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

[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 that restrict the development of lithium-ion batteries. When the battery is in continuous charge and discharge or extreme usage conditions such as high temperature, the positive and negative electrodes may short-circuit due to the heat shrinkage and deformation of the separator, which may cause a series of thermal runaway phenomena and seriously affect the safety of the lithium-ion battery. In addition, in conventional lithium-ion batteries, during continuous charge and discharge cycles, the electrodes are prone to expansion and contraction, which may form gaps between the electrodes and the separator, leading to a possible decrease in the cycle life of the battery. Therefore, it is necessary to enhance the adhesion between the electrodes 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 coated on one or both sides with a polymer layer mainly formed by mixing a first polymer, a second polymer, first ceramic particles, and second ceramic particles. 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 particles is 0.01 μm to 0.3 μm.

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

[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 fraction 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 fraction of the first ceramic particles to the second ceramic particles is 10% to 35%: 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 adhesion of 20 N / m or more and a wet press adhesion of 8 N / m or more.

[0011] In some embodiments, the high-viscosity polymer resin includes a copolymer of polyvinylidene fluoride and hexafluoropropene (hereinafter abbreviated as PVDF-HFP copolymer), sodium carboxymethyl cellulose (CMC), and a polymethacrylate-based polymer (for example, PMMA).

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

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

[0014] In some embodiments, the heat-resistant polymer resin includes one or two of polyetherimide [PEI], polyimide [PI], poly(vinylidene fluoride - tetrafluoroethylene - propylene) [P(PVDF - TFE - P)] terpolymer, and poly(vinylidene fluoride - trifluoroethylene - chlorotrifluoroethylene) [P(VDF - TrFE - CTFE)] terpolymer.

[0015] In some embodiments, the mass fraction ratio of the first polymer to the second polymer is 10% - 40%:60% - 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% - 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] The second aspect of the present invention provides a battery separator. The battery separator includes a substrate with a polymer layer coated on one or both sides. The polymer layer mainly contains ceramic particles, and an island-like structure protruding from the surface of the polymer layer is formed.

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

[0019] The third aspect of the present invention provides a method for preparing a battery separator for preparing the battery separator according to any one of the above items. This preparation method includes the following steps.

[0020] Take a first polymer and a second polymer, mix the first polymer and the second polymer and dissolve them in a solvent to obtain a premixed slurry A.

[0021] Select the first ceramic particles and the second ceramic particles, and add two types of ceramic particles with different median diameters to the premixed slurry A simultaneously or sequentially, and mix them to obtain a polymer layer coating slurry. The median diameters of the first ceramic particles and the second ceramic particles are 0.01 μm to 1 μm, and the specific surface area of the first ceramic particles is 50 m2 / g or more.

[0022] Apply the polymer layer coating slurry to one side or both sides of the substrate to obtain the battery separator.

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

[0024] The battery separator, its preparation method, and the battery according to the present invention apply a polymer layer to one side or both sides of a substrate, and two types of ceramic particles with different median diameters are added to this polymer layer in addition to the first polymer and the second polymer. 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 particles is 50 m2 / g or more. Thereby, the technical solution of the present invention has at least the following technical effects compared with 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, the first polymer and the second polymer in the solvent are not compatible with each other, but the first ceramic particles function as a surfactant and can make the first polymer and the second polymer compatible in the solvent. In addition, the first ceramic particles can improve the adhesion of the polymer slurry to the substrate. The second ceramic particles, as a filler for increasing the surface roughness of the polymer layer in the present invention, have a surface coated with a polymer and increase 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 engage with the first ceramic layer at the bottom to produce an anchoring effect, enhance the adhesion effect between coating layers, and increase the roughness of the outer surface of the separator. Thereby, the engagement 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, and the liquid absorption effect can be enhanced. 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 higher can be suppressed, thereby further improving the thermal stability of the separator.

[0029] 5) The present invention selects two types of ceramic particles with different median diameters, sets the median diameter of the ceramic particles with a small median diameter as 0.01 μm ≤ D50 ≤ 0.3 μm, and sets the median diameter of the ceramic particles with a large median diameter as 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, and can increase 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

Figure 2

Figure 3

Figure 4

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 goes without saying that the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without using inventive capabilities 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 separator is fabricated as follows. First, a high-temperature resistant inorganic ceramic coating layer obtained by applying a water-soluble slurry to one or both sides of a PE, PP, or PE / PP composite substrate and drying it is applied, and then organic adhesive coating layers are applied to both sides of the high-temperature resistant inorganic ceramic coating layer. The applicant has found that in this method, in the process of applying the organic adhesive, some of the inorganic ceramic particles in the ceramic layer fall off after passing through the coagulation bath and undergoing the water washing process, significantly reducing the high-temperature stability of the separator. Also, in the process of applying the organic adhesive, only a single layer of pure PVDF-based polymer resin layer is applied to the outer surface of the separator, and since the interfacial adhesive force between this polymer resin layer and the electrode sheet is generally 20 - 50 gf / 25 mm, it has been difficult to further improve the adhesive force in the prior art.

[0036] Furthermore, the applicant has analyzed the organic adhesive-coated separator and found that this organic adhesive-coated separator is basically 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 on the bottom ceramic layer and does not have an anchoring effect or an interlocking effect. The applicant has found that even when inorganic ceramic particles are added to the polymer adhesive resin coating layer, only a slight increase in adhesive force is observed. The reason is that due to the addition of ceramic particles, the content of the polymer resin decreases relatively, limiting the overall improvement of the adhesive force. Also, the applicant has found that the PVDF-based resin may penetrate into the ceramic layer under the action of the solvent, resulting in a partial loss of adhesiveness.

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

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

[0039] The battery separator according to the present invention includes a substrate on one or both sides of which a polymer layer formed by mixing a first polymer, a second polymer, first ceramic particles, and second ceramic particles is coated. The median diameters of the first ceramic particles and the second ceramic particles are from 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 ceramic particles and the second ceramic particles can be, for example, any value among 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, 1 μm or a range consisting of any two of these values.

[0041] The specific surface area of the first ceramic particles can be, for example, any value among 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 or a range consisting of any two of these values.

[0042] In one embodiment, the median diameter of the first ceramic particles is from 0.01 μm to 0.3 μm. Further, the median diameter of the second ceramic particles is from 0.3 μm to 1 μm and is larger than the median diameter of the first ceramic particles.

[0043] As 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 adhesiveness under dry pressing conditions and maintain excellent adhesiveness even after being immersed in an electrolytic solution and wetted. Further, the high-viscosity polymer resin refers to one having a wet pressing adhesive strength of 8 N / m or more and a dry pressing adhesive strength of 20 N / m or more. The wet pressing adhesive strength is the adhesive strength when pressed after being immersed in the electrolytic solution and then peeled off. The dry pressing adhesive strength is the adhesive strength when directly hot-pressed after the separator and the electrode sheet are laminated and then peeled off. In some examples, the high-viscosity polymer resin can 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. Note that the present invention is not limited thereto, and other high-viscosity polymer resins are also included within the protection scope of the present invention.

[0044] As one embodiment, the second polymer is a heat-resistant polymer resin. Further, 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 has a first ceramic layer coated on one or both sides of the substrate, compared with other organic adhesive-coated layer separators. This first ceramic layer can be a conventional ceramic coating layer such as a nanofiber coating layer or an alumina coating layer of nanosize (order). Also, a polymer layer is coated on the surface of one or both sides of the first ceramic layer. Since two types of ceramic particle fillers with different median diameters are added to the polymer layer, a skeletal support structure is formed, and the adhesiveness is stronger compared to a pure polymer adhesive resin coating layer.

[0046] The pure organic adhesive only has a PVDF resin layer on its surface. The PVDF resin layer has an ordinary adhesion effect on the bottom ceramic layer and does not have an anchoring effect or an interlocking effect. Also, since PVDF can penetrate into the ceramic layer under the action of a solvent, the adhesiveness of PVDF is lost. On the other hand, in the case of the mixed coating of a polymer and ceramics, due to the adsorption effect of the surface groups of the ceramic particles on the polar groups on the surface of the polymer, the ceramic particles are uniformly dispersed in the slurry, and after coating, the ceramic particles can be uniformly distributed on the surface of the coating layer. The heat resistance of the separator can be improved by the characteristics of the ceramics themselves, and the heat can be uniformly distributed. Furthermore, a plurality of protruding island-like structures formed from such ceramic particles can engage with the first ceramic layer at the bottom to exhibit an anchoring effect and enhance the adhesion effect of the coating layer.

[0047] In the present invention, the presence of the 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 the adhesive layer difficult to peel off. The protruding structure on the surface of the polymer layer is like a rivet, which can deeply penetrate into the gaps of the ceramic layer at the bottom and form adhesion strengthening points, thus making the adhesive layer difficult to peel off.

[0048] The battery separator according to the present invention has excellent high-temperature thermal stability, especially the thermal stability under high-temperature conditions of 150 °C or higher is superior to that of the prior art, and the safety of the battery can be further improved. Also, the special high-viscosity heat-resistant polymer resin coating layer has better adhesiveness with the electrode sheet than the conventional PVDF coating layer, can improve the hardness of the battery, and suppress the decrease in cycle life caused by the gap formed between the electrode sheet and the separator during the charge and discharge cycles of the battery.

[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 holding at 150 °C for 0.5 hours), its adhesive force reaches 50 - 80 gf / 25 mm, and the liquid absorption amount is 6.5 g / m2 or more.

[0050] In another embodiment, it further comprises a first ceramic coating layer. The battery separator comprises a substrate with the first ceramic coating layer coated on one or both sides, and the polymer layer is coated on the first ceramic coating layer. Other structures are the same as those in the above embodiments and the description thereof is omitted.

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

[0052] If the ceramic particles in the polymer layer are too large, they are likely to combine with small ceramic particles to form secondary particles with a larger median diameter, making it difficult to control the thickness of the coating layer. As a result, the thickness of the coating layer may deviate from the required range. Consequently, it is difficult for the adhesive layer to become a dense layer, and the polymer resin is likely to penetrate into the micropores formed in the first ceramic layer together with the solvent, increasing the permeability and affecting the lithium ion permeability. In some embodiments, the first ceramic particles with a median diameter of 0.01 μm ≤ D50 ≤ 0.3 μm and the 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. Due to the surface energy and the action of the hydrogen bond of -OH, the heat-resistant resin and PVDF-HFP form 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 due to the solvation effect of the solvent molecules and the hydrogen bond 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 the polymer network structure by the uniform colloidal resin layer through non-solvent-induced phase separation, so they are uniformly embedded in the network structure of the coating layer. Also, because of the large median diameter, the ceramic particles with a large median diameter form a plurality of protruding island-like structures. Furthermore, the ceramic with a large median diameter as an additive to increase the roughness of the coating layer can improve the adhesion and bonding strength of the separator, increase the liquid absorption rate for the electrode liquid (since the -OH on the surface of the ceramic particles forms a hydrogen bond with the electrolyte and the polar groups on the surface of the ceramic particles are easily attracted to the polar groups in the electrolyte molecules, the wettability of the electrolyte and the liquid absorption rate of the electrolyte can be increased), increase the porosity of the coating layer, and suppress the increase in permeability. The ceramics with a small median diameter enhance the compatibility of the slurry.Due to their high surface activity and certain surface energy, nano-sized ceramic particles can attract the oxygen atoms of the -C=O groups in polyimide molecules and the lone pair electrons of the N atoms in the molecules, making it easy to form hydrogen bonds, and also act on the -CF3, which is a polar group of PVDF-HFP. As a result, the two are emulsified throughout the slurry system, enabling them to coexist stably without layer separation and improving their compatibility.

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

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

[0055] The substrate in the present invention may be a base film such as a polyolefin film, a PET film, or a BOPP film, or may be a coated film formed by coating the above base film. The polyolefin film can be PE, PP, a composite separator of PP and PE, etc.

[0056] In some embodiments, the polymer layer is coated on both sides of the base film. In some other embodiments, a first ceramic coating layer is first coated on one side or both sides of the base film, and then the polymer layer is coated. Single-sided coating means coating only one side, and one side becomes adhesive. Double-sided coating has adhesiveness on both sides, so it can realize the adhesion between both sides of the separator and the positive electrode sheet and the negative electrode sheet, suppress the growth of lithium dendrites, and further improve the wettability of the separator with 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 thickness of the polymer layer is too thick, it will affect the energy density, and if it is too thin, the adhesive force 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 can 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, a titanium oxide ceramic coating layer, etc. 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, nanofibers), acrylate adhesives, polyacrylate adhesives, dispersants, wetting agents, thickeners, and defoamers.

[0058] In order to impart high adhesiveness, the present invention employs a mixture of a polymer resin having high tackiness and a heat-resistant polymer resin as the composition of the polymer layer. Also, different from the general PVDF-based adhesive coating layer, in this high-tack heat-resistant polymer resin mixture coating layer, inorganic particles are used as fillers, so a plurality of protruding island-like structures are formed on the outer surface of the separator, increasing the roughness of the outer surface of the separator. Therefore, the meshing between the surface of the separator and the electrode sheet becomes stronger, and thus the adhesive force between the separator and the electrode sheet is further improved.

[0059] In particular, 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 (that is, the total ratio of the two types of ceramic particles with median diameters). Specifically, the total mass fraction of the two types of ceramic particles with median diameters in the polymer layer can be, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%. Note that the mass fraction can also be other values between 30% and 70%.

[0060] In some embodiments, the first polymer in the polymer layer is selected from PVDF-HFP copolymers, and the second polymer is selected from at least one of polyetherimide and polyimide. Polyimide and polyetherimide are mainly characterized by a high melting point, and since their melting point exceeds 200°C, they have high heat resistance. This is a property that cannot be achieved by general resin materials. In addition, since polyimide and polyetherimide have a high dielectric constant, the resistance to the breakdown voltage of the coating layer becomes higher.

[0061] Note that the second polymer is not limited to this, and can be any one or two of polyetherimide, polyimide, polymethyl methacrylate, polyvinylidene fluoride-tetrafluoroethylene-propylene terpolymer, and polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene terpolymer.

[0062] In some embodiments, in the PVDF-HFP copolymer, the proportion of HFP relative to the mass of the copolymer is 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, any value among 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, 500,000 or a range consisting of any two of these values. When the molecular weight exceeds 500,000, the adhesion when attaching to the separator of the substrate deteriorates, so that the slurry is likely to fall off and elute. The proportion of HFP relative to the mass of the copolymer is any value among 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range consisting of any two of these values. When the content of HFP exceeds 20%, the wet press adhesion between the separator and the electrode sheet becomes less than 3 N / m.

[0063] In some embodiments, the polymer in the polymer layer is prepared by mixing a PVDF-HFP copolymer and polyimide, and the mass fraction ratio of PVDF-HFP to polyimide is 30% to 50%: 50% to 70%. The mass fraction ratio of PVDF-HFP to polyimide is 30%: 50% to 70%, 35%: 50% to 70%, 40%: 50% to 70%, 45%: 50% to 70%, 50%: 50% to 70%. In this mixing ratio, the proportion of polyimide should not be too low. If it is too low, the heat resistance and adhesiveness of the polyimide will be impaired. If it is too high, the adhesiveness of the slurry will decrease, and the coating layer passing through the coagulation bath groove will easily fall off.

[0064] The battery separator according to the present invention has its structure shown in FIG. 2. As shown in FIG. 2, the battery separator includes a base film 101 coated with a first ceramic coating layer 102 on both sides, and a polymer layer 103 is coated on the first ceramic layer 102. The polymer layer 103 mainly contains ceramic particles that form island-like structures 104 protruding on its surface.

[0065] In this embodiment, a first ceramic coating layer 102 is coated on both sides of the base film 101, and a polymer layer 103 is coated on the first ceramic coating layer 102. Further, in the present invention, it is also possible to coat the first ceramic coating layer on only one side of the base film and coat the polymer layer on the first ceramic coating layer. In addition, in other embodiments, as shown in FIG. 1, the first ceramic coating layer 102 can be omitted, and the polymer layer 103 can be directly coated on one side or both sides of the base film 101.

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

[0067] The diameter of the protruding island structure 104 is close to the median diameter of the ceramic particles with a larger median diameter. Specifically, the diameter of the island structure 104 is, for example, 0.8 μm to 2 μm. Since the ceramic particles with a larger median diameter are embedded in the network structure of the coating layer, the height of the protruding island structure 104 is about 1 / 3 to 1 / 2 of 0.3 μm to 1 μm. The diameter of the island structure means the average value of the length of the line connecting the edges of the island structure formed in the plane of the separator, and the height of the protruding island structure means the height of the island structure exceeding the surface of the coating layer.

[0068] To obtain the above battery separator, an embodiment of the present invention further provides a method for preparing a battery separator for preparing the battery separator described in any one of the above items.

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

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

[0071] S2: 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.

[0072] S3: Select the first ceramic particles and the second ceramic particles, where the median diameter of the first ceramic particles and the second ceramic particles is 0.01 μm to 1 μm, and the difference in the median diameter between the first ceramic particles and the second ceramic particles is 0.2 μm to 0.99 μm. Add two types of ceramic particles with different median diameters to the premixed slurry A simultaneously or sequentially and mix them to obtain a polymer layer coating slurry.

[0073] S4: Apply the coating slurry of the first ceramic layer to one or both sides of the substrate film, and cure it to obtain a substrate.

[0074] S5: Apply the coating slurry of the polymer layer to the substrate, and cure it to obtain the battery separator.

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

[0076] In another embodiment, as shown in FIG. 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: Select the first ceramic particles and the second ceramic particles, where 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 to 150 m2 / g. Add two types of ceramic particles with different median diameters to the premixed slurry A simultaneously or sequentially, and mix them to obtain a polymer layer coating slurry.

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

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

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

[0082] Hereinafter, the product performance of some embodiments of the present invention will be analyzed by experiments.

[0083] Example 1

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

[0085] The PVDF-HFP copolymer of the first polymer (weight average molecular weight: 300,000, hexafluoropropene (HFP): 4%), the polyetherimide of the second polymer, the first ceramic powder (median diameter D50 = 0.05 μm), and the 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 an N-methyl-2-pyrrolidone (NMP) solvent (stirred sufficiently at 60 °C for 24 h) to obtain a premixed slurry A. After the polymers in the premixed slurry A were completely dissolved, 20 wt% of the first ceramic powder was added to the premixed slurry A and stirred sufficiently at 30 °C and 1800 rpm for 60 minutes to be uniformly mixed and dispersed to obtain a mixed slurry B. 50 wt% of the second ceramic powder was added to the mixed slurry B and stirred sufficiently at 30 °C and 1800 rpm for 60 minutes, and the total solid content of the slurry was controlled to be 10% to obtain the coating slurry used in the present invention.

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

[0087] The coated separator was fabricated by the following steps.

[0088] A ceramic layer was applied to two opposing surfaces of a PE separator to obtain a ceramic substrate (the preparation method will be described later). The prepared coating slurry was applied to two opposing surfaces of the ceramic substrate by a microgravure roll. The coated substrate was immersed in a coagulation bath groove at a temperature of 20°C and a concentration of 20% (mass ratio concentration of the first solvent: the mixture of the first solvent and the second solvent) for phase conversion, and after non-solvent washing and oven drying, a coated separator (i.e., a battery separator) was obtained. The first solvent includes at least one of acetone, dichloromethane, benzene, toluene, xylene, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, cyclohexane, cyclohexanone, toluene cyclohexanone, 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, N-methyl-2-pyrrolidone. The second solvent includes at least one of ethanol, water, glycerin, ethyl acetate, 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 applying 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 put into 57 kg of deionized water and stirred for 30 minutes with a mixer for dispersion. Then, 10 kg of an aqueous solution of CMC (sodium carboxymethyl cellulose) with a concentration of 2% was added and stirred for 30 minutes for dispersion. Next, 1.0 kg of a polyacrylate adhesive (emulsion solid content 35%) was added and stirred for 30 minutes for dispersion. Sanding was carried out for 60 minutes (flow rate: 1000 L / h, speed: 750 rpm, stirring speed: 20 rpm). Finally, 0.15 kg of a wetting agent, 0.15 kg of an antifoaming agent, and 26 kg of deionized water were added and stirred for 30 minutes for dispersion to obtain a ceramic coating slurry with a total solid content of 35%.

[0092] (2) Preparation of the ceramic substrate in the examples of the present invention is as follows.

[0093] The ceramic layer was coated on both sides by gravure roll coating. 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 preheating oven temperature before coating was 60 °C, and the oven drying temperature was 60 °C.

[0094] By changing the experimental parameters, different examples and comparative examples were prepared. The experimental parameters and product parameters of each example and comparative example are shown in Tables 1 to 3 below. Also, the molecular weight of the PVDF-HFP copolymer used in the examples and comparative examples was 300,000 in all cases, and only the ratio of HFP to the copolymer was different. 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 their specific surface area was 50 m2 / g or more.

[0095]

Table 1

[0096]

Table 2

[0097]

Table 3

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

[0099] In addition, the ratio of the first polymer and the ratio of the second polymer in the table mean the respective ratios of the first polymer and the second polymer to the dry weight of the coating layer. The ratio of the first ceramic and the ratio of the second ceramic mean the respective ratios of the first ceramic and the second ceramic to the dry weight of the coating layer. The adhesiveness of the electrode sheet is the experimental result of the adhesive force of the electrode sheet to both opposite surfaces 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 adhesiveness, a heat shrinkage rate at 150 °C of 5.0% or less, and a liquid absorption amount maintained at 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 produced by the following steps.

[0102] The prepared polymer coating slurry was applied to two opposing surfaces of a PE separator by a microgravure roll. The coated substrate was immersed in a coagulation bath groove at a temperature of 20 °C and a concentration of 20% (mass ratio concentration of the first solvent: the first solvent + the second solvent) for phase conversion, and after non-solvent washing and oven drying, a coated separator (i.e., a battery separator) was obtained. The first solvent includes at least one of acetone, dichloromethane, benzene, toluene, xylene, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, cyclohexane, cyclohexanone, toluene cyclohexanone, 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, N-methyl-2-pyrrolidone. The second solvent includes at least one of ethanol, water, glycerin, ethyl acetate, 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 in Tables 4 to 5 are substantially the same as the preparation methods in Tables 1 to 3, but are different in that the steps of the ceramic substrate are omitted, that is, 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 a significantly improved adhesive force, a thermal shrinkage rate of 8.0% or less at 150 °C (under the experimental conditions of 0.5 hours), and the liquid absorption amount is maintained at 6.0 g / m2 or more.

[0107] An embodiment of the present invention further provides a battery including the battery separator according to the above technical solution.

[0108] In the description of this specification, references to descriptions such as "one embodiment", "one example", "specific implementation process", "one example", etc. mean that the specific features, structures, materials, or characteristics described by using the embodiment or example 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. And the specific features, structures, materials, or characteristics to be described can be appropriately combined in any one or more embodiments or examples.

[0109] Finally, it should be noted that the above embodiments are only for explaining the technical solution of the present invention and do not limit it. Although the present invention has been described in detail using the above embodiments, for those skilled in the art, it is also possible to change the technical solutions described in the above embodiments or perform equivalent substitutions for some or all of the technical features therein. These changes or substitutions do not deviate the essence of the corresponding technical solution from the scope of the technical solutions of the embodiments of the present invention.

Description of Reference Numerals

[0110] 101 Substrate film 102 First ceramic coating layer 103 Polymer layer 104 Island structure

Claims

1. A substrate having a polymer layer applied on one or both sides, the polymer layer being mainly formed by mixing 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. A battery separator characterized by the above.

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

3. The battery separator according to claim 1, wherein the median diameter of the second ceramic particles is 0.3 μm to 1 μm and is larger than the median diameter of the first ceramic particles.

4. The battery separator according to claim 1, wherein the ratio of the mass fraction of the first ceramic particles to the second ceramic particles is 10% to 50%: 50% to 90%.

5. The battery separator according to claim 4, wherein the ratio of the mass fraction of the first ceramic particles to the second ceramic particles is 10% to 35%: 65% to 90%.

6. The first polymer is a high-viscosity polymer resin, and the high-viscosity polymer resin is a binder resin. The battery separator has a dry press adhesion of 20 N / m or more and a wet press adhesion of 8 N / m or more. The battery separator according to any one of claims 1 to 5, characterized by the above.

7. The battery separator according to claim 6, wherein the high-viscosity polymer resin contains a copolymer of polyvinylidene fluoride and hexafluoropropene, sodium carboxymethyl cellulose, and a polymethacrylate-based polymer.

8. In the copolymer of polyvinylidene fluoride and hexafluoropropene, the proportion of hexafluoropropene to the mass of the copolymer is 4% to 20%, the molecular weight of the copolymer of polyvinylidene fluoride and hexafluoropropene is 300,000 to 500,000, the melting point is 125°C to 150°C, and the melt viscosity is 15 cps to 35 cps. The battery separator according to claim 7, characterized by the above.

9. The battery separator according to claim 1, wherein the second polymer is a heat-resistant polymer resin having a melting point of 180°C or higher.

10. The heat-resistant polymer resin contains one or two of polyetherimide, polyimide, poly(vinylidene fluoride-tetrafluoroethylene-propylene) terpolymer, and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer. The battery separator according to claim 9 is characterized by this.

11. The ratio of the mass fraction of the first polymer to the second polymer is 10 to 40%: 60 to 90%. The battery separator according to claim 1 is characterized by this.

12. 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. The battery separator according to claim 1.

13. A substrate having a polymer layer coated on one or both sides, The polymer layer contains ceramic particles, and an island-like structure protruding from the surface of the polymer layer is formed. The battery separator is characterized by this.

14. The diameter of the island-like structure is 0.8 μm to 2 μm. The battery separator according to claim 13 is characterized by this.

15. A method for preparing a battery separator for preparing the battery separator according to any one of claims 1 to 14, Taking a first polymer and a second polymer, mixing the first polymer and the second polymer and dissolving them in a solvent to obtain a premixed slurry A, Selecting first ceramic particles and second ceramic particles, adding two types of ceramic particles with different median diameters to the premixed slurry A simultaneously or sequentially, mixing to obtain a polymer layer coating slurry, the median diameters of the first ceramic particles and the second ceramic particles being 0.01 μm to 1 μm, and the specific surface area of the first ceramic particles being 50 m2 / g or more, Coating the polymer layer coating slurry on one or both sides of a substrate to obtain the battery separator. The method for preparing a battery separator is characterized by including this. The method for preparing a battery separator is characterized by this.

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

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