Battery diaphragm, preparation method thereof and secondary battery

Abstract

The invention discloses a battery diaphragm and a preparation method thereof, and a secondary battery, and belongs to the field of secondary batteries, the battery diaphragm comprises a base film and a coating laminated on at least one side surface of the base film, and the coating comprises organic colloidal particles, inorganic particles, a first dispersant, a second dispersant, a first binder, a second binder, a first thickener and a second thickener. The organic colloidal particles are arranged on the surface, away from the base film, of the coating in a protruding mode, and the inorganic particles, the first dispersing agent, the second dispersing agent, the first binding agent, the second binding agent, the first thickening agent and the second thickening agent are embedded in the coating. The first dispersing agent is selected from at least one of polyoxyethylene ether derivatives, polyol ester and siloxane, and the second dispersing agent is selected from at least one of sodium polycarboxylate, ammonium polyacrylate and sulfonate. The battery diaphragm has good adhesion, liquid absorption and retention properties, heat resistance and mechanical strength.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery separator and a preparation method thereof, and a secondary battery. Background Art

[0002] Battery separators are used in secondary batteries, mainly to isolate the positive and negative electrodes and allow ions to pass freely.

[0003] Currently, the surface of the base film of battery separators is coated with a mixture of boehmite particles and polyvinylidene fluoride. The boehmite particles impart heat resistance to the coating, while the polyvinylidene fluoride imparts adhesion. However, the adhesion of the coating on this type of battery separator still needs to be improved, and its electrolyte absorption and retention is poor. Summary of the Invention

[0004] In view of this, the present invention provides a battery separator and a method for preparing the same, as well as a secondary battery, which can solve the technical problem in related technologies that battery separators are difficult to achieve both high adhesion and liquid absorption and retention. Specifically, it includes the following technical solutions:

[0005] In one aspect, a battery separator is provided, comprising: a base film and a coating layer laminated on at least one surface of the base film, the coating layer comprising: organic colloid particles, inorganic particles, a first dispersant, a second dispersant, a first binder, a second binder, a first thickener, and a second thickener;

[0006] The organic colloidal particles are protruded on the surface of the coating layer facing away from the base film, and the inorganic particles, the first dispersant, the second dispersant, the first binder, the second binder, the first thickener and the second thickener are all embedded in the coating layer.

[0007] The first dispersant is selected from at least one of polyoxyethylene ether derivatives, polyol esters, and silicones, and the second dispersant is selected from at least one of polycarboxylic acid sodium salts, polyacrylate ammonium salts, and sulfonates.

[0008] In some possible implementations, the protrusion height of the organic colloidal particles relative to the coating layer is 2 μm-6 μm;

[0009] The coverage area of ​​the organic colloid particles on the coating layer accounts for 70% to 80% of the area of ​​the coating layer.

[0010] In some possible implementations, the particle size distribution of the organic colloid particles is as follows: D10 is 1.0 μm-2.0 μm, D50 is 3.0 μm-8.0 μm, and D90 is 9.0 μm-10.0 μm;

[0011] The particle size D50 of the inorganic particles is less than 1 μm.

[0012] In some possible implementations, the organic particles include at least one of (meth)acrylate polymers, styrene-acrylonitrile copolymers, and butadiene-styrene copolymers.

[0013] In some possible implementations, the inorganic particles are at least one of boehmite particles, magnesium hydroxide particles, barium carbonate particles, magnesium carbonate particles, and zirconium oxide particles.

[0014] In some possible implementations, the first thickener and the second thickener are each independently selected from at least one of hydroxymethyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and polypropylene alcohol;

[0015] The first binder and the second binder are each independently selected from at least one of polyacrylic acid, polyacrylate, and polyacrylamide.

[0016] In some possible implementations, the mass ratio of the organic colloid particles to the inorganic particles is 1-30:1-30.

[0017] In another aspect, a method for preparing a battery separator is provided. The battery separator is as described above, and the method for preparing the battery separator comprises:

[0018] Obtaining an organic colloid particle slurry, wherein the organic colloid particle slurry comprises: organic colloid particles, a first dispersant, a first thickener, a first binder, and water;

[0019] Obtaining an inorganic particle slurry, wherein the inorganic particle slurry comprises: inorganic particles, a second dispersant, a second thickener, a second binder, and water;

[0020] uniformly mixing the organic colloidal particle slurry and the inorganic particle slurry to obtain a mixed slurry;

[0021] The mixed slurry is coated on the surface of the base film, and dried to form a coating to obtain the battery separator.

[0022] In some possible implementations, in the organic colloid slurry, the mass ratio of water, organic colloid, first dispersant, first thickener, and first binder is 25-30:5-10:0.1-0.5:0.1-0.5:0.5-5;

[0023] In the inorganic particle slurry, the mass ratio of water, inorganic particles, second dispersant, second thickener and second binder is 25-35:15-25:0.1-0.5:0.1-0.5:0.5-5.

[0024] In some possible implementations, the mixed slurry has a solid content of 15%-20% and a viscosity of 100 mPa.s-120 mPa.s.

[0025] In another aspect, a secondary battery is provided, comprising: a housing, an electrolyte contained within the housing, and a thermal composite battery cell, wherein the thermal composite battery cell comprises a plurality of positive electrode sheets, a plurality of negative electrode sheets, and the battery separator as described above;

[0026] The negative electrode sheets and the positive electrode sheets are alternately stacked and arranged, and the adjacent negative electrode sheets and the positive electrode sheets are separated by the battery separator, and the battery separator is bonded to the corresponding electrode sheets through the coating.

[0027] The beneficial effects of the technical solution provided by the embodiment of the present invention include at least:

[0028] The battery separator provided by the embodiment of the present invention uses a first dispersant and a second dispersant so that the organic colloid particles float relative to the inorganic particles and are arranged in a raised manner on the coating surface. The raised arrangement of the organic colloid particles is, on the one hand, beneficial for increasing the adhesive contact points on the coating surface, and the molecular chains of the raised organic colloid particles are more easily entangled with the molecular chains on the surface of the electrode, thereby enhancing the adhesion between the battery separator and the electrode. On the other hand, it is also beneficial for increasing the gap between the separator and the electrode, which is beneficial for the infiltration, diffusion and retention of the electrolyte, thereby improving the liquid absorption and liquid retention of the separator. The mechanical strength and heat resistance of the coating are improved by using inorganic particles. As a result, the battery separator provided by the embodiment of the present invention has good adhesion, liquid absorption and liquid retention, heat resistance and mechanical strength. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0030] On the one hand, an embodiment of the present invention provides a battery separator, which includes: a base film and a coating layer stacked on at least one side of the base film, the coating layer including: organic colloids, inorganic particles, a first dispersant, a second dispersant, a first binder, a second binder, a first thickener and a second thickener.

[0031] The organic colloidal particles are protrudingly arranged on the surface of the coating layer facing away from the base film, and the inorganic particles, the first dispersant, the second dispersant, the first binder, the second binder, the first thickener, and the second thickener are all embedded within the coating layer. The first dispersant is selected from at least one of a polyoxyethylene ether derivative, a polyol ester, and a siloxane, and the second dispersant is selected from at least one of a sodium salt of a polycarboxylate, an ammonium salt of polyacrylate, and a sulfonate.

[0032] As mentioned above, the first dispersant is selected from at least one of a polyoxyethylene ether derivative, a polyol ester, and a silicone, and examples are given below to illustrate each of them.

[0033] Derivatives of polyoxyethylene ether can be fatty alcohol polyoxyethylene ether (such as lauryl alcohol polyoxyethylene ether, etc.), alkylphenol polyoxyethylene ether (such as nonylphenol polyoxyethylene ether, etc.), fatty acid polyoxyethylene ester (such as stearic acid polyoxyethylene ester, etc.), polyoxyethylene ether sulfate (such as sodium lauryl polyoxyethylene ether sulfate, etc.), polyoxyethylene ether phosphate, etc.

[0034] Examples of the polyol ester include ethylene glycol esters (eg, ethylene glycol stearate, ethylene glycol laurate, etc.), propylene glycol esters (eg, propylene glycol stearate, propylene glycol oleate, etc.), and pentaerythritol esters (pentaerythritol stearate, pentaerythritol oleate, etc.).

[0035] Examples of silicone include polydimethylsiloxane and its derivatives (eg, polydimethylsiloxane, amino-modified polydimethylsiloxane, carboxyl-modified polydimethylsiloxane, etc.), and silicone-polyether copolymers (polyether-modified silicone, silicone-polyether block copolymers, etc.).

[0036] The second dispersant mentioned above is selected from at least one of polycarboxylate sodium salt, polyacrylate ammonium salt, and sulfonate, and examples are given below to illustrate each of them.

[0037] The sodium polycarboxylate salt may be sodium salt for polycarboxylate high-performance water reducer, sodium polycarboxylate dispersant SN-5040, etc. The ammonium polyacrylate salt may be polyammonium polyacrylate dispersant PAAS-NH4, low molecular weight ammonium polyacrylate, etc. The sulfonate salt may be sodium lignin sulfonate, sodium alkyl naphthalene sulfonate, sodium polynaphthalene sulfonate formaldehyde condensate, etc.

[0038] During the coating preparation process, the first dispersant can be present in the organic colloid slurry, and the second dispersant can be present in the inorganic particle slurry. The first dispersant and the second dispersant cause different interfacial tensions between the organic colloid and the inorganic particles and water, thereby causing different affinities between the organic colloid and the inorganic particles and water. This results in the organic colloid floating upward when water evaporates after coating, ensuring that the organic colloid protrudes to the surface of the coating while the inorganic particles remain relatively stable within the coating. Thus, the coating formed on the surface of the base film includes a layered body, organic colloid protruding from the surface of the layered body facing away from the base film, and inorganic particles embedded within the layered body.

[0039] It can be seen that the battery separator provided by the embodiment of the present invention, through the use of the first dispersant and the second dispersant, makes the organic colloid particles float relative to the inorganic particles and are arranged in a raised manner on the coating surface. The raised arrangement of the organic colloid particles, on the one hand, is conducive to increasing the adhesive contact points on the coating surface, and the molecular chains of the raised organic colloid particles are more likely to entangle with the molecular chains on the surface of the electrode, thereby enhancing the adhesion between the battery separator and the electrode. On the other hand, it is also conducive to increasing the gap between the separator and the electrode, which is conducive to the infiltration, diffusion and retention of the electrolyte, thereby improving the liquid absorption and liquid retention of the separator. The mechanical strength and heat resistance of the coating are improved by using inorganic particles. As a result, the battery separator provided by the embodiment of the present invention has good adhesion, liquid absorption and liquid retention, heat resistance and mechanical strength.

[0040] The protruding height of the organic colloid particles relative to the coating of the adhesive layer has an impact on the adhesion performance, air permeability, ion transmission efficiency and mechanical properties of the battery separator. In order to ensure that the above-mentioned properties of the battery separator are well balanced, the protruding height of the organic colloid particles relative to the coating of the adhesive layer can be made 2μm-6μm, which includes but is not limited to: 2μm, 3μm, 4μm, 5μm, 6μm, etc.

[0041] Furthermore, the coverage area of ​​the organic colloid particles on the coating layer accounts for 70%-80% of the area of ​​the coating layer, including but not limited to 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, etc. The ratio of the coverage area of ​​the organic colloid particles on the coating layer to the area of ​​the coating layer can be considered as the coverage rate of the organic colloid particles. By setting the coverage rate as described above, the adhesion, liquid retention, and air permeability of the battery separator can be further optimized.

[0042] The base film involved in the embodiment of the present invention can be a common base film type in battery separators, for example, a polypropylene base film, a polyethylene base film, etc., and a suitable base film type can be selected according to actual needs.

[0043] It should be noted that the base film can be a separate polypropylene base film or polyethylene base film, etc. It is not excluded that the surface of the polypropylene base film or the polyethylene base film can be further provided with a functional coating such as a nanofiber layer, a heat-sensitive layer, etc., and the adhesive layer is further stacked on the surface of the functional coating, which can be selected according to actual needs.

[0044] In some examples, the particle size distribution of the organic colloid particles is as follows: D10 is 1.0 μm-2.0 μm, D50 is 3.0 μm-8.0 μm, and D90 is 9.0 μm-10.0 μm. The values ​​of the particle size D10 of the organic colloid particles include, but are not limited to, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, etc. The values ​​of the particle size D50 of the organic colloid particles include, but are not limited to, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc. The values ​​of the particle size D90 of the organic colloid particles include but are not limited to the following: 9.0μm, 9.1μm, 9.2μm, 9.3μm, 9.4μm, 9.5μm, 9.6μm, 9.7μm, 9.8μm, 9.9μm, 10μm, etc.

[0045] By limiting the particle size of the organic colloid particles as above, on the one hand, it is ensured that the organic colloid particles are in the form of large particles to ensure that the organic colloid particles can stably protrude from the layered surface of the coating. On the other hand, the D10, D50, and D90 of the organic colloid particles are distributed in this way, which is also conducive to improving the adhesion of the organic colloid particles and their wettability with the electrode.

[0046] In some examples, the mass ratio of the organic colloid particles to the inorganic particles is 1-30:1-30, further 1:1-10, and even further 1:1-5, for example, 1:1, 1:2, 1:3, 1:4, 1:5, etc. Through the above scheme, it is possible to ensure that the inorganic particles are evenly distributed in the gaps between the different organic colloid particles, thereby ensuring that the adhesion, heat resistance, and mechanical strength of the battery separator are simultaneously improved.

[0047] On the other hand, an embodiment of the present invention provides a method for preparing a battery separator, the method comprising the following steps:

[0048] Step S1: obtaining organic colloid particle slurry, the organic colloid particle slurry comprising: organic colloid particles, a first dispersant, a first thickener, a first binder and water.

[0049] Step S2: Obtaining inorganic particle slurry, the inorganic particle slurry includes: inorganic particles, a second dispersant, a second thickener, a second binder and water.

[0050] Step S3: uniformly mix the organic colloidal particle slurry and the inorganic particle slurry to obtain a mixed slurry.

[0051] Step S4: coating the mixed slurry on the surface of the base film, forming a coating after drying to obtain a battery separator.

[0052] The first dispersant in the organic colloidal particle slurry and the second dispersant in the inorganic particle slurry may refer to the relevant technical solutions involved in the above-mentioned battery separator, and will not be described in detail here.

[0053] The first and second dispersants described above create different interfacial tensions between the organic colloid particles and the inorganic particles, resulting in different affinities between the organic colloid particles and water. This results in the organic colloid particles floating upward when the water evaporates after coating, ensuring that the organic colloid particles protrude to the coating surface while the inorganic particles remain relatively stable within the coating. Consequently, the coating formed on the base film surface comprises a layered body, organic colloid particles protruding from the surface of the layered body facing away from the base film, and inorganic particles embedded within the layered body.

[0054] The preparation method of the battery separator provided by the embodiment of the present invention introduces organic colloid particles into the coating on the surface of the base film through an organic colloid slurry, thereby enhancing the adhesion of the coating. Inorganic particles are introduced into the coating through an inorganic particle slurry to improve the mechanical strength and heat resistance of the coating. In particular, the dispersants in the organic colloid slurry and the inorganic particle slurry are different, so that the affinity of the organic colloid particles and the inorganic particles with water are distinguished. After the mixed slurry is applied, as the water evaporates, the organic colloid particles have a floating effect relative to the inorganic particles, and are more likely to protrude to the surface of the coating, while the inorganic particles are embedded in the coating. In this way, the protruding arrangement of the organic colloid particles, on the one hand, is conducive to increasing the sticky contact points on the surface of the coating, and the molecular chains of the protruding organic colloid particles are more likely to entangle with the molecular chains on the surface of the electrode, thereby enhancing the adhesion between the battery separator and the electrode. On the other hand, it is also conducive to increasing the gap between the separator and the electrode, which is conducive to the infiltration, diffusion and retention of the electrolyte, thereby improving the liquid absorption and liquid retention of the separator. It can be seen that the battery separator prepared by the preparation method of the battery separator provided by the embodiment of the present invention has good adhesion, liquid absorption and retention, heat resistance and mechanical strength.

[0055] The following is an illustrative description of each implementation step and its effect.

[0056] For step S1, obtaining the organic colloid particle slurry can include: adding organic colloid particles, a first dispersant, and a first thickener into water, stirring evenly, and then performing sand grinding to make the components therein evenly dispersed, and then adding a first binder thereto and stirring evenly to prepare the organic colloid particle slurry.

[0057] As mentioned above, the particle size distribution of the organic colloid particles is as follows: D10 is 1.0μm-2.0μm, D50 is 3.0μm-8.0μm, and D90 is 9.0μm-10.0μm. By limiting the particle size of the organic colloid particles as described above, on the one hand, the organic colloid particles are ensured to be in a large particle form, so that the organic colloid particles can stably protrude from the surface of the layered body of the coating. On the other hand, the D10, D50, and D90 of the organic colloid particles, according to this distribution, also help improve the adhesion of the organic colloid particles and their wettability with the electrode.

[0058] In some examples, in order to obtain an organic colloid particle slurry with an appropriate solid content, facilitate uniform mixing of the organic colloid particle slurry and the inorganic particle slurry, and ensure better synergy between the components in the organic colloid particles, the mass ratio of water, organic colloid particles, first dispersant, first thickener, and first binder in the organic colloid particle slurry can be 25-30: 5-10: 0.1-0.5: 0.1-0.5: 0.5-5. For example, the mass ratio of organic colloid particles in the organic colloid particle slurry includes, but is not limited to, 5, 6, 7, 8, 9, 10, etc., the mass ratio of the first dispersant in the organic colloid particle slurry includes, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc., the mass ratio of the first thickener in the organic colloid particle slurry includes, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc., and the mass ratio of the first binder in the organic colloid particle slurry includes, but is not limited to, 1, 2, 3, 4, 5, etc.

[0059] Regarding the battery separator and its preparation method involved above, some applicable organic colloids include at least one of (meth)acrylate polymers, styrene-acrylonitrile copolymers, and butadiene-styrene copolymers. They can all exhibit good adhesion at high temperatures (that is, the organic colloids are in a bonding state when the temperature is higher than their glass transition temperature). In addition, the colloids of acrylate polymers also exhibit good chemical stability, which is beneficial to improving the service life of the battery separator, and the colloids of styrene-acrylonitrile copolymers also exhibit good insulation, processability, and lyophilicity, which is beneficial to improving the ion conduction efficiency and safety of the separator. The colloids of butadiene-styrene copolymers also exhibit good strength and toughness as well as good electrical insulation. The type of organic colloid can be selected according to actual needs.

[0060] For further example, the organic colloid particles may include at least one of the following monomers: acrylonitrile, methacrylonitrile; and styrene, α-methylstyrene, butoxystyrene, vinyl naphthalene aromatic vinyl monomers; and phenylmaleimide and its derivatives; and 1,4-butadiene, isoprene, vinyl chloride, vinylidene chloride; and vinylamine monomers such as acrylamide and methacrylamide; and monomers such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, heptyl acrylate, isooctyl acrylate, 2-ethylethyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and its alkali metal salts; and monomers such as methyl methacrylate, ethyl methacrylate, methyl acrylate Monomers such as propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, heptyl methacrylate, isooctyl methacrylate, 2-ethylethyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetracosyl methacrylate, stearyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, propyl methacrylate, ethylene glycol dimethacrylate and alkali metal salts thereof; monomers such as vinyl sulfonic acid and alkali metal salts thereof; monomers such as methylvinyl sulfonic acid and alkali metal salts thereof; monomers such as styrene sulfonic acid and alkali metal salts thereof; monomers such as vinyl acetate and alkali metal salts thereof, etc., all of the above monomers can impart good adhesion to the organic colloid particles.

[0061] In the battery separator and its preparation method described above, the first thickener can be selected from at least one of hydroxymethyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and polypropylene alcohol. These first thickeners form a cross-linked network within the organic colloid particles after curing, maintaining the structure and shape of the organic colloid particles. Furthermore, they contribute to the separator's liquid retention and air permeability.

[0062] With respect to the battery separator and its preparation method involved above, the first binder can be selected from at least one of polyacrylate, polyacrylic acid, and polyacrylamide. For example, the polyacrylate can be polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, etc., so that the organic colloid particles and inorganic particles can be bonded at room temperature, and it is also beneficial for the coating to be stably bonded to the base film.

[0063] For step S2, obtaining the inorganic particle slurry can include: adding inorganic particles, a second dispersant, and a second thickener to water, stirring evenly, and then performing sand grinding to uniformly disperse the components therein, and then adding a second binder thereto and stirring evenly to prepare the inorganic particle slurry.

[0064] Regarding the battery separator and its preparation method mentioned above, in some examples, the particle size D50 of the inorganic particles is less than 1 μm. By limiting the particle size of the inorganic particles as described above, the inorganic particles are in a small particle size form, so that they are evenly dispersed in the coating and allow the protruding arrangement of the organic colloid particles.

[0065] In some examples, in order to obtain an inorganic particle slurry with an appropriate solid content, facilitate uniform mixing of the inorganic particle slurry and the organic colloidal particle slurry, and ensure better synergy between the components in the inorganic particle slurry, the mass ratio of water, inorganic particles, second dispersant, second thickener, and second binder in the inorganic particle slurry can be 25-35:15-25:0.1-0.5:0.1-0.5:0.5-5. For example, the mass ratio of inorganic particles in the slurry includes but is not limited to 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc., the mass ratio of the second dispersant in the slurry includes but is not limited to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc., the mass ratio of the second thickener in the slurry includes but is not limited to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, etc., and the mass ratio of the second binder in the slurry includes but is not limited to 1, 2, 3, 4, 5, etc.

[0066] For the battery separator and its preparation method mentioned above, some suitable inorganic particles are at least one of boehmite particles, magnesium hydroxide particles, barium carbonate particles, magnesium carbonate particles, and zirconium oxide particles. These inorganic particles not only help improve the thermal stability and mechanical strength of the coating, but also help improve the air permeability of the adhesive layer, thereby improving ion conductivity and electrolyte adsorption performance. For example, the inorganic particles can be boehmite particles.

[0067] In the battery separator and its preparation method described above, the second thickener can be selected from at least one of hydroxymethyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and polypropylene alcohol. The first thickener forms a cross-linked network within the organic colloid particles after curing, maintaining the structure and shape of the organic colloid particles. This also contributes to the separator's liquid retention and air permeability.

[0068] With respect to the battery separator and its preparation method mentioned above, the second binder can be selected from at least one of polyacrylic acid, polyacrylate, and polyacrylamide, so that the organic colloid particles and the inorganic particles can be bonded at room temperature, and it is also beneficial for the coating to be stably bonded to the base film.

[0069] In some examples, the first thickener and the second thickener may be the same, and the first binder and the second binder may be the same, thereby enhancing the compatibility between the organic colloidal particle slurry and the inorganic particle slurry.

[0070] For step S3, the organic colloid slurry and the inorganic particle slurry are mixed evenly to obtain a mixed slurry. The amount of each slurry mentioned above can be adaptively selected according to the amount of organic colloid and inorganic particles. For example, in some examples, the mass ratio of the organic colloid slurry and the inorganic particle slurry can be 1-10:1, which includes but is not limited to 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0071] In some examples, the solid content of the mixed slurry is 15%-20%, which includes but is not limited to 15%, 16%, 17%, 18%, 19%, 20%, etc., and the viscosity of the mixed slurry is 100mpa.s-120mpa.s, which includes but is not limited to 100mpa.s, 102mpa.s, 105mpa.s, 107mpa.s, 109mpa.s, 110mpa.s, 111mpa.s, 112mpa.s, 113mpa.s, 114mpa.s, 115mpa.s, 116mpa.s, 117mpa.s, 118mpa.s, 119mpa.s, 120mpa.s, etc.

[0072] The solid content of the mixed slurry within the above range ensures the thickness and strength of the resulting coating while also facilitating the volatilization of water and the solidification of other components during the drying process. The viscosity of the mixed slurry within the above range provides the mixed slurry with suitable fluidity and thixotropy, enhancing its coating performance. It also helps maintain uniform dispersion of the organic colloid particles and inorganic particles in the slurry.

[0073] In step S4, the mixed slurry is coated on the surface of the base film, and a coating is formed after drying to obtain a battery separator.

[0074] Among them, the coating process can be a micro-gravure roller coating process, and its coating speed can be 30m / min-60m / min, for example, this includes but is not limited to 30m / min, 35m / min, 40m / min, 45m / min, 50m / min, 55m / min, 60m / min, etc.

[0075] In some examples, the coating is formed by one coating, and the thickness of the mixed slurry in a single coating may be greater than or equal to 2 μm, and further may be less than or equal to 4 μm, to ensure that the formed coating can completely cover the base film.

[0076] In some examples, the drying process may be a baking process performed at a temperature of 60° C. to 80° C. to effectively dry the coating. For example, the drying temperature includes but is not limited to 60° C., 65° C., 70° C., 75° C., 80° C., etc.

[0077] In another aspect, embodiments of the present invention provide a secondary battery comprising: a housing, an electrolyte contained within the housing, and a thermal composite cell, the thermal composite cell comprising a plurality of positive electrode sheets, a plurality of negative electrode sheets, and a battery separator as described above. The negative electrode sheets and the positive electrode sheets are alternately stacked, and adjacent negative and positive electrode sheets are separated by a battery separator, which is bonded to the corresponding electrode sheets via a coating.

[0078] The secondary battery provided by the embodiment of the present invention has all the advantages of the battery separator mentioned above, which will not be described in detail here. For example, the secondary battery can be a lithium ion battery, a sodium ion battery, etc.

[0079] The secondary battery shell involved in the embodiment of the present invention is applied to electrical equipment. For example, the electrical equipment can be portable electronic devices (mobile phones, laptops, smart wearable devices, etc.), new energy transportation equipment (new energy vehicles, etc.), energy storage systems, etc.

[0080] Below will be described in more detail exemplary embodiments of the present invention. Although the following describes exemplary embodiments of the present invention, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. In the examples, if specific techniques or conditions are not indicated, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents or instruments used that do not indicate the manufacturer are conventional products that can be obtained commercially.

[0081] Example 1

[0082] This embodiment prepares a battery separator, which is prepared by the following method:

[0083] Step 1. Preparation of organic colloidal particle slurry: 5 kg of polymethyl methacrylate colloidal particles, 0.2 kg of dispersant (lauryl polyoxyethylene ether), and 0.2 kg of thickener (polypropylene alcohol) were added to 25 kg of deionized water and stirred for 3.0 hours. The mixture was then sand-milled (0.4 hours, 1000 rpm) to achieve uniform dispersion. 0.5 kg of binder (polymethyl acrylate) was then added and stirred to obtain an organic colloidal particle slurry. The particle size distribution of the polymethyl methacrylate colloidal particles was as follows: D10: 2.0 μm, D50: 6.0 μm, and D90: 8.0 μm.

[0084] Step 2: Prepare boehmite slurry: add 0.20 kg of dispersant (sodium lignin sulfonate), 15 kg of boehmite particles (D50 less than 1 μm), and 0.2 kg of thickener (polypropylene alcohol) to 25 kg of deionized water, stir evenly, and then sand grind (0.4 h, 1000 rpm) to disperse it evenly, then add 0.5 kg of binder (polymethyl acrylate) and stir evenly to prepare boehmite slurry.

[0085] Step 3: Prepare a mixed coating slurry: Take 25 kg of organic colloidal particle slurry and 5 kg of boehmite slurry, stir for 0.5 h until the mixture is uniform, and obtain a mixed coating slurry.

[0086] Step 4: Prepare a battery separator. The preparation steps are as follows: Use a micro-gravure roller coating process to coat the mixed slurry on the surface of the base film at a coating speed of 65 m / min, and then dry it in an oven at 70°C for 5 minutes to form a coating on the surface of the base film to prepare the battery separator.

[0087] Among them, the battery separator includes a PE base film with a thickness of 12um and a coating with a thickness of 2μm coated on one side of the base film. The coating includes polymethyl methacrylate particles, the above-mentioned dispersants, thickeners and binders. The polymethyl methacrylate particles are raised on the surface of the coating, and boehmite particles, dispersants, thickeners and binders are embedded in the coating.

[0088] Example 2

[0089] This embodiment prepares a battery separator, which is prepared by the following method:

[0090] Step 1: Prepare an organic colloidal particle slurry: Add 5 kg of styrene-acrylonitrile copolymer colloidal particles, 0.2 kg of a dispersant (lauryl polyoxyethylene ether), and 0.2 kg of a thickener (polypropylene alcohol) to 25 kg of deionized water, mix and stir for 3.0 hours, then sand grind (0.4 hours, 1000 rpm) to uniformly disperse the particles. Then, add 0.5 kg of a binder (polymethyl acrylate) and stir evenly to prepare an organic colloidal particle slurry. The particle size distribution of the styrene-acrylonitrile copolymer colloidal particles is as follows: D10 is 1.0 μm, D50 is 5.0 μm, and D90 is 7.0 μm.

[0091] Step 2, prepare boehmite slurry: add 0.20kg dispersant (sodium lignin sulfonate), 15kg boehmite particles (D50 less than 1μm) and 0.2kg thickener (polypropylene alcohol) to 25kg deionized water, stir evenly and then sand grind (0.4h, 1000rpm) to make it evenly dispersed, then add 0.5kg binder (polymethyl acrylate) and stir evenly to prepare boehmite slurry.

[0092] Step 3: Prepare a mixed coating slurry: Take 25 kg of organic colloidal particle slurry and 5 kg of boehmite slurry, stir for 0.5 h until the mixture is uniform, and obtain a mixed coating slurry.

[0093] Step 4: Prepare a battery separator. The preparation steps are as follows: Use a micro-gravure roller coating process to coat the mixed slurry on the surface of the base film at a coating speed of 65 m / min, and then dry it in an oven at 70°C to form a coating on the surface of the base film to prepare the battery separator.

[0094] Among them, the battery separator includes a PE base film with a thickness of 12um and a coating with a thickness of 2μm coated on one side of the base film. The coating includes styrene-acrylonitrile copolymer particles, the above-mentioned dispersants, thickeners and binders. The styrene-acrylonitrile copolymer particles are raised on the surface of the coating, and the boehmite particles, dispersants, thickeners and binders are embedded in the coating.

[0095] Example 3

[0096] This embodiment prepares a battery separator, which is prepared by the following method:

[0097] Step 1: Prepare an organic colloidal particle slurry: Add 5 kg of butadiene-styrene copolymer colloidal particles, 0.2 kg of a dispersant (pentaerythritol stearate), and 0.2 kg of a thickener (polypropylene alcohol) to 25 kg of deionized water, mix and stir for 3.0 hours, then sand grind (0.4 hours, 1000 rpm) to uniformly disperse the particles. Then, add 0.5 kg of a binder (polymethyl acrylate) and stir evenly to prepare an organic colloidal particle slurry. The particle size distribution of the styrene-acrylonitrile copolymer colloidal particles is as follows: D10 is 1.5 μm, D50 is 7.0 μm, and D90 is 10.0 μm.

[0098] Step 2: Prepare boehmite slurry: Add 0.20 kg of dispersant (sodium polycarboxylate dispersant SN-5040), 15 kg of boehmite particles (D50 less than 1 μm) and 0.2 kg of thickener (polypropylene alcohol) to 25 kg of deionized water, stir evenly and then sand grind (0.4 h, 1000 rpm) to disperse evenly, then add 0.5 kg of binder (polymethyl acrylate) and stir evenly to prepare boehmite slurry.

[0099] Step 3: Prepare a mixed coating slurry: Take 25 kg of organic colloidal particle slurry and 5 kg of boehmite slurry, stir for 0.5 h until the mixture is uniform, and obtain a mixed coating slurry.

[0100] Step 4: Prepare a battery separator. The preparation steps are as follows: Use a micro-gravure roller coating process to coat the mixed slurry on the surface of the base film at a coating speed of 65 m / min, and then dry it in an oven at 70°C for 3 minutes to form a coating on the surface of the base film to prepare the battery separator.

[0101] Among them, the battery separator includes a PP base film with a thickness of 12um and a coating with a thickness of 2μm coated on one side of the base film. The coating includes butadiene-styrene copolymer particles, the above-mentioned dispersants, thickeners and binders. The butadiene-styrene copolymer particles are arranged in protrusions on the surface of the coating, and the boehmite particles, dispersants, thickeners and binders are embedded in the coating.

[0102] Comparative Example 1

[0103] This comparative example prepared a battery separator, which was prepared by the following method:

[0104] Step 1: Prepare a boehmite slurry: Add 0.20 kg of a dispersant (lauryl polyoxyethylene ether), 15 kg of boehmite particles (D50 less than 1 μm), and 0.2 kg of a thickener (polypropylene alcohol) to 25 kg of deionized water. Stir thoroughly and then sand grind (0.4 h, 1000 rpm) to disperse uniformly. Then, add 0.5 kg of a binder (polymethyl acrylate) and stir thoroughly to prepare a boehmite slurry. The boehmite particles have a particle size D50 less than 1 μm.

[0105] Step 2: Coating boehmite slurry: Take a base film (PE film with a thickness of 12 μm), and coat the boehmite slurry on the base film using a micro-gravure roller coating method (coating speed of 65 m / min), and then dry it in an oven at 70° C. for 1 minute.

[0106] Step 3: Prepare an organic colloidal particle slurry: Add 5 kg of polymethyl methacrylate colloidal particles, 0.2 kg of a dispersant (lauryl polyoxyethylene ether), and 0.2 kg of a thickener (polypropylene alcohol) to 25 kg of deionized water, mix and stir for 3.0 hours, then sand grind (0.4 hours, 1000 rpm) to evenly disperse the particles. Add 0.5 kg of a binder (polymethyl acrylate) and stir evenly to obtain a mixed coating slurry. The particle size D50 of the polymethyl methacrylate colloidal particles is 1 μm to 2 μm.

[0107] Step 4: Applying organic colloidal slurry: Applying the organic colloidal slurry to the boehmite coating by high-speed rotary spraying, with a coating speed of 30 m / min and a rotation speed of the rotary nozzle of 10,000 rpm / min, and drying to obtain a lithium-ion battery separator.

[0108] Comparative Example 2

[0109] This comparative example prepared a battery separator, which was prepared by the following method:

[0110] Step 1: Prepare PVDF slurry: Add 5 kg of PVDF particles, 0.2 kg of a fatty acid dispersant (stearic acid), and 0.2 kg of a thickener (PVA) to 25 kg of deionized water and stir for 3 hours. Then, sand grind (0.4 hours, 1000 rpm) to evenly disperse the particles. Then, add 0.5 kg of a binder (polyacrylate) and stir evenly to obtain a water-based PVDF slurry. The PVDF particles have a particle size (D50) of 2.0-10.0 μm.

[0111] Step 2: Prepare boehmite slurry: Add 0.20 kg of a fatty alcohol dispersant (sodium lauryl sulfate), 15 kg of boehmite, and 0.2 kg of a thickener (PVA) to 25 kg of deionized water. Stir thoroughly and then sand grind (0.4 h, 1000 rpm) to achieve uniform dispersion. Then, add 0.5 kg of a binder (polyacrylate) and stir thoroughly to obtain a boehmite slurry. The boehmite particles have a particle size (D50) of less than 1 μm.

[0112] Step 3, preparing a mixed coating slurry: taking 25 kg of PVDF slurry and 5 kg of boehmite slurry, stirring for 0.5 h until the mixture is uniform, to prepare a mixed coating slurry.

[0113] Step 4: Prepare a battery separator, which includes a base film (a 12 μm thick PP film) and a coating (2 μm thick) applied to one side of the base film. The preparation steps are as follows: Use a micro-gravure roller coating process to apply the mixed slurry to the surface of the base film at a coating speed of 65 m / min. Then, dry it in an oven at 70°C for 1 minute to form a coating on the surface of the base film, thereby preparing the battery separator.

[0114] Test Case

[0115] The battery separators provided in Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to performance tests. The test results are shown in Table 1. The specific test items are as follows:

[0116] (1) Adhesion test between diaphragm and electrode:

[0117] The battery diaphragm samples were assembled into batteries and the adhesion between the diaphragm and the electrode was tested. The test method was: using an electronic tensile test to test the adhesion between the diaphragm and the electrode. The test parameters were: test pressure of 0.3 MPa, test temperature of 80°C, and voltage and temperature stabilization time of 60s.

[0118] (2) Electrolyte retention test:

[0119] Cutting area is 100cm 2The electrolyte retention capacity test of the diaphragm samples is carried out, and the test method is as follows: use a precision density balance to measure the weight of the diaphragm samples, recorded as M1, and soak the diaphragm samples in electrolyte (the electrolyte composition is EC:PC:EMC=30:5:65 (mass ratio)). After soaking at 85℃ for 24h, take out the diaphragm samples, wipe off the residual electrolyte on the surface of the diaphragm with dust-free paper, weigh it, recorded as M2, and calculate the liquid absorption rate as an indicator of the electrolyte retention capacity of the diaphragm.

[0120] Calculation method of liquid absorption rate: Liquid absorption rate (%) = (M2-M1) / M1*100%, where M1: initial weight of the diaphragm sample; M2: weight of the diaphragm sample after soaking.

[0121] (3) 130℃@1h heat shrinkage rate: The test method is carried out in accordance with GB / T17-2004. Take 5 pieces of battery separator samples and measure their dimensions before heating. The samples are sandwiched between A4 papers and placed in a 130℃ oven for 1 hour. The dimensions of the separator samples after heating are measured and their heat shrinkage rate in the MD direction is calculated.

[0122] Table 1

[0123]

[0124] As can be seen from Table 1, the battery separators prepared in Examples 1-3 of the present invention are prepared by using suitable dispersants for the organic colloid slurry and the boehmite slurry respectively, and thereby forming a mixed slurry for coating preparation. During this process, the organic colloid particles float relative to the boehmite particles, thereby protruding from the surface of the coating, so that the battery separator has excellent adhesion, liquid absorption and retention, and heat resistance (low thermal shrinkage).

[0125] Compared with Examples 1-3, in the battery separator prepared in Comparative Example 1, the boehmite coating and the organic colloid coating are applied in sequence, and the organic colloid is dispersed inside the adhesive layer and is not arranged protrudingly, which significantly deteriorates the adhesion, liquid absorption and heat resistance of the battery separator.

[0126] Compared with Examples 1-3, the battery separator prepared in Comparative Example 2, although its organic colloid slurry and boehmite slurry each use suitable dispersants to form a mixed slurry for coating preparation, however, due to the use of organic colloids different from those in the embodiments of the present invention and dispersants different from those in the embodiments of the present invention, its adhesion, liquid absorption and heat resistance to the battery separator are better than those of Comparative Example 1, but still inferior to those of Examples 1-3 of the present invention.

[0127] The above description is only for the purpose of facilitating those skilled in the art to understand the technical solution of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A battery separator, characterized in that: The battery separator comprises: a base film and a coating layer stacked on at least one side of the base film, wherein the coating layer comprises: organic colloid particles, inorganic particles, a first dispersant, a second dispersant, a first binder, a second binder, a first thickener and a second thickener; The organic colloidal particles are protruded on the surface of the coating layer facing away from the base film, and the inorganic particles, the first dispersant, the second dispersant, the first binder, the second binder, the first thickener and the second thickener are all embedded in the coating layer. The first dispersant is selected from at least one of polyoxyethylene ether derivatives, polyol esters, and silicones, and the second dispersant is selected from at least one of polycarboxylic acid sodium salts, polyacrylate ammonium salts, and sulfonates.

2. The battery separator according to claim 1, characterized in that The protrusion height of the organic colloidal particles relative to the coating is 2 μm-6 μm; The coverage area of ​​the organic colloid particles on the coating layer accounts for 70% to 80% of the area of ​​the coating layer.

3. The battery separator according to claim 1, characterized in that The particle size distribution of the organic colloid particles is as follows: D10 is 1.0 μm-2.0 μm, D50 is 3.0 μm-8.0 μm, and D90 is 9.0 μm-10.0 μm; The particle size D50 of the inorganic particles is less than 1 μm.

4. The battery separator according to claim 1, characterized in that The organic colloid particles include at least one of (meth)acrylate polymers, styrene-acrylonitrile copolymers, and butadiene-styrene copolymers.

5. The battery separator according to claim 1, characterized in that The inorganic particles are at least one of boehmite particles, magnesium hydroxide particles, barium carbonate particles, magnesium carbonate particles, and zirconium oxide particles.

6. The battery separator according to claim 1, characterized in that The first thickener and the second thickener are each independently selected from at least one of hydroxymethyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and polypropylene alcohol; The first binder and the second binder are each independently selected from at least one of polyacrylic acid, polyacrylate, and polyacrylamide.

7. The battery separator according to any one of claims 1 to 6, characterized in that: The mass ratio of the organic colloid particles to the inorganic particles is 1-30:1-30.

8. A method for preparing a battery separator, characterized in that: The battery separator according to any one of claims 1 to 7, wherein the preparation method of the battery separator comprises: Obtaining an organic colloid particle slurry, wherein the organic colloid particle slurry comprises: organic colloid particles, a first dispersant, a first thickener, a first binder, and water; Obtaining an inorganic particle slurry, wherein the inorganic particle slurry comprises: inorganic particles, a second dispersant, a second thickener, a second binder, and water; uniformly mixing the organic colloidal particle slurry and the inorganic particle slurry to obtain a mixed slurry; The mixed slurry is coated on the surface of the base film, and dried to form a coating to obtain the battery separator.

9. The method for preparing a battery separator according to claim 8, wherein: In the organic colloid slurry, the mass ratio of water, organic colloid, first dispersant, first thickener and first binder is 25-30:5-10:0.1-0.5:0.1-0.5:0.5-5; In the inorganic particle slurry, the mass ratio of water, inorganic particles, second dispersant, second thickener and second binder is 25-35:15-25:0.1-0.5:0.1-0.5:0.5-5.

10. The method for preparing a battery separator according to any one of claims 8 to 9, characterized in that: The solid content of the mixed slurry is 15%-20%, and the viscosity is 100mPa.s-120mPa.s.

11. A secondary battery, characterized in that: The secondary battery comprises: a shell, an electrolyte contained in the shell, and a thermal composite battery cell, wherein the thermal composite battery cell comprises a plurality of positive electrode sheets, a plurality of negative electrode sheets, and a battery separator according to any one of claims 1 to 7; The negative electrode sheets and the positive electrode sheets are alternately stacked and arranged, and the adjacent negative electrode sheets and the positive electrode sheets are separated by the battery separator, and the battery separator is bonded to the corresponding electrode sheets through the coating.

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