Ceramic slurry and method for preparing the same, lithium ion battery separator and method for preparing the same, and lithium ion battery

Abstract

The present application relates to the field of lithium battery material, discloses ceramic slurry and its preparation method, lithium ion battery diaphragm and its preparation method and lithium ion battery.Ceramic slurry, it includes: ceramic powder 40-50%, binder 1-5%, thickening agent 0.03-1% and solvent 48.9-58.87%;Thickening agent includes the mass ratio of high viscosity thickening agent and low viscosity thickening agent is 1.5-9:1.Preparation method of slurry, including: the above components are mixed uniformly.Lithium ion battery diaphragm, including the base film and the ceramic layer adhered to the surface of the polyolefin base film, the ceramic layer is obtained after the above ceramic slurry is coated.Preparation method of lithium ion battery diaphragm, including the ceramic slurry is coated on the surface of the base film.The diaphragm prepared by the ceramic slurry provided in the application has low water content, low air permeability and high thermal stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery materials, in particular to a ceramic slurry and a preparation method thereof, a lithium ion battery diaphragm and a preparation method thereof, and a lithium ion battery. BACKGROUND

[0002] A lithium ion battery is composed of four main parts: a positive electrode material, a negative electrode material, a diaphragm, and an electrolyte. The lithium battery diaphragm is located between the positive and negative electrodes inside the battery, ensuring the passage of lithium ions while preventing the transmission of electrons. It is a thin film with a microporous structure and is the key inner component with the most technical barriers in the lithium ion battery industry chain. The performance of the diaphragm determines the interface structure and internal resistance of the battery, directly affecting the capacity, cycle, and safety performance of the battery. An excellent diaphragm plays an important role in improving the overall performance of the battery.

[0003] The air permeability of the battery diaphragm is an important indicator of the diaphragm, which can be represented by the Gurley value to indicate the size of the porosity. The Gurley value test is the time required for a certain amount of air to pass through a unit area of diaphragm under certain pressure conditions. Air permeability can be used as an indicator to characterize the influence of lithium ion battery diaphragm on battery performance, which is as important as the thickness, porosity, pore size distribution, and pore size of the diaphragm.

[0004] At present, the most commonly used lithium ion battery is polyethylene and polypropylene diaphragm, but these two diaphragms have low melting temperature and poor heat resistance, and are prone to deformation or melting when the battery overheats, resulting in short circuit of the positive and negative electrodes and safety hazards. In recent years, with the maturity of coating technology, the diaphragm produced by dry or wet method can maintain the integrity of the diaphragm after large-area heat release during the coating process of the above high-temperature coating, which can well solve the problem of poor heat resistance of the diaphragm. The lithium ion battery diaphragm coated with aluminum oxide inorganic material will greatly improve the safety performance of the lithium ion battery, expand the application field, and gradually enter the middle and high-end market covering power lithium ion batteries.

[0005] In the prior art, the common production process of lithium ion battery ceramic diaphragm is to prepare a slurry: ceramic powder, thickening agent, dispersant, and binder are mixed according to a certain ratio to prepare an aqueous ceramic slurry, and the slurry is transferred to a polyolefin diaphragm through a fine coating process.

[0006] However, the ceramic slurry in the prior art adopts the water-based slurry process, the micro-nano ceramic of the ceramic coating body has a large specific surface area, and a considerable amount of exposed hydroxyl groups on the surface have strong water absorption, so that the ceramic coating of the ceramic separator has a high water content; in addition, the drying residues of the additives such as the binder and the thickening agent can seriously affect the performance of the battery; the residues can also block the micropores of the separator, increase the air permeability, and affect the internal resistance of the battery.

[0007] In view of this, the present application is proposed. SUMMARY

[0008] The present application aims to provide a ceramic slurry and a preparation method thereof, a lithium ion battery separator and a preparation method thereof, and a lithium ion battery, and aims to improve at least one problem mentioned in the background art.

[0009] The present application is implemented as follows:

[0010] In a first aspect, the present application provides a ceramic slurry, which comprises, in terms of mass percentage: ceramic powder 40-50%, binder 1-5%, thickening agent 0.03-1%, and solvent 48.9-58.87%.

[0011] The thickening agent comprises a high-viscosity thickening agent and a low-viscosity thickening agent in a mass ratio of 1.5-9:1.

[0012] The high-viscosity thickening agent is selected from at least one of sodium carboxymethyl cellulose, polymethacrylate, methylhydroxyethyl cellulose, polyethylene oxide, polyurethane, and polyacrylamide with a viscosity value of 3000-5000 mpa·s.

[0013] The low-viscosity thickening agent is selected from at least one of sodium carboxymethyl cellulose, polymethacrylate, methylhydroxyethyl cellulose, polyethylene oxide, polyurethane, and polyacrylamide with a viscosity value of 5-100 mpa·s.

[0014] The viscosity value is obtained by testing in a 1wt% aqueous solution at 25℃.

[0015] In an optional embodiment, the solvent mainly comprises deionized water.

[0016] In an optional embodiment, it further comprises a dispersant 0.1-0.5%.

[0017] Preferably, the dispersant is selected from at least one of isopropyl alcohol, ethylene glycol, methyl ether, ethyl ether, propylene glycol, glycerol, sodium polyacrylate, polyacrylic acid amine, and polyethylene glycol.

[0018] In an optional embodiment, the binder is at least one of an acrylic polymer, a styrene-butadiene rubber, a polyvinyl alcohol, an acrylonitrile polymer, a polyurethane, a polystyrene-acrylate, and a resorcinol formaldehyde resin.

[0019] In an optional embodiment, the average particle size of the ceramic powder is 0.5-1.2 μm, and the ceramic powder does not contain fine powder with a particle size less than 300 nm.

[0020] Preferably, the ceramic powder is selected from at least one of the group consisting of aluminum oxide, boehmite, silicon dioxide, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, calcium oxide, and magnesium hydroxide.

[0021] In a second aspect, the present application provides a method for preparing the slurry as described in the preceding embodiments, comprising: mixing the components contained in the slurry uniformly.

[0022] In an optional embodiment, the method for preparing comprises:

[0023] mixing the solvent and the thickening agent uniformly to obtain a glue solution;

[0024] mixing the glue solution and the ceramic powder uniformly to obtain an aqueous ceramic slurry precursor;

[0025] mixing the aqueous ceramic slurry precursor and the binder uniformly to obtain the aqueous ceramic slurry.

[0026] In an optional embodiment, the solvent is deionized water.

[0027] In an optional embodiment, the method for mixing the deionized water and the thickening agent uniformly is:

[0028] mixing the solvent and the thickening agent at a revolution speed of 10-30 r / m and a dispersion speed of 1000-3000 r / m for 2-5 h to obtain a glue solution;

[0029] Preferably, the method for mixing the glue solution and the ceramic powder uniformly is:

[0030] mixing the glue solution and the ceramic powder at a revolution speed of 10-50 r / m and a dispersion speed of 800-5000 r / m for 0.5-2 h to obtain an aqueous ceramic slurry precursor;

[0031] Preferably, the method for mixing the aqueous ceramic slurry precursor and the binder is:

[0032] adding the binder to the aqueous ceramic slurry precursor at a revolution speed of 10-30 r / m and a dispersion speed of 1000-3000 r / m for 0.2-1 h, and then sanding using a sand mill at a flow rate of 30-150 L / min for 10-30 min, and filtering through a 150-mesh gauze to obtain the aqueous ceramic slurry;

[0033] Preferably, the slurry further comprises a dispersant at 0.1-0.5%, and the dispersant is mixed with the glue solution and the ceramic powder.

[0034] In a third aspect, the present application provides a lithium ion battery separator, comprising a polyolefin base film and a ceramic layer adhered to the surface of the polyolefin base film, wherein the ceramic layer is formed by coating the slurry of any one of the preceding embodiments or the slurry prepared by the preparation method of the preceding embodiments on the surface of the polyolefin base film and then removing the dispersant, thickener and binder by heat treatment.

[0035] In a fourth aspect, the present application provides a preparation method of a lithium ion battery separator, comprising coating the slurry of any one of the preceding embodiments or the slurry prepared by the preparation method of the preceding embodiments on the surface of a polyolefin base film, and then removing the dispersant, thickener and binder by heat treatment.

[0036] In an optional embodiment, the coating thickness is 2-6 μm.

[0037] In a fifth aspect, the present application provides a lithium ion battery, comprising the lithium ion battery separator of the preceding embodiments or the lithium ion battery separator prepared by the preparation method of the preceding embodiments.

[0038] The present application has the following advantages:

[0039] Due to the reasonable proportioning of the high-viscosity thickener and the low-viscosity thickener, the total amount of the thickener used in the present application is less than half of the amount of the conventional thickener (generally 0.2-0.8%), and the thickening effect is comparable. In the prior art, the amount of the binder is generally about 2-6%, and the mutual promotion between the different types of thickeners, the cooperation of the long and short chains and the promotion of the binder can reduce the amount of the binder to achieve a comparable powder bonding effect. The reduction of the amount of the binder and the stabilizer can reduce the water absorption of the high molecular binder after drying and the pore blocking, and reduce the moisture and air permeability of the coated separator. Therefore, the separator prepared from the ceramic slurry provided by the present application has good performance. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0041] Figure 1 SEM image of the base film of Example 4;

[0042] Figure 2 SEM image of the separator prepared by coating the slurry on the surface of the base film of Example 4. DETAILED DESCRIPTION

[0043] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not indicated in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not indicated, the conventional products that can be purchased in the market are adopted.

[0044] The ceramic slurry, the preparation method thereof, the lithium ion battery separator and the lithium ion battery provided by the embodiments of the present application will be described in detail below.

[0045] The ceramic slurry provided by the embodiments of the present application comprises, in percentage by mass: 40-50% of ceramic powder, 1-5% of binder, 0.03-1% of thickening agent and 48.9-58.87% of solvent;

[0046] The thickening agent comprises high-viscosity thickening agent and low-viscosity thickening agent in a mass ratio of 1.5-9:1;

[0047] The high-viscosity thickening agent is selected from at least one of sodium carboxymethyl cellulose, polymethacrylate, methylhydroxyethyl cellulose, polyethylene oxide, polyurethane and polyacrylamide with a viscosity value of 3000-5000 mpa·s;

[0048] The low-viscosity thickening agent is selected from at least one of sodium carboxymethyl cellulose, polymethacrylate, methylhydroxyethyl cellulose, polyethylene oxide, polyurethane and polyacrylamide with a viscosity value of 5-100 mpa·s;

[0049] The viscosity value is obtained by testing in a 1 wt% aqueous solution at 25℃.

[0050] The inventors have found that the high-molecular binder and thickening agent have a certain moisturizing effect, and reducing the amount of the high-molecular binder and thickening agent facilitates sufficient drying of the separator and reduces the water content of the prepared separator. However, the amount of the binder and thickening agent cannot be blindly reduced in the actual production process, and if the amount is blindly reduced, the bonding strength between the ceramic layer and the base film will be reduced.

[0051] The ceramic slurry provided by the embodiments of the present application has a reasonable ratio of the high-viscosity thickening agent and the low-viscosity thickening agent, so that the total amount of the thickening agent used in the present solution is less than half of the amount of the conventional thickening agent (generally 0.2-0.8 wt%) and can achieve a comparable thickening effect. In the prior art, the amount of the binder is generally about 2-6 wt%, and the mutual promotion between the different types of thickening agents, the cooperation of long and short chains and the promotion of the binder can reduce the amount of the binder to achieve a comparable powder bonding effect. The reduction of the amount of the binder and the stabilizer can reduce the water absorption of the high-molecular binder and the pore blocking after drying, and reduce the moisture and the air permeability of the coated separator.

[0052] In particular, when the thickening agent is selected as polymethacrylate, the polymethacrylate has strong adhesion to the fibers, which can assist in improving the adhesion of the thickening agent on the surface of the ceramic powder, thereby reducing the number of pores on the surface of the ceramic powder, and facilitating the free water to be dried more easily after the ceramic slurry is coated on the base film, thereby reducing the combined water content adsorbed on the surface of the separator, and further reducing the water content of the ceramic separator obtained by coating the ceramic slurry.

[0053] Preferably, the solvent mainly includes deionized water. Generally, most of the solvent in the slurry is deionized water, and a small part is organic solvent brought in together with the additives during the addition of dispersants, binders and other additives.

[0054] Preferably, the average particle size of the ceramic powder is 0.5-1.2 μm (for example, 0.5 μm, 0.8 μm, 1 μm or 1.2 μm), and the specific surface area is less than 7 m2 / g.

[0055] The ceramic powder with a particle size of 0.5-1.2 μm has the characteristics of high particle size concentration and small specific surface area, which can indirectly reduce the amount of binder, thereby reducing the water absorption of the binder macromolecule after drying and blocking the pores, and reducing the moisture and air permeability of the coated separator. In addition, since the fine powder with a particle size less than 300 nm is not included, the possibility of reducing water absorption and completely blocking the pores of the separator to cause the moisture and air permeability of the coated separator to be reduced is reduced.

[0056] Further, in order to ensure the performance of the ceramic separator prepared from the slurry, the ceramic powder is selected from at least one of the powders of aluminum oxide, boehmite, silicon dioxide, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, calcium oxide and magnesium hydroxide.

[0057] Preferably, the binder is at least one of acrylic polymer, styrene-butadiene rubber, polyvinyl alcohol, acrylonitrile polymer, polyurethane, polystyrene-acrylate and resorcinol formaldehyde resin.

[0058] The above-mentioned binder in combination with several thickening agents defined in the present application can ensure the effect of reducing the overall amount of the binder.

[0059] Preferably, the slurry further includes 0.1-0.5% (for example, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%) of a dispersant. The addition of the dispersant is beneficial to the uniform dispersion of each component in the slurry.

[0060] Specifically, the dispersant is selected from at least one of isopropyl alcohol, ethylene glycol, methyl ether, ethyl ether, propylene glycol, glycerol, polyacrylic acid sodium, polyacrylic acid ammonia and polyethylene glycol.

[0061] The preparation method of the slurry provided by the embodiment of the application is as follows:

[0062] S1, preparing ceramic powder.

[0063] The ceramic powder is subjected to classification treatment by using an impeller rotor classifier, and the superfine powder of 100-300 nm is removed, so that the ceramic powder particle size distribution is concentrated to medium particle size, and the ceramic powder with an average particle size of 0.5-1.2 μm, high particle size concentration, and a specific surface area of less than 7 m 2 / g is prepared.

[0064] S2, mixing deionized water and a thickening agent uniformly to obtain a glue solution.

[0065] To ensure sufficient mixing, the specific method of this step is as follows:

[0066] The thickening agent powder (the mass ratio of the high-viscosity thickening agent to the low-viscosity thickening agent is 1.5-9:1, for example, 1.5:1, 2:1, 4:1, 6:1, 8:1 or 9:1) is added to the deionized water, and then stirring is performed, the revolution speed is 10-30 r / m (for example, 10 r / m, 20 r / m or 30 r / m), the dispersion speed is 1000-3000 r / m (for example, 1000 r / m, 2000 r / m or 3000 r / m), and the time is 2-5 h (for example, 2 h, 3 h, 4 h or 5 h), to obtain the glue solution.

[0067] S3, mixing the glue solution, the ceramic powder and a dispersant uniformly to obtain an aqueous ceramic slurry precursor.

[0068] To ensure sufficient mixing, the specific method of this step is as follows:

[0069] The ceramic powder and the dispersant are added to the glue solution, and stirring is performed, the revolution speed is 10-50 r / m (for example, 10 r / m, 20 r / m, 30 r / m, 40 r / m or 50 r / m), the dispersion speed is 800-5000 r / m (for example, 800 r / m, 1000 r / m, 2000 r / m, 3000 r / m or 5000 r / m), and the mixing time is 0.2-1 h (for example, 0.2 h, 0.5 h or 1 h) to obtain the aqueous ceramic slurry precursor.

[0070] S4, mixing the aqueous ceramic slurry precursor and a binder uniformly to obtain an aqueous ceramic slurry.

[0071] To ensure sufficient mixing, the specific method of this step is as follows:

[0072] The dispersant, thickener and binder are added to the aqueous ceramic slurry precursor, and then stirring is performed at a revolution speed of 10-30 r / m (for example, 10 r / m, 20 r / m or 30 r / m) and a dispersion speed of 1000-3000 r / m (for example, 1000 r / m, 2000 r / m or 3000 r / m) for 0.2-1 h (for example, 0.2 h, 0.5 h or 1 h); then sand milling is performed using a sand mill at a flow rate of 30-150 L / min (for example, 30 L / min, 80 L / min, 100 L / min or 150 L / min) for 10-30 min (for example, 10 min, 20 min or 30 min), and the aqueous ceramic slurry is obtained by filtering through a 150-mesh gauze.

[0073] The lithium ion battery separator provided in the embodiments of the present application comprises a polyolefin-based film and a ceramic layer adhered to the surface of the polyolefin-based film, wherein the ceramic layer is formed by coating the slurry provided in the embodiments of the present application or the slurry prepared by the method provided in the embodiments of the present application on the surface of the polyolefin-based film and then removing the dispersant, thickener and binder by heating treatment.

[0074] The lithium ion battery separator is prepared by coating the slurry provided in the embodiments of the present application on the surface of the base film, and thus has a low moisture content, a low air permeability, a small battery internal resistance, a high peeling strength and a good thermal stability.

[0075] The method for preparing the lithium ion battery separator provided in the embodiments of the present application comprises: coating the slurry provided in the embodiments of the present application or the slurry prepared by the method provided in the embodiments of the present application on the surface of a polyolefin-based film, and then removing the dispersant, thickener and binder by heating treatment.

[0076] Preferably, the heating is performed at a temperature of 30-70 ℃ for 10-30 min. For example, the temperature can be 30 ℃, 40 ℃, 50 ℃, 60 ℃ or 70 ℃, and the treatment time can be 10 min, 20 min or 30 min.

[0077] Preferably, the coating thickness is 2-6 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm.

[0078] The lithium ion battery separator prepared by the above coating thickness has excellent use performance.

[0079] The lithium ion battery provided in the embodiments of the present application comprises the lithium ion battery separator provided in the embodiments of the present application or the lithium ion battery separator prepared by the method provided in the embodiments of the present application.

[0080] The lithium ion battery comprises the above lithium ion battery separator, and thus has good performance.

[0081] The features and properties of the present application are further described in detail below in conjunction with the examples.

[0082] Example 1

[0083] The present example provides a method for preparing a ceramic slurry, specifically comprising:

[0084] The raw materials are prepared according to the following mass percentages: 40% ceramic powder, 1% binder, 0.03% thickening agent, 0.1% dispersant, and the balance being deionized water. The thickening agent is composed of a high-viscosity thickening agent and a low-viscosity thickening agent in a mass ratio of 1.5:1.

[0085] The ceramic powder is:

[0086] The raw material aluminum trioxide powder (D50=0.46, BET=7.98) is classified using a impeller rotor classifier under dry nitrogen protection to remove ultra-fine powder with a particle size less than 300 nm, thereby producing aluminum trioxide powder (D50=0.71, BET=5.62).

[0087] The binder is an acrylic polymer, which is added as an acrylic polymer solution with a solid content of 40%; the high-viscosity thickening agent is polyethylene oxide with a viscosity of 3500 mpa·s (1% aqueous solution, 25°C); the low-viscosity thickening agent is sodium carboxymethyl cellulose with a viscosity of 60 mpa·s (1% aqueous solution, 25°C); and the dispersant is isopropyl alcohol.

[0088] The high-viscosity thickening agent powder and the low-viscosity thickening agent powder are added to 91.8 kg of deionized water, and then stirred at a revolution speed of 10 r / m and a dispersion speed of 1000 r / m for 3 h, thereby obtaining a glue solution.

[0089] The ceramic powder and isopropyl alcohol are added to the glue solution, and then stirred at a revolution speed of 10 r / m and a dispersion speed of 800 r / m for 0.5 h, thereby obtaining an aqueous ceramic slurry precursor.

[0090] The acrylic polymer solution is added to the aqueous ceramic slurry precursor, and then stirred at a revolution speed of 10 r / m and a dispersion speed of 1000 r / m for 0.2 h; then a sand mill is used to sand mill at a flow rate of 30 L / min for 30 min, and then filtered through a 150-mesh gauze to obtain an aqueous ceramic slurry.

[0091] The present example provides a method for preparing a lithium ion battery separator, specifically comprising:

[0092] The water-based ceramic slurry prepared above was coated on the surface of a 14-μm polyolefin-based film using microgravure printing in a thickness of 2 μm, and then air-dried at a temperature of 60°C for 15 min to obtain a lithium-ion battery separator.

[0093] Example 2

[0094] The present embodiment provides a method for preparing a ceramic slurry, specifically:

[0095] The raw materials were prepared according to the mass percentages of ceramic powder 50%, binder 5%, thickening agent 1%, dispersant 0.5%, and the balance being deionized water, wherein the thickening agent was composed of a high-viscosity thickening agent and a low-viscosity thickening agent in a mass ratio of 9:1.

[0096] The ceramic powder was:

[0097] The raw material aluminum oxide powder (D50 = 0.46, BET = 7.98) was classified using a rotor classifier under dry nitrogen protection to remove ultra-fine powder with a particle size less than 300 nm, thereby preparing aluminum oxide powder (D50 = 0.71, BET = 5.62).

[0098] The binder was polyvinyl alcohol, which was added as a 40% solid content polyvinyl alcohol solution; the high-viscosity thickening agent was methylhydroxyethyl cellulose with a viscosity of 5000 mpa·s (1% aqueous solution, 25°C); the low-viscosity thickening agent was polyurethane with a viscosity of 5 mpa·s (1% aqueous solution, 25°C); and the dispersant was ethylene glycol.

[0099] 288 g of high-viscosity thickening agent powder and 32 g of low-viscosity thickening agent powder were added to 11.52 kg of deionized water, which was then stirred at a revolution speed of 30 r / m and a dispersion speed of 3000 r / m for 2 h to obtain a glue solution.

[0100] To the glue solution, 16 kg of ceramic powder and 160 g of ethylene glycol were added, which was then stirred at a revolution speed of 50 r / m and a dispersion speed of 5000 r / m for 1 h to obtain a water-based ceramic slurry precursor.

[0101] To the water-washed ceramic slurry precursor, 4 kg of polyvinyl alcohol solution was added, which was then stirred at a revolution speed of 30 r / m and a dispersion speed of 3000 r / m for 1 h; then a sand mill was used to sand mill at a flow rate of 150 L / min for 10 min, and the resulting mixture was filtered through a 150-mesh gauze to obtain a water-based ceramic slurry.

[0102] The present embodiment provides a method for preparing a lithium-ion battery separator, specifically:

[0103] The water-based ceramic slurry prepared above was coated on the surface of a 14-μm polyolefin-based film using microgravure printing in a thickness of 6 μm, and then air-dried at a temperature of 60°C for 15 min to obtain a lithium-ion battery separator.

[0104] Example 3

[0105] The present embodiment provides a method for preparing a ceramic slurry, specifically:

[0106] The raw materials were prepared according to the mass percentages of ceramic powder 45%, binder 3%, thickening agent 0.1%, dispersant 0.2%, and the balance being deionized water, wherein the thickening agent was composed of a high-viscosity thickening agent and a low-viscosity thickening agent in a mass ratio of 4:1.

[0107] The ceramic powder was:

[0108] The raw material aluminum oxide powder (D50 = 0.46, BET = 7.98) was classified by a impeller rotor classifier under dry nitrogen protection to remove ultra-fine powder with a particle size less than 300 nm, thereby obtaining aluminum oxide powder (D50 = 0.71, BET = 5.62).

[0109] The binder was an acrylic polymer, which was added as an acrylic polymer solution with a solid content of 40%; the high-viscosity thickening agent was polyacrylamide with a viscosity of 3000 mpa·s (1% aqueous solution, 25°C); the low-viscosity thickening agent was polyacrylamide with a viscosity of 100 mpa·s (1% aqueous solution, 25°C); and the dispersant was diethyl ether.

[0110] 40 g of high-viscosity thickening agent powder and 10 g of low-viscosity thickening agent powder were added to 23.6 kg of deionized water, and then stirred at a revolution speed of 20 r / m and a dispersion speed of 2000 r / m for 5 h to obtain a glue solution.

[0111] 22.5 kg of ceramic powder and 100 g of dispersant were added to the glue solution, and then stirred at a revolution speed of 30 r / m and a dispersion speed of 2000 r / m for 0.5 h to obtain a water-based ceramic slurry precursor.

[0112] 3.75 kg of binder was added to the water-washed ceramic slurry precursor, and then stirred at a revolution speed of 20 r / m and a dispersion speed of 2000 r / m for 1 h; then a sand mill was used to sand mill at a flow rate of 100 L / min for 20 min, and then filtered through a 150-mesh gauze to obtain a water-based ceramic slurry.

[0113] The present embodiment provides a method for preparing a lithium-ion battery separator, specifically:

[0114] The water-based ceramic slurry prepared above is coated on the surface of a 14-μm polyolefin-based film using microgravure printing in a thickness of 4 μm, and then is subjected to drum drying at a temperature of 60°C for 15 min to obtain a lithium ion battery separator.

[0115] Example 4

[0116] The present embodiment provides a method for preparing a ceramic slurry, specifically:

[0117] The raw materials are prepared according to the mass percentages of ceramic powder 40.76%, binder 1.30%, thickening agent 0.13%, dispersant 0.16%, and the balance being deionized water, wherein the thickening agent is composed of high-viscosity thickening agent and low-viscosity thickening agent in a mass ratio of 4:1.

[0118] The ceramic powder is:

[0119] The raw material aluminum oxide powder (D50=0.46, BET=7.98) is subjected to classification treatment under dry nitrogen protection using an impeller rotor classifier to remove ultra-fine powder with a particle size of less than 300 nm, thereby preparing aluminum oxide powder (D50=0.71, BET=5.62).

[0120] The binder is an acrylic polymer, which is added in the form of an acrylic polymer solution with a solid content of 40%; the high-viscosity thickening agent is sodium carboxymethyl cellulose with a viscosity of 3500 mpa·s; the low-viscosity thickening agent is polymethyl acrylate with a viscosity of 60 mpa·s; and the dispersant is sodium polyacrylate, which is added in the form of a sodium polyacrylate solution with a solid content of 40%.

[0121] High-viscosity thickening agent powder 128 g and low-viscosity thickening agent powder 32 g are added to 68 kg of deionized water, which is then stirred at a revolution speed of 15 r / m and a dispersion speed of 1000 r / m for 3 h to obtain a glue solution.

[0122] To the glue solution, 50 kg of ceramic powder and 0.5 kg of sodium polyacrylate solution are added, which is then stirred at a revolution speed of 30 r / m and a dispersion speed of 4000 r / m for 1 h to obtain a water-based ceramic slurry precursor.

[0123] To the water-washed ceramic slurry precursor, 4 kg of acrylic polymer solution is added, which is then stirred at a revolution speed of 10 r / m and a dispersion speed of 1000 r / m for 1 h; then a sand mill is used to sand mill at a flow rate of 50 L / min for 10 min, and the resulting product is filtered through a 150-mesh gauze to obtain a water-based ceramic slurry.

[0124] The present embodiment provides a method for preparing a lithium ion battery separator, specifically:

[0125] The water-based ceramic slurry prepared above was coated on the surface of a 14-μm polyolefin-based film using microgravure printing in a thickness of 4 μm, and then air-dried at a temperature of 60°C for 15 min to obtain a lithium-ion battery separator.

[0126] Example 5

[0127] The present embodiment provides a method for preparing a ceramic slurry, specifically:

[0128] The raw materials were prepared according to the mass percentages of ceramic powder 41.36%, binder 1.25%, thickening agent 0.13%, dispersant 0.16%, and the balance being deionized water, wherein the thickening agent was composed of a high-viscosity thickening agent and a low-viscosity thickening agent in a mass ratio of 2.81:1.

[0129] The ceramic powder was:

[0130] The raw material boehmite (D50=0.52, BET=7.23) was subjected to classification treatment under dry nitrogen protection using a impeller rotor classifier to remove ultra-fine powder with a particle size less than 300 nm, thereby preparing boehmite powder (D50=0.78, BET=4.83).

[0131] The binder was an acrylic polymer, which was added in the form of an acrylic polymer solution with a solid content of 40%; the high-viscosity thickening agent was sodium carboxymethyl cellulose with a viscosity of 3500 mpa·s (1% aqueous solution, 25°C); the low-viscosity thickening agent was polymethyl acrylate with a viscosity of 60 mpa·s (1% aqueous solution, 25°C); and the dispersant was sodium polyacrylate, which was added in the form of a sodium polyacrylate solution with a solid content of 40%.

[0132] High-viscosity thickening agent powder 118 g and low-viscosity thickening agent powder 42 g were added to 70 kg of deionized water, which was then stirred at a revolution speed of 15 r / m and a dispersion speed of 1000 r / m for 3 h to obtain a glue solution.

[0133] The glue solution was added to 53 kg of ceramic powder and 0.52 kg of a sodium polyacrylate solution, which was then stirred at a revolution speed of 30 r / m and a dispersion speed of 4000 r / m for 1 h to obtain a water-based ceramic slurry precursor.

[0134] The water-washed ceramic slurry precursor was added to 4 kg of an acrylic polymer solution, which was then stirred at a revolution speed of 10 r / m and a dispersion speed of 1000 r / m for 1 h; then a sand mill was used to sand mill at a flow rate of 50 L / min for 10 min, and the resulting product was filtered through a 150-mesh gauze to obtain a water-based ceramic slurry.

[0135] The present embodiment provides a method for preparing a lithium-ion battery separator, specifically:

[0136] The water-based ceramic slurry prepared above was coated on the surface of a 20-μm polyolefin-based film using a microgravure method to a thickness of 4 μm, and then air-dried at a temperature of 60°C to obtain a lithium-ion battery separator.

[0137] Example 6

[0138] This example is substantially the same as Example 5, except that the ceramic powder used is a ceramic powder that has not been subjected to a classification process: boehmite (D50 = 0.52, BET = 7.23).

[0139] Comparative Example 1

[0140] This comparative example is substantially the same as Example 1, except that the ratio of the high-viscosity thickener to the low-viscosity thickener is 1:1.

[0141] Comparative Example 2

[0142] This comparative example is substantially the same as Example 2, except that the ratio of the high-viscosity thickener to the low-viscosity thickener is 11:1.

[0143] Comparative Example 3

[0144] This comparative example is substantially the same as Example 1, except that the high-viscosity thickener is replaced with an equal amount of the low-viscosity thickener.

[0145] Comparative Example 4

[0146] This comparative example is substantially the same as Example 1, except that the low-viscosity thickener is replaced with an equal amount of the high-viscosity thickener.

[0147] Comparative Example 5

[0148] This comparative example is substantially the same as Example 4, except that the amount of the thickener is 670 g of sodium carboxymethyl cellulose having a viscosity of 60 mpa-s, and the amount of the binder is 5 kg.

[0149] Comparative Example 6

[0150] This comparative example is substantially the same as Example 5, except that the amount of the thickener is 500 g of sodium carboxymethyl cellulose having a viscosity of 60 mpa-s, and the amount of the binder is 5 kg.

[0151] Experimental Example 1

[0152] The viscosity of the ceramic slurry prepared in Examples 1-6 and Comparative Examples 1-6, the thickness, air permeability, moisture content, heat shrinkage, peel strength, and puncture strength of the lithium ion battery separator were tested. The obtained ceramic separator was cut to the required width, and assembled with a positive electrode and a negative electrode to form a 25 Ah battery cell; the battery cell was dried in an oven at a drying temperature of 120°C for 5 h, and the lithium ion battery cell was obtained after drying.

[0153] The test methods were thickness (GB / T 6672-2001), air permeability (GB / T 458-2008), puncture strength (GB / T 21302-2007), heat shrinkage (GB / T 12027-2004), tensile strength (GB / T 1040.3-2006), peel strength (GB / T 6283-2008), moisture (using a Karl Fischer moisture meter), and internal resistance (battery internal resistance tester).

[0154] The test results were recorded in Table 1.

[0155] Table 1: Performance test results of each experimental group

[0156]

[0157] As can be seen from the above table, the lithium ion separators prepared in the embodiments of the present application all have low air permeability, low moisture content, low heat shrinkage, high peel strength and puncture strength, and low internal resistance. Comparing Examples 1 and 2 with Comparative Examples 1 and 2, respectively, it can be seen that the performance of the separator prepared in Example 1 is better than that of Comparative Example 1, and the performance of the separator prepared in Example 2 is better than that of Comparative Example 2, indicating that the ratio of the high-viscosity thickening agent and the low-viscosity thickening agent should be within the range claimed in the present application, and that if the ratio exceeds the range, the performance of the separator will decrease in many aspects; comparing Example 1 with Comparative Examples 3 and 4, the performance of Comparative Examples 3 and 4 is significantly worse than that of Example 1, indicating that it is difficult to prepare a separator with good performance using only a high-viscosity thickening agent or a low-viscosity thickening agent, and that the use of a combination of a high-viscosity thickening agent and a low-viscosity thickening agent can achieve significantly better results; comparing Example 4 and 5 with Comparative Examples 5 and 6, respectively, the peel strength and puncture strength of Comparative Examples 5 and 6 are comparable to those of Examples 4 and 5, but the performance of Comparative Examples 5 and 6 is significantly worse than that of Examples 4 and 5 in many other aspects, indicating that the use of a significantly smaller amount of thickening agent and binder in Examples 4 and 5 achieves the same effect as the use of a large amount of thickening agent and binder in the preparation of existing separators, and also achieves the effects of reducing air permeability and moisture content; comparing Example 5 with Example 6, the performance of Example 6 is worse than that of Example 5, indicating that the classification and removal of fine powders from the ceramic powder can improve the performance of the separator.

[0158] Experimental Example 2

[0159] SEM images of the base film before and after coating with the slurry of Example 4, Figure 1 SEM image of the base film, Figure 2 SEM image of the separator prepared after coating the slurry on the surface of the base film. As can be seen from the image, the separator prepared in the application has a large number of pores on the surface and the pores are uniformly distributed.

[0160] In summary, the ceramic slurry provided in the application has a reasonable proportion of high-viscosity thickening agent and low-viscosity thickening agent, so that the total amount of thickening agent used in the application is less than half of the amount of conventional thickening agent (generally 0.2-0.8 wt%) and can achieve equivalent thickening effect. In the prior art, the amount of binder is generally about 2-6 wt%, and the mutual promotion between different types of thickening agents, the cooperation of long and short chains, and the promotion of the binder can reduce the amount of binder to achieve equivalent powder bonding effect. The reduction of the amount of binder and stabilizer can reduce the water absorption of high molecular binder and the blocking of pores after drying, and reduce the moisture and air permeability of the coated separator. Therefore, the separator prepared from the ceramic slurry provided in the application has good performance.

[0161] The above only describes the preferred embodiments of the application and is not intended to limit the application. Those skilled in the art can make various modifications and changes to the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A ceramic slurry, characterized by, By mass percentage, it includes: 40-50% ceramic powder, 1-5% binder, 0.03-1% thickener, and 48.9-58.87% solvent; The thickener comprises a high-viscosity thickener and a low-viscosity thickener in a mass ratio of 1.5 to 9:1; The high-viscosity thickener is selected from at least one of sodium carboxymethyl cellulose, polymethyl methacrylate, methyl hydroxyethyl cellulose, polyethylene oxide, polyurethane, and polyacrylamide with a viscosity value of 3000-5000 mpa·s. The low-viscosity thickener is selected from at least one of sodium carboxymethyl cellulose, polymethyl methacrylate, methyl hydroxyethyl cellulose, polyethylene oxide, polyurethane, and polyacrylamide with a viscosity value of 5 to 100 mPa·s. The viscosity value was obtained by testing in a 1 wt% aqueous solution at 25°C.

2. The slurry of claim 1, wherein, It also includes 0.1-0.5% of a dispersant; said dispersant is selected from at least one of isopropanol, ethylene glycol, methyl ether, diethyl ether, propylene glycol, glycerol, sodium polyacrylate, ammonium polyacrylate, and polyethylene glycol.

3. The slurry of claim 1, wherein, The adhesive is at least one of acrylic polymer, styrene-butadiene rubber, polyvinyl alcohol, acrylonitrile polymer, polyurethane, polystyrene-acrylate and resorcinol formaldehyde resin.

4. The slurry of claim 1, wherein, The ceramic powder has an average particle size of 0.5 to 1.2 μm and a specific surface area of ​​less than 7 m² / g; the ceramic powder is selected from at least one of the following: aluminum oxide, boehmite, silicon dioxide, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, calcium oxide, and magnesium hydroxide.

5. The method for preparing the slurry as described in claim 1, characterized in that, include: Mix all the components contained in the slurry evenly.

6. The preparation method according to claim 5, characterized in that, Methods for uniformly mixing the various components contained in the slurry include: The solvent and the thickener are mixed evenly to obtain a glue solution; The adhesive solution and the ceramic powder are mixed evenly to obtain an aqueous ceramic slurry precursor. The water-based ceramic slurry precursor is mixed evenly with the binder to obtain the water-based ceramic slurry.

7. The preparation method according to claim 6, characterized in that, The solvent and the thickener are mixed evenly as follows: The solvent and the thickener are mixed and stirred at a revolution speed of 10-30 r / m and a dispersion speed of 1000-3000 r / m for 2-5 hours to obtain the adhesive solution; The method for uniformly mixing the adhesive solution and the ceramic powder is as follows: The adhesive and the ceramic powder are mixed at a revolution speed of 10-50 r / m and a dispersion speed of 800-5000 r / m, and stirred for 0.2-1 h to obtain the water-based ceramic slurry precursor. The method for mixing the aqueous ceramic slurry precursor with the binder is as follows: A binder is added to the water-based ceramic slurry precursor, and the mixture is stirred for 0.2 to 1 hour at a revolution speed of 10 to 30 r / m and a dispersion speed of 1000 to 3000 r / m. Then, the mixture is milled in a sand mill at a flow rate of 30 to 150 L / min for 10 to 30 minutes, and then filtered through a 150-mesh gauze to obtain the water-based ceramic slurry.

8. A lithium-ion battery separator, characterized by, A polyolefin-based membrane including a ceramic layer adhered to a surface of the polyolefin-based membrane, the ceramic layer being formed by coating a slurry as claimed in any one of claims 1 to 4 or a slurry prepared by the method as claimed in any one of claims 5 to 7 on the surface of the polyolefin-based membrane and removing the thickening agent and the binder by heat treatment.

9. A method of producing a lithium ion battery separator, characterized by, A method of preparing a polyolefin-based membrane including coating a slurry as claimed in any one of claims 1 to 4 or a slurry prepared by the method as claimed in any one of claims 5 to 7 on a surface of a polyolefin-based membrane and removing the thickening agent and the binder by heat treatment.

10. A lithium-ion battery, characterized by, A lithium ion battery separator including the lithium ion battery separator as claimed in claim 8 or a lithium ion battery separator prepared by the method as claimed in claim 9.

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