A composite coated diaphragm for lithium ion battery and preparation method thereof

Abstract

The present invention relates to the technical field of battery separators, and specifically to a composite coated separator for lithium-ion batteries and a preparation method thereof. The preparation method comprises: coating an aramid polymer slurry on a base film, forming the aramid polymer slurry through a coagulation bath, and drying the aramid coated separator intermediate; the aramid polymer slurry comprises a cross-linked aramid polymer solution, a porogen, and a cosolvent; the cross-linked aramid polymer in the cross-linked aramid polymer solution has a weight-average molecular weight of 15-30W; coating the surface of the aramid coated separator intermediate with a TiO2 treatment solution, and finally drying the aramid coated separator intermediate; the TiO2 treatment solution comprises a TiO2 sol and an aqueous adhesive. The composite coated separator has higher heat resistance, higher film rupture temperature, higher puncture strength, and lower water absorption; and exhibits better electrochemical and safety performance after battery assembly.

Description

Technical Field

[0001] The invention relates to a composite coating diaphragm for lithium ion batteries and a preparation method thereof, belonging to the technical field of battery diaphragms. Background Art

[0002] Lithium-ion battery separators are porous, electrically insulating films. As a crucial component of lithium batteries, their primary function is to separate the positive and negative plates, preventing internal short circuits. The separators contain nanoscale pores that enable rapid lithium ion transport between the positive and negative electrodes during electrochemical charge and discharge, making them a key determinant of battery capacity, cycle life, and safety.

[0003] As applications become increasingly widespread and in-depth, the market demand for lithium-ion batteries is developing towards high capacity, fast charging and discharging, long battery life and a wide temperature range. However, high-intensity continuous operation may cause the battery to be in a high temperature state for a long time, so the market has put forward higher requirements on its temperature resistance.

[0004] In recent years, aramid-coated separators have become a new lithium battery separator solution, and many separator manufacturers are pinning their hopes on aramid materials for high-temperature-resistant coated separators. Chinese patent application CN110444714A discloses a ceramic aramid-coated separator for lithium-ion batteries and its preparation method. However, due to limitations of the aramid material itself, its heat resistance (heat shrinkage) at 150°C only reaches 10%, failing to meet requirements for higher temperature resistance. Other aramid-coated separators have also failed to achieve higher temperature resistance levels. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a composite coated diaphragm for lithium-ion batteries and a preparation method thereof, which solves the problems of poor heat shrinkage of the coated diaphragm (the diaphragm shrinks and deforms severely at a high temperature of 180°C), uneven coating, insufficient composite force between coatings, and easy peeling of the coating.

[0006] The present invention solves the above technical problems by providing a technical solution as follows: a method for preparing a composite coated diaphragm for a lithium ion battery, the preparation method comprising:

[0007] S1. Preparation of aramid coated diaphragm intermediate:

[0008] Aramid polymer slurry is coated on the base membrane, and subjected to coagulation bath molding and drying treatment to obtain an aramid coated diaphragm intermediate; the aramid polymer slurry includes a cross-linked aramid polymer solution, a porogen and a cosolvent;

[0009] The cross-linked aramid polymer solution is prepared by cross-linking a meta-aramid polymer solution with an isocyanate inducer, and the weight average molecular weight of the cross-linked aramid polymer in the cross-linked aramid polymer solution is 15-30W;

[0010] S2. Preparation of composite coated diaphragm:

[0011] A TiO2 treatment liquid is coated on the surface of the aramid coated diaphragm intermediate, and finally a drying treatment is performed to obtain a composite coated diaphragm; the TiO2 treatment liquid includes TiO2 sol and water-based adhesive.

[0012] Furthermore, the cross-linked polymer in the cross-linked aramid polymer solution is selected from the following chemical formula:

[0013] 、 ;

[0014] R is selected from any one of the following structures: ;

[0015] 0≤n≤150, 80≤x≤150, 80≤m≤150.

[0016] Furthermore, the porogen is any one of polyethylene glycol, polyvinyl alcohol, and polyvinyl pyrrolidone;

[0017] The cosolvent is any one of calcium chloride and lithium chloride;

[0018] The isocyanate inducer is at least one of 2,4- / 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, and triphenylmethane triisocyanate.

[0019] Furthermore, in step S1, the mass ratio of the cross-linked aramid polymer solution to the porogen and the cosolvent is (80-89): (5-8): (6-12);

[0020] The solid content of the cross-linked aramid polymer solution is 5%-15%.

[0021] Furthermore, in step S1, the coagulation bath is a DMAC aqueous solution with a mass concentration of 20-65%; and the coagulation bath temperature is 10-40°C.

[0022] Furthermore, in step S2, the preparation method of TiO2 sol is:

[0023] (1) Add tetrabutyl titanate and acid to alcohol and stir and mix them. Control the temperature to 10-45°C, the stirring speed to 300-800 rpm, and the stirring time to 1-3 hours to obtain a mixed solution A.

[0024] (2) After the alcohol and water are evenly mixed, slowly add them into the mixed solution A and stir to mix. Control the temperature to 10-45°C, the stirring speed to 500-1500 rpm, and the stirring time to 2-4 hours to obtain TiO2 sol.

[0025] Furthermore, the mass ratio of tetrabutyl titanate to acid is 1:(0.5-3);

[0026] The mass ratio of the total mass of the alcohol in step (1) and step (2) to the tetrabutyl titanate is (2-5):1;

[0027] The mass ratio of water to tetrabutyl titanate is (0.5-3):3;

[0028] The mass ratio of the alcohol in step (1) to the alcohol in step (2) is (1.8-2.2):1;

[0029] The alcohol is any one of methanol, ethanol, isopropanol, and n-butanol;

[0030] The acid is any one of acetic acid, nitric acid and phosphoric acid.

[0031] Furthermore, the water-based adhesive is at least one of polypropylene resin, polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, and poly(meth)acrylate;

[0032] The mass proportion of the water-based adhesive in the TiO2 treatment solution is 1-10%.

[0033] Furthermore, in step S2, the method of coating the surface of the aramid coated diaphragm intermediate with TiO2 treatment liquid is as follows: immersing the aramid coated diaphragm intermediate in the TiO2 treatment liquid for multiple times, controlling the immersion penetration speed to 20-80m / min, the immersion penetration number to 2-5 times, and finally drying and processing to obtain a composite coated diaphragm.

[0034] A composite coating diaphragm for a lithium ion battery is prepared according to the preparation method of the present invention.

[0035] The beneficial effects of the present invention are:

[0036] The present invention discloses a composite coated diaphragm for lithium-ion batteries and a preparation method thereof. The cross-linked structure polymer and TiO2 sol inorganic material coating layer used in the preparation process have better uniformity and low water absorption properties, so that the prepared composite coated diaphragm has higher heat resistance, film rupture temperature, puncture strength and low water absorption performance; in addition, due to the larger coating pore structure and the unique chemical structure of the amide bond after the aramid polymer is formed into a film, the prepared product has more excellent liquid retention performance, and exhibits better electrochemical and safety performance after the battery is assembled.

[0037] In the preparation method of the present invention, by controlling the coating process conditions of each layer, it is more conducive to obtaining a composite coated diaphragm with a suitable pore structure, so that the composite coated diaphragm has good air permeability and good mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of the preparation method of the aramid coated diaphragm intermediate of the present invention;

[0039] Figure 2 is a flow chart of the preparation method of the composite coating diaphragm described in Example 1;

[0040] Figure 3 is a surface morphology diagram of the composite coating diaphragm in Example 1;

[0041] Figure 4 This is a test diagram of the film rupture temperature of the composite coated diaphragm in Example 1. DETAILED DESCRIPTION

[0042] The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0044] A method for preparing a composite coated diaphragm for a lithium ion battery, the preparation method comprising:

[0045] S1. Preparation of aramid coated diaphragm intermediate:

[0046] Aramid polymer slurry is coated on the base membrane, and a uniform porous structure is formed by coagulation bath molding to construct a stable porous coating structure, and then an aramid coated diaphragm intermediate is obtained by drying.

[0047] The aramid polymer slurry comprises a cross-linked aramid polymer solution, a porogen and a cosolvent;

[0048] The cross-linked aramid polymer solution is prepared by cross-linking a meta-aramid polymer solution with an isocyanate inducer, and the weight average molecular weight of the cross-linked aramid polymer in the cross-linked aramid polymer solution is 15-30W; the process flow is as follows: Figure 1 shown.

[0049] S2. Preparation of composite coated diaphragm:

[0050] The TiO2 treatment liquid is coated on the surface of the aramid coated diaphragm intermediate, and finally dried to obtain a composite coated diaphragm; the TiO2 treatment liquid includes TiO2 sol and water-based adhesive. Figure 2 shown.

[0051] Specifically, the cross-linked structure polymer in the cross-linked structure aramid polymer solution is selected from the following chemical formula:

[0052] 、 ;

[0053] R is selected from any one of the following structures: ;

[0054] 0≤n≤150, 80≤x≤150, 80≤m≤150; this type of cross-linked structure material has better temperature resistance and higher strength.

[0055] Specifically, the porogen is any one of polyethylene glycol (PEG), polyvinyl alcohol (PVA), and polyvinyl pyrrolidone (PVP);

[0056] The cosolvent is any one of calcium chloride and lithium chloride;

[0057] The isocyanate inducer is at least one of 2,4- / 2,6-toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), p-phenylene diisocyanate (PPDI), and triphenylmethane triisocyanate (PMDI).

[0058] More specifically, the preparation method of the cross-linked aramid polymer solution is as follows: dissolving the meta-aramid polymer stock solution in DMAC, controlling the system temperature to 25-35° C., slowly adding an isocyanate inducer for reaction, controlling the reaction time to 10-15 minutes, and obtaining the cross-linked aramid polymer solution after the reaction is completed.

[0059] Specifically, the solvent in the meta-aramid polymer stock solution is DMAC, the polymer mass percentage is 11-35%, and the viscosity (25° C.) is 80,000-120,000 mPa·s.

[0060] More specifically, to better illustrate the impact of various process conditions on the product, the same meta-aramid polymer stock solution was used in each of the Examples and Comparative Examples of the present invention. The meta-aramid polymer stock solution used in each of the Examples and Comparative Examples of the present invention contained DMAC as the solvent, 20% polymer by mass, and a viscosity (at 25°C) of 100,000 mPa·s. However, this is not intended to limit the technical solutions of the present invention.

[0061] Specifically, in step S1, the mass ratio of the cross-linked aramid polymer solution to the porogen and the cosolvent is (80-89): (5-8): (6-12);

[0062] The solid content of the cross-linked aramid polymer solution is 5%-15%.

[0063] More specifically, when preparing the aramid-coated diaphragm intermediate in step S1, the aramid polymer slurry is coated on one side or both sides of the base membrane.

[0064] Specifically, in step S1, the coagulation bath is a DMAC aqueous solution with a mass concentration of 20-65%; the coagulation bath temperature is 10-40°C.

[0065] Specifically, in step S2, the precursor tetrabutyl titanate is first hydrolyzed under suitable conditions by a sol-gel method to obtain a transparent TiO2 sol. The specific preparation process is as follows:

[0066] (1) Add tetrabutyl titanate and acid to alcohol and stir and mix them. Control the temperature to 10-45°C, the stirring speed to 300-800 rpm, and the stirring time to 1-3 hours to obtain a mixed solution A.

[0067] (2) After the alcohol and water are evenly mixed, slowly add them into the mixed solution A and stir to mix. Control the temperature to 10-45°C, the stirring speed to 500-1500 rpm, and the stirring time to 2-4 hours to obtain TiO2 sol.

[0068] Specifically, the mass ratio of tetrabutyl titanate to acid is 1:(0.5-3);

[0069] The mass ratio of the total mass of the alcohol in step (1) and step (2) to the tetrabutyl titanate is (2-5):1;

[0070] The mass ratio of water to tetrabutyl titanate is (0.5-3):3;

[0071] The mass ratio of the alcohol in step (1) to the alcohol in step (2) is (1.8-2.2):1.

[0072] The alcohol is any one of methanol, ethanol, isopropanol, and n-butanol;

[0073] The acid is any one of acetic acid, nitric acid and phosphoric acid.

[0074] Specifically, the water-based adhesive is at least one of polypropylene resin (CAS No.: 9003-07-0, ExxonMobil Corporation), polyacrylic acid (CAS No.: 9003-21-8, Shandong Xiya Chemical Co., Ltd.), polyvinyl alcohol (CAS No.: 96734-39-3, Jiangsu Runfeng Synthetic Technology Co., Ltd.), polyacrylonitrile (CAS No.: 25014-41-9, Jiangsu Leien Environmental Protection Technology Co., Ltd.), and poly (meth)acrylate (CAS No.: 9003-63-8, Jiangsu Bosite Chemical Technology Co., Ltd.);

[0075] The mass proportion of the water-based adhesive in the TiO2 treatment solution is 1-10%.

[0076] Specifically, in step S2, the method for coating the TiO2 treatment liquid on the surface of the aramid coated membrane intermediate is: immersing the aramid coated membrane intermediate in the TiO2 treatment liquid for multiple times, controlling the immersion penetration speed to 20-80m / min, and the immersion penetration number to 2-10 times, to adjust the coating thickness and uniformity, and finally drying and processing to obtain a composite coated membrane.

[0077] More specifically, the base film is any one of a polyethylene film, a polypropylene film, a polypropylene / polyethylene / polypropylene three-layer composite microporous membrane, a polypropylene / polyethylene / polypropylene three-layer composite microporous membrane, a polyvinylidene fluoride microporous membrane, a polyvinylidene fluoride-hexafluoropropylene microporous membrane, a polyimide microporous membrane, a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyester non-woven fabric, and a polyimide non-woven fabric.

[0078] A composite coating diaphragm for a lithium ion battery is prepared according to the preparation method of the present invention.

[0079] Example 1

[0080] S1. Preparation of aramid coated diaphragm intermediate:

[0081] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of MDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0082] A cross-linked aramid polymer solution, PEG (molecular weight 800), and lithium chloride were mixed in a mass ratio of 89:5:6 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane was then placed in a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0083] S2. Preparation of composite coated diaphragm:

[0084] (1) Take a certain amount of anhydrous ethanol, add tetrabutyl titanate and acetic acid, the mass ratio of tetrabutyl titanate to acetic acid is 1:1, and stir at 30°C and 500 rpm for 1.5 h to obtain mixed solution A.

[0085] (2) Mix anhydrous ethanol and water evenly, slowly add them to mixed solution A, and stir at 30°C and 500 rpm for 3 h to obtain TiO2 sol;

[0086] The mass ratio of anhydrous ethanol to tetrabutyl titanate in the TiO2 sol system is 3:1, and the mass ratio of water to tetrabutyl titanate is 1:3. The mass ratio of anhydrous ethanol in step (1) to anhydrous ethanol in step (2) is 2:1.

[0087] (3) Add poly(meth)acrylate to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of poly(meth)acrylate in the TiO2 treatment solution is 5%.

[0088] The aramid coated diaphragm intermediate obtained in step S1 is immersed in the TiO2 treatment solution at a speed of 50m / min, then placed in an oven for drying at 60°C, and then immersed in the TiO2 treatment solution again after drying, and dried at 60°C, and repeated three times. A composite coated diaphragm is obtained. The process flow is as follows: Figure 2 shown.

[0089] Example 2

[0090] S1. Preparation of aramid coated diaphragm intermediate:

[0091] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of NDI was slowly added. The treatment time was 10 minutes to obtain a cross-linked aramid polymer solution.

[0092] A cross-linked aramid polymer solution, PEG (molecular weight 800), and lithium chloride were mixed in a mass ratio of 89:5:6 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane was then placed in a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0093] S2. Preparation of composite coated diaphragm:

[0094] (1) Take a certain amount of anhydrous ethanol, add tetrabutyl titanate and acetic acid, the mass ratio of tetrabutyl titanate to acetic acid is 1:1, and stir at 30℃ and 500 rpm for 1.5 hours to obtain mixed solution A.

[0095] (2) Mix anhydrous ethanol and water evenly, slowly add them into mixed solution A, and stir at 30°C and 500 rpm for 3 h to obtain TiO2 sol.

[0096] The mass ratio of anhydrous ethanol to tetrabutyl titanate in the TiO2 sol system is 3:1, and the mass ratio of water to tetrabutyl titanate is 1:3. The mass ratio of the alcohol in step (1) to the anhydrous ethanol in step (2) is 2:1.

[0097] (3) Add poly(meth)acrylate to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of poly(meth)acrylate in the TiO2 treatment solution is 5%.

[0098] The aramid coated diaphragm intermediate obtained in step S1 was immersed in the TiO2 treatment solution at a speed of 50 m / min, then dried in an oven at 60°C, immersed in the TiO2 treatment solution again after drying, and dried at 60°C, and repeated three times to obtain a composite coated diaphragm.

[0099] Example 3

[0100] S1. Preparation of aramid coated diaphragm intermediate:

[0101] 10 kg of meta-aramid polymer stock solution was dissolved in 15 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of MDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0102] A cross-linked aramid polymer solution, PEG (molecular weight 800), and lithium chloride were mixed in a mass ratio of 80:8:12 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane was then placed in a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0103] S2. Preparation of composite coated diaphragm:

[0104] (1) Take a certain amount of anhydrous ethanol, add tetrabutyl titanate and acetic acid to 2 / 3 of the amount, with the mass ratio of tetrabutyl titanate to acetic acid being 1:1, and stir at 30°C and 500 rpm for 1.5 h to obtain mixed solution A.

[0105] (2) Mix anhydrous ethanol and water evenly, slowly add them into mixed solution A, and stir at 30°C and 500 rpm for 3 h to obtain TiO2 sol.

[0106] The mass ratio of anhydrous ethanol to tetrabutyl titanate in the TiO2 sol system is 3:1, and the mass ratio of water to tetrabutyl titanate is 1:3. The mass ratio of anhydrous ethanol in step (1) to anhydrous ethanol in step (2) is 2:1.

[0107] (3) Add poly(meth)acrylate to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of poly(meth)acrylate in the TiO2 treatment solution is 5%.

[0108] The aramid coated diaphragm intermediate obtained in step S1 was immersed in the TiO2 treatment solution at a speed of 50 m / min, then dried in an oven at 60°C, immersed in the TiO2 treatment solution again after drying, and dried at 60°C, and repeated three times to obtain a composite coated diaphragm.

[0109] Example 4

[0110] S1. Preparation of aramid coated diaphragm intermediate:

[0111] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of MDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0112] A cross-linked aramid polymer solution, PEG (molecular weight 800), and lithium chloride were mixed in a mass ratio of 89:5:6 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane was then placed in a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0113] S2. Preparation of composite coated diaphragm:

[0114] (1) Take a certain amount of anhydrous ethanol, add tetrabutyl titanate and nitric acid, the mass ratio of tetrabutyl titanate to acrylic acid is 1:1, and stir at 30℃ and 500 rpm for 1.5 hours to obtain mixed solution A.

[0115] (2) Mix anhydrous ethanol and water evenly, slowly add them into mixed solution A, and stir at 30°C and 1000 rpm for 3 h to obtain TiO2 sol.

[0116] The mass ratio of anhydrous ethanol to tetrabutyl titanate in the TiO2 sol system is 3:1, and the mass ratio of water to tetrabutyl titanate is 1:3. The mass ratio of anhydrous ethanol in step (1) to anhydrous ethanol in step (2) is 2:1.

[0117] (3) Add poly(meth)acrylate to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of poly(meth)acrylate in the TiO2 treatment solution is 5%.

[0118] The aramid coated diaphragm intermediate obtained in step S1 was immersed in the TiO2 treatment solution at a speed of 50 m / min, then dried in an oven at 60°C, immersed in the TiO2 treatment solution again after drying, and dried at 60°C, and repeated three times to obtain a composite coated diaphragm.

[0119] Example 5

[0120] S1. Preparation of aramid coated diaphragm intermediate:

[0121] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of MDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0122] A cross-linked aramid polymer solution, PEG (molecular weight 800), and lithium chloride were mixed in a mass ratio of 89:5:6 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane was then placed in a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0123] S2. Preparation of composite coated diaphragm:

[0124] (1) Take a certain amount of anhydrous ethanol, add tetrabutyl titanate and acetic acid, the mass ratio of tetrabutyl titanate to acrylic acid is 1:1, and stir at 30℃ and 500 rpm for 1.5 hours to obtain mixed solution A.

[0125] (2) Anhydrous ethanol and water were mixed evenly, slowly added to the mixed solution A, and stirred at 30°C and 1000 rpm for 3 h to obtain TiO2 sol.

[0126] The mass ratio of anhydrous ethanol to tetrabutyl titanate in the TiO2 sol system is 3:1, and the mass ratio of water to tetrabutyl titanate is 1:3. The mass ratio of anhydrous ethanol in step (1) to anhydrous ethanol in step (2) is 2:1.

[0127] (3) Add poly(meth)acrylate to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of poly(meth)acrylate in the TiO2 treatment solution is 5%.

[0128] The aramid coated diaphragm intermediate obtained in step S1 was immersed in the TiO2 treatment solution at a speed of 50 m / min, and repeated twice, and then placed in an oven for drying at 60° C. to obtain a composite coated diaphragm.

[0129] Example 6

[0130] S1. Preparation of aramid coated diaphragm intermediate:

[0131] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of PPDI was slowly added. The treatment time was 15 minutes to obtain a cross-linked aramid polymer solution.

[0132] A cross-linked aramid polymer solution, polyvinyl alcohol (PVA) (molecular weight 8000), and calcium chloride were mixed in a mass ratio of 85:6:9 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane then passed through a coagulation bath (a solution of water and DMAC) at a concentration of 20% and a temperature of 10°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0133] S2. Preparation of composite coated diaphragm:

[0134] (1) Take a certain amount of methanol, add tetrabutyl titanate and nitric acid, the mass ratio of tetrabutyl titanate to nitric acid is 1:0.5, and stir at 45°C and 300 rpm for 1 hour to obtain mixed solution A.

[0135] (2) Methanol and water were mixed evenly, slowly added to the mixed solution A, and stirred at 45°C and 1000 rpm for 2 h to obtain TiO2 sol;

[0136] The mass ratio of methanol to tetrabutyl titanate in the TiO2 sol system is 2:1, and the mass ratio of water to tetrabutyl titanate is 0.5:3. The mass ratio of methanol in step (1) to methanol in step (2) is 2.2:1.

[0137] (3) Add polyacrylic acid to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of polyacrylic acid in the TiO2 treatment solution is 1%.

[0138] The aramid coated diaphragm intermediate obtained in step S1 was immersed in the TiO2 treatment solution at a speed of 20 m / min, then dried in an oven at 60°C, immersed in the TiO2 treatment solution again after drying, and dried at 60°C, and repeated twice to obtain a composite coated diaphragm.

[0139] Example 7

[0140] S1. Preparation of aramid coated diaphragm intermediate:

[0141] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of PMDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0142] A cross-linked aramid polymer solution, polyvinyl pyrrolidone (molecular weight 6000), and lithium chloride were mixed in a mass ratio of 82:8:10 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane then passed through a coagulation bath (a solution of water and DMAC) at a concentration of 65% and a temperature of 40°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate had a coating thickness of 1.5μm on both sides.

[0143] S2. Preparation of composite coated diaphragm:

[0144] (1) Take a certain amount of isopropanol, add tetrabutyl titanate and phosphoric acid, the mass ratio of tetrabutyl titanate to phosphoric acid is 1:3, and stir at 10°C and 800 rpm for 3 h to obtain mixed solution A.

[0145] (2) Mix isopropyl alcohol and water evenly, slowly add them into mixed solution A, and stir at 10°C and 1500 rpm for 4 h to obtain TiO2 sol;

[0146] The mass ratio of isopropyl alcohol to tetrabutyl titanate in the TiO2 sol system is 5:1, and the mass ratio of water to tetrabutyl titanate is 3:3. The mass ratio of isopropyl alcohol in step (1) to isopropyl alcohol in step (2) is 1.8:1.

[0147] (3) Add polyacrylonitrile to the TiO2 sol and stir at 30°C and 1000 rpm for 30 min to obtain a TiO2 treatment solution, wherein the mass proportion of polyacrylonitrile in the TiO2 treatment solution is 10%.

[0148] The aramid coated diaphragm intermediate obtained in step S1 was immersed in the TiO2 treatment solution at a speed of 80 m / min, then dried in an oven at 60°C, immersed in the TiO2 treatment solution again after drying, and dried at 60°C, and repeated five times to obtain a composite coated diaphragm.

[0149] Comparative Example 1

[0150] The difference between Comparative Example 1 and Example 1 is that the TiO2 treatment solution is not used for treatment, and the aramid-coated diaphragm intermediate coated with the cross-linked aramid polymer solution is directly used as the final product.

[0151] The specific method is as follows:

[0152] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of MDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0153] A cross-linked aramid polymer solution, PEG (molecular weight 800), and lithium chloride were mixed in a mass ratio of 89:5:6 to prepare an aramid polymer slurry. The aramid polymer slurry was then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane was then placed in a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane was rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane had a coating thickness of 1.5μm on both sides.

[0154] Comparative Example 2

[0155] In this comparative example 2, the aramid polymer solution and the TiO2 treatment solution are not used for coating treatment. The ceramic slurry is directly coated on the surface of the base film to obtain a ceramic coated diaphragm.

[0156] The specific preparation method is as follows:

[0157] 80 parts of aluminum oxide, 15 parts of a poly(meth)acrylate emulsion with a solid content of 50% and 120 parts of deionized water were mixed, stirred at 30°C and 1200 rpm for 1 hour, and then 100 parts of a thickener (a 2% by mass CMC aqueous solution) and 0.5 parts of polyethylene glycol ether were added, and stirred at 30°C and 1000 rpm for 1.5 hours to obtain a ceramic slurry;

[0158] The ceramic slurry was coated on a polyethylene diaphragm with a thickness of 7 μm by micro-gravure coating, and the ceramic coated diaphragm was obtained after drying.

[0159] Comparative Example 3

[0160] In Comparative Example 3, no TiO2 treatment solution was used for treatment. The aramid-coated diaphragm intermediate was coated with composite oxide particles on its surface using conventional roller coating to obtain an aramid-ceramic composite coated diaphragm.

[0161] The specific preparation method is as follows:

[0162] 10 kg of meta-aramid polymer stock solution was dissolved in 30 kg of DMAC. After complete dissolution, the temperature was maintained at 30° C., stirring was continued, and 0.2 kg of MDI was slowly added for 10 minutes to obtain a cross-linked aramid polymer solution.

[0163] A coating slurry is prepared by mixing a cross-linked aramid polymer solution with PEG (molecular weight 800) and lithium chloride in a mass ratio of 89:5:6. The aramid polymer slurry is then evenly coated onto a 7μm-thick polyethylene membrane using micro-gravure coating. The membrane then enters a coagulation bath (a solution of water and DMAC) at a concentration of 45% and a temperature of 25°C. After exiting the coagulation bath, the membrane is rinsed in 55°C water and then dried at 70°C. After winding, the resulting aramid-coated membrane intermediate has a coating thickness of 1.5μm on both sides.

[0164] 80 parts of aluminum oxide, 15 parts of a poly(meth)acrylate emulsion with a solid content of 50% and 120 parts of deionized water were mixed, stirred at 30°C and 1200 rpm for 1 hour, and then 100 parts of a thickener (a 2% by mass CMC aqueous solution) and 0.5 parts of polyethylene glycol ether were added, and stirred at 30°C and 1000 rpm for 1.5 hours to obtain a ceramic slurry;

[0165] The ceramic slurry was coated on the aramid coated diaphragm intermediate by micro-gravure coating, and the aramid-ceramic coated diaphragm was obtained after drying. The thickness of the ceramic layer on one side was 1.5 μm.

[0166] Comparative Example 4

[0167] The composite coated diaphragm was prepared by the same method as in Example 1, except that the concentration of the coagulation bath in step S1 was reduced to 10% in this comparative example 4. Other process conditions were the same as in Example 1.

[0168] Comparative Example 5

[0169] The composite coated diaphragm was prepared by the same method as in Example 1, except that the concentration of the coagulation bath in step S1 was increased to 80% in this comparative example 5. Other process conditions were the same as in Example 1.

[0170] Comparative Example 6

[0171] The composite coated diaphragm was prepared by the same method as in Example 1, except that the amount of the aqueous adhesive added in step S2 was reduced. In this comparative example 6, the mass proportion of the aqueous adhesive poly(meth)acrylate in the TiO2 treatment solution was 0.5%.

[0172] Comparative Example 7

[0173] The composite coated diaphragm was prepared by the same method as in Example 1, except that the amount of the aqueous adhesive added in step S2 was increased. In this comparative example 7, the mass proportion of the aqueous adhesive poly(meth)acrylate in the TiO2 treatment solution was 12%.

[0174] Comparative Example 8

[0175] A composite coated diaphragm was prepared using the same method as in Example 1, except that the number of times the aramid-coated diaphragm intermediate was immersed in the TiO2 treatment solution was reduced. In Comparative Example 8, the aramid-coated diaphragm intermediate was immersed in the TiO2 treatment solution only once. Other process conditions were the same as in Example 1.

[0176] Comparative Example 9

[0177] A composite coated diaphragm was prepared using the same method as in Example 1, except that the aramid-coated diaphragm intermediate was immersed in the TiO2 treatment solution more frequently. In Comparative Example 9, the aramid-coated diaphragm intermediate was immersed in the TiO2 treatment solution 10 times. Other process conditions were the same as in Example 1.

[0178] The coated separators obtained in the above examples and comparative examples were tested for thickness, air permeability, thermal shrinkage, and film rupture temperature. The test results are shown in Table 1. Thickness, air permeability, puncture strength, and thermal shrinkage were tested according to the methods specified in GB / T 36363-2018, film rupture temperature was tested according to the methods specified in GB / T 36800.1-2018, and moisture content was tested according to the methods specified in T / SGX 002-2018.

[0179] Table 1 Performance data of the diaphragm of the embodiment and the comparative example

[0180]

[0181] Note: “-” indicates that measurement is not possible under this condition; MD stands for longitudinal direction and TD stands for transverse direction.

[0182] The coated separators obtained in Example 1 and Comparative Examples 1 and 2 were assembled into soft-pack batteries, where the positive electrode was made of NCM811, the negative electrode was made of graphite, and the electrolyte was lithium hexafluorophosphate (LBED8-240421). Specifically, the batteries were assembled using a Kejing semi-automatic lamination machine through a series of steps: lamination, hot pressing, tab welding, top and side sealing, liquid injection, formation, and final sealing.

[0183] The assembled batteries were tested for ionic conductivity, room-temperature charge-discharge rate, high-temperature discharge rate, and battery heating test performance. The test results are shown in Table 2. Ionic conductivity was tested according to the method specified in NB / T 10827-2021, room-temperature rate discharge, room-temperature rate charge, and high-temperature rate discharge were tested according to the methods specified in GB / T 31486-2015, and the battery heating test was conducted according to the method specified in GB / T 31485-2015.

[0184] Table 2 Performance test data of the diaphragm assembled battery of the embodiment and the comparative example

[0185]

[0186] The data in Tables 1 and 2 above demonstrate that Examples 1-7, the composite coated separators produced using the preparation method described herein, exhibit improved thermal shrinkage, air permeability, puncture strength, membrane rupture temperature, and moisture content. Furthermore, after battery assembly, the composite coated separator (Example 1) demonstrated improved electrochemical and safety performance. In the 130°C heating test, both the Example and the Comparative Example passed. Further increasing the test conditions to 160°C, Example 1 passed, while Comparative Examples 1 and 2 failed. The present invention's combined process of layered treatment of a cross-linked aramid polymer and a TiO2 treatment solution maintains the original aramid coating structure, ensuring a high membrane rupture temperature. Furthermore, the TiO2 particles are more evenly distributed on the coating surface, providing improved thermal shrinkage and further improving the membrane rupture temperature, resulting in a higher pass rate for battery safety testing. Furthermore, the immersion treatment process results in a relatively low packing density of the TiO2 coating, providing more pathways for lithium ions in the battery and resulting in higher ionic conductivity.

[0187] The surface morphology of the composite coating membrane prepared in Example 1 is as follows: Figure 3 As shown, from Figure 3 It can be seen that the TiO2 particles prepared using this process are more evenly distributed and the coating is more evenly stacked, thus providing better thermal shrinkage performance. Figure 4 As shown by Figure 4 It can be seen that the composite coating membrane has a higher membrane rupture temperature.

[0188] Comparing the data from Comparative Example 1 and Examples 1-2 reveals that without the TiO2 treatment solution, the separator's thermal shrinkage, puncture strength, and rupture temperature all decline, while its water content increases. The performance of the assembled battery also significantly deteriorates. Therefore, the separator obtained by co-treating the cross-linked aramid polymer solution with the TiO2 treatment solution exhibits superior performance.

[0189] From the comparison of the data of Comparative Examples 2-3 and Example 1, it can be seen that compared with the conventional ceramic coating method, the inorganic coating is introduced on the aramid coating by layering treatment with TiO2 treatment liquid, and the diaphragm has a thinner thickness, higher puncture strength, heat shrinkage performance and film rupture temperature.

[0190] From the comparison of the data of Comparative Example 4 and Example 1, it can be seen that if the concentration of the coagulation bath is reduced, the pore structure of the aramid coating deteriorates, thereby reducing the air permeability of the product; at the same time, the film-forming property of the aramid coating deteriorates, the coating is easy to fall off, and the film-breaking temperature of the product is significantly reduced.

[0191] Comparing the data from Comparative Example 5 with Example 1 reveals that increasing the coagulation bath concentration leads to excessively rapid film formation, excessively large pores in the aramid coating, and uneven coating. This results in decreased puncture strength and rupture temperature, and increased water content. Therefore, employing the coagulation bath concentration defined by the present invention is more conducive to obtaining a composite coated diaphragm with superior performance.

[0192] From the comparison of the data of Comparative Example 6 and Example 1, it can be seen that if the amount of water-based adhesive added in step S2 is reduced, the adhesion force of the TiO2 particles on the surface of the diaphragm is too low, the particles cannot adhere to the surface of the diaphragm normally, and the coating is uneven, resulting in reduced puncture strength and heat shrinkage performance of the product.

[0193] Comparing the data from Comparative Example 7 and Example 1, it can be seen that increasing the amount of water-based adhesive added in step S2 causes the adhesive to clog the membrane surface, resulting in abnormal air permeability and a significant increase in moisture. Therefore, using the adhesive dosage specified in the present invention is more conducive to obtaining a composite coated membrane with excellent performance.

[0194] From the comparison of the data of Comparative Example 8 and Example 1, it can be seen that if the number of times the aramid-coated diaphragm intermediate is immersed in the TiO2 treatment solution is reduced, TiO2 cannot evenly cover the surface of the diaphragm intermediate, and the coating is thinner, resulting in poor puncture strength and heat shrinkage performance of the product.

[0195] From the comparison of the data of Comparative Example 9 and Example 1, it can be seen that if the number of times the aramid-coated diaphragm intermediate is immersed in the TiO2 treatment solution is increased, the inorganic particle coating is thicker. Although the heat shrinkage performance of the product is improved, the total thickness of the product is thicker and the air permeability is significantly deteriorated, which affects the normal assembly of the battery.

[0196] The cross-linked aramid polymer solution material used in the preparation method of the present invention has better heat resistance and higher strength. It is prepared into an aramid slurry and coated on the surface of the substrate by a phase inversion method to obtain an aramid diaphragm intermediate. Then, a TiO2 sol is pre-prepared by a sol-gel method, and then an appropriate amount of aqueous adhesive is mixed to obtain a treatment liquid. The aramid diaphragm intermediate is graded and treated with a TiO2 treatment liquid to compound TiO2 particles on its surface, further improving the heat resistance and puncture strength to obtain a composite coated diaphragm. The composite coated diaphragm of the present invention has higher heat resistance, membrane rupture temperature, puncture strength and low water absorption. In addition, the good coating pore structure of the aramid polymer after film formation and the unique chemical structure of the amide bond make the manufactured product have better liquid retention performance, and exhibit better electrochemical and safety performance after assembling the battery.

[0197] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] For those skilled in the art, several variations and improvements may be made without departing from the scope of the present invention, which all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be based on the appended claims.

Claims

1. A method for preparing a composite coating diaphragm for a lithium ion battery, characterized in that: The preparation method is: S1. Preparation of aramid coated diaphragm intermediate: Aramid polymer slurry is coated on the base membrane, and subjected to coagulation bath molding and drying treatment to obtain an aramid coated diaphragm intermediate; the aramid polymer slurry includes a cross-linked aramid polymer solution, a porogen and a cosolvent; The cross-linked aramid polymer solution is prepared by cross-linking a meta-aramid polymer solution with an isocyanate inducer, wherein the weight average molecular weight of the cross-linked aramid polymer in the cross-linked aramid polymer solution is 15-30W; and the solid content of the cross-linked aramid polymer solution is 5%-15%. In step S1, the coagulation bath is a DMAC aqueous solution with a mass concentration of 20-65%; the coagulation bath temperature is 10-40°C; In step S1, the mass ratio of the cross-linked aramid polymer solution to the porogen and the cosolvent is (80-89): (5-8): (6-12); S2. Preparation of composite coated diaphragm: A TiO2 treatment liquid is coated on the surface of the aramid coated diaphragm intermediate, and finally dried to obtain a composite coated diaphragm; the TiO2 treatment liquid comprises a TiO2 sol and a water-based adhesive; the mass proportion of the water-based adhesive in the TiO2 treatment liquid is 1-10%; the water-based adhesive is at least one of polypropylene resin, polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, and poly(meth)acrylate; In step S2, the method for coating the surface of the aramid coated diaphragm intermediate with TiO2 treatment liquid is as follows: immersing the aramid coated diaphragm intermediate in the TiO2 treatment liquid for multiple times, controlling the immersion speed to be 20-80m / min, the immersion times to be 2-5 times, and finally drying and treating to obtain a composite coated diaphragm.

2. The method for preparing a composite coating diaphragm for a lithium ion battery according to claim 1, characterized in that: The cross-linked structure polymer in the cross-linked structure aramid polymer solution is selected from the following chemical formula: 、 ； R is selected from any one of the following structures: ; 0≤n≤150, 80≤x≤150, 80≤m≤150.

3. The method for preparing a composite coating diaphragm for a lithium ion battery according to claim 1, characterized in that: The porogen is any one of polyethylene glycol, polyvinyl alcohol, and polyvinyl pyrrolidone; The cosolvent is any one of calcium chloride and lithium chloride; The isocyanate inducer is at least one of 2,4- / 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, and triphenylmethane triisocyanate.

4. The method for preparing a composite coating diaphragm for a lithium ion battery according to claim 1, characterized in that: In step S2, the preparation method of TiO2 sol is: (1) Add tetrabutyl titanate and acid to alcohol and stir and mix them. Control the temperature to 10-45°C, the stirring speed to 300-800 rpm, and the stirring time to 1-3 hours to obtain a mixed solution A. (2) After the alcohol and water are evenly mixed, slowly add them into the mixed solution A and stir to mix. Control the temperature to 10-45°C, the stirring speed to 500-1500 rpm, and the stirring time to 2-4 hours to obtain TiO2 sol.

5. The method for preparing a composite coating diaphragm for a lithium ion battery according to claim 4, characterized in that: The mass ratio of tetrabutyl titanate to acid is 1:(0.5-3); The mass ratio of the total mass of the alcohol in step (1) and step (2) to the tetrabutyl titanate is (2-5):1; The mass ratio of water to tetrabutyl titanate is (0.5-3):3; The mass ratio of the alcohol in step (1) to the alcohol in step (2) is (1.8-2.2):1; The alcohol is any one of methanol, ethanol, isopropanol, and n-butanol; The acid is any one of acetic acid, nitric acid and phosphoric acid.

6. A composite coated diaphragm for lithium ion batteries, characterized in that: The composite coated diaphragm is prepared according to the preparation method according to any one of claims 1 to 5.

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