Separator, and electrochemical device and electronic apparatus comprising same

Abstract

The invention discloses a diaphragm as well as an electrochemical device and electronic equipment containing the diaphragm. The diaphragm comprises a base membrane and a composite material layer on at least one surface of the base membrane, the composite material layer comprises a polyurethane substrate and a filler dispersed in the polyurethane substrate, and the filler comprises ceramic and polydopamine coating the surface of the ceramic. The diaphragm has excellent electrolyte wettability, thermal stability and ionic conductivity.

Description

Technical Field

[0001] This invention relates to a diaphragm and an electrochemical device and electronic device containing the diaphragm. Background Technology

[0002] Currently, polyolefin separators (mainly PP and PE) are widely used in lithium-ion batteries due to their high mechanical strength, good electrochemical stability, small pore size, and low cost. However, commonly used polyolefin separators have poor high-temperature stability (PE separators have a melting point of 125℃-140℃, and PP separators have a melting point of 165℃-170℃). At high temperatures, dimensional changes can occur, leading to contact between the positive and negative electrodes and causing internal short circuits, thus posing safety risks. Furthermore, the poor electrolyte wettability and low electrolyte absorption rate of polyolefin separators also result in low ionic conductivity and high internal resistance, significantly impacting the electrochemical performance of lithium-ion batteries. With the increasing demand for high-performance lithium-ion batteries, the inherent defects of polyolefin separators limit their application and development in the field of high-performance lithium-ion batteries. Summary of the Invention

[0003] To address the shortcomings of existing diaphragm electrolytes in terms of poor wettability, thermal stability, and ionic conductivity, this invention provides a diaphragm and an electrochemical or electronic device incorporating it. This diaphragm exhibits excellent electrolyte wettability, thermal stability, and ionic conductivity.

[0004] To achieve the above objectives, the present invention employs the following technical solutions.

[0005] In a first aspect, the present invention provides a diaphragm, characterized in that it comprises a base membrane and a composite material layer on at least one surface of the base membrane;

[0006] The composite material layer includes a polyurethane substrate and fillers dispersed in the polyurethane substrate, wherein the fillers include ceramics and polydopamine coated on the surface of the ceramics.

[0007] In a second aspect, the present invention provides an electrochemical device, characterized in that it comprises a diaphragm as described above.

[0008] Thirdly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0009] The positive and progressive effects of this invention are as follows:

[0010] This invention provides a separator in which a composite material layer is formed on a base membrane. The composite material layer contains a polydopamine-coated ceramic material, which can effectively improve the thermal stability and electrolyte wettability of the separator. The polydopamine-coated ceramic material is dispersed in a cross-linked network structure provided by a polyurethane substrate. The polyurethane substrate has incompatible soft and hard segments, which can provide mechanical strength and thermal stability on the one hand, and ionic conductivity on the other. The separator formed by the above composite material layer and the base membrane has excellent electrolyte wettability, thermal stability and ionic conductivity, and can be used in the design of high mass margin battery cells. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the diaphragm structure in Examples 1-24.

[0012] The attached figures are labeled as follows:

[0013] 1-Base film; 2-Polyurethane substrate; 3-Polydopamine; 4-Ceramic. Detailed Implementation

[0014] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0015] diaphragm

[0016] The diaphragm according to the first aspect of the present invention includes a base membrane and a composite material layer on at least one surface of the base membrane;

[0017] The composite material layer includes a polyurethane substrate and fillers dispersed in the polyurethane substrate, wherein the fillers include ceramics and polydopamine coated on the surface of the ceramics.

[0018] In some specific embodiments, the polyurethane substrate is made of polyether polyurethane and / or polyester polyurethane.

[0019] In some specific embodiments, the weight-average molecular weight of the polyether polyurethane is 5000-20000.

[0020] In one specific embodiment, the polyether-type polyurethane has a weight-average molecular weight of 12,000.

[0021] In some specific implementations, the polyester-type polyurethane is a polycarbonate-type polyurethane.

[0022] In some specific embodiments, the polycarbonate-type polyurethane has a weight-average molecular weight of 8000.

[0023] In some specific embodiments, the molecular weight of the polycarbonate-type polyurethane is 5000-20000.

[0024] In some specific embodiments, the content of hard segments in the polyether polyurethane is 10%-40%, and the content of soft segments in the polyether polyurethane is 60%-90%; wherein, in the content of hard segments in the polyether polyurethane, % means the percentage of the mass of hard segments in the polyether polyurethane to the mass of polyether polyurethane, and in the content of soft segments in the polyether polyurethane, % means the percentage of the mass of soft segments in the polyether polyurethane to the mass of polyether polyurethane.

[0025] In one specific embodiment, the polyether polyurethane contains 25% hard segments and 75% soft segments.

[0026] In one specific embodiment, the polyether polyurethane contains 10% hard segments and 90% soft segments.

[0027] In one specific embodiment, the polyether polyurethane contains 40% hard segments and 60% soft segments.

[0028] In some specific embodiments, the content of the hard segment of the polyester polyurethane is 10%-40%, and the content of the soft segment of the polyester polyurethane is 60%-90%; wherein, in the content of the hard segment of the polyester polyurethane, % means the percentage of the mass of the hard segment of the polyester polyurethane to the mass of the polyester polyurethane, and in the content of the soft segment of the polyester polyurethane, % means the percentage of the mass of the soft segment of the polyester polyurethane to the mass of the polyester polyurethane.

[0029] In one specific embodiment, the content of the hard segment of the polyester-type polyurethane is 20%, and the content of the soft segment of the polyether-type polyurethane is 80%.

[0030] In some specific embodiments, the tensile strength of the polyurethane substrate is 20-60 MPa.

[0031] In some specific embodiments, the tensile strength of the polyurethane substrate is 25-50 MPa, for example 30 MPa.

[0032] In some specific embodiments, the polyurethane substrate has an oxygen index ≥ 28% and a flammability rating of V-0. The oxygen index refers to the minimum oxygen concentration required for the polyurethane substrate to undergo flaming combustion in an oxygen-nitrogen mixed gas stream.

[0033] In one specific embodiment, the polyurethane substrate has a tensile strength of 25-50 MPa, an oxygen index ≥28%, and a flammability rating of V-0.

[0034] In some specific embodiments, the mass content of the polyurethane substrate in the composite material layer is 30%-75%. Here, % represents the percentage of the mass of the polyurethane substrate relative to the mass of the composite material layer.

[0035] In some specific embodiments, the mass content of the polyurethane substrate in the composite material layer is 42%-57%.

[0036] In some specific embodiments, the mass content of the polyurethane substrate in the composite material layer is 42%, 46%, 53%, 56%, 57%, 58%, 63%, 68%, or 70%.

[0037] In some specific embodiments, the base membrane is made of polyolefin.

[0038] In some specific embodiments, the polyolefin is polyethylene and / or polypropylene.

[0039] In some specific embodiments, the thickness of the base film is 5-30 μm, for example, 9 μm.

[0040] In some specific embodiments, the porosity of the base membrane is 30%-60%, for example, 40%.

[0041] In some specific embodiments, the thickness of the composite material layer is 2-5 μm, for example, 3 μm.

[0042] In some specific embodiments, the ceramic comprises one or more of silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide, calcium oxide, boehmite, hydrotalcite, barium carbonate, and magnesium hydroxide.

[0043] In some specific embodiments, the composite material layer further includes a binder, a dispersant, and a wetting agent.

[0044] In some specific embodiments, the adhesive includes polyvinylpyrrolidone and / or polyacrylic acid compounds.

[0045] In one specific embodiment, the adhesive is polymethyl methacrylate.

[0046] In some specific embodiments, the dispersant includes one or more of polyethylene glycol, sodium polyacrylate, and ammonium polyacrylate.

[0047] In some specific embodiments, the wetting agent includes one or more of alkynyl alcohol surfactants, polyol ester surfactants, and silanol surfactants.

[0048] Methods for preparing diaphragms

[0049] In some specific embodiments, the preparation method of the diaphragm includes the following steps: coating the base membrane with a composite material slurry and then drying it to obtain the diaphragm; the composite material slurry includes a composite material, and the preparation method of the composite material includes the following steps: mixing ceramic and dopamine monomer to obtain polydopamine-coated ceramic material (PDA@CCS); mixing the polydopamine-coated ceramic material and a polyurethane solution to obtain a dried composite material.

[0050] In some specific implementations, the dopamine monomer is dopamine or dopamine hydrochloride.

[0051] In some specific embodiments, the mass ratio of the ceramic to the dopamine monomer is 1:(1-5), for example, 1:2.

[0052] In some specific embodiments, the mass concentration of polyurethane in the polyurethane solution is 5%-10%, for example, 8%.

[0053] In some specific embodiments, the organic solvent in the polyurethane solution includes one or more of DMF, DMSO, THF, NMP, acetone, and ethyl acetate.

[0054] In some specific embodiments, the mass ratio of the polydopamine-coated ceramic material to the polyurethane solution is 1:(1.2-4.5), for example, 1:3.

[0055] In some specific embodiments, the preparation method of the polydopamine-coated ceramic material includes the following steps: adding ceramic to Tris-HCl buffer solution and sonicating it to form a dispersion, then adding dopamine monomer to the dispersion solution and mixing to obtain the polydopamine-coated ceramic material.

[0056] In some embodiments, the mass ratio of the ceramic to the volume ratio of the Tris-HCl buffer is 1:(50-200), where mass is in g and volume is in mL.

[0057] In some implementations, the ultrasonic treatment time is 0.5-2 hours.

[0058] In some implementations, the mixing method is stirring, and the stirring speed is 200-800 r / min.

[0059] In some embodiments, the mixture further includes a step of centrifugation, washing, and drying to obtain PDA@CCS.

[0060] In some implementations, the centrifugation speed is 6000-10000 r / min.

[0061] In some implementations, the detergent used for washing is deionized water.

[0062] In some implementations, the washing is performed 2-3 times.

[0063] In some embodiments, the drying temperature is 60-100°C.

[0064] In some implementations, the drying time is 8-16 hours.

[0065] In some specific embodiments, the method for preparing the polyurethane solution includes the following steps: mixing polyurethane and the organic solvent and heating in a water bath to obtain a polyurethane solution.

[0066] In some implementations, the water bath heating temperature is 30-60°C.

[0067] In some implementations, the mixing method is stirring, and the stirring time is 3-6 hours.

[0068] In some specific embodiments, the PDA@CCS and the polyurethane solution are mixed and then subjected to centrifugation, washing and drying steps in sequence to obtain a composite material.

[0069] In some implementations, the centrifugation speed is 6000-10000 r / min.

[0070] In some implementations, the detergent used for washing is deionized water.

[0071] In some implementations, the washing is performed 2-4 times.

[0072] In some embodiments, the drying temperature is 60-80°C.

[0073] In some implementations, the drying time is 8-16 hours.

[0074] In some specific embodiments, the preparation method of the composite material slurry includes the following steps: mixing the binder, dispersant, wetting agent, solvent and the composite material to obtain the composite material slurry.

[0075] In some specific embodiments, the mass concentration of the composite material in the composite slurry is 25%-60%, for example, 35%, 45% or 55%. Here, % means the percentage of the mass of the composite material in the mass of the composite slurry.

[0076] In some specific embodiments, the mass concentration of the binder in the composite slurry is 5%-12%, for example, 7%. Here, % means the percentage of the mass of the binder to the mass of the composite slurry.

[0077] In some embodiments, the adhesive is a compound comprising polyvinylpyrrolidone and / or polyacrylic acid compounds.

[0078] In one specific embodiment, the adhesive is polymethyl methacrylate.

[0079] In some specific embodiments, the mass concentration of the dispersant in the composite slurry is 0.5%-5%, for example, 1.3%. Here, % means the percentage of the mass of the dispersant to the mass of the composite slurry.

[0080] In some embodiments, the dispersant is one or more selected from polyethylene glycol, isopropanol, n-butanol, sodium polyacrylate, and ammonium polyacrylate. When the dispersant is isopropanol and / or n-butanol, during the drying process after the composite slurry is coated onto the base film, the dispersant evaporates, resulting in very little residual isopropanol and / or n-butanol in the final composite layer, which is negligible.

[0081] In one specific embodiment, the dispersant is polyethylene glycol.

[0082] In some specific embodiments, the mass concentration of the wetting agent in the composite slurry is 0.1%-1%, for example, 0.5%. Here, % means the percentage of the mass of the wetting agent to the mass of the composite slurry.

[0083] In some embodiments, the wetting agent includes one or more of alkynyl alcohol surfactants, polyol ester surfactants, and silanol surfactants.

[0084] In one specific embodiment, the wetting agent is an alkynyl alcohol surfactant.

[0085] In some specific implementations, the solvent is ultrapure water.

[0086] In some embodiments, the method for preparing the composite material slurry includes the following steps: first mixing the composite material, the dispersant and the solvent, then adding the binder for a second mixing, and then adding a wetting agent for a third mixing to obtain the composite material slurry.

[0087] In one embodiment, the first mixing method is magnetic stirring, the magnetic stirring time is 2 hours, and the magnetic stirring speed is 600 r / min.

[0088] In one embodiment, the second mixing method is stirring, the stirring time is 2 hours, and the stirring speed is 800 r / min.

[0089] In one embodiment, the third mixing method is stirring, the stirring time is 1.5 hours, and the stirring speed is 500 r / min.

[0090] In some specific embodiments, the preparation method of the diaphragm includes the following steps: coating the composite material slurry onto the base film using a microgravure roller coating process, and baking it in an oven at 75°C and then winding it up to obtain the diaphragm.

[0091] Electrochemical device

[0092] The electrochemical device described in the second aspect of the present invention includes the diaphragm as described above.

[0093] In this invention, the electrochemical device can be a sodium-ion battery or a lithium-ion battery, preferably a lithium-ion battery.

[0094] In some alternative embodiments, the lithium-ion battery further includes a negative electrode, a positive electrode, and an electrolyte.

[0095] The electrolyte is a conventionally used electrolyte in the art.

[0096] negative electrode sheet

[0097] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0098] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener.

[0099] In some specific embodiments, the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickener is 97:0.7:1.8:0.5.

[0100] The negative electrode active material can be a negative electrode active material conventionally used in the art to prepare negative electrode sheets, and can be selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon suboxide and silicon carbide.

[0101] In one specific implementation, the negative electrode active material is artificial graphite.

[0102] The addition of the thickener can increase the viscosity of the system of each component in the negative electrode slurry. It can be a thickener commonly used in the art to prepare negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0103] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc.

[0104] The type of adhesive is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers.

[0105] In one specific embodiment, the adhesive is styrene-butadiene rubber.

[0106] For the negative electrode current collector, the negative electrode current collector can be a current collector conventionally used for negative electrodes in the art, and can be a common current collector or a composite current collector. The negative electrode current collector can be made of a non-chemically reactive and conductive material without limitation. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum-cadmium alloys can be used, or copper, stainless steel, or aluminum-cadmium alloys surface-treated with carbon, nickel, titanium, or silver. Furthermore, to enhance the adhesion of the negative electrode active material, micro-embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as a membrane, sheet, foil, mesh, or porous body.

[0107] In some alternative implementations, the thickness of the negative electrode current collector is 5-10 μm.

[0108] In some specific implementations, the negative electrode current collector is a copper foil with a thickness of 6 μm.

[0109] In some alternative embodiments, the negative electrode sheet can be prepared using conventional methods in the art, such as the following method: mixing the negative electrode active material, conductive agent, binder and thickener in a certain mass ratio, adding solvent and mixing evenly to obtain a negative electrode slurry; then uniformly coating the negative electrode slurry onto the negative electrode current collector; and then preparing the negative electrode sheet through processes such as drying, rolling, and cutting.

[0110] In one specific implementation, the solvent is water.

[0111] Positive electrode film

[0112] In this invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector.

[0113] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant.

[0114] In some specific embodiments, the mass ratio of the positive electrode active material, the conductive agent, the binder, and the dispersant is 97:1:1.9:0.1.

[0115] The positive electrode active material is a positive electrode active material conventionally used in the art to prepare positive electrode sheets, such as one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium-rich manganese-based materials.

[0116] In one specific embodiment, the positive electrode active material is LiFePO4.

[0117] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc.

[0118] The binder serves to improve the adhesion between the positive electrode active materials and the adhesion between the positive electrode active materials and the positive electrode current collector. There are no particular limitations on the type of binder. Specific examples of binders may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0119] The dispersant may be a dispersant conventionally used in the art, such as a modified styrene-maleic anhydride copolymer.

[0120] For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without restriction. Commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. To enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the positive electrode current collector. Positive electrode current collectors can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0121] In some alternative implementations, the thickness of the positive current collector is 8-16 μm.

[0122] In some specific implementations, the positive current collector is an aluminum foil with a thickness of 16 μm.

[0123] In some alternative embodiments, the positive electrode sheet can be prepared using methods conventional in the art, such as the following method: mixing positive electrode active material, conductive agent, binder and dispersant in a certain mass ratio, adding solvent and mixing evenly to obtain a positive electrode slurry; then uniformly coating the positive electrode slurry onto the positive electrode current collector; and then drying, cold pressing and slitting to obtain the positive electrode sheet.

[0124] In one specific embodiment, the solvent is NMP.

[0125] electronic devices

[0126] The electronic device described in the third aspect of the present invention includes the electrochemical device as described above.

[0127] For example, the electronic devices described in this invention may be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0128] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0129] The reagents and raw materials used in this invention are all commercially available.

[0130] Example 1

[0131] The preparation of polyurethane solution includes the following steps:

[0132] 2.4 g of polyether polyurethane was slowly added to 48 mL of organic solvent DMF and sealed. The solution was heated in a water bath at 45 °C and stirred at 700 r / min for 5 h to obtain a polyurethane solution with a mass concentration of 5%. The polyether polyurethane had a weight-average molecular weight of 12,000, and the content of hard segments was 25% and the content of soft segments was 75%.

[0133] The preparation method of composite materials includes the following steps:

[0134] S1. Add 150 mL of Tris-HCl buffer to 1.5 g of ceramic SiO2 and sonicate for 1 h to form a dispersion. Then weigh 3 g of dopamine hydrochloride and add it to the dispersion. Stir at room temperature for 24 h at a stirring speed of 500 r / min. After stirring, centrifuge, wash and dry in sequence to obtain polydopamine-coated ceramic material (PDA@CCS). The centrifugation speed is 8000 r / min, the washing agent is deionized water, the washing is performed 3 times, the drying temperature is 80℃ and the drying time is 12 h.

[0135] S2. Weigh 1.2g of the above PDA@CCS and add it to the above polyurethane solution in 6 portions under ultrasonic conditions, stirring at room temperature for 12 hours at a stirring speed of 600r / min. After stirring, the composite material is obtained by centrifugation, washing and drying in sequence. The centrifugation speed is 8000r / min, the washing detergent is deionized water, the washing is performed 3 times, the drying temperature is 80℃, and the drying time is 12 hours.

[0136] The preparation method of composite material slurry includes the following steps:

[0137] The composite material, dispersant polyethylene glycol, and solvent water obtained above were stirred for 2 hours under magnetic stirring at a stirring speed of 800 r / min. Then, the binder polymethyl methacrylate was added and the stirring was continued at a stirring speed of 800 r / min for 2 hours. Subsequently, the wetting agent alkynyl alcohol surfactant was added and the stirring was continued at a stirring speed of 500 r / min for 1.5 hours. Finally, the mixture was filtered through a 400-mesh sieve to obtain the composite material slurry.

[0138] In the composite slurry, the mass concentration of the composite material is 45%, the mass concentration of the binder is 7%, the mass concentration of the dispersant is 1.3%, the mass concentration of the wetting agent is 0.5%, and the balance is solvent.

[0139] The preparation method of the diaphragm includes the following steps:

[0140] The above-mentioned composite material slurry was coated onto a 9µm thick PE base film using a micro-gravure roller coating process, and then baked in a 75°C oven and wound up to obtain a separator.

[0141] A schematic diagram of the structure of the diaphragm prepared by the above method is shown below. Figure 1 As shown, it includes a 9µm thick PE base film 1 and a composite material layer on one surface of the PE base film 1; the composite material layer includes a polyether polyurethane substrate 2 and fillers, binders, dispersants and wetting agents dispersed in the polyether polyurethane substrate 2, the fillers including ceramic 4 and polydopamine 3 coated on the surface of ceramic 4.

[0142] The tensile strength of the polyurethane substrate is 30 MPa, the mass content of the polyurethane substrate in the composite layer is 56%, the porosity of the base film is 40%, and the thickness of the composite layer is 3 ± 0.1 μm.

[0143] The thickness of the composite material layer was tested in accordance with GB / T 36363-2018;

[0144] The test method for the tensile strength of polyurethane substrate is as follows: the above polyurethane solution is coated separately and dried to form a film. The tensile strength of the film is tested according to the method of GB / T 1040.1-2018, which is the tensile strength of polyurethane substrate.

[0145] The test method for the mass content W (%) of polyurethane substrate in the composite material layer is as follows: the amount of polyurethane used in the composite material preparation process is recorded as W1, the weight of the diaphragm after the composite material layer is coated is recorded as W2, and the weight of the base film is recorded as W3. The result is calculated by the formula: W=W1 / (W2-W3).

[0146] The porosity of the base membrane was tested according to GB / T 36363-2018.

[0147] Example 2-24

[0148] The preparation methods of polyurethane solution, composite material, composite slurry and diaphragm in Examples 2-24 are the same as those in Example 1. The different parameters in the preparation process are listed in Table 1 below, and the remaining parameters are the same as those in Example 1.

[0149] The diaphragm prepared by the above preparation method in Examples 2-24 includes a base membrane and a composite material layer on one surface of the base membrane; the composite material layer includes a polyurethane substrate and fillers, binders, dispersants and wetting agents dispersed in the polyurethane substrate, the fillers including ceramics and polydopamine coated on the surface of the ceramics.

[0150] Except for the parameters in Table 1 below, the diaphragms in Examples 2-24 are the same as those in Example 1.

[0151] Among them, the polyurethane substrates of Examples 1-24 all meet the following requirements: oxygen index ≥28% and flammability rating V-0.

[0152] Table 1

[0153] Types of polyurethane weight-average molecular weight of polyurethane Content of hard segments in polyurethane The content of soft segments in polyurethane mass concentration of polyurethane in polyurethane solution mass ratio of ceramic to dopamine monomer Mass ratio of PDA@CCS and polyurethane Mass concentration of composite material in composite slurry Types of ceramics Tensile strength (MPa) of polyurethane substrate Mass content of polyurethane substrate in composite material layer Example 1 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 2 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 45% <![CDATA[Al2O3]]> 30 56% Example 3 Polyester-type polyurethane 8000 20% 80% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 4 Polyether polyurethane 12000 25% 75% 5% 1：2 1：3 45% <![CDATA[SiO2]]> 30 63% Example 5 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 55% <![CDATA[SiO2]]> 30 57% Example 6 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 35% <![CDATA[SiO2]]> 30 53% Example 7 Polyether polyurethane 12000 25% 75% 5% 1：2 1：1.2 45% <![CDATA[SiO2]]> 30 46% Example 8 Polyether polyurethane 12000 25% 75% 5% 1：2 1：4.5 45% <![CDATA[SiO2]]> 30 68% Example 9 Polyether polyurethane 12000 25% 75% 5% 1：2 1：1 45% <![CDATA[SiO2]]> 30 42% Example 10 Polyether polyurethane 12000 25% 75% 5% 1：2 1：1.5 45% <![CDATA[SiO2]]> 30 70% Example 11 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 25 56% Example 12 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 50 56% Example 13 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 20 56% Example 14 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 60 56% Example 15 Polyether polyurethane 12000 10% 90% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 16 Polyether polyurethane 12000 40% 60% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 17 Polyether polyurethane 5000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 18 Polyether polyurethane 20000 25% 75% 5% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 19 Polyether polyurethane 12000 25% 75% 5% 1：1 1：2 45% <![CDATA[SiO2]]> 30 56% Example 20 Polyether polyurethane 12000 25% 75% 5% 1：5 1：2 45% <![CDATA[SiO2]]> 30 56% Example 21 Polyether polyurethane 12000 25% 75% 10% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 22 Polyether polyurethane 12000 25% 75% 8% 1：2 1：2 45% <![CDATA[SiO2]]> 30 56% Example 23 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 20% <![CDATA[SiO2]]> 30 46% Example 24 Polyether polyurethane 12000 25% 75% 5% 1：2 1：2 60% <![CDATA[SiO2]]> 30 58%

[0154] Comparative Example 1

[0155] Compared with Example 1, Comparative Example 1 differs in that no polyurethane was added, while the rest of the steps are the same as in Example 1.

[0156] The membrane of Comparative Example 1 specifically includes the following preparation steps:

[0157] 150 mL of Tris-HCl buffer solution was added to 1.5 g of ceramic SiO2 and ultrasonically dispersed for 1 h to form a dispersion. Then, 3 g of dopamine hydrochloride was weighed and added to the dispersion. The mixture was stirred at room temperature for 24 h at a stirring speed of 500 r / min. After stirring, the composite material was obtained by centrifugation, washing and drying. The centrifugation speed was 8000 r / min, the washing agent was deionized water, the washing was performed 3 times, the drying temperature was 80℃ and the drying time was 12 h.

[0158] The composite material, dispersant polyethylene glycol, and solvent water obtained above were stirred for 2 hours under magnetic stirring at a stirring speed of 800 r / min. Then, the binder polymethyl methacrylate was added and the stirring was continued at a stirring speed of 800 r / min for 2 hours. Subsequently, the wetting agent alkynyl alcohol surfactant was added and the stirring was continued at a stirring speed of 500 r / min for 1.5 hours. Finally, the mixture was filtered through a 400-mesh sieve to obtain the composite material slurry.

[0159] The above-mentioned composite material slurry was coated onto a 9µm thick PE base film using a micro-gravure roller coating process, and then baked in a 75°C oven and wound up to obtain a separator.

[0160] Comparative Example 2

[0161] Compared with Example 1, Comparative Example 2 differs in that no dopamine monomer was added, while the rest of the steps are the same as in Example 1.

[0162] The membrane of Comparative Example 2 specifically includes the following preparation steps:

[0163] The preparation of polyurethane solution includes the following steps:

[0164] 2.4 g of polyether polyurethane was slowly added to 48 mL of organic solvent DMF and sealed. The solution was heated in a water bath at 45 °C and stirred at 700 r / min for 5 h to obtain a polyurethane solution with a mass concentration of 5%. The polyether polyurethane had a weight-average molecular weight of 12,000, and the content of hard segments was 25% and the content of soft segments was 75%.

[0165] 1.2g of SiO2 was weighed and added to the polyurethane solution in 6 portions under ultrasonic conditions, each 0.2g. The mixture was stirred at room temperature for 12 hours at a stirring speed of 600 r / min. After stirring, the composite material was obtained by centrifugation, washing and drying. The centrifugation speed was 8000 r / min, the washing agent was deionized water, the washing was performed 3 times, the drying temperature was 80℃, and the drying time was 12 hours.

[0166] The composite material, dispersant polyethylene glycol, and solvent water obtained above were stirred for 2 hours under magnetic stirring at a stirring speed of 800 r / min. Then, the binder polymethyl methacrylate was added and the stirring was continued at a stirring speed of 800 r / min for 2 hours. Subsequently, the wetting agent alkynyl alcohol surfactant was added and the stirring was continued at a stirring speed of 500 r / min for 1.5 hours. Finally, the mixture was filtered through a 400-mesh sieve to obtain the composite material slurry.

[0167] The above-mentioned composite material slurry was coated onto a 9µm thick PE base film using a micro-gravure roller coating process, and then baked in a 75°C oven and wound up to obtain a separator.

[0168] Comparative Example 3

[0169] The diaphragm of Comparative Example 3 is a 9µm thick PE base film.

[0170] Example 1

[0171] The following tests were performed on Examples 1-24 and Comparative Examples 1-3:

[0172] 1. Testing of the diaphragm's liquid absorption rate, liquid retention rate, air permeability, longitudinal heat shrinkage rate, and transverse heat shrinkage rate: Tested in accordance with GB / T 36363-2018.

[0173] 2. Testing the ionic conductivity of the diaphragm:

[0174] A symmetrical battery was assembled by using two stainless steel gaskets as electrodes and sandwiching a separator that had fully absorbed the electrolyte between the gaskets. The AC impedance was then measured at room temperature using an electrochemical workstation, and the AC impedance value was denoted as Rs.

[0175] The electrolyte is LB-007 lithium-ion battery electrolyte purchased from Duoduo Chemical Technology Co., Ltd.

[0176] The ionic conductivity (σ) of the diaphragm is calculated using the following formula: σ = d / (Rs * S); where d is the thickness of the diaphragm (µm) and S is the area of ​​a single stainless steel gasket (cm²). 2 ).

[0177] The test results of Examples 1-24 and Comparative Examples 1-3 are listed in Table 2:

[0178] Table 2

[0179] Liquid absorption rate of the diaphragm (%) Liquid retention rate of the diaphragm (%) Membrane permeability (s / mL) Longitudinal thermal shrinkage rate of the diaphragm (%) Transverse thermal shrinkage rate of the diaphragm (%) σ (mS / cm) Example 1 251 104 158 1.7 1 0.75 Example 2 243 98 164 1.2 0.7 0.73 Example 3 248 95 175 2 1.1 0.7 Example 4 235 107 142 1.5 0.8 0.77 Example 5 270 110 153 1.2 0.8 0.82 Example 6 216 89 136 2.1 1.2 0.68 Example 7 278 98 179 1.3 0.8 0.68 Example 8 232 107 135 1.8 1.2 0.79 Example 9 282 78 183 1.2 0.8 0.63 Example 10 205 110 127 2 1.5 0.82 Example 11 252 101 156 1.6 1.1 0.72 Example 12 255 98 153 1.4 0.7 0.69 Example 13 250 103 156 1.7 2.2 0.7 Example 14 257 109 158 1.4 0.6 0.67 Example 15 260 110 165 2 1.5 0.83 Example 16 245 103 152 1.6 0.8 0.62 Example 17 248 101 154 2.3 1.7 0.73 Example 18 250 108 150 1.8 1 0.75 Example 19 243 96 151 1.1 0.7 0.63 Example 20 257 110 163 1.9 1 0.67 Example 21 248 105 158 1.6 1.1 0.74 Example 22 249 102 155 1.7 1 0.73 Example 23 243 103 152 1.4 0.8 0.67 Example 24 236 94 145 1.8 1.1 0.76 Comparative Example 1 204 80 132 4.2 3 0.58 Comparative Example 2 187 74 127 3.4 2.5 0.69 Comparative Example 3 125 58 94 12.8 11.4 0.5

[0180] Based on the results in Tables 1 and 2, the diaphragm prepared in the examples has a liquid absorption rate of over 205%, a liquid retention rate of over 78%, and an air permeability of over 127 S / mL, indicating that it has excellent electrolyte wettability; a longitudinal thermal shrinkage rate of less than 2.3% and a transverse thermal shrinkage rate of less than 2.2%, indicating that it has excellent thermal stability; and an ionic conductivity of over 0.063 mS / cm, indicating that it has excellent ionic conductivity.

[0181] Based on the results of Examples 1, 4, and 7-10, it can be seen that a mass ratio of PDA@CCS to polyurethane in the polyurethane solution of 1:(1.2-4.5) can increase the liquid absorption rate of the diaphragm to over 232%, the liquid retention rate to over 98%, the air permeability to over 135 S / mL, and the ionic conductivity to over 0.068 mS / cm. This indicates that this mass ratio can further improve the electrolyte wettability and ionic conductivity of the diaphragm.

[0182] Based on the results of Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that Comparative Example 1 did not add polyurethane, and Comparative Example 2 did not add dopamine monomer. This resulted in a decrease in the liquid absorption rate, liquid retention rate, air permeability, and ionic conductivity of the membranes in Comparative Example 1 and Comparative Example 2, while their longitudinal thermal shrinkage rate and transverse thermal shrinkage rate both increased. This indicates that the absence of polyurethane is detrimental to the electrolyte wettability, thermal stability, and ionic conductivity of the membrane.

[0183] Based on the results of Example 1 and Comparative Example 3, it can be seen that the base membrane containing the composite material layer in Example 1 has significantly improved electrolyte wettability, thermal stability and ionic conductivity compared with the base membrane alone.

[0184] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that, It includes a base film and a composite material layer on at least one surface of the base film; The composite material layer includes a polyurethane substrate and fillers dispersed in the polyurethane substrate, wherein the fillers include ceramics and polydopamine coated on the surface of the ceramics.

2. The diaphragm as described in claim 1, characterized in that, The polyurethane substrate satisfies one or more of the following conditions (a)-(c): (a) The polyurethane substrate is made of polyether polyurethane and / or polyester polyurethane; (b) The tensile strength of the polyurethane substrate is 25-50 MPa; (c) The mass content of the polyurethane substrate in the composite material layer is 30%-75%.

3. The diaphragm as described in claim 2, characterized in that, The polyurethane substrate satisfies one or both of the following conditions (a)-(d): (a) The weight-average molecular weight of the polyether polyurethane is 5,000-20,000; (b) The weight-average molecular weight of the polyester polyurethane is 5,000-20,000; (c) The content of hard segments in the polyether polyurethane is 10%-40%, and the content of soft segments in the polyether polyurethane is 60%-90%; (d) The content of the hard segment of the polyester polyurethane is 10%-40%, and the content of the soft segment of the polyester polyurethane is 60%-90%; (e) The polyester polyurethane is a polycarbonate polyurethane.

4. The diaphragm as described in claim 1, characterized in that, The diaphragm satisfies one or more of the following conditions (a)-(f): (a) The material of the base membrane is polyolefin; (b) The thickness of the base film is 5-30 μm; (c) The porosity of the base membrane is 30%-60%; (d) The thickness of the composite material layer is 2-5 μm; (e) The ceramic comprises one or more of the following: silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide, calcium oxide, boehmite, hydrotalcite, barium carbonate, and magnesium hydroxide; (f) The composite material layer also includes a binder, a dispersant and a wetting agent.

5. The diaphragm as described in claim 4, characterized in that, The diaphragm satisfies one or more of the following conditions (a)-(d): (a) The polyolefin is polyethylene and / or polypropylene; (b) The adhesive comprises polyvinylpyrrolidone and / or polyacrylic acid compounds; (c) The dispersant comprises one or more of polyethylene glycol, sodium polyacrylate, and ammonium polyacrylate; (d) The wetting agent includes one or more of alkynyl alcohol surfactants, polyol ester surfactants and silanol surfactants.

6. The diaphragm according to any one of claims 1-5, characterized in that, The method for preparing the diaphragm includes the following steps: A diaphragm is obtained by coating the base film with a composite material slurry and then drying it. The composite material slurry includes a composite material, and the preparation method of the composite material includes the following steps: mixing ceramic and dopamine monomer to obtain polydopamine-coated ceramic material; mixing the polydopamine-coated ceramic material and polyurethane solution and then drying it to obtain a composite material.

7. The diaphragm as described in claim 6, characterized in that, The method for preparing the diaphragm satisfies one or more of the following conditions (a)-(e): (a) The mass ratio of the ceramic to the dopamine monomer is 1:(1-5); (b) The mass concentration of polyurethane in the polyurethane solution is 5%-10%; (c) The organic solvent of the polyurethane solution includes one or more of DMF, DMSO, THF, NMP, acetone and ethyl acetate; (d) The mass ratio of the polydopamine-coated ceramic material to the polyurethane in the polyurethane solution is 1:(1.2-4.5). (e) The preparation method of the composite material slurry includes the following steps: mixing the binder, dispersant, wetting agent, solvent and the composite material to obtain the composite material slurry.

8. The diaphragm as described in claim 6, characterized in that, The method for preparing the diaphragm satisfies one or more of the following conditions (a)-(d): (a) The mass concentration of the composite material in the composite slurry is 25%-60%; (b) The mass concentration of the binder in the composite slurry is 5%-12%; (c) The mass concentration of the dispersant in the composite slurry is 0.5%-5%; (d) The mass concentration of the wetting agent in the composite slurry is 0.1%-1%.

9. An electrochemical device, characterized in that, It includes the diaphragm as described in any one of claims 1-8.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

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