Separator and secondary battery

Abstract

A separator and a secondary battery. The separator comprises a base material and a bonding layer arranged on at least one surface of the base material, the bonding layer comprises secondary microspheres and a binder, the secondary microspheres comprise a plurality of primary particles, and at least some of the secondary microspheres have a hollow structure. Lithium ion transmission is facilitated, the hot pressing deformation quantity of the bonding layer is greater, the thickness of the separator after hot pressing is reduced, the energy density of the battery is improved, the blockage degree of pores of the base material of the separator after hot pressing is smaller, and the impedance of a lithium ion battery is reduced.

Description

Separator and secondary battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 27, 2023, with application number 202310767343.X and application name “A Diaphragm and Secondary Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to, but is not limited to, the field of new energy technology, and specifically to a diaphragm and a secondary battery. Background Art

[0003] Lithium-ion battery separator materials provide a pathway for lithium ion transmission during operation and also act as a physical barrier, preventing direct physical contact between the positive and negative electrodes and causing a short circuit. Separator materials must have ample pores and a good bonding interface between the separator and the electrodes to allow lithium ions to flow smoothly through the separator material and between the positive and negative electrodes.

[0004] The use of a polymer bonding layer creates a bond between the separator and the positive and negative electrodes. This bonding requires a certain level of pressure and temperature during the hot pressing process during manufacturing. Under these conditions, the bonding layer deforms, forming a physical and mechanical bond with the electrode surface. Molecular contact between the bonding layer and the electrode surface creates intermolecular forces, ultimately bonding the separator to the electrodes. Technical issues

[0005] During the battery hot-pressing manufacturing process, the adhesive layer forms a bond with the electrodes under the influence of pressure and temperature. However, the adhesive layer deforms during hot pressing, which can clog the pores on the surface of the separator substrate, ultimately affecting the battery's impedance and long-term cycle life. Furthermore, the introduction of the adhesive layer increases the thickness of the separator itself, hindering the improvement of battery energy density. Technical Solutions

[0006] The embodiments of the present application provide a diaphragm and a secondary battery, which improve the current problems of the diaphragm being too thick after hot pressing and the deformation after hot pressing easily causing blockage of the pores of the diaphragm substrate.

[0007] According to the diaphragm in the embodiment of the present application, it includes a substrate and a bonding layer arranged on at least one surface of the substrate, the bonding layer contains secondary microspheres and a binder, the secondary microspheres contain multiple primary particles, and at least some of the secondary microspheres have a hollow structure.

[0008] Optionally, in other embodiments of the present application, the primary particles include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethyl methacrylate or acrylate copolymer derivatives.

[0009] Optionally, in other embodiments of the present application, the particle size of the secondary microspheres ranges from 4 μm to 15 μm.

[0010] Optionally, the shell thickness of the secondary microspheres ranges from 0.6 μm to 5 μm.

[0011] Optionally, in other embodiments of the present application, the particle size of the primary particles is from 20 nm to 500 nm.

[0012] Optionally, in other embodiments of the present application, the adhesive includes at least one of an acrylate copolymer adhesive, an acrylonitrile copolymer adhesive, a polyvinyl alcohol adhesive, a polyacrylamide adhesive, or a polyurethane adhesive.

[0013] Optionally, in other embodiments of the present application, the mass ratio of the secondary microspheres to the binder is from 3:1 to 15:1.

[0014] Optionally, in other embodiments of the present application, the substrate includes a porous substrate, and the porous substrate includes at least one of a polyolefin substrate, a polyethylene terephthalate substrate, a polyimide substrate, or a polyvinylidene fluoride substrate.

[0015] Optionally, in other embodiments of the present application, the thickness of the porous substrate is from 4 μm to 19 μm.

[0016] Optionally, in other embodiments of the present application, the porosity of the porous substrate is from 30% to 60%.

[0017] Optionally, in other embodiments of the present application, the substrate includes a heat-resistant coating, and the heat-resistant coating is disposed on at least one surface of the porous substrate.

[0018] Optionally, in other embodiments of the present application, the material of the heat-resistant coating includes at least one of alumina, boehmite, zirconium oxide, silicon dioxide, aluminum hydroxide, magnesium hydroxide, cellulose, aramid or polyimide.

[0019] Optionally, in other embodiments of the present application, the thickness of the heat-resistant coating is from 0.6 μm to 4 μm.

[0020] Optionally, in other embodiments of the present application, the coverage area of ​​the adhesive layer on the surface of the substrate is from 5% to 90%.

[0021] Optionally, in other embodiments of the present application, the adhesive is spread flat on the surface of the substrate.

[0022] Optionally, in other embodiments of the present application, the binder is coated on the surface of or between the secondary microspheres.

[0023] Optionally, in other embodiments of the present application, the adhesive layer is provided on one side or both sides of the substrate.

[0024] Optionally, in other embodiments of the present application, the coating density of the adhesive layer is from 0.1 g / m 2 to 2g / m 2 .

[0025] Optionally, in other embodiments of the present application, at 95° C. and a pressure ranging from 1 MPa to 4 MPa, the compression rate of the bonding layer is from 20% to 95%.

[0026] According to the secondary battery in the second embodiment of the present application, it includes a positive electrode, a negative electrode, an electrolyte and a separator, and the separator is the separator described above. Beneficial effects:

[0027] 1) The bonding layer of the present application comprises secondary microspheres, which are formed by agglomeration of multiple primary particles. There are gaps between the primary particles, which is conducive to the transmission of lithium ions.

[0028] 2) Since the secondary microspheres have a hollow structure, the adhesive layer undergoes compression deformation during hot pressing. Under a smaller hot pressing pressure, the secondary microspheres can undergo irreversible deformation, which makes the adhesive layer less likely to block the substrate. At the same time, the smaller shaping pressure can ensure that the pores of the diaphragm substrate do not change, the membrane permeability value increment is smaller, and the membrane impedance increment is smaller.

[0029] 3) Since hollow secondary microspheres are used in the bonding layer, under the same shaping and hot pressing conditions, the coating thickness compression rate is greater, and the overall thickness of the diaphragm is thinner after hot pressing, which is beneficial to improving the battery energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0031] FIG1 is a cross-sectional morphology diagram of the first microsphere according to an embodiment of the present application.

[0032] Implementation Methods of the Application

[0033] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0034] The present application provides a separator and a secondary battery. These are described in detail below. It should be noted that the order in which the following embodiments are described does not limit the preferred order of the embodiments.

[0035] The present invention provides a separator comprising a substrate and a bonding layer disposed on at least one surface of the substrate. The bonding layer comprises secondary microspheres and a binder. The secondary microspheres comprise a plurality of primary particles, at least some of which have a hollow structure. A cross-sectional morphology of the secondary microspheres is shown in Figure 1.

[0036] Secondary microspheres are formed by the aggregation of multiple primary particles. There are gaps between the primary particles, which is conducive to the transmission of lithium ions. The secondary microspheres with a hollow structure formed by the aggregation of primary particles make the secondary microspheres more fluffy and have a relatively smaller specific gravity. At the same time, due to the hollow secondary microspheres in the bonding layer, the bonding layer can be deformed more during hot pressing, which is conducive to reducing the thickness of the diaphragm after hot pressing and improving the energy density of the battery. In addition, the design of the hollow secondary microspheres makes the pores of the diaphragm substrate less blocked after hot pressing, the increase in the diaphragm permeability value after hot pressing is smaller, the increase in the diaphragm impedance is smaller, and the battery impedance is lower.

[0037] The bonding layer comprises secondary microspheres and a binder. The binder is applied flatly to the substrate surface and / or coated on or between the secondary microspheres. The bonding layer can be applied to one or both sides of the substrate. After hot pressing and shaping during battery manufacturing, the bonding layer forms a bond between the separator and the electrodes, ensuring a good bonding interface between the separator and the electrodes.

[0038] In some embodiments of the present application, the primary particles include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethyl methacrylate, or acrylate copolymer derivatives.

[0039] In some embodiments of the present application, the particle size of the secondary microspheres ranges from 4 μm to 15 μm, for example, it can be 4 μm, 6 μm, 9 μm, 11 μm, 12 μm, 13 μm, 15 μm or a range consisting of any two values ​​therein. In some embodiments of the present application, the particle size of the secondary microspheres can be from 4 μm to 10 μm. In some embodiments of the present application, the particle size of the secondary microspheres can be from 5 μm to 8 μm. The particle size of the secondary microspheres is within the above range, which can ensure that the residual thickness of the bonding layer of the diaphragm after hot pressing is appropriate, which is beneficial to reducing the internal resistance of the battery. Not only that, it is also beneficial to the construction of hollow secondary microspheres.

[0040] In some embodiments of the present application, the secondary microspheres include a spherical shell formed by primary particles, and the thickness of the spherical shell of the secondary microspheres ranges from 0.6 μm to 5 μm, for example, it can be 0.6 μm, 3 μm, 4 μm, 5 μm or a range consisting of any two values ​​therein. In some embodiments of the present application, the thickness of the spherical shell of the secondary microspheres can be from 1 μm to 5 μm. In some embodiments of the present application, the thickness of the spherical shell of the secondary microspheres can be from 2 μm to 5 μm. The spherical shell thickness is within the above range to ensure that the first microspheres can be compressed and deformed without excessive pressure during hot pressing of the diaphragm, thereby reducing the risk of compression deformation of the diaphragm substrate.

[0041] In some embodiments of the present application, the particle size of the primary particles is from 20nm to 500nm, for example, it can be 50nm, 150nm, 250nm, 350nm, 450nm or a range consisting of any two values ​​therein. In some embodiments of the present application, the particle size of the primary particles can be from 100nm to 400nm. In some embodiments of the present application, the particle size of the primary particles can be from 200nm to 300nm. When the hollow secondary microspheres composed of primary particles are applied to the diaphragm bonding layer, the shaping pressure required for the diaphragm to reach the target compression thickness by hot pressing is smaller, which is beneficial to reduce the damage to the pores of the diaphragm substrate caused by the shaping; and the hollow secondary microspheres composed of primary particles have a smaller degree of blockage on the diaphragm substrate after being compressed and deformed, which is more conducive to the transmission of lithium ions and reduces battery impedance. The particle size of the primary particles is within the above range, ensuring that a better hollow structure of the secondary microspheres can be formed.

[0042] In some embodiments of the present application, the bonding layer 1 further includes a binder, which includes a compound containing at least one of C=O, -CN, -OH, -COOH, -COOLi, -COONa, -CONH-, or -NHCOO-. The inclusion of polar functional groups in the binder's molecular structure helps enhance the intermolecular polar forces between the separator and the electrode surface, thereby improving the bonding strength between the separator and the electrode.

[0043] In some embodiments of the present application, the adhesive includes at least one of an acrylate copolymer adhesive, an acrylonitrile copolymer adhesive, a polyvinyl alcohol adhesive, a polyacrylamide adhesive, or a polyurethane adhesive.

[0044] In some embodiments of the present application, the mass ratio of the secondary microspheres to the binder is from 3:1 to 15:1, for example, it can be 4:1, 7:1, 8:1, 11:1, 12:1, 13:1 or a range consisting of any two values ​​therein. In some embodiments of the present application, the mass ratio of the secondary microspheres to the binder can be from 5:1 to 10:1. In some embodiments of the present application, the mass ratio of the secondary microspheres to the binder can be from 6:1 to 9:1. When the mass of the secondary microspheres to the binder is within the above range, the adhesive layer has good adhesion to the surface of the substrate, is not easy to fall off, and is not easy to block the ion transmission channel.

[0045] In some embodiments of the present application, the substrate includes a porous substrate, and the porous substrate includes at least one of a polyolefin substrate, a polyethylene terephthalate substrate, a polyimide substrate, or a polyvinylidene fluoride substrate.

[0046] In some embodiments of the present application, the thickness of the porous substrate ranges from 4 μm to 19 μm, for example, 6 μm, 7 μm, 8 μm, 12 μm, 13 μm, 16 μm, or a range consisting of any two values ​​thereof. In some embodiments of the present application, the thickness of the porous substrate ranges from 5 μm to 18 μm. In some embodiments of the present application, the thickness of the porous substrate ranges from 10 μm to 15 μm. When the thickness of the porous substrate is within the above range, the porous substrate has good mechanical properties.

[0047] In some embodiments of the present application, the porosity of the porous substrate is from 30% to 60%, for example, 35%, 45%, 55%, or a range consisting of any two values ​​thereof. In some embodiments of the present application, the porosity of the porous substrate is from 40% to 50%. The porosity of the porous substrate within the above range controls the number of lithium ions passing through the separator per unit time, thereby affecting the rapid charge and discharge capability of the battery.

[0048] In some embodiments of the present application, the substrate includes a heat-resistant coating disposed on at least one surface of the porous substrate. The heat-resistant coating is made of at least one of alumina, boehmite, zirconium oxide, silicon dioxide, aluminum hydroxide, magnesium hydroxide, cellulose, aramid, or polyimide. The heat-resistant coating can improve the substrate's high-temperature resistance.

[0049] In some embodiments of the present application, the thickness of the heat-resistant coating ranges from 0.6 μm to 4 μm, for example, 0.8 μm, 1.5 μm, 2.5 μm, 3.5 μm, or a range consisting of any two values ​​thereof. In some embodiments of the present application, the thickness of the heat-resistant coating ranges from 0.7 μm to 3 μm. In some embodiments of the present application, the thickness of the heat-resistant coating ranges from 1 μm to 2 μm.

[0050] In some embodiments of the present application, the coverage area of ​​the adhesive layer on the surface of the substrate ranges from 5% to 90%, for example, 30%, 40%, 50%, 60%, or a range consisting of any two of these values. In some embodiments of the present application, the coverage area of ​​the adhesive layer on the surface of the substrate can range from 10% to 80%. In some embodiments of the present application, the coverage area of ​​the adhesive layer on the surface of the substrate can also range from 20% to 70%. The coverage rate of the adhesive layer on the substrate surface within the above range is beneficial to the bonding strength of the adhesive layer and helps reduce ion transport resistance.

[0051] In some embodiments of the present application, the coating density of the adhesive layer is from 0.1 g / m 2 to 2g / m 2 , for example, it can be 0.2g / m 2 , 0.8g / m 2 , 1.3g / m 2 , 1.6g / m 2 , 2g / m 2 Or a range consisting of any two values ​​thereof. In some embodiments of the present application, the coating surface density of the adhesive layer can be from 0.5 g / m 2 to 1.8g / m 2 In some embodiments of the present application, the coating density of the adhesive layer can also be from 1g / m 2 to 1.5g / m 2 The coating surface density is positively correlated with the coverage area of ​​the adhesive layer on the substrate surface. Hollow secondary microspheres help reduce the specific gravity of the material. When providing the same adhesive layer coating thickness, the coating surface density of the adhesive layer is lighter and can achieve the same level of bonding strength.

[0052] In some embodiments of the present application, at 95°C and a pressure of 1 MPa to 4 MPa, the compression rate of the adhesive layer can be from 20% to 95%, from 30% to 90%, or from 50% to 80%. The adhesive layer of the present application comprises hollow secondary microspheres composed of a plurality of primary particles, which have a greater compression rate under the same shaping and hot pressing conditions.

[0053] Accordingly, an embodiment of the present application provides a method for preparing a diaphragm, the method for preparing a diaphragm comprising: forming a substrate and an adhesive layer separately; transferring the adhesive layer to at least one surface of the substrate; wherein the adhesive layer comprises secondary microspheres, and the method for preparing the secondary microspheres comprises: mixing a polymer emulsion with a gas, passing the mixture into a high-pressure pump, and atomizing and drying the mixture to obtain secondary microspheres; the polymer comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethacrylate or acrylate copolymer derivatives.

[0054] In some embodiments of the present application, the gas includes at least one of carbon dioxide or nitrogen.

[0055] In some embodiments of the present application, the adhesive layer is transferred to at least one surface of the diaphragm substrate by any one of micro-gravure roller coating, spin spray coating, dip coating or doctor blade coating.

[0056] In practice, the hollow polymer secondary microspheres are obtained by spray drying a polymer emulsion. Prior to spray drying, the polymer emulsion is mixed with an inert gas (carbon dioxide or nitrogen) and then fed into a high-pressure pump. The gas is intensely compressed by the high-pressure pump and then mixed with the polymer emulsion through a mixer before entering a spray tower. At the moment the emulsion is atomized, the droplets enter the drying tower, where they are affected by the high-temperature airflow, causing the vapor pressure inside the droplets to increase instantaneously and causing the particles to expand, resulting in a hollow structure in the resulting dried polymer secondary microspheres.

[0057] An embodiment of the present application further provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator. The separator is the above-mentioned separator or the separator prepared by the above-mentioned preparation method.

[0058] Specifically, the negative electrode material used in the negative electrode can be at least one of artificial graphite, natural graphite, mesophase carbon microbeads, amorphous carbon, lithium titanate or silicon-carbon alloy.

[0059] Specifically, the type of positive electrode active material used in the positive electrode is not particularly limited, as long as it can electrochemically absorb and release metal ions (e.g., lithium ions). In some embodiments of the present application, the positive electrode active material includes at least one of lithium iron phosphate (LFP), lithium manganese oxide (LMO), or a ternary material.

[0060] In some embodiments of the present application, the bonding force between the separator and the positive electrode is greater than or equal to 2.6 N / m.

[0061] In some embodiments of the present application, the bonding force between the separator and the positive electrode is greater than or equal to 3.0 N / m.

[0062] In some embodiments of the present application, the bonding force between the separator and the positive electrode is greater than or equal to 3.2 N / m.

[0063] In some embodiments of the present application, the bonding force between the separator and the positive electrode is greater than or equal to 3.5 N / m.

[0064] In some embodiments of the present application, the bonding force between the separator and the positive electrode is greater than or equal to 3.8 N / m.

[0065] In some embodiments of the present application, the bonding force between the separator and the positive electrode is greater than or equal to 4.0 N / m.

[0066] In some embodiments of the present application, the bonding force between the separator and the negative electrode is greater than or equal to 1.1 N / m.

[0067] In some embodiments of the present application, the bonding force between the separator and the negative electrode is greater than or equal to 1.3 N / m.

[0068] In some embodiments of the present application, the bonding force between the separator and the negative electrode is greater than or equal to 1.5 N / m.

[0069] In some embodiments of the present application, the bonding force between the separator and the negative electrode is greater than or equal to 1.8 N / m.

[0070] In some embodiments of the present application, the bonding force between the separator and the negative electrode is greater than or equal to 2.0 N / m.

[0071] The present invention also provides an electrical device comprising the above-mentioned battery. The electrical device of the present invention includes, but is not limited to, a backup power supply, a motor, an electric car, an electric motorcycle, a power-assisted bicycle, a bicycle, an electric tool, a large household battery, and the like.

[0072] The following describes the details in conjunction with specific embodiments.

[0073] Example 1

[0074] The present embodiment provides a method for preparing a diaphragm, comprising the following steps:

[0075] 1) Coating substrate selection: A polypropylene porous polymer substrate with a thickness of 16 μm and a porosity of 40% was selected;

[0076] 2) Coating Material Preparation: A polyvinylidene fluoride-hexafluoropropylene copolymer emulsion with a particle size of 650 nm and a solid content of 30% was spray-dried. The high-pressure pump pressure was controlled at 0.2 MPa, and the polymer emulsion to nitrogen flow ratio was 4:1. The emulsion was sprayed into a drying tower at 160°C. After spray drying, a hollow polyvinylidene fluoride-hexafluoropropylene secondary microsphere powder was obtained. The prepared secondary microspheres had an average particle size of 18 μm and a shell thickness of 8 μm.

[0077] 3) Preparation of coating slurry: 3.30 kg of pure water and 23.00 kg of LA133 (15% solids) were added to a stirring tank and stirred for 15 minutes. 6.90 kg of the hollow polyvinylidene fluoride-hexafluoropropylene powder prepared in 2) was added and stirred for 20 minutes. Another 44.80 kg of water was added and stirred for 90 minutes before discharging the mixture to obtain the coating slurry.

[0078] 4) Diaphragm coating: Select the substrate in 1) and adjust the spray flow and spray speed of the sprayer to coat the adhesive layer on each side of the substrate with a density of 3g / m 2Through the slurry formula design in 3), the mass ratio of secondary microspheres to adhesive LA133 in the coated bonding layer is 2:1.

[0079] Preparation of negative electrode sheet:

[0080] Graphite, the negative electrode active material, conductive agent (SP), sodium carboxymethyl cellulose (CMC), and binder (SBR) are mixed in deionized water at a ratio of 96:1:1:2 to form a uniform slurry. The prepared negative electrode slurry is coated on both sides of copper foil and baked to dry. The coated electrode is then cold-pressed, slit, and cut to obtain lithium-ion battery negative electrode sheets.

[0081] Preparation of positive electrode:

[0082] The positive electrode active material (NCM523), conductive agent (SP), and binder PVDF were mixed and stirred in N-methylpyrrolidone (NMP) at a mass ratio of 98:1:1 to form a positive electrode slurry. The prepared slurry was evenly coated on both sides of aluminum foil and baked to dry. The coated electrode was then cold pressed, slit, and cut to obtain positive electrode sheets.

[0083] Preparation of electrolyte:

[0084] The preparation method of the electrolyte comprises the following steps:

[0085] Lithium hexafluorophosphate is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate to prepare an electrolyte, wherein the mass ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1.2:1.9:0.9; the mass percentage of lithium hexafluorophosphate in the electrolyte is 12.8%.

[0086] Preparation of lithium-ion batteries:

[0087] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets. The bare battery cell is obtained by winding, hot pressing and shaping, and the tabs are welded. The bare battery cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The prepared electrolyte is injected into the dried battery, allowed to stand, formed, and divided to complete the preparation of the lithium-ion soft-pack battery.

[0088] The preparation methods of the remaining examples and comparative examples refer to Example 1, with the differences shown in Table 1.

[0089] Table 1

[0090] The performance tests of the diaphragms obtained in the examples and comparative examples were performed, and the test methods included:

[0091] The separators obtained from the Examples and Comparative Examples were laminated with positive and negative electrode sheets in a hot pressing test at a pressure of 2 MPa, a temperature of 95°C, and a time of 60 seconds. The compression ratio of the adhesive layer of the separators obtained from the Examples and Comparative Examples after hot pressing, the increase in the permeability of the separators before and after hot pressing, the increase in the impedance of the separators, and the bond strength between the separators and the electrodes were evaluated.

[0092] Bonding layer compression test: A micrometer is used to measure the initial thickness of the freshly coated separator, h0, along with the corresponding separator substrate thickness, h, positive electrode thickness, m, and negative electrode thickness, n. A positive electrode layer, a separator layer, and a negative electrode layer are laminated and hot-pressed. The total thickness of the positive electrode, separator, and negative electrode unit after hot-pressing is measured, s. Separator bond coating compression = 1 - (smnh) / (h0 - h).

[0093] The incremental permeability value of the separator before and after hot pressing is measured using a Gurley tester to measure the initial permeability value (G0) of a freshly coated film. A positive electrode, a separator, and a negative electrode are laminated and hot pressed. The separator is removed from the hot-pressed positive electrode + separator + negative electrode unit and the permeability value (G1) is measured using a Gurley tester. The incremental permeability value of the separator before and after hot pressing = G1 - G0. Gurley tester parameters: 20-ounce internal air cylinder, 1.0 square-inch round hole, 100cc of air.

[0094] Diaphragm impedance growth: A positive electrode layer, a separator layer, and a negative electrode layer were laminated and hot-pressed. The separator was removed from the hot-pressed positive electrode + separator + negative electrode unit to fabricate and test symmetrical cells. The symmetrical cells were assembled using a copper foil + blue glue + separator + copper foil structure. The blue glue was punched with a 12mm diameter circular hole in the center (the actual effective area for lithium ions to pass through). The number of separator layers was designed to be 1, 2, 3, or 4. Three parallel symmetrical cells were fabricated under each separator layer. After drying, the cells were filled with liquid and encapsulated. The impedance of the symmetrical cells was measured using an electrochemical workstation at test frequencies ranging from 3 MHz to 200 MHz. The impedance values ​​obtained from the symmetrical cells with 1, 2, 3, and 4 separator layers were linearly fitted, and the slope of the line was defined as the separator impedance. The impedance of the freshly coated separator before hot pressing was measured as R0, and the impedance of the separator after hot pressing was measured as R1. The impedance growth rate = (R1-R0) / R0.

[0095] Diaphragm and electrode bonding strength: A layer of diaphragm and a layer of electrode are laminated and hot pressed. The hot-pressed electrode + diaphragm unit is cut into 50mm wide strips. An electronic tensile testing machine is used to perform a 180° glass test on the diaphragm and electrode on the strips to obtain the bonding strength between the diaphragm and the electrode.

[0096] The test results are shown in Table 2:

[0097] Table 2

[0098] From the comparison between Examples 1 to 22 and Comparative Example 1, it can be seen that when the diaphragm contains secondary microspheres with a hollow structure, hollow secondary microspheres formed by primary particles are used. During hot pressing, the adhesive layer undergoes compression deformation, and the hollow secondary microspheres can undergo irreversible deformation under a smaller hot pressing pressure. The adhesive layer has a smaller degree of blockage of the substrate. At the same time, the smaller shaping pressure can ensure that the pores of the diaphragm substrate do not change, the diaphragm permeability value increment is smaller, and the diaphragm impedance increment is smaller.

[0099] Comparing Example 16 and Comparative Example 2, the primary particles of Example 16 and Comparative Example 2 are both selected from acrylate copolymers, the bonding layer of Example 16 adopts hollow secondary microspheres, and the bonding layer of Comparative Example 2 adopts non-hollow secondary microspheres. The incremental air permeability value of Example 16 before and after hot pressing is significantly reduced, and the impedance growth rate decreases, indicating that the performance of the diaphragm using hollow secondary microspheres in the bonding layer is better than that using non-hollow secondary microspheres.

[0100] The present application provides hollow secondary microspheres composed of primary particles. The presence of gaps between the primary particles on the surface of the sphere shell facilitates lithium ion transport. The hollow secondary microspheres allow for greater deformation of the adhesive layer during hot pressing, which helps reduce the thickness of the diaphragm after hot pressing and improves battery energy density. The design of the hollow secondary microspheres minimizes blockage of the pores in the diaphragm substrate after hot pressing, thereby reducing the impedance of the lithium-ion battery.

[0101] The above is a detailed introduction to a diaphragm and a secondary battery provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the idea of ​​the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A diaphragm, wherein: The invention comprises a substrate and a bonding layer arranged on at least one surface of the substrate, wherein the bonding layer comprises secondary microspheres and a bonding agent, the secondary microspheres comprise a plurality of primary particles, and at least part of the secondary microspheres have a hollow structure.

2. The diaphragm according to claim 1, wherein: The primary particles include at least one of polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethyl methacrylate, or an acrylate copolymer derivative.

3. The diaphragm according to claim 1, wherein The particle size of the secondary microspheres ranges from 4 μm to 15 μm.

4. The diaphragm according to claim 1, wherein The shell thickness of the secondary microspheres ranges from 0.6 μm to 5 μm.

5. The diaphragm according to claim 1, wherein The particle size of the primary particles ranges from 20 nm to 500 nm.

6. The diaphragm according to claim 1, wherein The adhesive comprises at least one of an acrylic copolymer adhesive, an acrylonitrile copolymer adhesive, a polyvinyl alcohol adhesive, a polyacrylamide adhesive or a polyurethane adhesive.

7. The diaphragm according to claim 1, wherein The mass ratio of the secondary microspheres to the binder is from 3:1 to 15:

1.

8. The diaphragm according to claim 1, wherein The substrate comprises a porous substrate, and the porous substrate comprises at least one of a polyolefin substrate, a polyethylene terephthalate substrate, a polyimide substrate or a polyvinylidene fluoride substrate.

9. The diaphragm according to claim 8, wherein The thickness of the porous substrate is from 4 μm to 19 μm.

10. The diaphragm according to claim 8, wherein The porosity of the porous substrate is from 30% to 60%.

11. The diaphragm according to claim 8, wherein The substrate comprises a heat-resistant coating, and the heat-resistant coating is disposed on at least one surface of the porous substrate.

12. The diaphragm according to claim 11, wherein The material of the heat-resistant coating includes at least one of alumina, boehmite, zirconium oxide, silicon dioxide, aluminum hydroxide, magnesium hydroxide, cellulose, aramid or polyimide.

13. The diaphragm according to claim 11, wherein The thickness of the heat-resistant coating ranges from 0.6 μm to 4 μm.

14. The diaphragm according to claim 1, wherein The coverage area of ​​the adhesive layer on the surface of the substrate is from 5% to 90%.

15. The diaphragm according to claim 1, wherein The adhesive is spread on the surface of the substrate.

16. The diaphragm according to claim 1, wherein The binder is coated on the surface or between the secondary microspheres.

17. The diaphragm according to claim 1, wherein The adhesive layer is disposed on one side or both sides of the substrate.

18. The diaphragm according to claim 1, wherein The coating surface density of the bonding layer is from 0.1 g / m 2 To 2g / m 2 .

19. The diaphragm according to claim 1, wherein At 95° C. and pressures ranging from 1 MPa to 4 MPa, the compression rate of the bonding layer ranges from 20% to 95%.

20. A secondary battery, wherein: The invention comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the separator is the separator according to any one of claims 1 to 19.

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