Battery separator and electrochemical device comprising same

Abstract

A battery separator and an electrochemical device comprising same. The battery separator comprises a base film and a coating located on at least one surface of the base film. The coating comprises a solid electrolyte, nanofibers, ceramic particles, and an adhesive polymer. The length-diameter ratio of the nanofibers is 2:1-30:1. By using the coating of the above composition and adjusting the length-diameter ratio of the nanofibers within the above range, a battery separator having good air permeability, high heat resistance, high adhesion and a high ionic conductivity can be obtained, thereby improving the safety performance of an electrochemical device.

Description

A battery separator and an electrochemical device comprising the same.

[0001] This application claims priority to Chinese Patent Application No. 202510224446.0, filed on February 27, 2025, entitled "A Battery Separator and an Electrochemical Device Containing the Same", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a battery separator and an electrochemical device comprising the same. Background Technology

[0003] With the rapid development of hybrid and electric vehicles, high energy density energy storage systems have become a research hotspot, among which lithium-ion batteries have received widespread attention due to their high energy density and long cycle life. However, they also pose safety hazards such as flammable and explosive electrolytes, shrinkage of battery separators at high temperatures, and poor bonding between the separator and electrodes, resulting in gaps and residual gas. Therefore, researchers began to study solid-state electrolytes. However, solid-state electrolytes suffer from poor mechanical properties, poor processing performance, unstable chemical properties, and poor compatibility with positive and negative electrode materials. Consequently, research on semi-solid-state batteries that reduce electrolyte usage has gained widespread attention.

[0004] To reduce the amount of electrolyte used, current technologies mainly focus on modifying existing battery separators with solid electrolyte materials that have high lithium-ion conductivity to prepare organic / inorganic composite electrolyte separators. However, while these materials can improve the ionic conductivity of the separator, they also face problems such as poor thermal shrinkage, poor air permeability, or poor adhesion, which greatly affects the safe operation of the battery. Summary of the Invention

[0005] The purpose of this application is to provide a battery separator and an electrochemical device comprising the same, to obtain a battery separator that combines good permeability, high heat resistance, high adhesion, and high ionic conductivity, thereby improving the safety performance of the electrochemical device. The specific technical solution is as follows:

[0006] A first aspect of this application provides a battery separator comprising a base membrane and a coating on at least one surface of the base membrane, the coating comprising a solid electrolyte, nanofibers, ceramic particles and a binding polymer, wherein the aspect ratio of the nanofibers is 2:1 to 30:1.

[0007] In some embodiments, the average length of the nanofibers is 60-800 nm, preferably 60-600 nm, more preferably 100-600 nm; the average diameter of the nanofibers is 10-40 nm.

[0008] In some embodiments, the aspect ratio of the nanofibers is 5:1 to 20:1.

[0009] In some embodiments, the solid electrolyte is selected from at least one of sodium superionic conductor solid electrolyte, perovskite solid electrolyte, and garnet solid electrolyte;

[0010] Preferably, the sodium superionic conductor solid electrolyte is lithium titanium aluminum phosphate;

[0011] Preferably, the perovskite-type solid electrolyte is lithium lanthanum titanium oxide;

[0012] Preferably, the garnet-type solid electrolyte is at least one of lithium lanthanum zirconium oxide and lithium lanthanum zirconium tantalum oxide;

[0013] Preferably, the solid electrolyte is selected from at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium tantalum oxide; and / or,

[0014] The ceramic particles are selected from at least one of boehmite, alumina, silicon dioxide, silicon carbide, and boron nitride.

[0015] Preferably, the ceramic particles are selected from boehmite or alumina.

[0016] In some embodiments, the adhesive polymer is selected from at least one of polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyethylene carbonate, polypropylene carbonate polyol, polytrimethylene carbonate, polyvinyl carbonate, polyacrylonitrile, polyethyleneimine, polyvinylidene fluoride-hexafluoropropylene, polyethylene glycol, and polyethylene glycol methyl ether acrylate.

[0017] Preferably, the adhesive polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polymethyl methacrylate, wherein the molecular weight of the polymethyl methacrylate is 50,000-200,000, the molecular weight of the polyvinylidene fluoride-hexafluoropropylene is 400,000-800,000, and the mass percentage of hexafluoropropylene in the polyvinylidene fluoride-hexafluoropropylene is 3-9%.

[0018] In some embodiments, based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%.

[0019] Preferably, the solid electrolyte has a mass percentage of 3-10%, the nanofibers have a mass percentage of 2-5%, and the ceramic particles have a mass percentage of 85-95%; and / or,

[0020] Based on the total mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the adhesive polymer is 1-20%.

[0021] In some embodiments, the coating comprises a mixed coating comprising the solid electrolyte, the nanofibers, the ceramic particles, and the binding polymer. Based on the total solid mass of the solid electrolyte, nanofibers, and ceramic particles, the solid electrolyte comprises 1-15% by mass, the nanofibers comprise 0.25-10% by mass, and the ceramic particles comprise 80-98% by mass. Based on the total solid mass of the solid electrolyte, nanofibers, and ceramic particles, the binding polymer comprises 1-20% by mass. The thickness of the mixed coating on one side is 1-5 μm.

[0022] And / or, the coating comprises a ceramic coating and an adhesive layer, the adhesive layer being located on the surface of the ceramic coating; the ceramic coating comprises the solid electrolyte, the nanofibers, and the ceramic particles, the adhesive layer comprises the adhesive polymer, wherein, based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%; the thickness of the ceramic coating on one side is 1-5 μm, and the thickness of the adhesive layer on one side is 0.3-3 μm.

[0023] The second aspect of this application provides a method for preparing the battery separator provided in the first aspect of this application, which includes the following steps:

[0024] Preparation of coating slurry: The first raw material is added to the first solvent and dispersed evenly to obtain the coating slurry. The first raw material includes the solid electrolyte, the nanofiber, the ceramic particles and the adhesive polymer. The first solvent is selected from at least one of water, acetone, N-methylpyrrolidone and N,N-dimethylacetamide. The solid content of the coating slurry is 15-30 wt%.

[0025] Preparation of the battery separator: The coating slurry is coated onto at least one surface of the base film, dried, and then heat-set to obtain the battery separator;

[0026] or,

[0027] The coating comprises a ceramic coating and an adhesive layer, the adhesive layer being located on the surface of the ceramic coating. The ceramic coating comprises the solid electrolyte, the nanofibers, and the ceramic particles. The adhesive layer comprises the adhesive polymer. The preparation method includes:

[0028] Preparation of ceramic coating slurry: The second raw material is added to the second solvent and dispersed evenly to obtain the ceramic coating slurry. The solid content of the ceramic coating slurry is 25-45 wt%. The second raw material includes the solid electrolyte, the nanofibers and the ceramic particles.

[0029] Preparation of the adhesive layer slurry: The third raw material is added to the third solvent and dispersed evenly to obtain the adhesive layer slurry. The solid content of the adhesive layer slurry is 3-30 wt%, and the third raw material includes the adhesive polymer.

[0030] Preparation of the battery separator: The ceramic coating slurry is coated on at least one surface of the base film and dried; the adhesive layer slurry is coated on the surface of the ceramic coating and dried; and then heat-set to obtain the battery separator.

[0031] The second solvent and the third solvent are each independently selected from at least one of water, N-methylpyrrolidone, and N,N-dimethylacetamide.

[0032] A third aspect of this application provides an electrochemical device comprising the battery separator provided in the first aspect of this application.

[0033] In some embodiments, the electrochemical device further includes a positive electrode and a negative electrode; the battery separator is located between the positive electrode and the negative electrode, and the ceramic coating is located on at least one surface of the base film facing the positive electrode.

[0034] This application provides a battery separator and an electrochemical device comprising the same. The battery separator includes a base membrane and a coating on at least one surface of the base membrane. The coating includes a solid electrolyte, nanofibers, ceramic particles, and a binding polymer. The aspect ratio of the nanofibers is 2:1-30:1. By using the composition of this application and controlling the aspect ratio of the nanofibers within the above range, the solid electrolyte and ceramic particles exhibit good heat resistance, the nanofibers exhibit good thermal stability, and hydrophilicity can be improved. Furthermore, the nanofibers can bridge ion transport between the solid electrolyte and ceramic particles, promoting ion transport. This can improve the ion transport effect while enhancing the thermal shrinkage and air permeability of the battery separator, enabling the battery separator to achieve high ionic conductivity. The use of the binding polymer, combined with the solid electrolyte, nanofibers, and ceramic particles, results in a battery separator with good air permeability, high heat resistance, high ionic conductivity, and high adhesion, thereby improving the safety performance of the electrochemical device.

[0035] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0036] The technical solutions of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0037] A first aspect of this application provides a battery separator comprising a base film and a coating disposed on at least one surface of the base film. The coating comprises a solid electrolyte, nanofibers, ceramic particles, and a binding polymer. The aspect ratio of the nanofibers is 2:1 to 30:1. For example, the aspect ratio of the nanofibers can be 2:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 22:1, 23:1, 25:1, 26:1, 28:1, 30:1, or a range consisting of any two of these values. The phrase "coating disposed on at least one surface of the base film" means that the coating can be disposed on one surface of the base film along its thickness direction, or on two surfaces of the base film along its thickness direction. In this application, the nanofibers are biomass nanofibers. There are no particular restrictions on the type of nanofibers used, as long as they achieve the purpose of this application. For example, they can be obtained by purchasing different types of commercially available nanofibers, or they can be prepared by the applicant, such as nanocellulose whiskers extracted from cotton. In this application, the adhesive polymer refers to a polymer with a large molecular weight that ensures high adhesiveness; there are no particular limitations on the specific molecular weight of each polymer.

[0038] If the aspect ratio of the nanofibers is too large, for example greater than 30:1, it will increase the viscosity of the coating slurry, making processing more difficult. If the aspect ratio of the nanofibers is too small, for example less than 2:1, it will reduce the smoothness of the coating surface, result in poor thermal stability, poor cross-linking network, poor hydrophilicity and wettability, and also reduce the ionic conductivity. By using the composition of this application and controlling the aspect ratio of the nanofibers within the above range, the solid electrolyte and ceramic particles have good heat resistance, the nanofibers have good thermal stability, and can improve hydrophilicity. Furthermore, the nanofibers can bridge the ion transport between the solid electrolyte and ceramic particles, promoting ion transport. This can improve the thermal shrinkage and air permeability of the battery separator while enhancing the ion transport effect, enabling the battery separator to achieve high ionic conductivity. At the same time, the use of a binding polymer in combination with the solid electrolyte, nanofibers, and ceramic particles results in a battery separator with good air permeability, high heat resistance, high ionic conductivity, and high adhesion, thereby improving the safety performance of electrochemical devices such as batteries.

[0039] In some embodiments, the average length of the nanofiber is 60-800 nm, preferably 60-600 nm, and more preferably 100-600 nm; the average diameter of the nanofiber is 10-40 nm. For example, the average length of the nanofiber can be 60 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, or any two of these values; the average diameter can be 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 23 nm, 25 nm, 27 nm, 30 nm, 32 nm, 35 nm, 38 nm, 40 nm, or any two of these values. If nanofibers are too long, for example, longer than 800 nm, they are difficult to disperse, causing the coating slurry to agglomerate, resulting in poor coating uniformity. They also form an overly dense structure within the coating, reducing porosity and decreasing the air permeability of the battery separator. Conversely, if nanofibers are too short, for example, shorter than 60 nm, the coating's structural stability is poor, its hydrophilicity and wettability are weak, and its ionic conductivity decreases. This application, by controlling the average length and average diameter of the nanofibers within the aforementioned range, enables the battery separator to possess better air permeability, while also improving its adhesion and thermal shrinkage properties, and enhancing its ionic conductivity.

[0040] In some embodiments, when the aspect ratio of the nanofibers is 5:1-30:1 and the average length of the nanofibers is 150-300nm, the battery separator of this application can simultaneously improve the coating permeability and the ionic conductivity, while having high bonding strength between the battery separator and the positive electrode, low thermal shrinkage, and high battery separator coating coverage on the surface of the positive electrode.

[0041] In some embodiments, the solid electrolyte is selected from at least one of sodium superionic conductor (NASICON) type solid electrolyte, perovskite type solid electrolyte, and garnet type solid electrolyte;

[0042] Preferably, the sodium superionic conductor solid electrolyte is lithium titanium aluminum phosphate (LATP, Li 1.3 Al 0.3 Ti 1.7 (PO4)3);

[0043] Preferably, the perovskite-type solid electrolyte is lithium lanthanum titanium oxide (lithium lanthanum titanate, LLTO, Li). 0.33 La 0.56 TiO3);

[0044] Preferably, the garnet-type solid electrolyte is lithium lanthanum zirconium oxide (LLZO, Li7La3Zr2O). 12 ), Lithium lanthanum zirconium tantalum oxide (LLZTO, Li 6.5 La3Zr 1.5 Ta 0.5 O 12 At least one of the following;

[0045] Preferably, the solid electrolyte is selected from at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium tantalum oxide; and / or,

[0046] The ceramic particles are selected from at least one of boehmite, alumina, silicon dioxide, silicon carbide, and boron nitride.

[0047] Preferably, the ceramic particles are selected from boehmite or alumina.

[0048] This application utilizes the aforementioned solid electrolyte with high ionic conductivity and good heat resistance, combined with nanofibers possessing good thermal stability. This enhances the ion transport performance of the battery separator, increases its ionic conductivity, and reduces the amount of electrolyte required. The resulting battery separator exhibits both good heat resistance and high ionic conductivity, thereby improving battery safety and kinetic performance. Furthermore, the use of the aforementioned ceramic particles, combined with nanofibers exhibiting good thermal stability and a binding polymer with good adhesion, further improves the heat resistance and adhesion of the battery separator, thus enhancing battery safety.

[0049] In some embodiments, the adhesive polymer is selected from at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyethylene carbonate, polypropylene carbonate polyol, polytrimethylene carbonate, polyvinyl carbonate, polyacrylonitrile (PAN), polyethyleneimine (PEI), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene glycol (PEG), and polyethylene glycol methyl ether acrylate (PEGMEA).

[0050] Preferably, the adhesive polymer is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HHA), and polymethyl methacrylate (PMMA). The PMMA has a molecular weight of 50,000-200,000, the PVDF-HHA has a molecular weight of 400,000-800,000, and the PMMA content of PVDF-HHA is 3-9% by mass. For example, the molecular weight of the PMMA can be 50,000, 60,000, 80,000, 100,000, 120,000, 150,000, 180,000, 200,000, or any combination of two of these values; the molecular weight of the PVDF-HHA can be 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, or any combination of two of these values; and the PMMA content of PVDF-HHA can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, or any combination of two of these values. By employing the aforementioned adhesive polymer in combination with the solid electrolyte, nanofibers, and ceramic particles described in this application, the battery separator can possess excellent air permeability, high heat resistance, and high ionic conductivity while also exhibiting high adhesion performance. This improves the bonding strength between the battery separator and the electrode, resulting in a tighter bond between them and further enhancing the battery's safety performance.

[0051] In some embodiments, based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%.

[0052] Preferably, the solid electrolyte has a mass percentage of 3-10%, the nanofibers have a mass percentage of 2-5%, and the ceramic particles have a mass percentage of 85-95%; and / or,

[0053] Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the adhesive polymer is 1-20%. For example, the mass percentage of the solid electrolyte can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any range of two such values; the mass percentage of the nanofibers can be 0.25%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range of two such values; and the mass percentage of the ceramic particles can be 80%, 81%, 82%, 83%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 95%, 96%, 98%, or any range of two such values. For example, the mass percentage of the adhesive polymer can be 1%, 2%, 3%, 5%, 6%, 8%, 10%, 12%, 13%, 15%, 16%, 18%, 20%, or a range of any two of these values.

[0054] When the amount of solid electrolyte is low, such as below 1%, the improvement in ionic conductivity is minimal. When the amount of solid electrolyte is high, such as above 15%, the porosity of the coating decreases, the liquid absorption and retention capacity of the ceramic particles declines, the rate of increase in ionic conductivity slows down, and the cost increases dramatically. When the amount of nanofiber is low, such as below 0.25%, the viscosity of the coating slurry decreases, reducing the drying efficiency of the coating and easily causing problems such as coating cracking, slurry particle agglomeration, and poor areal density consistency. It also reduces the thermal shrinkage performance of the battery separator. When the amount of nanofiber is high, such as above 10%, the thermal shrinkage performance of the battery separator improves, but at the same time, the viscosity of the coating slurry increases dramatically, causing a rapid increase in coating permeability, which is detrimental to the transport of ions inside the battery. This application controls the content of solid electrolyte, nanofiber, and ceramic particles within the above ranges, which is beneficial for the battery separator to simultaneously achieve good permeability, high heat resistance, high ionic conductivity, and low production cost. By controlling the content of the adhesive polymer within the above-mentioned range, the battery separator can have good air permeability, high heat resistance, high ionic conductivity and low production cost, while also having high adhesive performance. This is beneficial to improving the bonding strength between the battery separator and the electrode, thereby improving the safety performance of the battery.

[0055] In some embodiments, the particle size Dv50 of the ceramic particles is 0.3-1.5 μm, the particle size Dv50 of the binder polymer is 0.2-8 μm, and the ratio of the particle size Dv50 of the binder polymer to the particle size Dv50 of the ceramic particles is (1.67-20):1, preferably (1.9-7.5):1. In this application, Dv50 represents the particle size of 50% of the particles in the volumetric particle size distribution of the material being smaller than this value. For example, the particle size Dv50 of the ceramic particles can be 0.3μm, 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, 0.85μm, 0.9μm, 1.0μm, 1.2μm, 1.3μm, 1.5μm, or a range of any two of these values; the particle size Dv50 of the adhesive polymer can be 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1.0μm, 1.2μm, 1.3μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, or 0.5μm. The particle size distribution (Dv50) of the adhesive polymer can be 1.67:1, 1.7:1, 1.9:1, 2.1:1, 2.3:1, 2.5:1, 2.7:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, or any two of these values. This application, by controlling the particle size Dv50 of ceramic particles, the particle size Dv50 of the binding polymer, and the ratio of the particle size Dv50 of the binding polymer to the particle size Dv50 of ceramic particles within the above-mentioned range, is beneficial to enable the battery separator to simultaneously possess good air permeability, high heat resistance, high ionic conductivity, and high adhesion performance.

[0056] In some embodiments, the coating comprises a mixed coating comprising the solid electrolyte, the nanofibers, the ceramic particles, and the binding polymer. Based on the total solid mass of the solid electrolyte, nanofibers, and ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, the mass percentage of the ceramic particles is 80-98%, and the mass percentage of the binding polymer is 1-20%. The thickness of the mixed coating on one side is 1-5 μm. For example, the thickness of the mixed coating can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range of any two of these values. Using the mixed coating of this application enables the battery separator to have high ionic conductivity, good thermal shrinkage performance, high adhesion performance, and good air permeability.

[0057] In some embodiments, the mixed coating further includes at least one of a dispersant, a thickener, a binder, and a wetting agent;

[0058] Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the solid mass percentage of the dispersant F0 is 0.05-3%, the solid mass percentage of the thickener Z0 is 0.1-10%, the solid mass percentage of the binder N0 is 0.1-15%, and the solid mass percentage of the wetting agent R0 is 0.05-5%.

[0059] The dispersant is selected from at least one of styrene-maleic anhydride, acrylonitrile / acrylic acid / acrylamide copolymer, polyacrylonitrile, ammonium polyacrylate, sodium dodecylbenzenesulfonate, sodium hexametaphosphate, sodium tripolyphosphate, sodium citrate, and ammonium citrate.

[0060] The thickener is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose;

[0061] The adhesive is selected from at least one of styrene-acrylate copolymer, polyacrylate, acrylic modified polymer, polyvinyl alcohol, styrene-butadiene rubber, and polyacrylic acid;

[0062] The wetting agent is selected from at least one of methyl acrylate, polyether-modified polysiloxane, dodecylphenol polyoxyethylene ether, ethanol, propylene glycol, glycerol, dimethyl sulfoxide, and sodium dodecyl sulfonate. For example, F0 can be 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, or a range of any two values ​​therein; Z0 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any two values ​​therein; and N0 can be 0. The percentages are 1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, or any range of two values ​​thereof, and R0 can be 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, or any range of two values ​​thereof. This application, by using an additive including at least one of the above-mentioned dispersants, thickeners, binders, and wetting agents in the mixed coating, enables the battery separator to have better air permeability, thermal shrinkage properties, adhesion properties, and ionic conductivity, which is beneficial to improving the safety performance of the battery.

[0063] In some embodiments, the mixed coating further includes a dispersant; the solid mass percentage F0 of the dispersant is 0.05-3% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0064] In some embodiments, the mixed coating further includes a thickener; the solid mass percentage Z0 of the thickener is 0.1-10% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0065] In some embodiments, the mixed coating further includes a binder; the solid mass percentage (NO) of the binder is 0.1-15% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0066] In some embodiments, the mixed coating further includes a wetting agent; the solid mass percentage R0 of the wetting agent is 0.05-5% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0067] In the mixed coating of this application, the dispersants, thickeners, binders and wetting agents within the above range can be used in any combination, as long as the purpose of this application can be achieved.

[0068] In some embodiments, the coating comprises a ceramic coating and an adhesive layer, the adhesive layer being located on the surface of the ceramic coating; the ceramic coating comprises the solid electrolyte, the nanofibers, and the ceramic particles, the adhesive layer comprises the adhesive polymer, wherein, based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%; the thickness of the ceramic coating on one side is 1-5 μm, and the thickness of the adhesive layer on one side is 0.3-3 μm. For example, the thickness of the ceramic coating on one side can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any combination of two such values; the thickness of the adhesive layer on one side can be 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any combination of two such values. Using the ceramic coating and adhesive layer of this application enables the battery separator to have good air permeability, high ionic conductivity, good thermal shrinkage performance, and good adhesion performance.

[0069] In some embodiments, when the aspect ratio of the nanofibers is 5:1-30:1 and the average length of the nanofibers is 150-300nm, the battery separator of this application can simultaneously improve the coating permeability and the ionic conductivity, while having high bonding strength between the battery separator and the positive electrode, low thermal shrinkage, and high coverage of the battery separator bonding layer on the surface of the positive electrode.

[0070] In some embodiments, the ceramic coating further includes at least one of a dispersant, a thickener, a binder, and a wetting agent;

[0071] Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the solid mass percentage of the dispersant F1 is 0.05-3%, the solid mass percentage of the thickener Z1 is 0.1-10%, the solid mass percentage of the binder N1 is 0.1-15%, and the solid mass percentage of the wetting agent R1 is 0.05-5%.

[0072] The dispersant is selected from at least one of styrene-maleic anhydride, acrylonitrile / acrylic acid / acrylamide copolymer, polyacrylonitrile, ammonium polyacrylate, sodium dodecylbenzenesulfonate, sodium hexametaphosphate, sodium tripolyphosphate, sodium citrate, and ammonium citrate.

[0073] The thickener is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose;

[0074] The adhesive is selected from at least one of styrene-acrylate copolymer, polyacrylate, acrylic modified polymer, polyvinyl alcohol, styrene-butadiene rubber, and polyacrylic acid;

[0075] The wetting agent is selected from at least one of methyl acrylate, polyether-modified polysiloxane, dodecylphenol polyoxyethylene ether, ethanol, propylene glycol, glycerol, dimethyl sulfoxide, and sodium dodecyl sulfonate. For example, F1 can be 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, or a range of any two values ​​therein; Z1 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any two values ​​therein; and N1 can be 0. The percentages are 1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, or any range of two values ​​thereof, and R1 can be 0.05%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, or any range of two values ​​thereof. This application, by using an additive comprising at least one of the above-mentioned dispersants, thickeners, binders, and wetting agents in the ceramic coating, enables the battery separator to possess better air permeability, thermal shrinkage properties, adhesion properties, and ionic conductivity, thereby improving the safety performance of the battery.

[0076] In some embodiments, the ceramic coating further includes a dispersant; the solid mass percentage F1 of the dispersant is 0.05-3% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0077] In some embodiments, the ceramic coating further includes a thickener; the solid mass percentage Z1 of the thickener is 0.1-10% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0078] In some embodiments, the ceramic coating further includes a binder; the solid mass percentage N1 of the binder is 0.1-15% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0079] In some embodiments, the ceramic coating further includes a wetting agent; the solid mass percentage R1 of the wetting agent is 0.05-5% based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles.

[0080] In the ceramic coating of this application, the dispersants, thickeners, binders and wetting agents within the above range can be used in any combination, as long as the purpose of this application can be achieved.

[0081] In some embodiments, the adhesive layer further includes at least one of a dispersant, a thickener, a binder, and a wetting agent;

[0082] Based on the solid mass of the adhesive polymer, the solid mass percentage of the dispersant F2 is 0.1-30%, the solid mass percentage of the thickener Z2 is 0.1-20%, the solid mass percentage of the binder N2 is 0.1-30%, and the solid mass percentage of the wetting agent R2 is 0.05-5%.

[0083] The dispersant is selected from at least one of styrene-maleic anhydride, acrylonitrile / acrylic acid / acrylamide copolymer, polyacrylonitrile, ammonium polyacrylate, sodium dodecylbenzenesulfonate, sodium hexametaphosphate, sodium tripolyphosphate, sodium citrate, and ammonium citrate.

[0084] The thickener is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose;

[0085] The adhesive is selected from at least one of styrene-acrylate copolymer, polyacrylate, acrylic modified polymer, polyvinyl alcohol, styrene-butadiene rubber, and polyacrylic acid;

[0086] The wetting agent is selected from at least one of methyl acrylate, polyether-modified polysiloxane, dodecylphenol polyoxyethylene ether, ethanol, propylene glycol, glycerol, dimethyl sulfoxide, and sodium dodecyl sulfonate. For example, F2 can be 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 13%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or a range of any two of these values; Z2 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 13%, 14%, 15%. The concentrations of N2 and R2 can be 0.1%, 0.5%, 1%, 2%, 4%, 5%, 7%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 27%, 30%, or any two of these values. The application uses an additive in the adhesive layer comprising at least one of the above-mentioned dispersants, thickeners, binders, and wetting agents to give the battery separator better air permeability, heat shrinkage properties, adhesion properties, and ionic conductivity, thereby improving the safety performance of the battery.

[0087] In some embodiments, the adhesive layer further includes a dispersant; the mass percentage of the dispersant F2 is 0.1-30% based on the solid mass of the adhesive polymer.

[0088] In some embodiments, the adhesive layer further includes a thickener; the mass percentage Z2 of the thickener is 0.1-20% based on the solid mass of the adhesive polymer.

[0089] In some embodiments, the adhesive layer further includes an adhesive; the mass percentage N2 of the adhesive is 0.1-30% based on the solid mass of the adhesive polymer.

[0090] In some embodiments, the adhesive layer further includes a wetting agent; the mass percentage R2 of the wetting agent is 0.05-5% based on the solid mass of the adhesive polymer.

[0091] In the adhesive layer of this application, the dispersants, thickeners, binders and wetting agents within the above range can be used in any combination, as long as the purpose of this application can be achieved.

[0092] In this application, there are no particular restrictions on the manufacturers or brands of the specific polymer materials among the above-mentioned dispersants, thickeners, binders, and wetting agents, as long as they can achieve the purpose of this application.

[0093] In some embodiments, the thickness of the base film is 5-20 μm. For example, the thickness of the base film can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, or a range of any two of these values. In this application, the base film is a polyolefin base film. This application does not specifically limit the type of polyolefin, as long as it achieves the purpose of this application. In some embodiments, the polyolefin is selected from one or more copolymers or blends of polyethylene, polypropylene, polybutene, and poly4-methylpentene. The weight-average molecular weight of the polyolefin is 100,000 to 7,000,000. For example, the weight-average molecular weight of the polyolefin can be 100,000, 300,000, 500,000, 700,000, 1,000,000, 1,200,000, 1,500,000, 1,700,000, 2,000,000, 2,200,000, 2,400,000, 2,600,000, 2,800,000, 3,000,000, 3,200,000, 3,400,000, 3,600,000, 3,800,000, 4,000,000, 4,200,000, 4,400,000, 4,600,000, 4,800,000, 5,500,000, 6,500,000, 7,000,000, or a range consisting of any two of these values.

[0094] In some embodiments, the MD heat shrinkage rate of the battery separator is ≤10.5%, and the TD heat shrinkage rate is ≤8.3%. For example, the MD heat shrinkage rate of the battery separator can be 0%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 10.5%, or a range of any two of these values; the TD heat shrinkage rate of the battery separator can be 0%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 7.5%, 8%, 8.3%, or a range of any two of these values. The heat shrinkage rate of the battery separator in this application is within the above range, indicating that the battery separator has good heat shrinkage performance, which is beneficial to improving the safety performance of the battery.

[0095] In some embodiments, the MD heat shrinkage rate of the battery separator is ≤2.3%, and the TD heat shrinkage rate is ≤2.0%. For example, the MD heat shrinkage rate of the battery separator can be 0%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, or a range of any two of these values; the TD heat shrinkage rate of the battery separator can be 0%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values. The heat shrinkage rate of the battery separator in this application is within the above range, indicating that the battery separator has good heat shrinkage performance, which is beneficial to improving the safety performance of the battery.

[0096] In some embodiments, the ionic conductivity of the battery separator is 1.0-2.0 mS / cm. For example, the ionic conductivity of the battery separator can be 1.0 mS / cm, 1.1 mS / cm, 1.2 mS / cm, 1.3 mS / cm, 1.4 mS / cm, 1.5 mS / cm, 1.6 mS / cm, 1.7 mS / cm, 1.8 mS / cm, 1.9 mS / cm, 2.0 mS / cm, or a range of any two values ​​therein. The battery separator of this application has a high ionic conductivity, which is beneficial for improving the migration speed of lithium ions, thereby increasing the charge and discharge speed of the battery; increasing the charge and discharge capacity of the battery at high rates, thus improving the power density of the battery; reducing the internal resistance of the battery, reducing polarization effects, and improving the cycle stability and lifespan of the battery; and improving the safety performance of the battery under high and low temperature conditions.

[0097] The second aspect of this application provides a method for preparing the battery separator provided in the first aspect of this application, which includes the following steps:

[0098] Preparation of the coating slurry: The first raw material is added to the first solvent and dispersed evenly to obtain the coating slurry. The first raw material includes the solid electrolyte, the nanofibers, the ceramic particles, and the adhesive polymer. The first solvent is selected from at least one of water, acetone, N-methylpyrrolidone, and N,N-dimethylacetamide. The solid content of the coating slurry is 15-30 wt%. For example, the solid content of the coating slurry is 15 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 23 wt%, 25 wt%, 26 wt%, 28 wt%, 30 wt%, or a range of any two values ​​therein.

[0099] Preparation of the battery separator: The coating slurry is coated onto at least one surface of the base film, dried, and then heat-set to obtain the battery separator;

[0100] or,

[0101] The coating comprises a ceramic coating and an adhesive layer, the adhesive layer being located on the surface of the ceramic coating. The ceramic coating comprises the solid electrolyte, the nanofibers, and the ceramic particles. The adhesive layer comprises the adhesive polymer. The preparation method includes:

[0102] Preparation of ceramic coating slurry: The second raw material is added to the second solvent and dispersed evenly to obtain the ceramic coating slurry. The solid content of the ceramic coating slurry is 25-45 wt%. The second raw material includes the solid electrolyte, the nanofibers, and the ceramic particles. For example, the solid content of the ceramic coating slurry is 25 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 33 wt%, 35 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 43 wt%, 45 wt%, or a range of any two values ​​therein.

[0103] Preparation of the adhesive layer slurry: A third raw material is added to a third solvent and dispersed evenly to obtain the adhesive layer slurry. The solid content of the adhesive layer slurry is 3-30 wt%, and the third raw material includes the adhesive polymer; for example, the solid content of the adhesive layer slurry is 3 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 13 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 26 wt%, 28 wt%, 30 wt%, or a range of any two of these values;

[0104] Preparation of the battery separator: The ceramic coating slurry is coated on at least one surface of the base film and dried; the adhesive layer slurry is coated on the surface of the ceramic coating and dried; and then heat-set to obtain the battery separator.

[0105] The second solvent and the third solvent are each independently selected from at least one of water, N-methylpyrrolidone, and N,N-dimethylacetamide. The battery separator preparation method provided in this application is simple in process and has low costs in terms of time and equipment. The resulting battery separator exhibits good air permeability, high heat resistance, high ionic conductivity, and good adhesion performance. This solves problems in existing technologies such as excessive electrolyte usage, poor thermal shrinkage performance of the battery separator leading to easy thermal shrinkage, or loose bonding between the battery separator and the electrode, resulting in gaps and residual gas. This ultimately improves battery safety performance.

[0106] In some embodiments, the drying temperature is 30-80°C, and the heat setting temperature is 30-70°C.

[0107] In some embodiments, the first raw material further includes an auxiliary agent selected from at least one of dispersants, thickeners, binders, and wetting agents. This application does not particularly limit the types of dispersants, thickeners, binders, and wetting agents, as long as they achieve the purpose of this application. For example, the dispersant, thickener, binder, and wetting agent can be at least one of the above-mentioned dispersants, thickeners, binders, and wetting agents.

[0108] In some embodiments, the second raw material further includes an auxiliary agent selected from at least one of dispersants, thickeners, binders, and wetting agents. This application does not particularly limit the types of dispersants, thickeners, binders, and wetting agents, as long as they achieve the purpose of this application. For example, the dispersant, thickener, binder, and wetting agent can be at least one of the above-mentioned dispersants, thickeners, binders, and wetting agents. In some embodiments, the third raw material further includes an auxiliary agent selected from at least one of dispersants, thickeners, binders, and wetting agents. This application does not particularly limit the types of dispersants, thickeners, binders, and wetting agents, as long as they achieve the purpose of this application. For example, the dispersant, thickener, binder, and wetting agent can be at least one of the above-mentioned dispersants, thickeners, binders, and wetting agents.

[0109] In this application, the dispersant, thickener, binder, and wetting agent materials themselves have a certain water content. The solid content mentioned in this application is the mass percentage of the solid components in the slurry relative to the total mass of the liquid and solid components of the slurry.

[0110] A third aspect of this application provides an electrochemical device comprising the battery separator provided in the first aspect of this application.

[0111] In some embodiments, the electrochemical device further includes a positive electrode and a negative electrode; the battery separator is located between the positive electrode and the negative electrode, and the coating is located on at least one surface of the base film facing the positive electrode.

[0112] In some embodiments, the positive electrode sheet is bonded to the battery separator and hot-pressed at 90°C and 2 MPa, then the positive electrode sheet and the battery separator are separated, with the battery separator coating on the surface of the positive electrode sheet having a coverage rate of ≥50%. For example, the coverage rate can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, or a range of any two of these values. In some embodiments, the battery separator coating on the surface of the positive electrode sheet has a coverage rate of ≥96%. In some embodiments, the battery separator coating on the surface of the positive electrode sheet is a mixed coating. In some embodiments, the battery separator coating on the surface of the positive electrode sheet is an adhesive layer. By controlling the coverage of the battery separator coating on the surface of the positive electrode sheet within the above-mentioned range, this application can ensure a good adhesion between the positive electrode sheet and the battery separator. After hot pressing, the battery separator coating can be bonded to the positive electrode sheet, thereby improving the structural stability of the cell and enhancing the safety performance of the electrochemical device.

[0113] In some embodiments, the bonding strength between the battery separator and the positive electrode sheet is ≥12 N / m, preferably 12-17 N / m. For example, the bonding strength between the battery separator and the positive electrode sheet can be 12 N / m, 12.5 N / m, 13 N / m, 13.5 N / m, 14 N / m, 14.5 N / m, 15 N / m, 15.5 N / m, 16 N / m, 17 N / m, or a range of any two of these values. This application controls the bonding strength between the battery separator and the positive electrode sheet within the above range to ensure a good adhesion between the bonding layer of the positive electrode sheet and the battery separator. After hot pressing, the bonding layer of the battery separator can be bonded to the positive electrode sheet, thereby improving the structural stability of the battery cell and enhancing the safety performance of the electrochemical device.

[0114] Example

[0115] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0116] Test methods and equipment:

[0117] Coating air permeability increase measurement:

[0118] Cut a 100mm×100mm base film or battery separator and test it using a Japanese Oken-type air permeability tester (EG01-55-1MR) with 100cc test gas mode. Record the time it takes for all the test gas to pass through the base film or battery separator to obtain the air permeability of the base film or battery separator. Coating air permeability increment = battery separator air permeability - base film air permeability.

[0119] Heat shrinkage rate test:

[0120] Cut a 150mm × 150mm base film or battery separator and mark it with 100mm markings in both the length direction (MD direction) and the width direction (TD direction). Use an electric heating drying oven to perform a heat shrinkage test on the base film or battery separator at 130℃ for 1 hour. Record the length and width values ​​marked on the base film or battery separator after heating, which are L1 mm and L2 mm, respectively. The heat shrinkage rate % in the TD direction is (100-L2) / 100 × 100%; the heat shrinkage rate % in the MD direction is (100-L1) / 100 × 100%.

[0121] Ion conductivity test:

[0122] 1. Sample Preparation: Cut 19mm diameter circular battery separator samples. A certain mass of electrolyte was dropped onto the surface of the separator to fully wet it. Then, an R2032 experimental battery ("Separator / Standard Stainless Steel Gasket") was assembled in the following order: negative electrode shell + gasket + spring sheet + negative electrode plate + electrolyte-immersed battery separator + positive electrode plate + positive electrode shell. The battery was sealed at a pressure of 5MPa and allowed to stand at 25℃ for 3 hours after assembly. The electrolyte composition was: 1mol / L LiPF6, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC), with an EC:EMC mass ratio of 3:7 and VC content of 2wt%. The positive electrode composition was: active material (LiFePO4): conductive agent (carbon black): binder (PVDF) mass ratio of 8:1:1. The negative electrode was a lithium metal negative electrode. The gasket... (That is, the diameter of the gasket is 15.8mm and the thickness is 0.5mm), spring sheet The negative electrode shell, gasket, spring, and positive electrode shell were purchased according to the specifications of the R2032 experimental battery.

[0123] 2. Testing: Open the electrochemical workstation (Metroën, PGSTAT204 BOOSTER10A), call the AC impedance method (EIS) program, set the test frequency range to 106Hz~0.1Hz, and the perturbation voltage to 10mV. Under the test conditions of 25℃ and humidity less than 50%, clamp the experimental battery in the fixture of the electrochemical workstation, click the "Start" button on the software interface to start the test, and obtain the corresponding Nyquist spectrum. The resistance of the battery separator is obtained by reading the intercept of the Nyquist spectrum with the x-axis. The ionic conductivity of the battery separator is calculated by the following formula:

[0124] Wherein, σ represents the ionic conductivity of the battery separator, measured in Siemens units per centimeter (S / cm).

[0125] L – The thickness of the battery separator, measured in centimeters (cm).

[0126] S – Cross-sectional area of ​​a standard stainless steel gasket, in square centimeters (cm²) 2 ),

[0127] R – The measured resistance of the battery separator, measured in ohms (Ω).

[0128] Bond strength test between battery separator and positive electrode:

[0129] Cut a 5cm × 30cm battery separator and a 5cm × 30cm positive electrode sheet (positive electrode sheet composition: active material (LiFePO4): conductive agent (carbon black): binder (PVDF) mass ratio = 8:1:1) along the MD direction using a slitting knife. The side of the battery separator with the ceramic coating faces the positive electrode sheet. Place the battery separator and the positive electrode sheet together in a vacuum hot press, set the temperature to 90℃ and the pressure to 2MPa, and perform hot pressing (hot press, Qmesys, QM940AS). Set the hot pressing time to 100s. After hot pressing, cut the sample using a 2.5cm × 30cm tooling die. Then, perform a tensile test on a tensile testing machine (Jinan Siker Testing Technology Co., Ltd., TSL-1002) at a speed of 50mm / min. Take the average value of three tests to obtain the bonding strength between the battery separator and the positive electrode sheet.

[0130] Battery separator coating coverage test on the surface of the positive electrode:

[0131] According to the above-mentioned test method for the bonding strength between the battery separator and the positive electrode, the battery separator and the positive electrode are attached together. After hot pressing at 2MPa and 90℃, the battery separator and the positive electrode are separated. Data acquisition, image synthesis and analysis of the positive electrode are performed using an ultra-depth-of-field microscope (Kunshan Gaopin Precision Instrument Co., Ltd., GP-300C) to obtain the coverage test results of the coating of the battery separator on the surface of the positive electrode.

[0132] Example 1-1

[0133] <Preparation of Mixed Coating Slurry>

[0134] Add 0.5 parts of the dispersant styrene-maleic anhydride (solid content 46%) to 353 parts of deionized water, stir to disperse evenly, and then add 3 parts of the solid electrolyte LATP:Li 1.3 Al 0.3 Ti 1.7 (PO4)3, 94 parts of ceramic boehmite powder and 30 parts of 10wt% aqueous solution of nanofibers (NF), 8 parts of thickener carboxymethyl cellulose (chemically pure, solid content 4%), 36 parts of adhesive polymer PMMA (solid content 30%) with a molecular weight of 50,000-100,000 (5w-10w), 15 parts of adhesive polyacrylate (solid content 40%) and 0.23 parts of wetting agent polyether-modified polysiloxane (solid content 100%) were uniformly dispersed to obtain a mixed coating slurry with a solid content of 21.78%, wherein the average length of NF is 300nm, the average diameter is 30nm, and the aspect ratio is 10:1; the particle size Dv50 of boehmite powder is 0.8μm, and the Dv50 of PMMA is 3.5μm.

[0135] <Preparation of Battery Separator>

[0136] A 9μm thick polyethylene base film was used, and a mixed coating slurry was applied to one side surface of the base film using a No. 30 wire rod. After the slurry was applied, it was dried and heat-set in an oven at 60℃ to obtain a battery separator. The thickness of the mixed coating was 3μm, and the mass percentage of the adhesive polymer was 10.8% based on the total mass of the solid electrolyte, nanofibers and ceramic particles.

[0137] Examples 1-2 to Examples 1-4

[0138] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0139] Example 2-1

[0140] <Preparation of Ceramic Coating Slurry>

[0141] Add 0.5 parts of the dispersant styrene-maleic anhydride (solid content 46%) to 131 parts of deionized water, stir to disperse evenly, and then add 3 parts of LATP:Li 1.3 Al 0.3 Ti 1.7 (PO4)3, 30 parts of 10wt% NF aqueous solution and 94 parts of boehmite powder, with the mass ratio of LATP, NF and boehmite M1:M2:M3 being 3:3:94, 32 parts of thickener carboxymethyl cellulose (chemically pure, solid content 4%), 15 parts of binder polyacrylate (solid content 40%) and 0.23 parts of wetting agent polyether modified polysiloxane (solid content 100%) were added and dispersed evenly to obtain a ceramic coating slurry with a solid content of 35wt%, wherein the average length of NF is 300nm, the average diameter is 30nm, the aspect ratio is 10:1, and the particle size Dv50 of boehmite powder is 0.8μm.

[0142] <Preparation of Adhesive Layer Grout>

[0143] 36 parts of PMMA with a molecular weight of 5w-10w (solid content 30%) were added to 41 parts of deionized water and dispersed evenly to obtain a bonding layer slurry with a solid content of 14wt%, wherein the Dv50 of PMMA was 1μm.

[0144] <Preparation of Battery Separator>

[0145] A 9μm thick polyethylene base film was taken, and a ceramic coating slurry was coated onto one side surface of the base film using a No. 30 wire rod. After coating, it was dried in an oven at 60℃ to form a 2μm thick ceramic coating.

[0146] The adhesive layer slurry is then coated onto the surface of the ceramic coating using a No. 30 wire rod. After coating, the coating is dried and heat-set in an oven at 60°C to obtain a battery separator that includes a ceramic coating and an adhesive layer, wherein the thickness of the adhesive layer is 0.5μm.

[0147] Examples 2-2 to 2-8

[0148] Except for adjusting the corresponding preparation parameters according to Table 2, the rest is the same as in Example 2-1.

[0149] Examples 3-1 to 3-9

[0150] Except for adjusting the corresponding preparation parameters according to Table 3 and keeping the solid content of the ceramic coating slurry constant by adjusting the amount of deionized water added, everything else is the same as in Examples 2-1, except that the LLZO in Examples 3-8 is Li7La3Zr2O. 12 .

[0151] Examples 3-10

[0152] Except for obtaining a battery separator with ceramic coating and adhesive layer on both sides by double-sided coating, the rest is the same as in Example 2-1. The base film thickness of the obtained battery separator is 9μm, the ceramic coating thickness on one side is 2μm, and the adhesive layer thickness is 0.5μm.

[0153] Examples 3-11 to 3-12

[0154] Except for adjusting the corresponding preparation parameters according to Table 3 and adjusting the amount of added deionized water to keep the solid content of the ceramic coating slurry unchanged, the rest is the same as in Example 2-1.

[0155] Comparative Examples 1-1 to 1-2

[0156] Except for adjusting the corresponding preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0157] Table 1 Note: " / " indicates that there is no corresponding parameter.

[0158] Table 2 Note: " / " indicates that there is no corresponding parameter.

[0159] Table 3

[0160] Table 4 Note: " / " indicates that there is no corresponding parameter.

[0161] As can be seen from Examples 1-1 to 1-4, Examples 2-1 to 2-8, Examples 3-1 to 3-12, and Comparative Examples 1-1 to 1-2, this application uses a battery separator comprising a solid electrolyte, nanofibers, ceramic particles, and an adhesive polymer. By controlling the aspect ratio of the nanofibers within the range of this application, the battery separator can have a suitable coating permeability increase, a high bonding strength between the battery separator and the positive electrode, a low thermal shrinkage rate, a high ionic conductivity, and a high battery separator coating coverage on the surface of the positive electrode. This indicates that the battery separator of this application has good permeability, high adhesion, high heat resistance, and high ionic conductivity.

[0162] As can be seen from Examples 2-1, 3-2 to 3-4, and 3-12, the ionic conductivity of the battery separator increases with the increase of LATP content. However, with a further increase in LATP content, as in Example 3-12, the ionic conductivity of the battery separator decreases. This is because when the LATP content is too high, the porosity of the ceramic coating decreases, which is not conducive to ion diffusion and thus reduces the ionic conductivity of the battery separator. Furthermore, the manufacturing cost of the battery separator increases dramatically with the increase of LATP content.

[0163] As can be seen from Examples 2-1, 3-1, and 3-11, with the increase of nanofiber content, the air permeability of the battery separator coating increases, and the air permeability deteriorates. By adjusting the nanofiber content within the scope of this application, the battery separator can have a suitable air permeability enhancement and better air permeability.

[0164] As can be seen from Examples 1-1 to 1-4, Examples 2-1 to 2-8, and Examples 3-1 to 3-12, by adjusting the amounts of solid electrolyte, nanofibers, ceramic particles, and adhesive polymer within the scope of this application, the battery separator exhibits good coating permeability enhancement, high adhesion strength to the positive electrode, low thermal shrinkage, high ionic conductivity, and high battery separator coating coverage on the surface of the positive electrode, while maintaining low manufacturing cost. This indicates that the battery separator of this application can achieve low manufacturing cost while simultaneously possessing good permeability, high heat resistance, high ionic conductivity, and high adhesion.

[0165] As can be seen from Examples 2-1 to 2-8 and Examples 3-1 to 3-12, when the positive electrode sheet is attached to the battery separator and hot-pressed at 90°C and 2MPa, and then the positive electrode sheet and the battery separator are separated, the coverage of the battery separator adhesive layer on the surface of the positive electrode sheet is relatively high. It can be seen that the bonding strength between the adhesive layer of the battery separator and the positive electrode sheet is greater than the bonding strength between the adhesive layer and the base film and the ceramic coating. The adhesive layer of the battery separator can be transferred to the positive electrode sheet relatively completely, which is beneficial to improving the safety performance of the battery.

[0166] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0167] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0168] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A battery separator comprising a base membrane and a coating on at least one surface of the base membrane, the coating comprising a solid electrolyte, nanofibers, ceramic particles and a binding polymer, wherein the aspect ratio of the nanofibers is 2:1 to 30:

1.

2. The battery separator according to claim 1, wherein, The average length of the nanofiber is 60-800 nm, preferably 60-600 nm, and more preferably 100-600 nm; the average diameter of the nanofiber is 10-40 nm.

3. The battery separator according to claim 2, wherein, The aspect ratio of the nanofibers is 5:1-20:

1.

4. The battery separator according to claim 1, wherein, The solid electrolyte is selected from at least one of sodium superionic conductor type solid electrolyte, perovskite type solid electrolyte, and garnet type solid electrolyte; Preferably, the sodium superionic conductor solid electrolyte is lithium titanium aluminum phosphate; Preferably, the perovskite-type solid electrolyte is lithium lanthanum titanium oxide; Preferably, the garnet-type solid electrolyte is at least one of lithium lanthanum zirconium oxide and lithium lanthanum zirconium tantalum oxide; Preferably, the solid electrolyte is selected from at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium tantalum oxide; and / or, The ceramic particles are selected from at least one of boehmite, alumina, silicon dioxide, silicon carbide, and boron nitride. Preferably, the ceramic particles are selected from boehmite or alumina.

5. The battery separator according to any one of claims 1-4, wherein, The adhesive polymer is selected from at least one of polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyethylene carbonate, polypropylene carbonate polyol, polytrimethylene carbonate, polyvinyl carbonate, polyacrylonitrile, polyethyleneimine, polyvinylidene fluoride-hexafluoropropylene, polyethylene glycol, and polyethylene glycol methyl ether acrylate. Preferably, the adhesive polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polymethyl methacrylate, wherein the molecular weight of the polymethyl methacrylate is 50,000-200,000, the molecular weight of the polyvinylidene fluoride-hexafluoropropylene is 400,000-800,000, and the mass percentage of hexafluoropropylene in the polyvinylidene fluoride-hexafluoropropylene is 3-9%.

6. The battery separator according to claim 1, wherein, Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%. Preferably, the solid electrolyte has a mass percentage of 3-10%, the nanofibers have a mass percentage of 2-5%, and the ceramic particles have a mass percentage of 85-95%; and / or, Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the adhesive polymer is 1-20%.

7. The battery separator according to claim 1, wherein, The coating comprises a mixed coating, which includes the solid electrolyte, the nanofibers, the ceramic particles, and the binding polymer. Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%. Based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the binding polymer is 1-20%. The thickness of the mixed coating on one side is 1-5 μm. And / or, the coating comprises a ceramic coating and an adhesive layer, the adhesive layer being located on the surface of the ceramic coating; the ceramic coating comprises the solid electrolyte, the nanofibers, and the ceramic particles, the adhesive layer comprises the adhesive polymer, wherein, based on the total solid mass of the solid electrolyte, the nanofibers, and the ceramic particles, the mass percentage of the solid electrolyte is 1-15%, the mass percentage of the nanofibers is 0.25-10%, and the mass percentage of the ceramic particles is 80-98%; the thickness of the ceramic coating on one side is 1-5 μm, and the thickness of the adhesive layer on one side is 0.3-3 μm.

8. A method for preparing a battery separator according to any one of claims 1-7, comprising the following steps: Preparation of coating slurry: The first raw material is added to the first solvent and dispersed evenly to obtain the coating slurry. The first raw material includes the solid electrolyte, the nanofiber, the ceramic particles and the adhesive polymer. The first solvent is selected from at least one of water, acetone, N-methylpyrrolidone and N,N-dimethylacetamide. The solid content of the coating slurry is 15-30 wt%. Preparation of the battery separator: The coating slurry is coated onto at least one surface of the base film, dried, and then heat-set to obtain the battery separator; Alternatively, the coating comprises a ceramic coating and an adhesive layer, the adhesive layer being located on the surface of the ceramic coating, the ceramic coating comprising the solid electrolyte, the nanofibers, and the ceramic particles, and the adhesive layer comprising the adhesive polymer, the preparation method comprising: Preparation of ceramic coating slurry: The second raw material is added to the second solvent and dispersed evenly to obtain the ceramic coating slurry. The solid content of the ceramic coating slurry is 25-45 wt%. The second raw material includes the solid electrolyte, the nanofibers and the ceramic particles. Preparation of the adhesive layer slurry: The third raw material is added to the third solvent and dispersed evenly to obtain the adhesive layer slurry. The solid content of the adhesive layer slurry is 3-30 wt%, and the third raw material includes the adhesive polymer. Preparation of the battery separator: The ceramic coating slurry is coated on at least one surface of the base film and dried; the adhesive layer slurry is coated on the surface of the ceramic coating and dried; and then heat-set to obtain the battery separator. The second solvent and the third solvent are each independently selected from at least one of water, N-methylpyrrolidone, and N,N-dimethylacetamide.

9. An electrochemical device comprising the battery separator according to any one of claims 1-7.

10. The electrochemical device according to claim 9, wherein, The electrochemical device further includes a positive electrode and a negative electrode; the battery separator is located between the positive electrode and the negative electrode, and the coating is located on at least one surface of the base film facing the positive electrode.

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