A high-temperature-resistant lithium ion battery coating diaphragm and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion battery separators, and discloses a high-temperature-resistant lithium ion battery coating separator and a preparation method thereof; the preparation method of the separator comprises the following operation steps: preparing high-temperature-resistant coating lithium ion battery paint by using an alumina-based waterborne PVDF, a leveling agent and a binder; coating the high-temperature-resistant coating lithium ion battery paint on two sides of a pretreated polyolefin-based film, and drying to obtain the separator; in the scheme, the waterborne PVDF is introduced with vinyl-alumina as a reinforcing phase, and modified carboxymethyl cellulose and butadiene-styrene rubber latex are used as binders, so that the high-temperature resistance and ion conductivity of the separator are effectively improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery separator membranes, in particular to a high-temperature-resistant lithium ion battery coating separator and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in new energy vehicles, energy storage and other fields due to their high energy density and long cycle life. However, the performance of the core component separator directly determines the safety and stability of the battery. Traditional polyolefin-based separators (such as polyethylene and polypropylene) have good ion permeability, but poor thermal stability. When the battery is heated or abnormally short-circuited during charging and discharging, high-temperature shrinkage or even melting of the separator may occur, leading to direct contact between the positive and negative electrodes and causing thermal runaway, which seriously restricts the safe application of the battery.

[0003] To solve this problem, researchers coat a high-temperature-resistant coating (such as ceramic or high-temperature-resistant resin) on the surface of the polyolefin-based membrane to improve the thermal stability of the separator. However, if the high-temperature-resistant filler is not uniformly dispersed or is added in excess, it may block the ion transmission channel, affecting the ion conductivity and high-temperature resistance.

[0004] In view of the above, it is of great significance to prepare a high-temperature-resistant lithium ion battery coating separator and a preparation method thereof. SUMMARY

[0005] The purpose of the present application is to provide a high-temperature-resistant lithium ion battery coating separator and a preparation method thereof to solve the problems in the prior art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] A preparation method of a high-temperature-resistant lithium ion battery coating separator, comprising the following operation steps:

[0008] Step 1: uniformly mix aluminum oxide-based waterborne PVDF, leveling agent and adhesive into deionized water to obtain high-temperature-resistant coating lithium ion battery coating;

[0009] Step 2: after pretreatment of the polyolefin-based membrane, coat the high-temperature-resistant coating lithium ion battery coating on both sides, dry and form a high-temperature-resistant coating to obtain the separator.

[0010] More preferably, the raw materials of the high-temperature-resistant coating include the following components: 15-25 parts of aluminum oxide-based waterborne PVDF, 0.2-0.4 parts of leveling agent, 4-6 parts of adhesive and 67-82 parts of deionized water by mass fraction; the adhesive includes modified carboxymethyl cellulose and styrene-butadiene latex in a mass ratio of 2:(0.5-0.7).

[0011] More preferably, the thickness of the high-temperature-resistant coating is 2-5 microns, and the thickness of the separator is 25-40 microns.

[0012] More preferably, the preparation method of the alumina-based waterborne PVDF is as follows: under the protection of nitrogen, a multi-fluoroalkyl amine oxide surfactant is added to deionized water and uniformly mixed, and then added to 90-95℃; then pentafluoroethylene and hexafluoropropylene are added and uniformly mixed; then ammonium persulfate aqueous solution is added; stirring is performed for 5-6 hours; unreacted monomers are discharged; the temperature is lowered to 70-75℃; then sodium dodecyl sulfate is added and uniformly mixed; then vinyl-alumina, glycidyl methacrylate, and hydroxypropyl acrylate are added and uniformly mixed; then ammonium persulfate aqueous solution and dodecanethiol are added; stirring is performed for 2-3 hours; the temperature is raised to 80-85℃; stirring is performed for 30-40 minutes; and then filtration, washing, and drying are performed; and the alumina-based waterborne PVDF is obtained.

[0013] More preferably, the raw materials of the alumina-based waterborne PVDF include the following components: 1.7-3 parts of multi-fluoroalkyl amine oxide surfactant, 20-30 parts of pentafluoroethylene, 6-10 parts of hexafluoropropylene, 1.5-3 parts of ammonium persulfate aqueous solution, 0.8-1.2 parts of sodium dodecyl sulfate, 6-8 parts of vinyl-alumina, 1-3 parts of glycidyl methacrylate, 1-2 parts of hydroxypropyl acrylate, 0.12-0.15 parts of dodecanethiol, and 100 parts of deionized water; and the concentration of the ammonium persulfate aqueous solution is 2-3wt%.

[0014] In the scheme, the preparation method of the vinyl-alumina is as follows: 3-acryloyloxypropyltrimethoxysilane is added to a toluene aqueous solution (the toluene content is 20wt%) to prepare a mixed solution with a concentration of 2.7mmol / L; alumina is ultrasonically dispersed in toluene; and then stirring is performed at 110℃ for 2 hours to obtain the vinyl-alumina.

[0015] More preferably, the preparation method of the modified carboxymethyl cellulose is as follows: (1) p-hydroxybenzoic acid and carboxymethyl cellulose are respectively added to a MES buffer solution containing NHS and EDC to obtain mixed solution A and mixed solution B; amino-alumina oxide is ultrasonically dispersed in the MES buffer solution, mixed solution B is added, stirring is performed for 8-10 hours, mixed solution A is further added and stirring is performed for 8-10 hours, dialysis, freeze-drying, and then hydroxybenzene-alumina oxide / carboxymethyl cellulose is obtained; (2) the hydroxybenzene-alumina oxide / carboxymethyl cellulose is ultrasonically dispersed in anhydrous tetrahydrofuran, freeze-cycled for 3-4 times, defrosted after nitrogen is introduced, phosphorus oxychloride and triethylamine are added and uniformly mixed, stirring is performed at 65-70℃ for 5-6 hours, and then washing and drying are performed to obtain the modified carboxymethyl cellulose.

[0016] More preferably, the raw material of the hydroxybenzene-aluminum oxide / carboxymethyl cellulose comprises the following components: 0.6-0.8 parts of p-hydroxybenzoic acid, 0.8-1.5 parts of carboxymethyl cellulose, 2-3 parts of aminated-aluminum oxide, 0.2-0.3 parts of NHS, 0.35-0.5 parts of EDC, and 30-50 parts of MES buffer solution; and the raw material of the modified carboxymethyl cellulose comprises the following components: 3-4 parts of hydroxybenzene-aluminum oxide / carboxymethyl cellulose, 1.2-1.5 parts of phosphorus oxychloride, 1.5-2 parts of triethylamine, and 30-40 parts of anhydrous tetrahydrofuran.

[0017] In the scheme, the preparation method of the aminated-aluminum oxide is as follows: γ-aminopropyltriethoxysilane is added into a toluene aqueous solution (20 wt% of toluene) to prepare a mixed solution with a concentration of 2.7 mmol / L; and the aluminum oxide is ultrasonically dispersed in toluene and stirred at 110℃ for 2 hours to obtain the aminated-aluminum oxide.

[0018] The concentration of the MES buffer solution is 50 mM, and the pH value is 6.0, which is adjusted by 1 mol / L sodium hydroxide solution.

[0019] More preferably, the process conditions of the polyolefin-based membrane pretreatment are as follows: the polyolefin-based membrane is immersed in a buffer solution containing tannic acid and heated at 50-60℃ for 2-3 hours; and the pretreated polyolefin-based membrane is obtained after being taken out and dried; in the buffer solution, 100-120 mM bis-Tris buffer solution and 600-620 mM NaCl aqueous solution are contained, the concentration of tannic acid is 1-2 mg / mL, and the pH value of the buffer solution is 7.0-7.5.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] In the scheme, the deionized water is uniformly mixed with the aluminum oxide-based waterborne PVDF, the leveling agent and the binder to obtain the high-temperature-resistant coating for lithium ion batteries; and then the coating is coated on the pretreated polyolefin-based membrane to obtain the separator after drying.

[0022] In the scheme, the polyfluoroalkyl amine oxide surfactant as the emulsifier can reduce the surface tension of water, form a stable emulsion system and ensure that the polymerization reaction is carried out in a uniform environment; the vinylidene fluoride and hexafluoropropylene are monomers for preparing polyvinylidene fluoride (PVDF) and its copolymer; the vinylidene fluoride has a carbon-fluorine structure and provides a high-temperature-resistant molecular backbone skeleton, thereby ensuring the structural stability of PVDF at high temperature; the introduction of hexafluoropropylene can reduce the close packing between macromolecular chains and avoid the brittle cracking of the coating due to the excessive rigidity of the crystalline region at high temperature, thereby balancing the high-temperature resistance and mechanical toughness; by adjusting the ratio of vinylidene fluoride to hexafluoropropylene, both the heat resistance and sufficient channels for ion transmission can be ensured.

[0023] As a chain transfer agent, dodecanethiol controls the molecular weight distribution by terminating the growing molecular chain, avoiding local overheating degradation at high temperature due to too large molecular weight difference; uniform molecular chain structure can form a more stable heat-resistant network, improving the overall high temperature resistance consistency of the coating.

[0024] In order to improve the high temperature resistance of PVDF, vinyl groups are introduced on the surface of alumina as inorganic reinforcing phase of PVDF. The interaction between alumina and the chain segment in modified PVDF forms crosslinking points, which limits the chain segment slip at high temperature, significantly improving the heat distortion temperature of the coating. Excessive amount of vinyl-alumina will increase the brittleness of the coating after curing, which will reduce the adhesion of the coating, thereby affecting the performance of the separator. The polar groups on glycidyl methacrylate and hydroxypropyl acrylate can enhance the affinity of the coating to the polar electrolyte, improve the wettability and retention capacity of the electrolyte, and form a weak coordination between the polar groups and lithium ions to accelerate ion migration. Through polarity regulation and network structure, the electrolyte compatibility and ion migration efficiency are improved.

[0025] In the scheme, the alumina-based waterborne PVDF only improves the high temperature resistance of the separator to a limited extent. However, carboxymethyl cellulose and styrene-butadiene latex are used as adhesives, and their high temperature resistance performance is poor, which will reduce the high temperature resistance of the separator. In order to solve the above problems, in the scheme, the amino group on the alumina and the carboxyl group on the carboxymethyl cellulose are first reacted, introducing the amino-alumina on the surface of the carboxymethyl cellulose, and then the remaining amino group on the amino-alumina and the carboxyl group on the p-hydroxybenzoic acid are reacted to obtain hydroxybenzoic acid-alumina / carboxymethyl cellulose. It can effectively improve the high temperature resistance of the adhesive. After phosphorylation modification, modified carboxymethyl cellulose is obtained. The amino-alumina and phosphorylation modification can synergistically improve the high temperature resistance of the modified carboxymethyl cellulose. The introduction of styrene-butadiene latex can reduce the brittleness of the modified carboxymethyl cellulose, and balance the improvement of the performance of the separator.

[0026] The polar groups on the molecular chain of the modified carboxymethyl cellulose can form hydrogen bonds or electrostatic interactions with active groups such as fluorocarbon chains of alumina-based waterborne PVDF, forming a continuous network, and styrene-butadiene latex can further improve the adhesion; after phosphorylation modification, the modified methyl cellulose improves the swelling resistance to electrolyte; and the groups reacted with the surface of the polyolefin-based film can be anchored on the surface of the base film through strong chemical bond absorption; the chemical stability of styrene-butadiene latex itself is excellent, and the combination of the two can avoid the dissolution or swelling of the adhesive in the electrolyte, improve the stability of the coating structure, and thus improve the high temperature resistance and ion conductivity of the separator. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0028] In the following specific embodiments, parts are mass parts. In the present embodiment, it should be noted that there is no special restriction on the purchase manufacturer of all raw materials involved in the present application, which exemplarily includes: the CAS number of vinylidene fluoride is 75-38-7; the CAS number of hexafluoropropene is 116-15-4; the CAS number of sodium dodecyl sulfate is 151-21-3; the CAS number of glycidyl methacrylate is 106-91-2; the CAS number of hydroxypropyl acrylate is 25584-83-2; the CAS number of dodecanethiol is 112-55-0; the CAS number of p-hydroxybenzoic acid is 99-96-7; carboxymethyl cellulose is food grade; the CAS number of NHS (N-hydroxysuccinimide) is 6066-82-6; the CAS number of EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) is 1378759-90-0; the CAS number of phosphorus oxychloride is 10025-87-3; the CAS number of triethylamine is 121-44-8; the cargo number of butylphenyl latex is 0231; the leveling agent is BYK-348.

[0029] Example 1, a preparation method of a high-temperature-resistant lithium ion battery coating separator, comprising the following operation steps:

[0030] Preparation: the preparation method of the alumina-based waterborne PVDF is as follows: under the protection of nitrogen, 2 parts of polyfluoroalkyl amine surfactant are added into 100 parts of deionized water for uniform mixing, heated to 90℃, 25 parts of vinylidene fluoride and 6 parts of hexafluoropropene are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution (concentration of 2wt%) are added, stirred for 5 hours, the unreacted monomers are discharged, cooled to 70℃, 0.8 parts of sodium dodecyl sulfate are uniformly mixed, 7 parts of vinyl-alumina, 2 parts of glycidyl methacrylate and 2 parts of hydroxypropyl acrylate are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution and 0.12 parts of dodecanethiol are added, stirred for 2 hours, heated to 80℃, stirred for 35 minutes, filtered, washed and dried; to obtain the alumina-based waterborne PVDF;

[0031] The preparation method of the modified carboxymethyl cellulose is as follows: (1) 1.2 parts of p-hydroxybenzoic acid and 0.4 parts of carboxymethyl cellulose are respectively added into 20 parts of MES buffer containing 0.15 parts of NHS and 0.2 parts of EDC to obtain mixed solution A and mixed solution B; 3 parts of aminooxidized aluminum is ultrasonically dispersed in 10 parts of MES buffer, mixed solution B is added, stirring is carried out for 8 hours, mixed solution A is continuously added and stirring is carried out for 8 hours, dialysis, freeze-drying are carried out, and hydroxybenzene-aluminum oxide / carboxymethyl cellulose is obtained; (2) 3 parts of hydroxybenzene-aluminum oxide / carboxymethyl cellulose is ultrasonically dispersed in 30 parts of anhydrous tetrahydrofuran, freeze-cycling is carried out for 3 times, nitrogen is introduced after thawing, 1.2 parts of phosphorus oxychloride and 2 parts of triethylamine are uniformly mixed, stirring is carried out at 70°C for 5 hours, washing and drying are carried out, and the modified carboxymethyl cellulose is obtained;

[0032] Step 1: 15 parts of alumina-based waterborne PVDF, 0.2 parts of leveling agent (BYK-348), and 4 parts of adhesive are uniformly mixed in 67 parts of deionized water to obtain the high-temperature-resistant coating lithium ion battery coating; the adhesive comprises modified carboxymethyl cellulose and butadiene-styrene latex at a mass ratio of 2:0.5;

[0033] Step 2: The polypropylene-based film (polyolefin-based film) is immersed in a buffer solution containing tannic acid (in the buffer solution, 100 mM bis-Tris buffer and 600 mM NaCl aqueous solution are contained, the concentration of tannic acid is 1.5 mg / mL, and the pH value of the buffer solution is 7.0), heated at 50°C for 2 hours, taken out and dried, and the high-temperature-resistant coating lithium ion battery coating is coated on both sides of the film, dried, and a high-temperature-resistant coating layer (with a single-side thickness of 2 µm) is formed to obtain a 36 µm separator.

[0034] Embodiment 2, a preparation method of a high-temperature-resistant lithium ion battery coating separator, comprising the following operation steps:

[0035] Preparation: the preparation method of the alumina-based waterborne PVDF is as follows: under the protection of nitrogen, 2 parts of polyfluoroalkyl amine oxide surfactant is uniformly mixed in 100 parts of deionized water, heated to 90°C, 25 parts of vinylidene fluoride and 6 parts of hexafluoropropylene are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution (with a concentration of 2 wt%) is added, stirring is carried out for 5 hours, unreacted monomers are discharged, the temperature is lowered to 70°C, 0.8 parts of sodium dodecyl sulfate is uniformly mixed, 7 parts of vinyl-aluminum oxide, 2 glycidyl methacrylate and 2 hydroxypropyl acrylate are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution and 0.12 parts of dodecanethiol are added, stirring is carried out for 2 hours, the temperature is raised to 80°C, stirring is carried out for 35 minutes, and filtration, washing and drying are carried out; and the alumina-based waterborne PVDF is obtained;

[0036] The preparation method of the modified carboxymethyl cellulose is as follows: (1) 1.2 parts of p-hydroxybenzoic acid and 0.4 parts of carboxymethyl cellulose are respectively added into 20 parts of MES buffer containing 0.15 parts of NHS and 0.2 parts of EDC to obtain mixed solution A and mixed solution B; 3 parts of aminooxidized aluminum is ultrasonically dispersed in 10 parts of MES buffer, mixed solution B is added, stirring is carried out for 8 hours, mixed solution A is continuously added and stirring is carried out for 8 hours, dialysis, freeze-drying are carried out, and hydroxybenzene-aluminum oxide / carboxymethyl cellulose is obtained; (2) 3 parts of hydroxybenzene-aluminum oxide / carboxymethyl cellulose is ultrasonically dispersed in 30 parts of anhydrous tetrahydrofuran, freeze-cycling is carried out for 3 times, nitrogen is introduced after thawing, 1.2 parts of phosphorus oxychloride and 2 parts of triethylamine are uniformly mixed, stirring is carried out at 70°C for 5 hours, washing and drying are carried out, and the modified carboxymethyl cellulose is obtained;

[0037] Step 1: 20 parts of aluminum oxide-based waterborne PVDF, 0.2 parts of a leveling agent, 4 parts of an adhesive are added into 67 parts of deionized water and uniformly mixed to obtain the high-temperature-resistant coating lithium ion battery coating; the adhesive comprises modified carboxymethyl cellulose and butadiene-styrene latex at a mass ratio of 2:0.5;

[0038] Step 2: A polypropylene-based film (polyolefin-based film) is immersed in a buffer solution containing tannic acid (in the buffer solution, 100 mM bis-Tris buffer and 600 mM NaCl aqueous solution are contained, the concentration of tannic acid is 1.5 mg / mL, and the pH value of the buffer solution is 7.0), heated at 50°C for 2 hours, taken out and dried, and the high-temperature-resistant coating lithium ion battery coating is coated on both sides of the film, dried, and a high-temperature-resistant coating layer (with a single-side thickness of 2 µm) is formed to obtain a 36 µm separator.

[0039] Embodiment 3, a preparation method of a high-temperature-resistant lithium ion battery coating separator, the separator comprising the following operation steps:

[0040] Preparation: the preparation method of the aluminum oxide-based waterborne PVDF is as follows: under the protection of nitrogen, 2 parts of a polyfluoroalkyl amine oxide surfactant is added into 100 parts of deionized water and uniformly mixed, heated to 90°C, 25 parts of vinylidene fluoride and 6 parts of hexafluoropropylene are uniformly mixed, 1.5 parts of an ammonium persulfate aqueous solution (with a concentration of 2 wt%) is added, stirring is carried out for 5 hours, unreacted monomers are discharged, the temperature is lowered to 70°C, 0.8 parts of sodium dodecyl sulfate is uniformly mixed, 7 parts of vinyl-aluminum oxide, 2 glycidyl methacrylate and 2 hydroxypropyl acrylate are uniformly mixed, 1.5 parts of an ammonium persulfate aqueous solution and 0.12 parts of dodecanethiol are added, stirring is carried out for 2 hours, the temperature is raised to 80°C, and stirring is carried out for 35 minutes; filtration, washing and drying are carried out; and the aluminum oxide-based waterborne PVDF is obtained;

[0041] The preparation method of the modified carboxymethyl cellulose is as follows: (1) 1.2 parts of p-hydroxybenzoic acid and 0.4 parts of carboxymethyl cellulose are respectively added into 20 parts of MES buffer containing 0.15 parts of NHS and 0.2 parts of EDC to obtain mixed solution A and mixed solution B; 3 parts of aminooxy-aluminum oxide is ultrasonically dispersed in 10 parts of MES buffer, mixed solution B is added, stirring is carried out for 8 hours, mixed solution A is continuously added and stirring is carried out for 8 hours, dialysis, freeze-drying are carried out, and hydroxybenzene-aluminum oxide / carboxymethyl cellulose is obtained; (2) 3 parts of hydroxybenzene-aluminum oxide / carboxymethyl cellulose is ultrasonically dispersed in 30 parts of anhydrous tetrahydrofuran, freeze-cycling is carried out for 3 times, nitrogen is introduced after thawing, 1.2 parts of phosphorus oxychloride and 2 parts of triethylamine are uniformly mixed, stirring is carried out at 70 DEG C for 5 hours, washing and drying are carried out, and the modified carboxymethyl cellulose is obtained.

[0042] Step 1: 25 parts of aluminum oxide-based waterborne PVDF, 0.3 parts of a leveling agent, and 5 parts of an adhesive are uniformly mixed in 80 parts of deionized water to obtain the high-temperature-resistant coating lithium ion battery coating; the adhesive comprises modified carboxymethyl cellulose and butadiene-styrene latex at a mass ratio of 2:0.6.

[0043] Step 2: A polypropylene-based film (polyolefin-based film) is immersed in a buffer solution containing tannic acid (in the buffer solution, 100 mM bis-Tris buffer and 600 mM NaCl aqueous solution are contained, the concentration of tannic acid is 1.5 mg / mL, and the pH value of the buffer solution is 7.0), heated at 50 DEG C for 2 hours, taken out and dried, coated with the high-temperature-resistant coating lithium ion battery coating on both sides, dried, and a high-temperature-resistant coating layer (the single-side thickness is 2 µm) is formed to obtain a 36 µm separator.

[0044] Comparative Example 1 is based on Example 3, and no vinyl-aluminum oxide is introduced into the aluminum oxide-based waterborne PVDF; the remaining operation steps are unchanged.

[0045] The preparation method of the aluminum oxide-based waterborne PVDF is as follows: under the protection of nitrogen, 2 parts of a polyfluoroalkyl amine oxide surfactant is uniformly mixed in 100 parts of deionized water, heated to 90 DEG C, 25 parts of vinylidene fluoride and 6 parts of hexafluoropropylene are uniformly mixed, 1.5 parts of an ammonium persulfate aqueous solution (the concentration is 2 wt%) is added, stirring is carried out for 5 hours, unreacted monomers are discharged, the temperature is lowered to 70 DEG C, 0.8 parts of sodium dodecyl sulfate is uniformly mixed, 2 parts of glycidyl methacrylate and 2 parts of hydroxypropyl acrylate are uniformly mixed, 1.5 parts of an ammonium persulfate aqueous solution and 0.12 parts of dodecanethiol are added, stirring is carried out for 2 hours, the temperature is raised to 80 DEG C, stirring is carried out for 35 minutes, filtration, washing and drying are carried out, and the aluminum oxide-based waterborne PVDF is obtained.

[0046] Comparative Example 2 is based on Example 3, and the addition amount of the vinyl-aluminum oxide introduced into the aluminum oxide-based waterborne PVDF is increased to 15 parts; the remaining operation steps are unchanged.

[0047] The preparation method of the alumina-based waterborne PVDF is: under the protection of nitrogen, 2 parts of polyfluoroalkyl amine oxide surfactant are added to 100 parts of deionized water for uniform mixing, heated to 90°C, 25 parts of vinylidene fluoride and 6 parts of hexafluoropropylene are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution (concentration of 2wt%) is added, stirred for 5 hours, the unreacted monomers are discharged, cooled to 70°C, 0.8 parts of sodium dodecyl sulfate is uniformly mixed, 15 parts of vinyl-alumina, 2 glycidyl methacrylate, 2 hydroxypropyl acrylate are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution, 0.12 parts of dodecanethiol are added, stirred for 2 hours, heated to 80°C, stirred for 35 minutes, filtered, washed and dried; to obtain alumina-based waterborne PVDF.

[0048] Comparative Example 3 is based on Example 3, without modification of carboxymethyl cellulose; the remaining operation steps are unchanged;

[0049] Step 1: 25 parts of alumina-based waterborne PVDF, 0.3 parts of leveling agent, 5 parts of adhesive are added to 80 parts of deionized water for uniform mixing to obtain a high-temperature-resistant coating lithium ion battery coating; the adhesive includes carboxymethyl cellulose: styrene-butadiene latex with a mass ratio of 2:0.6;

[0050] Step 2: The polypropylene-based film (polyolefin-based film) is immersed in a buffer solution containing tannic acid (the buffer solution contains 100mM bis-Tris buffer and 600mM NaCl aqueous solution, the concentration of tannic acid is 1.5mg / mL, and the pH value of the buffer solution is 7.0), heated at 50°C for 2 hours, taken out and dried, coated with a high-temperature-resistant coating lithium ion battery coating on both sides, dried to form a high-temperature-resistant coating layer (the single-sided thickness is 2µm), and a 36µm separator is obtained.

[0051] Comparative Example 4 is based on Example 3, and nano-alumina is directly added to the high-temperature-resistant coating lithium ion battery coating for mixing;

[0052] Preparation: the preparation method of the waterborne PVDF is: under the protection of nitrogen, 2 parts of polyfluoroalkyl amine oxide surfactant are added to 100 parts of deionized water for uniform mixing, heated to 90°C, 25 parts of vinylidene fluoride and 6 parts of hexafluoropropylene are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution (concentration of 2wt%) is added, stirred for 5 hours, the unreacted monomers are discharged, cooled to 70°C, 0.8 parts of sodium dodecyl sulfate is uniformly mixed, 2 glycidyl methacrylate, 2 hydroxypropyl acrylate are uniformly mixed, 1.5 parts of ammonium persulfate aqueous solution, 0.12 parts of dodecanethiol are added, stirred for 2 hours, heated to 80°C, stirred for 35 minutes, to obtain waterborne PVDF;

[0053] The preparation method of the modified carboxymethyl cellulose is as follows: (1) 1.2 parts of carboxymethyl cellulose is added to 20 parts of MES buffer containing 0.15 parts of NHS and 0.2 parts of EDC, and the mixture B; 3 parts of 3-aminophenol is added to the MES buffer, and the mixture B is added, stirred for 10 hours, dialyzed, and freeze-dried to obtain hydroxybenzene-carboxymethyl cellulose; (2) 3 parts of hydroxybenzene-carboxymethyl cellulose is ultrasonically dispersed in 30 parts of anhydrous tetrahydrofuran, and freeze-cycled for 3 times, and after thawing under nitrogen, 1.2 parts of phosphorus oxychloride and 2 parts of triethylamine are added and uniformly mixed, and stirred at 70°C for 5 hours, and washed and dried to obtain the modified carboxymethyl cellulose;

[0054] Step 1: 0.3 parts of a leveling agent is added to 80 parts of deionized water, 10 parts of nano-aluminum oxide is ultrasonically mixed, 25 parts of water-based PVDF and 5 parts of a binder are uniformly mixed to obtain a high-temperature-resistant coating lithium ion battery coating; the binder comprises modified carboxymethyl cellulose and butadiene-styrene latex in a mass ratio of 2:0.6;

[0055] Step 2: The polypropylene-based film is immersed in a buffer solution containing tannic acid (in the buffer solution, 100 mM bis-Tris buffer and 600 mM NaCl aqueous solution are contained, the concentration of tannic acid is 1.5 mg / mL, and the pH value of the buffer solution is 7.0), heated at 50°C for 2 hours, taken out and dried, coated with a high-temperature-resistant coating lithium ion battery coating on both sides, dried to form a high-temperature-resistant coating layer (the single-sided thickness is 2 µm), and a 36 µm separator is obtained.

[0056] Detection experiment; the ion conductivity of Examples 1-3 and Comparative Examples 1-4 is detected; and the thermal shrinkage rate of Examples 1-3 and Comparative Examples 1-4 treated at 200°C for 2 hours is detected;

[0057]

[0058] Conclusion: Comparative Example 1 is based on Example 3, without introducing vinyl-alumina in the alumina-based aqueous PVDF; leading to the heat resistance of the alumina-based aqueous PVDF and the performance of the separator to decrease; Comparative Example 2 is based on Example 3, increasing the addition amount of vinyl-alumina in the alumina-based aqueous PVDF to 15 parts; the coating compactness is too high, the migration resistance is large; and the brittleness of the high-temperature resistant coating is increased, which is easy to form gaps, which will increase the difficulty of lithium ions from the electrode to pass through the separator into the other side electrode, the continuity of ion transport is destroyed, thereby reducing the ion conductivity; Comparative Example 3 is based on Example 3, without modifying carboxymethyl cellulose; thus leading to the performance of the separator to decrease; without modifying carboxymethyl cellulose, it also better absorbs electrolyte, so the influence on ion conductivity is small; but the thermal shrinkage rate is reduced, because the introduction of aminated-alumina and phosphorylated modification can synergistically improve the high-temperature resistance of the modified carboxymethyl cellulose; Comparative Example 4 is based on Example 3, directly mixing nano-alumina with the slurry; leading to the poor compatibility of the alumina surface with the electrolyte, reducing the electrolyte wettability, and easy to agglomerate and block the pores, thus the performance of the separator decreases.

[0059] It will be obvious to a person skilled in the art that the application is not limited to the details of the above-described exemplary embodiments, but that the application can be implemented in other concrete forms without departing from the spirit or essential characteristics of the application. The embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein.

Claims

1. A method for preparing a high-temperature resistant lithium-ion battery coated separator, characterized in that: The following steps are included: Step 1: By weight, add 15-25 parts of alumina-based waterborne PVDF, 0.2-0.4 parts of leveling agent, and 4-6 parts of binder to 67-82 parts of deionized water and mix evenly to obtain a high-temperature resistant coating for lithium-ion batteries. Step 2: After pretreatment of the polyolefin-based membrane, high-temperature resistant lithium-ion battery coating is applied to both sides and dried to form a high-temperature resistant coating, thus obtaining the separator; The adhesive comprises modified carboxymethyl cellulose and styrene-butadiene latex in a mass ratio of 2:(0.5~0.7); The preparation method of the alumina-based aqueous PVDF is as follows: Under nitrogen protection, 1.7-3 parts by mass of a polyfluoroalkylamine oxide surfactant are added to 100 parts of deionized water and mixed evenly. The mixture is heated to 90-95°C, then 20-30 parts of vinylidene fluoride and 6-10 parts of hexafluoropropylene are added and mixed evenly. 1.5-3 parts of ammonium persulfate aqueous solution are added and stirred for 5-6 hours. Unreacted monomers are removed, and the temperature is lowered to 70-75°C. 0.8-1.2 parts of sodium dodecyl sulfate are added and mixed evenly. 6-8 parts of vinyl-alumina, 1-3 parts of glycidyl methacrylate, and 1-2 parts of hydroxypropyl acrylate are added and mixed evenly. Ammonium persulfate aqueous solution and 0.12-0.15 parts of dodecanethiol are added and stirred for 2-3 hours. The temperature is raised to 80-85°C and stirred for 30-40 minutes. The mixture is then filtered, washed, and dried to obtain the alumina-based aqueous PVDF. The concentration of the ammonium persulfate aqueous solution is 2-3 wt%. The modified carboxymethyl cellulose is prepared as follows: (1) 0.6-0.8 parts of p-hydroxybenzoic acid and 0.8-1.5 parts of carboxymethyl cellulose are added to 30-50 parts of MES buffer containing 0.2-0.3 parts of NHS and 0.35-0.5 parts of EDC, respectively, to obtain mixture A and mixture B; 2-3 parts of aminated alumina are ultrasonically dispersed in MES buffer, mixture B is added, and the mixture is stirred for 8-10 hours. (1) Continue stirring the mixture A for 8-10 hours, dialyze, freeze dry to obtain hydroxybenzene-alumina / carboxymethyl cellulose; (2) Disperse 3-4 parts of hydroxybenzene-alumina / carboxymethyl cellulose ultrasonically in 30-40 parts of anhydrous tetrahydrofuran, freeze cycle 3-4 times, thaw by passing nitrogen gas, add 1.2-1.5 parts of phosphorus oxychloride and 1.5-2 parts of triethylamine and mix evenly, stir at 65-70℃ for 5-6 hours, wash and dry to obtain modified carboxymethyl cellulose.

2. The method for preparing a high-temperature resistant lithium-ion battery coated separator according to claim 1, characterized in that: The thickness of the high-temperature resistant coating is 2~5µm; the thickness of the diaphragm is 25~40µm.

3. The method for preparing a high-temperature resistant lithium-ion battery coating separator according to claim 1, characterized in that: The pretreatment process conditions for the polyolefin-based membrane are as follows: the polyolefin-based membrane is immersed in a buffer solution containing tannic acid and heated at 50-60°C for 2-3 hours; it is then removed and dried to obtain the pretreated polyolefin-based membrane. The buffer solution contains 100-120 mM bis-Tris buffer and 600-620 mM NaCl aqueous solution, the concentration of tannic acid is 1-2 mg / mL, and the pH value of the buffer solution is 7.0-7.

5.

4. The separator prepared by the method for preparing a high-temperature resistant lithium-ion battery coated separator according to any one of claims 1 to 3.

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