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 in a winding structure, the electrode assembly comprising a positive electrode sheet, a negative electrode sheet, a first separator and a second separator, the negative electrode sheet being located between the first separator and the second separator; the first separator comprises a first base film, a first adhesive layer and a first ceramic coating layer, the first adhesive layer being located on both sides of the first base film, the first ceramic coating layer being located on a surface of one side of the first base film, and the first ceramic coating layer being located between the first base film and the first adhesive layer; the first ceramic particles in the first ceramic coating layer comprise at least one of aluminum trioxide, zirconium dioxide, titanium dioxide or silicon dioxide; the second separator comprises a second base film, a second adhesive layer and a second ceramic coating layer, the second adhesive layer being located on both sides of the second base film, the second ceramic coating layer being located on a surface of one side of the second base film, and the second ceramic coating layer being located between the second base film and the second adhesive layer; the second ceramic particles in the second ceramic coating layer comprise boehmite.

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, and electric vehicle fields. Lithium-ion batteries consist of components such as positive electrode plates, negative electrode plates, and separators, among which the performance of the separator plays 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, with the negative electrode located between the first separator and the second separator. The first separator includes a first base film, a first adhesive layer, and a first ceramic coating. The first adhesive layer is located on both sides of the first base film, and the first ceramic coating is located on the surface of one side of the first base film, with the first ceramic coating located between the first base film and the first adhesive layer. 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 located on both sides of the second base film, and the second ceramic coating is located on the surface of one side of the second base film, with the second ceramic coating located between the second base film and the second adhesive layer. The second ceramic coating 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. Oxide coatings 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 boehmite 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 the shrinkage of the second separator during charging and discharging, leading to contact between the positive and negative electrodes. This results in good safety performance for the secondary battery. Using first and second separators with different ceramic coatings allows the secondary battery to balance safety, cycle performance, economy, and energy density. Since boehmite can give the second separator 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 under high temperature and puncture conditions, thus ensuring good safety performance for the secondary battery.

[0007] 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 located 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 located on one side of the first negative electrode material layer of the negative electrode sheet, and a second separator is located on one side of the second negative electrode material layer of the negative electrode sheet. The oxide ceramic material gives the first separator better wettability and liquid absorption and retention capabilities, which can improve the cycle performance of the secondary battery. The first separator is located on the side of the longer first negative electrode material layer in the negative electrode sheet, allowing more negative electrode active material to contact 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.

[0008] In some embodiments of this application, the material of the first base film includes at least one selected from polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, or aramid sulfone; the material of the second base film includes polyolefin, wherein 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 first base film using the above materials has a high glass transition temperature and good thermal stability. As the internal temperature rises during the charging and discharging of the secondary battery, the first base film maintains high porosity while possessing high mechanical strength, ensuring smooth electrolyte flow and improving the lithium-ion transport rate. The stable pore structure of the first base film also enhances its liquid absorption and retention capacity; however, the first base film is relatively thick. The combination of the first base film and the first ceramic coating compensates for the poor heat resistance of the first ceramic coating, resulting in higher stability of the first separator at high temperatures. Furthermore, the combined high liquid retention of the first base film further improves the cycle performance of the secondary battery. The second base film, while having a lower glass transition temperature, can be prepared using wet or dry processes with uniaxial or biaxial stretching to achieve a thinner film, compensating for the energy density loss caused by the thicker first base film. The second base film, combined with the heat-resistant and puncture-resistant second ceramic coating, better prevents shrinkage or pore blockage of the second base film at high temperatures, thus ensuring good safety for the second separator.

[0009] 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. By controlling the average particle sizes of the first and second ceramic particles within the aforementioned ranges, the first and second ceramic particles possess higher specific surface areas, which can improve the liquid storage capacity and wetting performance of the first and second separators. This, in turn, helps to further improve the cycle performance of the secondary battery while maintaining both energy density and safety performance.

[0010] 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 percentages of the first and second ceramic particles in the first and second ceramic coatings within these ranges ensures the appropriate content of ceramic particles in the ceramic coatings, allowing them to fully exert their functions, while also considering the energy density and manufacturing cost of the secondary battery. This results in a secondary battery with good cycle performance, safety performance, and energy density.

[0011] In some embodiments of this application, the material of the first base film includes polyethylene terephthalate, and the material of the second base film includes at least one of polypropylene or polyethylene. When materials within the above range are selected, the safety performance of the secondary battery can be improved while maintaining energy density, and the cycle performance of the secondary battery can be enhanced.

[0012] In some embodiments of this application, the glass transition temperature of the first base film is 80°C to 100°C, and the glass transition temperature of the second base film is 25°C to 50°C. When the glass transition temperatures of the first and second base films are within the above ranges, the safety performance of the secondary battery can be better improved and the cycle performance of the secondary battery can be enhanced while taking into account the energy density.

[0013] In some embodiments of this application, the porosity of the first base film is 40% to 70%, and the porosity of the second base film is 5% to 50%. When the porosities of the first and second base films are within the above ranges, the safety performance of the secondary battery can be better improved and the cycle performance of the secondary battery can be enhanced while taking into account the energy density.

[0014] In some embodiments of this application, the pore size of the first base film is from 80 nm to 700 nm, and the pore size of the second base film is from 50 nm to 200 nm. When the pore sizes of the first and second base films are within the above ranges, the safety performance of the secondary battery can be better improved, the cycle performance of the secondary battery can be enhanced, and the production cost can be reduced while taking into account the energy density.

[0015] 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.

[0016] The beneficial effects of this application are:

[0017] This application provides a secondary battery and an electrical device. The secondary battery utilizes a combination of a first separator and a second separator with different types of single-layer ceramic coatings. By 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, the first and second separators achieve a smaller thickness, thereby reducing the volume of the secondary battery and enabling it to achieve a higher energy density. This also gives the secondary battery good electrolyte storage capacity and wetting performance, and the second separator exhibits good stability at high temperatures and low thermal shrinkage, reducing 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. This results in good safety performance for the secondary battery. Therefore, the secondary battery can achieve a balance between energy density, cycle performance, and safety performance.

[0018] 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

[0019] 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.

[0020] 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;

[0021] 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;

[0022] Figure 3 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.

[0023] Figure label:

[0024] 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

[0025] 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.

[0026] 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.

[0027] 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 negative electrode is located between the first and second separators, and the positive electrode is located on the outermost layer of the electrode assembly. The first separator includes a first base film, a first adhesive layer, and a first ceramic coating. The first adhesive layer is located on both sides of the first base film, and the first ceramic coating is located on one side of the surface of the first base film. The first ceramic coating is located between the first base film and the first adhesive layer. On the side of the first base film where the first ceramic coating is not present, the first adhesive layer is directly disposed on the surface of the first base film. It is understood that the first ceramic coating can be located on either side of the first base film. Specifically, in some embodiments, the first ceramic coating is disposed on the surface of the first base film facing away from the negative electrode; in other embodiments, the first ceramic coating is disposed on the surface of the first base film closer to the negative electrode. 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 located on both sides of the second base film, and the second ceramic coating is located on one side of the surface of the second base film. The second ceramic coating is located between the second base film and the second adhesive layer. On the side of the second base film where the second ceramic coating is not present, the second adhesive layer is directly disposed on the surface of the second base film. It is understood that the second ceramic coating can be located on either side of the second base film. Specifically, in some embodiments, the second ceramic coating is located on the surface of the second base film facing away from the negative electrode; in other embodiments, the second ceramic coating is located on the surface of the second base film closer to the negative electrode. The second ceramic coating includes second ceramic particles, which include boehmite.

[0028] 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. Figure 1As 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 positive electrode 40 is located on 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, and the first ceramic coating 13 is located on the surface of the first base film 11 near the negative electrode 30. The first ceramic coating 13 is located between the first base film 11 and the first adhesive layer 12. On the side of the first base film 11 where the first ceramic coating 13 is not provided, i.e., on the surface of the first base film 11 away from the negative electrode 30, the first adhesive layer 12 is directly disposed on the surface of the first base film 11. The second diaphragm 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 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 21 where the second ceramic coating 23 is not present, i.e., on the surface of the second base film 21 near 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 first ceramic coating 13 may also be disposed on the surface of the first base film 11 facing away from the negative electrode 30; in other embodiments, the second ceramic coating 23 may also be disposed on the surface of the second base film 21 near the negative electrode 30.

[0029] By providing a first ceramic coating on one side of the first base membrane in the first separator and a second ceramic coating on one side of the second base membrane in the second separator, the first and second separators can have smaller thicknesses, reducing the volume of the secondary battery and decreasing the possibility of energy density loss due to increased volume, thereby improving the energy density of the secondary battery.

[0030] 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.

[0031] This application combines different types of single-layer ceramic-coated first and second separators, and controls the types of first ceramic particles in the first separator and second ceramic particles in the second separator to be within the scope of this application. This allows the first and second separators to have smaller thicknesses, reducing the volume of the secondary battery and enabling it to have a higher energy density. It also balances the advantages of both first and second ceramic particles: the first separator has good electrolyte storage capacity and wetting performance, while the second separator is low-cost and low-density, improving the energy density of the secondary battery. Furthermore, the second separator exhibits good stability at high temperatures and low thermal shrinkage, reducing 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 providing good safety performance for the secondary battery. Therefore, the secondary battery can achieve a balance of energy density, cycle performance, and safety performance.

[0032] 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 located 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 located on one side of the first negative electrode material layer of the negative electrode sheet, and a second separator is located on one side of the second negative electrode material layer of the negative electrode sheet. For example... 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 is located on the outermost layer of the electrode assembly 100. 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. This arrangement allows more negative electrode active material to come into contact with more electrolyte, reducing the risk of lithium deposition at the interface between the electrolyte and the negative electrode sheet due to electrolyte bridging in the later stages of the secondary battery cycle. In this way, the secondary battery can further improve its cycle performance while maintaining both energy density and safety.

[0033] In some embodiments of this application, the second ceramic coating is disposed on the side of the second base film facing away from the negative electrode sheet. For example... Figure 1 and Figure 2 As shown, the second separator 20 includes a second base film 21, a second adhesive layer 22, and a second ceramic coating 23. The second ceramic coating 23 is disposed on the surface of the second base film 21 facing away from the negative electrode 30, that is, on the surface of the second base film 21 close to and facing the positive electrode 40. The second ceramic coating 23 is located between the second base film 21 and the second adhesive layer 22. The second ceramic coating 23 is not disposed on the side of the second base film 21 close to the negative electrode 30, and the second adhesive layer 22 is directly disposed on the surface of the second base film 21 close to the negative electrode 30. When the positive electrode active material particles in the positive electrode are large in size or sharp, during the production or use of secondary batteries, the positive electrode 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.

[0034] In some embodiments of this application, the material of the first base film includes at least one selected from polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, or aramid sulfone. The material of the second base film includes polyolefin, and 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. The first base film using the above materials has a large glass transition temperature and good thermal stability. As the internal temperature rises during the charging and discharging of the secondary battery, the first base film maintains high porosity while possessing high mechanical strength, allowing for smooth electrolyte flow and improving the lithium-ion transport rate. The stable pore structure of the first base film also improves the liquid absorption and retention capacity. However, the first base film is relatively thick. The combination of the first base film and the first ceramic coating can compensate for the poor heat resistance of the first ceramic coating, resulting in higher stability of the first separator at high temperatures. Furthermore, the combined high liquid retention of the first base film and the second base film can further improve the cycle performance of the secondary battery. The material of the second base film has a lower glass transition temperature, but a thinner second base film can be prepared by uniaxial or biaxial stretching using wet or dry processes, compensating for the energy density loss caused by the thicker first base film. The second base film, combined with the second ceramic coating which has good heat resistance and puncture resistance, allows the second ceramic coating to better prevent shrinkage or pore blockage of the second base film at high temperatures, resulting in good safety for the second separator. This application does not impose any particular limitation on the weight-average molecular weight of the material of the first base film, as long as it achieves the purpose of this application. For example, the weight-average molecular weight of the material of the first base film 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 .

[0035] In some embodiments of this application, the material of the first base membrane includes polyethylene terephthalate, and the material of the second base membrane includes at least one of polypropylene or polyethylene. When the materials of the first and second base membranes described above are selected, a double-membrane structure including the first and second base membranes is provided in the secondary battery, which is beneficial to further improve the safety and cycle performance of the secondary battery while taking into account energy density.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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%.

[0041] In some embodiments of this application, the glass transition temperature of the first base film is between 80°C and 100°C, and the glass transition temperature of the second base film is between 25°C and 50°C. For example, the glass transition temperature of the first base film is 80°C, 83°C, 85°C, 87°C, 90°C, 92°C, 95°C, 97°C, 100°C, or any value between any two of the above ranges. For example, the glass transition temperature of the second base film is 25°C, 27°C, 30°C, 32°C, 35°C, 37°C, 40°C, 42°C, 45°C, 47°C, 50°C, or any value between any two of the above ranges. When the glass transition temperatures of the first and second base films are within the above ranges, using a double-membrane structure of the first and second base films in the secondary battery can improve the safety performance and cycle performance of the secondary battery while maintaining energy density.

[0042] This application does not impose any particular restrictions on the method of controlling the glass transition temperature of the first base film and the glass transition temperature of the second base film, as long as the purpose of this application can be achieved. For example, it can be controlled by selecting different types of first and second base films.

[0043] In some embodiments of this application, the porosity of the first base membrane is 40% to 70%, and the porosity of the second base membrane is 5% to 50%. For example, the porosity of the first base membrane is 40%, 44%, 49%, 55%, 60%, 65%, 70%, or any value between any two of the above ranges. For example, the porosity of the second base membrane is 5%, 10%, 15%, 22%, 25%, 32%, 40%, 50%, or any value between any two of the above ranges. By controlling the porosity of the first and second base membranes within the above ranges, the strength of the first and second separators is higher, improving the safety performance of the secondary battery. The secondary battery exhibits better kinetic performance during charge and discharge, and can adsorb more electrolyte. The good wetting properties of the first and second separators are beneficial to lithium-ion transport, thereby improving the cycle performance and extending the cycle life of the secondary battery.

[0044] This application does not impose any particular restrictions on the method of controlling the porosity of the first base film and the second base film, as long as the purpose of this application can be achieved. For example, commercially available first and second base films with different porosities can be selected, and the porosity of the first and second base films can be determined by combining the test method of "porosity test of the first and second base films" in this application, and the first and second base films with the desired porosity can be selected.

[0045] In some embodiments of this application, the pore size of the first base film is from 80 nm to 700 nm, and the pore size of the second base film is from 50 nm to 200 nm. For example, the pore size of the first base film is 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or any value between any two of the above ranges. For example, the pore size of the second base film is 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 180 nm, 200 nm, or any value between any two of the above ranges. By controlling the average pore size of the first base film and the average pore size of the second base film within the above ranges, it is beneficial to the transport of lithium ions. Lithium ions exhibit better kinetic performance during the charge and discharge transport process of the secondary battery. At the same time, more electrolyte can be adsorbed, and the wetting performance of the first and second separators is better, thereby improving the cycle performance of the secondary battery. Therefore, secondary batteries, while balancing energy density, also possess good safety and cycle performance.

[0046] This application does not impose any particular restrictions on the method of controlling the pore size of the first base film and the second base film, as long as the purpose of this application can be achieved. For example, commercially available first base films and second base films with different pore sizes can be selected, and the average pore size of the first base film and the micro second base film can be determined by combining the test method of "pore size test of the first base film and the second base film" in this application, and the first base film and the second base film with the required average pore size can be selected.

[0047] 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.

[0048] 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 6.5 μm to 12.5 μm, and the thickness of the second diaphragm is 4.8 μm to 7.5 μm.

[0049] In some embodiments of this application, the first adhesive layer includes a first adhesive, and the second adhesive layer includes a second adhesive. The first and second adhesives are each independently selected from at least one of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or polyimide. By selecting the aforementioned first and second adhesives, it is beneficial to improve the adhesion between the first base film and the first adhesive layer, and between the second base film and the second adhesive layer. This also improves the adhesion between the first separator and the positive electrode, between the first separator and the negative electrode, and between the second separator and the negative electrode. Furthermore, it strengthens the interfaces between the first separator and the positive electrode, between the first separator and the negative electrode, and between the second separator and the negative electrode, which is beneficial for lithium-ion transport. Simultaneously, it reduces the possibility of the first and second ceramic coatings detaching, thereby improving the cycle performance of the secondary battery. Thus, the secondary battery, while maintaining energy density, has a long cycle life and good safety performance. This application does not impose any particular limitation on the weight-average molecular weight of the first and second adhesives, as long as the objectives of this application are achieved. For example, the weight-average molecular weight of the first and second adhesives can be 1.5 × 10⁻⁶. 4 Up to 9×10 6 .

[0050] In some embodiments of the present application, the first adhesive layer may further comprise a first thickener, and the second adhesive layer may further comprise a second thickener. Based on the mass of the first adhesive layer, 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 thickener is 0.3% to 6%. Applying the first thickener to the first adhesive layer and the second thickener to the second adhesive layer is beneficial to improving the stability of the slurry of the first adhesive layer and the slurry of the second adhesive layer, and preventing sedimentation of each component in the slurry of the first adhesive layer and the slurry of the second adhesive layer. The present application has no particular limitation on the types of the first thickener and the second thickener, as long as the object of the present application can be achieved. For example, the first thickener and the second thickener are each independently selected from at least one of hydroxyethyl cellulose, methyl hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyacrylamide or sodium alginate.

[0051] 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 comprise 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 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 object 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 composites, SiO x (0<x<2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO₂, lithium titanate Li₄Ti₅O with spinel structure 12 , 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 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 object of the present application can be achieved.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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) coating only the first adhesive layer slurry on the other surface of the first base film, drying it to obtain the first diaphragm.

[0056] 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) coating only the second adhesive layer slurry on the other surface of the second base film, drying it to obtain the second diaphragm.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Example

[0062] 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.

[0063] Test methods and equipment:

[0064] Sampling methods for the first and second septa:

[0065] 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.

[0066] Sampling methods for the first and second base films:

[0067] The obtained first and second septa were placed in separate containers, and an appropriate amount of N-methylpyrrolidone (NMP) was added. The containers were then placed in an ultrasonic instrument with heating function for ultrasonication at 45°C for 3 hours. Once both septa became completely transparent, they were removed to obtain the first and second base films. The above method was used to obtain the first and second base films in the subsequent tests of their glass transition temperature, porosity, and pore size.

[0068] Average particle size test of the first and second ceramic particles:

[0069] 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.

[0070] Glass transition temperature tests of the first and second base films:

[0071] The glass transition temperatures of the first and second base films were tested using differential scanning calorimetry (DSC). The specific steps are as follows:

[0072] Samples are prepared by punching the first and second base films using molds (those skilled in the art can select molds of common sizes and shapes in the field according to factors such as the size and shape of the test object and the requirements of the test equipment). The prepared samples are sealed in self-sealing bags to avoid contamination. During testing, the samples are taken out and placed in a crucible. The crucible is placed in a furnace and heated from -100°C to 800°C at a heating rate of 5°C / min. The temperature change is controlled by a program. While the temperature changes, the relationship between the power difference (heat flow rate) between the sample and the reference material and the temperature is measured. This yields information such as the melting point, crystallinity, and crystallization temperature of the test sample. The glass transition temperature of the test sample is obtained through DSC curves.

[0073] Porosity testing of the first and second base films:

[0074] The gas displacement method was used for testing. Samples were prepared by punching the first and second base films using molds (those skilled in the art can select molds of common sizes and shapes in the field according to factors such as the size and shape of the test object and the requirements of the test equipment). The true volume V0 of the sample was measured using a true density meter. The apparent volume V of the sample can be calculated by measuring the area and thickness of the sample. Then, the percentage of the sample pore volume to the total area P = (V-V0) / V×100%, which gives the porosity of the first or second base film.

[0075] Pore ​​size testing of the first and second base films:

[0076] The specific steps are as follows:

[0077] ① The pores of the substrate film to be tested are completely wetted and filled with anhydrous ethanol. Due to capillary action, a positive pressure is formed inside the pores.

[0078] ② Place the base membrane in a sealed tank and use gas pressure to force the liquid out of the capillary channels;

[0079] ③ Based on the relative relationship between the pressure ΔP applied when the liquid in a single channel is completely squeezed out of the capillary channel and the channel diameter d, the diaphragm pore size can be obtained according to the Laplace equation, as shown in the following equation:

[0080] d = -4γcosθ / ΔP × 100%

[0081] In the formula, d is the pore diameter, ΔP is the pressure, γ is the surface tension of anhydrous ethanol, and θ is the contact angle between the diaphragm and anhydrous ethanol. Under different pressures, the liquid in the diaphragm will be successively squeezed out, generating a certain gas permeation flow rate. The pore size and pore size distribution can be calculated based on the relationship between pressure and flow rate changes.

[0082] Lithium-ion battery thickness testing:

[0083] 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.

[0084] The thickness of a lithium-ion battery characterizes its energy density; for the same volume, a greater thickness indicates a lower energy density.

[0085] High-temperature hot box testing:

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Cyclic performance testing:

[0090] 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.

[0091] Capacity retention rate (%) = (Discharge capacity after 1000 cls of cycling / Discharge capacity of the first cycle) × 100%.

[0092] A higher capacity retention rate indicates better cycle performance of the lithium-ion battery.

[0093] Example 1-1

[0094] <Preparation of the first diaphragm>

[0095] A first base film with a thickness of 12 μm and a glass transition temperature (Tg1) of 90 °C was used. The material of the first base film was polyethylene terephthalate (PET). The porosity of the first base film was 55%, and the pore size of the first base film was 300 nm (manufacturer: DuPont, grade: FR543).

[0096] Polyvinylidene fluoride (PVDF, Mw = 8.5 × 10⁻⁶) 6 ) and thickener sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.0:2.0, add deionized water as a solvent, and stir evenly to form a first adhesive layer slurry with a solid content of 75wt%.

[0097] 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%.

[0098] 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 coating weight of the first adhesive layer is 1 mg / cm³. 2 The coating weight of the first ceramic coating is 10 mg / mm². 2The average particle size of the first ceramic particles is 1 μm. 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%. The thickness of the first ceramic coating is 2.2 μm, and the thickness of the first adhesive layer is 1.3 μm.

[0099] <Preparation of the Second Diaphragm>

[0100] A second base film with a thickness of 7 μm and a glass transition temperature (Tg2) of 40 °C was used. The material of the second base film was polypropylene and polyethylene, with a mass ratio of polypropylene to polyethylene of 1:1. The porosity of the second base film was 18%, and the pore size of the second base film was 100 nm (manufacturer: Celgard, grade: 2325).

[0101] Polyvinylidene fluoride (PVDF, Mw = 8.5 × 10⁻⁶) 6 ) and thickener sodium carboxymethyl cellulose (Mw = 8 × 10) 5 Mix them at a mass ratio of 98.0:2.0, add deionized water as a solvent, and stir evenly to form a second adhesive layer slurry with a solid content of 75wt%.

[0102] 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%.

[0103] 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 coating weight of the second adhesive layer is 0.6 mg / cm³. 2 The coating weight CW2 of the second ceramic coating is 10 mg / cm³. 2 The average particle size of the second ceramic particles is 0.5 μm. 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%. The thickness of the second ceramic coating is 2.0 μm, and the thickness of the first adhesive layer is 1.0 μm.

[0104] <Preparation of Negative Electrode Sheets>

[0105] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 98.0:1.0:1.0, and then 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 70 mm × 800 mm dimensions for later use. The compaction density of the first negative electrode material layer was 1.755 g / cm³. 3 The length is 720mm, and the compaction density of the second negative electrode material layer is 1.755g / cm³. 3 It is 680mm long.

[0106] <Preparation of the positive electrode>

[0107] Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (positive electrode binder) were mixed in a mass ratio of 97:2.0:1.0. 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 current collector 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 62 mm × 760 mm dimensions for later use. The compaction density of the positive electrode material layer was 4.50 g / cm³. 3 .

[0108] <Preparation of Electrolyte>

[0109] 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.

[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 the electrode assembly. The positive electrode tab is spot-welded with aluminum tabs, and the negative electrode tab is spot-welded with nickel tabs. Specifically, the first ceramic coating in the first separator faces away from the negative electrode, and the second ceramic coating in the second 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 (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.

[0112] Examples 1-2

[0113] 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 3 But not with Figure 3 Except for (limited), the rest is the same as in Example 1-1.

[0114] Examples 1-3 to Examples 1-5

[0115] Except for adjusting the type of the first ceramic particles according to Table 1, the rest is the same as in Example 1-1.

[0116] Examples 2-1 to 2-4

[0117] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-1.

[0118] Examples 3-1 to 3-16

[0119] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0120] 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%.

[0121] Examples 4-1 to 4-16

[0122] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-1.

[0123] Comparative Example 1

[0124] 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.

[0125] <Preparation of Lithium-ion Batteries>

[0126] 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.

[0127] Comparative Example 2

[0128] 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.

[0129] <Preparation of Lithium-ion Batteries>

[0130] 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.

[0131] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0132] Table 1

[0133]

[0134] Note: In Table 1, "\" indicates that there is no corresponding parameter.

[0135] As can be seen from Examples 1-1 to 1-5, Comparative Examples 1 and 2, 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 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 and 2 use the same type of separator, or in other words, the types of ceramic particles in the two separators do not meet the limitations of this application. Therefore, the secondary batteries of the comparative examples cannot simultaneously achieve high capacity retention, small thickness, and high hot box test pass rates at 130°C and 132°C. This indicates that the secondary batteries of the comparative examples cannot balance cycle performance, energy density, and safety performance.

[0136] Table 2

[0137]

[0138] The material and glass transition temperature of the second base film typically affect the cycle performance, energy density, and safety performance of a secondary battery. As can be seen from Examples 1-1, 2-1, and 2-2, secondary batteries using second base film materials and glass transition temperatures 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.

[0139] The material and glass transition temperature of the first base film typically affect the cycle performance, energy density, and safety performance of a secondary battery. As can be seen from Examples 1-1, 2-3, and 2-4, secondary batteries using first base film materials and glass transition temperatures 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.

[0140] Table 3

[0141]

[0142]

[0143] 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... 11The 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, 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 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.

[0144] 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... 21 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, 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 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.

[0145] The average particle size of the first ceramic particles typically affects the cycle performance, energy density, and safety performance of a secondary battery. As seen in Examples 1-1, 3-9 to 3-12, 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, 3-9, and 3-10, Example 3-11 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 3-12 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.

[0146] The average particle size of the second ceramic particles typically affects the cycle performance, energy density, and safety performance of a secondary battery. As seen in Examples 1-1, 3-13 to 3-16, 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, 3-13, and 3-14, the second ceramic particle average particle size in Example 3-15 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 3-16 is larger, increasing the possibility of short circuits caused by puncturing the separator during hot-box tests, thus resulting in slightly weaker safety performance.

[0147] Table 4

[0148]

[0149] The porosity of the first base film typically affects the cycle performance, energy density, and safety performance of a secondary battery. As seen in Examples 1-1, 4-1 to 4-4, secondary batteries with a first base film porosity 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. With a fixed pore size, compared to Examples 1-1, 4-1, and 4-2, Example 4-3 has a lower first base film porosity, resulting in slightly greater lithium-ion transport resistance; therefore, the cycle performance of the secondary battery is slightly worse. Example 4-4 has a higher first base film porosity and lower strength, resulting in a lower pass rate in the hot-box test. The porosity of the second base film typically affects the cycle performance, energy density, and safety performance of a secondary battery. As can be seen from Examples 1-1, 4-5 to 4-8, the secondary battery using a second base film with a porosity within the range of this application 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. With a fixed pore size, compared to Examples 1-1, 4-5, and 4-6, the second base film in Example 4-7 has a lower porosity and slightly greater lithium-ion transport resistance, resulting in slightly poorer cycle performance. The second base film in Example 4-8 has a higher porosity and lower strength, leading to a lower pass rate in the hot box test.

[0150] The pore size of the first base film typically affects the cycle performance, energy density, and safety performance of a secondary battery. As seen in Examples 1-1, 4-9 to 4-12, secondary batteries using a first base film with a pore size within the scope 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. With a fixed porosity, compared to Examples 1-1, 4-9, and 4-10, Example 4-11 has a lower first base film pore size and higher lithium-ion transport resistance, resulting in slightly poorer cycle performance. Example 4-12 has a higher first base film pore size and lower strength, leading to a lower pass rate in the hot-box test.

[0151] The pore size of the second base film typically affects the cycle performance, energy density, and safety performance of a secondary battery. As seen in Examples 1-1, 4-13 to 4-16, secondary batteries using second base film pore sizes within the scope 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. With a fixed porosity, compared to Examples 1-1, 4-13, and 4-14, Example 4-15 has a lower second base film pore size and higher lithium-ion transport resistance, resulting in slightly poorer cycle performance. Example 4-16 has a higher second base film pore size and lower strength, leading to a lower pass rate in the hot-box test.

[0152] 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.

[0153] 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.

[0154] 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 located on both sides of the first base membrane, and the first ceramic coating is located on the surface of one side of the first base membrane. The first ceramic coating is located between the first base membrane and the first adhesive layer. The first ceramic coating includes first ceramic particles, which include at least one of alumina, zirconium dioxide, titanium dioxide, or silicon dioxide. The second membrane includes a second base membrane, a second adhesive layer, and a second ceramic coating. The second adhesive layer is located on both sides of the second base membrane, and the second ceramic coating is located on the surface of one side of the second base membrane. The second ceramic coating is located between the second base membrane and the second adhesive layer. The second ceramic coating includes second ceramic particles, and the second ceramic particles include boehmite. The negative electrode sheet includes a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer located on both sides of the negative electrode 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 located on one side of the first negative electrode material layer of the negative electrode sheet, and the second separator is located on one side of the second negative electrode material layer of the negative electrode sheet. The porosity of the first base film is 40% to 70%, and the porosity of the second base film is 5% to 50%.

2. The secondary battery according to claim 1, wherein, The material of the first base film includes at least one of polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyetheretherketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenyleneamide), polyarylether sulfone ketone, aramid, or aramid sulfone. The material of the second base film includes polyolefin, and the polymerizing 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.

3. The secondary battery according to claim 1 or 2, 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.

4. The secondary battery according to claim 1 or 2, 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%.

5. The secondary battery according to claim 1 or 2, wherein, The material of the first base film includes polyethylene terephthalate, and the material of the second base film includes at least one of polypropylene or polyethylene.

6. The secondary battery according to claim 5, wherein, The glass transition temperature of the first base film is 80°C to 100°C, and the glass transition temperature of the second base film is 25°C to 50°C.

7. The secondary battery according to claim 5, wherein, The first base film has a pore size of 80 nm to 700 nm, and the second base film has a pore size of 50 nm to 200 nm.

8. An electrical device comprising a secondary battery as described in any one of claims 1 to 7.

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