Coating slurry, coating separator, method of manufacturing the same

Abstract

The present invention discloses a coating slurry applied to a battery separator, comprising an organic polymer, a solvent, and a photoinitiator as main components. The present invention further discloses a coated separator produced by the coating slurry and a method for producing the coated separator, wherein the coating slurry is coated onto at least one surface of the base and subjected to ultraviolet radiation treatment with set energy and wavelength to obtain a UV-crosslinked coated separator. Through the above technical method, the present invention improves the thermomechanical strength and film rupture temperature of the separator by forming a crosslinked structure in the separator simply and at a low cost.

Description

Technology Field

[0001] The present invention relates to the field of battery separator technology, and in particular to a slurry used for coating a battery separator, a separator coated with said slurry, and a method for manufacturing said separator. Background Technology

[0002] A battery separator refers to the membrane material located between the positive and negative electrodes of a battery. As a critical component of a battery, it directly impacts battery safety and cost. Its primary function is to separate the positive and negative electrodes to prevent electrons from passing freely within the battery, while allowing ions in the electrolyte to pass freely between them.

[0003] The ion conductivity of the battery separator is directly related to the overall performance of the battery, and the function of separating the positive and negative electrodes can limit the rise in current when the battery is overcharged or the temperature rises, thereby preventing explosions caused by battery short circuits, and the micropores provide a self-protective function, serving as a safety protection for the battery user and the device.

[0004] Considering the universality and economic feasibility of mass production, conventional technology utilizes polyolefin-based polymers as base film materials, with a melting point of 130°C–160°C and a rupture temperature of 140°C–170°C for manufactured separator products. While conventional products can sufficiently meet requirements when the battery is used normally, if battery overcharging, internal or external short circuits, or collision compression occur, the internal temperature of the battery can rapidly rise above 150°C. Furthermore, if the separator melts and ruptures too quickly, failing to prevent direct contact between the positive and negative electrodes of the battery, a large amount of heat accumulates within a short period, leading to thermal runaway and potentially causing a fire or even an explosion of the battery; thus, separator performance is critical to battery safety.

[0005] Existing solutions to address the above problem are as follows: In the process of manufacturing the base film, a crosslinking agent (e.g., organic silanes) is directly mixed into the raw material and extruded at high temperatures to induce direct crosslinking; however, this method has the following disadvantages:

[0006] 1. Processing difficulty is high, and production costs are high;

[0007] 2. Because the crosslinking agent is difficult to disperse sufficiently and react completely within the material system, the consistency of the product is not high, making large-scale production difficult.

[0008] To solve the above problem, the present invention provides a coating slurry to which a photoinitiator has been added, a coating separation membrane produced by said coating slurry, and a method for producing said coating separation membrane.

[0009] The technical solution of the present invention is as follows:

[0010] The coating slurry includes an organic polymer, a solvent, and a photoinitiator as major components.

[0011] Preferably, the amount of the organic polymer added is 0.05 to 50 wt%, and the organic polymer is selected from one or more of polyvinylidene fluoride homopolymer, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a polyvinylidene fluoride-trichloroethylene copolymer, polyacrylonitrile, polymethacrylate or derivatives thereof, polyacrylamide, polyimide, polyoxyethylene, and cellulose.

[0012] Preferably, the amount of the photoinitiator added is 0.001-5.0 wt%, and the photoinitiator is selected from one of azobisisobutyronitrile, xantone, isopropylthioxantone, benzophenone, and benzoyl peroxide or a combination thereof.

[0013] Preferably, the solvent is selected from one or more of dimethylformamide (DMF), dimethylacetamide (DMAC), dichloroethane, trichloroethane, dichloromethane, chloroform, dimethyl sulfoxide (DMSO), sulfolane, tetramethylurea, N-methylpyrrolidone (NMP), acetone, water, trimethylphosphate, and triethylphosphate.

[0014] Preferably, the coating slurry further includes an inorganic material, and the share of the inorganic material in the coating slurry is 50-95 wt%.

[0015] Preferably, the inorganic material is selected from ceramic materials, nanowire materials, or nanotube materials, and the ceramic material may be selected from a combination of one or more of Al2O3, SiO2, TiO2, ZrO2, MgO, CaO, AlOOH, and SiC; the nanowire material may be selected from one or more of carbon nanowires, ettapulgite, silver nanowires, boron carbide nanowires, nanocellulose, copper hydroxide nanowires, silicon monoxide nanowires, and hydroxyapatite nanowires, and the nanotube material may be selected from one or more of carbon nanotubes, silver nanotubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, and hydroxyapatite nanotubes. Preferably, the inorganic material is a high-heat-resistant inorganic material.

[0016] Based on the same inventive concept, the present invention further provides a coating separation membrane comprising a coating layer prepared by any one of the coating slurries of the above-described invention, wherein the coating layer comprises a three-dimensional network structure, the proportion of the mass of the three-dimensional network structure to the total organic polymer is 50% or more, and the proportion to the total mass of the coating layer is 1.0% or more. Based on the same inventive concept, the present invention further provides a coating separation membrane comprising any of the coating slurries and a base as described above, wherein the coating slurry is coated on at least one surface of the base and radiated with ultraviolet light having a set energy and wavelength to obtain the UV-crosslinked coating separation membrane.

[0017] Preferably, the base is selected from one or more of a polyolefin microporous membrane, a polyimide microporous membrane, a nonwoven membrane, a multilayer composite membrane, a ceramic coated membrane, and a polymer coated membrane.

[0018] Based on the same inventive concept, the present invention further provides a method for manufacturing the above-described coating separation membrane, and said method,

[0019] (1) A slurry preparation step in which 49 wt% or less of an organic polymer, 0.001-5.0 wt% of a photoinitiator, 50-95 wt% of an inorganic material and 0-5 wt% of other auxiliary agents are added to a solvent and uniformly stirred to obtain a slurry;

[0020] (2) A coating step of coating the above-described slurry onto at least one surface of the base;

[0021] (3) A phase transition step for transitioning the phase of the separation membrane obtained after coating;

[0022] (4) A drying step in which the product obtained in the above step (3) is washed and dried to obtain a composite separation membrane after drying;

[0023] (5) A UV crosslinking step in which the above composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane;

[0024] In a method for manufacturing a coating separator,

[0025] (1) A slurry preparation step in which 0.001-5.0 wt% of a photoinitiator, 50-95 wt% of an inorganic material, and 0-5 wt% of other auxiliary agents are added to a solvent and uniformly stirred to obtain a slurry;

[0026] (2) A immersion step in which a base is immersed in the above-prepared slurry to obtain a separation membrane after immersion;

[0027] (3) Phase transition step for transitioning the membrane;

[0028] (4) A drying step in which the product obtained in the above step (3) is washed and dried to obtain a composite separation membrane after drying;

[0029] (5) A UV crosslinking step in which the above composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane;

[0030] The above other auxiliary agents may be one or more of dispersants, wetting agents, thickeners, and conductive auxiliary agents.

[0031] Based on the same inventive concept, the present invention further provides a method for manufacturing another coating separation membrane, and said method,

[0032] (1) A slurry preparation step in which 0.001~5.0 wt% or less of a photoinitiator, 50-95 wt% of a high heat-resistant material, and 0-5 wt% of other auxiliary agents are added to a solvent and uniformly stirred to obtain a slurry;

[0033] (2) A coating step of coating at least one surface of a base with the above-described slurry, or a immersion step of immersing the base in the above-described slurry to obtain a separation membrane after immersion;

[0034] (3) A drying step in which the product obtained in the above step (2) is dried to obtain a composite separation membrane after drying;

[0035] (4) A UV crosslinking step may be further included, in which the above composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane.

[0036] The above drying step can be carried out by means such as hot air or infrared irradiation.

[0037] Preferably, the wavelength of the ultraviolet light is within the range of 210 nm to 420 nm, the UV crosslinking time is 0.001 s to 10 s, and the radiant light intensity is 50 mj / cm² 2 That is all.

[0038] Compared to conventional technology, the advantages of the present invention are as follows:

[0039] Through UV crosslinking, crosslinking sites on different organic molecule segments within the slurry are activated and combined to form a network crosslinking structure, successfully increasing the film temperature of the separator with a simple formulation method and process and lower cost, and significantly improving the safety of the battery. Brief explanation of the drawing

[0040] Figure 1 is a schematic diagram of the reaction process in the ultraviolet radiation treatment process of the coating separation membrane of the present invention. Figure 2 is a schematic diagram of a micronetwork macromolecular structure formed by ultraviolet radiation treatment of the coating separation membrane of the present invention. Figure 3 compares membrane samples before and after being left in an oven at 180°C for 30 minutes. Specific details for implementing the invention

[0041] In order to overcome the disadvantages of the current base film crosslinking method, such as difficulty in processing, high cost, and low crosslinking consistency, the present invention provides a method of adding a photoinitiator to a coating slurry by changing the method of mixing a crosslinking agent into the existing base film raw material, and by coating the slurry onto the base film and proceeding with crosslinking by ultraviolet light to obtain a crosslinked battery separator, thereby realizing an improvement in battery separator performance, particularly an improvement in film breaking temperature.

[0042] Specifically, the present invention first provides a coating slurry comprising an organic polymer, a solvent, and a photoinitiator as major components.

[0043] The amount of the organic polymer added is 0.05 to 50 wt%, and the organic polymer may be selected from one or more of polyvinylidene fluoride homopolymer, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a polyvinylidene fluoride-trichloroethylene copolymer, polyacrylonitrile, polymethacrylate or derivatives thereof, polyacrylamide, polyimide, polyoxyethylene, polyacrylonitrile, and cellulose. The amount of the organic polymer added affects the performance of the battery separator; if the amount added is too small, it is difficult to form a coating layer with sufficient adhesion performance, and if the amount added is too large, the microporous structure of the separator becomes clogged, affecting the internal resistance and circulation of the battery. More preferably, the amount of the organic polymer added is 3 to 45 wt%.

[0044] For example, the amount of the organic polymer added is 0.05%, 0.1%, 0.5%, 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 39%, 41%, 43%, 45%, 49%.

[0045] The amount of the photoinitiator added is 0.001-5.0 wt%, and the photoinitiator is selected from a combination of one or more of azobisisobutyronitrile (AIBN), xantone (XAN), isopropylthioxantone (ITX), benzophenone (BP), and benzoyl peroxide (BPO). Since the amount of the photoinitiator added is closely related to the performance of the separator, if the amount of the photoinitiator added is too small, the degree of crosslinking curing is insufficient, and the improvement in the membrane rupture temperature may not meet expectations; if the amount of the photoinitiator added is too large, too much remains in the separator, leading to an increase in costs. More preferably, the amount of the photoinitiator added is 0.01-5 wt%.

[0046] For example, the amount of the photoinitiator added is 0.001%, 0.01%, 0.05%, 0.07%, 0.1%, 0.5%, 0.9%, 1%, 1.3%, 1.7%, 1.9%, 2.1%, 2.5%, 2.9%, 3.1%, 3.5%, 3.9%, 4.1%, 4.5%, 4.9%, 5.1%, 5.5%, 5.9%, 6.3%, 6.7%, 6.9%, 7.3%, 7.7%, 7.9%, 8.3%, 8.7%, 8.9%, 9.1%, 9.5%, 9.7%, 9.9%.

[0047] Preferably, the solvent may be selected from one or more of dimethylformamide (DMF), dimethylacetamide (DMAC), dichloroethane, trichloroethane, dichloromethane, chloroform, dimethyl sulfoxide (DMSO), sulfolane, tetramethylurea, N-methylpyrrolidone (NMP), acetone, water, trimethylphosphate, and triethylphosphate.

[0048] Additionally, the coating slurry may further include an inorganic material, and the share of the inorganic material in the coating slurry is 50-95 wt%.

[0049] Preferably, the inorganic material may be selected from ceramic materials, nanowire materials, or nanotube materials, and the ceramic material may be selected from a combination of one or more of Al2O3, SiO2, TiO2, ZrO2, MgO, CaO, AlOOH, and SiC; the nanowire material may be selected from one or more of carbon nanowires, ettapulgite, silver nanowires, boron carbide nanowires, nanocellulose, copper hydroxide nanowires, silicon monoxide nanowires, and hydroxyapatite nanowires; and the nanotube material may be selected from one or more of carbon nanotubes, silver nanotubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, and hydroxyapatite nanotubes.

[0050] The present invention further provides a coating separation membrane comprising a coating layer prepared by the coating slurry described above, wherein the coating layer comprises a three-dimensional network molecular structure, and the proportion of the mass of the three-dimensional network molecular structure to the total organic polymer is 50% or more, and the proportion to the total mass of the coating layer is 1.0% or more. Linear organic polymer molecular chains in the slurry are connected to form a three-dimensional network structure through branched chains after coating (or dipping), drying, and crosslinking, and the coating layer tightly encloses inorganic materials distributed therein using the three-dimensional network crosslinking structure as a framework. If the proportion of the mass of the network structure to the total organic polymer after crosslinking is less than 50%, or the proportion to the total mass of the coating layer is less than 1.0%, the degree of crosslinking reaction is insufficient, so sufficient connections are not formed between the crosslinked sites, and the formed three-dimensional network structure cannot maintain sufficient strength under high temperature or external force.

[0051] Those skilled in the art will be aware that while linear organic polymers can be dissolved in both solvents, cross-linked three-dimensional network structures can only swell in both solvents and cannot be dissolved. To measure the mass share of the three-dimensional network structure, a coating membrane or coating layer is placed in a volatile both solvent for Soxhlet extraction, and after drying, the three-dimensional network structure and inorganic material remain. By calcining using TGA or a crucible, the share of the inorganic material can be obtained, thereby allowing the mass share of the three-dimensional network structure to be obtained. Of course, the present invention is not limited to the above measurement method, and those skilled in the art may determine the mass of the three-dimensional organic molecule after cross-linking using other measurement methods as needed.

[0052] The present invention further provides a coating separation membrane comprising the coating slurry and a base, wherein the coating slurry is coated on at least one surface (which may be one side or both sides) of the base and subjected to ultraviolet radiation treatment with set energy and wavelength to obtain the UV-crosslinked coating separation membrane.

[0053] The above base includes, but is not limited to, polyolefin microporous membranes (polyethylene, polypropylene, polybutylene, etc.), polyimide microporous membranes, nonwoven fabric membranes, multilayer composite membranes, ceramic coated membranes, polymer coated membranes, etc.

[0054] In the ultraviolet radiation treatment process of the coating separation membrane of the present invention, the photoinitiator in the slurry transitions from a ground state to an excited state under ultraviolet radiation with a set wavelength and energy, thereby capturing H ions from the CH structure in the organic system and simultaneously generating organic macromolecule free radicals. When these terminate, the organic macromolecules become cross-linked, and this reaction process is as illustrated in FIG. 1. After the reaction, a cross-linked structure is formed between the long chain macromolecules, and a fine network macromolecule structure is formed as illustrated in the right-hand diagram of FIG. 2. Although the degree of reaction may differ under different conditions, the above reaction can proceed simultaneously within the porous base layer and the organic polymer coating layer.

[0055] The present invention further provides a method for manufacturing the above-mentioned coating separation membrane, and the method comprises:

[0056] (1) A slurry preparation step in which 49 wt% or less of an organic polymer, 0.001-5.0 wt% of a photoinitiator, 50-95 wt% of an inorganic material, and 0-5 wt% of other auxiliary agents are added to a solvent and uniformly stirred to obtain a slurry;

[0057] (2) A coating step of coating the above-mentioned manufactured slurry onto at least one surface of the base (which may be one side surface or both sides surface);

[0058] (3) A phase transition step in which the separation membrane obtained after coating is phase transitioned. The phase transition step can be carried out by methods such as immersing in a coagulation bath or heating, and it can be understood that there are no limitations on the technical means of phase transition here. Preferably, a phase transition can be carried out by immersion in a coagulation bath, and the immersion in the coagulation bath method involves replacing the original solvent with a non-solvent having a low boiling point and incompatible with the coating organic material to form a coating layer having micropores, and said non-solvent may be selected from one or more of pure water, glycerin, ethyl acetate, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), acetone, methyl acetate (MAC), formic acid, acetic acid, propionic acid, ethanol (EtOH), methanol, isopropanol (i-PrOH), n-butanol (BtOH), n-octanol (OtOH), dodecanol (DoOH), lithium chloride (LiCl), and lithium perchlorate (LiClO4);

[0059] (4) A drying step in which the product obtained in the above step (3) is washed and dried to obtain a composite separation membrane after drying;

[0060] (5) A UV crosslinking step in which the above composite separation membrane is crosslinked by ultraviolet radiation to obtain the above coating film, which is a UV-crosslinked composite separation membrane;

[0061] When using the above slurry coating method, an organic polymer is included in the slurry.

[0062] The present invention further provides a method for manufacturing another coating separator, and the method comprises:

[0063] (1) A slurry preparation step of adding 0.001-5.0 wt% of a photoinitiator, 50-95 wt% of an inorganic material, and 0-5 wt% of other auxiliary agents to a solvent and stirring uniformly to obtain a slurry;

[0064] (2) A immersion step in which a base is immersed in the above-prepared slurry to obtain a separation membrane after immersion;

[0065] (3) Phase transition step in which the membrane is immersed in a non-solvent to transition phase;

[0066] (4) A drying step in which the product obtained in the above step (3) is washed and dried to obtain a composite separation membrane after drying;

[0067] (5) The above composite separation membrane may further include a UV crosslinking step to obtain a UV-crosslinked composite separation membrane by crosslinking the above composite separation membrane by ultraviolet radiation.

[0068] By using the above slurry immersion method, the slurry may contain only a photoinitiator and not an organic polymer.

[0069] The present invention further provides a method for manufacturing another coating separator, and the method comprises:

[0070] (1) A slurry preparation step in which 0.001~5.0 wt% or less of a photoinitiator, 50-95 wt% of a high heat-resistant material, and 0-5 wt% of other auxiliary agents are added to a solvent and uniformly stirred to obtain a slurry;

[0071] (2) A coating step of coating at least one surface of a base with the above-described slurry, or a immersion step of immersing the base in the above-described slurry to obtain a separation membrane after immersion;

[0072] (3) A drying step in which the product obtained in the above step (2) is dried to obtain a composite separation membrane after drying;

[0073] (4) A UV crosslinking step may be further included, in which the above composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane.

[0074] The above drying step can be carried out by means such as hot air or infrared irradiation.

[0075] As can be seen from this, the solvent selected in this application can generally be completely removed by a heating method to form a coating layer. However, if some solvents have high boiling points and are difficult to completely remove from the coating layer by direct heating, or if removing them by heating requires significant energy costs, the original solvent is replaced with a solvent having a low boiling point and incompatible with the organic coating material to form a coating layer with micropores, and then the solvent within the coating layer is removed through drying.

[0076] In some preferred embodiments, the wavelength of the ultraviolet light is in the range of 210 nm to 420 nm, the UV crosslinking time is 0.001 s to 10 s, and the radiant light intensity is 50 mj / cm² 2 That is all.

[0077] The present invention provides a method for adding a photoinitiator to a coating layer slurry and forming a thermosetting network polymer structure through a crosslinking means, thereby improving the thermomechanical strength and film rupture temperature of a porous base, and when the characteristics of the manufactured separator product are analyzed by TMA, the film rupture temperature can be improved by 20-80°C compared to a product that undergoes UV curing without adding a photoinitiator, and the separator does not rupture even when left at 180°C for 30 minutes.

[0078] At the same time, a certain degree of organic polymer layer crosslinking structure can reduce swelling in the electrolyte at room temperature (25°C) or high temperature (60°C) while maintaining sufficient adhesion, thereby preventing deformation inside the battery, reduction of coating layer porosity, and blockage of lithium ion transport pathways, and improving the long-term circulation performance of the battery.

[0079] Example 1

[0080] (1) Slurry preparation:

[0081] 9.2 wt% of polyvinylidene fluoride and 0.3 wt% of benzophenone are added to 90.5 wt% of N-methylpyrrolidone and stirred uniformly to obtain a slurry.

[0082] (2) Coating: The above-prepared slurry is coated on two surfaces of a polyethylene porous base having a ceramic coating layer, wherein the base thickness is 9 μm, the ceramic coating layer is 3 μm, and the coating layer on each side of the slurry is 0.5 to 1.0 μm.

[0083] (3) Phase transition: The membrane obtained after coating is immersed in water to transition phases.

[0084] (4) Drying: The product obtained in step (3) is washed and dried to obtain a composite separation membrane.

[0085] (5) UV Crosslinking: The dried composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane. The ultraviolet wavelength used is within the range of 250 nm to 390 nm, the UV crosslinking time is 0.1 s, and the radiation intensity is at least 100 mj / cm² 2 It reaches.

[0086] As a result of TMA measurement, a UV-cured composite separation membrane exceeding 180°C can be obtained.

[0087] Example 2

[0088] (1) Slurry preparation:

[0089] 7.5 wt% of polyimide, 7.5 wt% of polyvinylidene fluoride, and 0.5 wt% of benzophenone are added to 84.5 wt% of acetone and stirred uniformly to obtain a slurry.

[0090] (2) Coating: The above-prepared slurry is coated on two surfaces of a polyethylene porous base having a ceramic coating layer, wherein the base thickness is 9 μm and the coating layer on one side is 2 μm.

[0091] (3) Drying: When the product obtained in step (2) is dried, a composite separation membrane is obtained.

[0092] (4) UV Crosslinking: The dried composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane. The ultraviolet wavelength used is within the range of 250 nm to 390 nm, the UV crosslinking time is 0.5 s, and the radiation intensity is at least 100 mj / cm² 2 It reaches.

[0093] As a result of TMA measurement, a UV-cured composite separation membrane exceeding 180°C can be obtained.

[0094] Example 3

[0095] (1) Slurry preparation:

[0096] 15 wt% of polyvinylidene fluoride, 20 wt% of alumina, 5 wt% of nanocellulose, and 0.3 wt% of benzophenone are added to 59.7 wt% of N-methylpyrrolidone and stirred uniformly to obtain a slurry.

[0097] (2) Coating: The above-prepared slurry is coated on two surfaces of a polyethylene porous base, with the base thickness being 9 μm and the coating layer thickness on each surface being 2 μm.

[0098] (3) Phase transition: The membrane obtained after coating is immersed in water to transition phases.

[0099] (4) Drying: When the product obtained in step (3) is dried, a composite separation membrane is obtained.

[0100] (5) UV Crosslinking: The dried composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane. The ultraviolet wavelength used is within the range of 240 nm to 380 nm, the UV crosslinking time is 0.8 s, and the radiation intensity is at least 150 mj / cm² 2 It reaches.

[0101] As a result of TMA measurement, a UV-cured composite separation membrane exceeding 180°C can be obtained.

[0102] Example 4

[0103] (1) Slurry preparation:

[0104] 3.5 wt% of polymethacrylate, 35 wt% of alumina, 0.5 wt% of benzophenone, and 1 wt% of other auxiliary agents are added to 60 wt% of water and stirred uniformly to obtain a slurry.

[0105] (2) Coating: The above-prepared slurry is coated on a surface of a polyethylene porous base, wherein the base thickness is 9 μm and the coating layer thickness is 3 μm.

[0106] (3) Drying: The product obtained in step (2) is dried by removing the solvent in the coating layer using methods such as hot air drying or infrared drying to obtain a composite separation membrane.

[0107] (4) UV Crosslinking: The dried composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane. The ultraviolet wavelength used is within the range of 240 nm to 380 nm, the UV crosslinking time is 0.8 s, and the radiation intensity is at least 150 mj / cm² 2 It reaches.

[0108] A UV-cured composite separator can be obtained with a heat shrinkage rate of less than 5% at 150°C for 1 hour and a TMA measurement result exceeding 180°C.

[0109] Example 5

[0110] (1) Slurry preparation:

[0111] 3.5 wt% of polymethacrylate, 30 wt% of alumina, 5 wt% of nanocellulose, 0.5 wt% of benzophenone, and 1 wt% of other auxiliary agents are added to 60 wt% of water and stirred uniformly to obtain a slurry.

[0112] (2) Coating: The above-prepared slurry is coated on a surface of a polyethylene porous base, wherein the base thickness is 9 μm and the coating layer thickness is 1.5 μm.

[0113] (3) Drying: The product obtained in step (2) is dried by removing the solvent in the coating layer using methods such as hot air drying or infrared drying to obtain a composite separation membrane.

[0114] (4) UV Crosslinking: The dried composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane. The ultraviolet wavelength used is within the range of 240 nm to 380 nm, the UV crosslinking time is 0.8 s, and the radiation intensity is at least 150 mj / cm² 2 It reaches.

[0115] A UV-cured composite separator can be obtained with a heat shrinkage rate of less than 5% at 150°C for 1 hour and a TMA measurement result exceeding 180°C.

[0116] The difference between Example 5 and Example 4 is as follows: the high heat-resistant material in the slurry is an alumina and nanocellulose composite, and the needle-shaped nanocellulose is dispersed in the coating layer and overlaps with each other, and the formed physical linkage structure and the organic chemical crosslinking structure in this example are combined with each other to further improve the heat resistance and high temperature melting performance of the coating layer.

[0117] Comparative Example 1

[0118] (1) Slurry preparation:

[0119] 9.5 wt% of polyvinylidene fluoride is added to 90.5 wt% of N-methylpyrrolidone and stirred uniformly to obtain a slurry.

[0120] (2) Coating: The above-prepared slurry is coated on two surfaces of a polyethylene porous base having a ceramic coating layer, wherein the base thickness is 9 μm, the ceramic coating layer is 3 μm, and the coating layer on each side of the slurry is 0.5 to 1.0 μm.

[0121] (3) Phase transition: The membrane obtained after coating is immersed in water to transition phases.

[0122] (4) Drying: The product obtained in step (3) is washed and dried to obtain a composite separation membrane.

[0123] The difference between Comparative Example 1 and Example 1 is as follows: Since the coating layer of Comparative Example 1 does not contain a photoinitiator and a crosslinking structure, the TMA measurement results were not improved.

[0124] Comparative Example 2

[0125] (1) Slurry preparation:

[0126] 4 wt% of polymethacrylate, 35 wt% of alumina, and 1 wt% of other auxiliary agents are added to 60 wt% of water and stirred uniformly to obtain a slurry.

[0127] (2) Coating: The above-prepared slurry is coated on a surface of a polyethylene porous base, wherein the base thickness is 9 μm and the coating layer thickness is 3 μm.

[0128] (3) Drying: When the product obtained in step (2) is dried, a composite separation membrane is obtained.

[0129] The difference between Comparative Example 2 and Example 4 is as follows: Since the coating layer of Comparative Example 2 does not contain a photoinitiator and a crosslinking structure, the TMA measurement results were not improved, and the 150°C heat shrinkage performance is relatively poor.

[0130] Comparative Example 3

[0131] (1) Slurry preparation:

[0132] 3.5 wt% of polymethacrylate, 35 wt% of alumina, 0.5 wt% of benzophenone, and 1 wt% of other auxiliary agents are added to 60 wt% of water and stirred uniformly to obtain a slurry.

[0133] (2) Coating: Coat the prepared slurry on a surface of a polyethylene porous base, wherein the base thickness is 9㎛ and the

[0134] The thickness of the tinting layer is 3㎛.

[0135] (3) Drying: The product obtained in step (2) is dried by removing the solvent in the coating layer using methods such as hot air drying or infrared drying to obtain a composite separation membrane.

[0136] (4) UV Crosslinking: The dried composite membrane is crosslinked by ultraviolet radiation to obtain a UV-crosslinked composite membrane. The ultraviolet wavelength used is within the range of 240 nm to 380 nm, the UV crosslinking time is 0.5 s, and the radiation intensity is at least 100 mj / cm² 2 am.

[0137] The difference between Comparative Example 3 and Example 4 is as follows: The organic material in the coating layer of Comparative Example 3 was not completely crosslinked (did not receive UV radiation of sufficient intensity), and the strength of the three-dimensional network organic molecular structure after crosslinking was insufficient, so the thermal shrinkage at 150°C and TMA measurements were both found to be relatively poor.

[0138] TMA measurements were performed on the manufactured composite separator membranes, and the measurement results are as shown in Table 1, wherein Table 1 represents the TMA measurement results of the composite coated separator membranes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3 of the present invention. The TMA measurement method is as follows: the measurement sample has a length of 8 mm and a width of 4 mm, the measured tensile force is 0.01 n, and the heating rate is 5 ℃ / min.

[0139] As shown in the data in the table, the film temperature of the samples in Examples 1 to 3 was improved by at least 30°C compared to the sample in Comparative Example 1 (not cross-linked).

[0140] number Base thickness (um) Coating layer thickness (um) Other coating layer thickness (um) Mass occupancy of 3D network structure after crosslinking Heat resistance of coated separator (150℃ 1h, %) Coating Separator TMA(°C) Proportion of organic polymer in the coating layer (%) Coating layer mass ratio (%) MD TD MD TD Example 1 9 1.0~2.0 3 70% 50% 3.1 2.2 234.95 227.22 Example 2 9 4 - 55% 30% - - 204.23 195.85 Example 3 9 6 - 60% 25% - - 214.51 220.36 Example 4 9 3 - 85% 3% 2.4 2 220.9 218.43 Example 5 9 1.5 - 85% 2.5% 2.2 2.2 230.85 231.4 Comparative Example 1 9 1.0~2.0 3 0% 0% 3.5 2.5 152.18 154.17 Comparative Example 2 9 3 - 0% 0% 4.0 3.8 155.48 152.76 Comparative Example 3 9 3 - 35% 0.8% 23.4 20.7 161.6 152.89

[0141] The method of the present invention has the following features.

[0142] 1. The present invention improves the thermomechanical strength and film breaking temperature of a separator (base film) by introducing a photoinitiator into a coating slurry of a lithium-ion battery separator and causing the separator coated with the coating layer to form a cross-linked structure under ultraviolet radiation of a selected wavelength and energy.

[0143] 2. By controlling the degree of crosslinking of the organic polymer coating layer, the hardness and solvent performance of the coating layer can be improved, and swelling of the coating layer in the electrolyte at room temperature and high temperature can be reduced, thereby improving the long-term circulation performance of the battery. Controlling the degree of crosslinking of the organic polymer can be achieved by adjusting the amount of photoinitiator added, selecting the UV crosslinking rate, and setting the radiant light intensity.

[0144] 3. The present invention can achieve an optimal balance of thermomechanical strength / film breakage temperature and adhesion of a separation membrane by controlling the content of a photoinitiator, the intensity and wavelength of ultraviolet radiation, and the UV crosslinking rate. At the same time, the UV reaction efficiency is matched with the production speed of current mass-produced products, thereby minimizing the production cost of the UV crosslinking process and improving the production added value.

[0145] 4. The technical solution of the present invention only requires adding a photoinitiator to induce crosslinking of organic matter within a general polymer coating membrane using the photoinitiator, and there is no need to additionally add a crosslinking agent, a crosslinking monomer, or a photocurable resin, so the formulation method is simpler, the cost is lower, and the performance effect of the obtained product is good.

[0146] 5. Compared to the conventional method of directly adding a photoinitiator when manufacturing a base film, the present invention is a process in which a photoinitiator is added to a coating layer to cause the coating layer to adhere to the surface of the base film and crosslinks the base film under photoinitiation conditions. Through this process, a product that satisfies the film breaking temperature requirements is obtained, and the process is simpler and more controllable, and the production cost is lower. At the same time, the problem of auxiliary agent precipitation caused by incompatibility between the initiator and the base is resolved, and consistency of product appearance and performance is improved.

[0147] 6. Compared to conventional unidirectional stretched separator products, the cross-linked separator product of the present invention can effectively improve tear resistance.

[0148] The foregoing description is merely an exemplary embodiment of the present invention, and those skilled in the art may additionally implement various modifications in accordance with the present invention, and all such modifications are included within the scope of protection of the present invention.

Claims

Claim 1 A coating slurry comprising an organic polymer, a solvent, and a photoinitiator, wherein the amount of the organic polymer added is 0.05 to 50 wt%, and the organic polymer is selected from one or more of polyvinylidene fluoride homopolymer, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a polyvinylidene fluoride-trichloroethylene copolymer, polyacrylonitrile, polymethacrylate or derivatives thereof, polyacrylamide, polyimide, polyoxyethylene, and cellulose, and the amount of the photoinitiator added is 0.001 to 5.0 wt%, and the photoinitiator is selected from a combination of one or more of azobisisobutyronitrile, xantone, isopropylthioxantone, benzophenone, and benzoyl peroxide. Claim 2 A coating slurry according to claim 1, wherein the solvent is selected from one or more of dimethylformamide, dimethylacetamide, dichloroethane, trichloroethane, dichloromethane, chloroform, dimethyl sulfoxide, sulfolane, tetramethylurea and N-methylpyrrolidone, acetone, water, trimethyl phosphate or triethyl phosphate. Claim 3 A coating slurry according to claim 1, wherein the coating slurry further comprises an inorganic material, and the occupancy rate of the inorganic material in the coating slurry is 0-95 wt%. Claim 4 A coating slurry according to claim 3, wherein the inorganic material is selected from ceramic material, nanowire material, or nanotube material, and the ceramic material is selected from a combination of one or more of Al2O3, SiO2, TiO2, ZrO2, MgO, CaO, AlOOH, and SiC; the nanowire material is selected from one or more of carbon nanowires, ettapulgite, silver nanowires, boron carbide nanowires, nanocellulose, copper hydroxide nanowires, silicon monoxide nanowires, and hydroxyapatite nanowires, and the nanotube material is selected from one or more of carbon nanotubes, silver nanotubes, boron carbide nanotubes, copper hydroxide nanotubes, silicon monoxide nanotubes, and hydroxyapatite nanotubes. Claim 5 A coating separation membrane comprising a coating layer prepared by the coating slurry of claim 1, wherein the coating layer comprises a three-dimensional network structure formed by the organic polymer molecules being connected to each other, and wherein the mass of the three-dimensional network structure accounts for 50% or more of the total organic polymer and accounts for 1.0% or more of the total mass of the coating layer. Claim 6 A coating separation membrane comprising a coating slurry of claim 1 and a base, wherein the coating slurry is coated on at least one surface of the base and subjected to ultraviolet radiation treatment with set energy and wavelength to obtain the UV-crosslinked coating separation membrane. Claim 7 In claim 6, the base is a coated separator selected from one or more of a polyolefin microporous membrane, a polyimide microporous membrane, a nonwoven separator, a multilayer composite separator, a ceramic coated separator, and a polymer coated separator. Claim 8 A method for manufacturing a coated separation membrane according to any one of claims 5 to 7, comprising: (1) a slurry preparation step of adding 49 wt% or less of an organic polymer, 0.001-5.0 wt% of a photoinitiator, 50-95 wt% of an inorganic material, and 0-5 wt% of other auxiliary agents to a solvent and stirring uniformly to obtain a slurry; (2) a coating step of coating the prepared slurry onto at least one surface of a base; (3) a phase transition step of immersing the separation membrane obtained after coating in a coagulation bath or heating to transition the phase; (4) a drying step of washing and drying the product obtained in step (3) to obtain a composite separation membrane after drying; and (5) a UV crosslinking step of crosslinking the composite separation membrane by ultraviolet radiation to obtain a UV-crosslinked composite separation membrane. Claim 9 A method for manufacturing a coating separation membrane according to any one of claims 5 to 7, comprising: (1) a slurry preparation step of adding 0.001 to 5.0 wt% or less of a photoinitiator, 50 to 95 wt% of a high heat-resistant material, and 0 to 5 wt% of other auxiliary agents to a solvent and stirring uniformly to obtain a slurry; (2) a dipping step of dipping a base into the prepared slurry to obtain a separation membrane after dipping; (3) a phase transition step of dipping the separation membrane into a coagulation bath or heating to transition the phases; (4) a drying step of washing and drying the product obtained in step (3) to obtain a composite separation membrane after drying; (5) a UV crosslinking step of crosslinking the composite separation membrane by ultraviolet radiation to obtain a UV crosslinked composite separation membrane. Claim 10 A method for manufacturing a coating separation membrane according to any one of claims 5 to 7, comprising: (1) a slurry preparation step of adding 0.001 to 5.0 wt% or less of a photoinitiator, 50 to 95 wt% of a high heat-resistant material, and 0 to 5 wt% of other auxiliary agents to a solvent and stirring uniformly to obtain a slurry; (2) a coating step of coating at least one surface of a base with the prepared slurry, or a dipping step of dipping the base into the prepared slurry to obtain a separation membrane after dipping; (3) a drying step of drying the product obtained in step (2) to obtain a composite separation membrane after drying; and (4) a UV crosslinking step of crosslinking the composite separation membrane by ultraviolet radiation to obtain a UV-crosslinked composite separation membrane. Claim 11 In claim 7, the wavelength of the ultraviolet light is within the range of 210 nm to 420 nm, the UV crosslinking time is 0.001 s to 10 s, and the radiant light intensity is 50 mj / cm² 2 Method for manufacturing a coating separator membrane, according to Lee Sang-in. Claim 12 delete Claim 13 delete

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