Composite separator, its manufacturing method and use

Abstract

The heat-resistant coating layer is a mixture of heat-resistant polymer particles and inorganic fillers, which adhere to each other to form a three-dimensional network structure, improving the thermal stability of the composite separator. The composite separator's rupture temperature is above 200°C, improving the safety performance of the battery and reaching the performance level of oil-based coatings. [Means] A composite separator, its manufacturing method and use, the composite separator comprising a porous substrate and a heat-resistant coating layer provided on one or both sides of the porous substrate, the heat-resistant coating layer comprising heat-resistant polymer particles, an inorganic filler and an auxiliary binder, the heat-resistant polymer particles comprising a heat-resistant resin having an average particle size of 10 nm to 200 nm and a glass transition temperature of Ts+40°C or higher.

Description

[Technical Field]

[0001] The present application is in the field of lithium ion batteries, for example, composite separators, their manufacturing methods and uses. [Background technology]

[0002] Conventional battery separators are typically coated with a ceramic coating, but ceramic-coated separators have little adhesion to the polar pieces. This causes the positive and negative electrodes to repeatedly shrink and expand during battery charging and discharging, leading to separation between the separator and polar pieces and resulting in problems with battery performance and stability. To address the shortcomings of conventional separators, researchers have applied an adhesive to the ceramic coating to ensure a certain degree of adhesion between the separator and polar pieces, improving battery stability. However, this process requires complex manufacturing processes and high production costs. In addition, organic-inorganic (ceramic) composite separators have been developed, but their thermal shrinkage performance is significantly worse than that of fully ceramic-coated separators. Oil-based coatings are highly safe, but they are expensive and pollute the environment.

[0003] With the increasing emphasis on new energy sources, the research, development, and application of lithium-ion battery technology are gradually expanding and maturing. As an energy carrier, the safety performance of lithium-ion batteries is one of the important standards for evaluating their quality. Separators are a key component in lithium batteries, playing a key protective role and significantly improving their safety performance. Compared with traditional polyolefin separators and their derived inorganic and organic coated separators, aramid-coated separators have advantages such as oxidation resistance, acid and base resistance, flame retardancy, abrasion resistance, and tear resistance, and their thermomechanical strength is far superior to other separators currently on the market. However, the manufacturing process for existing aramid-coated separators requires the use of large amounts of organic solvents for dissolution and extraction, resulting in increasingly severe environmental stress and increased product costs.

[0004] With the development of new energy vehicle technology, lithium-ion batteries have attracted widespread attention due to their advantages such as high energy density and long cycle life, but occasional safety incidents involving lithium-ion batteries are unfortunate. While the separator, as one of the key components of a lithium-ion battery, does not provide energy, it plays an important role in the safety performance of the battery. The separator separates the positive and negative electrodes of the battery, preventing short circuits caused by direct contact between the positive and negative electrodes, and providing a lithium ion transmission path to block electronic transmission. Therefore, the safety of lithium-ion batteries places higher requirements on the separator.

[0005] Polyolefin separators are widely used as separators for lithium-ion batteries due to their advantages such as low cost, good stretchability, and rich pore structure. However, single-layer polyethylene (PE) and polypropylene (PP) separators have poor high-temperature resistance and soften and shrink at temperatures above 120°C, causing short circuits in the battery. Furthermore, lithium dendrites generated during cycling can penetrate the separator, leading to short circuits and, in severe cases, safety hazards such as battery fire and even explosion. Therefore, single-layer polyolefin separators cannot ensure the safe use of lithium-ion batteries.

[0006] One conventional solution involves using a polyolefin membrane as the base membrane and then coating its surface with a high-temperature-resistant inorganic ceramic coating to form a composite separator. Common inorganic particles include alumina (Al2O3), silica (SiO2), zirconium oxide (ZrO2), and boehmite. While this method effectively improves the separator's high-temperature resistance and hydrophilicity, the ceramic particles have poor bonding properties with the substrate and are prone to falling off the coating. Using a binder to increase the bonding strength can clog the separator's pores, reducing its breathability. Another approach involves coating the surface of a polyolefin separator with a high-temperature-resistant organic PVDF coating. Because PVDF is a water-repellent polymer, the PVDF coating process is primarily oil-based. However, this oil-based coating process requires the use of large amounts of organic solvents, which causes significant environmental pollution and is expensive.

[0007] Compared with conventional polyolefin separators and their derivative inorganic and organic coatings, aramid-coated separators offer advantages such as oxidation resistance, acid and base resistance, flame retardancy, abrasion resistance, and tear resistance, and their thermomechanical strength is far superior to other separators currently on the market. However, the manufacturing process for existing aramid-coated separators requires the use of large amounts of organic solvents for dissolution and extraction, resulting in increasingly severe environmental stress and increased product costs. Therefore, there is an urgent need to develop relatively green and environmentally friendly materials that have extremely high strength and modulus, excellent high-temperature and chemical resistance, and other characteristics. Furthermore, to address the technical and environmental problems of oil-based coating slurries, such as poor bonding strength between the coating layer and the base membrane, low porosity, and difficulty in controlling pore formation uniformity, a corresponding water-based coating solution needs to be developed. Summary of the Invention [Problem to be solved by the invention]

[0008] The following is a summary of the subject matter described in detail herein. This summary does not limit the scope of the claims.

[0009] To address the problems of poor stability of lithium-ion battery separators, poor bonding strength between the coating layer and the base membrane, and environmental pollution, the present application provides a composite separator, its manufacturing method, and use. The heat-resistant coating layer of the composite separator employs a mixed coating of heat-resistant polymer particles and inorganic fillers. The heat-resistant polymer particles or the heat-resistant polymer particles and ceramic particles bond to each other to form a three-dimensional network structure, improving the thermal stability of the composite separator. The composite separator has a film rupture temperature above 200°C, improving battery safety performance and reaching the performance level of oil-based coating films. It also exhibits stronger bonding strength between the coating layer and the base membrane and better electrolyte wettability. Furthermore, the water-based coating significantly reduces the use of oil-based solvents, reducing costs, improving production safety, and being environmentally friendly. [Means for solving the problem]

[0010] One object of the present application is to A porous substrate and a heat-resistant coating layer provided on one or both sides of the porous substrate, the heat-resistant coating layer including heat-resistant polymer particles, an inorganic filler, and an auxiliary binder. The object is to provide a composite separator.

[0011] In one embodiment, the heat-resistant polymer particles contain a heat-resistant resin having an average particle size of 10 nm to 200 nm and a glass transition temperature of Ts+40°C or higher, where Ts is the melting point of the porous substrate, and the weight-average molecular weight of the heat-resistant resin is 4.0 × 10 4 ~2×10 6 g / mol. When a heat-resistant resin having a weight-average molecular weight within this range is selected and the aqueous coating slurry formed is applied to a porous substrate, it is advantageous for forming a better and more uniform heat-resistant particle coating layer, and when the average particle size of the heat-resistant polymer particles is within the range of 10 nm to 200 nm, better bonding between the heat-resistant polymer particles or between the heat-resistant polymer particles and the inorganic filler can be achieved to form a network structure.

[0012] In one embodiment, the heat-resistant resin is at least one selected from polyimide, aramid 1414 (polyparaphenylene terephthalamide), aramid 1413 (polymetaphenylene terephthalamide), aramid 1313 (polymetaphenylene isophthalamide), thiophene aramid, pyrrolyl aramid, furyl aramid, pyridyl polyamide, polyamide imide, polyether imide, polysulfone, polyketone, polyether ketone, polyether ether ketone, polyparaphenylene benzobisoxazole, and cellulose.

[0013] In one embodiment, the inorganic filler has an average particle size of 10 nm to 1000 nm, and is at least one selected from ceramics, metal oxides, metal hydroxides, metal carbonates, silicates, kaolin, talc, minerals, and glasses.

[0014] In one embodiment, the inorganic filler is at least one selected from boehmite, alumina, silica, barium titanate, titania, zinc oxide, magnesium oxide, magnesium hydroxide, zirconium oxide, and oxide solid electrolytes.

[0015] In one embodiment, the oxide solid electrolyte is at least one selected from a perovskite-type electrolyte, a NASICON-type electrolyte, a LISICON-type electrolyte, a garnet-type electrolyte, and a LiPON-type electrolyte.

[0016] In one embodiment, when the volume concentration of the heat-resistant polymer particles in the heat-resistant polymer particles and the inorganic filler is VP1, the critical volume concentration of the heat-resistant polymer particles is VP0, and the volume concentration of the inorganic filler having a particle size of less than 100 nm in the heat-resistant polymer particles and the inorganic filler is VP2, VP0, VP1, and VP2 satisfy the following relationship: When the inorganic filler is a mixture of one or more fillers and the average particle size of the inorganic filler is greater than 100 nm, VP0≦VP1≦100% is satisfied; When the inorganic filler is a mixture of a plurality of fillers and at least one filler has an average particle size of less than 100 nm, VP0≦VP1+VP2≦100% is satisfied; Here, VP0=0.685×DP / (0.685×DP+0.5233DT), DP is the average diameter of the heat-resistant polymer particles, and DT is the average diameter of the inorganic filler.

[0017] Because heat-resistant polymer particles have lower hardness and poorer thermal shrinkage resistance than inorganic fillers, the lower the proportion of heat-resistant polymer particles, the better the separator's heat shrinkage performance. However, if the proportion is too low, the separator will not achieve the high membrane rupture effect (when maintained at a temperature of Ts + 40°C for 1 hour). A high proportion of heat-resistant polymer particles increases the porosity, allowing for more electrolyte storage and improving the battery's electrochemical performance. A low-density heat-resistant polymer reduces the density of the coating layer, increasing the mass energy density of the battery. However, if the proportion of heat-resistant polymer particles is too high, the coating layer is likely to develop numerous cracks, which is detrimental to battery safety. Therefore, to ensure the composite separator's high membrane rupture temperature and stability, the volume ratio of the heat-resistant polymer particles to the total volume of the heat-resistant polymer particles and inorganic filler is preferably VP0 to 0.5 × (VP0 + 1).

[0018] In view of the high cost of heat-resistant polymers and from the viewpoint of cost saving, in one embodiment, the volume ratio of the heat-resistant polymer particles to the total volume of the heat-resistant polymer particles and the inorganic filler is VP0 to 0.5 × (VP0 + 0.7).

[0019] In one embodiment, the auxiliary binder comprises a binder and a coupling agent, the amount of the binder being 0.5 wt% to 10 wt% of the total mass of the heat-resistant polymer particles and the inorganic filler, and the amount of the coupling agent being 1 wt% to 20 wt% of the total mass of the heat-resistant polymer particles and the inorganic filler. The auxiliary binder can enhance adhesion between the heat-resistant polymer particles, between the heat-resistant polymer particles and the inorganic filler, and between the inorganic filler and the porous substrate.

[0020] In one embodiment, the coupling agent is a silane coupling agent, and the content of Si atoms introduced from the silane coupling agent in the heat-resistant coating layer accounts for 0.05 wt% to 5 wt% of the mass of the heat-resistant coating layer.

[0021] In one embodiment, the binder is at least one selected from polyvinyl alcohol, polyacrylic, polyurethane, polyimide polymers, and carboxymethyl cellulose, and the silane coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane. In addition to the above coupling agents, an aluminate coupling agent or a titanate coupling agent may also be selected as the coupling agent.

[0022] From the viewpoint of obtaining good mechanical properties and internal resistance, the thickness of the porous substrate is preferably 1 μm to 25 μm in the present application. From the viewpoint of suppressing short circuits in the battery and obtaining sufficient ion permeability, the Gurley value of the porous substrate is preferably 20 seconds / 100 cc to 300 seconds / 100 cc in the present application. The porous substrate preferably contains a thermoplastic resin to impart a closing function to the porous substrate. The so-called closing function refers to the function in which, when the temperature of the battery rises, the constituent material of the porous substrate melts and closes the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. In the present application, the material of the porous substrate is preferably a thermoplastic resin with a melting point of less than 200°C.

[0023] In one embodiment, the thermoplastic resin is selected from polyethylene terephthalate and / or polyolefins.

[0024] In one embodiment, the polyolefin has a weight-average molecular weight Mw of 100,000 to 5,000,000, and is polyethylene and / or polypropylene. When the polyolefin has an Mw of 100,000 or more, the porous substrate can be provided with sufficient mechanical properties, while when the polyolefin has an Mw of 5,000,000 or less, the porous substrate formed from the polyolefin has good closing properties and can be easily formed into a porous membrane.

[0025] In order to obtain a heat-resistant coating layer with a suitable thickness and uniformity, the loading of the heat-resistant coating layer in this application is 1 to 9 g / m 2 It is preferable that:

[0026] Another object of the present application is to (1) synthesizing a heat-resistant resin; Step (2) of preparing a dispersion of heat-resistant polymer particles using the heat-resistant resin produced in step (1); Step (3) of preparing a coating slurry, which comprises adding the dispersion of heat-resistant polymer particles obtained in step (2), an inorganic filler, a binder, and a coupling agent to an aqueous solvent (the dispersion system of the coating slurry according to the present invention is considered to be an aqueous solvent) and mixing them uniformly to obtain a coating slurry; and (4) applying the coating slurry to any one or both sides of the porous substrate and curing it to obtain a composite separator. Another object of the present invention is to provide a method for producing the composite separator.

[0027] In one embodiment, the aqueous solvent in step (3) is a mixed solution of one or more solvents selected from deionized water, ethanol, ethylene glycol, glycerin, isopropyl alcohol, propylene glycol, butanol, and acetic acid. This application eliminates the use of oil-based solvents such as NMP and DMAc, which are commonly used in conventional techniques, and instead uses a more benign aqueous solvent, thereby reducing production costs and environmental pollution caused by the coating process and improving production safety.

[0028] The coating slurry further comprises one or more of a surfactant in an amount of 0.05 wt% to 7 wt%, a dispersant in an amount of 0.05 wt% to 9 wt%, a wetting agent in an amount of 0.02 wt% to 7 wt%, and an antifoaming agent in an amount of 0.04 wt% to 4 wt%, based on the mass of the coating slurry.

[0029] In one embodiment, the solid content of the coating slurry described in step (3) is 2% to 80%, and the coating method described in step (4) is at least one selected from electrostatic spraying, blade coating, spin coating, slit die coating, transfer coating, dipping coating, gravure coating, and microgravure coating.

[0030] In one embodiment, the coating slurry has a solids content of 4% to 40%.

[0031] In one embodiment, in order to improve the wettability of the porous substrate with a coating slurry for forming a heat-resistant coating layer, it is preferable that the present invention further includes a surface treatment of the porous substrate in step (4), the surface treatment being any one of corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment, provided that the properties of the porous substrate are not damaged.

[0032] A further object of the present application is to provide a use of said composite separator in a lithium ion battery comprising a positive electrode, a negative electrode and said composite separator. [Effects of the Invention]

[0033] The beneficial effects of the present invention are as follows:

[0034] (1) This application employs a mixed coating of heat-resistant polymer particles and inorganic fillers, and in the resulting heat-resistant coating layer, a three-dimensional network structure can be formed between the heat-resistant polymer particles or between the heat-resistant polymer particles and the inorganic filler, improving the thermal stability of the composite separator. Furthermore, the auxiliary binder can better bond the heat-resistant polymer particles or between the heat-resistant polymer particles and the inorganic filler to form a three-dimensional network structure, and improve the bonding strength between the heat-resistant coating layer and the porous substrate, significantly improving the stability of the composite separator. The composite separator's film rupture temperature can be increased to above 200°C, improving the safety performance of the battery and reaching the performance level of an oil-based coating film.

[0035] (2) This application uses a thermoplastic resin with a melting point of less than 200°C. When the temperature rises, the porous substrate melts and flows into the pores of the heat-resistant coating layer, sealing the pores and achieving the closing effect of the separator, thereby blocking the movement of ions, preventing thermal runaway of the battery, and improving the safety performance of the battery.

[0036] (3) The manufacturing method of the present invention avoids the use of oil-based solvents and instead uses water-based solvents, which are more environmentally friendly, thereby reducing the production cost of coating and environmental pollution caused by the coating process, and improving production safety.

[0037] Other aspects may be understood upon reading and understanding the drawings and detailed description. [Brief explanation of the drawings]

[0038] The drawings are intended to provide a further understanding of the technical solution of the present specification, constitute a part of the specification, and are used to interpret the technical solution of the present specification together with the examples of the present specification, but are not intended to limit the technical solution of the present specification.

[0039] The present application will now be further described with reference to the figures and examples.

[0040] [Figure 1] FIG. 2 is a structural schematic diagram of the composite separator produced in Example 1 of the present application. [Figure 2] FIG. 2 is an SEM image of the surface of the composite separator produced in Example 1 of the present application. [Figure 3] FIG. 2 is a structural schematic diagram of a composite separator produced in Example 4 of the present application. [Figure 4] 1 is a graph showing the film rupture temperature measured by TMA for composite separators produced in Examples 2 and 7 of the present application, where a is the curve for Example 2 and b is the curve for Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0041] The technical solutions in the embodiments of the present application will be described below clearly and completely. Obviously, the described embodiments are only some of the embodiments of the present application, not all of the embodiments. The following description of at least one exemplary embodiment is merely explanatory in nature and does not impose any limitations on the present application and its application or use. According to the embodiments of the present application, other embodiments that can be obtained by those skilled in the art without performing creative work are all within the scope of protection of the present application.

[0042] Unless otherwise specified, the numerical values ​​described in these examples do not limit the scope of the present application. Techniques and methods known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques and methods should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as illustrative only and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0043] In the following examples, experimental methods without specific conditions are generally measured according to Chinese national standards, and if there is no corresponding Chinese national standard, they are performed according to general international standards or standard requirements submitted by relevant companies. Unless otherwise specified, all parts are parts by weight, and all percentages are percentages by weight. [Example]

[0044] Step 1: Synthesis of heat-resistant resin

[0045] Under Ar gas atmosphere and stirring conditions, the temperature of the system was controlled at 90°C, and calcium chloride, a co-solvent, was added to NMP (N-methylpyrrolidone) and dissolved therein. The amount of the co-solvent added was 5% of the mass of NMP. After stirring for about 1 hour, the temperature of the reaction system was lowered to room temperature, metaphenylenediamine was added, and stirring was continued. After the metaphenylenediamine was completely dissolved, the temperature of the reaction system was lowered to 3°C, and then isophthaloyl chloride (added in an amount equimolar to the metaphenylenediamine) was added. The rotation speed was increased to 800 r / min until the isophthaloyl chloride was completely dissolved. After the reaction was continued for 40 minutes, the temperature of the reaction system was raised to 75°C, and the reaction was continued to obtain meta-aramid (i.e., aramid 1313).

[0046] Step 2: Preparation of heat-resistant polymer particle dispersion

[0047] (1) 2.0 kg of the meta-aramid prepared in step 1 was added to a mixer, 28.0 kg of NMP was added, and the mixture was stirred for 20 minutes. While stirring, water was added until a cloudy meta-aramid dispersion was obtained, and then 9 kg of isopropyl alcohol was added and the mixture was continued to be stirred uniformly to obtain a first dispersion.

[0048] (2) 33 kg of deionized water and 7 kg of isopropyl alcohol were added to a stirrer and mixed uniformly to obtain a second dispersion.

[0049] (3) The first dispersion was gradually added to the second dispersion, and the stirring speed was set to 5000 r / min to obtain a mixed dispersion containing heat-resistant polymer particles.

[0050] (4) After filtering and washing the mixed dispersion, it was subjected to high-pressure homogenization in deionized water to obtain a uniform and stable dispersion of heat-resistant polymer particles.

[0051] Step 3, Preparation of coating slurry

[0052] The heat-resistant polymer particle dispersion obtained in the above step, alumina particles (inorganic filler), PVA (binder), γ-glycidoxypropyltrimethoxysilane (coupling agent), and deionized water were uniformly mixed, and then 0.05 wt% of the coating slurry mass (a wetting agent, alkylphenol polyethylene oxide) was added, followed by thorough and uniform stirring to obtain a coating slurry with a solid content of 38.3%.

[0053] The dry weight ratio of the heat-resistant polymer particles to the alumina particles was 8:92, the dry weight of the PVA accounted for 4 wt% of the total mass of the heat-resistant polymer particles and the alumina particles, and the dry weight of the γ-glycidoxypropyltrimethoxysilane accounted for 10 wt% of the total mass of the heat-resistant polymer particles and the alumina particles. The average particle size of the heat-resistant polymer particles was 30 nm, and the particle size D50 of the alumina particles was 420 nm.

[0054] Step 4: Applying the coating slurry and curing

[0055] The coating slurry obtained in step 3 was uniformly roll coated onto both sides of a 9 μm thick PE separator (porous substrate), and thoroughly dried in an oven at 60°C to obtain a composite separator.

[0056] FIG. 1 is a structural schematic diagram of the composite separator produced in this example, where 001 is a heat-resistant coating layer applied to both sides of the porous substrate, 002 is the porous substrate, the thickness of the single-layer heat-resistant coating layer was 2.5 μm, and the total thickness of the composite separator was 14 μm.

[0057] FIG. 2 is an SEM image of the surface of the composite separator produced in this example, and it can be seen that the surface structure is a three-dimensional network structure.

[0058] It should be noted that commercially available meta-aramid may be used directly in place of the meta-aramid prepared in this example, and the same effect will be obtained. [Example]

[0059] Step 1: Synthesis of heat-resistant resin

[0060] The system temperature was controlled at 25°C under an Ar gas atmosphere and stirring conditions. DMAC (N,N-dimethylacetamide) and ODA (4,4-diaminodiphenyl ether) were added to the reaction vessel, followed by the addition of an equimolar amount of 2,5-thiophenedicarbonyl dichloride to the ODA. The reaction mixture was then stirred at 25°C for 0.5 hours to react and produce thiophene polyamide.

[0061] Step 2: Preparation of heat-resistant polymer particle dispersion

[0062] (1) 2.67 kg of the thiophene polyamide prepared in step 1 was added to a mixer, 17.33 kg of DMAC was added, and the mixture was stirred for 20 minutes. While stirring, water was added until a cloudy thiophene polyamide dispersion was obtained, and then 3 kg of isopropyl alcohol was added and the mixture was stirred uniformly to obtain a first dispersion.

[0063] (2) 25 kg of deionized water and 5 kg of isopropyl alcohol were added to a stirrer and mixed uniformly to obtain a second dispersion.

[0064] (3) The first dispersion was gradually added to the second dispersion, and the stirring speed was set to 5000 r / min to obtain a mixed dispersion containing heat-resistant polymer particles.

[0065] (4) After filtering and washing the mixed dispersion, it was subjected to high-pressure homogenization in deionized water to obtain a uniform and stable dispersion of heat-resistant polymer particles.

[0066] Step 3, Preparation of coating slurry

[0067] The heat-resistant polymer particle dispersion obtained in the above step, boehmite particles (inorganic filler), PVA (binder), γ-glycidoxypropyltrimethoxysilane (coupling agent), and deionized water were uniformly mixed, and then 0.05 wt% of the coating slurry mass (a wetting agent, alkylphenol polyethylene oxide) was added, followed by thorough and uniform stirring to obtain a coating slurry with a solid content of 38.3%.

[0068] The dry weight ratio of the heat-resistant polymer particles to the boehmite particles was 5:95, the dry weight of the PVA accounted for 4 wt% of the combined mass of the heat-resistant polymer particles and the boehmite particles, and the dry weight of the γ-glycidoxypropyltrimethoxysilane accounted for 10 wt% of the combined mass of the heat-resistant polymer and the boehmite particles. The average particle size of the heat-resistant polymer particles was 85 nm, the particle size D50 of boehmite particles 1 was 530 nm, and the particle size D50 of boehmite particles 2 was 50 nm. The mass ratio of boehmite particles 1 to boehmite particles 2 was 90:5.

[0069] Step 4: Applying the coating slurry and curing

[0070] The coating slurry obtained in step 3 was uniformly roll coated onto both sides of a 9 μm thick PE separator (porous substrate), and thoroughly dried in an oven at 60°C to obtain a composite separator.

[0071] The structural schematic diagram of the composite separator prepared in this example can be seen in Figure 1, where 001 is the heat-resistant coating layer applied to both sides of the porous substrate, 002 is the porous substrate, the thickness of the single-layer heat-resistant coating layer was 2.5 μm, and the total thickness of the composite separator was 14 μm.

[0072] The SEM image of the surface of the composite separator produced in this example is not significantly different from that shown in FIG. 2, and the surface structure is a three-dimensional network structure. [Example]

[0073] Step 1: Synthesis of heat-resistant resin

[0074] Polyetherimide was produced by polycondensation reaction of tetracarboxylic dianhydride and metaphenylenediamine. Commercially available polyetherimide may also be used directly.

[0075] Step 2: Preparation of heat-resistant polymer particle dispersion

[0076] (1) 2.5 kg of the polyetherimide prepared in step 1 or a commercially available polyetherimide was added to a mixer, 17.5 kg of DMAC was added, and the mixture was stirred for 20 minutes. Water was added while stirring until a cloudy polyetherimide dispersion was obtained, and then 6 kg of isopropyl alcohol was added and the mixture was stirred uniformly to obtain a first dispersion.

[0077] (2) 26 kg of deionized water and 4 kg of isopropyl alcohol were added to a stirrer and mixed uniformly to obtain a second dispersion.

[0078] (3) The first dispersion was gradually added to the second dispersion, and the stirring speed was set to 5000 r / min to obtain a mixed dispersion containing heat-resistant polymer particles.

[0079] (4) After filtering and washing the mixed dispersion, it was subjected to high-pressure homogenization in deionized water to obtain a uniform and stable dispersion of heat-resistant polymer particles.

[0080] Step 3, Preparation of coating slurry

[0081] The heat-resistant polymer particle dispersion obtained in the above step, magnesium hydroxide particles (inorganic filler), PVA (binder), γ-glycidoxypropyltrimethoxysilane (coupling agent), and deionized water were uniformly mixed, and then 0.05 wt% of the coating slurry mass (a wetting agent, alkylphenol polyethylene oxide) was added, followed by thorough and uniform stirring to obtain a coating slurry with a solid content of 20%.

[0082] The dry weight ratio of the heat-resistant polymer particles to the magnesium hydroxide particles was 10:90, the dry weight of the PVA accounted for 4 wt% of the combined mass of the heat-resistant polymer particles and the magnesium hydroxide particles, and the dry weight of the γ-glycidoxypropyltrimethoxysilane accounted for 10 wt% of the combined mass of the heat-resistant polymer particles and the magnesium hydroxide particles. The average particle size of the heat-resistant polymer particles was 50 nm, and the particle size D50 of the magnesium hydroxide particles was 800 nm.

[0083] Step 4: Applying the coating slurry and curing

[0084] The coating slurry obtained in step 3 was uniformly roll coated onto both sides of a 9 μm thick PE separator (porous substrate), and thoroughly dried in an oven at 60°C to obtain a composite separator.

[0085] The structural schematic diagram of the composite separator prepared in this example can be seen in Figure 1, where 001 is the heat-resistant coating layer applied to both sides of the porous substrate, 002 is the porous substrate, the thickness of the single-layer heat-resistant coating layer was 2.5 μm, and the total thickness of the composite separator was 14 μm.

[0086] The SEM image of the surface of the composite separator produced in this example is not significantly different from that shown in FIG. 2, and the surface structure is a three-dimensional network structure. [Example]

[0087] This embodiment is almost the same as the second embodiment, with the following differences.

[0088] In step 3, no inorganic filler was added, the dry weight of PVA accounted for 5 wt % of the heat-resistant polymer particle mass, and γ-glycidoxypropyltrimethoxysilane accounted for 20 wt % of the heat-resistant polymer mass.

[0089] In step 4, the coating slurry obtained in step 3 was uniformly applied by roll coating to one side of a 9 μm-thick PE separator (porous substrate) to obtain a composite separator.

[0090] The structural schematic diagram of the composite separator prepared in this example can be seen in Figure 3, where 001 is a heat-resistant coating layer applied to one side of the porous substrate, 002 is the porous substrate, the thickness of the heat-resistant coating layer was 3 μm, and the total thickness of the composite separator was 12 μm. [Example]

[0091] This embodiment is almost the same as the second embodiment, with the following differences.

[0092] In step 2, 5 kg of thiophene polyamide and 20 kg of DMAc were added to a stirrer and stirred uniformly, and the average particle size of the heat-resistant polymer particles in the obtained heat-resistant polymer particle dispersion was 200 nm.

[0093] In step 3, the dry weight ratio of the heat-resistant polymer particles to the boehmite particles was 30:70, the dry weight of PVA accounted for 5 wt% of the total mass of the heat-resistant polymer particles and the boehmite particles, and the dry weight of γ-glycidoxypropyltrimethoxysilane accounted for 20 wt% of the total mass of the heat-resistant polymer particles and the boehmite particles. The particle diameter D50 of the boehmite particles was 530 nm.

[0094] In step 4, the coating slurry obtained in step 3 was uniformly roll coated onto one side of a 9 μm thick PE separator (porous substrate) to obtain a composite separator, the total thickness of which was 14 μm. [Example]

[0095] This embodiment is almost the same as the second embodiment, with the following differences.

[0096] In step 2, 3.33 kg of thiophene polyamide and 16.67 kg of DMAC were added to a stirrer and stirred uniformly, and the average particle size of the heat-resistant polymer particles in the obtained heat-resistant polymer particle dispersion was 120 nm.

[0097] In step 3, the dry weight ratio of the heat-resistant polymer particles to the boehmite particles was 5:95, the dry weight of PVA accounted for 5 wt% of the total mass of the heat-resistant polymer particles and the boehmite particles, and the dry weight of γ-glycidoxypropyltrimethoxysilane accounted for 20 wt% of the total mass of the heat-resistant polymer particles and the boehmite particles. The particle diameter D50 of the boehmite particles was 530 nm.

[0098] In step 4, the coating slurry obtained in step 3 was uniformly roll coated onto one side of a 9 μm thick PE separator (porous substrate) to obtain a composite separator, the total thickness of which was 12 μm. [Example]

[0099] This embodiment is almost the same as the second embodiment, with the following differences.

[0100] In step 3, the dry weight ratio of the heat-resistant polymer particles to the boehmite particles was 10:90, and the dry weight of the PVA accounted for 5 wt% of the total mass of the heat-resistant polymer particles and the boehmite particles. The particle diameter D50 of the boehmite particles was 530 nm.

[0101] In step 4, the coating slurry obtained in step 3 was uniformly applied by roll coating to one side of a 9 μm thick PE separator (porous substrate) to obtain a composite separator, the total thickness of which was 12 μm.

[0102] PVDF-HFP particles, boehmite particles, PVA, γ-glycidoxypropyltrimethoxysilane (coupling agent), and deionized water were mixed uniformly, and then 0.05 wt% of the coating slurry mass (a wetting agent, alkylphenol polyethylene oxide) was added, followed by thorough and uniform stirring to obtain a coating slurry with a solid content of 35%.

[0103] The dry weight ratio of PVDF-HFP particles to boehmite particles was 30:70, the dry weight of PVA accounted for 5 wt% of the total mass of the PVDF-HFP particles and the boehmite particles, and the dry weight of γ-glycidoxypropyltrimethoxysilane accounted for 10 wt% of the total mass of the PVDF-HFP particles and the boehmite particles. The particle diameter D50 of the boehmite particles was 530 nm, and the average particle diameter of the PVDF-HFP particles was 230 nm.

[0104] The coating slurry was uniformly applied to one side of a 9 μm PE separator using a roll, and then thoroughly dried in an oven at 60° C. to obtain a composite separator, the total thickness of which was 12 μm.

[0105] The relevant parameters of the raw materials in Examples 1 to 7 and Comparative Example 1 are shown in Table 1 below. Performance tests were conducted on the composite separators obtained in Examples 1 to 7 and Comparative Example 1, and the test results are shown in Table 2.

[0106] [Table 1]

[0107] [Table 2]

[0108] There are two common methods for measuring membrane rupture temperature in the prior art:

[0109] The first method uses the resistance method to detect the rupture temperature. The separator is impregnated with electrolyte and attached to a button battery. A resistance test device is connected to both ends of the battery. The entire device is placed in an oven and heated at a temperature rise rate of 2°C / min. The temperature and resistance are measured continuously to obtain a resistance-temperature curve. The temperature when the resistance exceeds 100Ω is the rupture temperature, and when the resistance reaches 100Ω again, the rupture temperature is reached. 3 The temperature at which the resistance drops to Ω is defined as the membrane rupture temperature.

[0110] The second type is tested using thermomechanical analysis (TMA). The effective test size between the test jigs is a sample width of 5 mm, length of 10 mm, and bias force of 20 mN. The heating rate is 5°C / min, and the temperature range is from room temperature to 400°C. The temperature is raised until the sample breaks (determined by the change in strain). The temperature at which the sample breaks is taken as the film rupture temperature.

[0111] In this application, the rupture temperature of the composite separator was measured using the above-mentioned thermomechanical analysis (TMA), and the composite separator was held at a temperature of Ts+40°C for 1 hour. None of the composite separators produced in this application experienced rupture.

[0112] The relevant parameters of the heat-resistant polymer particles and inorganic filler in Examples 1 to 7 and Comparative Example 1 are shown in Table 3 below.

[0113] [Table 3] Remarks: DP is the average particle size of the heat-resistant polymer particles, ρP is the density of the heat-resistant polymer particles, DT is the average particle size of the inorganic filler, ρT is the density of the inorganic filler, VP0 is the critical volume concentration of the heat-resistant polymer particles, VT0 is the critical volume concentration of the inorganic filler, and MP0 is the critical mass concentration of the heat-resistant polymer particles.

[0114] From the results in Tables 1 to 3 above, it can be seen that the composite separators containing heat-resistant polymer particles and inorganic filler prepared in Examples 1 to 5 not only have good thermal shrinkage resistance, but also have high film rupture temperatures, all of which exceeded 200°C. This significantly improves the thermal stability of the composite separator in lithium-ion batteries, a performance that cannot be achieved by aqueous ceramic coating methods.

[0115] In Example 2, the concentration of the heat-resistant polymer particles was lower than the critical concentration VP0 corresponding to the particle size. However, by adding a small (50 nm) inorganic filler, the heat-resistant polymer particles and the small inorganic filler formed a heat-resistant three-dimensional network structure together, achieving a high film rupture temperature. When the concentration of the heat-resistant polymer particles was lower than the critical concentration corresponding to the particle size, the heat-resistant polymer particles were unable to bond to each other to form a heat-resistant three-dimensional network structure. The resulting coating film had good heat shrinkage resistance, but its film rupture temperature was only 150°C. For example, in Example 6, the inorganic fillers all had particle sizes greater than 100 nm. When the concentration of the heat-resistant polymer particles was lower than the critical concentration VP0 corresponding to the particle size, it was difficult to form a three-dimensional network structure, which affected the thermal stability of the composite separator and ultimately prevented it from achieving a high film rupture temperature.

[0116] In Example 7, the concentration of heat-resistant polymer particles was higher than the limit concentration corresponding to the particle size, but because no silane coupling agent was added, the adhesive strength between the heat-resistant particles was weak, and the heat-resistant polymer particles were unable to form a heat-resistant three-dimensional network structure. The coating film had good heat shrinkage resistance, but its film rupture temperature was only 150°C.

[0117] Since the composite separator in Example 4 does not contain inorganic filler and only contains heat-resistant polymer particles, a large number of cracks occur on the surface of the heat-resistant coating layer, the coating film has poor heat shrinkage resistance, and its wettability to the electrolyte is low. Therefore, compounding heat-resistant polymer particles with inorganic filler is more favorable for the performance of the composite separator.

[0118] On the other hand, in Comparative Example 1, the applied coating layer was produced using PVDF-HFP as the polymer, and PVDF-HFP was prone to losing its strength at high temperatures, causing cracks in the separator and peeling off from the porous substrate.

[0119] The composite separator rupture temperature was measured using the oven method. The composite separators in Example 2 and Comparative Example 1 were heat-treated at 180°C for 1 hour, and the separator state and separator resistance before and after the heat treatment were recorded. The separators were attached to button batteries before and after the heat treatment, and the resistance was measured. The measurement results are shown in Table 4.

[0120] [Table 4]

[0121] The separator in Example 2 was not broken after heat treatment at 180°C for 1 hour, and the separator resistance was 10 3 The resistance change of the composite separator exceeded Ω, which indicates that the composite separator has a thermo-off effect, and the composite separator has a high rupture temperature, which improves the safety of the battery. On the other hand, the rupture of the separator in Comparative Example 1 after heat treatment is often an important cause of battery accidents.

[0122] FIG. 4 is a graph showing the rupture temperatures measured by TMA for the composite separators produced in Examples 2 and 7, where a is the curve for Example 2 and b is the curve for Example 7. It can be seen that the composite separator produced in Example 7 ruptured at 150°C, while the rupture temperature of the composite separator of Example 2 exceeded 200°C.

[0123] The above description is intended to provide an ideal embodiment of the present application, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. The technical scope of the present application is not limited to the content of the specification, but should be determined by the claims.

Claims

1. A porous substrate and a heat-resistant coating layer provided on one or both sides of the porous substrate, the heat-resistant coating layer including heat-resistant polymer particles, an inorganic filler, and an auxiliary binder; The volume concentration of the heat-resistant polymer particles in the heat-resistant polymer particles and the inorganic filler is defined as VP １ , the critical volume concentration of the heat-resistant polymer particles is VP ０ , the volume concentration of inorganic fillers with a particle size of less than 100 nm in the heat-resistant polymer particles and inorganic fillers is VP ２ In that case, VP ０ , V.P. １ and V.P. ２ satisfies the following relationship, (a) When the inorganic filler is a mixture of one or more fillers and the average particle size of the inorganic filler is greater than 100 nm, VP ０ ≦VP １ ≦100% is satisfied, (b) When the inorganic filler is a mixture of multiple fillers and at least one filler has an average particle size of less than 100 nm, VP ０ ≦VP １ +VP ２ ≦100% is satisfied, However, VP ０ = 0.685 × DP / (0.685 × DP + 0.5233 DT), where DP is the average diameter of the heat-resistant polymer particles and DT is the average diameter of the inorganic filler. Composite separator.

2. The heat-resistant polymer particles contain a heat-resistant resin having an average particle size of 10 nm to 200 nm and a glass transition temperature Ts+40°C or higher, where Ts is the melting point of the porous substrate, and the weight-average molecular weight of the heat-resistant resin is 4.0 × 10 ４ ~2 x 10 ６ g / mol, the inorganic filler has an average particle size of 10 nm to 1000 nm, and the inorganic filler is at least one selected from ceramics, metal oxides, metal hydroxides, metal carbonates, silicates, kaolin, talc, minerals, and glasses; The composite separator of claim 1 .

3. The heat-resistant resin is at least one selected from polyimide, aramid 1414, aramid 1413, aramid 1313, thiophene aramid, pyrrolyl aramid, furyl aramid, pyridyl polyamide, polyamide imide, polyether imide, polysulfone, polyketone, polyether ketone, polyether ether ketone, polyparaphenylene benzobisoxazole, and cellulose. The composite separator of claim 2 .

4. The inorganic filler is at least one selected from boehmite, alumina, silica, barium titanate, titania, zinc oxide, magnesium oxide, magnesium hydroxide, zirconium oxide, and oxide solid electrolytes. The composite separator of claim 2 .

5. The volume ratio of the heat-resistant polymer particles to the total volume of the heat-resistant polymer particles and the inorganic filler is VP ０ ~0.5 x (VP ０ +1), The composite separator of claim 1 .

6. The volume ratio of the heat-resistant polymer particles to the total volume of the heat-resistant polymer particles and the inorganic filler is VP ０ ~0.5 x (VP ０ +0.7), The composite separator of claim 5 .

7. the auxiliary binder includes a binder and a coupling agent, the amount of the binder added is 0.5 wt % to 10 wt % of the total mass of the heat-resistant polymer particles and the inorganic filler, and the amount of the coupling agent added is 1 wt % to 20 wt % of the total mass of the heat-resistant polymer particles and the inorganic filler; The composite separator of claim 1 .

8. the coupling agent is a silane coupling agent, and the content of Si atoms introduced from the silane coupling agent in the heat-resistant coating layer is 0.05 wt % to 5 wt % of the mass of the heat-resistant coating layer; The composite separator of claim 7.

9. the binder is at least one selected from polyvinyl alcohol, polyacrylic, polyurethane, and polyimide polymers, and carboxymethyl cellulose; and the silane coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane. The composite separator of claim 8 .

10. The thickness of the porous substrate is 1 μm to 25 μm, the Gurley value of the porous substrate is 20 sec / 100 cc to 300 sec / 100 cc, the material of the porous substrate is a thermoplastic resin having a melting point of less than 200°C, and the load of the heat-resistant coating layer is 1 to 9 g / m ２ That is, The composite separator of claim 1 .

11. the thermoplastic resin is selected from polyethylene terephthalate and / or polyolefin, the weight average molecular weight Mw of the polyolefin is 100,000 to 5,000,000, and the polyolefin is polyethylene and / or polypropylene; The composite separator of claim 10.

12. A method for producing the composite separator according to any one of claims 1 to 11, Step (1) of synthesizing a heat-resistant resin; Step (2) of preparing a dispersion of heat-resistant polymer particles using the heat-resistant resin produced in step (1); Step (3) of preparing a coating slurry, which comprises adding the dispersion of heat-resistant polymer particles obtained in step (2), an inorganic filler, a binder, and a coupling agent to an aqueous solvent and uniformly mixing them to obtain a coating slurry; (4) applying the coating slurry to any one or both sides of the porous substrate and curing it to obtain a composite separator; The aqueous solvent is a mixed solution of one or more selected from deionized water, ethanol, ethylene glycol, glycerin, isopropyl alcohol, propylene glycol, butanol, and acetic acid, and the coating slurry further contains one or more of a surfactant in an amount of 0.05 wt % to 7 wt %, a dispersant in an amount of 0.05 wt % to 9 wt %, a wetting agent in an amount of 0.02 wt % to 7 wt %, and an antifoaming agent in an amount of 0.04 wt % to 4 wt %, based on the mass of the coating slurry; A method for manufacturing a composite separator.

13. The solid content of the coating slurry described in step (3) is 2% to 80%, and the coating method described in step (4) is at least one selected from electrostatic spraying, blade coating, spin coating, slit die coating, transfer coating, dipping coating, gravure coating, and microgravure coating. A method for producing the composite separator according to claim 12.

14. The solid content of the coating slurry is 4% to 40%; A method for producing the composite separator according to claim 13.

15. Step (4) further includes surface treatment of the porous substrate, and the surface treatment is any one of corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment. A method for producing the composite separator according to claim 12.

16. Use of the composite separator of any one of claims 1 to 11 in a lithium ion battery comprising a positive electrode, a negative electrode and said composite separator.

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