battery separator. The difference between Example 4 and Example 1 is that in step 2, the amount of barium titanate powder added is 70 g, and the amount of aluminum oxide added is 30 g.

[0054] Example 5

[0055] This embodiment provides a method for preparing a high-heat-resistant ceramic coating battery separator. The difference between Example 5 and Example 1 is that in step 2, the amount of barium titanate powder added is 90 g, and the amount of aluminum oxide added is 10 g.

[0056] Example 6

[0057] This embodiment provides a method for preparing a high-heat-resistant ceramic coating battery separator. The difference between Example 6 and Example 1 is that in step 2, the amount of barium titanate powder added is 100 g, and the amount of aluminum oxide added is 0 g.

[0058] Example 7

[0059] This embodiment provides a method for preparing a high heat-resistant ceramic coating battery separator. The difference between Example 7 and Example 1 is that the amount of barium titanate powder added in step 2 is 30g, and alumina is replaced by boehmite (density 3g / cm 3 ), the added amount is 70g.

[0060] Comparative Example 1

[0061] To compare the effect of barium titanate on improving the heat resistance of the diaphragm, the difference between Comparative Example 1 and Example 1 is that the amount of barium titanate powder added in step 2 is 0 g, and the amount of aluminum oxide added is 100 g.

[0062] Comparative Example 2

[0063] To compare the effect of barium titanate on improving the heat resistance of the diaphragm, the difference between Comparative Example 2 and Example 1 is that in step 2, the barium titanate powder is replaced with boehmite, the addition amount is 30g, and the addition amount of aluminum oxide is 70g.

[0064] Comparative Example 3

[0065] To compare the effect of barium titanate on improving the heat resistance of the diaphragm, the difference between Comparative Example 3 and Example 1 is that in step 2, the barium titanate powder is replaced with boehmite, the addition amount is 50g, and the addition amount of aluminum oxide is 50g.

[0066] Comparative Example 4

[0067] To compare the effect of barium titanate on improving the heat resistance of the diaphragm, the difference between Comparative Example 4 and Example 1 is that in step 2, the barium titanate powder is replaced with boehmite, the addition amount is 70g, and the addition amount of aluminum oxide is 30g.

[0068] Comparative Example 5

[0069] To compare the effect of barium titanate on improving the heat resistance of the diaphragm, the difference between Comparative Example 5 and Example 1 is that in step 2, the barium titanate powder is replaced with boehmite, the addition amount is 90g, and the addition amount of aluminum oxide is 10g.

[0070] [Coating average unit surface density test]

[0071] Test method: Cut three pieces of diaphragm, each with a base film and a ceramic coating film measuring 40mm*60mm in MD*TD. First, place the three base films on an analytical balance and weigh them to obtain m1, m2, and m3. Then, use a thickness gauge to measure the thickness of the three base films to obtain h1, h2, and h3. Similarly, place the three ceramic coating films on an analytical balance and weigh them to obtain m4, m5, and m6. Then, use a thickness gauge to measure the thickness of the three ceramic coating films to obtain h4, h5, and h6. According to the calculation formula average areal density ρ = (m1+m2+m3) / 3 / 0.0024, the average areal density of the base film is ρ1, and the average areal density of the ceramic coating film is ρ2. Since the average coating thickness h is (h4+h5+h6) / 3-(h1+h2+h3) / 3, the final average unit areal density of the coating is ρ = (ρ2-ρ1) / h.

[0072] [Heat shrinkage test]

[0073] Test method: Cut 6 pieces of ceramic coated membrane with a size of 60mm*40mm in MD*TD direction, and poke 2 small holes in the MD and TD directions at the same position of all ceramic coated membranes. The hole spacing in the MD direction is measured as d1, and the hole spacing in the TD direction is measured as d2. The 6 coated membranes are divided into 2 groups, and placed on 10 A4 papers respectively. 10 A4 papers are pressed on the coated membranes and fixed with paper clips. One group is placed in a constant temperature oven at 150℃, and the other group is placed in a constant temperature oven at 220℃ for 1h. Finally, the hole spacing in the MD and TD directions of the membrane after heating is measured, which are d3 and d4 respectively. Finally, the thermal shrinkage rate of the membrane in the MD direction p = (d1-d3) / d1*100%, and the thermal shrinkage rate in the TD direction p = (d2-d4) / d2*100% are calculated.

[0074] [Hot nail test]

[0075] Test method: Cut a 50mm diameter ceramic coating film and fix it to the test mold of the hot nail penetration tester using a fixing clamp, trying to keep the surface flat and the force evenly distributed. Select a hot nail with a pointed corner diameter of 0.2mm, set the temperature to 250℃, and the distance to -0.1mm. Run the program. After the test is completed, observe and analyze the shape and size of the black spots or holes punctured in the diaphragm under a digital microscope.

[0076] The performance of the coated membranes prepared in Examples 1-7 and Comparative Examples 1-5 was tested, and the test results are shown in Table 1 below:

[0077] According to Table 1, we can see that:

[0078] From Examples 1-6, it can be found that as the ratio of inorganic substance A to ceramic powder increases, the average unit area density of the coating increases, and the thermal shrinkage of the diaphragm at 150°C and 220°C decreases accordingly, and the thermal shrinkage at 150°C is <3%; the rupture diameter of the membrane in the hot nail puncture test also decreases accordingly.

[0079] Comparing the results of Examples 1-7 and Comparative Examples 1-5, it can be seen that adding inorganic substance A to the ceramic powder can significantly improve the thermal shrinkage of the separator and reduce the diameter of the membrane ruptured by thermal puncture, thereby improving battery safety.

[0080] Comparing the results of Example 7 and Comparative Examples 1-2, it can be seen that the addition of inorganic substance A to the ceramic powder can significantly improve the thermal shrinkage rate of the separator and reduce the diameter of the membrane ruptured by thermal puncture, thereby improving battery safety, even though the average unit surface density of the coating of Example 7 is lower than that of Comparative Examples 1-2.

[0081] However, the above is only a preferred embodiment of the present invention, and it cannot be used to limit the scope of patent protection of the present invention; therefore, any simple equivalent changes and modifications made according to the scope of patent protection of the present invention and the contents of the specification still fall within the scope of patent protection of the present invention.

Claims

1. A battery separator with a high heat-resistant ceramic coating, characterized in that: The battery separator comprises a base film and a ceramic coating coated thereon, wherein the ceramic coating comprises ceramic powder and a binder, the binder binds the ceramic powder to the base film, and the ceramic powder comprises at least one inorganic substance A, and its density is 5-15 g / cm 3 .

2. The battery separator according to claim 1, characterized in that: The ceramic powder further comprises at least one density of 0.1-5 g / cm 3 The inorganic particles make the average density of the ceramic powder be 1-15g / cm 3 , wherein the density of the inorganic substance A is greater than that of the inorganic particles.

3. The battery separator according to claim 2, characterized in that: The inorganic particles include titanium oxide, aluminum hydroxide, magnesium hydroxide, aluminum oxide, boehmite, magnesium oxide, calcium oxide, beryllium oxide, or any combination thereof.

4. The battery separator according to claim 1, characterized in that: The inorganic substance A includes barium titanate, cerium oxide, zirconium dioxide, yttrium oxide, or any combination thereof.

5. The battery separator according to claim 1, characterized in that: The ceramic coating is coated on one side or both sides of the base film, and the ceramic powder and the binder contained in each ceramic coating are the same or different in proportion.

6. The battery separator according to claim 1, characterized in that: The ceramic powder has a particle size of 0.05 μm to 2 μm and a specific surface area of ​​1 to 200 m 2 / g.

7. The battery separator according to claim 1, characterized in that: The inorganic substance A has a particle size of 0.05 μm-2 μm and a specific surface area of ​​1 to 200 m 2 / g.

8. The battery separator according to claim 1, characterized in that: The mass ratio of the inorganic substance A to the ceramic powder is 1:(1-100).

9. A method for preparing a battery separator with a high heat-resistant ceramic coating, characterized in that: The following steps are involved: S1: adding a dispersant to deionized water and stirring well to obtain a dispersant solution; S2: will contain at least one density of 5-15g / cm 3 The ceramic powder of inorganic substance A is added into the dispersant solution and stirred continuously, and then added into the grinder for dispersion; S3: adding a thickener, a binder, and a wetting agent to the mixture ground in step S2 in sequence and stirring the mixture evenly, and then performing demagnetization filtration to obtain a coating slurry; S4: coating the coating slurry obtained in step S3 on the base film, and then drying it to obtain a diaphragm with a coating layer.

10. The preparation method according to claim 9, characterized in that: The mass ratio of the inorganic substance A to the ceramic powder is 1:(1-100).

11. The preparation method according to claim 9, characterized in that: The particle size of the ceramic powder D50 is 0.05 μm-2 μm, and the particle size of the inorganic substance A is 0.05 μm-2 μm.

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