Battery separator, method for preparing the same, and battery

Abstract

A battery separator, a method for preparing the same, and a battery. The battery separator includes a base film having a polymer layer formed by mixing mainly a first polymer, a second polymer, first ceramic particles, and second ceramic particles applied on one or both sides. The first ceramic particles have a median diameter of 0.01 μm to 0.3 μm, high surface activity, a specific surface area of 50 m2 / g or more, and can play a role in compatibilizing the first polymer and the second polymer in a slurry system, and can improve the adhesion of the polymer slurry to the substrate. The second ceramic particles are used as a filler for increasing the surface roughness of the polymer layer, the surface of which is coated with a polymer, and increase the adhesion of the polymer to the electrode sheet.

Description

Technical Field

[0003]

[0001] The present invention relates to the technical field of batteries, and particularly to battery separators, their preparation methods, and batteries.

Background Art

[0002] A lithium battery separator is one of the four core components of a lithium-ion battery. It separates the positive and negative electrodes of the lithium-ion battery, allows lithium ions to pass through, and plays a role in insulating electrons. The performance of the separator directly affects the performance of the lithium-ion battery and is one of the important technologies restricting the development of lithium-ion batteries. When the battery is in continuous charge and discharge or extreme usage conditions such as high temperature, there is a risk that the positive and negative electrodes will short-circuit due to the heat shrinkage and deformation of the separator, resulting in a series of thermal runaway phenomena, which seriously affects the safety of the lithium-ion battery. In addition, in conventional lithium-ion batteries, electrode expansion and contraction are likely to occur during continuous charge and discharge cycles, which may form gaps between the electrodes and the separator, leading to a possible reduction in the cycle life of the battery. Therefore, it is necessary to enhance the adhesion between the electrode and the separator and further improve the safety of the separator.

Summary of the Invention

[0003] The present invention provides a battery separator, its preparation method, and a battery for improving the heat resistance and adhesion of the battery separator.

[0004] The first aspect of the present invention provides a battery separator. The battery separator includes a substrate on one or both sides of which a polymer layer mainly formed by mixing a first polymer, a second polymer, first ceramic particles, and second ceramic particles is coated. The median diameter of the first ceramic particles and the second ceramic particles is 0.01 μm to 1 μm, and the first ceramic particles have high surface activity and a specific surface area of 50 m2 / g or more.

[0005] In some embodiments, the median diameter of the first ceramic particle is 0.01 μm to 0.3 μm.

[0006] In some embodiments, the median diameter of the second ceramic particle is 0.3 μm to 1 μm, which is larger than the median diameter of the first ceramic particle.

[0007] In some embodiments, the absolute value of the difference in median diameter between the first ceramic particles and the second ceramic particles is 0.2 μm to 0.99 μm, and the first ceramic particles have a smaller median diameter than the second ceramic particles.

[0008] In some embodiments, the ratio of the mass fractions of the first ceramic particles to the second ceramic particles is 10% to 50%: 50% to 90%.

[0009] In some embodiments, the ratio of the mass fractions of the first ceramic particles to the second ceramic particles is 10% to 35% and 65% to 90%.

[0010] In some embodiments, the first polymer is a high-viscosity polymer resin, the high-viscosity polymer resin is a binder resin, and the battery separator has a dry press adhesive strength of 20 N / m or more and a wet press adhesive strength of 8 N / m or more.

[0011] In some examples, the high-viscosity polymer resin comprises a copolymer of polyvinylidene fluoride and hexafluoropropene (hereinafter abbreviated as PVDF-HFP copolymer), sodium carboxymethylcellulose (CMC), and a polymethacrylate polymer (e.g., PMMA).

[0012] In some examples, the PVDF-HFP copolymer has a ratio of HFP to the mass of the copolymer of 4% to 20%, a molecular weight of 300,000 to 500,000, a melting point of 125°C to 150°C, and a melt viscosity of 15 cps to 35 cps.

[0013] In some examples, the second polymer is a heat-resistant polymer resin with a melting point of 180°C or higher.

[0014] In some examples, the heat-resistant polymer resin comprises one or two of the following: polyetherimide [PEI], polyimide [PI], polyvinylidene fluoride-tetrafluoroethylene-propylene [P(PVDF-TFE-P)] ternary copolymer, and polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene [P(VDF-TrFE-CTFE)] ternary copolymer.

[0015] In some examples, the ratio of the mass fractions of the first polymer to the second polymer is 10% to 40%:60% to 90%.

[0016] In some embodiments, the total mass fraction of the first ceramic particles and the second ceramic particles in the polymer layer is 30% to 70%, based on the sum of the masses of the first polymer, the second polymer, the first ceramic particles, and the second ceramic particles in the polymer layer.

[0017] A second aspect of the present invention provides a battery separator. The battery separator comprises a substrate on which a polymer layer is coated on one or both sides, the polymer layer mainly containing ceramic particles, and island-like structures are formed on the surface of the polymer layer.

[0018] In some embodiments, the diameter of the island-like structure is 0.8 μm to 2 μm.

[0019] A third aspect of the present invention provides a method for preparing a battery separator for preparing a battery separator as described in any one of the above sections, the method comprising the following steps.

[0020] The first polymer and the second polymer are taken together, and the first polymer and the second polymer are mixed and dissolved in a solvent to obtain a premixed slurry A.

[0021] First ceramic particles and second ceramic particles are separated, and the two types of ceramic particles with different median diameters are added simultaneously or sequentially to the premixed slurry A and mixed to obtain a polymer layer coating slurry, wherein the median diameter of the first and second ceramic particles is 0.01 μm to 1 μm, and the specific surface area of ​​the first ceramic particles is 50 m2 / g or more.

[0022] The polymer layer coating slurry is applied to one or both sides of the substrate to obtain the battery separator.

[0023] A fourth aspect of the present invention provides a battery. The battery comprises a battery separator, a positive electrode, a negative electrode, and an electrolyte, wherein the battery separator is a battery separator as described in any one of the above claims.

[0024] The battery separator, its preparation method, and battery according to the present invention involve coating a polymer layer on one or both sides of a substrate, and adding two types of ceramic particles with different median diameters to this polymer layer in addition to a first polymer and a second polymer, wherein the median diameters of the two types of ceramic particles are 0.01 μm to 1 μm, and the specific surface area of ​​the first ceramic particle is 50 m² / g or more. As a result, the technical proposal of the present invention has at least the following technical advantages compared to the prior art.

[0025] 1) The first ceramic particles according to the present invention have high surface activity and can play a role in making the first polymer and the second polymer compatible in a slurry system. That is, although the first polymer and the second polymer are not compatible in the solvent themselves, the first ceramic particles function as a surfactant and can make the first polymer and the second polymer compatible in the solvent. Furthermore, the first ceramic particles can improve the adhesion of the polymer slurry to the substrate. The second ceramic particles, in the present invention, are used as a filler to increase the surface roughness of the polymer layer, and their surface is coated with polymer, increasing the adhesion of the polymer to the electrode sheet.

[0026] 2) By using ceramic particles as fillers in the polymer layer, the ceramic particles form a plurality of protruding island-like structures on the outer surface of the polymer layer. As a result, they mesh with the first ceramic layer at the bottom to produce an anchoring effect, enhance the adhesion effect between the coating layers, and increase the roughness of the outer surface of the separator. Thereby, the meshing between the surface of the separator and the electrode sheet becomes stronger, further improving the adhesion force between the separator and the electrode sheet.

[0027] 3) In the preparation of the polymer layer coating slurry, due to the adsorption effect of the polar groups contained on the surfaces of the first polymer and the second polymer in the polymer layer on the surface groups of the ceramic particles, the ceramic particles are uniformly dispersed in the slurry, enhancing the liquid absorption effect. Furthermore, after coating, the ceramic particles can be uniformly distributed on the surface of the coating layer, and since the heat resistance of the separator can be improved by the characteristics of the ceramic particles themselves, the heat on the surface of the separator becomes uniformly distributed.

[0028] 4) By blending ceramic particles with different median diameters in the polymer layer, the tap density of the coating layer can be improved, and the thermal shrinkage of the separator at a high temperature of 150 °C or above can be suppressed, further improving the thermal stability of the separator.

[0029] 5) The present invention selects two types of ceramic particles with different median diameters. The median diameter of the ceramic particles with a small median diameter is set to 0.01 μm ≤ D50 ≤ 0.3 μm, and the median diameter of the ceramic particles with a large median diameter is set to 0.3 μm ≤ D50 ≤ 1 μm. The ceramic particles with a small median diameter have a large surface energy. Specifically, since the specific surface area is 50 m2 / g or more, they can stabilize the mixed slurry of the first polymer and the second polymer with different heat resistances, solve the compatibility problem, and form a completely uniform mixed slurry system. On the other hand, the ceramic particles with a large median diameter form protruding island-like structures on the surface of the polymer layer, increasing the adhesion force of the coating layer.

[0030] None of the technical solutions of the present invention need to achieve the above technical effects simultaneously.

[0031] The present invention will be further described below with reference to the drawings and specific embodiments.

Brief Description of the Drawings

[0032] [Figure 1] It is a schematic diagram of the structure of a battery separator according to an embodiment of the present invention. [Figure 2] It is a schematic diagram of the structure of a battery separator according to another embodiment of the present invention. [Figure 3] It is a flowchart of a method for preparing a battery separator according to an embodiment of the present invention. [Figure 4] It is a flowchart of a method for preparing a battery separator according to another embodiment of the present invention.

Modes for Carrying Out the Invention

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. It is understood that the described embodiments are only a part of the embodiments of the present invention, and of course not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without using the inventive ability belong to the protection scope of the present invention.

[0034] Before filing this application, the applicant conducted a series of research and experiments on the conventional separator as follows.

[0035] The organic adhesive coated layer separator is manufactured as follows: First, a high-temperature resistant inorganic ceramic coating layer, obtained by applying a water-soluble slurry and drying it, is applied to one or both sides of a PE, PP, or PE / PP composite substrate. Then, an organic adhesive coating layer is applied to both sides of the high-temperature resistant inorganic ceramic coating layer. The applicant has found that in this method, during the organic adhesive coating step, some of the inorganic ceramic particles in the ceramic layer detach after passing through the solidification bath and the water washing step, significantly reducing the high-temperature stability of the separator. Furthermore, in the organic adhesive coating step, only a single layer of pure PVDF-based polymer resin is applied to the outer surface of the separator, and the interfacial adhesion between this polymer resin layer and the electrode sheet is generally 20-50 gf / 25 mm, making it difficult to further improve the adhesion using conventional techniques.

[0036] Furthermore, the applicant analyzed the organic adhesive coating layer separator and found that it is essentially a pure polymer adhesive resin coating layer with only a PVDF-based resin layer on the surface. The PVDF-based resin layer has an ordinary adhesive effect to the ceramic layer at the bottom and does not have an anchoring or interlocking effect. The applicant found that even when inorganic ceramic particles were added to the polymer adhesive resin coating layer, only a slight increase in adhesive strength was observed. This is because the addition of ceramic particles relatively reduces the polymer resin content, limiting the overall improvement in adhesive strength. The applicant also found that the PVDF-based resin may penetrate the ceramic layer under the action of a solvent, resulting in a loss of some of the adhesive properties.

[0037] In view of the above, the present invention provides a battery separator, a method for preparing the same, and a battery in order to improve the heat resistance and adhesiveness of the battery separator.

[0038] The technical aspects of the present invention will be described in detail below using specific examples. The following specific examples can be combined with each other. In some examples, the same or similar concepts or processes will be omitted from the explanation.

[0039] The battery separator according to the present invention comprises a substrate on which a polymer layer is coated on one or both sides, the polymer layer being a mixture of a first polymer, a second polymer, first ceramic particles, and second ceramic particles, wherein the median diameter of the first ceramic particles and the second ceramic particles is 0.01 μm to 1 μm, and the specific surface area of ​​the first ceramic particles is 50 m² / g or more.

[0040] The median diameters of the first and second ceramic particles may be in the range of any two of the following values, for example: 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, and 1 μm.

[0041] The specific surface area of ​​the first ceramic particle may be any of the following values, or any two of the following values, for example: 50 m² / g, 60 m² / g, 70 m² / g, 80 m² / g, 90 m² / g, 100 m² / g, 110 m² / g, 120 m² / g, 130 m² / g, 140 m² / g, 150 m² / g.

[0042] In one embodiment, the median diameter of the first ceramic particle is 0.01 μm to 0.3 μm. Furthermore, the median diameter of the second ceramic particle is 0.3 μm to 1 μm, which is larger than the median diameter of the first ceramic particle.

[0043] In one embodiment, the first polymer is a high-viscosity polymer resin. The high-viscosity polymer resin refers to a binder resin that can ensure high adhesion under dry pressing conditions and maintain excellent adhesion even after being wetted by immersion in an electrolyte. Furthermore, the high-viscosity polymer resin refers to one that has a wet press adhesive strength of 8 N / m or more and a dry press adhesive strength of 20 N / m or more. The wet press adhesive strength is the adhesive strength when pressed after immersion in an electrolyte and then peeled off. The dry press adhesive strength is the adhesive strength when the separator and electrode sheet are hot-pressed directly after lamination and then peeled off. In some examples, the high-viscosity polymer resin may be, for example, a PVDF-HFP copolymer. Specifically, the high-viscosity polymer resin is a PVDF-HFP copolymer having a melting point of 125°C to 150°C and a melt viscosity of 15 to 35 cps. However, the present invention is not limited thereto, and other high-viscosity polymer resins are also included within the scope of protection of the present invention.

[0044] In one embodiment, the second polymer is a heat-resistant polymer resin. Furthermore, the heat-resistant polymer resin is a heat-resistant polymer resin material having a melting point of 180°C or higher.

[0045] The battery separator according to the present invention, compared to other organic adhesive coated layer separators, has a first ceramic layer coated on one or both sides of the substrate, and this first ceramic layer may be a conventional ceramic coated layer such as a nanofiber coated layer or a nano-sized (order of magnitude) alumina coated layer. Furthermore, a polymer layer is coated on one or both sides of the surface of the first ceramic layer. Since the polymer layer has two types of ceramic particle fillers with different median diameters added, it forms a skeletal support structure, resulting in stronger adhesion compared to a pure polymer adhesive resin coated layer.

[0046] Pure organic adhesives only have a PVDF resin layer on their surface. The PVDF resin layer typically has an adhesive effect to the ceramic layer at the bottom, but does not have an anchoring or interlocking effect. Furthermore, PVDF can penetrate the ceramic layer under the action of a solvent, causing the PVDF's adhesive properties to be lost. On the other hand, in the case of mixed coating of polymer and ceramics, the adsorption effect of the polar groups on the polymer surface to the surface groups of the ceramic particles allows the ceramic particles to be uniformly dispersed in the slurry, and after coating, the ceramic particles can be uniformly distributed on the surface of the coated layer. The properties of the ceramics themselves can improve the heat resistance of the separator, and heat can be distributed uniformly. In addition, the multiple protruding island-like structures formed from such ceramic particles interlock with the first ceramic layer at the bottom, creating an anchoring effect and enhancing the adhesive effect of the coated layer.

[0047] In this invention, the presence of ceramic particles increases the roughness of the polymer layer, and the frictional force between its surface and the surface of the first ceramic layer at the bottom also increases, making it more difficult for the adhesive layer to peel off. The protruding structure on the surface of the polymer layer acts like a rivet, penetrating deeply into the gaps in the ceramic layer at the bottom and forming adhesive strengthening points, thus making it more difficult for the adhesive layer to peel off.

[0048] The battery separator according to the present invention has excellent high-temperature thermal stability, and in particular, its thermal stability under high-temperature conditions of 150°C or higher is superior to that of the conventional technology, further enhancing the safety of the battery. In addition, the special high-viscosity heat-resistant polymer resin coating layer has better adhesion to the electrode sheet than conventional PVDF coating layers, improving the hardness of the battery and suppressing the reduction in cycle life caused by gaps formed between the electrode sheet and the separator during the battery's charge-discharge cycle.

[0049] In particular, the separator according to the present invention can achieve a heat shrinkage rate of 10% or less at 150°C for 0.5 hours (after being held at 150°C for 0.5 hours), its adhesive strength reaches 50-80 gf / 25 mm, and its liquid absorption capacity is 6.5 g / m2 or more.

[0050] In another embodiment, the first ceramic coating layer is further included. The battery separator comprises a substrate on which the first ceramic coating layer is coated on one or both sides, and the polymer layer is coated on the first ceramic coating layer. The other structures are the same as in the above embodiment and will not be described.

[0051] In particular, when a polymer layer is applied to the first ceramic coating layer, the separator can achieve a thermal shrinkage rate of 5% or less at 150°C for 0.5 hours, its adhesive strength reaches 50-80 gf / 25 mm, and its liquid absorption is 6.5 g / m2 or more.

[0052] If the ceramic particles in the polymer layer are too large, they tend to combine with smaller ceramic particles to form secondary particles with a larger median diameter, making it difficult to control the thickness of the coating layer, and the thickness of the coating layer may fall outside the required range. As a result, the adhesive layer does not easily become a dense layer, and the polymer resin, along with the solvent, easily penetrates the micropores formed in the first ceramic layer, increasing permeability and affecting the lithium ion transmittance. In some examples, first ceramic particles with a median diameter of 0.01 μm ≤ D50 ≤ 0.3 μm and second ceramic particles with a median diameter of 0.3 μm ≤ D50 ≤ 1 μm are blended. The ceramic particles with a small median diameter (0.01 μm to 0.3 μm) have a specific surface area of ​​50 m² / g or more, and due to their surface energy and the action of hydrogen bonding of -OH, the heat-resistant resin and PVDF-HFP are formed into a uniform and stable colloidal slurry. At this time, the ceramic particles with a large median diameter float in the colloidal slurry like suspended particles. The ceramic particles with a large median diameter are uniformly dispersed throughout the slurry system and stably suspended in the slurry by the solvent effect of solvent molecules and hydrogen bonding between the polar groups on the surface of the ceramic particles with a large median diameter and the resin. The ceramic particles with a large median diameter are firmly held in a polymer network structure formed by a uniform colloidal resin layer through non-solvent-induced phase separation, and are uniformly embedded in the network structure of the coating layer. In addition, because of their large median diameter, the ceramic particles with a large median diameter form multiple convex island-like structures. Furthermore, ceramics with a large median diameter, used as additives to increase the roughness of the coating layer, improve the adhesion and bonding strength of the separator, and increase the electrolyte absorption rate (hydrogen bonds are formed between the -OH groups on the surface of the ceramic particles and the electrolyte, and the polar groups on the surface of the ceramic particles are easily attracted to the polar groups in the electrolyte molecules, thereby increasing the wettability and electrolyte absorption rate of the electrolyte), thereby increasing the porosity of the coating layer and suppressing the increase in permeability. Ceramics with a small median diameter improve the compatibility of the slurry.Nano-sized ceramic particles have high surface activity and a certain surface energy, making them more likely to attract the oxygen atom of the -C=O group in polyimide molecules and the lone pair electrons of the N atom in the molecule, thus forming hydrogen bonds. They also act on the polar group -CF3 of PVDF-HFP. As a result, both are emulsified throughout the slurry system, allowing them to coexist stably without layer separation and improving compatibility.

[0053] In particular, in the polymer layer, by incorporating ceramic particles with different median diameters to improve the thermal stability of the separator, the tap density of the coating layer is increased, suppressing the shrinkage of the separator at high temperatures above 150°C. Here, the mixing ratio of inorganic ceramic particles with a median diameter of 0.01 μm ≤ D50 ≤ 0.3 μm to inorganic ceramic particles with a median diameter of 0.3 μm ≤ D50 ≤ 1 μm is 10%~50%:50%~90%. In other examples, the mixing ratio of inorganic ceramic particles with a median diameter of 0.01 μm ≤ D50 ≤ 0.3 μm to inorganic ceramic particles with a median diameter of 0.3 μm ≤ D50 ≤ 1 μm is 10%~35%:65%~90%.

[0054] The first and second ceramic particles in the polymer layer may be gas-phase ceramic particles or nanoceramic particles. For example, the ceramic particles may be at least one of alumina, boehmite, SiO2, CaCO3, ZrO2, and TiO2.

[0055] The substrate in this invention may be a base film such as a polyolefin film, PET film, or BOPP film, or it may be a coated film obtained by coating the above base film. The polyolefin film may be made of PE, PP, or a composite separator of PP and PE.

[0056] In some embodiments, the polymer layer is applied to both sides of the base film. In some other embodiments, the first ceramic coating layer is first applied to one or both sides of the base film, and then the polymer layer is applied. Single-sided coating means that only one side is coated, and one side becomes adhesive. Double-sided coating allows adhesion to both sides, thus enabling adhesion between both sides of the separator and the positive and negative electrode sheets, suppressing the growth of lithium dendrites and further improving the wettability of the separator to the electrolyte. The thickness of the base film is 5 μm to 12 μm. The thickness of the first ceramic coating layer on one side of the base film is 0.5 μm to 2.5 μm. The thickness of the polymer layer on one side is 0.3 μm to 2.5 μm. If the polymer layer is too thick, it will affect the energy density, and if it is too thin, the adhesive strength will be insufficient.

[0057] In some embodiments, the first ceramic coating layer is a high-temperature resistant inorganic ceramic coating layer, and the high-temperature resistant inorganic ceramic coating layer may be a conventional high-temperature resistant inorganic ceramic coating layer such as a nanofiber coating layer, a nano-sized alumina coating layer, a silica ceramic coating layer, or a titanium oxide ceramic coating layer. For example, the high-temperature resistant inorganic ceramic coating layer includes inorganic ceramic filler particles (inorganic ceramic particles such as silica, alumina, boehmite, titanium oxide, magnesium oxide, and nanofibers), an acrylate adhesive, a polyacrylate adhesive, a dispersant, a wetting agent, a thickener, and an antifoaming agent.

[0058] In order to impart high adhesion, this invention employs a mixture of a highly tacky polymer resin and a heat-resistant polymer resin as the composition of the polymer layer. Furthermore, unlike general PVDF-based adhesive coating layers, this highly tacky, heat-resistant polymer resin mixture coating layer uses inorganic particles as fillers, so that multiple protruding island-like structures are formed on the outer surface of the separator, increasing the roughness of the outer surface of the separator. As a result, the interlocking between the surface of the separator and the electrode sheet becomes stronger, and therefore the adhesive strength between the separator and the electrode sheet is further improved.

[0059] In particular, the total mass fraction of the first and second ceramic particles in the polymer layer is 30% to 70% based on the sum of the masses of the first polymer, the second polymer, the first ceramic particles, and the second ceramic particles in the polymer layer (i.e., the total proportion of ceramic particles of two different median diameters). Specifically, the total mass fraction of the ceramic particles of two different median diameters in the polymer layer may be, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. Note that this mass fraction may also be other values ​​between 30% and 70%.

[0060] In some embodiments, the first polymer in the polymer layer is selected from a PVDF-HFP copolymer, and the second polymer is selected from at least one of polyetherimide and polyimide. Polyimide and polyetherimide are mainly characterized by their high melting points, exceeding 200°C, and therefore possess high heat resistance. This is a property that cannot be achieved with general resin materials. Furthermore, because polyimide and polyetherimide have high dielectric constants, they have greater resistance to the dielectric breakdown voltage of the coated layer.

[0061] The second polymer is not limited to the above, and may be one or two of the following: polyetherimide, polyimide, polymethyl methacrylate, polyvinylidene fluoride-tetrafluoroethylene-propylene terpolymer, or polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene terpolymer.

[0062] In some examples, the PVDF-HFP copolymer has a ratio of HFP to the mass of the copolymer of 4% to 20%, and the molecular weight of the PVDF-HFP copolymer is 300,000 to 500,000. The molecular weight of the PVDF-HFP copolymer is, for example, within the range of any two values ​​from 300,000, 310,000, 320,000, 330,000, 340,000, 350,000, 360,000, 370,000, 380,000, 390,000, 400,000, 410,000, 420,000, 430,000, 440,000, 450,000, 460,000, 470,000, 480,000, 490,000, and 500,000. If the molecular weight exceeds 50 wt, the adhesion to the substrate separator deteriorates, making the slurry more prone to detachment and elution. The ratio of HFP to the mass of the copolymer is within the range of any two values ​​from the following: 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%. If the HFP content exceeds 20%, the wet press adhesion strength between the separator and the electrode sheet will be less than 3 N / m.

[0063] In some examples, the polymer in the polymer layer is prepared by mixing a PVDF-HFP copolymer and polyimide, with a mass fraction ratio of PVDF-HFP to polyimide of 30%~50%:50%~70%. The mass fraction ratios of PVDF-HFP to polyimide are 30%:50%~70%, 35%:50%~70%, 40%:50%~70%, 45%:50%~70%, and 50%:50%~70%. In this blending ratio, the proportion of polyimide must not be too low; if it is too low, the heat resistance and adhesiveness of the polyimide will be impaired, and if it is too high, the adhesion of the slurry will decrease, and the coated layer that has passed through the solidification bath groove will be more likely to fall off.

[0064] The structure of the battery separator according to the present invention is shown in Figure 2. As shown in Figure 2, the battery separator comprises a base film 101 on which a first ceramic coating layer 102 is coated on both sides, and a polymer layer 103 is coated on the first ceramic layer 102, the polymer layer 103 mainly containing ceramic particles that form island-like structures 104 that protrude from its surface.

[0065] In this embodiment, the first ceramic coating layer 102 is applied to both sides of the base film 101, and the polymer layer 103 is applied to the first ceramic coating layer 102. In addition, in this invention, it is also possible to apply the first ceramic coating layer to only one side of the base film and apply the polymer layer to that first ceramic coating layer. Furthermore, in other embodiments, as shown in Figure 1, the first ceramic coating layer 102 can be omitted, and the polymer layer 103 can be directly applied to one or both sides of the base film 101.

[0066] As described above, the polymer layer 103 mainly comprises a first polymer, a second polymer, first ceramic particles, and second ceramic particles, with median diameters of 0.01 μm to 1 μm for the first and second ceramic particles, and a specific surface area of ​​50 m² / g to 150 m² / g for the first ceramic particles.

[0067] The diameter of the protruding island-like structures 104 is close to the median diameter of the ceramic particles with a larger median diameter; specifically, the diameter of the island-like structures 104 is, for example, 0.8 μm to 2 μm. Because the ceramic particles with a larger median diameter are embedded in the network structure of the coating layer, the protruding height of the island-like structures 104 is approximately 1 / 3 to 1 / 2 of 0.3 μm to 1 μm. The diameter of the island-like structures refers to the average length of the lines connecting the edges of the island-like structures formed in the plane of the separator, and the protruding height of the island-like structures refers to the height of the island-like structures that exceeds the surface of the coating layer.

[0068] To obtain the above-mentioned battery separator, the embodiments of the present invention further provide a method for preparing a battery separator for preparing the battery separator described in any one of the above-mentioned items.

[0069] As shown in Figure 3, in one embodiment, the method for preparing the coating layer for the battery separator includes the following steps.

[0070] S1: Prepare the coating slurry for the first ceramic coating layer.

[0071] S2: The first polymer and the second polymer are taken together, and the first polymer and the second polymer are mixed and dissolved in a solvent to obtain a premixed slurry A.

[0072] S3: First ceramic particles and second ceramic particles are separated so that the median diameter of the first and second ceramic particles is 0.01 μm to 1 μm, and the difference in median diameter between the first and second ceramic particles is 0.2 μm to 0.99 μm. Two types of ceramic particles with different median diameters are added to the premixed slurry A simultaneously or sequentially and mixed to obtain a polymer layer coating slurry.

[0073] S4: The coating slurry of the first ceramic layer is applied to one or both sides of the base film, and after curing, a substrate is obtained.

[0074] S5: The polymer layer coating slurry is applied to the substrate and cured to obtain the battery separator.

[0075] In other embodiments, it is possible to divide one step into multiple steps or change the order of steps according to this method, provided that it does not affect the experimental results. For example, in the above steps, it is possible to precede S4 with S2, and the present invention is not limited thereto.

[0076] In another embodiment, as shown in Figure 4, the method for preparing the coating layer for the battery separator includes the following steps.

[0077] S10: Take the first polymer and the second polymer, mix the first polymer and the second polymer and dissolve them in a solvent to obtain a premixed slurry A.

[0078] S20: First ceramic particles and second ceramic particles are selected, and the median diameter of the first and second ceramic particles is 0.01 μm to 1 μm, and the specific surface area of ​​the first ceramic particles is 50 m² / g to 150 m² / g. Two types of ceramic particles with different median diameters are added to the premixed slurry A simultaneously or sequentially and mixed to obtain a polymer layer coating slurry.

[0079] S30: The polymer layer coating slurry is applied to one or both sides of the base film, and after curing, the battery separator is obtained.

[0080] The polymer layer (high heat resistance, high adhesive separator) according to the present invention is realized by the NIPS process. NIPS is a film formation method using a non-solvent-induced phase separation method, and its specific process includes the steps of applying a coating slurry to both sides of a substrate, then immersing it in a solidification bath to perform phase conversion, followed by washing, drying, and winding.

[0081] The molecular weight of the PVDF-HFP used in this invention is 300,000 to 500,000, and within this range, the realization of the NIPS process can be ensured. In the NIPS process, after coating is complete, the separator enters a mixed phase of non-solvent and solvent, so the wet-coated slurry layer needs to have fairly high adhesion to the separator on the substrate. Otherwise, the slurry layer will be easily washed away by the mixed solution of non-solvent and solvent, or scraped off during the transport of the separator.

[0082] The following describes the experimental analysis of the product performance of several embodiments of the present invention.

[0083] Example 1

[0084] The polymer layer coating slurry was prepared mainly by the following steps.

[0085] A PVDF-HFP copolymer (weight-average molecular weight 300,000, hexafluoropropene (HFP) 4%) was prepared as the first polymer, polyetherimide as the second polymer, and a first ceramic powder (median diameter D50 = 0.05 μm) and a second ceramic powder (median diameter D50 = 0.6 μm) were prepared. A slurry was prepared according to the following steps. Based on the total mass of the first polymer, the second polymer, the first ceramic particles, and the second ceramic particles, 11 wt% of the first polymer and 19 wt% of the second polymer were dissolved in N-methyl-2-pyrrolidone (NMP) solvent (stirred thoroughly at 60°C for 24 hours) to obtain premixed slurry A. After the polymers in premixed slurry A were completely dissolved, 20 wt% of the first ceramic powder was added to the premixed slurry A and stirred thoroughly at 30°C and 1800 rpm / min for 60 minutes to uniformly mix and disperse to obtain mixed slurry B. 50 wt% of the second ceramic powder was added to the above mixed slurry B, and the mixture was thoroughly stirred for 60 minutes at 30°C and 1800 rpm / min, controlling the total solid content of the slurry to 10%, thereby obtaining the coating slurry used in the present invention.

[0086] In this embodiment and comparative example, the first ceramic powder is fumed alumina ceramics, and the second ceramic powder is silica ceramics.

[0087] The coating separator was prepared by the following steps.

[0088] A ceramic layer was applied to two opposing surfaces of a PE separator to obtain a ceramic substrate (preparation method described later). The prepared coating slurry was applied to the two opposing surfaces of the ceramic substrate using a microgravure roll. The coated substrate was immersed in a solidification bath groove at a temperature of 20°C and a concentration of 20% (mass ratio concentration of the first solvent to the mixture of the first and second solvents) to perform a phase change. After non-solvent washing and oven drying, a coated separator (i.e., a battery separator) was obtained. The first solvent comprises at least one of acetone, dichloromethane, benzene, toluene, xylene, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, cyclohexane, cyclohexanone, toluenecyclohexanone, chlorobenzene, dichlorobenzene, dichloromethane, diethyl ether, propylene oxide, methyl ethyl ketone, methyl-normal-butyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, tetrahydrofuran, trichloromethane, and N-methyl-2-pyrrolidone. The second solvent comprises at least one of ethanol, water, glycerin, ethyl acetate, and polyethylene glycol. In the examples and comparative examples of the present invention, the first solvent is N-methyl-2-pyrrolidone, and the second solvent is water.

[0089] The preparation of the ceramic substrate is as follows:

[0090] (1) The preparation of the slurry for coating the first ceramic layer in the examples and comparative examples of the present invention is as follows.

[0091] 50 kg of inorganic ceramic powder was placed in 57 kg of deionized water and mixed in a mixer for 30 minutes to disperse. 10 kg of 2% aqueous CMC (sodium carboxymethyl cellulose) solution was added and mixed for 30 minutes to disperse. 1.0 kg of polyacrylate adhesive (emulsion solids content 35%) was added and mixed for 30 minutes to disperse. Sanding was performed for 60 minutes (flow rate: 1000 L / h, speed: 750 rpm, stirring speed: 20 rpm). Finally, 0.15 kg of wetting agent, 0.15 kg of defoaming agent, and 26 kg of deionized water were added and mixed for 30 minutes to disperse, obtaining a ceramic coating slurry with a total solids content of 35%.

[0092] (2) Examples of the present invention The preparation of the ceramic substrate is as follows.

[0093] The ceramic layer was applied by gravure roll coating on both sides. The base film was a microporous film of polyethylene or polypropylene with a thickness of 7 μm, the thickness of the coating layer on one side was 2.5 μm, the coating speed was 60 m / min, the preheated oven temperature before coating was 60°C, and the oven drying temperature was 60°C.

[0094] Different examples and comparative examples were prepared by changing the experimental parameters. The experimental and product parameters for each example and comparative example are shown in Tables 1 to 3 below. The molecular weight of the PVDF-HFP copolymer used in both the examples and comparative examples was 300,000, with only the ratio of HFP to copolymer differing. Furthermore, the total thickness of the polymer layers on both sides was 4 μm. The first ceramic particles were ceramic particles with a small median diameter (0.01 μm to 0.3 μm) and a specific surface area of ​​50 m² / g or more.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] Of these, PEI is polyetherimide, and PI is polyimide.

[0099] Furthermore, the percentages of the first polymer and the second polymer in the table refer to the respective percentages of the first polymer and the second polymer relative to the dry weight of the coated layer. The percentages of the first ceramics and the second ceramics refer to the respective percentages of the first ceramics and the second ceramics relative to the dry weight of the coated layer. The electrode sheet adhesion is the experimental result of the adhesive strength to the electrode sheets on both opposing sides of the separator.

[0100] As can be seen from the above examples and comparative examples, the separator according to the present invention has significantly improved adhesive strength, a heat shrinkage rate of 5.0% or less at 150°C, and maintains a liquid absorption amount of 6.0 g / m2 or more.

[0101] In some other embodiments, the polymer layer was applied to both sides of the base film, and the coated separator was prepared by the following steps.

[0102] The prepared polymer coating slurry was applied to two opposing surfaces of a PE separator using a microgravure roll. The coated substrate was immersed in a solidification bath groove at a temperature of 20°C with a concentration of 20% (mass ratio concentration of first solvent: first solvent + second solvent) to perform a phase change, followed by non-solvent washing and oven drying to obtain a coated separator (i.e., a battery separator). The first solvent contains at least one of the following: acetone, dichloromethane, benzene, toluene, xylene, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, cyclohexane, cyclohexanone, toluenecyclohexanone, chlorobenzene, dichlorobenzene, dichloromethane, diethyl ether, propylene oxide, methyl ethyl ketone, methyl-normal-butyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, tetrahydrofuran, trichloromethane, and N-methyl-2-pyrrolidone. The second solvent comprises at least one of ethanol, water, glycerin, ethyl acetate, and polyethylene glycol. In the examples and comparative examples of the present invention, the first solvent is N-methyl-2-pyrrolidone, and the second solvent is water.

[0103] The preparation methods shown in Tables 4 and 5 are almost the same as those shown in Tables 1 and 3 above, except that the ceramic substrate step is omitted, meaning the polymer layer is directly applied to the PE separator.

[0104] [Table 4]

[0105] [Table 5]

[0106] As can be seen from the above examples and comparative examples, the separator according to the present invention has significantly improved adhesive strength, a thermal shrinkage rate of 8.0% or less at 150°C (under experimental conditions of 0.5 hours), and a liquid absorption rate maintained at 6.0 g / m2 or more.

[0107] An embodiment of the present invention further provides a battery equipped with a battery separator according to the above-described technical proposal.

[0108] In this specification, when we refer to descriptions such as "one embodiment," "one example," "specific implementation process," or "one example," we mean that the specific features, structures, materials, or properties described using such embodiments or examples are included in at least one embodiment or example of the present invention. In this specification, exemplary expressions for the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or properties described can be appropriately combined in any one or more embodiments or examples.

[0109] Finally, it is important to note 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 using the above embodiments, those skilled in the art may modify the technical concepts described in the above embodiments or make equivalent substitutions to some or all of the technical features therein. These modifications or substitutions will not cause the essence of the technical concept to deviate from the scope of the technical concepts described in the embodiments of the present invention. [Explanation of Symbols]

[0110] 101 Base film 102 First ceramic coating layer 103 Polymer layer 104 Island-like structure

Claims

1. The device comprises a substrate on which a polymer layer is coated on one or both sides, the polymer layer being mainly composed of a mixture of a first polymer, a second polymer, first ceramic particles, and second ceramic particles, wherein the median diameter of the first and second ceramic particles is 0.01 μm to 1 μm, and the specific surface area of ​​the first ceramic particles is 50 m². ２ / g or more, The first polymer is a high-viscosity polymer resin, and the high-viscosity polymer resin comprises at least one of a copolymer of polyvinylidene fluoride and hexafluoropropene, sodium carboxymethylcellulose, and a polymethacrylate polymer. The second polymer is a heat-resistant polymer resin, and the heat-resistant polymer resin comprises one or two of the following: polyetherimide, polyimide, polyvinylidene fluoride-tetrafluoroethylene-propylene terpolymer, and polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene terpolymer. The first ceramic particles and the second ceramic particles are at least one of alumina, boehmite, SiO2, CaCO3, ZrO2, and TiO2. A battery separator characterized by the following features.

2. The battery separator according to claim 1, characterized in that the median diameter of the first ceramic particles is 0.01 μm to 0.3 μm.

3. The battery separator according to claim 1, characterized in that the median diameter of the second ceramic particle is 0.3 μm to 1 μm, and is larger than the median diameter of the first ceramic particle.

4. The battery separator according to claim 1, characterized in that the ratio of the mass fractions of the first ceramic particles and the second ceramic particles is 10% to 50%: 50% to 90%.

5. The battery separator according to claim 4, characterized in that the ratio of the mass fractions of the first ceramic particles and the second ceramic particles is 10% to 35%:65% to 90%.

6. The high viscosity polymer resin is a binder resin, The aforementioned battery separator has a dry press adhesive strength of 20 N / m or more and a wet press adhesive strength of 8 N / m or more. The battery separator according to feature 1.

7. The battery separator according to claim 6, characterized in that the copolymer of polyvinylidene fluoride and hexafluoropropene has a ratio of hexafluoropropene to the mass of the copolymer of 4% to 20%, a molecular weight of the copolymer of polyvinylidene fluoride and hexafluoropropene of 300,000 to 500,000, a melting point of 125°C to 150°C, and a melt viscosity of 15 cps to 35 cps.

8. The battery separator according to claim 1, characterized in that the melting point of the second polymer is 180°C or higher.

9. The battery separator according to claim 1, characterized in that the ratio of the mass fractions of the first polymer and the second polymer is 10-40%:60-90%.

10. The total mass fraction of the first ceramic particles and the second ceramic particles in the polymer layer is characterized by being 30% to 70%, based on the sum of the masses of the first polymer, the second polymer, the first ceramic particles, and the second ceramic particles in the polymer layer. The battery separator according to claim 1.

11. Island-like structures are formed on the surface of the polymer layer, The battery separator according to feature 1.

12. The battery separator according to claim 11, characterized in that the diameter of the island-like structure is 0.8 μm to 2 μm.

13. A method for preparing a battery separator according to any one of claims 1 to 12, The first polymer and the second polymer are taken, the first polymer and the second polymer are mixed and dissolved in a solvent to obtain a premixed slurry A. The first step is to select first ceramic particles and second ceramic particles, add the two types of ceramic particles with different median diameters to the premixed slurry A simultaneously or sequentially, and mix to obtain a polymer layer coating slurry, wherein the median diameter of the first and second ceramic particles is 0.01 μm to 1 μm, and the specific surface area of ​​the first ceramic particles is 50 m² / g or more. The step of applying the polymer layer coating slurry to one or both sides of the substrate to obtain the battery separator is included. A method for preparing a battery separator, characterized by the following:

14. A battery comprising a battery separator, a positive electrode, a negative electrode, and an electrolyte, wherein the battery separator is the battery separator described in any one of claims 1 to 12.

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