High-heat-resistant and high-adhesion composite paste, preparation method and application thereof

Abstract

The application provides a high-heat-resistance high-adhesion composite paste, a preparation method and application thereof, and belongs to the technical field of composite paste preparation. The composite paste comprises the following raw materials in parts by weight: 5-20 parts by weight of MOF paste, 3-8 parts by weight of polyolefin emulsion, 40-80 parts by weight of ceramic paste, 3-8 parts by weight of adhesive, 0.5-1 part by weight of wetting agent and 10-80 parts by weight of solvent. The composite paste is applied to a battery separator, and the cycle performance, stability and safety of the lithium ion battery during use are improved. In addition, multifunctionality can be realized by one-time coating, and compared with the traditional coating mode of one layer and one function or multiple layers and multiple functions, the coating thickness is lower, the process steps are fewer, and the wet adhesion strength is higher.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite slurry preparation, and particularly relates to a high-heat-resistant and high-adhesion composite slurry, a preparation method thereof and application thereof. BACKGROUND

[0002] The separator is one of the key parts of the lithium ion battery, which prevents the positive and negative electrodes from contacting and short-circuiting, and also provides a channel for ion conduction. The most commonly used polyolefin separator substrate has a porosity controllable at more than 50%, which ensures the transmission of lithium ions, has good electrochemical stability, mechanical strength and low cost, and also has some shortcomings. For example, under high temperature conditions of 130℃, the thermal shrinkage rate of the separator substrate is as high as 40%, which can cause direct contact between the positive and negative electrodes, accelerate the thermal runaway of the battery, and eventually lead to safety problems. Therefore, a layer of slurry is needed to be coated on the separator substrate as a heat-resistant layer to resist the thermal shrinkage of the substrate, while maintaining the porosity. However, the heat-resistant layer does not have adhesion, and has no adhesion with the electrode sheet, so the hardness of the battery cannot be guaranteed, which affects the use of the battery.

[0003] The current status of the separator coating slurry is: 1. Using alumina, boehmite and other ceramic materials as a heat-resistant layer to improve the thermal shrinkage performance of the separator, but the effect is limited, and the coated separator has obvious anti-thermal shrinkage phenomenon at 130℃, and when the temperature rises, the shrinkage rate of the separator increases, and the safety of the battery is insufficient; 2. The ceramic material as a coating layer has limited ability to store electrolyte by using the accumulation of particles to form voids, which further affects the long cycle characteristics of the battery. 3. The battery will be accompanied by different degrees of gas expansion during normal charging and discharging cycles, and the ceramic has no gas adsorption capacity. In the case of overcharging, the internal temperature of the battery rises sharply, making multiple side reactions more intense, resulting in a large amount of gas accumulated in the battery, affecting the consistency and cycle stability of the battery, and even the bulging phenomenon becomes more serious, eventually leading to explosion and fire.

[0004] The ceramic material as a heat-resistant coating layer has no adhesion between the positive and negative electrodes, and the battery shows a soft collapse phenomenon, so a layer of glue layer needs to be coated on the heat-resistant layer to ensure the hardness of the battery. The selection of the glue layer can be PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate) and the like. The adhesion of PVDF with the electrode sheet is too low, which does not meet the demand of the separator market; the adhesion of PMMA is strong, but it will swell when immersed in electrolyte, resulting in too low wet adhesion strength; and moreover, the particle size of PMMA is too large, and the coating thickness is too large (5-8μm), so PMMA is rarely used on the market to improve the adhesion of the separator with the electrode sheet.

[0005] The polyolefin microspheres can also be used as an adhesion layer of the separator in the field of lithium batteries to enhance the adhesion with the electrode sheet and improve the hardness of the battery. The swelling rate of the polyolefin microspheres in the electrolyte is lower, and the wet adhesion strength of the polyolefin microspheres is higher than that of PMMA, which helps to improve the long cycle and rate performance of the battery.

[0006] Patent CN115926195A mentions that the polyolefin microspheres of the invention have an acrylate on the surface, have certain bonding ability, and when used as a coating material, help to improve the hardness of the battery and strengthen the stability of the battery.

[0007] However, patent CN114976492A uses microspheres as a separator adhesive layer, which requires multiple coating processes, i.e., first coating a ceramic coating, then coating a layer of polyolefin microspheres on the ceramic layer, to simultaneously achieve the performance requirements of heat shrinkage resistance and adhesion. The main reason why this patent cannot achieve one-time coating is that the microspheres in this patent have a small particle size and are easily buried in the heat-resistant layer, making it difficult to emerge. Therefore, the coating process steps of such an invention are too many, and the coating separator cannot adsorb and store the gas generated inside the lithium battery, which has certain application defects.

[0008] Metal-organic frameworks (MOFs) have high thermal stability and can maintain structural stability at high temperatures. MOFs are cubic porous materials, and the interlayer particles are dispersed and stacked to form certain gaps. The internal pores of the framework can also disperse heat, helping the battery separator to effectively suppress thermal shrinkage and effectively prevent physical deformation and thermal runaway of the battery separator, thereby improving the safety performance and cycle stability of the battery. MOFs have a very high specific surface area and porosity, which can form a stable pore network in the battery separator, promoting the penetration of electrolyte and the transmission of ions. MOFs also have a low thermal expansion coefficient, and after introducing MOFs, the battery separator will not produce significant volume changes at high temperatures, which is very important for the cycle life and safety of the battery. MOFs can also adsorb and store the gas generated inside the battery through their porous structure, such as adsorbing carbon dioxide, hydrogen, etc. through the pores in the MOFs, which can adsorb gas and avoid problems such as bulging, further improving the safety of the battery.

[0009] Patent CN115954616A mentions that mixing porous materials with ceramic materials and coating them on the surface of the base film can improve the wettability and thermal stability of the base film. However, MOFs are rigid materials and do not have adhesion, even with an external adhesive, it is difficult to achieve adhesion with the pole piece, and the hardness of the battery cannot be improved.

[0010] In view of the above shortcomings, a new type of functionalized separator needs to be developed to improve the heat resistance and adhesion performance of the battery and improve the liquid storage capacity of the separator. By optimizing material selection and preparation process, as well as optimizing the coating method of the separator, the performance of the composite slurry can be further improved, and the development and application of the separator coating technology can be promoted. SUMMARY

[0011] The application aims to provide a high-heat-resistant and high-adhesion composite slurry, a preparation method and application thereof. The ceramic and MOF in the application are rigid materials with excellent heat resistance, which can be used as a heat-resistant layer of the separator. The polyolefin microspheres are used as an adhesive layer of the separator. The polyolefin microspheres in the application have a smaller density than water, and the ceramic material and MOF have a larger density than water. The ceramic material itself has a high surface energy barrier, which is easy to produce electrostatic adsorption with the MOF in the application, and is easy to agglomerate and accelerate sinking in water. In the drying process of the coated separator, due to the density difference, the ceramic material and MOF sink to the lowermost layer as the heat-resistant layer, and the polyolefin microspheres float in the upper layer as the adhesive layer, so that the one-time coating purpose is achieved. The composite slurry is applied to the battery separator, which improves the cycle performance, stability and safety of the lithium ion battery during use. The one-time coating can achieve multifunctionality, and compared with the traditional coating method with one layer and one function or multiple layers and multiple functions, the coating thickness is lower, the process steps are fewer, and the wet adhesion strength is higher.

[0012] To achieve the above object, the application adopts the following technical scheme:

[0013] The application first provides a high-heat-resistant and high-adhesion composite slurry, which comprises the following raw materials in parts by weight: 5-20 parts by weight of MOF slurry, 3-8 parts by weight of polyolefin emulsion, 40-80 parts by weight of ceramic slurry, 3-8 parts by weight of adhesive, 0.5-1 part by weight of wetting agent, and 10-80 parts by weight of solvent.

[0014] Preferably, the MOF slurry is obtained by mixing MOF material and water, wherein the single-particle particle size of the MOF material is 0.1-1 μm, the specific surface area is 10-3500 m 2 / g, the pore size distribution is 0.5-8 nm, and the total pore volume is 0.2-5.0 mL / g.

[0015] Preferably, the MOF material is at least one of the IRMOF series, the PCN series, the UiO series, the MIL series or the ZiF series.

[0016] Preferably, the ceramic slurry is obtained by mixing ceramic material and dispersant, and the ceramic material is at least one of aluminum oxide, silicon dioxide, magnesium hydroxide, rutile titanium dioxide, magnesium oxide, boehmite, zirconium dioxide, barium titanate and zinc oxide.

[0017] Preferably, the polyolefin emulsion is at least one of a homopolymer emulsion or a copolymer emulsion of polyethylene, polypropylene or polybutylene.

[0018] Preferably, the adhesive is at least one of polymethacrylic acid, styrene-butadiene rubber, polyacrylate, polyurethane, polyvinyl acetate, acrylic polymer or acrylonitrile polymer.

[0019] Preferably, the wetting agent is at least one of oxyethylene alkyl phenol ether, polyoxyethylene fatty alcohol ether or fluorine-containing polyoxyethylene ether.

[0020] Preferably, the solvent is deionized water.

[0021] The application also provides a preparation method of the high-heat-resistance and high-adhesion composite slurry.

[0022] The MOF slurry, polyolefin microsphere slurry and ceramic slurry are weighed according to the proportion, mixed and stirred at a stirring speed of 200-1000 rpm / min at room temperature for 20-60 min, then the adhesive, wetting agent and solvent are sequentially added, and sequentially stirred at a stirring speed of 200-1000 rpm / min at room temperature for 20-60 min to obtain the composite slurry.

[0023] The application also provides application of the high-heat-resistance and high-adhesion composite slurry in a lithium ion battery separator.

[0024] Advantages of the application

[0025] 1. The application provides a preparation method and application of a high-heat-resistance and high-adhesion composite slurry, which mainly comprises MOF, polyolefin microspheres and ceramic particles, and the three are combined and coated on a separator once to improve the heat resistance and adhesion of the battery and improve the liquid storage capacity of the separator.

[0026] 2. The application also discloses a preparation method and application of the coating slurry, which is coated on a substrate separator once to obtain a thinner coating thickness (1-3 pm) and a lower area density (1.2-3 g / m 2 ), realizes lightweight coating, and increases the weight energy density of the battery.

[0027] 3. The coated separator of the application can realize rapid adhesion of the separator and the pole piece, has high adhesion strength (3-15 N), and is beneficial to improving the hardness and cycle stability of the battery.

[0028] 4. The coated separator of the application realizes closure of the separator at 130 DEG C, has a shrinkage rate of only 1.5-3.0% at 150 DEG C, is superior to the heat shrinkage resistance of a ceramic separator, and greatly improves the stability and safety performance of the lithium ion battery during use.

[0029] 5. The coated separator of the application applied in a lithium ion battery can adsorb and store a small amount of gas (such as carbon dioxide and hydrogen) generated in the battery, can also store electrolyte by using the large pores and high specific surface area of the MOF, further improves the safety of the battery, and improves the long cycle stability of the battery.

[0030] 6、The MOF designed in the application has a good wettability to electrolyte, the framework structure can store more electrolyte, avoids electrolyte dryness caused by cycle diving in the later stage of battery cycle, and ensures the cycle stability of the battery.

[0031] 7、The application can realize multifunctional coating in one coating process, and compared with the traditional coating method of one layer and one function or multi-layer and multifunction, the coating thickness is lower, the process steps are less, and the wet adhesion strength is higher. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the nitrogen adsorption desorption curve of MOF1;

[0033] Figure 2 is the nitrogen adsorption desorption curve of MOF2;

[0034] Figure 3 is the contact angle of the coated diaphragm in electrolyte of Example 1, 4 and Comparative Example 4;

[0035] Figure 4 is the adsorption curve of MOF1 and MOF2 to hydrogen;

[0036] Figure 5 is the diaphragm picture after heating at 130 DEG C for one hour in Example 1;

[0037] Figure 6 is the scanning electron microscope picture of Example 1, 4 and Comparative Example 1, 2. DETAILED DESCRIPTION

[0038] In order to further understand the present application, the preferred embodiments of the present application are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations to the claims of the present application.

[0039] The present application first provides a high heat-resistant and high-adhesion composite paste, which comprises the following raw materials in parts by weight: 5-20 parts by weight of MOF paste, 3-8 parts by weight of polyolefin emulsion, 40-80 parts by weight of ceramic paste, 3-8 parts by weight of adhesive, 0.5-1 part by weight of wetting agent, and 10-80 parts by weight of solvent.

[0040] According to the present application, the MOF paste is obtained by mixing MOF material and water, and comprises the following raw materials in parts by weight: 5-40 parts of MOF material powder and 60-100 parts of deionized water. The single particle size of the MOF material is 0.1-1 μm, preferably 0.4-0.8 μm, the specific surface area of the MOF material is 10-3500 m 2 / g, preferably 500-2800 m 2 / g, more preferably 1000-2000 m2 The MOF material has a pore size distribution of 0.5-8 nm, preferably 0.8-6 nm, and a total pore volume of 0.2-5.0 mL / g, preferably 0.9-3.7 mL / g. The MOF material is preferably at least one of the IRMOF series, the PCN series, the UiO series, the MIL series or the ZiF series.

[0041] The MOF material of the present application has high heat resistance (90-500℃), large specific surface area (10-3500 m 2 The MOF material can not only adsorb the gas (such as hydrogen) generated in the battery, but also store the electrolyte, thereby improving the cycle stability of the battery.

[0042] According to the present application, the ceramic slurry is obtained by mixing a ceramic material and a dispersant, and stirring and dispersing for 30 min. The ceramic slurry comprises 10-35 parts by weight of the ceramic material and 0.3-4 parts by weight of the dispersant. The dispersant is preferably at least one of sodium polyacrylate, polyethylene glycol, sodium dodecyl sulfate, sodium dibutyl naphthalene sulfonate, potassium polyacrylate, polyacrylamide or polyethylene glycol fatty acid ester. The ceramic material is preferably at least one of aluminum oxide, silicon dioxide, magnesium hydroxide, rutile titanium dioxide, magnesium oxide, boehmite, zirconium dioxide, barium titanate and zinc oxide.

[0043] According to the present application, the polyolefin emulsion is preferably at least one of a homopolymer emulsion or a copolymer emulsion of polyethylene, polypropylene or polybutylene. The polyolefin microsphere emulsion has a core-shell structure and a particle size of 0.5-2 μm, and is in a single dispersion state. The acrylate monomer itself has a certain bonding ability, and the polyolefin microsphere emulsion coated on the separator can realize good bonding strength between the separator and the pole piece.

[0044] According to the present application, the binder is preferably at least one of polymethacrylic acid, styrene-butadiene rubber, polyacrylate, polyurethane, polyvinyl acetate, an acrylic polymer or an acrylonitrile polymer.

[0045] According to the present application, the wetting agent is preferably at least one of an oxyethylene alkyl phenol ether, a polyoxyethylene fatty alcohol ether or a fluorine-containing polyoxyethylene ether.

[0046] According to the present application, the solvent is preferably deionized water.

[0047] The present application also provides a preparation method of the high-heat-resistance and high-bonding composite slurry.

[0048] (1) Preparation of the MOF slurry:

[0049] The organic ligand and deionized water are stirred and dissolved respectively, and the solution is marked as solution A; the metal salt compound and deionized water are stirred and dissolved, and the solution is marked as solution B; solution A is slowly added to solution B under the action of stirring, and the stirring is stopped after 1 h, to obtain a mixed solution C; the mixed solution C is transferred into a microwave reactor, and continuous heating and stirring are maintained for 30-60 min, to obtain a mixed solution D; the lower layer solid of the mixed solution D is washed with water and ethanol under ultrasonic wave after high-speed centrifugation (10000-20000 rpm / min), and then dried in a blast drying oven (70-90℃) for 30-60 min, to obtain a porous regular MOF material powder; the powder is dispersed and sand-milled in water, to obtain an MOF slurry.

[0050] The organic ligand is at least one of a tetracarboxylic porphyrin molecule, an aromatic carboxylic acid, and an imidazole organic molecule. More preferably, the organic ligand is an imidazole organic molecule.

[0051] The metal salt compound is at least one of chromium, zirconium, iron, cobalt, nickel, copper, and zinc.

[0052] The mass ratio of the organic ligand to deionized water is preferably 1:3-8, and the mass ratio of the metal salt compound to deionized water is preferably 1:2-5.5. The mass ratio of the solution A to the solution B is preferably 1:2-6.

[0053] (2) Preparation of a composite slurry:

[0054] The MOF slurry, the polyolefin microsphere slurry, and the ceramic slurry are weighed, and mixed and stirred at a stirring speed of 200-1000 rpm / min, preferably 600 rpm / min, at room temperature for 20-60 min, preferably 40 min. The adhesive, the wetting agent, and the solvent are sequentially added, and stirred at a stirring speed of 200-1000 rpm / min, preferably 500 rpm / min. The stirring is sequentially performed at room temperature for 20-60 min, preferably 30 min, to finally obtain a composite slurry.

[0055] (3) Coating of a functional separator

[0056] The above-obtained composite slurry is coated on both sides of a polyolefin separator, and dried in an oven at 80℃ for 5 min, to obtain a functional separator coated with the above composite slurry.

[0057] The coating method of the separator is at least one of gravure roll coating, dip coating, narrow coating, and spraying.

[0058] The separator is at least one of a polyethylene film, a polypropylene film, or a polyolefin multilayer co-extrusion composite porous film. The thickness of the polymeric porous base film is 2-20 μm.

[0059] The thickness of the coating of the separator is 0.2-3 μm, and the coating is double-sided coating.

[0060] The application will be further described in detail below in combination with examples. The raw materials involved in the examples are commercially available.

[0061] Example 1

[0062] (1) Preparation of MOF slurry

[0063] Phtalic acid and deionized water were stirred and dissolved according to a mass ratio of 1:4, and the solution was labeled as solution A; zirconium oxychloride metal salt compound and deionized water were stirred and dissolved according to a mass ratio of 1:2, and the solution was labeled as solution B; solution A was slowly added to solution B under stirring, and the stirring was stopped after 1 h, to obtain a mixed solution C; the mass ratio of solution A to solution B was 1:3; the mixed solution C was transferred into a microwave reactor, and continuous heating and stirring were maintained for 40 min, to obtain a mixed solution D; the lower solid of the mixed solution D was washed with water and ethanol under ultrasonic after high-speed centrifugation at 15000 rpm / min, and then dried in a blast drying oven at 80℃, and the drying time was 50 min, to finally obtain MOF1 powder (MOF belonging to the UiO series). 20 parts by weight of MOF1 powder (single particle size of 0.6 μm, specific surface area of 1481 m 2 / g, pore size distribution of 0.7-5 nm, and total pore volume of 3.4 mL / g; stable at 400℃) and 80 parts by weight of deionized water were stirred and dispersed and sand-milled for 1 h, to obtain MOF1 slurry. The specific surface area and contact angle of the MOF1 powder are shown in Figure 1 and Figure 3 .

[0064] (2) Preparation of composite slurry

[0065] 17 parts by weight of MOF1 slurry, 6 parts by weight of polyethylene microsphere emulsion, 45 parts by weight of alumina slurry (28 parts by weight of alumina and 1.2 parts by weight of sodium polyacrylate), 4 parts by weight of polyacrylate, and 0.8 parts by weight of oxyethylene alkyl phenol ether were sequentially added after stirring at a speed of 600 rpm / min for 30 min at room temperature, and 44.2 parts by weight of deionized water was added, and the stirring speed was 500 rpm / min, and sequentially stirred at room temperature for 40 min, to obtain a composite slurry.

[0066] (3) Coating of functional separator

[0067] The above-obtained composite slurry was double-sided coated on a polyolefin separator, and dried in an oven at 80℃ for 5 min, to obtain a functional separator coated with the above composite slurry.

[0068] The obtained separator has a coating thickness of 1.8 μm, an area density of 2.4 g / m 2 , a dry adhesion strength of 12.5 N / m, and a wet adhesion strength of 5.5 N / m.

[0069] Example 2

[0070] The difference between this example and Example 1 is that in step (2), the MOF1 slurry is 10 parts by weight, the polypropylene microsphere emulsion is 8 parts by weight, the alumina trihydrate slurry is 60 parts by weight, 5 parts by weight of butadiene-styrene rubber, and 0.9 parts by weight of polyoxyethylene fatty alcohol ether, and 16.1 parts by weight of deionized water. The coating thickness of the composite slurry coating is about 2.0 μm, the area density is 2.09 g / m 2 , the dry adhesion strength is 15.6 N / m, and the wet adhesion strength is 7.5 N / m.

[0071] Example 3

[0072] The difference between this example and Example 1 is that in step (2), the MOF1 slurry is 5 parts by weight, the polyethylene microsphere emulsion is 8 parts by weight, the boehmite slurry (20 parts by weight of boehmite and 2.9 parts by weight of potassium polyacrylate) is 45 parts by weight, 5 parts by weight of polyacrylate, and 1.0 parts by weight of polyoxyethylene fatty alcohol ether, and 41.2 parts by weight of deionized water. The coating thickness of the composite slurry coating is about 1.75 μm, the area density is 2.05 g / m 2 , the dry adhesion strength is 14.6 N / m, and the wet adhesion strength is 6.9 N / m.

[0073] Example 4

[0074] (1) Preparation of MOF slurry

[0075] 4,5-dimethyl-1H imidazole and deionized water were stirred and dissolved at a mass ratio of 1:4, and labeled as solution A; cobalt chloride metal salt compound and deionized water were stirred and dissolved at a mass ratio of 1:6, and labeled as solution B; under the action of stirring, solution A was slowly added to solution B, and stirring was continued for 1 h and then stopped, to obtain a mixed solution C; the mass ratio of solution A to solution B was 1:5; mixed solution C was transferred into a microwave reactor, and continuous heating and stirring were maintained for 40 min, to obtain a mixed solution D; after high-speed centrifugation at 15000 rpm / min, the lower solid of mixed solution D was ultrasonically washed with water and ethanol, respectively, and then dried in a blast drying oven at 80℃ for 50 min, to finally obtain MOF2 powder (a MOF belonging to the ZiF series). 20 parts by weight of MOF2 powder (single particle size of 0.5 μm, specific surface area of 1745 m 2 / g, the pore size distribution is 0.5-7 nm, the total pore volume is 4.7 mL / g, and it is stable at 450°C. Figure 2 and Figure 3 as shown in the table.

[0076] (2) Preparation of the composite slurry

[0077] 20 parts by weight of the MOF2 slurry, 6 parts by weight of the polybutylene microsphere emulsion, 45 parts by weight of the boehmite slurry, 3 parts by weight of the polymethylacrylic acid, and 0.6 parts by weight of the polyoxyethylene fatty alcohol ether were weighed, and 25.4 parts by weight of deionized water was added. The stirring speed was 450 rpm / min, and the stirring was carried out at room temperature for 25 min, to obtain the composite slurry.

[0078] (3) Coating of the functional separator

[0079] The composite slurry obtained above was coated on both sides of the polyolefin separator, and the coated separator was dried in an oven at 80°C for 5 min, to obtain the functional separator coated with the composite slurry.

[0080] The separator obtained above had a coating thickness of 2.2 μm, an areal density of 2.3 g / m 2 , a dry adhesive strength of 13.4 N / m, and a wet adhesive strength of 6.8 N / m.

[0081] Example 5

[0082] The difference between this example and Example 4 is that in step (2), the MOF2 slurry is 10 parts by weight, the polyethylene microsphere emulsion is 8 parts by weight, the silica slurry (20 parts by weight of silica and 2.3 parts by weight of polyethylene glycol) is 60 parts by weight, 5 parts by weight of polyurethane and 1.0 part by weight of polyoxyethylene ether, and deionized water is 16 parts by weight. The coating thickness of the functional separator coated with the composite slurry is about 1.85 μm, the areal density is 2.13 g / m 2 , the dry adhesive strength is 17.5 N / m, and the wet adhesive strength is 7.2 N / m.

[0083] Example 6

[0084] The difference between this example and Example 4 is that in step (2), the MOF2 slurry is 5 parts by weight, the polypropylene microsphere emulsion is 6 parts by weight, the boehmite slurry is 45 parts by weight, 5 parts by weight of acrylonitrile polymer and 0.6 parts by weight of polyoxyethylene ether, and deionized water is 38.4 parts by weight. The coating thickness of the functional separator coated with the composite slurry is about 1.6 μm, the areal density is 2.0 g / m 2, dry adhesion strength 14.6 N / m, wet adhesion strength 5.5 N / m.

[0085] Comparative Example 1

[0086] (1) Preparation of composite slurry

[0087] The polyethylene microsphere emulsion was weighed as 8 parts by weight, the alumina trihydrate slurry was 80 parts by weight, after stirring at room temperature at a speed of 600 rpm / min for 30 min, 5 parts by weight of acrylonitrile polymer and 0.6 parts by weight of polyoxyethylene ether were sequentially added, deionized water was 6.4 parts by weight, and the stirring speed was 450 rpm / min. The composite slurry was sequentially stirred at room temperature for 25 min to obtain the composite slurry.

[0088] (2) Coating of functional separator

[0089] The composite slurry obtained above was coated on both sides of the polyolefin separator, and dried in an oven at 80°C for 5 min to obtain the functional separator coated with the composite slurry. The coating thickness of the composite slurry coating was about 2.5 μm, and the areal density was 4.0 g / m 2 , dry adhesion strength 0 N / m, wet adhesion strength 0 N / m.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Comparative Example 1 is that in step (1), the material is polyethylene microsphere emulsion 36 parts by weight, zinc oxide slurry (30 parts by weight of silicon dioxide and 3.6 parts by weight of sodium dodecyl sulfate) 40 parts by weight, 5 parts by weight of acrylonitrile polymer and 0.6 parts by weight of polyoxyethylene ether, and deionized water is 8.4 parts by weight. The coating thickness of the composite slurry coating is about 2.8 μm, and the areal density is 3.5 g / m 2 , dry adhesion strength 8.5 N / m, wet adhesion strength 3.5 N / m.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 1 is that in step (2), the MOF1 slurry is 17 parts by weight, the zinc oxide slurry (30 parts by weight of silicon dioxide and 3.6 parts by weight of sodium dodecyl sulfate) is 80 parts by weight, 5 parts by weight of acrylonitrile polymer and 0.6 parts by weight of polyoxyethylene ether, and deionized water is 6.4 parts by weight. The coating thickness of the composite slurry coating is about 3.0 μm, and the areal density is 3.8 g / m 2 , dry adhesion strength 0 N / m, wet adhesion strength 0 N / m.

[0094] Comparative Example 4

[0095] The difference between this comparative example and Comparative Example 1 is that the material in step (1) is barium titanate slurry (26 parts by weight of silicon dioxide and 3.1 parts by weight of polyacrylamide) 80 parts by weight, (no addition of MOF1 slurry and polyolefin microsphere slurry), 8 parts by weight of acrylonitrile polymer and 1 part by weight of polyoxyethylene ether, and deionized water is 11 parts by weight. The coating thickness of the composite slurry coated layer is about 2.7 μm, the areal density is 4 g / m 2 , the dry adhesion strength is 0 N / m, and the wet adhesion strength is 0 N / m.

[0096] Comparative Example 5

[0097] The difference between this comparative example and Example 1 is that the material in step (2) is barium titanate slurry (26 parts by weight of silicon dioxide and 3.1 parts by weight of polyacrylamide) 45 parts by weight, MOF1 slurry 17 parts by weight, polymethyl methacrylate 6, 8 parts by weight of acrylonitrile polymer and 1 part by weight of polyoxyethylene ether, and deionized water is 23 parts by weight. The coating thickness of the composite slurry coated layer is about 7.5 μm, the areal density is 3.6 g / m 2 , the dry adhesion strength is 12.4 N / m, and the wet adhesion strength is 0 N / m.

[0098] Comparative Example 6

[0099] The difference between this comparative example and Example 1 is that the material in step (2) is PVDF emulsion 8 parts by weight, MOF1 slurry 17 parts by weight, zinc oxide slurry (30 parts by weight of silicon dioxide and 3.6 parts by weight of sodium dodecyl sulfate) 40 parts by weight, 5 parts by weight of acrylonitrile polymer and 0.6 parts by weight of polyoxyethylene ether, and deionized water is 29.4 parts by weight. The coating thickness of the composite slurry coated layer is about 2.9 μm, the areal density is 3.5 g / m 2 , the dry adhesion strength is 0 N / m, and the wet adhesion strength is 0 N / m.

[0100] Comparative Example 7

[0101] The difference between this comparative example and Example 1 is that the material in step (2) is alumina slurry 40 parts by weight and MOF1 slurry 17 parts by weight, 4 parts by weight of polyacrylate and 0.8 parts by weight of oxyethylene alkyl phenol ether are sequentially added, and 15.2 parts by weight of deionized water is stirred at a speed of 600 rpm / min for 30 min at room temperature to prepare coating slurry 1. Prepare PVDF slurry: use 50 parts by weight of PVDF emulsion, sequentially add 4 parts by weight of polyacrylate and 0.8 parts by weight of oxyethylene alkyl phenol ether, and 45.2 parts by weight of deionized water, and stir at a speed of 600 rpm / min for 30 min at room temperature to prepare coating slurry 2.

[0102] In step (3), the coated slurry 1 of step (2) is coated on both sides of the polyolefin separator, dried in an oven at 80℃ for 5 min, to obtain a single-layer heat-resistant separator 1, and then the coated slurry 2 is further coated on the separator 1, dried in an oven at 80℃ for 5 min, to obtain a multi-layer coated functionalized separator. The thickness of the separator coating is about 2.5 μm, the areal density is 4.0 g / m 2 , the dry adhesion strength is 4.0 N / m, and the wet adhesion strength is 1.0 N / m.

[0103] The beneficial effects of the present application are described in detail:

[0104] (1) To prove the porous framework structure of the MOF material in the present application, the specific surface area of the MOF1 and MOF2 powders prepared in step 1 was tested, and the results are shown in Figure 1 and Figure 2 . The specific surface area of MOF1 is 1481 m 2 / g, and the specific surface area of MOF2 is 1745 m 2 / g. Both MOFs have a large specific surface area and a large porosity.

[0105] (2) To prove the infiltration effect of the MOF material in the present application on the electrolyte, the contact angle test (sessile drop analysis method) was performed on the MOF1 and MOF2 powders prepared in step 1. When the electrolyte (EC:PC = 1:1, mass ratio) is dropped onto the surface of the sample, the MOF1 and MOF2 can absorb the electrolyte within 5 seconds, proving that the two MOF materials have good infiltration effect on the electrolyte (as shown in Figure 3 ), indicating that both of them have a certain storage capacity for the electrolyte.

[0106] (3) To prove that the MOF material in the present application can absorb the gas generated during the operation of the battery, the hydrogen adsorption test was performed on the MOF1 and MOF2 powders prepared in step 1, and the results are shown in Figure 4 . The hydrogen adsorption capacity of MOF1 and MOF2 can reach 1.5 mmol / g and 1.1 mmol / g, respectively. It is proved that the composite slurry of the present application coated on the separator can absorb and store a small amount of gas (such as hydrogen) generated inside the battery, further improving the safety of the battery and being beneficial to improve the long cycle stability of the battery.

[0107] (4) The data of the separator coating thickness, areal density, air permeability increment, and adhesion strength of Examples 1-6 and Comparative Examples 1-7 are summarized in Table 1:

[0108] Table 1

[0109]

[0110]

[0111] The thickness of Examples 1-6 is smaller than that of Comparative Example 5, only 1-3 μm, and the coating is thinner, which is beneficial to increase the energy density of the battery; the wet adhesion strength in Examples 1-6 is greater due to the lower swelling degree of the polyolefin microspheres in the electrolyte, which is beneficial to improve the long cycle performance of the battery. In contrast, the PMMA spheres in Comparative Example 5 are too large (about 5-8 μm), so the coating thickness is large, which reduces the energy density of the battery; in addition, the swelling degree of PMMA in the electrolyte is large, resulting in a wet adhesion strength of the coating separator of 0 N / m.

[0112] As can be seen from the comparison of Examples 1-6 with Comparative Examples 6 and 7, the adhesion of PVDF to the pole piece is weak, and multiple layers of coating are required, while the present application can achieve multifunctionality with one coating, which has a lower coating thickness, fewer process steps, and higher wet adhesion strength compared with the conventional coating method of one layer and one function or multiple layers and multiple functions.

[0113] In Examples 1-6, the coating thickness of the composite slurry is 1-3 μm, forming a thin coating and a low area density (1.2-3 g / m 2 ). Compared with the ceramic separator (Comparative Example 4), the coating separator of the present application has the advantage of lightweight; the coating separator of the present application has a low air permeability increment (compared with Comparative Examples 1, 2, 5, and 6), which is beneficial to the transmission of lithium ions; the coating separator of the present application has high dry adhesion and wet adhesion strength, which can improve the hardness of the battery to some extent and enhance the long cycle performance of the battery.

[0114] (5) To prove that the composite slurry of the present application can resist the high-temperature heat shrinkage of the separator, the coated separators in Examples 1-6 and Comparative Examples 1-4 and Comparative Example 7 were subjected to heat shrinkage measurement at 150°C. Experimental steps: take out the cutting sample plate (100 mm*100 mm), cut out the separator sample, measure the length A1 of the cut sample; set the oven temperature to 150°C, put the sample into the oven, and keep it for 1 h. Take out the separator. After cooling for 10 min, measure the length A2 of the sample; shrinkage rate calculation: separator heat shrinkage = (A1-A2) / A1*100. MD is the longitudinal direction of the separator, and TD is the transverse direction of the separator. The performance parameters are shown in Table 2:

[0115] Table 2

[0116] Example / Comparative Example MD (%) TD (%) Example 1 2.10 1.98 Example 2 2.46 2.34 Example 3 2.53 2.46 Example 4 1.83 1.74 Example 5 2.28 2.16 Example 6 2.34 2.26 Comparative Example 1 6.53 6.29 Comparative Example 2 50.63 50.19 Comparative Example 3 3.42 3.21 Comparative Example 4 25.89 23.80 Comparative Example 7 3.58 3.62

[0117] As can be seen from the heat shrinkage data of Examples 1-6 and Comparative Examples 1-4 and Comparative Example 7, the shrinkage rate of the separator in Examples 1-6 at 150°C is less than 3%. It is measured that the air permeation time of the separator in Example 1 is infinite after heating at 130°C for 1 h, indicating that the pores of the separator are closed (for example, the air permeation time of the separator in Comparative Example 1 is 0.5 s after heating at 130°C for 1 h, indicating that the pores of the separator are not closed). Figure 5As shown, the length of the membrane MD direction is 99.5 mm, which improves the safety and stability of the battery. In Comparative Examples 1 and 2, by adjusting the ratio of polyolefin microspheres and ceramic slurry, it can be seen that the polyolefin microspheres are not heat-resistant. Increasing the ratio of microspheres can achieve bonding performance, but cannot have heat shrinkage resistance.

[0118] From the data of the examples and comparative examples, it can be concluded that the composite coating slurry of the present application can help the battery separator to effectively suppress thermal shrinkage (and also have the function of bonding with the pole piece), effectively prevent the physical deformation and thermal runaway of the battery separator, and thus improve the safety performance and cycle stability of the battery.

[0119] (6) To prove that the composite slurry of the present application has the effect of absorbing and containing electrolyte, the coated separators in Examples 1-6 and Comparative Examples 4-7 were subjected to liquid absorption determination. Test method: take the coated separator sample, size 100mm*100mm (MD*TD), and weigh it as m0; soak in electrolyte (EC:PC=1:1, mass ratio) at room temperature for 24h, then take out and wipe the electrolyte on the surface of the separator, and then weigh it as m1. The liquid absorption rate calculation formula is: x=(m1-m0) / m0. The test parameters are shown in Table 3:

[0120] Table 3

[0121] Example / Comparative Example Liquid uptake (%) Example 1 160.78 Example 2 134.65 Example 3 123.12 Example 4 192.06 Example 5 167.09 Example 6 135.10 Comparative Example 4 100.12 Comparative Example 5 158.20 Comparative Example 6 132.32 Comparative Example 7 134.3

[0122] Examples 1-3 added MOF1 slurry components, and Examples 4-6 added MOF2 slurry, wherein the specific surface area of MOF2 is larger and the liquid absorption rate is also larger. The liquid absorption amount of Examples 1-6 and Comparative Examples 5-7 is larger than that of Comparative Example 4, because in Comparative Example 4, the main component is ceramic, which can only use the voids formed by the particles to store electrolyte, and the storage capacity is worse compared to Examples 1-6 and Comparative Examples 5-7, which have MOF components with a specific surface area as high as 1500m 2 / g, which can absorb more electrolyte and ensure the long cycle stability of the battery. Figure 3 The contact angle of the coated separators of Examples 1, 4 and Comparative Example 4 in the electrolyte can also show that the MOF material of the present application has a stronger absorption capacity for electrolyte than the ceramic material.

[0123] (7) To prove that the coated separator of the present application can absorb the gas generated by the battery and improve the cycle stability of the battery, the coated separators in Examples 1-6 and Comparative Examples 3-5, 7 were applied to lithium batteries and the performance of the batteries was tested.

[0124] ①Cycling performance test: charge at 1C to 4.20V, then constant voltage charge to current drop to 0.1C, then discharge at 1C to 3.0V, so on and so forth for 700 cycles, record the discharge capacity of the 1st week and the 700th week, calculate the capacity retention rate of the battery cycle: capacity retention rate = the discharge capacity of the 700th week / the discharge capacity of the 1st week*100%.

[0125] ②High temperature storage performance test: according to the cycling performance test method, cycle for 1 week, record the volume of the battery in the 1st week, then charge at 1C to the formation cut-off voltage, and constant voltage charge to current drop to 0.1C, stand in a 60℃ constant temperature oven for 30 days, then cycle for 2 weeks at room temperature according to the cycling performance test method, record the volume of the battery after high temperature storage. Calculate the volume expansion rate of the battery after high temperature storage: volume expansion rate = (volume after storage-volume in the 1st week) / volume in the 1st week*100%.

[0126] The above test results are shown in Table 4:

[0127] Table 4

[0128] Example / Comparative Example Volume expansion (%) Volume retention (%) Example 1 1.6 91.9 Example 2 2.4 92.5 Example 3 3.1 92.9 Example 4 1.2 93.8 Example 5 2.0 94.2 Example 6 2.6 94.6 Comparative Example 3 3.6 83.5 Comparative Example 4 39.0 80.0 Comparative Example 5 3.5 79.9 Comparative Example 7 3.5 87.6

[0129] From Table 4, it can be seen that the MOF material added in Examples 1-6 and Comparative Examples 3, 5 and 7 can reduce the volume expansion rate of the battery caused by gas production during charging and discharging, which provides a guarantee for the cycle stability of the battery. However, the capacity retention rate of Comparative Examples 3, 5 and 7 is low, which shows that only using porous material MOF to reduce the volume expansion rate of the battery is not enough to maintain the stability of the battery, and it is also necessary to combine the adhesion strength and other properties to make the battery stable during use. 100 batteries of Examples 1 and 4 were repeatedly tested, and it was found that the batteries did not have a drop, and the capacity was not less than 80% after 1500 cycles.

[0130] Both the ceramic and the MOF are rigid materials with excellent heat resistance, which can be used as a heat-resistant layer of the separator; the polyolefin microspheres are used as an adhesion layer of the separator. The polyolefin microspheres in the present application have a smaller density than water, and the ceramic material and the MOF have a larger density than water; the ceramic material itself has a high surface energy barrier, which is easy to produce electrostatic adsorption with the MOF in the present application, and agglomerate to accelerate sinking in water. During the drying process of the coated separator in the present application, the ceramic material and the MOF sink to the lowermost layer as the heat-resistant layer, and the polyolefin microspheres float on the upper layer as the adhesion layer, thereby achieving the purpose of one-time coating. From the above, it can be seen that the coated separator in the present application has the advantages of low cost, simple process, and the like. Figure 6It can be seen that the microspheres in Example 1 and Example 4 are above the heat-resistant layer, while the microspheres in Comparative Example 1 are less and almost buried in the heat-resistant layer, resulting in no adhesion; the microspheres in Comparative Example 2 are more and the number of microspheres floating on the heat-resistant layer is more, having adhesion, but the heat resistance of the coating is insufficient. Without adding MOF, whether increasing or decreasing the proportion of polyolefin microspheres, the functions of adhesion and heat shrinkage cannot be achieved. Comparative Example 1 also shows that after the microspheres are mixed with the ceramic, the electrostatic adsorption of the ceramic itself is weak, which is not enough to form a strong density difference with the microspheres, so that the microspheres are difficult to completely float on the heat-resistant layer.

[0131] In summary, the coating slurry of the present application can be coated on the substrate separator at one time, has lower coating thickness, fewer process steps, higher wet adhesion strength, can realize rapid adhesion of the separator and the pole piece, has high adhesion strength, realizes the closure of the separator at 130℃, and the shrinkage rate at 150℃ is only 3.0%, which is better than the heat shrinkage resistance of the ceramic separator; and the framework structure of MOF can not only adsorb and store the gas generated inside the battery, but also store the electrolyte in the large pores and high specific surface area of MOF. The composite slurry of the present application applied to the battery separator greatly improves the cycle performance, stability and safety of the lithium ion battery in use.

Claims

1. A high heat resistant high bonding composite paste, characterized by, According to the weight parts, the following raw materials are included: 5-20 parts by weight of MOF slurry, 3-8 parts by weight of polyolefin emulsion, 40-80 parts by weight of ceramic slurry, 3-8 parts by weight of adhesive, 0.5-1 parts by weight of wetting agent, and 10-80 parts by weight of solvent; The MOF slurry is obtained after mixing MOF material and water, wherein the single particle size of the MOF material is 0.1-1 μm, the specific surface area is 10-3500 m 2 / g, the pore size distribution is 0.5-8 nm, and the total pore volume is 0.2-5.0 mL / g. The high-heat-resistant and high-adhesion composite slurry is applied to coating a separator, and during the drying process at 80℃ for 5min, due to the density difference, the ceramic material and the MOF sink to the lowermost layer as a heat-resistant layer, and the polyolefin microspheres float in the upper layer as an adhesive layer, achieving one-time coating. The MOF material is a UiO series or a ZiF series. The ceramic slurry is obtained by mixing a ceramic material and a dispersant. The polyolefin emulsion is at least one of a homopolymer emulsion or a copolymer emulsion of polyethylene, polypropylene, or polybutylene, and the polyolefin microsphere emulsion has a core-shell structure and an acrylate on the surface of the polyolefin microspheres.

2. The high heat resistant and high adhesive composite paste according to claim 1, wherein, The ceramic material is at least one of aluminum oxide, silicon dioxide, magnesium hydroxide, rutile titanium dioxide, magnesium oxide, boehmite, zirconium dioxide, barium titanate, and zinc oxide.

3. The high heat resistant and high adhesive composite paste according to claim 1, wherein, The adhesive is at least one of polymethacrylic acid, styrene butadiene rubber, polyacrylate, polyurethane, polyvinyl acetate, an acrylic polymer, or an acrylonitrile polymer.

4. The high heat resistant and high adhesive composite paste according to claim 1, wherein, The wetting agent is at least one of an oxyethylene alkyl phenol ether, a polyoxyethylene fatty alcohol ether, or a fluorine-containing polyoxyethylene ether.

5. The high heat resistant and high adhesive composite paste according to claim 1, wherein, The solvent is deionized water.

6. The method for preparing the high heat-resistant and high-adhesion composite slurry according to claim 1, characterized in that, The method comprises: The MOF slurry, the polyolefin microsphere slurry, and the ceramic slurry are weighed in proportion, stirred at a speed of 200-1000 rpm / min, mixed and stirred at room temperature for 20-60 min, then the adhesive, the wetting agent, and the solvent are added in sequence, stirred at a speed of 200-1000 rpm / min, and sequentially stirred at room temperature for 20-60 min to obtain the composite slurry.

7. Application of the high-heat-resistant and high-adhesion composite slurry of claim 1 in a lithium ion battery separator.

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