A secondary battery and an electric device

Abstract

The application provides a secondary battery and a power consumption device. By using different kinds of first and second separators, and by regulating the first binder and the first ceramic particles in the first adhesive layer and the first ceramic coating layer of the first separator and the second binder and the second ceramic particles in the second adhesive layer and the second ceramic coating layer of the second separator within the scope of the application, the adhesion between the first separator and the negative electrode sheet and the adhesion between the second separator and the positive and negative electrode sheets can be improved, and the secondary battery can have good expansion performance, cycle performance and high-temperature hot box performance.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) have advantages such as high energy density, long cycle life, low self-discharge rate, and environmental friendliness, and are widely used in aviation, aerospace, marine, electric vehicles, mobile devices, and other fields. Lithium-ion batteries consist of components such as positive electrode plates, negative electrode plates, and separators. The performance of the separator determines the interface structure and internal resistance of the lithium-ion battery, directly affecting its capacity, cycle life, and safety performance. A high-performance separator plays a crucial role in improving the overall performance of lithium-ion batteries. Existing separators typically have a ceramic coating and an adhesive layer on the base film. The ceramic coating prevents the base film from shrinking at high temperatures and has a certain liquid retention effect; the adhesive layer enhances the adhesion between the electrode plates and the separator, prevents separator shrinkage, removes air from the internal gaps of the lithium-ion battery, increases the battery's hardness, maintains consistent thickness, and thus improves the stability during cycling. However, existing separators used in lithium-ion batteries often struggle to simultaneously address the battery's expansion performance, cycle performance, and high-temperature thermal performance. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery that can take into account the expansion performance, cycle performance and high temperature box performance of the secondary battery, and to provide an electrical device using the secondary battery.

[0004] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0005] The first aspect of this application provides a secondary battery, which includes an electrode assembly having a wound structure. The electrode assembly includes a positive electrode, a negative electrode, a first separator, and a second separator. The first separator includes a first base film, a first adhesive layer, and a first ceramic coating. The first adhesive layer is disposed on both sides of the first base film, and the first ceramic coating is disposed on at least one side of the first base film and located between the first base film and the first adhesive layer. The first adhesive layer includes a first adhesive, which includes at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer. The first ceramic coating includes first ceramic particles, which include at least one of alumina, zirconium dioxide, titanium dioxide, or silicon dioxide. The second separator includes a second base film, a second adhesive layer, and a second ceramic coating. The second adhesive layer is disposed on both sides of the second base film, and the second ceramic coating is disposed on at least one side of the second base film and located between the second base film and the second adhesive layer. The second adhesive layer includes a second adhesive, which includes at least one of polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose. The second ceramic coating includes second ceramic particles, which include boehmite.

[0006] Currently, ceramic coatings in separators are typically of two types: oxides and boehmite, both of which significantly impact the performance of secondary batteries. Oxide coatings offer excellent wettability and liquid absorption / retention capabilities, improving the cycle performance of secondary batteries. However, oxides are harder, causing greater wear on machinery and increasing equipment costs. Furthermore, oxides are denser and lack flame retardancy, negatively impacting the energy density and safety of secondary batteries. In contrast, boehmite has lower hardness, higher heat resistance, lower density, and better adhesion, improving the separator's heat resistance and puncture resistance, thus enhancing the safety and energy density of secondary batteries. However, boehmite exhibits poor electrolyte wettability, which is detrimental to liquid retention and the cycle performance of secondary batteries.

[0007] The adhesives used in existing diaphragm bonding layers typically include low-melting-point adhesives (melting points approximately 115°C to 170°C) such as polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and high-melting-point adhesives (melting points > 200°C) such as polyimide (PI), polyvinyl alcohol (PVA), and sodium carboxymethyl cellulose (CMC-Na). PVDF or PVDF-HFP has advantages such as low crystallinity and glass transition temperature, excellent compatibility with electrolytes, and good adhesion to the electrodes. However, due to their low melting point, when the ambient temperature approaches the adhesive's melting point, the adhesive melts and cannot effectively adhere to the ceramic coating, thus failing to further prevent the shrinkage of the diaphragm base membrane. PI, PVA, and CMC-Na can effectively adhere ceramic coatings at higher temperatures, improving the high-temperature safety and stability of secondary batteries. However, these binders cannot swell in the electrolyte like PVDF and PVDF-HFP and have low ionic conductivity. Therefore, PI, PVA, and CMC-Na are detrimental to the cycle performance of secondary batteries.

[0008] This application prepares a first separator by using the aforementioned first binder and first ceramic particles, and a second separator by using the aforementioned second binder and second ceramic particles. When the first and second separators are used together, the advantages of each material are effectively utilized. This ensures adhesion between the separator and the electrode, increases the hardness of the secondary battery, improves the thickness consistency of the secondary battery, thereby improving the stability of the secondary battery during cycling and enhancing its expansion performance. Since the oxide ceramic coating has strong liquid retention but poor adhesion, its combination with PVDF or PVDF-HFP, which have good swelling properties in the electrolyte and good adhesion at room temperature, can improve the adhesion between the first separator and the electrode. The boehmite ceramic coating provides excellent adhesion and improves the cycle performance of the secondary battery. Due to its good adhesion and heat resistance, and the fact that boehmite promotes the swelling of the binder in the electrolyte, its combination with high-melting-point PI, PVA, and CMC-Na binder layers significantly enhances the room-temperature adhesion between the second separator and the electrode while improving the high-temperature performance of the second separator. The first and second separators possess high mechanical strength, mitigating shrinkage during battery cycling and in high-temperature environments. This reduces the likelihood of short circuits caused by separator shrinkage leading to contact between the positive and negative electrodes during charging and discharging, thus improving the high-temperature thermal performance of the secondary battery. Simultaneously, the first and second separators exhibit good wetting and electrolyte retention properties, further enhancing the cycle performance of the secondary battery. Therefore, the secondary battery of this application, by using different types of first and second separators in combination, and by controlling the types of first ceramic particles and first binder in the first separator and the types of second ceramic particles and second binder in the second separator within the scope of this application, can enable the separator to have a high adhesion force to the positive electrode and / or negative electrode, and the secondary battery takes into account expansion performance, cycle performance and high temperature box performance.

[0009] In some embodiments of this application, the first binder comprises polyvinylidene fluoride-hexafluoropropylene copolymer, and the first ceramic particles comprise alumina; the second binder comprises polyimide, and the second ceramic particles comprise boehmite. Using the aforementioned types of first binder, first ceramic particles, second binder, and second ceramic particles is beneficial for further improving the expansion performance, cycle performance, and high-temperature thermal performance of the secondary battery.

[0010] In some embodiments of this application, the negative electrode is located between the first and second separators. The negative electrode includes a negative current collector and a first and second negative electrode material layers disposed on both sides of the negative current collector. Along the winding direction of the electrode assembly, the length of the first negative electrode material layer is greater than the length of the second negative electrode material layer. The first separator is disposed on one side of the first negative electrode material layer of the negative electrode, and the second separator is disposed on one side of the second negative electrode material layer of the negative electrode. Since boehmite can give the second separator higher heat resistance and puncture resistance, placing the second separator between the positive and negative electrode can better prevent short circuits between the positive and negative electrodes of the secondary battery under conditions such as high temperature and puncture. The first ceramic particles give the first separator better wettability and liquid absorption and retention capacity, which can improve the cycle performance of the secondary battery. The first separator being disposed on the side of the longer first negative electrode material layer in the negative electrode allows more negative electrode active material to contact with more electrolyte, further improving the cycle performance of the secondary battery and preventing lithium plating. The above settings enable secondary batteries to further improve their cycle performance while maintaining energy density and safety.

[0011] In some embodiments of this application, a first ceramic coating is disposed on both sides of the first base membrane. By disposing the first ceramic coating on both sides of the first base membrane, the first separator can retain more electrolyte, thereby further improving the cycle performance of the secondary battery while taking into account both expansion performance and high-temperature thermal performance.

[0012] In some embodiments of this application, the second separator is located between the positive and negative electrode plates, and the second ceramic coating is only disposed on the side of the second base film facing away from the negative electrode plate. First, as mentioned above, under the same conditions, the high-temperature resistance of the second separator is significantly better than that of the first separator. Therefore, placing it between the positive and negative electrode plates can prevent short circuits between the positive and negative electrode plates at high temperatures. Second, because the positive active material particles on the positive electrode plate are relatively hard, occasionally larger or sharper positive active particles protrude from the positive electrode plate. During the production or use of secondary batteries, these positive active material particles may puncture the separator between the positive and negative electrode plates, causing a short circuit between the positive and negative electrode plates. The second ceramic coating on the second separator is only disposed on the side of the second base membrane away from the negative electrode, that is, the second ceramic coating faces the positive electrode. Since boehmite can improve the puncture resistance of the separator, it can reduce the occurrence of the positive electrode active material puncturing the separator and better protect the second base membrane. At the same time, the single-layer second ceramic coating can reduce the cost and increase the energy density of the secondary battery while further improving the safety performance.

[0013] In some embodiments of this application, the average particle size of the first ceramic particles is 0.2 μm to 1.2 μm, and the average particle size of the second ceramic particles is 0.1 μm to 1.0 μm. Controlling the average particle size of the first and second ceramic particles within the aforementioned ranges is beneficial for further improving the cycle performance of the secondary battery while maintaining energy density, expansion performance, and safety performance.

[0014] In some embodiments of this application, the thickness of the first ceramic coating is from 0.5 μm to 2.5 μm, and the thickness of the second ceramic coating is from 0.3 μm to 2.5 μm. Controlling the thicknesses of the first and second ceramic coatings within these ranges is beneficial for further improving the energy density of the secondary battery, while maintaining good cycle performance, expansion performance, and safety performance.

[0015] In some embodiments of this application, the mass percentage of the first ceramic particles is 10% to 50% based on the mass of the first ceramic coating; and the mass percentage of the second ceramic particles is 10% to 50% based on the mass of the second ceramic coating. By controlling the mass percentages of the first ceramic particles in the first ceramic coating and the second ceramic particles in the second ceramic coating within these ranges, the ceramic particles are present in sufficient quantities in the ceramic coatings, allowing them to fully exert their respective functions, while also considering the energy density and manufacturing cost of the secondary battery, resulting in a secondary battery with good cycle performance, expansion performance, and high-temperature thermal performance.

[0016] In some embodiments of this application, the thickness of the first adhesive layer is 0.2 μm to 5 μm, and the thickness of the second adhesive layer is 0.2 μm to 5 μm. By adjusting the thicknesses of the first and second adhesive layers within the above ranges, the first and second separators have high adhesion to the positive and / or negative electrode sheets, and the secondary battery balances expansion performance, cycle performance, high-temperature thermal performance, and energy density.

[0017] In some embodiments of this application, the materials of the first and second base membranes independently include at least one selected from polyimide, polyamide, polysulfone, polyacrylonitrile, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, aramid sulfone, or polyolefin. The polymerizing monomer of the polyolefin includes at least one selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene. The materials of the first and second base membranes within the above range all possess high strength and ion permeability, enabling the first and second separators to have good basic strength and ion permeability, which is beneficial for improving the expansion performance, high-temperature thermal performance, and cycle performance of the secondary battery.

[0018] A second aspect of this application provides an electrical device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electrical device exhibits good performance.

[0019] The beneficial effects of this application are:

[0020] This application provides a secondary battery and an electrical device. By using different types of first and second separators, and by adjusting the first adhesive layer and the first ceramic coating of the first separator to be within the scope of this application, and the second adhesive layer and the second ceramic coating of the second separator to be within the scope of this application, the adhesion between the first separator and the negative electrode sheet can be improved, and the adhesion between the second separator and the positive and negative electrode sheets can be improved. The secondary battery can balance its expansion performance, cycle performance and high-temperature heat box performance.

[0021] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0023] Figure 1 This is a partial structural diagram of the electrode assembly after it has been unwound along the winding direction according to some embodiments of this application;

[0024] Figure 2 This is a partial structural diagram of the electrode assembly after it has been unwound along the winding direction in some other embodiments of this application;

[0025] Figure 3 This is a schematic cross-sectional view of the first diaphragm in its unfolded state along its thickness and width directions, representing some embodiments of this application.

[0026] Figure 4 This is a schematic cross-sectional view of the second diaphragm in its unfolded state along its thickness and width directions, according to some embodiments of this application.

[0027] Figure 5 This is a partial structural diagram of the electrode assembly after it has been unwound along the winding direction according to some embodiments of this application.

[0028] Figure label:

[0029] Electrode assembly 100; first separator 10; first base film 11; first adhesive layer 12; first ceramic coating 13; second separator 20; second base film 21; second adhesive layer 22; second ceramic coating 23; negative electrode 30; negative current collector 31; first negative electrode material layer 33; second negative electrode material layer 34; positive electrode 40; positive current collector 41; positive electrode material layer 42. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0031] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0032] The first aspect of this application provides a secondary battery, including an electrode assembly with a wound structure. The electrode assembly includes a positive electrode, a negative electrode, a first separator, and a second separator. The first separator includes a first base film, a first adhesive layer, and a first ceramic coating. The first adhesive layer is disposed on both sides of the first base film, and the first ceramic coating is disposed on at least one side of the first base film and located between the first base film and the first adhesive layer. The phrase "the first ceramic coating is disposed on at least one side of the first base film" means that the first ceramic coating can be disposed on either side of the first base film or on both sides. On the side of the first base film without the first ceramic coating, the first adhesive layer is directly disposed on the surface of the first base film. The first adhesive layer includes a first adhesive, which includes at least one of polyvinylidene fluoride (PVDF) or PVDF-hexafluoropropylene copolymer. The first ceramic coating includes first ceramic particles, which include at least one of alumina, zirconium dioxide, titanium dioxide, or silicon dioxide. The second diaphragm includes a second base membrane, a second adhesive layer, and a second ceramic coating. The second adhesive layer is disposed on both sides of the second base membrane, and the second ceramic coating is disposed on at least one side of the second base membrane and located between the second base membrane and the second adhesive layer. The phrase "the second ceramic coating is disposed on at least one side of the second base membrane" means that the second ceramic coating can be disposed on one side or both sides of the second base membrane. On the side of the second base membrane without the second ceramic coating, the second adhesive layer is directly disposed on the surface of the second base membrane. The second adhesive layer includes a second adhesive, which includes at least one of polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose. The second ceramic coating includes second ceramic particles, which include boehmite.

[0033] In this application, the electrode assembly has a wound structure, and the winding direction of the electrode assembly is defined as W. Those skilled in the art should understand that the winding directions of the positive electrode, negative electrode, first diaphragm, and second diaphragm are the same as the winding direction of the electrode assembly. To facilitate understanding of the positional relationship between the positive electrode, negative electrode, first diaphragm, and second diaphragm in the electrode assembly, Figure 1 A partial structural schematic diagram of the electrode assembly after it has been unwound along the winding direction W is shown. In this application, the length direction of the positive electrode, negative electrode, first diaphragm, and second diaphragm after unwound is defined as X, the width direction as Y, and the thickness direction as Z. It can be understood that in the structural schematic diagram of the electrode assembly after unwound along the winding direction W, the winding direction W is parallel to the length direction X. Figure 1 As shown, the electrode assembly 100 includes a first separator 10, a second separator 20, a negative electrode 30, and a positive electrode 40. The negative electrode 30 is located between the first separator 10 and the second separator 20, the second separator 20 is located between the negative electrode 30 and the positive electrode 40, and the positive electrode 40 is located as the outermost layer of the electrode assembly 100. The first separator 10 includes a first base film 11, a first adhesive layer 12, and a first ceramic coating 13. The first adhesive layer 12 is located on both sides of the first base film 11, the first ceramic coating 13 is located on both sides of the first base film 11, and the first ceramic coating 13 is located between the first base film 11 and the first adhesive layer 12. It is understood that in some embodiments, the first ceramic coating 13 may be disposed on the surface of the first base film 11 facing away from the negative electrode 30; in other embodiments, the first ceramic coating 13 may also be disposed on the surface of the first base film 11 close to the negative electrode 30. When the first ceramic coating 13 is only disposed on the surface of one side of the first base film 11, the first ceramic coating 13 is located between the first base film 11 and the first adhesive layer 12 on the side where the first ceramic coating 13 is disposed. On the side where the first ceramic coating 13 is not disposed, the first adhesive layer 12 is directly disposed on the surface of the first base film 11. The second separator 20 includes a second base film 21, a second adhesive layer 22, and a second ceramic coating 23. The second adhesive layer 22 is located on both sides of the second base film 21. The second ceramic coating 23 is located on the surface of the second base film 21 facing away from the negative electrode 30. The second ceramic coating 23 is located between the second base film 21 and the second adhesive layer 22. On the surface of the second base film 22 where the second ceramic coating 23 is not disposed, that is, on the surface of the second base film 22 close to the negative electrode 30, the second adhesive layer 22 is directly disposed on the surface of the second base film 21. It should be understood that in some embodiments, the second ceramic coating 23 in the second diaphragm 20 may be disposed on the surface of the second base membrane 21 near the negative electrode 30; in other embodiments, the second ceramic coating 23 in the second diaphragm 20 may also be disposed on both sides of the second base membrane 21.

[0034] Polyvinylidene fluoride (PVDF) and PVDF-hexafluoropropylene copolymers exhibit low crystallinity and glass transition temperature. When used as binders in separators, they demonstrate good compatibility with the electrolyte and good adhesion to both positive and negative electrode plates. Polyimide, polyvinyl alcohol, and sodium carboxymethyl cellulose, when used as separator binders, can adhere ceramic particles in the ceramic coating at higher temperatures, resulting in strong adhesion between the ceramic coating and the binder layer. Furthermore, their low swelling degree in the electrolyte reduces the probability of separator expansion, thus improving the expansion performance of the secondary battery.

[0035] The first ceramic particles have good wettability and liquid absorption and retention capabilities. Using the above-mentioned type of first ceramic particles in the first ceramic coating can improve the liquid storage capacity and wetting performance of the first separator, thereby improving the cycle performance of the secondary battery. The second ceramic particles have the characteristics of high heat resistance, high puncture resistance, and low density. Using the above-mentioned type of second ceramic particles in the second ceramic coating can slow down the shrinkage of the second separator at high temperatures, reduce the possibility of short circuit caused by the contact between the positive and negative electrode plates due to the shrinkage of the second separator during the charging and discharging process of the secondary battery, and improve the binding ability of the second separator, thereby improving the high-temperature thermal performance of the secondary battery.

[0036] This application prepares a first separator by using the aforementioned first binder and first ceramic particles, and a second separator by using the aforementioned second binder and second ceramic particles. When the first and second separators are used together, the advantages of each material are effectively utilized. This ensures adhesion between the separator and the electrode, increases the hardness of the secondary battery, improves the thickness consistency of the secondary battery, thereby improving the stability of the secondary battery during cycling and enhancing its expansion performance. Since the oxide ceramic coating has strong liquid retention but poor adhesion, its combination with PVDF or PVDF-HFP, which have good swelling properties in the electrolyte and good adhesion at room temperature, can improve the adhesion between the first separator and the electrode. The boehmite ceramic coating provides excellent adhesion and improves the cycle performance of the secondary battery. Due to its good adhesion and heat resistance, and the fact that boehmite promotes the swelling of the binder in the electrolyte, its combination with high-melting-point PI, PVA, and CMC-Na binder layers significantly enhances the room-temperature adhesion between the second separator and the electrode while improving the high-temperature performance of the second separator. The first and second separators possess high mechanical strength, mitigating shrinkage during battery cycling and in high-temperature environments. This reduces the likelihood of short circuits caused by separator shrinkage leading to contact between the positive and negative electrodes during charging and discharging, thus improving the high-temperature thermal performance of the secondary battery. Simultaneously, the first and second separators exhibit good wetting and electrolyte retention properties, further enhancing the cycle performance of the secondary battery. Therefore, the secondary battery of this application, by using different types of first and second separators in combination, and by controlling the types of first ceramic particles and first binder in the first separator and the types of second ceramic particles and second binder in the second separator within the scope of this application, can enable the separator to have a high adhesion force to the positive electrode and / or negative electrode, and the secondary battery takes into account expansion performance, cycle performance and high temperature box performance.

[0037] In some embodiments of this application, the first binder comprises polyvinylidene fluoride-hexafluoropropylene copolymer, and the first ceramic particles comprise alumina; the second binder comprises polyimide, and the second ceramic particles comprise boehmite. Using the aforementioned types of first binder, first ceramic particles, second binder, and second ceramic particles is beneficial for further improving the adhesion of the separator to the positive and / or negative electrode sheets, and for further improving the expansion performance, cycle performance, and high-temperature thermal performance of the secondary battery.

[0038] In some embodiments of this application, the negative electrode sheet includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer disposed on both sides of the negative current collector. Along the winding direction of the electrode assembly, the length of the first negative electrode material layer is greater than the length of the second negative electrode material layer. A first separator is disposed on one side of the first negative electrode material layer of the negative electrode sheet, and a second separator is disposed on one side of the second negative electrode material layer of the negative electrode sheet. For example... Figure 2As shown, the electrode assembly 100 includes a first separator 10, a second separator 20, a negative electrode 30, and a positive electrode 40. The negative electrode 30 is located between the first separator 10 and the second separator 20, and the second separator 20 is located between the positive electrode 40 and the negative electrode 30. The positive electrode 40 includes a positive current collector 41 and positive electrode material layers 42 disposed on both sides of the positive current collector 41. The negative electrode 30 includes a negative current collector 31 and a first negative electrode material layer 33 and a second negative electrode material layer 34 disposed on both sides of the negative current collector 31. Along the winding direction W of the electrode assembly 100, the length L of the first negative electrode material layer 33 is... 33 The length L is greater than the length of the second negative electrode material layer 34. 34 The first separator 10 is disposed on one side of the first negative electrode material layer 33 of the negative electrode sheet 30, which can also be understood as the first separator 10 being adjacent to the first negative electrode material layer 33. The second separator 20 is disposed on one side of the second negative electrode material layer 34 of the negative electrode sheet 30, which can also be understood as the second separator 20 being adjacent to the second negative electrode material layer 34. Since boehmite provides the second separator with higher heat resistance and puncture resistance, placing the second separator between the positive and negative electrodes can better prevent short circuits between the positive and negative electrodes of the secondary battery under conditions such as high temperature and puncture. Oxide ceramics provide the first separator with better wettability and liquid absorption and retention capabilities, which can improve the cycle performance of the secondary battery. The first separator being disposed on the side of the longer first negative electrode material layer in the negative electrode sheet allows more negative electrode active material to come into contact with more electrolyte, further improving the cycle performance of the secondary battery and preventing lithium plating. Through the above arrangement, the cycle performance of the secondary battery can be further improved while maintaining energy density and safety performance.

[0039] In some embodiments of this application, a first ceramic coating is disposed on both sides of a first base film. For example... Figure 3 As shown, the first separator 10 includes a first base membrane 11 and a first ceramic coating 13, with the first ceramic coating 13 disposed on both sides of the first base membrane 11. By providing the first ceramic coating on both sides of the first base membrane, the electrolyte storage capacity and wetting performance of the first separator are improved, allowing the first separator to retain more electrolyte, thereby further enhancing the electrolyte storage capacity and wetting performance of the secondary battery. This enables the secondary battery to further improve its cycle performance while maintaining good expansion performance and high-temperature thermal performance.

[0040] In some embodiments of this application, the second separator is located between the positive and negative electrode plates, and the second ceramic coating is only disposed on the side of the second base film facing away from the negative electrode plate. For example... Figure 1 and Figure 2As shown, the second separator 20 is located between the positive electrode 40 and the negative electrode 30. The second separator 20 includes a second base film 21, a second adhesive layer 22, and a second ceramic coating 23. The second adhesive layer 22 is located on both sides of the second base film 21, and the second ceramic coating 23 is only disposed on the side of the second base film 21 facing away from the negative electrode 30. That is, the second ceramic coating 23 is disposed on the side of the second base film 21 that is close to and faces the positive electrode 40, and the side of the second base film 21 that is close to the negative electrode 30 does not have the second ceramic coating 23. The second separator is disposed between the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode at high temperatures. When the positive active material particles in the positive electrode are large in size or sharp, during the production or use of secondary batteries, the positive active material particles may squeeze or even puncture the separator between the positive and negative electrodes, causing a short circuit between the positive and negative electrodes. In the above configuration, by placing the second ceramic coating on the side of the second base membrane facing away from the negative electrode, i.e., with the second ceramic coating facing the positive electrode, boehmite can improve the puncture resistance of the separator. Therefore, it can reduce the possibility of large-diameter or sharp positive electrode active material particles puncturing the second separator, better protecting the second base membrane and thus improving the safety performance of the secondary battery. Furthermore, by placing the second ceramic coating only on one side of the second base membrane, the thickness of the second separator can be reduced, thereby reducing the thickness of the secondary battery and increasing its energy density. Thus, while maintaining good cycle performance, the safety performance and energy density of the secondary battery can be further improved.

[0041] In some embodiments of this application, the average particle size of the first ceramic particles is from 0.2 μm to 1.2 μm, and the average particle size of the second ceramic particles is from 0.1 μm to 1.0 μm. For example, the average particle size of the first ceramic particles is 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, or any value between any two of the above ranges. For example, the average particle size of the second ceramic particles is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or any value between any two of the above ranges. By controlling the average particle size of the first and second ceramic particles within the above ranges, the first and second ceramic particles have a higher specific surface area, which can improve the liquid storage capacity and wetting performance of the first and second separators, thereby helping to further improve the cycle performance of the secondary battery while taking into account energy density, expansion performance, and safety performance.

[0042] In this application, there are no particular restrictions on the method of controlling the average particle size of the first ceramic particles and the second ceramic particles, as long as the purpose of this application can be achieved. For example, it can be achieved by crushing, sieving, etc.

[0043] In some embodiments of this application, such as Figure 3 As shown, the thickness T of the first ceramic coating 13 13 The range is from 0.5μm to 2.5μm, such as Figure 4 As shown, the thickness T of the second ceramic coating 23 23 The thickness ranges from 0.3 μm to 2.5 μm. For example, the thickness of the first ceramic coating is 0.5 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, or any value between any two of the above ranges. Similarly, the thickness of the second ceramic coating is 0.3 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, or any value between any two of the above ranges. Controlling the thickness of the first and second ceramic coatings within the above ranges allows for smaller thicknesses of the first and second separators, resulting in a smaller volume for the secondary battery. This, in turn, helps to further improve the energy density of the secondary battery while maintaining good cycle performance, expansion performance, and safety performance.

[0044] In some embodiments of this application, the mass percentage of the first ceramic particles is between 10% and 50%, based on the mass of the first ceramic coating. For example, the mass percentage of the first ceramic particles is 10%, 20%, 25%, 30%, 36%, 42%, 50%, or any value between any two of the above ranges. Controlling the mass percentage of the first ceramic particles in the first ceramic coating within the above range ensures that the ceramic particles have a sufficient content in the ceramic coating, allowing them to fully exert their corresponding functions. This results in a first separator with good liquid storage capacity and wetting properties. Applying this first separator to a secondary battery helps to achieve good cycle performance while simultaneously considering expansion performance and high-temperature thermal performance.

[0045] In some embodiments of this application, the mass percentage of the second ceramic particles is between 10% and 50%, depending on the mass of the second ceramic coating. For example, the mass percentage of the second ceramic particles is 10%, 20%, 25%, 30%, 36%, 42%, 50%, or any value between any two of the above ranges. Controlling the mass percentage of the second ceramic particles in the second ceramic coating within the above range is beneficial for obtaining a second ceramic coating with good performance, thereby obtaining a second separator with good thermal stability and puncture resistance. Applying the second separator to a secondary battery helps to achieve good high-temperature thermal performance while balancing manufacturing cost, expansion performance, and cycle performance.

[0046] In some embodiments of this application, the first ceramic coating further includes a first ceramic coating adhesive, and the second ceramic coating further includes a second ceramic coating adhesive. This application does not impose any particular limitation on the types of the first and second ceramic coating adhesives, as long as they achieve the purpose of this application. For example, the first and second ceramic coating adhesives may each independently include at least one of styrene-butadiene rubber, polyvinyl alcohol, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, or polyacrylonitrile. This application does not impose any particular limitation on the content of the first and second ceramic coating adhesives in the first and second ceramic coatings; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved. For example, based on the mass of the first ceramic coating, the mass percentage of the first ceramic coating adhesive is 50% to 90%; based on the mass of the second ceramic coating, the mass percentage of the second ceramic coating adhesive is 50% to 90%.

[0047] In some embodiments of this application, such as Figure 3 As shown, the thickness T of the first adhesive layer 12 12 The range is from 0.2μm to 5μm, such as Figure 4 As shown, the thickness T of the second adhesive layer 22 22 The thickness is between 0.2 μm and 5 μm. For example, the thickness of the first adhesive layer is 0.2 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value between any two of the above ranges. For example, the thickness of the second adhesive layer is 0.2 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value between any two of the above ranges. Controlling the thickness of the first and second adhesive layers within the above ranges helps to control the thickness of the first and second separators within a smaller range, thereby resulting in a smaller volume for the secondary battery. This reduces the risk of energy density loss due to excessive volume. Furthermore, the first and second adhesive layers enable good adhesion between the first and second separators, respectively. The first and second separators have high adhesion to the positive and / or negative electrode plates, allowing the secondary battery to balance expansion performance, cycle performance, high-temperature thermal performance, and energy density.

[0048] In some embodiments of this application, the materials of the first and second base membranes each independently include at least one selected from polyimide, polyamide, polysulfone, polyacrylonitrile, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, aramid sulfone, or polyolefin. The polymer monomer of the polyolefin includes at least one selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene. When the materials of the first and second base membranes within the above range are selected, the double-membrane structure of the first and second separators in the secondary battery is beneficial to improving the expansion performance, high-temperature thermal performance, and cycle performance of the secondary battery. This application does not impose any particular limitation on the weight-average molecular weight of the material of the first base membrane, as long as it can achieve the purpose of this application. For example, the weight-average molecular weight of the material of the first base membrane can be 2 × 10⁻⁶. 5 Up to 1.5×10 6 This application does not impose any particular limitation on the weight-average molecular weight of the material of the second base film, as long as it can achieve the purpose of this application. For example, the weight-average molecular weight of the material of the second base film can be 2 × 10⁻⁶. 5 Up to 1.5×10 6 .

[0049] This application does not impose any particular limitation on the thickness of the first base film and the second base film, as long as the purpose of this application can be achieved.

[0050] This application does not impose any particular limitation on the thickness of the first and second diaphragms, as long as the purpose of this application can be achieved. For example, the thickness of the first diaphragm is 12 μm to 25 μm, and the thickness of the second diaphragm is 5 μm to 15 μm.

[0051] In some embodiments of this application, the first adhesive layer may further include a first thickener, and the second adhesive layer may further include a second thickener. Based on the mass of the first adhesive layer, the mass percentage of the first adhesive is 94% to 99.7%, and the mass percentage of the first thickener is 0.3% to 6%. Based on the mass of the second adhesive layer, the mass percentage of the second adhesive is 94% to 99.7%, and the mass percentage of the second thickener is 0.3% to 6%. Applying the first thickener to the first adhesive layer and the second thickener to the second adhesive layer helps to increase the stability of the first and second adhesive layer slurries and prevents the sedimentation of the components in the first and second adhesive layer slurries. This application does not particularly limit the types of the first and second thickeners, as long as they can achieve the purpose of this application. For example, the first and second thickeners are each independently selected from at least one of hydroxyethyl cellulose, methyl hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyacrylamide, or sodium alginate.

[0052] The present application has no particular limitation on the negative electrode current collector, as long as the object of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collectors (e.g., carbon-copper composite current collectors, nickel-copper composite current collectors, titanium-copper composite current collectors), etc. The first negative electrode material layer and the second negative electrode material layer of the present application each independently contain a negative electrode active material. The present application has no particular limitation on the type of the negative electrode active material, as long as the object of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO x (0<x<2), Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO₂, lithium titanate Li₄Ti₅O with spinel structure 12 , at least one of Li-Al alloy or metallic lithium. In the present application, there is no particular limitation on the thicknesses of the negative electrode current collector, the first negative electrode material layer and the second negative electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, the thickness of the first negative electrode material layer is 30 μm to 130 μm, and the thickness of the second negative electrode material layer is 30 μm to 130 μm. Optionally, the first negative electrode material layer and the second negative electrode material layer may further include a conductive agent and a binder. The present application has no particular limitation on the mass ratio of the negative electrode active material, the conductive agent and the binder in the first negative electrode material layer and the second negative electrode material layer, as long as the object of the present application can be achieved.

[0053] In some embodiments of this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on one or both sides of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The positive electrode material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the type of positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also include non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 9 μm to 15 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm. In this application, the positive electrode material layer may also include a conductive agent and a binder. There are no particular limitations on the types of conductive agents and binders in the positive electrode material layer, as long as the purpose of this application can be achieved. There are no particular limitations on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0054] This application does not impose any particular limitation on the types of conductive agents used in the positive electrode material layer, the first negative electrode material layer, and the second negative electrode material layer, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (SuperP), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the types of binders used in the positive electrode material layer, the first negative electrode material layer, and the second negative electrode material layer, as long as they can achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The types of conductive agent and binder in the positive electrode material layer, the first negative electrode material layer, and the second negative electrode material layer may be the same or different.

[0055] In some embodiments of this application, the secondary battery further includes an electrolyte and a packaging bag, with the electrode assembly and electrolyte contained within the packaging bag. This application does not impose any particular limitations on the electrolyte and packaging bag; those skilled in the art can select any electrolyte and packaging bag known in the art, as long as the purpose of this application can be achieved.

[0056] This application does not impose any particular limitation on the preparation method of the first diaphragm, as long as it can achieve the purpose of this application. For example, the preparation method of the first diaphragm includes, but is not limited to, the following steps: (1) mixing the material of the first adhesive layer and the first thickener evenly to obtain the first adhesive layer slurry; (2) mixing the first ceramic particles and the first ceramic coating adhesive evenly to obtain the first ceramic coating slurry; (3) coating the first ceramic coating slurry on one surface of the first base film, drying it to form the first ceramic coating on one surface of the first base film, coating the first adhesive layer slurry on the surface of the first ceramic coating away from the first base film, drying it to obtain the first diaphragm with the first ceramic coating and the first adhesive layer coated on one side; (4) repeating the above steps on the other surface of the first base film to obtain the first diaphragm. In one embodiment of this application, after step (3) above, only the first adhesive layer slurry can be coated on the other surface of the first base film, and the first diaphragm can be obtained after drying.

[0057] This application does not impose any particular limitation on the preparation method of the second diaphragm, as long as it can achieve the purpose of this application. For example, the preparation method of the second diaphragm includes, but is not limited to, the following steps: (1) mixing the second binder and the second thickener evenly to obtain a second adhesive layer slurry; (2) mixing the second ceramic particles and the second ceramic coating binder evenly to obtain a second ceramic coating slurry; (3) coating the second ceramic coating slurry on one surface of the second base film, drying it to form a second ceramic coating on one surface of the second base film, coating the second adhesive layer slurry on the surface of the second ceramic coating away from the second base film, drying it to obtain a second diaphragm with a single-sided coating of the second ceramic coating and the second adhesive layer; (4) repeating the above steps on the other surface of the second base film to obtain the second diaphragm. In one embodiment of this application, after step (3) above, only the second adhesive layer slurry can be coated on the other surface of the second base film, and the second diaphragm can be obtained after drying.

[0058] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion secondary batteries, sodium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0059] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, the second separator, the negative electrode, and the first separator in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery.

[0060] A second aspect of this application provides an electrical device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electrical device exhibits good performance.

[0061] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. For example, the electrical device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0062] Example

[0063] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0064] Test methods and equipment:

[0065] Sampling methods for the first and second septa:

[0066] The lithium-ion batteries in the tested examples and comparative examples were disassembled, and the first and second separators were removed. The separators were soaked in dimethyl carbonate (DMC) for 20 minutes to remove electrolyte residue. Then, the first and second separators were placed in an oven and dried at 60°C for 12 hours to obtain the first and second separator samples. The average particle size of the first and second ceramic particles was measured using the above method.

[0067] Average particle size test of the first and second ceramic particles:

[0068] The first or second diaphragm was prepared by argon ion polishing. The cross-section of the first or second diaphragm was observed by scanning electron microscopy (SEM). The equivalent diameter of 10 first ceramic particles or 10 second ceramic particles was measured (that is, the diameter of a circle with an irregular cross-section converted into a circle with an equal area). The average value of each was calculated to obtain the average particle size of the first ceramic particle or the average particle size of the second ceramic particle.

[0069] Thickness testing of the first ceramic coating, the second ceramic coating, the first adhesive layer, and the second adhesive layer:

[0070] The first diaphragm was argon-ion polished to obtain its cross-section. The morphology of the cross-section along the thickness direction of the first diaphragm was observed and scanned electron microscopy (SEM) images were taken using a field emission scanning electron microscope (Philips XL-30). The thickness T of the first ceramic coating was measured using the SEM. 13 and the thickness T of the first adhesive layer 12 ;

[0071] The second diaphragm was argon-ion polished to obtain its cross-section. The morphology of the cross-section along the thickness direction of the second diaphragm was observed and scanned electron microscopy (SEM) images were taken using a field emission scanning electron microscope (Philips XL-30). The thickness T of the second ceramic coating was measured using SEM. 23 The thickness T of the second adhesive layer 22 .

[0072] Test of the adhesion between the diaphragm and the electrode:

[0073] The dry-press adhesion between the separator and the electrode was measured using a 180° peel test standard. The lithium-ion batteries in the tested examples and comparative examples were disassembled, and the positive electrode, negative electrode, first separator, and second separator were peeled off. The electrode and separator to be tested were soaked in dimethyl carbonate for 20 minutes to remove the electrolyte. Then, the separator and electrode were laminated together using a hot press at 85°C, 1 MPa, and 85 seconds. The laminated sample was cut into 15mm × 54.2mm strips to obtain test strips for testing the adhesion strength between the separator and the electrode. A 15mm × 55mm double-sided adhesive tape (NITTO.NO5000NS) was attached to a steel plate, and the test strips were then attached to the tape with the test side facing down. A 15mm × 70mm paper tape was connected to one end of the test strip using the double-sided adhesive tape. A 2kg roller was manually pushed across the test strip 8 times to obtain the test sample. A tensile testing machine was used for the final test. The test sample is fixed on the test stage, the paper tape is folded upwards 180° and secured with clamps, and then the tensile testing machine starts pulling the paper tape at a speed of 50 mm / min until the test diaphragm and the test electrode on the double-sided adhesive surface separate, ending the test and saving the test data. The adhesion force F between the test diaphragm and the test electrode is calculated based on the tensile force and displacement during separation, in N / m. The adhesion force F1 between the first diaphragm and the negative electrode is calculated in N / m; the adhesion force F2 between the second diaphragm and the positive electrode is calculated in N / m; and the adhesion force F3 between the second diaphragm and the negative electrode is calculated in N / m.

[0074] High-temperature hot box testing:

[0075] At 25°C, lithium-ion batteries that have been charged at a constant current of 2C to 4.5V and then at a constant voltage of 4.5V to 0.02C are placed in a test chamber with circulating air convection, a temperature of 25°C, and a humidity of 80%. After standing for 5 minutes, the test chamber is heated to 130°C at a rate of 5°C / min and maintained at 130°C for 10 minutes. The test is then stopped, and the lithium-ion batteries are checked for fire or explosion. A battery that does not fire or explode is considered to have passed the test. Ten batteries are tested in each example and comparative example. The pass rate of the 130°C hot chamber test = the number of batteries that pass the 130°C hot chamber test / 10.

[0076] At 25°C, lithium-ion batteries charged at a constant current of 2C to 4.5V, and then charged at a constant voltage of 4.5V to a current of 0.02C, were placed in a test chamber with circulating air convection, a temperature of 25°C, and a humidity of 80%. After standing for 5 minutes, the test chamber was heated to 132°C at a rate of 5°C / min and maintained at 132°C for 10 minutes. The test was then stopped, and the lithium-ion batteries were checked for fire or explosion. A battery that did not fire or explode was considered to have passed the test. Five batteries were tested in each example and comparative example. The pass rate of the 132°C hot chamber test = the number of batteries that passed the 132°C hot chamber test / 10.

[0077] The high-temperature thermal performance of lithium-ion batteries is characterized by the pass rate of thermal test. The higher the pass rate, the better the high-temperature thermal performance of the lithium-ion battery.

[0078] Cyclic performance testing:

[0079] At 25°C, the lithium-ion battery was charged at a constant current of 2C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.02C. After resting for 5 minutes, it was discharged at a constant current of 0.7C to 3.0V. This was the first cycle, and the discharge capacity was recorded. The lithium-ion battery was subjected to charge-discharge cycles according to the above process. The test was stopped after 1000 cycles (cls), and the capacity retention rate was calculated as an indicator to evaluate the cycle performance of the lithium-ion battery.

[0080] Capacity retention rate (%) = (Discharge capacity after 1000 cls of cycling / Discharge capacity of the first cycle) × 100%.

[0081] A higher capacity retention rate indicates better cycle performance of the lithium-ion battery.

[0082] Expansion performance testing:

[0083] The lithium-ion batteries in each embodiment and comparative example were placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow them to reach a constant temperature. The thickness at the center of the lithium-ion battery was measured and recorded as the initial thickness. The batteries were then charged at a constant current of 0.5C to 4.3V, and then charged at a constant voltage of 4.3V to a current of 0.025C. After standing for 5 minutes, the batteries were discharged at a constant current of 0.5C to 3.0V. This charge-discharge cycle was repeated 800 times, and the thickness at the center of the lithium-ion battery was measured and recorded as the thickness after 800 cycles. The thickness expansion rate (%) of the lithium-ion battery was calculated as: (Thickness after 800 cycles - Initial thickness) / Initial thickness × 100%.

[0084] Thickness expansion rate is used to characterize the expansion performance of lithium-ion batteries. The smaller the thickness expansion rate, the better the expansion performance of the lithium-ion battery.

[0085] Example 1-1

[0086] <Preparation of the first diaphragm>

[0087] The second base film is made of polyethylene and polypropylene (mass ratio 1:1) (manufacturer: Celgard, model 2325) and has a thickness of 7μm.

[0088] The first adhesive is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, Mw = 8.5 × 10⁻⁶). 6 ) and the first thickener, sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.5:1.5, add deionized water as a solvent, and stir evenly to form a first adhesive layer slurry with a solid content of 75wt%.

[0089] The first ceramic particles, alumina (Al2O3), and the first ceramic coating adhesive, styrene-butadiene rubber (Mw = 7 × 10⁻⁶), were combined. 6 Mix them together, add deionized water as a solvent, and stir evenly to form a first ceramic coating slurry with a solid content of 30wt%.

[0090] A first ceramic coating slurry is applied to one surface of a first base film and dried at 60°C to form a first ceramic coating on that surface. A first adhesive layer slurry is then applied to the surface of the first ceramic coating away from the first base film and dried at 60°C to obtain a first diaphragm with a single-sided coating of the first ceramic coating and the first adhesive layer. The above steps are then repeated on the other surface of the first base film to obtain the first diaphragm. The thickness T of the first diaphragm is... 10 =13μm, the thickness T of the first ceramic coating 13 =2.0μm, the thickness T of the first adhesive layer 12 =1.0μm, the average particle size of the first ceramic particles is 1.0μm. Based on the mass of the first ceramic coating, the mass percentage of the first ceramic particles is W. 11 =30%, the mass percentage of the first ceramic coating adhesive is W 12 =70%.

[0091] <Preparation of the Second Diaphragm>

[0092] The second base film is made of polyethylene and polypropylene (mass ratio 1:1) (manufacturer: Celgard, model 2325) and has a thickness of 7μm.

[0093] The second adhesive, polyimide (PI, Mw = 6 × 10), is used. 5 ) and the second thickener, sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.5:1.5, add deionized water as a solvent, and stir evenly to form a second adhesive layer slurry with a solid content of 75wt%.

[0094] The second ceramic particle, boehmite (γ-AlOOH), and the second ceramic coating adhesive, styrene-butadiene rubber (Mw = 7 × 10⁻⁶). 6 Mix them together, add deionized water as a solvent, and stir evenly to form a second ceramic coating slurry with a solid content of 40wt%.

[0095] A second ceramic coating slurry is applied to one surface of the second base film and dried at 60°C to form a second ceramic coating. A second adhesive layer slurry is then applied to the surface of the first ceramic coating away from the first base film and dried at 60°C to obtain a second diaphragm with a single-sided coating of the second ceramic coating and the second adhesive layer. Subsequently, a second adhesive layer slurry is applied to the other surface of the second base film and dried at 60°C to obtain the second diaphragm. The thickness T of the second diaphragm is... 20 =11μm, the thickness T of the second ceramic coating 23 =2.0μm, the thickness T of the second adhesive layer 22 =1.0μm, and the average particle size of the second ceramic particles is 0.5μm. Based on the mass of the second ceramic coating, the mass percentage of the second ceramic particles is W. 21 =30%, the mass percentage of the second ceramic coating adhesive is W 22 =70%.

[0096] <Preparation of Negative Electrode Sheets>

[0097] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.0:1.5:1.5, and deionized water was added as a solvent. After stirring evenly, a first negative electrode slurry with a solid content of 75 wt% was obtained. This first negative electrode slurry was also used as a second negative electrode slurry. The first negative electrode slurry was coated onto one surface of a 6 μm thick copper foil current collector and dried at 90°C to form a 50 μm thick first negative electrode material layer. The second negative electrode slurry was coated onto the other surface of the copper foil current collector and dried at 90°C to form a 50 μm thick second negative electrode material layer, resulting in a 106 μm thick negative electrode sheet. The coated negative electrode sheet was cold-pressed and then cut into 64 mm × 817 mm dimensions for later use. The compaction density of the first negative electrode material layer was 1.725 g / cm³. 3 The length is 710 mm, and the compaction density of the second negative electrode material layer is 1.725 g / cm³. 3 It is 670mm long.

[0098] <Preparation of the positive electrode>

[0099] Lithium cobalt oxide (CCO), conductive carbon black (CCO), and polyvinylidene fluoride (PVDF) (PVDF binder) were mixed in a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was thoroughly stirred to form a positive electrode slurry with a solid content of 75 wt%. This slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 90°C to form a 55 μm thick positive electrode material layer. The same slurry was then coated onto the other surface of the aluminum foil and dried at 90°C to form a 55 μm thick positive electrode material layer, resulting in a double-coated positive electrode sheet with a thickness of 120 μm. The coated positive electrode sheets were then cold-pressed and cut into 60 mm × 796 mm dimensions for later use. The compaction density of the positive electrode material layers was 4.23 g / cm³. 3 .

[0100] <Preparation of Electrolyte>

[0101] In a glove box filled with a dry argon atmosphere, propylene carbonate (PC), diethyl carbonate (DEC), and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent, dissolved, and thoroughly mixed to obtain the electrolyte. The mass percentage of LiPF6 in the electrolyte was 14%, with the remainder being the base solvent.

[0102] <Preparation of Lithium-ion Batteries>

[0103] The prepared positive electrode, second separator, negative electrode, and first separator are stacked sequentially and then wound to obtain the electrode assembly. The positive electrode tab is spot-welded with an aluminum tab, and the negative electrode tab is spot-welded with a nickel tab. The second ceramic coating in the second separator faces away from the negative electrode and is opposite to the positive electrode. The first separator is disposed on one side of the first negative electrode material layer of the negative electrode, and the second separator is disposed on one side of the second negative electrode material layer of the negative electrode (see structure). Figure 2 But not with Figure 2 (Limited). The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Then, the electrolyte is injected, and the lithium-ion battery is obtained after vacuum sealing, standing, formation (0.02C constant current charging to 3.5V, and then 0.1C constant current charging to 3.9V), capacity testing, and shaping.

[0104] Examples 1-2

[0105] In addition to the method described in "Preparation of Lithium-ion Batteries," where the second separator is disposed on one side of the first negative electrode material layer of the negative electrode sheet and the first separator is disposed on one side of the second negative electrode material layer of the negative electrode sheet (see structure),... Figure 5 But not with Figure 5 Except for (limited), the rest is the same as in Example 1-1.

[0106] Examples 1-3

[0107] <Preparation of the first diaphragm>

[0108] A first ceramic coating slurry is applied to one surface of a first base film and dried at 60°C to form a first ceramic coating. A first adhesive layer slurry is applied to the surface of the first ceramic coating away from the first base film and dried at 60°C to obtain a first diaphragm with a single-sided coating of the first ceramic coating and the first adhesive layer. Then, a first adhesive layer slurry is applied to the other surface of the first base film and dried at 60°C to obtain the first diaphragm.

[0109] <Preparation of Lithium-ion Batteries>

[0110] The prepared positive electrode, second separator, negative electrode, and first separator are stacked sequentially and then wound to obtain an electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. The second ceramic coating in the second separator faces away from the negative electrode and is opposite to the positive electrode; the first ceramic coating in the first separator faces away from the negative electrode. The first separator is located on one side of the first negative electrode material layer of the negative electrode, and the second separator is located on one side of the second negative electrode material layer of the negative electrode. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes to obtain a lithium-ion battery.

[0111] The rest is the same as in Example 1-1.

[0112] Examples 1-4

[0113] <Preparation of the Second Diaphragm>

[0114] A second ceramic coating slurry is applied to one surface of the second base film and dried at 60°C to form a second ceramic coating. A second adhesive layer slurry is applied to the surface of the first ceramic coating away from the first base film and dried at 60°C to obtain a second diaphragm with a single-sided coating of the second ceramic coating and the second adhesive layer. Then, the above steps are repeated on the other surface of the second base film to obtain the second diaphragm.

[0115] <Preparation of Lithium-ion Batteries>

[0116] The prepared positive electrode, second separator, negative electrode, and first separator are stacked sequentially and then wound to obtain an electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. The first separator is disposed on one side of the first negative electrode material layer of the negative electrode, and the second separator is disposed on one side of the second negative electrode material layer of the negative electrode. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes to obtain a lithium-ion battery.

[0117] The rest is the same as in Example 1-1.

[0118] Examples 1-5 to Examples 1-12

[0119] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0120] Examples 2-1 to 2-10

[0121] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0122] Examples 3-1 to 3-8

[0123] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-1.

[0124] Among them, the mass percentage of the first ceramic particle W 11 When changes occur, the mass percentage W of the first ceramic coating adhesive 12 Consequently, the sum of the mass percentages of the first ceramic particles and the first ceramic coating binder is 100%; the mass percentage of the second ceramic particles is W. 21 When changes occur, the mass percentage W of the second ceramic coating adhesive 22 Consequently, the sum of the mass percentages of the second ceramic particles and the second ceramic coating binder is 100%.

[0125] Examples 4-1 to 4-16

[0126] Except for adjusting the relevant preparation parameters according to Table 5, the rest is the same as in Examples 2-9.

[0127] Comparative Example 1

[0128] Except for the absence of a second separator and the preparation of the lithium-ion battery according to the following method, the rest is the same as in Example 1-1.

[0129] <Preparation of Lithium-ion Batteries>

[0130] The prepared positive electrode sheet, first separator, negative electrode sheet, and first separator are stacked sequentially and then wound to obtain the electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. After that, electrolyte is injected, and the lithium-ion battery is obtained after vacuum sealing, standing, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping.

[0131] Comparative Example 2

[0132] Except for the absence of a first separator and the preparation of the lithium-ion battery according to the following method, the rest is the same as in Example 1-1.

[0133] <Preparation of Lithium-ion Batteries>

[0134] The prepared positive electrode, second separator, negative electrode, and second separator are stacked sequentially and then wound to obtain the electrode assembly. The positive electrode tab is spot-welded out using aluminum tabs, and the negative electrode tab is spot-welded out using nickel tabs. The second ceramic coating in the second separator faces away from the negative electrode. The electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes to obtain a lithium-ion battery.

[0135] The rest is the same as in Example 1-1.

[0136] Comparative Example 3

[0137] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0138] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 5.

[0139] Table 1

[0140]

[0141]

[0142] Note: In Table 1, "\" indicates that there is no corresponding parameter.

[0143] Table 2

[0144]

[0145] As can be seen from Examples 1-1 to 1-9, Examples 1-12, and Comparative Examples 1 to 3, the secondary battery of this application, by combining different types of first and second separators, and by controlling the types of first ceramic particles and first binder in the first separator and the types of second ceramic particles and second binder in the second separator within the scope of this application, can enable the first separator to have a high adhesion force F1 with the negative electrode, and the second separator to have a high adhesion force F2 and F3 with the positive and negative electrode. The secondary battery also has a high capacity retention rate, a small thickness expansion rate, and a high heat box pass rate at 130°C and 132°C, indicating that the lithium-ion battery of this application can take into account cycle performance, expansion performance, and high temperature heat box performance. The secondary batteries in the comparative examples, while those in Comparative Examples 1 to 3, used the same type of separator, or rather, the types of ceramic particles and binders in the two separators did not meet the limitations of this application. The separators in the comparative examples had low adhesion to the positive and negative electrode plates. The secondary batteries in the comparative examples could not simultaneously satisfy the following requirements: high capacity retention, low thickness expansion rate, and high pass rate in hot box tests at 130°C and 132°C. This indicates that the secondary batteries in the comparative examples could not simultaneously achieve cycle performance, expansion performance, and high-temperature hot box performance. Comparing Examples 1-1 with Examples 1-5 to 1-8, it can be seen that the combination of PVDF-HFP as the first binder and alumina (alumina) as the first ceramic particle in the first separator has the best overall performance. Comparing Examples 1-1 with Examples 1-9 and 1-12, it can be seen that the combination of PI as the second binder and boehmite as the second ceramic particle in the second separator has the best overall performance.

[0146] The materials of the first and second base films typically affect the cycle performance, expansion performance, and high-temperature thermal chamber performance of secondary batteries. As can be seen from Examples 1-1, 1-10, and 1-11, secondary batteries using materials for both the first and second base films that fall within the scope of this application exhibit high capacity retention, low thickness expansion, and high thermal chamber test pass rates at both 130°C and 132°C, indicating that the secondary batteries can balance cycle performance, expansion performance, and high-temperature thermal chamber performance.

[0147] Table 3

[0148]

[0149] The average particle size of the first ceramic particles typically affects the cycle performance, expansion performance, and high-temperature thermal chamber performance of a secondary battery. As can be seen from Examples 1-1, 2-1 to 2-4, 2-9, and 2-10, secondary batteries using first ceramic particles with an average particle size within the range of this application exhibit high capacity retention, low thickness expansion, and high thermal chamber test pass rates at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature thermal chamber performance. Compared to Examples 1-1, 2-1, and 2-2, Example 2-3 has a smaller average particle size of the first ceramic particles, resulting in slightly weaker liquid retention and a slightly weaker effect on improving the cycle performance of the secondary battery. Example 2-4 has a larger average particle size of the first ceramic particles, increasing the possibility of short circuits caused by puncturing the separator during thermal chamber testing, thus resulting in slightly weaker thermal chamber performance.

[0150] The average particle size of the second ceramic particles typically affects the cycle performance, expansion performance, and safety performance of a secondary battery. As can be seen from Examples 1-1, 2-5 to 2-8, 2-9, and 2-10, secondary batteries using second ceramic particles with an average particle size within the range of this application exhibit high capacity retention, low thickness expansion, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared to Examples 1-1, 2-5, and 2-6, the second ceramic particle average particle size in Example 2-7 is smaller, resulting in slightly weaker liquid retention and a slightly weaker effect on improving the cycle performance of the secondary battery. The second ceramic particle average particle size in Example 2-8 is larger, increasing the possibility of short circuits caused by puncturing the separator during hot box testing, thus resulting in slightly weaker hot box performance.

[0151] Table 4

[0152]

[0153] The mass percentage of the first ceramic particles W 11 This typically affects the cycle performance, expansion performance, and safety performance of secondary batteries. As can be seen from Examples 1-1, 3-1 to 3-4, the mass percentage W of the first ceramic particles selected... 11The secondary battery within the scope of this application simultaneously exhibits high capacity retention, low thickness expansion rate, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared with Examples 1-1, 3-1, and 3-2, the first ceramic particles in Example 3-3 have a lower mass percentage content in the first ceramic coating, resulting in slightly weaker liquid retention and less binding effect on the first base film at high temperatures, thus having a slightly weaker effect on improving the cycle performance and hot box performance of the secondary battery. In Example 3-4, the first ceramic particles have a higher mass percentage content in the first ceramic coating, increasing the possibility of the first ceramic particles puncturing the separator and causing a short circuit in the hot box test, thus resulting in slightly weaker hot box performance.

[0154] The mass percentage of the second ceramic particles W 21 This typically affects the cycle performance, expansion performance, and safety performance of secondary batteries. As can be seen from Examples 1-1, 3-5 to 3-8, the mass percentage W of the selected second ceramic particles... 21 The secondary battery within the scope of this application simultaneously exhibits high capacity retention, low thickness expansion rate, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared with Examples 1-1, 3-5, and 3-6, the second ceramic particles in Example 3-7 have a lower mass percentage content in the second ceramic coating, resulting in slightly weaker liquid retention and less binding effect on the second base film at high temperatures, thus having a slightly weaker effect on improving the cycle performance and hot box performance of the secondary battery. In Example 3-8, the second ceramic particles have a higher mass percentage content in the second ceramic coating, increasing the possibility of the second ceramic particles puncturing the separator and causing a short circuit in the hot box test, thus resulting in slightly weaker hot box performance.

[0155] Table 5

[0156]

[0157] The thickness T of the first ceramic coating 13 This typically affects the cycle performance, expansion performance, and safety performance of secondary batteries. As can be seen from Examples 2-9 and Examples 4-1 to 4-4, the thickness T of the first ceramic coating is selected... 13The secondary battery within the scope of this application simultaneously exhibits high capacity retention, low thickness expansion rate, and high pass rate in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared with Examples 2-9, 4-1, and 4-2, the first ceramic coating in Example 4-3 is thinner, has slightly weaker liquid retention, and exerts less binding effect on the first base film at high temperatures, resulting in a slightly weaker improvement in the cycle performance and hot box performance of the secondary battery. The first ceramic coating in Example 4-4 is thicker, resulting in a slight loss in energy density, and an increased possibility of the first ceramic particles puncturing the separator and causing a short circuit during the hot box test, thus resulting in slightly weaker hot box performance.

[0158] The thickness T of the first adhesive layer 12 This typically affects the cycle performance, expansion performance, and safety performance of secondary batteries. As can be seen from Examples 1-1, 4-5 to 4-8, the thickness T of the first adhesive layer is selected... 12 The secondary battery within the scope of this application simultaneously exhibits high capacity retention, low thickness expansion rate, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared with Examples 2-9, 4-5, and 4-6, the first adhesive layer in Example 4-7 is thinner, resulting in a relatively weaker binding effect on the electrode sheets. Furthermore, the first adhesive layer may melt at high temperatures, leading to a slightly weaker effect on inhibiting separator shrinkage. Therefore, its improvement effect on the expansion performance and hot box performance of the secondary battery is slightly weaker. The first adhesive layer in Example 4-8 is thicker, resulting in a slight loss in energy density. Moreover, the thicker first adhesive layer lengthens the lithium-ion transport path during charging and discharging, leading to a slightly weaker improvement in the cycle performance of the secondary battery.

[0159] The thickness T of the second ceramic coating 23 This typically affects the cycle performance, energy density, and safety performance of secondary batteries. As can be seen from Examples 1-1, 4-9 to 4-12, the thickness T of the second ceramic coating is selected... 23 The secondary battery within the scope of this application simultaneously exhibits high capacity retention, low thickness expansion rate, and high pass rate in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared with Examples 2-9, 4-9, and 4-10, the second ceramic coating in Example 4-11 is thinner, resulting in less binding effect of the second ceramic coating on the second base film at high temperatures, and thus a slightly weaker effect on improving the hot box performance of the secondary battery. The second ceramic coating in Example 4-12 is thicker, resulting in a slight loss in energy density, and an increased possibility of the second ceramic particles puncturing the separator and causing a short circuit during the hot box test, thus leading to slightly weaker hot box performance.

[0160] The thickness T of the second adhesive layer 22 This typically affects the cycle performance, expansion performance, and safety performance of secondary batteries. As can be seen from Examples 1-1, 4-13 to 4-16, the thickness T of the second adhesive layer is selected... 22 The secondary battery within the scope of this application simultaneously exhibits high capacity retention, low thickness expansion rate, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, expansion performance, and high-temperature hot box performance. Compared with Examples 2-9, 4-13, and 4-14, the second adhesive layer in Example 4-15 is thinner, resulting in a relatively weaker binding effect on the electrode sheets and a slightly weaker effect on inhibiting the shrinkage of the separator at high temperatures. Therefore, its improvement effect on the expansion performance and hot box performance of the secondary battery is slightly weaker. The second adhesive layer in Example 4-16 is thicker, resulting in a slight loss in energy density. Furthermore, the thicker second adhesive layer lengthens the lithium-ion transport path during charging and discharging, leading to a slightly weaker improvement in the cycle performance of the secondary battery.

[0161] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0162] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0163] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly having a wound structure, the electrode assembly comprising a positive electrode, a negative electrode, a first separator, and a second separator, the negative electrode being located between the first separator and the second separator; The first diaphragm includes a first base membrane, a first adhesive layer, and a first ceramic coating. The first adhesive layer is disposed on both sides of the first base membrane, and the first ceramic coating is disposed on at least one side of the first base membrane and located between the first base membrane and the first adhesive layer. The first adhesive layer includes a first adhesive, which includes at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer. The first ceramic coating includes first ceramic particles, which include at least one of alumina, zirconium dioxide, titanium dioxide, or silicon dioxide. The second diaphragm includes a second base membrane, a second adhesive layer, and a second ceramic coating. The second adhesive layer is disposed on both sides of the second base membrane, and the second ceramic coating is disposed on at least one side of the second base membrane and located between the second base membrane and the second adhesive layer. The second adhesive layer includes a second adhesive, which includes at least one of polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose. The second ceramic coating includes second ceramic particles, which include boehmite. The materials of the first base film and the second base film each independently include at least one of polyimide, polyamide, polysulfone, polyacrylonitrile, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, aramid sulfone, or polyolefin, wherein the polymerization monomer of the polyolefin includes at least one of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene.

2. The secondary battery according to claim 1, wherein, The first adhesive comprises polyvinylidene fluoride-hexafluoropropylene copolymer, and the first ceramic particles comprise aluminum oxide; The second binder comprises polyimide, and the second ceramic particles comprise boehmite.

3. The secondary battery according to claim 1, wherein, The negative electrode sheet includes a negative current collector and a first negative electrode material layer and a second negative electrode material layer disposed on both sides of the negative current collector. Along the winding direction of the electrode assembly, the length of the first negative electrode material layer is greater than the length of the second negative electrode material layer. The first diaphragm is disposed on one side of the first negative electrode material layer of the negative electrode sheet, and the second diaphragm is disposed on one side of the second negative electrode material layer of the negative electrode sheet.

4. The secondary battery according to claim 3, wherein, The first ceramic coating is disposed on both sides of the first base film.

5. The secondary battery according to claim 3, wherein, The second separator is located between the positive electrode and the negative electrode, and the second ceramic coating is only disposed on the side of the second base film away from the negative electrode.

6. The secondary battery according to any one of claims 1 to 5, wherein, The average particle size of the first ceramic particles is 0.2 μm to 1.2 μm, and the average particle size of the second ceramic particles is 0.1 μm to 1.0 μm.

7. The secondary battery according to any one of claims 1 to 5, wherein, The thickness of the first ceramic coating is 0.5 μm to 2.5 μm, and the thickness of the second ceramic coating is 0.3 μm to 2.5 μm.

8. The secondary battery according to any one of claims 1 to 5, wherein, Based on the quality of the first ceramic coating, the mass percentage of the first ceramic particles is 10% to 50%; based on the quality of the second ceramic coating, the mass percentage of the second ceramic particles is 10% to 50%.

9. The secondary battery according to any one of claims 1 to 5, wherein, The thickness of the first adhesive layer is 0.2 μm to 5 μm, and the thickness of the second adhesive layer is 0.2 μm to 5 μm.

10. An electrical device comprising a secondary battery as described in any one of claims 1 to 9.

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