Diaphragm, method for manufacturing the same, secondary battery, and electric device

Abstract

The application provides a diaphragm and a preparation method thereof, a secondary battery and an electric device, wherein the diaphragm comprises a base film and a ceramic coating arranged on at least one surface of the base film, the ceramic coating comprises a binder and inorganic particles, and the swelling degree of the diaphragm is 0.1% to 6% after being soaked in an organic solvent for 24 hours, the organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate, and the mass ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate in the mixed solvent is 2:2:1. The diaphragm has the characteristics of good thermal stability, low impedance and ceramic coating not easy to fall off, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of secondary battery separators, specifically to a separator and its preparation method, a secondary battery, and electrical equipment. Background Technology

[0002] The separator provides ion transport channels and isolates the positive and negative electrodes to prevent physical contact short circuits. Currently used ceramic separators experience significant dimensional shrinkage under high temperatures, making them prone to severe fire and explosion failures during overcharging, short circuits, or heating, thus failing to meet battery safety requirements. Furthermore, the ceramic layer is prone to detachment during battery winding, stacking, or immersion in electrolyte, posing a significant safety risk. Additionally, the binder components in the ceramic layer swell after being dissolved in the electrolyte, resulting in high impedance that cannot meet battery power requirements.

[0003] Therefore, it is necessary to provide a separator to meet the safety and power requirements of batteries. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor reliability of the diaphragm in the prior art, thereby providing a diaphragm and its preparation method, a secondary battery and an electrical device.

[0005] A first aspect of the present invention provides a diaphragm comprising a base membrane and a ceramic coating disposed on at least one surface of the base membrane, the ceramic coating comprising an adhesive and inorganic particles, and the diaphragm having a swelling degree of 0.1% to 6% after being immersed in an organic solvent for 24 hours, wherein the organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate, wherein the mass ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate in the mixed solvent is 2:2:1.

[0006] Optionally, the swelling degree of the adhesive after soaking in an organic solvent for 24 hours is 5% to 200%.

[0007] Optionally, the glass transition temperature of the adhesive is 40℃~180℃.

[0008] Optionally, the peel strength of the ceramic coating is 15 N / m to 35 N / m.

[0009] Optionally, the longitudinal thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is T1%, where 0 ≤ T1 ≤ 0.7.

[0010] Optionally, the lateral thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is T2%, where 0 ≤ T2 ≤ 0.6.

[0011] Optionally, the diaphragm impedance is less than or equal to 0.9 ohms.

[0012] Optionally, the membrane conductivity is 1 ms / cm to 1.6 ms / cm.

[0013] Optionally, the adhesive comprises one or more of the following: acrylate polymers, styrene-acrylic polymers, styrene-butadiene polymers, polyurethane-modified acrylate polymers, epoxy polymers, or acrylamide-modified acrylate polymers containing hydrophilic groups, wherein the hydrophilic groups include -COO. - NH4 + -COO - Na + -COO - Li + -COO - K + -SO3 - NH4 + -SO3 - Na + -SO3 - Li + and -SO3 - K + At least one of them.

[0014] Optionally, the inorganic particles include at least one of silicon dioxide, aluminum oxide, boehmite, zirconium oxide, titanium dioxide, barium sulfate, and calcium sulfate.

[0015] A second aspect of the present invention provides a method for preparing a diaphragm, comprising the following steps: coating a slurry comprising inorganic particles and a binder prepolymer onto at least one side of a base membrane, and then crosslinking and curing the diaphragm to obtain the diaphragm.

[0016] Optionally, the binder prepolymer includes crosslinking functional groups, which include at least one of carbon-carbon unsaturated bonds, siloxane groups, and isocyanate groups.

[0017] Optionally, the number average molecular weight of the binder prepolymer is 1000~20000.

[0018] A third aspect of the present invention provides a secondary battery comprising the aforementioned separator or a separator prepared by the aforementioned preparation method.

[0019] A fourth aspect of the present invention provides an electrical device including the aforementioned secondary battery.

[0020] The technical solution of the present invention can produce the following beneficial effects:

[0021] The diaphragm of the present invention includes a base membrane and a ceramic coating disposed on the base membrane. The ceramic coating includes a binder and inorganic particles. When the diaphragm is heated, the ceramic coating provides strong support to the base membrane, the diaphragm undergoes small dimensional changes when heated, and the thermal safety performance of the diaphragm is improved. At the same time, the diaphragm has a small degree of swelling in organic solvents, and its structure is not easy to collapse when it is eroded by organic solvents, resulting in a small overall impedance of the diaphragm. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of this disclosure and are not intended to limit this disclosure.

[0023] Figure 1 This is a schematic diagram of the diaphragm structure according to an embodiment of the present invention;

[0024] Figure 2 This is a partial enlarged view of the ceramic coating in the diaphragm according to an embodiment of the present invention;

[0025] Figure 3 This is a flowchart of a method for preparing a diaphragm according to an embodiment of the present invention;

[0026] Figure 4 This is a flowchart of a slurry preparation method according to an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1-Base film; 2-Ceramic coating; 3-Inorganic particles; 4-Binder; 41-Binder molecular skeleton; 42-Binder crosslinking point. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] See Figure 1 and Figure 2One or more embodiments of the present invention provide a diaphragm, comprising a base membrane 1 and a ceramic coating 2 disposed on at least one surface of the base membrane 1. The ceramic coating 2 comprises an adhesive 4 having a cross-linked network structure and inorganic particles 3 dispersed in the cross-linked network structure. The diaphragm has a swelling degree of 0.1% to 6% after being immersed in an organic solvent for 24 hours. The organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate, wherein the mass ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate in the mixed solvent is 2:2:1.

[0032] The diaphragm provided in this embodiment of the invention includes a base membrane and a ceramic coating disposed on the base membrane. The ceramic coating includes a binder and inorganic particles. When the diaphragm is heated, the ceramic coating provides strong support to the base membrane, the diaphragm undergoes small dimensional changes when heated, the thermal safety performance of the diaphragm is improved, and the diaphragm has a small degree of swelling in organic solvents, resulting in a small overall impedance.

[0033] In some embodiments, the method for testing the swelling degree of the diaphragm includes the following steps: cutting the diaphragm into 10mm*10mm samples and weighing them as m0; immersing the cut diaphragm in a solvent system of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (the mass ratio of ethylene carbonate, dimethyl carbonate, and diethyl carbonate is 2:2:1) for 10 minutes, then removing it and wiping off the free solvent on the surface with lint-free paper, weighing the sample at this point as m1; further immersing the sample in the solvent system of ethylene carbonate, dimethyl carbonate, and diethyl carbonate and letting it stand for 24 hours, then removing it and wiping off the surface solvent, and then weighing the sample at this point as m2. Diaphragm swelling degree = (m2-m1) / m0.

[0034] Specifically, the material of the base film 1 includes, but is not limited to, any one of polyethylene, polyethylene and polypropylene composite, polyimide nonwoven fabric, and polyester nonwoven fabric.

[0035] Specifically, binder 4 can be generated from the crosslinking reaction of the binder prepolymer. See also Figure 2 In some embodiments, the binder prepolymer forms binder crosslinking points 42 through a crosslinking reaction of self-crosslinkable groups, and the molecular chains of the binder prepolymer form the binder molecular backbone 41 of the binder 4. The inorganic particles 3 are located in the grid surrounded by the binder crosslinking points 42 and the binder molecular backbone 41.

[0036] It is understandable that the binder 4 is formed from a binder prepolymer that can undergo a self-crosslinking reaction, which makes the size of the grid surrounded by the binder crosslinking points 42 and the binder molecular skeleton 41 more uniform. This is beneficial to enhance the uniform dispersion of inorganic particles 3 in the binder 4. The binder 4 surrounds the inorganic particles 3 and constrains the position of the inorganic particles 3, thus effectively fixing the inorganic particles 3 and improving the reliability of the membrane.

[0037] In some embodiments, the adhesive comprises one or more of the following: acrylate polymers, styrene-acrylic polymers, styrene-butadiene polymers, polyurethane-modified acrylate polymers, epoxy polymers, or acrylamide-modified acrylate polymers containing hydrophilic groups, wherein the hydrophilic groups include -COO. - NH4 + -COO - Na + -COO - Li + -COO - K + -SO3 - NH4 + -SO3 - Na + -SO3 - Li + and -SO3 - K + At least one of them.

[0038] It is understandable that since the binder 4 includes hydrophilic groups, which are highly polar, they can form strong intermolecular forces with the hydroxyl groups on the surface of the inorganic particles 3, thereby enhancing the adhesion between the inorganic particles 3 and the binder 4.

[0039] In some embodiments, the swelling degree of the adhesive after soaking in an organic solvent for 24 hours is 5% to 200%. Exemplarily, the swelling degree of the adhesive after soaking in an organic solvent for 24 hours can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, or a range consisting of any two of the above values. This reduces the impedance of the diaphragm.

[0040] In some embodiments, the method for testing the swelling degree of the adhesive includes the following steps: the adhesive is introduced into a mold and dried at 100°C to form a film with a thickness of 1 mm; the film is cut into 2 mm * 2 mm size films and weighed with a balance to measure the initial weight M0; the films are immersed in a solvent system of ethylene carbonate, dimethyl carbonate and diethyl carbonate (the mass ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate is 2:2:1) at 25°C for 24 h, and then removed and weighed again to measure the weight M1; the swelling degree = M1 / M0 * 100%.

[0041] In some embodiments, the glass transition temperature of the adhesive is 40°C to 180°C. For example, the glass transition temperature of the adhesive can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, or a range consisting of any two of the above values. The test method for the glass transition temperature refers to "GB / T 40396-2021 Test Method for Glass Transition Temperature of Polymer-Based Composite Materials".

[0042] In some embodiments, the inorganic particles include at least one of silicon dioxide, aluminum oxide, boehmite, zirconium oxide, titanium dioxide, barium sulfate, and calcium sulfate.

[0043] In some embodiments, the peel strength of the ceramic coating is 15 N / m to 35 N / m. For example, the peel strength of the ceramic coating is 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, or a range consisting of any two of the above values.

[0044] In some embodiments, the longitudinal thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is T1%, where 0 ≤ T1 ≤ 0.7. For example, the longitudinal thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or a range consisting of any two of the above values.

[0045] In some embodiments, the lateral thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is T2%, where 0 ≤ T2 ≤ 0.6. For example, the lateral thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or a range consisting of any two of the above values.

[0046] In some embodiments, the diaphragm impedance is less than or equal to 0.9 ohms. Exemplarily, the diaphragm impedance is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or a range consisting of any two of the above values.

[0047] In some embodiments, the membrane conductivity is 1 ms / cm to 1.6 ms / cm. For example, the membrane resistivity is 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or a range consisting of any two of the above values.

[0048] The present invention also provides a method for preparing a diaphragm, comprising the following steps: coating a slurry comprising inorganic particles and a binder prepolymer onto at least one side of a base membrane, and then crosslinking and curing to obtain a diaphragm.

[0049] For details, see Figure 3 The method for preparing the diaphragm according to an embodiment of the present invention includes the following steps:

[0050] Step S1: Provide the base film and slurry;

[0051] Step S2: Coat at least one surface of the base membrane with a slurry comprising inorganic particles and binder prepolymer, and cure to form a diaphragm.

[0052] Specifically, in step S2, the base film is first placed on a coating machine; the prepared slurry is transferred to the slurry storage tank of the coating machine, and the slurry is coated onto one or both sides of the base film by dip coating or microgravure roller coating; the base film coated with slurry is transferred to a sealed oven via the guide rollers of the coating machine, where it is heated to cure the slurry on the surface of the base film while removing the solvent. During the curing process of the slurry on the surface of the base film, the binder prepolymer in the slurry on the surface of the base film undergoes a cross-linking reaction, thereby forming a ceramic coating. In other embodiments, after removing the solvent from the slurry on the surface of the base film, the base film coated with slurry is irradiated with an ultraviolet lamp to cure the slurry on the surface of the base film. During the curing process of the slurry on the surface of the base film, the binder prepolymer in the slurry on the surface of the base film undergoes a cross-linking reaction, thereby forming a ceramic coating.

[0053] In some embodiments, the curing time of the slurry on the surface of the base film is 10s to 600s, for example, 10s, 20s, 50s, 80s, 100s, 150s, 200s, 250s, 300s, 350s, 400s, 450s, 500s, 500s, or 600s; the curing temperature is 25℃ to 100℃, for example, 40℃, 45℃, 50℃, 60℃, 70℃, 80℃, 90℃, 95℃, or 100℃. It is understood that when the binder prepolymer of the slurry on the surface of the base film undergoes a self-crosslinking reaction under heating conditions, heating is maintained throughout the curing process; when the binder prepolymer of the slurry on the surface of the base film undergoes a self-crosslinking reaction under light irradiation, heating is stopped during ultraviolet lamp irradiation.

[0054] Specifically, the slurry includes inorganic particles, binder prepolymers, and solvents.

[0055] Specifically, after curing, the slurry on the surface of the base film forms a ceramic coating with a mesh structure, in which inorganic particles fill the mesh.

[0056] In some embodiments, the adhesive prepolymer includes a crosslinking functional group, which includes at least one of carbon-carbon unsaturated bonds, siloxane groups, and isocyanate groups. Preferably, the adhesive prepolymer includes only one of the above-mentioned crosslinking functional groups, which is capable of undergoing a self-crosslinking reaction.

[0057] This invention employs a crosslinkable binder prepolymer to prepare a ceramic coating for a diaphragm, resulting in a ceramic coating with a network structure. This network structure is formed by the crosslinking reaction of the binder prepolymer. The binder molecules in the network structure are bound by the crosslinking points, making the network structure stable. Therefore, the stable structure of the ceramic coating is less prone to deformation at high temperatures, resulting in minimal diaphragm dimensional changes and high heat resistance. Secondly, the network structure is formed by the crosslinking reaction of the binder prepolymer, thus ensuring stable chemical properties and low swelling. Thirdly, the binder prepolymer includes crosslinking functional groups capable of self-crosslinking, allowing the use of a single binder prepolymer. This results in a more uniform distribution of the binder prepolymer in the slurry, leading to good mesh size uniformity and a more stable network structure. The network structure exhibits good thermal and chemical stability, ensuring good adhesion between the ceramic coating and the base membrane. The mesh structure exhibits good uniformity in mesh size, allowing inorganic particles to be evenly dispersed within it. The mesh structure surrounds and constrains the position of the inorganic particles, effectively fixing them and enhancing their contribution to the thermal stability of the diaphragm. In summary, this improves the reliability of the diaphragm.

[0058] It is understood that the number of self-crosslinkable groups in the adhesive prepolymer of the present invention embodiments is one or more, and the present invention embodiments do not impose specific limitations on this.

[0059] The adhesive prepolymer includes acrylate prepolymers, styrene-acrylic prepolymers, styrene-butadiene prepolymers, polyurethane-modified acrylate prepolymers, epoxy prepolymers, or acrylamide-modified acrylate prepolymers.

[0060] In some embodiments, the number-average molecular weight of the adhesive prepolymer is 1,000 to 20,000. For example, the number-average molecular weight of the adhesive prepolymer can be 1,000, 3,000, 6,000, 8,000, 10,000, 12,000, 15,000, 18,000, 20,000, or a range consisting of any two of the above values.

[0061] Specifically, the number average molecular weight of the carbon-carbon unsaturated bond modified crosslinked adhesive prepolymer is 1000~18000, preferably 6000; the number average molecular weight of the siloxane-modified polyurethane crosslinked adhesive prepolymer is 1500~20000, preferably 8000; the number average molecular weight of the siloxane-modified acrylate copolymer crosslinked self-adhesive prepolymer is 1000~16000, preferably 5000; and the number average molecular weight of the isocyanate group modified crosslinked adhesive prepolymer is 2000~20000, preferably 10000.

[0062] In some embodiments, the inorganic particles include silicon dioxide, aluminum oxide, boehmite, zirconium oxide, titanium dioxide, barium sulfate, or calcium sulfate.

[0063] In some embodiments, the size of the inorganic particles is 0.01 μm to 3 μm. For example, the size of the inorganic particles is 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a range consisting of any two of the above values.

[0064] In some embodiments, the slurry further includes a dispersant and an initiator, or the slurry further includes a dispersant and a catalyst.

[0065] The dispersant contains at least one of sodium carboxymethyl cellulose, polyacrylamide, and sodium polyacrylate.

[0066] The initiator includes photoinitiators or thermal initiators; the photoinitiator is selected from any one of aromatic ketone initiators, polycyclic aromatic hydrocarbon initiators, polysiloxane initiators, acylphosphonate initiators, azo initiators, and organometallic complex initiators; the thermal initiator is selected from any one of azo initiators, organic peroxide initiators, and diacyl peroxide initiators. The catalyst includes at least one of tertiary amine catalysts, imidazole catalysts, boron trifluoride complex catalysts, and organotin catalysts.

[0067] In some embodiments, when the self-crosslinking groups of the binder prepolymer contain carbon-carbon unsaturated groups, the slurry further includes an initiator, which includes a photoinitiator or a thermal initiator. The photoinitiator includes at least one of aromatic ketone initiators, polycyclic aromatic hydrocarbon initiators, polysiloxane initiators, acylphosphonate initiators, azo initiators, and organometallic complex initiators; the thermal initiator includes at least one of azo initiators, organic peroxide initiators, and diacyl peroxide initiators.

[0068] In some embodiments, when the self-crosslinkable groups of the binder prepolymer include epoxy groups, the slurry further includes a dispersant or a first catalyst. The first catalyst includes at least one of tertiary amine catalysts, imidazole catalysts, and boron trifluoride complex catalysts.

[0069] In some embodiments, when the self-crosslinkable groups of the binder prepolymer include siloxane groups, hydroxymethylamide groups, or hydroxyethylamide groups, it is not necessary to add an initiator or catalyst.

[0070] In some embodiments, when the self-crosslinking groups of the binder prepolymer include isocyanate groups, the slurry further includes a dispersant and a second catalyst. The second catalyst includes an organotin catalyst.

[0071] See Figure 4 The slurry preparation method includes the following steps: Step S211, adding inorganic particles and dispersant to a mixing tank and performing a first stirring treatment on the inorganic particles and dispersant; Step S212, after performing the first stirring treatment, adding solvent to the mixing tank and performing a second stirring treatment; Step S213, after performing the second stirring treatment, adding binder prepolymer and initiator to the mixing tank and performing a third stirring treatment, or, after performing the second stirring treatment, adding binder prepolymer and catalyst to the mixing tank and then performing a third stirring treatment.

[0072] In some embodiments, the binder prepolymer is a binder prepolymer emulsion, and the process of adding the binder prepolymer to the mixing tank is as follows: adding the binder prepolymer emulsion to the mixing tank.

[0073] Specifically, inorganic particles and a dispersant are added to a mixing tank and continuously stirred to ensure uniform mixing. Next, a solvent is added to the mixing tank and stirring continues to ensure uniform distribution of the inorganic particles in the solvent under the action of the dispersant. The solvent may include, but is not limited to, deionized water, and may be a single solvent or a mixture of solvents; this embodiment of the invention does not impose specific limitations on this. Finally, a binder prepolymer and an initiator are added to the mixing tank and stirring continues to ensure uniform distribution of the binder prepolymer and initiator in the slurry. Alternatively, a binder prepolymer and a catalyst are added to the mixing tank and stirring continues to ensure uniform distribution of the binder prepolymer and catalyst in the slurry, thereby forming a slurry.

[0074] In some embodiments, the binder prepolymer further includes hydrophilic groups, including -COO groups. - NH4 + -COO - Na + -COO - Li + -COO - K+ -SO3 - NH4 + -SO3 - Na + -SO3 - Li + and -SO3 - K + At least one of the following. It is understood that the number of hydrophilic groups in the adhesive prepolymer of the embodiments of the present invention can be one or more, and the embodiments of the present invention do not impose specific limitations on this, as long as the adhesive prepolymer has a hydrophilic emulsifying effect. It should be noted that the hydrophilic groups do not participate in the crosslinking reaction.

[0075] In some embodiments, the slurry further includes a curing agent, which is added to the mixing tank after the second mixing treatment and before the third mixing treatment.

[0076] In some embodiments, during the third stirring process, nitrogen gas is introduced into the stirring tank to prevent the binder prepolymer and / or initiator from coming into contact with air, to prevent the binder prepolymer and / or initiator from being oxidized by the oxygen component in the air, and to avoid insufficient crosslinking reaction of the binder prepolymer.

[0077] The mixing speeds of the first, second, and third mixing processes may be the same or different, and / or the mixing times of the first, second, and third mixing processes may be the same or different. The mixing speed and / or mixing time may be adjusted according to the actual condition of the slurry. For example, during the first mixing process, the mixing speed may be 200 rpm to 600 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, or 600 rpm; the mixing time may be 10 min to 60 min, such as 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min. For example, during the second mixing process, the mixing speed is 600 rpm to 2000 rpm, for example, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, or 2000 rpm; the duration of the second mixing process is 20 min to 80 min, for example, 20 min, 40 min, 60 min, or 80 min. Similarly, during the third mixing process, the mixing speed is 100 rpm to 300 rpm, for example, 100 rpm, 120 rpm, 150 rpm, 180 rpm, 200 rpm, 220 rpm, 250 rpm, 280 rpm, or 300 rpm; the duration of the third mixing process is 10 min to 30 min, for example, 10 min, 15 min, 20 min, 25 min, or 30 min.

[0078] Because the slurry is continuously stirred at high speed during preparation, and because the slurry has a high viscosity, a large number of air bubbles are inevitably generated during the preparation process. These air bubbles are detrimental to the uniform distribution of the binder prepolymer in the slurry. Therefore, in some embodiments, after the third stirring treatment, the slurry is defoamed.

[0079] In some embodiments, defoaming is performed using low-speed stirring, with a stirring speed of 50 rpm to 100 rpm. For example, the stirring speed may be 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, or 100 rpm. The stirring time for defoaming is 60 min to 180 min, for example, 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, or 180 min. During the defoaming process, the low stirring speed allows air bubbles at the bottom of the slurry to rise to the surface and be eliminated under atmospheric pressure, thus improving the uniformity of the final ceramic coating. The stirring direction during the defoaming process may be the same as or different from the stirring direction of the first, second, or third stirring processes described above.

[0080] In some embodiments, the solid content of the slurry is 10% to 50%. The solid content of the slurry is expressed as the mass percentage of the binder prepolymer and inorganic particles in the slurry. For example, the solid content of the slurry is 10%, 12%, 15%, 20%, 25%, 28%, 30%, 35%, 40%, 45%, or 50%.

[0081] In some embodiments, the thickness of the ceramic coating is 0.5 μm to 6 μm. For example, the thickness of the ceramic coating is 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm.

[0082] In some embodiments, the mass of the mesh structure in the ceramic coating is 1% to 12% of the mass of the inorganic particles. For example, the mass of the mesh structure is 1%, 3%, 3.2%, 3.8%, 4%, 4.2%, 4.7%, 5%, 6%, 8%, 9%, 10%, or 12% of the mass of the inorganic particles.

[0083] In some embodiments, the mass of the dispersant in the ceramic coating is 0.1% to 5% of the mass of the inorganic particles. For example, the mass of the dispersant is 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5% of the mass of the inorganic particles.

[0084] In some embodiments, the initiator in the ceramic coating is 0.001% to 1% of the mass of the inorganic particles; or, the catalyst in the ceramic coating is 0.001% to 1% of the mass of the inorganic particles. Exemplarily, the initiator is 0.001%, 0.005%, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, or 1% of the mass of the inorganic particles. Exemplarily, the catalyst is 0.001%, 0.005%, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, or 1% of the mass of the inorganic particles.

[0085] In some embodiments, the thickness of the base membrane is 3μm to 30μm. For example, the thickness of the base membrane is 3μm, 5μm, 8μm, 10μm, 15μm, 18μm, 20μm, 25μm, or 30μm. The porosity of the base membrane is 30% to 80%. For example, the porosity of the base membrane is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%. The air permeability of the base membrane is less than or equal to 400s / 100cc. In this application, the air permeability of the base membrane is measured using a testing instrument, which is the time required for a certain amount of air to pass through the diaphragm under a certain pressure and test area. For example, under a pressure of 1.22KPa and a test area of ​​1in... 2 The time required for 100cc of air to pass through the diaphragm in a test area of ​​(square inches).

[0086] Furthermore, one or more embodiments of the present invention also provide a secondary battery, including the aforementioned separator or a separator prepared by the aforementioned preparation method.

[0087] It is understood that the secondary battery provided in the embodiments of the present invention includes the aforementioned separator, and thus can produce the same beneficial effects as the aforementioned separator, which will not be repeated here.

[0088] Furthermore, one or more embodiments of the present invention also provide an electrical device including the aforementioned secondary battery. The electrical device includes, but is not limited to, electric vehicles and energy storage devices.

[0089] The inventive concept of the present invention will be described below with reference to specific embodiments.

[0090] Example 1

[0091] This embodiment provides a diaphragm, such as Figure 1 and Figure 2As shown, the membrane includes a base membrane 1 and a ceramic coating 2 disposed on at least one surface of the base membrane 1. The ceramic coating 2 includes a binder 4 having a cross-linked network structure and inorganic particles 3 dispersed in the cross-linked network structure. The binder 4 has a swelling degree of 68% and a glass transition temperature of 102°C after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours. The membrane has a swelling degree of 1.5% after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours.

[0092] The method for preparing the above-mentioned diaphragm includes the following steps:

[0093] Add 10.0g of 20% sodium carboxymethyl cellulose (CMC) solution and 450.0g of boehmite ceramic powder to a mixing tank, and stir at 400rpm for 10min at 25℃. Then, add 500.0g of water and stir at 1300rpm for 60min. The slurry is then passed through a grinder twice. After grinding, add 75.0g (30% by mass) of double-bond-terminated acrylate-modified polyurethane prepolymer latex with a number average molecular weight of 6000 and 0.6g of photoinitiator. Continue stirring at 150rpm for 30min under nitrogen protection. Then, stir at 80rpm for 120min to defoam and discharge the material. A polyethylene base film is provided, with a thickness of 7 μm, a porosity of 36%, and an air permeability of 160 s / 100 cc. The prepared slurry is coated on one side of the base film with a coating thickness controlled at 3 μm. After coating, the diaphragm is baked in an oven at 80°C for 5 min and then subjected to ultraviolet curing treatment to finally obtain the diaphragm.

[0094]

[0095] Schematic diagram of double-bond-terminated acrylate-modified polyurethane prepolymer (-R1-, -R2- are omitted polymers).

[0096] Example 2

[0097] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 1 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 16% and a glass transition temperature of 162°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 0.3%.

[0098] The difference between the above-mentioned method for preparing the diaphragm and the method described in Example 1 is that: after grinding, 56.3g (40% by mass) of double-bond-terminated acrylate-modified polyurethane prepolymer latex with a number average molecular weight of 1000 is added.

[0099] Example 3

[0100] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 1 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 180% and a glass transition temperature of 41°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 4.1%.

[0101] The difference between the above-mentioned method for preparing the diaphragm and the method described in Example 1 is that: after grinding, 90.0 g (25% by mass) of double-bond-terminated acrylate-modified polyurethane prepolymer latex with a number-average molecular weight of 18,000 is added.

[0102] Example 4

[0103] This embodiment provides a diaphragm, such as Figure 1 and Figure 2 As shown, the membrane includes a base membrane 1 and a ceramic coating 2 disposed on at least one surface of the base membrane 1. The ceramic coating 2 includes a binder 4 having a cross-linked network structure and inorganic particles 3 dispersed in the cross-linked network structure. The binder 4 has a swelling degree of 25% and a glass transition temperature of 126°C after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours. The membrane has a swelling degree of 0.45% after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours.

[0104] The method for preparing the diaphragm described in this embodiment includes the following steps:

[0105] 10.0 g of 20% CMC solution and 450.0 g of boehmite ceramic powder were added to a mixing tank and stirred at 400 rpm for 10 min at 25 °C. Then, 500.0 g of water was added and stirred at 1300 rpm for 60 min. The slurry was then passed through a grinder twice. After grinding, 36.0 g (50% by mass) of siloxane-modified waterborne acrylate copolymer binder prepolymer with a number average molecular weight of 5000 was added, and stirring was continued at 150 rpm for 40 min. Then, stirring was carried out at 80 rpm for 120 min, followed by reverse stirring to defoam and discharge the material. A polyethylene base film with a thickness of 7 μm, a porosity of 36%, and an air permeability of 160 s / 100 cc was provided. The prepared slurry was coated onto one side of the base film using a gravure roller coating method, with a coating thickness controlled at 3 μm. After coating, the film was baked in a 90 °C oven for 5 min to obtain a diaphragm.

[0106]

[0107] A schematic diagram of the structure of a siloxane-modified aqueous acrylate copolymer adhesive prepolymer.

[0108] Example 5

[0109] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 4 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 16% and a glass transition temperature of 176°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 0.29%.

[0110] The difference between the above-mentioned method for preparing the diaphragm and the method described in Example 4 is that: after grinding, 30.0 g (60% by mass) of a siloxane-modified aqueous acrylate copolymer binder prepolymer with a number average molecular weight of 1000 is added.

[0111] Example 6

[0112] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 4 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 108% and a glass transition temperature of 52°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 1.9%.

[0113] The difference between the above-mentioned method for preparing the diaphragm and the method described in Example 4 is that: after grinding, 45.0 g (40% by mass) of a siloxane-modified aqueous acrylate copolymer binder prepolymer with a number average molecular weight of 16000 is added.

[0114] Example 7

[0115] This embodiment provides a diaphragm, such as Figure 1 and Figure 2 As shown, the membrane includes a base membrane 1 and a ceramic coating 2 disposed on at least one surface of the base membrane 1. The ceramic coating 2 includes a binder 4 having a cross-linked network structure and inorganic particles 3 dispersed in the cross-linked network structure. The binder 4 has a swelling degree of 32% and a glass transition temperature of 93°C after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours. The membrane has a swelling degree of 0.6% after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours.

[0116] The method for preparing the above-mentioned diaphragm includes the following steps:

[0117] 10.0 g of 20% CMC solution and 450.0 g of boehmite ceramic powder were added to a mixing tank and stirred at 400 rpm for 10 min at 25 °C. Then, 500.0 g of water was added and stirred at 1300 rpm for 60 min. The slurry was then passed through a grinder twice. After grinding, 40.0 g (50% by mass) of siloxane-modified polyurethane binder prepolymer with a number average molecular weight of 8000 was added, and stirring was continued at 150 rpm for 40 min. Then, stirring was carried out at 80 rpm for 120 min to defoam and discharge the material. A polyethylene base film with a thickness of 7 μm, a porosity of 36%, and an air permeability of 160 s / 100 cc was provided. The prepared slurry was coated on one side of the base film using a gravure roller coating method with a coating thickness controlled at 3 μm. After coating, the film was baked in a 90 °C oven for 5 min to obtain a diaphragm.

[0118]

[0119] A schematic diagram of the structure of a siloxane-modified polyurethane adhesive prepolymer (-R1-, -R2- are omitted polymers).

[0120] Example 8

[0121] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 7 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, exhibits a swelling degree of 8% and a glass transition temperature of 173°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, exhibits a swelling degree of 0.16%.

[0122] The difference between the above-mentioned method for preparing the diaphragm and the method described in Example 7 is that: after grinding, 33.3g (60% by mass) of a polyurethane binder prepolymer modified with siloxane with a number average molecular weight of 1500 is added.

[0123] Example 9

[0124] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 7 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, exhibits a swelling degree of 192% and a glass transition temperature of 49°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, exhibits a swelling degree of 3.8%.

[0125] The difference between the above-mentioned membrane preparation method and Example 7 is that: after grinding, 50.0g (40% by mass) of siloxane-modified polyurethane binder prepolymer with a number average molecular weight of 20,000 is added.

[0126] Example 10

[0127] This embodiment provides a diaphragm, such as Figure 1 and Figure 2 As shown, the membrane includes a base membrane 1 and a ceramic coating 2 disposed on at least one surface of the base membrane 1. The ceramic coating 2 includes a binder 4 having a cross-linked network structure and inorganic particles 3 dispersed in the cross-linked network structure. The binder 4 has a swelling degree of 136% and a glass transition temperature of 72°C after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours. The membrane has a swelling degree of 2.7% after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours.

[0128] The method for preparing the above-mentioned diaphragm includes the following steps:

[0129] Add 10.0g of 20% CMC solution and 450.0g of boehmite ceramic powder to a mixing tank, and stir at 400rpm for 10min at 25℃. Then, add 500.0g of water and stir at 1300rpm for 60min. The slurry is then passed through a grinder twice. After grinding, add 40.0g (50% by mass) of isocyanate-terminated polyurethane binder prepolymer emulsion with a number average molecular weight of 10000 and 2.0g of triethylenetetramine catalyst, and continue stirring at 150rpm for 40min. Then, stir at 80rpm for 120min to defoam and discharge the material. A polyethylene base film is provided, with a thickness of 7 μm, a porosity of 36%, and an air permeability of 160 s / 100 cc. The prepared slurry is coated on one side of the base film using a gravure roller coating method, with the coating thickness controlled at 3 μm. After coating, the film is baked in a 90℃ oven for 5 min to obtain a diaphragm.

[0130]

[0131] A schematic diagram of the structure of isocyanate group-terminated polyurethane adhesive prepolymer.

[0132] Example 11

[0133] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 10 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 12% and a glass transition temperature of 148°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, has a swelling degree of 0.24%.

[0134] The difference between the above-mentioned membrane preparation method and Example 10 is that: after grinding, 33.3g (60% by mass) of isocyanate group-terminated polyurethane binder prepolymer emulsion with a number average molecular weight of 2000 and 2.0g of triethylenetetramine catalyst are added.

[0135] Example 12

[0136] The difference between the diaphragm described in this embodiment and the diaphragm described in Example 10 is that the binder 4, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, exhibits a swelling degree of 198% and a glass transition temperature of 45°C. The diaphragm, after being immersed in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 hours, exhibits a swelling degree of 4.0%.

[0137] The difference between the above-mentioned preparation method of the diaphragm and that of Example 10 is that: after grinding, 50.0g (40% by mass) of isocyanate group-terminated polyurethane binder prepolymer emulsion with a number average molecular weight of 20,000 and 2.0g of triethylenetetramine catalyst are added.

[0138] Comparative Example 1

[0139] Add 2.0g of sodium polyacrylate dispersant, 10.0g of 20% CMC solution, and 450.0g of alumina ceramic powder to a mixing tank. Stir at 400rpm for 10min at 25℃. Add 500.0g of water and stir at 1300rpm for 60min. Then pass the slurry through a grinder twice. After grinding, add 90.0g of polyacrylate binder (50% by mass, glass transition temperature -38°C, swelling degree of 260% at 25°C for 24h), which is currently widely used in the market. Continue stirring at 150rpm for 30min. Then stir at 80rpm for 120min and reverse stirring to defoam and discharge the material. A polyethylene base film with a thickness of 7 μm, a porosity of 36%, and an air permeability of 160 s / 100 cc was provided. A prepared slurry was coated onto one side of the base film using a gravure roller coating method, with a coating thickness controlled at 3 μm. After coating, the film was baked in an oven at 80℃ for 5 min to obtain a diaphragm. The resulting diaphragm exhibited a swelling degree of 8.5% after immersion in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 h.

[0140] Comparative Example 2

[0141] Add 2.0g of sodium polyacrylate dispersant, 10.0g of 20% CMC solution, and 450.0g of boehmite ceramic powder to a mixing tank. Stir at 400rpm for 10min at 25℃. Add 500.0g of water and stir at 1300rpm for 60min. Then, pass the slurry through a grinder twice. After grinding, add 90.0g of polyacrylate binder (50% by mass, glass transition temperature -38°C, swelling degree of 260% at 25°C for 24h), which is widely used in the market. Continue stirring at 150rpm for 30min. Then, stir at 80rpm for 120min to defoam and discharge the material. A polypropylene base film with a thickness of 12 μm, a porosity of 40%, and an air permeability of 160 s / 100 cc was provided. The prepared slurry was coated onto one side of the base film using a gravure roller coating method, with a coating thickness controlled at 3 μm. After coating, the film was baked in an oven at 80℃ for 5 min to obtain a diaphragm. The diaphragm exhibited a swelling degree of 7.2% after immersion in a mixed solution of ethylene carbonate, dimethyl carbonate, and diethyl carbonate for 24 h.

[0142] test

[0143] The membranes prepared in Examples 1-12 and Comparative Examples 1-2 were tested for thickness, ceramic peeling force, thermal shrinkage, air permeability and ionic conductivity.

[0144] Thickness testing was conducted using a Marl thickness gauge. The average value of 32 test points was taken as the membrane thickness, and the results are recorded in Table 1.

[0145] The ceramic peel strength was tested using a universal electronic tensile testing machine. A 15mm wide 3M green adhesive was bonded to the surface of the membrane ceramic layer under a pressure of 0.1MPa. The green adhesive and the membrane were subjected to a 180° peel tensile test using a universal tensile testing machine. The tensile speed was 50mm / min and the tensile stroke was 100mm. The tensile strength under the stroke of 50mm-100mm was taken as the average value as the peel strength and recorded in Table 1.

[0146] Heat shrinkage tests were conducted on the samples at 100℃ for 1 hour, 130℃ for 1 hour, and 160℃ for 1 hour, measuring shrinkage in the machine direction (MD) and transverse direction (TD). Specifically, the release liner material was punched into standard dimensions of MD*TD = 100mm*50mm using a punching machine. The samples were then clamped at the top and bottom with A4 paper (without additional pressure) and placed in an oven (oven accuracy ±3℃). After baking, the samples were removed and the lengths of MD and TD were measured using a 2D image measuring instrument. The MD shrinkage rate was calculated as (100 - MD length after baking) / 100, and the TD shrinkage rate was calculated as (50 - MD length after baking) / 50. The data were recorded in Table 1.

[0147] Breathability was measured at a pressure of 1.22 kPa and a pressure of 1 inch. 2 The time required for 100cc of air to pass through the diaphragm in a test area of ​​(square inches) is recorded in Table 2.

[0148] The membrane impedance and ionic conductivity were tested by assembling symmetrical cells, including: (1) Fabrication and testing of symmetrical cells: The symmetrical cells were assembled using a structure of copper foil + blue glue + separator + copper foil. A 12mm diameter hole (the actual effective area through which lithium ions can pass) was punched in the center of the blue glue. The number of separator layers was designed to be 1, 2, 3, and 4 layers respectively. Three parallel samples of the symmetrical cells were made under each separator layer. After drying, the samples were injected with liquid and sealed. The impedance of the symmetrical cells was tested using an electrochemical workstation at a frequency of 3MHz to 200MHz. ② Membrane impedance: The impedance values ​​obtained from the tests of the symmetrical cells with 1, 2, 3, and 4 separator layers were linearly fitted. The slope of the straight line was defined as the membrane impedance. The data were recorded in Table 2.

[0149] A positive electrode sheet was prepared using NCM523 as the positive electrode active material, and a negative electrode sheet was prepared using graphite as the negative electrode active material. These were then wound with the separators from Examples 1-12 and Comparative Examples 1-2 to obtain a bare battery cell. The bare battery cell was placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery was obtained. The electrolyte used was 1M lithium hexafluorophosphate dissolved in ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mass ratio 2:2:1).

[0150] The assembled lithium-ion batteries were subjected to DC internal resistance, cycle testing, and thermal chamber safety tests. The test results are shown in Table 3. The methods for DC internal resistance, cycle testing, and thermal chamber safety testing are as follows:

[0151] DC internal resistance: The cell underwent three capacity tests in a 25℃ chamber, and the average capacity C0 (2.8-4.3V) was recorded. The cell was fully charged to 4.3V with a constant current and voltage of 1C0 (cutoff current 0.05C0). It was then allowed to stand for 10 minutes; after discharging with a 1C0 current for 30 minutes, it was allowed to stand for 10 minutes, and the cell was adjusted to 50% SOC; it was then further discharged with a 5C0 current for 10 seconds, and the voltages before and after discharge, U0 and U1, were recorded. DCR = (U0-U1) / 5C0.

[0152] Cycling: The battery cell was subjected to three capacity tests in a constant temperature room at 25℃, and the average capacity C0 was taken. The battery cell was charged to 4.3V with a constant current and constant voltage of 1C0, left to stand for 10 minutes, discharged to 2.8V, left to stand for 10 minutes, and the charge and discharge cycle test was continuously carried out. The charge and discharge capacity Cn of each cycle was recorded. The capacity retention rate = cycle discharge capacity Cn / initial capacity C0.

[0153] Hot box safety: The battery cell is heated from 25°C to 120°C in the hot box at a rate of 1°C / min with 100% SOC, and then left to stand for 10 minutes. It is then heated to 130°C at a rate of 1°C / min and left to stand for 10 minutes. It is then heated to 140°C at a rate of 1°C / min and left to stand for 10 minutes. This heating process is continued until the battery cell catches fire. The test is then stopped and the temperature at which the battery cell catches fire is recorded.

[0154] Referring to Table 1, based on the peel strength parameters of the ceramic coating, it can be determined that the ceramic formulation designed in this invention exhibits a significantly improved peel strength compared to ceramic formulations widely used in the market, thus effectively resisting coating detachment. Simultaneously, based on the thermal shrinkage rates in the MD and TD directions, it can be determined that the high-temperature heat resistance of the separator designed in this invention is also significantly improved (the thermal shrinkage rate is far lower than the industry average), which is beneficial for reducing battery safety.

[0155] Referring to Table 2, the membrane designed in this invention was tested for membrane impedance and ionic conductivity using a symmetrical cell. The test results show that the membrane's ionic conductivity is higher than that of membranes on the market. This is mainly because the binder in the slurry formulation of this invention uses a polymer prepolymer that can undergo a cross-linking reaction. After the ceramic coating is cured, the binder forms a cross-linked network structure, which is beneficial for resisting the erosion and swelling of organic solvents. The network structure with less swelling results in less clogging of the ceramic pores.

[0156] Referring to Table 3, the separator designed in this invention underwent battery-level performance testing. Because the separator solution provided by this invention has low impedance and high conductivity, the battery has lower DC internal resistance, and its cycle life is longer than that of conventional separators during cycle testing. Furthermore, because the separator provided by this invention has low thermal shrinkage and good heat resistance, its application in batteries significantly improves battery safety, resulting in a higher temperature at which the battery experiences thermal runaway and ignition during hot-box testing.

[0157] Table 1

[0158]

[0159] Table 2

[0160]

[0161] Table 3

[0162]

[0163] In the description of this specification, the references to terms such as "this embodiment," "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0164] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and simple improvements made on the substantive content of the present invention should be included within the protection scope of the present invention.

[0165] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A diaphragm, characterized in that, The membrane includes a base membrane and a ceramic coating disposed on at least one surface of the base membrane. The ceramic coating includes a binder having a cross-linked network structure and inorganic particles dispersed in the cross-linked network structure. The membrane has a swelling degree of 0.1% to 6% after being immersed in an organic solvent for 24 hours. The organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate, wherein the mass ratio of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in the mixed solvent is 2:2:

1. The adhesive comprises one or more of the following: acrylate polymers, styrene-acrylic polymers, styrene-butadiene polymers, polyurethane-modified acrylate polymers, epoxy polymers, or acrylamide-modified acrylate polymers containing hydrophilic groups, wherein the hydrophilic groups include -COO. - NH4 + -COO - Na + -COO - Li + -COO - K + -SO3 - NH4 + -SO3 - Na + -SO3 - Li + and -SO3 - K + At least one of them; The glass transition temperature of the adhesive is 40℃~180℃; The adhesive is formed from an adhesive prepolymer that can undergo a self-crosslinking reaction.

2. The diaphragm according to claim 1, characterized in that, The swelling degree of the adhesive after soaking in an organic solvent for 24 hours is 5% to 200%.

3. The diaphragm according to claim 1, characterized in that, The diaphragm satisfies at least one of the following conditions: (1) The peel strength of the ceramic coating is 15 N / m to 35 N / m; (2) The longitudinal thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is T1%, 0≤T1≤0.7; (3) The lateral thermal shrinkage rate of the diaphragm after standing at 100°C for 1 hour is T2%, 0≤T2≤0.6; (4) The diaphragm impedance is less than or equal to 0.9 ohms; (5) The membrane conductivity is 1 ms / cm~1.6 ms / cm.

4. The diaphragm according to claim 1, characterized in that, The inorganic particles include at least one of silicon dioxide, aluminum oxide, boehmite, zirconium oxide, titanium dioxide, barium sulfate, and calcium sulfate.

5. A method for preparing a diaphragm, used to prepare the diaphragm according to any one of claims 1 to 4, characterized in that, The process includes the following steps: coating a slurry comprising inorganic particles and a binder prepolymer onto at least one side of a base membrane, and then crosslinking and curing it to obtain the diaphragm.

6. The method for preparing the diaphragm according to claim 5, characterized in that, The binder prepolymer includes crosslinking functional groups, which include at least one of carbon-carbon unsaturated bonds, siloxane groups, and isocyanate groups.

7. The method for preparing the diaphragm according to claim 5, characterized in that, The number-average molecular weight of the binder prepolymer is 1000~20000.

8. A secondary battery, characterized in that, It includes the diaphragm according to any one of claims 1 to 4 or the diaphragm prepared by the preparation method according to any one of claims 5 to 7.

9. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 8.

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