A secondary battery and an electric device

Abstract

The application provides a secondary battery and a power consumption device. The secondary battery comprises an electrode assembly, the electrode assembly is in a winding structure, and the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, a first separator and a second separator. The first separator comprises a first base film and a first ceramic coating layer, the first ceramic coating layer is arranged on at least one side of the first base film, the first ceramic coating layer comprises first ceramic particles, and the first ceramic particles comprise at least one of aluminum oxide, zirconium dioxide, titanium dioxide or silicon dioxide. The second separator comprises a second base film and a second ceramic coating layer, the second ceramic coating layer is arranged on at least one side of the second base film, the second ceramic coating layer comprises second ceramic particles, and the second ceramic particles comprise boehmite. Through the above arrangement, the secondary battery can have energy density, cycle performance and safety 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, and mobile electronic products. Lithium-ion batteries consist of components such as positive electrode plates, negative electrode plates, and separators, with the performance of the separator playing a crucial role in the overall performance of the lithium-ion battery. However, existing separators used in lithium-ion batteries often struggle to simultaneously achieve optimal energy density, cycle performance, and safety. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery that can balance the energy density, cycle performance and safety performance of a 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 and a first ceramic coating. The first ceramic coating is disposed on at least one side of the first base film and 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 and a second ceramic coating. The second ceramic coating is disposed on at least one side of the second base film and includes second ceramic particles, which include boehmite.

[0006] In existing technologies, the ceramic coating of the separator is usually made of two types: oxide and boehmite, both of which have a significant impact on the performance of secondary batteries. Oxides have good wettability and liquid absorption and retention capabilities, which can improve the cycle performance of secondary batteries. However, oxides have high hardness, which causes greater wear on machinery and increases equipment costs. In addition, oxides have a high specific gravity and do not have flame retardancy, which is detrimental to the energy density and safety of secondary batteries. Compared with oxides, boehmite has low hardness, high heat resistance, low density, and good adhesion, which can improve the heat resistance and puncture resistance of the separator, thereby improving the safety performance and energy density of secondary batteries. However, boehmite has poor electrolyte wettability, which is detrimental to liquid retention and the cycle performance of secondary batteries. This application regulates the types of first ceramic particles in the first separator and the types of second ceramic particles in the second separator, allowing the separators in the secondary battery to have ceramic coatings with different characteristics. This combines the advantages of oxide ceramic coatings and boehm ceramic coatings. The first separator has good electrolyte storage capacity and wetting performance, while the second separator is low in cost and density, which can improve the energy density of the secondary battery. The second separator also has good stability at high temperatures and low thermal shrinkage, which can reduce the possibility of short circuits caused by contact between the positive and negative electrodes due to the shrinkage of the second separator during charging and discharging, thus giving the secondary battery good safety performance. By using first and second separators with different ceramic coatings, the secondary battery achieves a balance of safety, cycle performance, economy, and energy density.

[0007] In some embodiments of this application, the negative electrode sheet is located between the first and second separators. 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 separator is disposed on one side of the first negative electrode material layer of the negative electrode sheet, and the second separator is disposed on one side of the second negative electrode material layer of the negative electrode sheet. Since boehmite can give the second separator higher heat resistance and puncture resistance, placing the second separator on the side of the second negative electrode material layer of the negative electrode sheet can better reduce the risk of positive and negative short circuits in the secondary battery under conditions such as high temperature and puncture. Oxide ceramics give the first separator better wettability and liquid absorption and retention capacity, which can improve the cycle performance of the secondary battery. Placing the first separator 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 reducing lithium plating. The above settings enable secondary batteries to further improve their cycle performance and safety performance while taking into account energy density and economy.

[0008] 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 maintaining energy density and safety performance.

[0009] In some embodiments of this application, the second separator is located between the positive and negative electrodes, and the second ceramic coating is only disposed on the side of the second base film facing away from the negative electrode. With the second separator located between the positive and negative electrodes, and the second ceramic coating disposed on the side of the second base film facing away from the negative electrode, the positive active material particles on the positive electrode are relatively hard, and occasionally large or sharp particles may protrude from the positive electrode. During the production or use of the secondary battery, these positive active material particles may puncture the separator between the positive and negative electrodes, causing a short circuit. Since the second ceramic coating on the second separator is only disposed on the side of the second base film facing away from the negative electrode, i.e., the second ceramic coating faces the positive electrode, the boehmite can improve the puncture resistance of the separator, thus reducing the possibility of the positive active material puncturing the separator and better protecting the second base film. Furthermore, a single-layer second ceramic coating allows the secondary battery to further improve safety performance while reducing cost and increasing energy density.

[0010] 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. 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 both energy density and safety performance.

[0011] In some embodiments of this application, the first separator includes a first adhesive layer disposed on both sides of the first base film, and a first ceramic coating disposed between the first base film and the first adhesive layer; the second separator includes a second adhesive layer disposed on both sides of the second base film, and a second ceramic coating disposed between the second base film and the second adhesive layer. This arrangement enables the first and second separators to have good adhesion, allowing for better fixation to the electrodes and reducing gaps between the positive electrode, negative electrode, and separator during the use of the secondary battery. This reduces the likelihood of electrolyte bridging, increasing the probability of lithium plating, black spots, reduced cycle performance, and reduced capacity. When the second separator has a second ceramic coating on only one side, the second adhesive layer is disposed on one surface of the second base film, and the second ceramic coating and the second adhesive layer are sequentially disposed on the other surface of the second base film. The same principle applies if the first separator has a first ceramic coating on only one side.

[0012] 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. Controlling the mass percentage of the first ceramic particles in the first ceramic coating and the mass percentage of the second ceramic particles in the second ceramic coating within the aforementioned ranges ensures the appropriate content of ceramic particles in the ceramic coating, allowing them to fully exert their corresponding functions, while also considering the energy density and manufacturing cost of the secondary battery.

[0013] In some embodiments of this application, the thickness of the first separator is 5.4 μm to 7.4 μm, and the thickness of the second separator is 5.1 μm to 6.3 μm. Controlling the thicknesses of the first and second separators within these ranges is beneficial for further improving the energy density of the secondary battery while maintaining good cycle performance and safety.

[0014] In some embodiments of this application, the thickness of the first ceramic coating is 0.5 μm to 1.5 μm, and the thickness of the second ceramic coating is 0.3 μm to 1.5 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 and safety.

[0015] In some embodiments of this application, the materials of the first and second adhesive layers each independently include at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose. The aforementioned first and second adhesive materials exhibit good adhesion in an electrolyte environment, enabling better bonding between the separator and the electrode.

[0016] 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.

[0017] The beneficial effects of this application are:

[0018] This application provides a secondary battery and an electrical device. By employing a first separator with an oxide ceramic coating and a second separator with a boehmite ceramic coating, the advantages of both types of ceramic coatings can be combined, enabling the secondary battery to simultaneously achieve high cycle performance, high safety performance, and high energy density. Furthermore, by combining the performance characteristics of the oxide ceramic coating and the boehmite ceramic coating with the structure of the secondary battery, the cycle performance and safety performance of the secondary battery can be further improved.

[0019] 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

[0020] 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.

[0021] 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;

[0022] 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;

[0023] Figure 3 This is a schematic diagram of the structure of the first diaphragm in the deployed state in some embodiments of this application;

[0024] Figure 4 This is a schematic diagram of the second diaphragm in its deployed state according to some embodiments of this application;

[0025] 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.

[0026] Figure label:

[0027] 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

[0028] 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.

[0029] 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.

[0030] 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 and a first ceramic coating, the first ceramic coating being disposed on at least one side of the first base film. "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 one side of the first base film or on both sides of the first base film. The first ceramic coating includes first ceramic particles, the first ceramic particles including at least one of alumina (Al2O3), zirconium dioxide (ZrO2), titanium dioxide (TiO2), or silicon dioxide (SiO2). The second separator includes a second base film and a second ceramic coating, the second ceramic coating being disposed on at least one side of the second base film. "The second ceramic coating is disposed on at least one side of the second base film" means that the second ceramic coating can be disposed on one side of the second base film or on both sides of the second base film. The second ceramic coating includes second ceramic particles, the second ceramic particles including boehmite (γ-AlOOH).

[0031] 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 diaphragm 10, a second diaphragm 20, a negative electrode 30, and a positive electrode 40, with the negative electrode 30 located between the first diaphragm 10 and the second diaphragm 20. Figure 2 As shown, the first diaphragm 10 includes a first base membrane 11 and a first ceramic coating 13. The first ceramic coating 13 is disposed on both sides of the first base membrane 11. It should be understood that in some embodiments, the first ceramic coating 13 may also be disposed on only one side of the first base membrane 11. Figure 4 As shown, the second diaphragm 20 includes a second base membrane 21 and a second ceramic coating 23. The second ceramic coating 23 is disposed on both sides of the second base membrane 21. It should be understood that in some embodiments, the second ceramic coating 23 may also be disposed on only one side of the second base membrane 21.

[0032] 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 in the secondary battery caused by the contact between the positive and negative electrode plates due to the shrinkage of the second separator during charging and discharging, and improve the binding ability of the second separator, thereby improving the safety performance and energy density of the secondary battery.

[0033] This application regulates the types of first ceramic particles in the first separator and the types of second ceramic particles in the second separator, allowing the separators in the secondary battery to have ceramic coatings with different characteristics. This combines the advantages of oxide ceramic coatings and boehm ceramic coatings. The first separator has good electrolyte storage capacity and wetting performance, while the second separator is low in cost and density, which can improve the energy density of the secondary battery. The second separator also has good stability at high temperatures and low thermal shrinkage, which can reduce the possibility of short circuits caused by contact between the positive and negative electrodes due to the shrinkage of the second separator during charging and discharging, thus giving the secondary battery good safety performance. By using first and second separators with different ceramic coatings, the secondary battery achieves a balance of safety, cycle performance, economy, and energy density.

[0034] In some embodiments of this application, the negative electrode sheet is located between the first and second separators. 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 separator is disposed on one side of the first negative electrode material layer of the negative electrode sheet, and the second separator is disposed on one side of the second negative electrode material layer of the negative electrode sheet. Figure 2 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, 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. 34The 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 on the side of the second negative electrode material layer of the negative electrode sheet can better reduce the risk of positive and negative electrode short circuits in 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. Disposing the first separator 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 reducing lithium plating. Through the above arrangement, the secondary battery can further improve its cycle performance and safety performance while balancing energy density and economy.

[0035] 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 disposing of 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. This further enhances the electrolyte storage capacity and wetting performance of the secondary battery, enabling the secondary battery to further improve its cycle performance while maintaining energy density and safety performance.

[0036] In some embodiments of this application, 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 facing away from the negative electrode. For example... Figure 2As shown, the second separator 20 includes a second base film 21 and a second ceramic coating 23. The second ceramic coating 23 is 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 close to and facing the positive electrode 40. The side of the second base film 21 close to the negative electrode 30 does not have the second ceramic coating 23. 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 be squeezed or even punctured in 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 film away from the negative electrode, that is, with the second ceramic coating facing the positive electrode, the 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, thus better protecting the second base film. At the same time, the single-layer setting of the second ceramic coating can reduce the cost and increase the energy density of the secondary battery while further improving its safety performance.

[0037] 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 both energy density and safety performance.

[0038] 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.

[0039] In some embodiments of this application, the first diaphragm includes a first base membrane, a first ceramic coating, and a first adhesive layer. The first adhesive layer is disposed on both sides of the first base membrane, and the first ceramic coating is disposed between the first base membrane and the first adhesive layer. In some embodiments, the first ceramic coating is disposed on both surfaces of the first base membrane, and the first adhesive layers on both sides of the first base membrane are each disposed on the surface of the first ceramic coating. For example, as... Figure 3As shown, the first separator 10 includes a first base film 11, a first ceramic coating 13, and a first adhesive layer 12. The first ceramic coating 13 is disposed on two opposite surfaces of the first base film 11 along the thickness direction Z. The first adhesive layers 12, disposed on both sides of the first base film 11, are respectively disposed on the surfaces of the first ceramic coating 13, with the first ceramic coating 13 located between the first base film 11 and the first adhesive layer 12. In other embodiments, the first ceramic coating is disposed on only one side of the first base film, the first adhesive layer is disposed on both sides of the first base film, and the first adhesive layer on the same side as the first ceramic coating is disposed on the surface of the first ceramic coating, so that the first ceramic coating is located between the first base film and the first adhesive layer. The first adhesive layer disposed on the other side of the first base film is directly disposed on the surface of the first base film. The placement of the first adhesive layer in the first separator enables the first separator to have good adhesion, which can better fix it to the electrode, reducing the gaps between the positive electrode, negative electrode, and separator during the use of the secondary battery, thus preventing electrolyte bridging and increasing the probability of lithium plating, black spots, reduced cycle performance, and reduced capacity.

[0040] In some embodiments of this application, the second diaphragm includes a second adhesive layer disposed on both sides of the second base membrane, and a second ceramic coating disposed between the second base membrane and the second adhesive layer. In some embodiments, the second ceramic coating is disposed on both surfaces of the second base membrane, and the second adhesive layers on both sides of the second base membrane are each disposed on the surface of the second ceramic coating. For example, as... Figure 4 As shown, the second separator 20 includes a second base film 21, a second ceramic coating 23, and a second adhesive layer 22. The second ceramic coating 23 is disposed on two opposite surfaces of the second base film 21 along the thickness direction Z. The second adhesive layers 22, disposed on both sides of the second base film 21, are respectively disposed on the surfaces of the second ceramic coating 23, with the second ceramic coating 23 located between the second base film 21 and the second adhesive layer 22. In other embodiments, the second ceramic coating is disposed on only one side of the second base film, the second adhesive layer is disposed on both sides of the second base film, and the second adhesive layer on the same side as the second ceramic coating is disposed on the surface of the second ceramic coating, so that the second ceramic coating is located between the second base film and the second adhesive layer. The second adhesive layer disposed on the other side of the second base film is directly disposed on the surface of the second base film. The placement of the second adhesive layer in the second separator enables the second separator to have good adhesion, which can better fix it to the electrode, reducing the gaps between the positive electrode, negative electrode, and separator during the use of the secondary battery, thus reducing the probability of electrolyte bridging and increasing the likelihood of lithium plating, black spots, reduced cycle performance, and reduced capacity.

[0041] In some embodiments of this application, the mass percentage of the first ceramic particles is between 10% and 50%, depending 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 content of the first ceramic particles in the first ceramic coating is sufficient, allowing the first ceramic particles to fully exert their corresponding functions, resulting in a first separator with good liquid storage capacity and wetting properties. Applying this first separator to a secondary battery is beneficial for achieving good cycle performance while also considering the energy density and manufacturing cost of the secondary battery.

[0042] 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 ensures that the content of the second ceramic particles in the second ceramic coating is sufficient, allowing the second ceramic particles to fully exert their corresponding functions, resulting in a second separator with good thermal stability and puncture resistance. Applying this second separator to a secondary battery improves the safety performance of the secondary battery while also considering the energy density and manufacturing cost.

[0043] 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%.

[0044] In some embodiments of this application, such as Figure 3 As shown, the thickness T of the first diaphragm 10 10 The range is from 5.4 μm to 7.4 μm, such as... Figure 4As shown, the thickness T of the second diaphragm 20 20 The thickness is between 5.1 μm and 6.3 μm. For example, the thickness of the first separator is 5.4 μm, 5.6 μm, 5.8 μm, 6.0 μm, 6.3 μm, 6.8 μm, 7.0 μm, 7.2 μm, 7.4 μm, or any value between any two of the above ranges. For example, the thickness of the second separator is 5.1 μm, 5.2 μm, 5.8 μm, 6.0 μm, 6.3 μm, or any value between any two of the above ranges. Controlling the thickness of the first and second separators within the above ranges helps to achieve a smaller volume in the secondary battery, reducing the risk of energy density loss due to excessive volume. This allows the secondary battery to further improve its energy density while maintaining good cycle performance and safety.

[0045] 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 1.5μm, such as Figure 4 As shown, the thickness T of the second ceramic coating 23 23 The thickness ranges from 0.3 μm to 1.5 μm. For example, the thickness of the first ceramic coating is 0.5 μm, 1.0 μm, 1.5 μm, or any value between any two of the above ranges. Similarly, the thickness of the second ceramic coating is 0.3 μm, 1.2 μm, 1.5 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 in both 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 and safety.

[0046] In some embodiments of this application, the materials of the first and second adhesive layers each independently include at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyvinyl alcohol, or sodium carboxymethyl cellulose. When the aforementioned first and second adhesive materials are used in the first and second separators, they exhibit good compatibility with the electrolyte and good adhesion to the positive and negative electrode sheets, thus contributing to good adhesion between the first and second separators. Therefore, applying the first and second separators to the secondary battery improves their electrolyte storage capacity and wetting properties, and also enhances the adhesion between the first and second separators and the positive and / or negative electrode sheets. Consequently, the secondary battery can achieve a balance between energy density, cycle performance, and safety performance.

[0047] The present application has no particular limitation on the materials of the first base film and the second base film, as long as the purpose of the present application can be achieved. For example, the materials of the first base film and the second base film each independently comprise at least one of polyimide, polyamide, polysulfone, polyacrylonitrile, cellulose, polyether ether ketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenylene terephthalamide), poly(aryl ether sulfone ketone), aramid fiber, polysulfone aramid fiber or polyolefin, and the polymerization monomers of the polyolefin comprise at least one of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene or cyclohexene. The present application has no particular limitation on the weight average molecular weight of the material of the first base film, as long as the purpose of the present application can be achieved. For example, the weight average molecular weight of the material of the first base film may be 2×10 5 to 1.5×10 6 . The present application has no particular limitation on the weight average molecular weight of the material of the second base film, as long as the purpose of the present application can be achieved. For example, the weight average molecular weight of the material of the second base film may be 2×10 5 to 1.5×10 6 . The present application has no particular limitation on the thicknesses of the first base film and the second base film, as long as the purpose of the present application can be achieved.

[0048] The present application has no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may comprise copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collectors (e.g., copper composite current collectors, 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 comprise 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 purpose of the present application can be achieved. For example, the negative electrode active material may comprise natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, 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 purpose 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 comprise 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 purpose of the present application can be achieved.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] This application does not impose any particular restrictions on the types of the first and second thickeners mentioned above, 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. This application does not impose any particular restrictions on the content of the first thickener in the first adhesive layer or the content of the second thickener in the second adhesive layer. Those skilled in the art can select them according to actual needs, as long as the purpose of this application can be achieved.

[0055] 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.

[0056] 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 first separator, the negative electrode, and the second 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.

[0057] 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.

[0058] 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.

[0059] Example

[0060] 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.

[0061] Test methods and equipment:

[0062] Sampling methods for the first and second septa:

[0063] 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, and the thickness of the first and second ceramic coatings, as well as the thickness of the first and second separators, were all measured using the above method.

[0064] Average particle size test of the first and second ceramic particles:

[0065] 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.

[0066] Thickness testing of the first ceramic coating, the second ceramic coating, the first diaphragm, and the second diaphragm:

[0067] 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 diaphragm 10 ;

[0068] 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 diaphragm 20 .

[0069] Lithium-ion battery thickness testing:

[0070] Adjust the test pressure to 600g by adding or removing weights; place a 3mm gauge block on the platform, press the white buttons on both sides, and the panel pressure gap battery thickness gauge (PPG battery thickness gauge) will automatically feed the gauge block in and test it. Test any 9 points in sequence, and verify the tolerance to be ±0.02mm. It can only be used if it is within the specification; hold the lithium-ion battery with one hand, barcode side up, on the platform, scan the barcode first, and then press the white buttons on both sides. The instrument will automatically feed the lithium-ion battery in and test it. Record the test result, which is the thickness of the lithium-ion battery.

[0071] The thickness of a lithium-ion battery characterizes its energy density; for the same volume, a greater thickness indicates a lower energy density.

[0072] High-temperature hot box testing:

[0073] 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.

[0074] 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. Ten 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.

[0075] The safety performance of lithium-ion batteries is characterized by the pass rate of the hot box test. The higher the pass rate of the hot box test, the better the safety performance of the lithium-ion battery.

[0076] Cyclic performance testing:

[0077] 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.

[0078] Capacity retention rate (%) = (Discharge capacity after 1000 cls of cycling / Discharge capacity of the first cycle) × 100%.

[0079] A higher capacity retention rate indicates better cycle performance of the lithium-ion battery.

[0080] Example 1-1

[0081] <Preparation of the first diaphragm>

[0082] The selected material is polyethylene (weight-average molecular weight Mw = 4 × 10⁻⁶). 6 The second base film (manufacturer: CoreSilicon Valley, model P492780) has a thickness of 3.5μm.

[0083] The second adhesive is polyimide (PI, Mw = 6 × 10⁻⁶). 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 first adhesive layer slurry with a solid content of 75wt%.

[0084] The first ceramic particles, alumina (Al2O3), and the first ceramic coating adhesive, styrene-butadiene rubber (Mw = 7 × 10⁻⁶), were combined. 6Mix them together, add deionized water as a solvent, and stir evenly to form a first ceramic coating slurry with a solid content of 30wt%.

[0085] 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 =7.2μm, the thickness T of the first ceramic coating 13 =1.4μm, the average particle size of the first ceramic particles is 1.0μm, and the thickness of the first adhesive layer is 0.45μm. 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%.

[0086] <Preparation of the Second Diaphragm>

[0087] The selected material is polyethylene (weight-average molecular weight Mw = 4 × 10⁻⁶). 6 The second base film (manufacturer: CoreSilicon Valley, model P492780) has a thickness of 4.0μm.

[0088] 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%.

[0089] 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%.

[0090] 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 =6.0μm, the thickness T of the second ceramic coating23 =1.2μm, the average particle size of the second ceramic particles is 0.5μm, and the thickness of the second adhesive layer is 0.4μm. Based on the quality 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%.

[0091] <Preparation of Negative Electrode Sheets>

[0092] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.6:1.1:1.3, and deionized water was added as a solvent. After stirring evenly, a first negative electrode slurry with a solid content of 70 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 74 mm × 824 mm dimensions for later use. The compaction density of the first negative electrode material layer was 1.735 g / cm³. 3 The length is 720mm, and the compaction density of the second negative electrode material layer is 1.735g / cm³. 3 It is 680mm in length.

[0093] <Preparation of the positive electrode>

[0094] Lithium cobalt oxide (CCO), conductive carbon black (CCO), and polyvinylidene fluoride (PVDF) (PVDF binder) were mixed in a mass ratio of 95:2.5:2.5. 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 sheet was then cold-pressed and cut into 70 mm × 800 mm dimensions for later use. The compaction density of the positive electrode material layer was 4.23 g / cm³. 3 .

[0095] <Preparation of Electrolyte>

[0096] 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 12%, with the remainder being the base solvent.

[0097] <Preparation of Lithium-ion Batteries>

[0098] The prepared positive electrode sheet, second 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 with aluminum tabs, and the negative electrode tab is spot-welded with nickel tabs. The second ceramic coating in the second separator faces away from the negative electrode sheet. The first separator is disposed on one side of the first negative electrode material layer of the negative electrode sheet, and the second separator is disposed on one side of the second negative electrode material layer of the negative electrode sheet (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, 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.

[0099] Examples 1-2

[0100] 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.

[0101] Examples 1-3

[0102] <Preparation of the first diaphragm>

[0103] 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 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. Subsequently, 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. The thickness T of the first diaphragm is... 10 =5.8μm.

[0104] <Preparation of Lithium-ion Batteries>

[0105] 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 the first ceramic coating in the first separator faces away from the negative 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. 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.

[0106] The rest is the same as in Example 1-1.

[0107] Examples 1-4

[0108] <Preparation of the Second Diaphragm>

[0109] 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. The above steps are then repeated on the other surface of the second base film to obtain the second diaphragm. The thickness T of the second diaphragm is specified. 20 =7.2μm.

[0110] <Preparation of Lithium-ion Batteries>

[0111] 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.

[0112] The rest is the same as in Example 1-1.

[0113] Examples 1-5 to Examples 1-7

[0114] Except for adjusting the type of the first ceramic particles according to Table 1, the rest is the same as in Example 1-1.

[0115] Examples 2-1 to 2-10

[0116] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0117] Examples 3-1 to 3-8

[0118] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0119] 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%.

[0120] Examples 4-1 to 4-8

[0121] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 2-9.

[0122] Comparative Example 1

[0123] 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.

[0124] <Preparation of Lithium-ion Batteries>

[0125] 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.

[0126] Comparative Example 2

[0127] 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 Examples 1-3.

[0128] <Preparation of Lithium-ion Batteries>

[0129] The prepared positive electrode, first 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 ceramic coating in the first 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.

[0130] Comparative Example 3

[0131] 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 Examples 1-4.

[0132] <Preparation of Lithium-ion Batteries>

[0133] 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 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.

[0134] Comparative Example 4

[0135] 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.

[0136] <Preparation of Lithium-ion Batteries>

[0137] 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.

[0138] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0139] Table 1

[0140]

[0141]

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

[0143] As can be seen from Examples 1-1 to 1-7 and Comparative Examples 1 to 4, the secondary batteries of this application, by using different types of first and second separators and controlling the types of first ceramic particles in the first separator and the types of second ceramic particles in the second separator within the scope of this application, can simultaneously achieve high capacity retention, small thickness, and high hot box test pass rates at both 130°C and 132°C. This indicates that the secondary batteries can balance cycle performance, energy density, and safety performance. However, the secondary batteries of Comparative Examples 1 to 4 use the same type of separator, or the types of ceramic particles in the two separators do not meet the limitations of this application. Therefore, the comparative secondary batteries cannot simultaneously achieve high capacity retention, small thickness, and high hot box test pass rates at both 130°C and 132°C, indicating that the comparative secondary batteries cannot balance cycle performance, energy density, and safety performance.

[0144] Table 2

[0145]

[0146] The average particle size of the first ceramic particles typically affects the cycle performance, energy density, and safety 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, small thickness, and high pass rates in hot-box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, energy density, and safety performance. Compared to Examples 1-1 and 2-1 to 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 hot-box tests, thus resulting in slightly weaker safety performance.

[0147] The average particle size of the second ceramic particles typically affects the cycle performance, energy density, 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, small thickness, and high pass rates in hot-box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, energy density, and safety performance. Compared to Examples 1-1 and 2-5 to 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 safety performance.

[0148] Table 3

[0149]

[0150] The mass percentage of the first ceramic particles W 11 This typically affects the cycle performance, energy density, 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... 11 The secondary battery within the scope of this application simultaneously exhibits high capacity retention, small thickness, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, energy density, and safety performance. Compared with Examples 1-1 and 3-1 to 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 safety 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 safety performance.

[0151] The mass percentage of the second ceramic particles W 21 This typically affects the cycle performance, energy density, 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... 21The secondary battery within the scope of this application simultaneously exhibits high capacity retention, small thickness, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, energy density, and safety performance. Compared with Examples 1-1 and 3-5 to 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 safety 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 safety performance.

[0152] Table 4

[0153]

[0154] The thickness T of the first ceramic coating 13 And the thickness T of the first diaphragm 10 This typically affects the cycle performance, energy density, 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... 13 And the thickness T of the first diaphragm 10 The secondary battery within the scope of this application simultaneously exhibits high capacity retention, small thickness, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, energy density, and safety performance. Compared with Examples 2-9 and Examples 4-1 to 4-2, the first ceramic coating and first separator thickness in Example 4-3 are thinner, resulting in slightly weaker liquid retention and less binding effect on the first base film at high temperatures, thus slightly weakening the improvement effect on the cycle performance and safety performance of the secondary battery. The first ceramic coating and first separator thickness in Example 4-4 are thicker, resulting in a slight loss in energy density, and an increased possibility of short circuits caused by first ceramic particles puncturing the separator during hot box testing, thus slightly weakening the safety performance.

[0155] The thickness T of the second ceramic coating 23 The thickness T of the second diaphragm 20 This typically affects the cycle performance, energy density, and safety performance of secondary batteries. As can be seen from Examples 2-9 and Examples 4-5 to 4-8, the thickness T of the second ceramic coating is selected... 23 The thickness T of the second diaphragm 20The secondary battery within the scope of this application simultaneously exhibits high capacity retention, small thickness, and high pass rates in hot box tests at both 130°C and 132°C, indicating that the secondary battery can balance cycle performance, energy density, and safety performance. Compared with Examples 2-9 and Examples 4-5 to 4-6, the second ceramic coating and first separator thicknesses in Examples 4-7 are thinner, resulting in a weaker binding effect of the second ceramic coating on the second base film at high temperatures and a slightly weaker improvement in the safety performance of the secondary battery. The second ceramic coating and second separator thicknesses in Examples 4-8 are 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 safety performance.

[0156] 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.

[0157] 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.

[0158] 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, the 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 is located between the first separator and the second separator. The first separator includes a first base film and a first ceramic coating. The first ceramic coating is disposed on at least one side of the first base film. The first ceramic coating includes first ceramic particles, which include at least one of aluminum oxide, zirconium dioxide, titanium dioxide, or silicon dioxide. The second membrane includes a second base membrane and a second ceramic coating, the second ceramic coating being disposed on at least one side of the second base membrane, the second ceramic coating including second ceramic particles, the second ceramic particles including boehmite; 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.

2. The secondary battery according to claim 1, wherein, The first ceramic coating is disposed on both sides of the first base film.

3. The secondary battery according to claim 1, 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.

4. The secondary battery according to any one of claims 1 to 3, 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.

5. The secondary battery according to any one of claims 1 to 3, wherein, The first diaphragm includes a first adhesive layer disposed on both sides of the first base membrane, and the first ceramic coating is disposed between the first base membrane and the first adhesive layer; The second diaphragm includes a second adhesive layer disposed on both sides of the second base membrane, and the second ceramic coating is disposed between the second base membrane and the second adhesive layer.

6. The secondary battery according to claim 4, 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%.

7. The secondary battery according to any one of claims 1 to 3, wherein, The thickness of the first diaphragm is 5.4 μm to 7.4 μm, and the thickness of the second diaphragm is 5.1 μm to 6.3 μm.

8. The secondary battery according to any one of claims 1 to 3, wherein, The thickness of the first ceramic coating is 0.5 μm to 1.5 μm, and the thickness of the second ceramic coating is 0.3 μm to 1.5 μm.

9. The secondary battery according to claim 5, wherein, The materials of the first adhesive layer and the second adhesive layer each independently include at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyvinyl alcohol or sodium carboxymethyl cellulose.

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

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