Composite diaphragm and preparation method and application thereof

Abstract

The application relates to the technical field of batteries, in particular to a composite diaphragm and a preparation method and application thereof. The composite diaphragm comprises a base film and a first coating layer arranged on the negative electrode side surface of the base film; the first coating layer comprises a ceramic layer and a binder material, the first coating layer is provided with a porous structure; the coverage C1 of the binder material on the surface of the base film satisfies 5%<=C1<=8%; the coverage C2 of the porous structure on the surface of the base film satisfies 5%<=C2<=11%. In the composite diaphragm, the porous structure has a suitable coverage, can absorb part of the pressure during hot pressing, avoid stress concentration, reduce the rigid contact between the first coating layer and the diaphragm base, and reduce the local pressure; the binder material has a suitable coverage, can guarantee the performance of the first coating layer, and can guarantee the bonding effect and transfer effect of the first coating layer and the negative electrode sheet during hot pressing, and can effectively prevent powder dropping.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a composite separator, its preparation method, and its application. Background Technology

[0002] The rapid development and widespread application of new energy technologies have made lithium-ion batteries an indispensable part of modern life, and their safety is of paramount importance, especially in applications in the aviation and automotive sectors. If a lithium-ion battery experiences thermal runaway due to mechanical abuse, thermal abuse, or electrical abuse, the internal temperature rises, and the battery may suddenly release heat in the form of a fire or explosion, seriously affecting its safety.

[0003] As the insulating layer between the positive and negative electrodes, the separator is the first line of defense against internal short circuits in the battery cell. The most mature and widely used separator types are those that have been treated on the surface of a PP / PE base film, such as coating it with a heat-resistant inorganic coating, such as a ceramic layer, alumina, or boehmite, to enhance the heat resistance of the separator. The ceramic layer mainly serves as a skeletal support. However, since the base film of ceramic separators is mostly a polyolefin base film, it has a large thermal shrinkage rate at high temperatures, making it difficult for the ceramic layer to fully support the separator and prevent deformation. This can lead to direct contact between the positive and negative electrode materials, causing a short circuit and resulting in insufficient safety of the secondary battery.

[0004] To address this, existing methods achieve in-situ transfer of the separator coating to the surface of the positive electrode by hot-pressing it during battery assembly. However, the hot-pressing temperature, pressure, and time required in this process are usually quite high, which can cause significant damage to the electrode sheets in the electrode assembly. This can lead to the risk of material loss from the negative electrode sheet and problems such as lithium plating during the charging and discharging of the battery cell, affecting the cycle life and safety of the battery cell.

[0005] Therefore, developing a coating diaphragm that can prevent negative electrode material loss during the coating transfer process is an urgent problem to be solved in this field and is crucial for the application of high-safety coating transfer diaphragms.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] One object of the present invention is to provide a composite diaphragm that can ensure the transfer effect of the first coating during the hot pressing process and prevent powder shedding.

[0008] Another objective of this invention is to provide a simple and easy method for preparing a composite membrane.

[0009] Another object of the present invention is to provide a battery.

[0010] Another object of the present invention is to provide an electrical device.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0012] A composite separator includes a base membrane and a first coating located on the negative electrode side surface of the base membrane; the first coating comprises a ceramic layer and an adhesive material, and the first coating is provided with a porous structure; the coverage C1 of the adhesive material on the surface of the base membrane satisfies: 5%≤C1≤8%; the coverage C2 of the porous structure on the surface of the base membrane satisfies: 5%≤C2≤11%.

[0013] In some implementations, C1 and C2 satisfy: C1≤C2.

[0014] In some embodiments, the adhesive material is spherical in shape with a diameter of 3 to 5 μm.

[0015] In some embodiments, the monomers used to synthesize the adhesive material include at least one of acrylic monomers or styrene monomers.

[0016] In some embodiments, the porous structures are spaced apart in the first coating.

[0017] In some embodiments, the pore size of the porous structure is 1~3μm.

[0018] In some embodiments, the porous structure has a shape including at least one of a circle or a polygon.

[0019] In some embodiments, the ceramic layer comprises a ceramic material, which includes at least one of alumina, boehmite, magnesium hydroxide, barium sulfate, and silicon dioxide.

[0020] In some embodiments, the thickness of the ceramic layer is 1~2.5 μm.

[0021] In some embodiments, a second coating is provided on the positive electrode side surface of the composite separator, the second coating comprising a high-safety transfer coating and an adhesive coating, the high-safety transfer coating being located between the adhesive coating and the base membrane.

[0022] The method for preparing the composite membrane as described above includes the following steps:

[0023] The first coating is obtained by applying a mixed slurry of ceramic material and binder material to the negative electrode side surface of the base film using a gravure coating method and drying it.

[0024] In some embodiments, the gravure coating employs a gravure roller, which includes a body roller and protrusions disposed on the surface of the body roller. The protrusions include a plurality of spaced columnar protrusions, and the cross-section of the columnar protrusions includes at least one of circular or polygonal shapes. The height of the protrusions is 1 to 2.5 μm.

[0025] In some embodiments, the mixed slurry further includes an aqueous binder, a thickener, and a wetting agent.

[0026] In some embodiments, the mixed slurry further includes a solvent.

[0027] In some embodiments, the drying temperature is 55~80°C.

[0028] In some embodiments, the method further includes: sequentially preparing a high-safety transfer coating and an adhesive coating on the positive electrode side surface of the base film to obtain a second coating.

[0029] A battery includes the composite separator described above; a first coating of the composite separator faces the negative electrode and a second coating faces the positive electrode; the battery is obtained by stacking and hot-pressing the negative electrode, the composite separator, and the positive electrode, such that the first coating of the composite separator is transferred to the surface of the negative electrode and the second coating is transferred to the surface of the positive electrode.

[0030] An electrical device comprising the battery described above.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) In the composite diaphragm of the present invention, the porous structure in the first coating has a suitable coverage rate and can be used as a "pressure buffer cavity". During hot pressing, it can absorb part of the pressure through the pore compression to avoid stress concentration. At the same time, the porous structure can reduce the rigid contact between the first coating and the diaphragm substrate and reduce the local pressure. If the coverage rate of the porous structure is too high, it will affect the heat shrinkage resistance of the ceramic coating. The binder material has a suitable coverage rate. During the hot pressing process, the binder material melts and softens when heated. The porous structure reserved in the first coating can be used as a container to store the melted and softened large particles of binder, reducing the point contact between the large particles of binder and the negative electrode surface, and avoiding the negative electrode sheet from being over-bonded and causing the negative electrode material to fall off.

[0033] (2) The preparation method of the composite diaphragm of the present invention is simple and easy to implement. By using gravure coating, the coverage range of ceramic materials and porous structures in the first coating is controlled, thereby ensuring the performance of the composite diaphragm. When the composite diaphragm is hot-pressed, it can better absorb some of the pressure through the porous structure to avoid stress concentration, improve the transfer effect of the first coating, and effectively prevent powder shedding.

[0034] (3) The battery of the present invention has structural stability and safety performance. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a cross-sectional structural schematic diagram of the composite diaphragm with a first coating according to the present invention.

[0037] Figure 2 A cross-sectional view of the composite diaphragm having a first coating and a second coating according to the present invention;

[0038] Figure 3 This is a schematic diagram of the gravure roller structure;

[0039] Figure 4 This is a scanning electron microscope image of the first coating of the composite diaphragm.

[0040] Figure label:

[0041] 1-Base film, 2-First coating, 201-Ceramic layer, 202-Adhesive material, 203-Porous structure, 3-Second coating, 301-High-safety transfer coating, 302-Adhesive coating. Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0043] According to one aspect of the present invention, the present invention relates to a composite membrane, comprising a base membrane and a first coating located on the negative electrode side surface of the base membrane; the first coating comprises a ceramic layer and an adhesive material, the first coating having a porous structure; the coverage C1 of the adhesive material on the surface of the base membrane satisfies: 5% ≤ C1 ≤ 8%; the coverage C2 of the porous structure on the surface of the base membrane satisfies: 5% ≤ C2 ≤ 11%.

[0044] In the composite diaphragm of the present invention, the porous structure in the first coating has a suitable coverage (e.g., 5%, 5.5%, 6%, 7%, 8.5%, 8%, etc.), which can serve as a "pressure buffer chamber". During hot pressing, it can absorb part of the pressure through the pores, avoiding stress concentration. At the same time, the porous structure can reduce the rigid contact between the first coating and the diaphragm substrate, reducing local pressure. If the coverage of the porous structure is too high, it will affect the heat shrinkage resistance of the ceramic coating. The binder material has a suitable coverage (e.g., 5%, 6%, 7%, 8%, 9%, 10%, 11%, etc.). During the hot pressing process, the binder material melts and softens due to heat. The porous structure reserved in the first coating can serve as a container for storing the molten and softened large particles of binder, reducing point contact between the large particles of binder and the negative electrode surface, and avoiding the negative electrode sheet from being over-bonded and losing material.

[0045] It should be noted that the coverage rate of the adhesive material in this invention refers to the percentage of the total projected area of ​​the adhesive material on the base membrane surface to the area of ​​one side of the base membrane. The adhesive material coverage rate test specifically includes: photographing the first coating of the composite membrane sample using a scanning electron microscope, and then selecting the adhesive material for area statistics and calculation. Similarly, the coverage rate of the porous structure refers to the percentage of the projected area of ​​the porous structure on the base membrane surface to the area of ​​one side of the base membrane.

[0046] In some embodiments, C1 and C2 satisfy: C1 ≤ C2. This invention ensures that there is sufficient porous structure available for storing the molten, softened, large-particle binder during hot pressing, thereby preventing powder shedding from the negative electrode.

[0047] In some embodiments, the binder material is spherical in shape with a diameter of 3-5 μm, such as 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. The binder material of the present invention has a spherical structure, which is more conducive to dispersion during the coating process, ensures the uniformity of the coating, can better match the particle size of the negative electrode material, and ensures the stability of the coating after transfer.

[0048] In some embodiments, the monomers used to synthesize the adhesive material include at least one of acrylic monomers or styrene-acrylic monomers. The adhesive material obtained from the monomer materials of the present invention exhibits suitable swelling properties and better adhesion to ceramic and electrode materials.

[0049] In some embodiments, the porous structures are spaced apart in the first coating, for example, in an array. In some embodiments, the shape of the porous structures includes at least one of circular or polygonal (e.g., rectangular). In some embodiments, the pore size of the porous structures is 1~3μm, for example 1μm, 1.5μm, 2μm, 2.5μm, 3μm, etc. The porous structure of the present invention has a suitable pore size, which is more conducive to reducing the rigid contact between the first coating and the membrane substrate, reducing local pressure, ensuring the effect of pore compression absorbing part of the pressure during hot pressing, and avoiding stress concentration. If the pore diameter is too small, the pressure absorbed by pore compression during hot pressing is insufficient, and it cannot play an excellent role in preventing the negative electrode from falling off. If the pore size is too large, it will affect the heat shrinkage resistance of the ceramic coating.

[0050] In some embodiments, the ceramic layer comprises a ceramic material, which includes at least one of alumina, boehmite, magnesium hydroxide, barium sulfate, and silicon dioxide, such as a combination of boehmite and magnesium hydroxide, or a combination of magnesium hydroxide, barium sulfate, and silicon dioxide. A suitable ceramic material ensures the thermal stability and mechanical strength of the first coating.

[0051] In some embodiments, the thickness of the ceramic layer is 1~2.5μm, for example, 1μm, 1.5μm, 2μm, 2.5μm, etc. The suitable ceramic layer thickness of the present invention is more conducive to ensuring the thermal stability and puncture resistance of the first coating.

[0052] In some embodiments, a second coating is disposed on the positive electrode side surface of the composite separator. This second coating comprises a high-safety transfer coating and an adhesive coating, with the high-safety transfer coating located between the adhesive coating and the base membrane. The composition of the high-safety transfer coating and the adhesive coating can be found in patent application CN202410862041.5. In some embodiments, based on the total mass of the high-safety transfer coating material (100%), the high-safety transfer coating material comprises 70%-92% ceramic material, 3%-24% ion-conducting material, and 3%-6% adhesive. In some embodiments, based on the total mass of the adhesive coating material (100%), the adhesive coating material comprises 85%-95% adhesive material; and based on the total mass of the adhesive coating material (100%), the adhesive coating material further comprises 5%-10% other adhesive and 1.5%-5% other additives.

[0053] In some embodiments, the composition of the second coating involved in the various embodiments of the present invention specifically includes: based on the total mass of the high-safety transfer coating as 100%, the materials of the high-safety transfer coating include 82.54% by mass of alumina (particle size of 400 nm), 13% by mass of ion-conducting material, 4% by mass of polyacrylamide adhesive (glass transition temperature of 145°C), 0.4% by mass of polyethylene glycol dispersant, and 0.06% by mass of polyether wetting agent (purchased from Tianjin Cyprus Co., Ltd., brand name E1206). The ion-conducting material includes a combination of lithium aluminum titanium phosphate (LATP) and lithium-modified nanofibers (based on the total mass of lithium-modified nanofibers as 100%, the mass percentage of lithium element is 0.195%) in a mass ratio of 4:1.5. The lithium-modified nanofibers are formed by carboxylation and grafting treatment of natural cellulose, and are rod-shaped with a diameter of 10 nm and a length of 100 nm. Based on the total mass of the adhesive coating material as 100%, the adhesive coating material includes 90% by mass of polyvinylidene fluoride with a particle size of 200 nm and a glass transition temperature of -40 °C, 5% of acrylic emulsion adhesive, 2% sodium carboxymethyl cellulose thickener, and 3% of water-based aliphatic siloxane dispersant.

[0054] In some embodiments, the base film includes at least one of polyethylene and polypropylene, and has a thickness of 6-12 μm.

[0055] According to another aspect of the present invention, the present invention also relates to a method for preparing the composite separator as described above, comprising the following steps:

[0056] The first coating is obtained by applying a mixed slurry of ceramic material and binder material to the negative electrode side surface of the base film using a gravure coating method and drying it.

[0057] The method for preparing the composite diaphragm of the present invention is simple and easy to implement. By using gravure coating, the coverage range of ceramic materials and porous structures in the first coating layer is controlled, thereby ensuring the performance of the composite diaphragm. During hot pressing, the composite diaphragm can better absorb some of the pressure through the porous structure to avoid stress concentration, improve the transfer effect of the first coating layer, and effectively prevent powder shedding.

[0058] In some embodiments, the gravure coating employs a gravure roller, which includes a body roller and protrusions disposed on the surface of the body roller. The protrusions include a plurality of spaced-apart columnar protrusions, the cross-section of which includes at least one of circular or polygonal shapes; the height of the protrusions is 1~2.5 μm. In some embodiments, the columnar protrusions are spaced apart or regularly arranged. This invention achieves the distribution of pores in the first coating layer through gravure roller transfer coating. Utilizing the cell capacity of the micro-gravure roller to carry the slurry from the slurry box, the roller carrying the slurry contacts the base film, transferring the slurry to the surface of the base film. After drying, a composite separator is obtained. Figure 3 This is a schematic diagram of the roller's surface structure; the circular areas are protrusions extending from the roller's surface. Compared to a conventional 45° diagonal gravure roller, the height of the columnar protrusions is selected based on the thickness of the ceramic coating. The coverage of the porous structure can be adjusted by varying the total number and diameter of the columnar protrusions.

[0059] In some embodiments, the mixed slurry further includes an aqueous adhesive, a thickener, and a wetting agent. In some embodiments, the aqueous adhesive includes at least one of acrylic acid and styrene-butadiene rubber, and the thickener includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and sodium alginate. In some embodiments, the wetting agent includes at least one of polyvinyl alcohol, polysiloxane, silanol, sodium polyacrylate, and alkylphenol polyoxyethylene ether. In some embodiments, in the overall system of ceramic material, adhesive material, aqueous adhesive, thickener, and wetting agent, the mass content of the aqueous adhesive is 5% to 8% (e.g., 5%, 5.5%, 6%, 7%, or 8%), the mass content of the thickener is 0.3% to 0.7% (e.g., 0.3%, 0.4%, 0.5%, 0.6%, 0.7%), and the mass content of the wetting agent is 0.05% to 0.12% (e.g., 0.05%, 0.08%, 0.1%, 0.12%).

[0060] In some embodiments, the mixed slurry further includes a solvent, including water. In some embodiments, the solid content (by mass percentage) of the mixed slurry is 30% to 40%, for example, 30%, 35%, 37%, or 40%.

[0061] In some embodiments, the drying temperature is 55~80℃, for example, 55℃, 60℃, 70℃, or 80℃. In some embodiments, the process further includes: sequentially preparing a high-safety transfer coating and an adhesive coating on the positive electrode side surface of the base film to obtain a second coating. Specific preparation methods can be found in the preparation method of patent application CN202410862041.5.

[0062] In some embodiments, the preparation of the second coating (high-safety transfer coating and adhesive coating) involved in the various embodiments of the present invention can be carried out according to the method of Example 1 of patent application CN202410862041.5. The preparation of the second coating specifically includes: preparing a first slurry from the material of the high-safety transfer coating; preparing a second slurry from the material of the adhesive coating; and coating the first slurry onto the positive electrode side surface of the polyethylene-based membrane at a coating amount of 7.8 g / m³. 2 After drying, a high-safety transfer coating is obtained; a second slurry is then applied to the surface of the high-safety transfer coating at a dosage of 1 g / m². 2 After drying, an adhesive coating is obtained.

[0063] According to another aspect of the invention, the invention also relates to a battery comprising the composite separator described above; a first coating of the composite separator faces the negative electrode and a second coating faces the positive electrode.

[0064] The battery of the present invention has structural stability and safety performance.

[0065] In some embodiments, the battery is obtained by stacking and hot-pressing a negative electrode, the composite separator, and a positive electrode, thereby transferring a first coating from the composite separator to the surface of the negative electrode and a second coating to the surface of the positive electrode. In some embodiments, the hot-pressing temperature is 90~95°C, the surface pressure is 1.8~2.5MPa, and the time is 80~90s.

[0066] According to another aspect of the invention, the invention also relates to an electrical device comprising the aforementioned battery. The electrical devices of the invention include electric vehicles, power tools, medical devices, etc.

[0067] The following explanation, combined with specific embodiments and comparative examples, further illustrates the point.

[0068] The adhesive used in the various embodiments of the present invention is Shenzhen Haodian SWA709 grade spherical particle adhesive material.

[0069] Example 1

[0070] A composite membrane, such as Figure 1 and Figure 2 As shown, the system includes a base film 1, a first coating 2 located on the negative electrode side surface of the base film 1, and a second coating 3 located on the positive electrode side surface of the base film 1. The first coating 2 comprises a ceramic layer 201 and an adhesive material 202, and has a porous structure 203. The adhesive material 202 is spherical with a diameter D1 of 5 μm, and its coverage C1 on the surface of the base film 1 is 8%. The porous structure 203 has a coverage C2 of 10% on the surface of the base film 1, and its pore diameter is 3 μm. The ceramic layer 201 has a thickness of 2 μm, and the ceramic material is boehmite. A scanning electron microscope image of the first coating 2 is shown below. Figure 4 As shown. The second coating 3 includes a high-safety transfer coating 301 and an adhesive coating 302, with the high-safety transfer coating 301 located between the adhesive coating 302 and the base film 1. The base film material is polyethylene, with a thickness of 9 μm.

[0071] The method for preparing the composite diaphragm in this embodiment includes:

[0072] (1) Ceramic materials, large-particle binders, water-based adhesives, thickeners, wetting agents, and deionized water are mixed. The water-based adhesive is acrylic acid, the thickener is sodium carboxymethyl cellulose, and the wetting agents are polyvinyl alcohol and polysiloxane (mass ratio 1:1) to obtain a mixed slurry. The mass ratio of the effective components of ceramic materials: large-particle binders: water-based adhesives: thickeners: wetting agents is 83.4%: 10%: 6%: 0.5%: 0.1%. The amount of deionized water added ensures that the solid content Wt of the mixed slurry meets the requirement of 35%.

[0073] (2) The mixed slurry is coated onto the negative electrode side surface of the base film 1 by a gravure roller to obtain the first coating 2.

[0074] (3) A high-safety transfer coating 301 and an adhesive coating 302 are sequentially prepared on the positive electrode side surface of the base film 1 to obtain the second coating 3.

[0075] Example 2

[0076] A composite diaphragm differs from that of Example 1 in that:

[0077] The binder material 202 has a diameter of 3 μm and a coverage rate C1 of 5%. The porous structure 203 has a coverage rate C2 of 8% on the surface of the base film 1 and a pore diameter of 1 μm.

[0078] The effective component mass ratio of ceramic material, large particle binder, water-based adhesive, thickener, and wetting agent is 85.9%, 7.5%, 6%, 0.5%, and 0.1%, respectively. The addition of deionized water ensures that the solid content (Wt) of the mixed slurry meets the requirement of 35%.

[0079] Example 3

[0080] A composite diaphragm differs from that of Example 1 in that:

[0081] The pore diameter is 0.5 μm.

[0082] Example 4

[0083] A composite diaphragm differs from that of Example 1 in that:

[0084] The pore diameter is 4μm.

[0085] Example 5

[0086] A composite diaphragm differs from that of Example 1 in that:

[0087] The coverage of the porous structure 203 on the surface of the base film 1, C2, is 7%.

[0088] Example 6

[0089] A composite diaphragm differs from that of Example 1 in that:

[0090] The coverage of the porous structure 203 on the surface of the base film 1, C2, is 10%.

[0091] Comparative Example 1

[0092] A composite diaphragm differs from that of Example 1 in that:

[0093] No pore structure is incorporated. The conventional method is used for co-coating large ceramic particles.

[0094] Comparative Example 2

[0095] A composite diaphragm differs from that of Example 1 in that:

[0096] The coverage rate C1 of the adhesive material 202 on the surface of the base film 1 is 4%; the coverage rate C2 of the porous structure 203 on the surface of the base film 1 is 3%.

[0097] The effective component mass ratio of ceramic material, large particle binder, water-based adhesive, thickener, and wetting agent is 88.4%, 5%, 6%, 0.5%, and 0.1%, respectively. The addition of deionized water ensures that the slurry solids content (Wt) meets the requirement of 35%.

[0098] Comparative Example 3

[0099] A composite diaphragm differs from that of Example 1 in that:

[0100] The coverage rate (C1) of the adhesive material 202 on the surface of the base film 1 is 9%; the coverage rate (C2) of the porous structure 203 on the surface of the base film 1 is 12%. Because the coverage rate of the pores in the ceramic coating is too high, it will affect the heat shrinkage resistance of the ceramic coating, making it unsuitable for application.

[0101] Ceramic materials: large particle binders: water-based adhesives: thickeners: wetting agents. The effective ingredient ratios are 81.4%: 12%: 6%: 0.5%: 0.1%. The addition of deionized water ensures the slurry solids content (Wt) meets the requirement of 35%.

[0102] Experimental Example

[0103] The composite separators of each embodiment and comparative example were stacked with the positive and negative electrode sheets, respectively, with the first coating of the composite separator facing the negative electrode sheet and the second coating facing the positive electrode sheet. Then, they were hot-pressed using a flat plate at a temperature of 90°C, a surface pressure of 2 MPa, and a time of 80 seconds. After disassembly, the amount of material loss from the negative electrode sheet was recorded.

[0104] The test results are shown in Table 1.

[0105] Table 1 Test Results

[0106]

[0107] As shown in Table 1, the composite separators of the various embodiments of the present invention face the negative electrode during the stacking process. During the hot pressing of the separator, the first coating structure can buffer the pressure, disperse the stress, reduce the overpressure problem caused by excessive local pressure, and effectively weaken or prevent the negative electrode from shedding powder.

[0108] The composite separator in Comparative Example 1 could not effectively alleviate local pressure during the hot pressing process of battery preparation, resulting in severe powder shedding from the negative electrode.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite diaphragm, characterized in that, The system includes a base film and a first coating located on the negative electrode side surface of the base film; the first coating comprises a ceramic layer and an adhesive material, and the first coating has a porous structure; the coverage C1 of the adhesive material on the surface of the base film satisfies: 5% ≤ C1 ≤ 8%; the coverage C2 of the porous structure on the surface of the base film satisfies: 5% ≤ C2 ≤ 11%. The condition C1 and C2 satisfy: C1≤C2.

2. The composite diaphragm according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The shape of the adhesive material includes spheres with a diameter of 3~5μm; (2) The monomers of the adhesive material include at least one of acrylic monomers or styrene monomers.

3. The composite diaphragm according to claim 1, characterized in that, It includes at least one of the following features (1) to (3): (1) The porous structure is distributed at intervals in the first coating; (2) The pore size of the porous structure is 1~3μm; (3) The shape of the porous structure includes at least one of a circle or a polygon.

4. The composite diaphragm according to claim 1, characterized in that, It includes at least one of the following features (1) to (2): (1) The ceramic layer contains a ceramic material, which includes at least one of alumina, boehmite, magnesium hydroxide, barium sulfate and silicon dioxide; (2) The thickness of the ceramic layer is 1~2.5μm.

5. The composite diaphragm according to claim 1, characterized in that, The positive electrode side surface of the composite separator is provided with a second coating, the second coating including a high-safety transfer coating and an adhesive coating, the high-safety transfer coating being located between the adhesive coating and the base membrane.

6. The method for preparing the composite separator according to any one of claims 1 to 5, characterized in that, Includes the following steps: The first coating is obtained by applying a mixed slurry containing ceramic materials and binder materials to the negative electrode side surface of the base film using a gravure coating method and drying it.

7. The method for preparing the composite diaphragm according to claim 6, characterized in that, It includes at least one of the following features (1) to (5): (1) The gravure coating uses a gravure roller, which includes a body roller and a protrusion disposed on the surface of the body roller. The protrusion includes a plurality of columnar protrusions distributed at intervals. The cross-section of the columnar protrusion includes at least one of a circle or a polygon. The height of the protrusion is 1~2.5μm. (2) The mixed slurry also includes a water-based binder, a thickener, and a wetting agent; (3) The mixed slurry also includes a solvent; (4) The drying temperature is 55~80℃; (5) It also includes: preparing a high-safety transfer coating and an adhesive coating sequentially on the positive electrode side surface of the base film to obtain a second coating.

8. A battery, characterized in that, The composite separator comprises any one of claims 1 to 5; the first coating of the composite separator faces the negative electrode and the second coating faces the positive electrode. The battery is obtained by stacking and hot pressing a negative electrode, the composite separator, and a positive electrode, so that the first coating in the composite separator is transferred to the surface of the negative electrode and the second coating is transferred to the surface of the positive electrode.

9. An electrical appliance, characterized in that, It includes the battery as described in claim 8.

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