Coating slurry, coating separator, method for manufacturing separator, and battery

Abstract

The invention relates to a coating slurry, a coating separator, a manufacturing method, and a battery. The coating slurry contains a solvent and an adhesive polymer resin as its main components, with the weight ratio of the adhesive polymer resin in the slurry being 5 to 20 wt%, and the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, or a combination of at least two types of polyimide-based adhesive resins, where the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer, or the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin, is 50 to 85:15 to 50. The separator has excellent heat resistance, high fracture resistance, and excellent adhesive performance, and can greatly improve the high safety performance and cycle stability performance of the lithium-ion battery obtained thereafter.

Description

Technical Field

[0006] ,

[0001] The present invention relates to the technical field of battery separators, and particularly to a coating slurry used in the coating of battery separators, a separator coated with the slurry, a method for manufacturing a separator, and a battery.

Background Art

[0002] A lithium battery separator is one of the four core modules in a lithium-ion battery. It separates the positive and negative electrodes in a lithium-ion battery, allows the passage of lithium ions, and plays a role in insulating electrons. The quality of the separator's performance directly affects the performance of the lithium-ion battery and is one of the important technologies that restricts the development of lithium-ion batteries.

[0003] Conventional coated separators for lithium-ion batteries, whether the base material is PP, PE, or a PP / PE / PP composite film, and whether it is a double-sided or single-sided coated ceramic film, have a breakdown voltage within the range of 1.0 to 2.0 kV. Due to the difficulty of further improving the breakdown voltage performance, the assembled lithium-ion battery has poor puncture resistance and generally has difficulty passing the puncture test.

[0004] Therefore, how to effectively improve the high-voltage resistance and puncture resistance of the separator has become an urgent technical problem to be solved in the industry.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a coating slurry, a coated separator, a method for manufacturing a separator, and a battery in order to improve the high-voltage resistance and puncture resistance of the battery separator.

Means for Solving the Problems

[0006] According to a first aspect of the present invention, a coating slurry comprising a solvent and an adhesive polymer resin in a weight ratio of 5 to 20 wt% in the slurry as its main components, The adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50-85:15-50. Alternatively, a coating slurry is provided in which the adhesive polymer resin comprises a combination of at least two polyimide-based adhesive resins, wherein the at least two polyimide-based adhesive resins comprise a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, and the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50-85:15-50.

[0007] In some examples, the glass transition temperature of the first polyimide adhesive resin is greater than 200°C, and the glass transition temperature of the second polyimide adhesive resin is greater than 140°C.

[0008] In some embodiments, the solvent is an organic solvent, and the polyimide-based adhesive resin is a modified polyimide soluble in the organic solvent.

[0009] In some embodiments, when the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, the polyimide-based adhesive resin is at least one selected from the polymer resins ether anhydride type polyimide, fluorine anhydride type polyimide, ketone anhydride type polyimide, bismaleimide, alkenyl-sealed polyimide, polyesterimide, polyamideimide, and polyetherimide. When the adhesive polymer resin includes a combination of at least two polyimide-based adhesive resins, the at least two polyimide-based adhesive resins are selected from polymer resins such as ether anhydride type polyimide, fluorine anhydride type polyimide, ketone anhydride type polyimide, bismaleimide, alkenyl-sealed polyimide, polyesterimide, polyamideimide, and polyetherimide.

[0010] In some examples, the coating layer pore expander is further included in a weight ratio of 0.05 to 5 wt% in the slurry.

[0011] In some examples, the coating layer pore expander is one of the following: water, ethanol, polyethylene glycol, methanol, or a combination thereof.

[0012] In some examples, the slurry further contains ceramic particles whose weight ratio is greater than 0 wt% and less than or equal to 5 wt%.

[0013] In some embodiments, the ceramic particles are one of aluminum oxide, boehmite, silicon oxide, magnesium oxide, titanium oxide, zirconium oxide, or a combination thereof.

[0014] In some examples, the weight ratio of the solvent in the slurry is 70-95 wt%.

[0015] In some examples, the solvent is one of acetone, N-methylpyrrolidone, DMAc, or a combination thereof.

[0016] In some embodiments, the substrate is one of the following: a PP film, a PE film, a PP / PE / PP composite film, a double-sided or single-sided ceramic coated film, or a double-sided or single-sided nanofiber coated film.

[0017] A second aspect of the present invention provides a coated separator comprising a substrate and a polymer layer coated on one or both sides of the substrate, wherein the polymer layer comprises at least two functional groups selected from imide groups, heteroaromatic rings, and aromatic rings, and at least one functional group selected from ester groups, ether bonds, sulfide bonds, ketone groups, amide groups, phenol hydroxyethers, methyl groups, methylene groups, trifluoromethyl groups, and CF bonds.

[0018] A second aspect of the present invention further provides a coating separator comprising a substrate and a polymer layer coated on one or both sides of the substrate and coated with a coating slurry according to the first aspect of the present invention.

[0019] A second aspect of the present invention provides a coated separator comprising a substrate and a polymer layer coated on one or both sides of the substrate, wherein the coated separator has a breakdown voltage of 2.1kV to 5.0kV and a breakdown strength greater than 4.5kV / mil.

[0020] In some embodiments, the surface layer of the polymer layer has a porous structure.

[0021] In some embodiments, the polymer layer further includes ceramic particles that are embedded to form an island-like structure.

[0022] In some examples, the size of the island-like structure is 0.5 μm to 2 μm.

[0023] In some embodiments, the pore structure is a dense, honeycomb-like pore structure.

[0024] According to a third aspect of the present invention, The steps include providing a substrate and In the step of preparing a slurry, 5 to 20 wt% of an adhesive polymer resin is added to a solvent and dissolved sufficiently to obtain a coating slurry, wherein the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50 to 85:15 to 50, or the adhesive polymer resin includes a combination of at least two polyimide-based adhesive resins, the at least two polyimide-based adhesive resins include a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, and the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50 to 85:15 to 50. A method for manufacturing a coated separator is provided, which includes a coating step of applying the prepared coating slurry to at least one surface of the substrate to form a polymer layer on the substrate.

[0025] According to a fourth aspect of the present invention, a battery including a coated separator, a positive electrode, a negative electrode, and an electrolyte is provided, wherein the coated separator is the coated separator according to the second aspect of the present invention.

Advantages of the Invention

[0026] Compared with the prior art, the present invention has at least the following technical effects.

[0027] The coating slurry and coating separator according to the present invention have an adhesive polymer resin weight ratio of 5 to 20 wt% in the slurry, and the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, with a mass ratio of 50 to 85:15 to 50 between the polyimide-based adhesive resin and the PVDF-based adhesive resin polymer, or the adhesive polymer resin includes a combination of at least two types of polyimide-based adhesive resins, with the at least two types of polyimide-based adhesive resins including a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, with a mass ratio of 50 to 85:15 to 50 between the first polyimide-based adhesive resin and the second polyimide-based adhesive resin. As a result, the resulting separator has excellent heat resistance, high fracture resistance, and interfacial adhesion performance of electrode pieces, which can greatly improve the safety performance and cycle stability performance of the lithium-ion battery obtained thereafter. [Brief explanation of the drawing]

[0028] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0029] [Figure 1] This is a comparison of the -40°C discharge capacity of a PI-coated separator and a CCS separator according to one embodiment of the present invention. [Figure 2A] This is a SEM diagram of the surface of a coating separator according to one embodiment of the present invention. [Figure 2B] This is a SEM diagram of the surface of a coating separator according to one embodiment of the present invention. [Figure 3] This is a flowchart of a method for manufacturing a coated separator according to one embodiment of the present invention. [Modes for carrying out the invention]

[0030] The following describes the technical concepts in the embodiments of the present invention clearly and completely. Clearly, the embodiments described are only a subset of the embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art without creative labor based on the embodiments of the present invention are within the scope of the protection of the present invention.

[0031] Prior to filing this application, the applicant conducted a series of studies and experiments on conventional separators.

[0032] Conventional coated separators for lithium-ion batteries, regardless of whether the substrate is PP, PE, or a PP / PE / PP composite film, or whether it is a double-sided or single-sided coated ceramic film or a high-heat-resistant nanofiber coated film, generally have low breakdown voltages, basically in the range of 1.0 to 2.0 kV / mm. It is difficult to further improve their breakdown voltage performance, which hinders further improvement of the safety performance of the assembled lithium-ion batteries, and generally makes it difficult to pass needle stick tests.

[0033] In view of this, the present application provides a coating slurry, a coating separator, a method for manufacturing a separator, and a battery in order to improve the high-voltage resistance and needle-piercing resistance of a battery separator.

[0034] The technical aspects of the present invention will be described in detail below with reference to specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described repeatedly in some embodiments.

[0035] An embodiment of the present invention first provides a coating slurry containing an adhesive polymer resin as the main component, with a weight ratio of 5 to 20 wt% of the solvent in the slurry, The adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50-85:15-50. Alternatively, the present invention provides a coating slurry in which the adhesive polymer resin comprises a combination of at least two polyimide-based adhesive resins, wherein the at least two polyimide-based adhesive resins comprise a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, and the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50-85:15-50.

[0036] Specifically, the weight ratio of the adhesive polymer resin in the slurry may be, for example, 5 wt%, 10 wt%, 15 wt%, or 20 wt%. In a more preferred embodiment, the weight ratio of the adhesive polymer resin in the slurry is 5 to 15 wt%. This is because when the weight of the adhesive polymer resin in the slurry is within this range, application is relatively easy, and when the ratio exceeds 15%, the viscosity of the slurry becomes high, which imposes certain requirements on the application process.

[0037] Here, the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer may be, for example, 50:15, 50:20, 50:25, 50:30, 60:15, 60:20, 60:25, 60:30, 60:35, 60:40, 60:45, 60:50, 70:15, 70:20, 70:25, 70:30, 70:35, 70:40, 70:45, 70:50, 80:15, 80:20, 80:25, 80:30, 80:35, 80:40, 80:45, 80:50, 85:15, 85:20, 85:25, 85:30, 85:35, 85:40, 85:45, or 85:50.

[0038] Here, the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin may be, for example, 50:15, 50:20, 50:25, 50:30, 60:15, 60:20, 60:25, 60:30, 60:35, 60:40, 60:45, 60:50, 70:15, 70:20, 70:25, 70:30, 70:35, 70:40, 70:45, 70:50, 80:15, 80:20, 80:25, 80:30, 80:35, 80:40, 80:45, 80:50, 85:15, 85:20, 85:25, 85:30, 85:35, 85:40, 85:45, or 85:50.

[0039] The present invention is not limited thereto, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer, and / or the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin may be other values, as long as the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50-85:15-50, or the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50-85:15-50.

[0040] Here, the glass transition temperature of the first polyimide adhesive resin is greater than 200°C, and the glass transition temperature of the second polyimide adhesive resin is greater than 140°C. The glass transition temperature of the first polyimide adhesive resin being greater than 200°C provides sufficient heat resistance and safety for the coating layer, and the glass transition temperature of the second polyimide adhesive resin does not need to be excessively high; it only needs to be greater than 140°C. In this way, the advantage is that a certain level of heat resistance for the separator can be ensured while providing stronger adhesive performance and tackiness to the substrate.

[0041] As an example, the solvent is an organic solvent, and the polyimide adhesive resin is a modified polyimide soluble in the organic solvent. The modified polyimide can be prepared by grafting functional groups onto the polyimide, and of course, it can also be made soluble in the organic solvent after being modified by other modification methods.

[0042] In some embodiments, when the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, the polyimide-based adhesive resin is at least one selected from the polymer resins ether anhydride type polyimide, fluorine anhydride type polyimide, ketone anhydride type polyimide, bismaleimide, alkenyl-sealed polyimide, polyesterimide, polyamideimide, and polyetherimide. When the adhesive polymer resin includes a combination of at least two polyimide-based adhesive resins, the at least two polyimide-based adhesive resins are selected from polymer resins such as ether anhydride polyimide, fluorine anhydride polyimide, ketone anhydride polyimide, bismaleimide, alkenyl-sealed polyimide, polyesterimide, polyamideimide, and polyetherimide. These polymer resins are merely illustrative examples, and the present invention is not limited to them. Those skilled in the art may select other polymer resins to achieve the objectives of the present invention.

[0043] In some embodiments, the coating layer pore expander is further included in a weight ratio of 0.05 to 5 wt% in the slurry. For example, the weight ratio of the coating layer pore expander in the slurry may be, for example, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or a range value between any two numbers. However, the present invention is not limited to these, and the weight ratio of the coating layer pore expander in the slurry may be any other value as long as it is within the range of 0.05 to 5 wt%.

[0044] In some embodiments, the coating layer pore expander is one of water, ethanol, polyethylene glycol, methanol, or a combination thereof. However, the present invention is not limited to these, and the coating layer pore expander may be other materials. By adding the coating layer pore expander to the slurry, the separator manufactured using the slurry has a honeycomb-like, dense pore structure formed on the surface of its coating layer. This ensures that the coating layer has a certain degree of permeability, adsorbs sufficient electrolyte, provides sufficient ion channels, reduces interfacial impedance, provides higher electronic insulation, and increases fracture resistance.

[0045] In some embodiments, the invention further includes ceramic particles whose weight ratio in the slurry is greater than 0 wt% and less than or equal to 5 wt%. For example, the weight ratio of ceramic particles in the slurry may be, for example, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or a range value between any two numbers. These numbers are merely examples, and the present invention is not limited to these. The weight ratio of ceramic particles in the slurry may be other values, as long as it is greater than 0 wt% and less than or equal to 5 wt%.

[0046] As an example, the ceramic particles are any one of aluminum oxide, boehmite, silicon oxide, magnesium oxide, titanium oxide, and zirconium oxide, or a combination thereof. However, the present invention is not limited to these, and the ceramic particles may be made of other materials. By adding ceramic particles to a slurry, the separator manufactured using the slurry has particulate ceramic particles distributed on the surface of the coating layer, and the particulate ceramic particles are embedded in the polymer layer, forming isolated island-like structures with a diameter of 0.5 μm to 2 μm. Here, the island-like structures are not perfectly regular cones, and the diameter here refers to the average value of the connecting lines from the projection center of the island-like structure onto the substrate surface to the edge. These isolated island-like structures can increase the porosity of the coating layer, improve permeability, increase the electrolyte absorption rate, increase the wettability of the electrolyte, and reduce the interfacial impedance inside the lithium-ion battery. Due to their special island-like structure, they can also increase the void for embedding at the coating layer interface to the electrode surface, increase interfacial adhesion, and improve the battery's cycle stability.

[0047] In some embodiments, the weight ratio of the solvent in the slurry is 70 to 95 wt%. For example, the weight ratio of the solvent in the slurry may be, for example, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or a range between any two values. These values ​​are merely examples, and the present invention is not limited to these; the weight ratio of the solvent in the slurry may be other values, as long as it is between 70 and 95 wt%.

[0048] As an example, the solvent is one of acetone, N-methylpyrrolidone, or DMAc, or a combination thereof. However, the present invention is not limited to these, and the solvent may be other materials as long as they can dissolve the adhesive polymer resin.

[0049] In some embodiments, the substrate is one of the following: PP, PE, PP / PE / PP composite film, double-sided or single-sided coated ceramic film, or double-sided or single-sided coated nanofiber film. However, the present invention is not limited to these, and other substrates are also within the scope of protection of the present invention.

[0050] Furthermore, the present invention provides a coating separator comprising a substrate and a polymer layer coated on one or both sides of the substrate, wherein the polymer layer comprises at least two functional groups selected from imide groups, heteroaromatic rings, and aromatic rings, and at least one functional group selected from ester groups, ether bonds, sulfide bonds, ketone groups, amide groups, phenol hydroxyethers, methyl groups, methylene groups, trifluoromethyl groups, and CF bonds. Specifically, if the adhesive polymer resin in the coating slurry comprises a combination of at least two polyimide-based adhesive resins, the polymer layer comprises at least two functional groups selected from imide groups, heteroaromatic rings, and aromatic rings, and at least one functional group selected from ester groups, ether bonds, sulfide bonds, ketone groups, amide groups, phenol hydroxyethers, methyl groups, methylene groups, trifluoromethyl groups, and CF bonds. If the adhesive polymer resin in the coating slurry includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, the polymer layer mainly consists of polyimide, and the functional groups are mainly functional groups of the polyimide molecule (for example, one of imide groups, heteroaromatic rings, or aromatic rings), as well as trifluoromethyl groups and CF-bonded functional groups of PVDF.

[0051] Furthermore, embodiments of the present invention further provide a coating separator comprising a substrate and a polymer layer, wherein the polymer layer is coated on one or both sides of the substrate, and the polymer layer is formed by coating the coating slurry according to the present invention.

[0052] In particular, referring to Figure 1, the high-voltage, needle-resistant lithium-ion battery separator according to the present invention has a low-temperature 1C discharge capacity of more than 90% of that of a lithium-ion battery, which is higher than that of a conventional ceramic-coated composite separator. By applying the coating slurry according to the present invention to a separator based on a double-sided or single-sided coated ceramic film, a double-sided or single-sided coated nanofiber film, or a PP or PE or PP / PE / PP composite film, superior heat resistance, high fracture resistance, and electrode piece adhesion performance are imparted to the lithium-ion battery separator, significantly improving the high safety performance and cycle stability performance of the lithium-ion battery. As a result, the lithium-ion battery according to the present invention is particularly suitable for application fields such as EVs and energy storage.

[0053] In some embodiments, the surface layer of the polymer layer has a porous structure. For example, the porous structure is a dense honeycomb-like structure. Here, dense means that the pore size observed in the SEM electron microscope image is on the nanoscale, as shown in Figure 2A, and refers to a dense coating layer structure. Because the surface layer of the polymer layer has a porous structure, the coating separator according to the present invention can ensure a certain degree of permeability, adsorb sufficient electrolyte, provide sufficient ion channels, reduce interfacial impedance, provide higher electronic insulation, and improve fracture resistance.

[0054] In some embodiments, as shown in Figure 2B, the polymer layer further includes ceramic particles that are embedded to form island-like structures. For example, the size of the island-like structures is 0.5 μm to 2 μm. These isolated island-like structures can increase the porosity of the polymer layer, improve permeability, increase the electrolyte absorption rate, increase the wettability of the electrolyte, and reduce the interfacial impedance inside the lithium-ion battery. Due to their special island-like structure, they can also increase the voids for embedding the coating layer interface to the electrode surface, increase interfacial adhesion, and improve the battery's cycle stability.

[0055] Referring to Figure 3, as shown in Figure 3, the embodiment of the present invention further provides a method for manufacturing a coated separator, which includes the following steps.

[0056] S1: Provides a base material.

[0057] Here, the substrate may be, for example, a PP film, a PE film, or a PP / PE / PP composite film, a double-sided or single-sided ceramic coated film, or a double-sided or single-sided nanofiber coated film.

[0058] S2: Prepare a slurry. Add 5-20 wt% of an adhesive polymer resin to a solvent and dissolve it thoroughly to obtain a coating slurry, wherein the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50-85:15-50, or the adhesive polymer resin includes a combination of at least two types of polyimide-based adhesive resins, wherein the at least two types of polyimide-based adhesive resins include a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, and the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50-85:15-50.

[0059] S3: Coating. The prepared coating slurry is applied to at least one surface of the substrate to form a polymer layer on the substrate.

[0060] Here, the slurry may be applied to one or both sides of the substrate. The application process may specifically be a NIPS process. For example, a porous gel-ceramic mixed coating layer can be manufactured by a double-sided microgravure coating method using an organic solvent such as NMP, acetone, or DMAc as the solvent and a polymer as the solute, followed by phase separation by solidified gel to form pores, and then a combination of washing and drying processes.

[0061] Separators manufactured using this method have a polymer layer containing an adhesive polymer resin, possessing properties such as high voltage resistance, insulation, flame retardancy, and adhesion. This allows them to provide excellent breakdown voltage resistance for lithium-ion battery separators, with a breakdown voltage in the range of 2.1kV to 5.0kV and a breakdown strength greater than 4.5kV / mil, along with excellent interfacial adhesion to electrode pieces. Lithium-ion batteries assembled using these separators exhibit superior needle puncture resistance and high breakdown voltage resistance.

[0062] Furthermore, embodiments of the present invention further provide a battery comprising a coated separator, a positive electrode, a negative electrode, and an electrolyte according to the embodiments enumerated in the present invention.

[0063] The following analyzes the product performance of some embodiments of the present invention through experiments. [Examples]

[0064] S1: A substrate was provided with ceramic layers coated on both sides. For convenience, this substrate will be abbreviated as a ceramic film.

[0065] S2: A slurry was prepared. 9 wt% adhesive polymer resin, 2.5 wt% coating layer pore expander, and 2 wt% ceramic particles were added to a solvent and thoroughly dissolved to obtain a coating slurry. Here, the adhesive polymer resin includes a first polymer resin and a second polymer resin, specifically, the first polymer resin is polyetherimide, the second polymer resin is polyamideimide, the ratio of the first polymer resin to the second polymer resin is 60:40, the solvent is acetone, the coating layer pore expander is water, and the ceramic particles are aluminum oxide.

[0066] S3: Coating. The prepared coating slurry was coated onto the ceramic film by simultaneous microgravure on both sides, and the solidified gel separated to form pores. A porous gel-ceramic mixed coating layer was produced by combining a water washing and drying process, and the corresponding coating separator was obtained.

[0067] Based on Example 1, Examples 2 to 17 and Comparative Examples 1 to 3 were obtained by changing the ratio of the first polymer resin to the second polymer resin, the ratio of the first polymer resin to the second polymer resin, the ratio of polymer in the slurry, the substrate, the thickness of the coating layer and the separator, and the ratio of ceramic particles in the slurry. Specifically, the differences between each example and comparative example are shown in Table 1. Here, the thickness of the coating layer in Table 1 refers to the thickness of the coating layers on both sides, that is, the thickness of the coating layers on both sides obtained by applying the prepared coating slurry to the ceramic film by simultaneous microgravure on both sides or step microgravure. Refer to Table 1, which shows the performance of the corresponding separators obtained in Examples 1 to 17 and Comparative Examples 1 to 3.

[0068] The method for measuring adhesive strength is as follows: A standard sample piece (coated film (25 mm × 180 mm), pole piece (20 mm × 150 mm)) was prepared from the coated film sample to be measured. The separator coated surface and the pole piece were bonded together using a hot press molding machine under constant pressure and at a temperature of 60°C. After that, the pole piece and the other end of the sample were clamped with a jig, and tensile force was applied until the stroke of the tensile machine was completed. The parameters of the tensile machine were set to positioning movement: 150 mm, and test speed: 300 mm / min.

[0069] The method for measuring the heat shrinkage rate at 130°C for 60 minutes is as follows: First, the separator was cut into 50mm x 50mm measurement samples along its horizontal and vertical directions. Next, the cut samples were placed between sheets of A4 paper, with five sheets of A4 paper on top and five sheets on the bottom. Then, the oven temperature was set to 130°C, and the temperature was raised to the specified temperature, allowing it to preheat sufficiently and ensuring that the internal temperature stabilized at the specified temperature. The sample, sandwiched between the prepared A4 sheets, was then quickly placed into the oven along with the A4 sheets. The sample needed to be placed in the middle of the upper layer of the oven, as the lower layer could not be left unattended, and the oven door was immediately closed. After closing the oven door, the measurement time was set to 60 minutes as requested. After the time had elapsed, the sample film was removed from the oven and allowed to cool to room temperature. The film was then lightly flattened, the distance between the separator edges in the horizontal and vertical directions was measured, the data was recorded, and the heat shrinkage rate was calculated. The formula for calculating the thermal shrinkage rate is: Thermal shrinkage rate % = (Length between initial marks - Length between marks after heating) / Length between initial marks × 100%.

[0070] The film rupture temperature was obtained by the TMA test. In the TMA test, the film rupture temperature is determined by applying constant force to the separator (simulating the internal conditions of a battery) and then gradually increasing the temperature until the film ruptures.

[0071] Voltage withstand test: Equipment used: The withstand voltage tester consists of a high-voltage boost circuit (which allows adjustment of the test voltage required for output), a leakage current detection circuit (which allows setting of the alarm current), and an indicating instrument (which directly reads the output voltage and leakage current value <or breakdown alarm current value>).

[0072] Operating principle: During testing, when the object under test reaches a predetermined time under the action of a predetermined test voltage, the device automatically shuts off the output voltage, and when damage occurs, i.e., when the leakage current exceeds a predetermined alarm current, the device emits an alarm sound, and the alarm value is the damage value.

[0073] Test Method: The film sample to be tested was cut to the size of an A4 sheet of paper and placed flat on clean, flat silver or aluminum foil paper. The instrument was set to an upper limit output voltage of 6KV, an output current of 1mA, and a rise time of 30S. A copper conductor column was lightly placed on the film sample, and the instrument's START button was clicked to start the test. During the current and voltage rise process, if breakdown occurred, i.e., if the leakage current exceeded a predetermined alarm current, the instrument emitted an alarm sound, and the alarm value was the breakdown value. Ten different points were uniformly taken on the film sample surface and the test was repeated 10 times. The average value was taken to obtain the breakdown voltage value described in this patent.

[0074] Dielectric strength is calculated as the breakdown voltage value × 25.4 / film sample thickness, and is expressed as the dielectric strength performance per unit thickness.

[0075] The increase in permeability is the difference between the permeability of the separator after coating and the permeability of the substrate, and indicates the increase in permeability of the film due to the coating layer. Permeability tests can be performed by referring to GB / T36363-2018 Polyolefin Separator for Lithium-ion Batteries. [Table 1]

[0076] As can be seen from Table 1, the present invention significantly improves the overall breakdown voltage resistance and adhesion of the separator. Examples 1 to 7, 8, 9, 10 to 12, and 13 to 15 involve applying the slurry to several different substrates: a ceramic coating film, a UV crosslinked coating film, a nanofiber coating film, a PE base film, and a PP base film, respectively. Regardless of the substrate used, the coated separators of the present invention achieve both high adhesion and low air permeability increase compared to the separators in the comparative examples, while also significantly improving breakdown resistance. Here, in Examples 1 to 7, polymers with different mixing ratios were mixed and then applied to the surface of a ceramic coated separator substrate. In Example 3, where the first polymer resin is polyetherimide and the ratio with the second polymer resin is 80:20, the coated separator exhibits excellent breakdown resistance, dielectric strength, and adhesion, as well as low air permeability increase, resulting in good overall performance. This is because the dielectric strength and breakdown resistance of the first polymer polyetherimide itself are good, and at a high ratio, it can provide excellent insulation and breakdown voltage performance to the separator. By controlling the blending ratio of the first polymer to the second polymer and the blending ratio of the polymer in the slurry, a good macroporous structure is provided to the coating layer, increasing permeability.

[0077] Example 8 was coated using a UV-crosslinked separator as the substrate. Compared to Example 3, Example 8 has a thinner coating layer, but it is equivalent to the dielectric strength and breakdown voltage of Example 3, and also possesses good adhesive properties and high-temperature resistance. This is because the crosslinked network structure formed by the adhesive in the UV-coated separator substrate coating layer makes it difficult for the polyimide-based coating layer to penetrate to the bottom layer, forming a chemical bond at the interface between the UV-coated separator substrate and the polyimide coating layer, creating a dense coating layer structure, increasing the adhesive effect of the coating layer, and resulting in superior dielectric strength.

[0078] Example 9 was coated using a nanofiber-coated separator as the substrate. Compared to Example 3, Example 9 had comparable dielectric strength and breakdown voltage, as well as good adhesion characteristics and high-temperature resistance. This is because the nanofiber-coated separator itself has excellent heat resistance, which is combined with the excellent voltage resistance of the polyimide-based coating layer. Example 10 was coated using a PE-based film as the substrate. Compared to a normal PE-based film, both the film rupture temperature and breakdown resistance were greatly improved (a normal PE-based film generally has a film rupture temperature of 145°C and a breakdown voltage of 1.4KV). Compared to Example 11, which used a PVDF-HFP copolymer as the second polymer resin, Example 10 has a higher film rupture temperature and breakdown resistance because the polyimide-based resin itself has high heat resistance and insulation performance.

[0079] Example 13 was coated using a PP-based film as the substrate, and compared to Example 10, which was coated using a PE-based film, the heat resistance performance was significantly improved. As can be seen from the comparison between Example 13 and Comparative Examples 2 and 3, the ratio of the first polymer resin and the second polymer resin in the slurry is very important. If it is lower than 5%, it is difficult to control the thickness of the coating layer, and the interfacial adhesion of the separator to the electrode piece and the tackiness to the substrate cannot be ensured, and there is a risk of the coating layer falling off. However, if the ratio is too high, for example, exceeding 20%, it is difficult to control the coating layer thickness, and the coating process cannot be successfully implemented, resulting in a very low porosity of the coating layer and an excessive increase in air permeability. Difficulty in controlling the thickness of the coating layer means that the uniformity of the thickness of the entire coating layer is poor during the coating process. For example, it is understood that the thickness of the coating layer may be lower than 3 μm in some areas of Comparative Example 3 and higher than 5 μm in other areas. As can be seen from the comparison between Example 13 and Examples 16 and 17, the separator formed without coating the polymer slurry with ceramic particles showed improved destructiveness, heat resistance, and adhesion compared to a normal separator. However, the increase in air permeability was significant, which may affect the ion permeability of the separator. When the proportion of ceramic particles exceeded 5%, it became difficult to control the coating thickness and the increase in air permeability, resulting in a significant decrease in the adhesive performance of the separator.

[0080] Example 15 is an embodiment in which the amount of pore expander added is 0%. As can be seen from the comparison with other examples and comparative examples, after adding the pore expander, the porosity of the coating layer is increased, providing sufficient ion channels and reducing the overall impedance of the lithium-ion battery. Without adding the pore expander, the impedance increases and the breakdown voltage increases slightly, but because the pores are relatively dense, the increase in air permeability is large, the cycle life of the cell decreases, the ion conductivity decreases, the energy density decreases, and the product is not satisfactory for use.

[0081] In this patent, the first polymer resin is selected as the main material to be a polyimide-based resin with excellent dielectric and insulating properties, and the material itself has good dielectric, insulating, and heat-resistant properties, providing high-pressure fracture performance to the separator. The second polymer resin material, while ensuring a certain level of heat resistance, provides high adhesion performance to the separator, good adhesion performance to the substrate, and excellent film formation performance, thereby ensuring process possibilities. By flexibly selecting substrates with different properties, it is possible to meet the different needs of users regarding heat resistance, film rupture temperature, and fracture voltage, ultimately enabling differentiation of product design and further improving the overall safety performance of the separator.

[0082] Furthermore, embodiments of the present invention provide a coated separator comprising a substrate and a polymer layer coated on one or both sides of the substrate, wherein the coated separator has a breakdown voltage of 2.1kV to 5.0kV and a breakdown strength greater than 4.5kV / mil.

[0083] Table 2 below shows the results of a comparative needle-stick test in which the PI-coated separator in Example 2 of the present invention and the CCS-coated separator, which uses the same substrate as in Example 2, were assembled into a lithium cobalt oxide cathode cylindrical battery. [Table 2]

[0084] In the table above, "voltage" refers to the voltage applied in the needle-pierce test. "Temperature" refers to the cell temperature. "Resistance" refers to the internal resistance of the assembled cell. According to the tests, when a constant voltage was applied to the CCS-coated separator, it ignited and burned intensely in the needle-pierce cell test, resulting in a "Failed" result. However, when a constant voltage was applied to the PI-coated separator in Example 2, there was no clear phenomenon of ignition or combustion in the needle-pierce cell test, resulting in a "Passed" result.

[0085] In this specification, any reference to terms such as “one embodiment,” “one example,” “specific implementation process,” or “one illustration” means that the specific features, structures, materials, or characteristics described in connection with such embodiment or illustration are included in at least one embodiment or illustration of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or illustration. Furthermore, the specific features, structures, materials, or characteristics described may be combined in an appropriate manner in any one or more embodiments or illustrations.

[0086] Finally, it should be noted that the above embodiments are merely for illustrating the technical concepts of the present invention and do not limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that it is still possible to modify the technical concepts described in the above embodiments or to make equivalent substitutions for some or all of the technical features therein, and that such modifications or substitutions do not cause the essence of the corresponding technical concepts to deviate from the scope of the technical concepts of the embodiments of the present invention.

Claims

1. A coating slurry comprising a solvent and an adhesive polymer resin in a weight ratio of 5 to 20 wt% in the slurry, wherein the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50 to 85:15 to 50. Alternatively, the coating slurry is characterized in that the adhesive polymer resin comprises a combination of at least two polyimide-based adhesive resins, wherein the at least two polyimide-based adhesive resins comprise a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, and the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50 to 85:15 to 50.

2. The coating slurry according to claim 1, characterized in that the glass transition temperature of the first polyimide-based adhesive resin is greater than 200°C, and the glass transition temperature of the second polyimide-based adhesive resin is greater than 140°C.

3. The coating slurry according to claim 1, characterized in that the solvent is an organic solvent and the polyimide-based adhesive resin is a modified polyimide soluble in the organic solvent.

4. When the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, the polyimide-based adhesive resin is at least one selected from the polymer resins ether anhydride type polyimide, fluorine anhydride type polyimide, ketone anhydride type polyimide, bismaleimide, alkenyl-sealed polyimide, polyesterimide, polyamideimide, and polyetherimide. The coating slurry according to claim 3, characterized in that, when the adhesive polymer resin includes a combination of at least two polyimide-based adhesive resins, the at least two polyimide-based adhesive resins are selected from polymer resins such as ether anhydride type polyimide, fluorine anhydride type polyimide, ketone anhydride type polyimide, bismaleimide, alkenyl-sealed polyimide, polyesterimide, polyamideimide, and polyetherimide.

5. The coating slurry according to any one of claims 1 to 4, further comprising a coating layer pore expander in a weight ratio of 0.05 to 5 wt% in the slurry.

6. The coating slurry according to claim 5, characterized in that the coating layer pore expander is one of water, ethanol, polyethylene glycol, methanol, or a combination thereof.

7. The slurry further contains ceramic particles whose weight ratio is greater than 0 wt% and less than or equal to 5 wt%, Preferably, the coating slurry according to claim 6 is characterized in that the ceramic particles are one of aluminum oxide, boehmite, silicon oxide, magnesium oxide, titanium oxide, zirconium oxide, or a combination thereof.

8. The weight ratio of the solvent in the slurry is 70 to 95 wt%, The coating slurry according to claim 7, characterized in that the preferred solvent is one of acetone, N-methylpyrrolidone, DMAc, or a combination thereof.

9. A coated separator comprising a substrate and a polymer layer coated on one or both sides of the substrate, The polymer layer is characterized by containing at least two functional groups selected from imide groups, heteroaromatic rings, and aromatic rings, and at least one functional group selected from ester groups, ether bonds, sulfide bonds, ketone groups, amide groups, phenol hydroxyethers, methyl groups, methylene groups, trifluoromethyl groups, and C-F bonds.

10. A coating separator characterized by comprising a base material and a polymer layer coated on one or both sides of the base material and coated with a coating slurry according to any one of claims 1 to 8.

11. A coated separator comprising a substrate and a polymer layer coated on one or both sides of the substrate, A coating separator characterized in that the breaking voltage of the coating separator is 2.1 kV to 5.0 kV and the breaking strength is greater than 4.5 kV / mil.

12. The surface layer of the polymer layer has a pore structure. Preferably, the pore structure is a honeycomb-like, dense pore structure, characterized in that the coating separator is as described in any one of claims 9 to 11.

13. The polymer layer further contains ceramic particles that are fitted into the polymer layer to form an island-like structure, Preferably, the coating separator according to claim 12, characterized in that the diameter of the island-like structure is 0.5 μm to 2 μm.

14. A method for manufacturing a coating separator according to any one of claims 11 to 13, The steps include providing a substrate and A slurry preparation step comprising adding 5 to 20 wt% of an adhesive polymer resin to a solvent, dissolving it thoroughly, and then obtaining a coating slurry, wherein the adhesive polymer resin includes a combination of a PVDF-based adhesive resin polymer and a polyimide-based adhesive resin, and the mass ratio of the polyimide-based adhesive resin to the PVDF-based adhesive resin polymer is 50 to 85:15 to 50, or the adhesive polymer resin includes a combination of at least two types of polyimide-based adhesive resins, wherein the at least two types of polyimide-based adhesive resins include a first polyimide-based adhesive resin and a second polyimide-based adhesive resin, and the mass ratio of the first polyimide-based adhesive resin to the second polyimide-based adhesive resin is 50 to 85:15 to 50, A manufacturing method characterized by comprising a coating step of applying the above-prepared coating slurry to at least one surface of the substrate to form a polymer layer on the substrate.

15. A battery comprising a coated separator, a positive electrode, a negative electrode, and an electrolyte, The battery is characterized in that the coating separator is the coating separator described in any one of claims 9 to 14.

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