Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a first electrode assembly and a second electrode assembly which are stacked in a first direction. The size of the first electrode assembly in a second direction is greater than the size of the second electrode assembly in the second direction. The first electrode assembly comprises a plurality of first electrode sheets, a plurality of second electrode sheets, and a plurality of first separators, and the polarities of the first electrode sheets and the second electrode sheets are opposite. The plurality of first electrode sheets include a first end electrode sheet closest to the second electrode assembly. The plurality of first separators include a first sub-separator and a second sub-separator, the first sub-separator is bonded to the side of the first end electrode sheet facing away from the second electrode assembly, and the bonding force is F1. The second sub-separator is bonded to any first electrode sheet other than the first end electrode sheet, and the bonding force is F2, satisfying that 1.2F2≤F1≤3F2. The risk of separation of the first sub-separator from the first end electrode sheet can be reduced, and the possibility of black spots occurring in the secondary battery can be reduced.

Description

Secondary batteries and electrical equipment Technical Field

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

[0002] With the rapid development of electronic information and new energy technologies, various electrical devices are also moving towards intelligence and multi-functionality, placing increasingly higher demands on battery safety and reliability. Therefore, improving battery safety and reliability has become a pressing issue in the battery industry. Summary of the Invention

[0003] This application provides a secondary battery and an electrical device that can improve the safety and reliability of the secondary battery.

[0004] In a first aspect, this application provides a secondary battery, including a first electrode assembly and a second electrode assembly, which are stacked along a first direction. The dimension of the first electrode assembly along a second direction is larger than that of the second electrode assembly along the second direction. The first direction is perpendicular to the second direction. The first electrode assembly includes a plurality of first electrodes, a plurality of second electrodes, and a plurality of first separators. The first electrodes and second electrodes have opposite polarities, and the first separators are disposed between the first electrodes and second electrodes. The plurality of first electrodes include first end electrodes, which are the electrodes in the first electrode assembly closest to the second electrode assembly. The plurality of first separators include first sub-separators and second sub-separators. The first sub-separators are bonded to the side of the first end electrodes facing away from the second electrode assembly, and the second sub-separators are bonded to any first electrode except the first end electrodes. The adhesive force between the first sub-separator and the first end electrodes is F1, and the adhesive force between the second sub-separator and the adjacent first electrode is F2, satisfying 1.2F2≤F1≤3F2.

[0005] In the above technical solution, by stacking the first electrode assembly and the second electrode assembly along a first direction, and making the dimension of the first electrode assembly along the second direction larger than that of the second electrode assembly along the second direction, a step is formed on at least one side of the second electrode assembly in the second direction. This allows other components in the battery compartment of the electrical device to be placed at the step when the secondary battery is installed, thereby improving the space utilization of the battery compartment and thus improving the compactness of the internal structure of the electrical device. However, after the first electrode assembly and the second electrode assembly are installed in the housing, a gap exists between the step and the housing during subsequent pressure processes such as cold pressing and hot pressing. The first area of ​​the first electrode assembly corresponding to this gap cannot directly bear force, while other areas bear force, causing the first area to warp. Therefore, there is a risk of separation between the first sub-diaphragm and the first end electrode located in the first area. When F1 is greater than or equal to 1.2F2, the first sub-separator has stronger adhesion than the second sub-separator, resulting in a greater bond between the first sub-separator and the first end electrode. This reduces the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation and interface problems such as black spots in the secondary battery. When F1 is less than or equal to 3F2, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure is reduced, thus facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Therefore, when 1.2F2≤F1≤3F2, both the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thus reducing the possibility of metal ion precipitation and interface problems such as black spots in the secondary battery, and the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure, thus facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery, are reduced.

[0006] In some schemes of this application, 1.2F2≤F1≤2F2.

[0007] In the above technical solution, when F1 is greater than or equal to 1.2F2, the adhesion between the first sub-separator and the first end electrode is greater, which reduces the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress. This reduces the possibility of metal ion precipitation in the secondary battery, leading to interface problems such as black spots. When F1 is less than or equal to 2F2, the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure is further reduced, making it easier for metal ions to pass through the first sub-separator and resulting in better internal circulation of the secondary battery. Therefore, when 1.2F2≤F1≤2F2, it can both reduce the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thus reducing the possibility of metal ion precipitation in the secondary battery and resulting in interface problems such as black spots, and further reduce the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure, thus making it easier for metal ions to pass through the first sub-separator and resulting in better internal circulation of the secondary battery.

[0008] In some schemes of this application, 10N≤F1≤24N.

[0009] In the above technical solution, when F1 is greater than or equal to 10N, the adhesion between the first sub-separator and the first end electrode is greater, which reduces the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots. When F1 is less than or equal to 24N, the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure is further reduced, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Therefore, when 10N≤F1≤24N, it can both reduce the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots, and further reduce the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery.

[0010] In some schemes of this application, 10N≤F1≤18N.

[0011] In the above technical solution, when F1 is greater than or equal to 10N, the adhesion between the first sub-separator and the first end electrode is greater, which reduces the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots. When F1 is less than or equal to 18N, the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure is further reduced, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Therefore, when 10N≤F1≤18N, it can both reduce the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots, and further reduce the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery.

[0012] In some embodiments of this application, the porosity of the first sub-diaphragm is K1 and the porosity of the second sub-diaphragm is K2, satisfying 1.04K2≤K1≤1.5K2.

[0013] In the above technical solution, when K1 is greater than or equal to 1.04K2, that is, the porosity of the first sub-separator is higher than that of the second sub-separator, this can reduce the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator and resulting in better internal circulation of the secondary battery. When K1 is less than or equal to 1.5K2, the strength of the first sub-separator is higher, which facilitates the fabrication of the first electrode assembly and reduces the risk of burrs on the two electrodes with opposite polarities on both sides of the first sub-separator directly contacting each other through the pores, thereby reducing the risk of short circuits in the secondary battery. To improve the safety of the secondary battery, when 1.04K2≤K1≤1.5K2, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure is reduced, thus facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Furthermore, the strength of the first sub-separator is increased, facilitating the fabrication of the first electrode assembly. Additionally, the risk of active materials and burrs on the two oppositely polarized electrodes on either side of the first sub-separator directly contacting each other through the pores is reduced, thereby decreasing the possibility of a short circuit in the secondary battery and improving its safety.

[0014] In some schemes of this application, 1.1K2≤K1≤1.5K2.

[0015] In the above technical solution, when K1 is greater than or equal to 1.1K2, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure can be further reduced, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. When K1 is less than or equal to 1.5K2, the strength of the first sub-separator is higher, which facilitates the fabrication of the first electrode assembly and reduces the risk of active materials and burrs on the two opposite polarities on both sides of the first sub-separator directly contacting each other through the pores, thereby reducing the possibility of short circuit in the secondary battery and improving the safety of the secondary battery. Therefore, when 1.1K2≤K1≤1.5K2, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure can be further reduced, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Furthermore, the strength of the first sub-separator is higher, which facilitates the fabrication of the first electrode assembly and reduces the risk of burrs on the two opposite polarities on both sides of the first sub-separator directly contacting each other through the pores, thereby reducing the possibility of short circuit in the secondary battery and improving the safety of the secondary battery.

[0016] In some embodiments of this application, the porosity of the first sub-membrane is K1, satisfying 50% ≤ K1 ≤ 60%.

[0017] In the above technical solution, when K1 is greater than or equal to 50%, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure is reduced, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. When K1 is less than or equal to 60%, the strength of the first sub-separator is higher, facilitating the fabrication of the first electrode assembly and reducing the risk of active materials and burrs on the two opposite polarities on both sides of the first sub-separator directly contacting each other through the pores, thereby reducing the possibility of short circuits in the secondary battery and improving the safety of the secondary battery. Therefore, when 50% ≤ K1 ≤ 60%, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure is reduced, facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Furthermore, the strength of the first sub-separator is higher, facilitating the fabrication of the first electrode assembly and reducing the risk of burrs on the two opposite polarities on both sides of the first sub-separator directly contacting each other through the pores, thereby reducing the possibility of short circuits in the secondary battery and improving the safety of the secondary battery.

[0018] In some embodiments of this application, the first sub-diaphragm includes a first base layer and a first adhesive layer, the first adhesive layer being disposed on the side of the first base layer facing the first end electrode; the second sub-diaphragm includes a second base layer and a second adhesive layer, the second adhesive layer being disposed on the side of the second base layer facing the first electrode; the coating weight of the first adhesive layer is greater than the coating weight of the second adhesive layer, and the coating weight of the first adhesive layer is 0.0004 mg / mm².2 Up to 0.002 mg / mm 2 The coating weight of the second adhesive layer is 0.0001 mg / mm². 2 Up to 0.001 mg / mm 2 .

[0019] In the above technical solution, by making the first sub-diaphragm include a first base layer and a first adhesive layer, with the first adhesive layer disposed on the side of the first base layer facing the first end electrode, the first sub-diaphragm can be bonded to the first end electrode through the first adhesive layer. By making the second sub-diaphragm include a second base layer and a second adhesive layer, with the second adhesive layer disposed on the side of the second base layer facing the first electrode, the second sub-diaphragm can be bonded to the first electrode through the second adhesive layer. By making the coating weight of the first adhesive layer greater than the coating weight of the second adhesive layer, the adhesive force between the first adhesive layer and the first end electrode can be greater than the adhesive force between the second adhesive layer and the first electrode, thereby reducing the risk of separation between the first sub-diaphragm and the first end electrode when the first electrode assembly is subjected to uneven stress.

[0020] When the coating weight of the first adhesive layer is greater than or equal to 0.0004 mg / mm 2 When the coating weight of the first adhesive layer is less than or equal to 0.002 mg / mm², it can increase the adhesion between the first sub-separator and the first end electrode. This reduces the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots. 2 This reduces the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery; therefore, when the coating weight of the first adhesive layer is 0.0004 mg / mm², 2 Up to 0.002 mg / mm 2 This design can reduce the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots. It can also reduce the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery.

[0021] When the coating weight of the second adhesive layer is greater than or equal to 0.0001 mg / mm 2When the coating weight of the second adhesive layer is less than or equal to 0.001 mg / mm², the adhesion between the second sub-separator and the first electrode is greater, which reduces the risk of separation between the second sub-separator and the first electrode when the first electrode assembly is under stress. This reduces the possibility of metal ion precipitation in the secondary battery, leading to interface problems such as black spots. 2 This reduces the risk of pore blockage in the second sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the second sub-separator and improving the internal circulation of the secondary battery. Therefore, when the coating weight of the second adhesive layer is 0.0001 mg / mm², 2 Up to 0.001 mg / mm 2 This design can reduce the risk of the second sub-separator separating from the first electrode plate when the first electrode assembly is under stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and interface problems such as black spots. It can also reduce the risk of the second sub-separator becoming clogged when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the second sub-separator and improving the internal circulation of the secondary battery.

[0022] In some embodiments of this application, the first adhesive layer includes at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide, and the second adhesive layer includes at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide.

[0023] In the above technical solution, by making the first adhesive layer include at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide, the adhesive force of the first adhesive layer is stronger. When the first electrode assembly is subjected to uneven force, the risk of separation between the first sub-separator and the first end electrode can be further reduced, thereby reducing the possibility of metal ion precipitation in the secondary battery and the resulting interface problems such as black spots.

[0024] By including at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide in the second adhesive layer, the adhesive force of the second adhesive layer can be made stronger. When the first electrode assembly is under stress, the risk of separation between the second sub-separator and the first electrode sheet can be further reduced, thereby reducing the possibility of metal ion precipitation in the secondary battery and the resulting interface problems such as black spots.

[0025] In some embodiments of this application, the first electrode is a negative electrode and the second electrode is a positive electrode.

[0026] In the above technical solution, by making the first electrode a negative electrode and the second electrode a positive electrode, when the first electrode assembly and the second electrode assembly are assembled in the steel shell, the first electrode can directly contact the steel shell, reducing the risk of electrochemical corrosion between the first electrode assembly and the steel shell during the charging and discharging process of the secondary battery, and improving the safety of the secondary battery.

[0027] In some embodiments of this application, the thickness of the first sub-membrane is H, satisfying 10μm≤H≤14μm.

[0028] In the above technical solution, when H is greater than or equal to 10 μm, the first base layer or the first adhesive layer of the first sub-separator is thicker. When the first base layer is thicker, the first sub-separator has stronger support and reduces the possibility of deformation. When the first adhesive layer is thicker, the adhesion between the first sub-separator and the first end electrode is greater, reducing the risk of separation between the first sub-separator and the first end electrode. When H is less than or equal to 14 μm, the space occupied by the first sub-separator is smaller, which is beneficial to improving the energy density of the secondary battery. Therefore, when 10 μm ≤ H ≤ 14 μm, the first sub-separator has stronger support and reduces the possibility of deformation, or the adhesion between the first sub-separator and the first end electrode is greater, reducing the risk of separation between the first sub-separator and the first end electrode, and the space occupied by the first sub-separator is smaller, which is beneficial to improving the energy density of the secondary battery.

[0029] Secondly, this application provides an electrical device including a secondary battery as described above, the secondary battery being used to provide electrical energy. Attached Figure Description

[0030] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings.

[0031] Figure 1 is a schematic diagram of a partial structure of a secondary battery provided in some embodiments of this application;

[0032] Figure 2 is a perspective view of a partial structure of a secondary battery provided in some embodiments of this application;

[0033] Figure 3 is a schematic diagram of a partial structure of a secondary battery provided in some embodiments of this application;

[0034] Figure 4 is a schematic diagram of the structure of the first sub-separator (second sub-separator) of a secondary battery provided in some embodiments of this application;

[0035] Figure 5 is a structural schematic diagram of the first sub-separator (second sub-separator) of a secondary battery provided in some other embodiments of this application;

[0036] Figure 6 is a three-dimensional structural diagram of a secondary battery provided in some embodiments of this application.

[0037] Icons: 10-Secondary battery; 100-First electrode assembly; 110-First electrode; 111-First end electrode; 120-Second electrode; 130-First separator; 131-First sub-separator; 131a-First base layer; 131b-First adhesive layer; 131c-First ceramic layer; 132-Second sub-separator; 132a-Second base layer; 132b-Second adhesive layer; 132c-Second ceramic layer; 200-Second electrode assembly; 300-Outer casing; 410-Positive electrode tab; 420-Negative electrode tab; X-First direction; Y-Second direction; Z-Third direction. Specific embodiments are described below.

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0039] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having" and any variations thereof in the specification, claims and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0040] The terms "first," "second," etc., in the specification, claims, or the accompanying drawings of this application are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0041] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0042] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0043] With the development of the new energy industry, batteries are gradually moving towards higher energy density and higher power density, and the requirements for battery safety and reliability are becoming increasingly stringent. To accommodate different battery compartment shapes in electrical devices, the shape of the battery has also changed. For example, a secondary battery with steps allows the components of the electrical device to be housed within the steps, improving the utilization rate of the battery compartment. In this type of secondary battery, multiple electrode assemblies of different sizes are arranged inside the casing, forming steps at the junctions of adjacent electrode assemblies. For example, the size of the first electrode assembly is larger than that of the second electrode assembly, forming a step on one side of the second electrode assembly. In some processes of secondary battery manufacturing, pressure needs to be applied to the electrode assemblies or through the casing (as shown by the arrows in Figure 1). However, due to process limitations, the steps cannot be directly stressed, resulting in uneven stress distribution between the first region of the first electrode assembly corresponding to the step and other regions. This weakens or even separates the adhesion between the first end electrode (the electrode closest to the second electrode assembly) and the separator in the first region. During battery charge-discharge cycles, the first end electrode in the first region may experience metal ion precipitation, affecting the safety and reliability of the secondary battery.

[0044] To improve the safety and reliability of secondary batteries, this application provides a secondary battery including a first electrode assembly and a second electrode assembly. The first electrode assembly and the second electrode assembly are stacked along a first direction, and the dimension of the first electrode assembly along a second direction is larger than the dimension of the second electrode assembly along the second direction. The first direction is perpendicular to the second direction. The first electrode assembly includes a plurality of first electrodes, a plurality of second electrodes, and a plurality of first separators. The first electrodes and second electrodes have opposite polarities, and the first separators are disposed between the first electrodes and second electrodes. The plurality of first electrodes include first end electrodes, which are the electrodes in the first electrode assembly closest to the second electrode assembly. The plurality of first separators include first sub-separators and second sub-separators. The first sub-separators are bonded to the side of the first end electrodes facing away from the second electrode assembly, and the second sub-separators are bonded to any first electrode except the first end electrodes. The adhesive force between the first sub-separator and the first end electrodes is F1, and the adhesive force between the second sub-separator and the adjacent first electrode is F2, satisfying 1.2F2≤F1≤3F2.

[0045] In this type of secondary battery structure, by stacking the first electrode assembly and the second electrode assembly along a first direction, and with the first electrode assembly having a larger dimension along a second direction than the second electrode assembly, a step is formed on at least one side of the second electrode assembly in the second direction. This allows other components within the battery compartment of an electrical device to be placed at the step, thereby improving the space utilization of the battery compartment and enhancing the compactness of the device's internal structure. However, after the first and second electrode assemblies are installed in the casing, a gap exists between the step and the casing during subsequent pressure processes such as cold pressing and hot pressing. The first region of the first electrode assembly corresponding to this gap cannot directly bear force, while other regions bear force, causing the first region to warp. Therefore, there is a risk of separation between the first sub-separator and the first end electrode located in the first region. When F1 is greater than or equal to 1.2F2, it means that the first sub-separator has stronger adhesion than the second sub-separator. This results in a greater bonding force between the first sub-separator and the first end electrode. When the first electrode assembly is subjected to uneven stress, it can reduce the risk of separation between the first sub-separator and the first end electrode, thereby reducing the possibility of metal ion precipitation in the secondary battery and the resulting interface problems such as black spots. Increasing the coating weight of the adhesive layer on the surface of the separator is a common method to improve the adhesion between the separator and the electrode. If the coating weight of the adhesive layer is too high, the adhesive layer is prone to melting and clogging the voids on the separator base layer during the subsequent hot pressing production process and high-temperature operation of the secondary battery, leading to a sharp increase in internal resistance. When F1 is less than or equal to 3F2, the risk of the first sub-separator becoming clogged when the first electrode assembly is subjected to heat and pressure is reduced, thus facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery. Therefore, when 1.2F2≤F1≤3F2, the risk of the first sub-separator separating from the first end electrode sheet is reduced when the first electrode assembly is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery and the resulting interface problems such as black spots. It also reduces the risk of the first sub-separator becoming clogged when the first electrode assembly is subjected to heat and pressure, thus facilitating the passage of metal ions through the first sub-separator and improving the internal circulation of the secondary battery.

[0046] The secondary battery provided in this application may be a lithium-ion battery, a sodium-ion battery, or a magnesium-ion battery, etc., and this application is not limited to this.

[0047] This application provides an electrical device that uses a secondary battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc.

[0048] Referring to Figures 1 to 3, Figure 1 is a schematic diagram of a partial structure of a secondary battery provided in some embodiments of this application; Figure 2 is a perspective schematic diagram of a partial structure of a secondary battery provided in some embodiments of this application; and Figure 3 is a schematic diagram of a partial structure of a secondary battery provided in some embodiments of this application.

[0049] This application provides a secondary battery 10, including a first electrode assembly 100 and a second electrode assembly 200. The first electrode assembly 100 and the second electrode assembly 200 are stacked along a first direction X. The dimension of the first electrode assembly 100 along a second direction Y is larger than the dimension of the second electrode assembly 200 along the second direction Y. The first direction X is perpendicular to the second direction Y.

[0050] By stacking the first electrode assembly 100 and the second electrode assembly 200 along the first direction X, and making the size of the first electrode assembly 100 along the second direction Y larger than the size of the second electrode assembly 200 along the second direction Y, a step 201 is formed on at least one side of the second electrode assembly 200 in the second direction Y. This allows other components in the battery compartment to be placed at the step 201 when the secondary battery 10 is installed in the battery compartment of the electrical device, thereby improving the space utilization of the battery compartment and thus improving the compactness of the internal structure of the electrical device.

[0051] In some embodiments, the first electrode assembly 100 includes a plurality of first electrodes 110, a plurality of second electrodes 120, and a plurality of first diaphragms 130, wherein the polarities of the first electrodes 110 and the second electrodes 120 are opposite, and the first diaphragms 130 are disposed between the first electrodes 110 and the second electrodes 120.

[0052] In some embodiments, the plurality of first electrodes 110 include a first end electrode 111, which is the electrode in the first electrode assembly 100 closest to the second electrode assembly 200. The plurality of first diaphragms 130 include a first sub-diaphragm 131 and a second sub-diaphragm 132. The first sub-diaphragm 131 is bonded to the side of the first end electrode 111 facing away from the second electrode assembly 200, and the second sub-diaphragm 132 is bonded to any of the first electrodes 110 except the first end electrode 111. The adhesive force between the first sub-diaphragm 131 and the first end electrode 111 is F1, and the adhesive force between the second sub-diaphragm 132 and the adjacent first electrode 110 is F2, satisfying 1.2F2 ≤ F1 ≤ 3F2. For example, F1 can be 1.2F2, 1.5F2, 2F2, 2.5F2, or 3F2, etc.

[0053] Since after the first electrode assembly 100 and the second electrode assembly 200 are installed in the housing 300, there is a gap between the step 201 and the housing 300 during subsequent pressure processes such as cold pressing and hot pressing. The first region 101 of the first electrode assembly 100 corresponding to the gap cannot be directly subjected to force, while other regions are subjected to force, which will cause the first region 101 to lift up. Therefore, there is a risk that the first sub-diaphragm 131 located in the first region 101 and the first end electrode 111 will separate. When F1 is greater than or equal to 1.2F2, meaning the first sub-separator 131 has stronger adhesion than the second sub-separator 132, the adhesion between the first sub-separator 131 and the first end electrode 111 is greater. This reduces the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. When F1 is less than or equal to 3F2, the risk of pore blockage in the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure is reduced, thereby reducing the risk of pore blockage in the first sub-separator 131. This facilitates the passage of metal ions through the first sub-separator 131, resulting in better internal circulation of the secondary battery 10. Therefore, when 1.2F2≤F1≤3F2, it can reduce the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven force, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. It can also reduce the risk of pore blockage in the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure, thus facilitating the passage of metal ions through the first sub-separator 131 and resulting in better internal circulation of the secondary battery 10.

[0054] In some embodiments, 1.2F2≤F1≤2F2. For example, F1 can be 1.2F2, 1.4F2, 1.6F2, 1.8F2, or 2F2, etc.

[0055] When F1 is greater than or equal to 1.2F2, the adhesion between the first sub-separator 131 and the first end electrode 111 is greater. This reduces the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. When F1 is less than or equal to 2F2, the risk of pore blockage of the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure is further reduced, thus facilitating the passage of metal ions through the first sub-separator 131. 31, which makes the internal circulation of the secondary battery 10 better; therefore, when 1.2F2≤F1≤2F2, it can reduce the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven force, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots, and can further reduce the risk of the first sub-separator 131 becoming blocked when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator 131, making the internal circulation of the secondary battery 10 better.

[0056] In some embodiments, 10N ≤ F1 ≤ 24N. For example, F1 can be 10N, 12N, 15N, 20N, or 24N, etc.

[0057] When F1 is greater than or equal to 10N, the adhesion between the first sub-separator 131 and the first end electrode 111 is greater. This reduces the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. When F1 is less than or equal to 24N, the risk of pore blockage of the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure is further reduced, thus facilitating the passage of metal ions through the first sub-separator 131. 31, which makes the internal circulation of the secondary battery 10 better; therefore, when 10N≤F1≤24N, it can reduce the risk of the first sub-separator 131 separating from the first end electrode 111 when the first electrode assembly 100 is subjected to uneven force, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots, and can further reduce the risk of the first sub-separator 131 becoming blocked when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator 131, making the internal circulation of the secondary battery 10 better.

[0058] In some embodiments, 10N ≤ F1 ≤ 18N. For example, F1 can be 10N, 11N, 13N, 17N, or 18N, etc.

[0059] When F1 is greater than or equal to 10N, the adhesion between the first sub-separator 131 and the first end electrode 111 is greater. This reduces the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. When F1 is less than or equal to 18N, the risk of pore blockage of the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure is further reduced, thus facilitating the passage of metal ions through the first sub-separator 131. 31, which makes the internal circulation of the secondary battery 10 better; therefore, when 10N≤F1≤18N, it can reduce the risk of the first sub-separator 131 separating from the first end electrode 111 when the first electrode assembly 100 is subjected to uneven force, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots, and can further reduce the risk of the first sub-separator 131 becoming blocked when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator 131, making the internal circulation of the secondary battery 10 better.

[0060] In some embodiments, the porosity of the first sub-membrane 131 is K1, and the porosity of the second sub-membrane 132 is K2, satisfying 1.04K2≤K1≤1.5K2. For example, K1 can be 1.04K2, 1.1K2, 1.2K2, 1.4K2, or 1.5K2, etc.

[0061] When K1 is greater than or equal to 1.04K2, meaning the porosity of the first sub-separator 131 is higher than that of the second sub-separator 132, this reduces the risk of pore blockage in the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure. This facilitates the passage of metal ions through the first sub-separator 131, resulting in better internal circulation of the secondary battery 10. When K1 is less than or equal to 1.5K2, the first sub-separator 131 has higher strength, which facilitates the fabrication of the first electrode assembly 100 and reduces the risk of active materials and burrs on the two electrodes with opposite polarities on both sides of the first sub-separator 131 directly contacting each other through the pores, thereby reducing the risk of short circuits in the secondary battery 10. This reduces the possibility of short circuits in the secondary battery 10 and improves its safety. Therefore, when 1.04K2≤K1≤1.5K2, it can reduce the risk of blockage in the first sub-separator 131 when the first electrode assembly 100 is heated and pressed, thus facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10. It can also increase the strength of the first sub-separator 131, making it easier to prepare the first electrode assembly 100. Furthermore, it can reduce the risk of active materials and burrs on the two electrodes with opposite polarities on both sides of the first sub-separator 131 directly contacting each other through the pores, thereby reducing the possibility of short circuits in the secondary battery 10 and improving its safety.

[0062] In some embodiments, 1.1K2≤K1≤1.5K2. For example, K1 can be 1.1K2, 1.2K2, 1.3K2, 1.4K2, or 1.5K2, etc.

[0063] When K1 is greater than or equal to 1.1K2, the risk of pore blockage in the first sub-separator 131 during the heating and pressing of the first electrode assembly 100 can be further reduced, thereby facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10. When K1 is less than or equal to 1.5K2, the strength of the first sub-separator 131 is higher, facilitating the fabrication of the first electrode assembly 100 and reducing the risk of active materials and burrs on the two opposite polarities on both sides of the first sub-separator 131 directly contacting each other through the pores, thereby reducing the possibility of short circuits in the secondary battery 10 and improving the performance of the secondary battery 10. Safety; therefore, when 1.1K2≤K1≤1.5K2, it can further reduce the risk of the first sub-separator 131 becoming clogged when the first electrode assembly 100 is heated and pressed, thereby facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10. It can also make the first sub-separator 131 stronger, which is convenient for the fabrication of the first electrode assembly 100. Furthermore, it can reduce the risk of active materials, burrs, etc. on the two electrodes with opposite polarities on both sides of the first sub-separator 131 directly contacting each other through the pores, thereby reducing the possibility of short circuit in the secondary battery 10 and improving the safety of the secondary battery 10.

[0064] In some embodiments, the porosity of the first sub-membrane 131 is K1, satisfying 50% ≤ K1 ≤ 60%. For example, K1 can be 50%, 52%, 55%, 58%, or 60%, etc.

[0065] When K1 is greater than or equal to 50%, the risk of pore blockage in the first sub-separator 131 during the heating and pressing of the first electrode assembly 100 is reduced, thus facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10. When K1 is less than or equal to 60%, the strength of the first sub-separator 131 is higher, facilitating the fabrication of the first electrode assembly 100 and reducing the risk of active materials and burrs on the two opposite polarities of the first sub-separator 131 directly contacting each other through the pores, thereby reducing the possibility of short circuits in the secondary battery 10 and improving the performance of the secondary battery 10. The safety of the secondary battery 10 is improved by ensuring that when 50% ≤ K1 ≤ 60%, the risk of blockage of the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure is reduced, thus facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10. This also ensures that the first sub-separator 131 has high strength, facilitating the fabrication of the first electrode assembly 100. Furthermore, it reduces the risk of burrs and other debris on the two electrodes with opposite polarities on both sides of the first sub-separator 131 directly contacting each other through the pores, thereby reducing the possibility of short circuit in the secondary battery 10 and improving the safety of the secondary battery 10.

[0066] Referring to Figure 4, Figure 4 is a schematic diagram of the structure of the first sub-separator (second sub-separator) of a secondary battery provided in some embodiments of this application.

[0067] In some embodiments, the first sub-diaphragm 131 includes a first base layer 131a and a first adhesive layer 131b, wherein the first adhesive layer 131b is disposed on the side of the first base layer 131a facing the first end electrode 111.

[0068] By making the first sub-diaphragm 131 include a first base layer 131a and a first adhesive layer 131b, with the first adhesive layer 131b disposed on the side of the first base layer 131a facing the first end electrode 111, the first sub-diaphragm 131 can be bonded to the first end electrode 111 through the first adhesive layer 131b.

[0069] In some embodiments, the second sub-diaphragm 132 includes a second base layer 132a and a second adhesive layer 132b, wherein the second adhesive layer 132b is disposed on the side of the second base layer 132a facing the first electrode 110.

[0070] In some embodiments, by making the second sub-diaphragm 132 include a second base layer 132a and a second adhesive layer 132b, with the second adhesive layer 132b disposed on the side of the second base layer 132a facing the first electrode 110, the second sub-diaphragm 132 can be bonded to the first electrode 110 through the second adhesive layer 132b.

[0071] In some embodiments, the coating weight of the first adhesive layer 131b is greater than the coating weight of the second adhesive layer 132b.

[0072] By making the coating weight of the first adhesive layer 131b greater than that of the second adhesive layer 132b, the adhesive force between the first adhesive layer 131b and the first end electrode 111 can be greater than the adhesive force between the second adhesive layer 132b and the first electrode 110. This reduces the risk of separation between the first sub-diaphragm 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress.

[0073] In some embodiments, the coating weight of the first adhesive layer 131b is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 For example, the coating weight of the first adhesive layer 131b can be 0.0004 mg / mm². 2 0.0006 mg / mm 2 0.0008 mg / mm 2 0.001 mg / mm 2 Or 0.002 mg / mm 2 wait.

[0074] When the coating weight of the first adhesive layer 131b is greater than or equal to 0.0004 mg / mm 2 When the first sub-separator 131 and the first end electrode 111 are subjected to uneven stress, the adhesion force between them can be increased. This reduces the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. When the coating weight of the first adhesive layer 131b is less than or equal to 0.002 mg / mm², the adhesion force between the first sub-separator 131 and the first end electrode 111 is increased. 2 This reduces the risk of pore blockage in the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10; therefore, when the coating weight of the first adhesive layer is 0.0004 mg / mm 2 Up to 0.002 mg / mm 2 This design can reduce the risk of separation between the first sub-separator 131 and the first end electrode 111 when the first electrode assembly 100 is subjected to uneven stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. It can also reduce the risk of pore blockage in the first sub-separator 131 when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator 131 and improving the internal circulation of the secondary battery 10.

[0075] In some embodiments, the coating weight of the second adhesive layer 132b is 0.0001 mg / mm². 2 Up to 0.001 mg / mm2 For example, the coating weight of the second adhesive layer 132b can be 0.0001 mg / mm². 2 0.0003 mg / mm 2 0.0005 mg / mm 2 0.0008 mg / mm 2 Or 0.001 mg / mm 2 wait.

[0076] When the coating weight of the second adhesive layer 132b is greater than or equal to 0.0001 mg / mm 2 When the second sub-separator 132 and the first electrode 110 are subjected to stress, the adhesion force between them is relatively large. This reduces the risk of separation between the second sub-separator 132 and the first electrode 110 when the first electrode assembly 100 is under stress, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. When the coating weight of the second adhesive layer 132b is less than or equal to 0.001 mg / mm², the adhesion force is relatively large. 2 This reduces the risk of pore blockage in the second sub-separator 132 when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the second sub-separator 132 and improving the internal circulation of the secondary battery 10; therefore, when the coating weight of the second adhesive layer is 0.0001 mg / mm 2 Up to 0.001 mg / mm 2 This design can reduce the risk of separation between the second sub-separator 132 and the first electrode 110 when the first electrode assembly 100 is subjected to force, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots. It can also reduce the risk of pore blockage in the second sub-separator 132 when the first electrode assembly 100 is subjected to heat and pressure, thereby facilitating the passage of metal ions through the second sub-separator 132 and improving the internal circulation of the secondary battery 10.

[0077] In some embodiments, the first base layer 131a includes at least one of polyethylene, polypropylene, and polyimide.

[0078] By making the first base layer 131a include at least one of polyethylene, polypropylene, and polyimide, the supporting force of the first base layer 131a can be strengthened, reducing the possibility of deformation of the first sub-diaphragm 131.

[0079] In some embodiments, the first adhesive layer 131b includes at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide.

[0080] By including at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide in the first adhesive layer 131b, the adhesive force of the first adhesive layer 131b can be made stronger. When the first electrode assembly 100 is subjected to uneven force, the risk of separation between the first sub-separator 131 and the first end electrode 111 can be further reduced, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and the resulting interface problems such as black spots.

[0081] In some embodiments, the second base layer 132a includes at least one of polyethylene, polypropylene, and polyimide.

[0082] By including at least one of polyethylene, polypropylene, and polyimide in the second base layer 132a, the supporting force of the second base layer 132a can be strengthened, reducing the possibility of deformation of the second sub-diaphragm 132.

[0083] In some embodiments, the second adhesive layer 132b includes at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide.

[0084] By including at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide in the second adhesive layer 132b, the adhesive force of the second adhesive layer 132b can be made stronger. When the first electrode assembly 100 is subjected to force, the risk of separation between the second sub-separator 132 and the first electrode 110 can be further reduced, thereby reducing the possibility of metal ion precipitation in the secondary battery 10 and interface problems such as black spots.

[0085] Referring to Figure 5, Figure 5 is a structural schematic diagram of the first sub-separator (second sub-separator) of a secondary battery provided in some other embodiments of this application.

[0086] In some other embodiments, the first sub-diaphragm 131 further includes a first ceramic layer 131c, which is disposed between the first base layer 131a and the first adhesive layer 131b.

[0087] By setting a first ceramic layer 131c between the first base layer 131a and the first adhesive layer 131b, the deformation resistance of the first sub-diaphragm 131 can be improved, which facilitates the stacking preparation of the first electrode assembly 100.

[0088] In some embodiments, the first ceramic layer 131c includes at least one of alumina, zirconium dioxide, and silicon nitride. This further enhances the deformation resistance of the first sub-diaphragm 131, facilitating the stacking fabrication of the first electrode assembly 100.

[0089] In some other embodiments, the second sub-diaphragm 132 further includes a second ceramic layer 132c, which is disposed between the second base layer 132a and the second adhesive layer 132b.

[0090] By setting a second ceramic layer 132c between the second base layer 132a and the second adhesive layer 132b, the deformation resistance of the second sub-diaphragm 132 can be improved, which facilitates the stacking preparation of the first electrode assembly 100.

[0091] In some embodiments, the second ceramic layer 132c includes at least one of alumina, zirconium dioxide, and silicon nitride. This further enhances the deformation resistance of the second sub-diaphragm 132, facilitating the stacking fabrication of the first electrode assembly 100.

[0092] In some embodiments, the thickness of the first sub-diaphragm 131 is H, satisfying 10μm≤H≤14μm. For example, H can be 10μm, 11μm, 12μm, 13μm, or 14μm, etc.

[0093] When H is greater than or equal to 10 μm, the first base layer 131a or the first adhesive layer 131b of the first sub-diaphragm 131 is thicker. When the first base layer 131a is thicker, the support force of the first sub-diaphragm 131 is stronger, reducing the possibility of deformation. When the first adhesive layer 131b is thicker, the adhesion force between the first sub-diaphragm 131 and the first end electrode 111 is larger, reducing the risk of separation between the first sub-diaphragm 131 and the first end electrode 111. When H is less than or equal to 14 μm, the first base layer 131a or the first adhesive layer 131b of the first sub-diaphragm 131 is thicker. The first sub-separator 131 occupies a small space, which is beneficial to improving the energy density of the secondary battery 10. Therefore, when 10μm≤H≤14μm, the first sub-separator 131 can be supported more strongly, reducing the possibility of deformation, or the adhesion between the first sub-separator 131 and the first end electrode 111 can be greater, reducing the risk of separation between the first sub-separator 131 and the first end electrode 111. At the same time, the first sub-separator 131 occupies a small space, which is beneficial to improving the energy density of the secondary battery 10.

[0094] In some embodiments, the first electrode 110 is a negative electrode and the second electrode 120 is a positive electrode.

[0095] By making the first electrode 110 a negative electrode and the second electrode 120 a positive electrode, when the first electrode assembly 100 and the second electrode assembly 200 are assembled in the steel shell, the first electrode 110 can directly contact the steel shell, reducing the risk of electrochemical corrosion between the first electrode assembly 100 and the steel shell during the charging and discharging process of the secondary battery 10, and improving the safety of the secondary battery 10.

[0096] In other embodiments, the first electrode 110 may be a positive electrode and the second electrode 120 a negative electrode. This reduces the risk of electrochemical corrosion between the first electrode assembly 100 and the aluminum-plastic film or aluminum shell during the charging and discharging process of the secondary battery 10, thus improving the safety of the secondary battery 10.

[0097] The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector. The portion of the positive current collector without the positive active material layer serves as the positive electrode tab, through which electrical energy is input or output. Taking a lithium-ion battery as an example, the material of the positive current collector can be aluminum, and the positive active material can be lithium cobalt oxide, lithium iron phosphate, ternary materials, or lithium manganese oxide, etc. The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative current collector. The portion of the negative current collector without the negative active material layer serves as the negative electrode tab, through which electrical energy is input or output. The material of the negative current collector can be copper, and the negative active material can be carbon or silicon, etc. The separator can be made of polypropylene (PP) or polyethylene (PE), etc.

[0098] Referring to Figure 6, Figure 6 is a three-dimensional structural schematic diagram of a secondary battery provided in some embodiments of this application.

[0099] In some embodiments, the secondary battery 10 further includes a housing 300 and an electrolyte (not shown in the figure). The first electrode assembly 100, the second electrode assembly 200, and the electrolyte are housed within the housing 300. The secondary battery 10 mainly relies on the movement of metal ions between the positive electrode and the negative electrode to operate.

[0100] In some embodiments, the housing 300 can be made of a high-strength material, such as steel, aluminum alloy or other metal materials, so that the housing 300 has high stress resistance, and thus the housing 300 is not easily deformed or damaged due to stress or environmental changes, thereby making the secondary battery 10 more reliable.

[0101] In other embodiments, the outer shell 300 may also be a high-strength non-metallic material such as carbon fiber or rigid plastic; or a composite material of metal and non-metal such as aluminum-plastic film.

[0102] In some embodiments, the secondary battery 10 further includes a positive electrode tab 410 and a negative electrode tab 420, which extend from the outer casing 300 along a third direction Z.

[0103] The first direction X, the second direction Y, and the third direction Z are perpendicular to each other.

[0104] This application provides an electrical device including a secondary battery 10 provided in any of the above embodiments, the secondary battery 10 being used to provide electrical energy.

[0105] The electrical equipment can be any of the aforementioned devices or systems that use the secondary battery 10.

[0106] The features and performance of the secondary battery of this application are further described in detail below with reference to embodiments.

[0107] The secondary batteries in each embodiment and comparative example were prepared and tested according to the following method.

[0108] Methods for preparing secondary batteries:

[0109] 1. Preparation of positive electrode sheet

[0110] Lithium cobalt oxide (LiCoO) was used as the positive electrode active material, mixed with superconducting carbon (Super P) as a conductive agent and polyvinylidene fluoride (PVDF, molecular weight 7×10) as a binder in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added as a solvent to construct a positive electrode slurry (solid content 50%, slurry viscosity approximately 6000 mPa·s). A comma-shaped doctor blade coater was used to coat both sides of the positive electrode slurry onto a 10 μm aluminum foil current collector (the positive electrode tabs were integrally formed on the current collector by cutting). Through segmented drying and rolling, the total thickness of the positive electrode sheet was reduced to 85 μm (single-sided active layer thickness 37.5 μm, single-sided active layer compaction density 4.1 g / cm³). 3 The first positive electrode sheet (second electrode sheet) of 60mm×58mm and the second positive electrode sheet (fourth electrode sheet) of 58mm×58mm are then cut out for later use.

[0111] 2. Preparation of negative electrode sheet

[0112] Artificial graphite (94.0% graphitization) was used as the negative electrode active material, combined with conductive agent Super P (1.0%), binder styrene-butadiene rubber (SBR, molecular weight 5×10, content 1.5%), and stabilizer sodium carboxymethyl cellulose (CMC-Na, molecular weight 7×10, content 1.0%), and deionized water was used as the solvent to construct the negative electrode slurry (solid content approximately 50%, slurry viscosity approximately 5000 mPa·s). A transfer coating machine was used to coat both sides of the negative electrode slurry onto an 8μm copper foil current collector (the negative electrode tabs were integrally formed on the negative electrode current collector by cutting). Through segmented drying and rolling, the total thickness of the negative electrode sheet was increased to 121μm (single-sided active layer thickness 56.5μm, corresponding to a compaction density of 1.66 g / cm³). 3 Cut out a 62mm×60mm first negative electrode sheet (first electrode sheet) and a 60mm×60mm second negative electrode sheet (third electrode sheet) for later use.

[0113] 3. Preparation of the diaphragm

[0114] A 7μm thick single-layer polypropylene film was used as the base layer of the diaphragm. Polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) solvent were weighed at a mass ratio of 1:9 and magnetically stirred at 800 rpm for 4 hours in a 60℃ water bath to form a homogeneous adhesive solution with a viscosity of approximately 9000 mPa·s. After standing to defoam for 2 hours, the solution was coated onto the base layer surface using a microgravure coating machine at a speed of 0.5 m / min, resulting in a wet film thickness of 5μm. Immediately after coating, the film was transferred to a nitrogen-protected drying oven for staged drying: initial drying at 80℃ for 5 minutes, followed by final drying at 100℃ for 5 minutes, ultimately forming a dense PVDF layer (adhesive layer). By changing the porosity of the base layer and the coating weight of the adhesive solution, a first diaphragm and a second diaphragm were prepared, respectively. The first diaphragm was further divided into a first sub-diaphragm and a second sub-diaphragm, both made of the same material.

[0115] 4. Preparation of electrolyte

[0116] An electrolyte was prepared in an environment with a water content of less than 10 ppm, using ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) (30:50:20) as solvent, LiPF6 (1.2 mol / L) as lithium salt, and adding vinylene carbonate (VC) (2%), fluoroethylene carbonate (FEC) (1%), lithium difluorooxalate borate (LiDFOB) (0.5%), and propylene sulfite (PS) (0.5%).

[0117] 5. Preparation of secondary batteries

[0118] Multiple first positive electrode plates, multiple first separators, and multiple first negative electrode plates are stacked sequentially to form a first electrode assembly. Multiple second positive electrode plates, multiple second separators, and multiple second negative electrode plates are stacked sequentially to form a second electrode assembly. Each of the multiple first negative electrode plates includes a first end electrode plate, which is the electrode plate in the first electrode assembly closest to the second electrode assembly. A first sub-separator is bonded to the side of the first end electrode plate facing away from the second electrode assembly, and a second sub-separator is bonded to any of the first negative electrode plates except for the first end electrode plate.

[0119] The second electrode assembly is superimposed on the first electrode assembly, and the first and second electrode assemblies are separated by a second sub-separator. They are then hot-pressed together at 4 MPa and 95 degrees Celsius to form a stepped bare cell. Multiple positive electrode tabs of the first and second electrode assemblies are overlapped and welded together, then spot-welded to a positive electrode adapter for lead-out. Similarly, multiple negative electrode tabs are overlapped and welded together, then spot-welded to a negative electrode adapter for lead-out.

[0120] The stepped bare cells are placed in a steel shell, dried, and then injected with electrolyte. After processes such as settling, formation, vacuum sealing, and capacity testing, a secondary battery is obtained.

[0121] The differences between the comparative examples and the embodiments are shown in Table 1. In Table 1, the first electrode of comparative examples 1-2 and embodiments 1-10 is the negative electrode.

[0122] Refer to Table 1. In Table 1, F1 is the adhesive force between the first sub-diaphragm and the first end electrode, F2 is the adhesive force between the second sub-diaphragm and the adjacent first electrode, K1 is the porosity of the first sub-diaphragm, K2 is the porosity of the second sub-diaphragm, M1 is the coating weight of the first adhesive layer, and M2 is the coating weight of the second adhesive layer.

[0123] The test methods for the adhesion between the first diaphragm and the first electrode include:

[0124] (1) Discharge the finished secondary battery to 0% SOC, disassemble the secondary battery and remove the bare cells (including the first electrode assembly and the second electrode assembly).

[0125] (2) Cut the bare cell along the long edge starting from the tab, and retain the stacked sample consisting of the first separator and the first electrode.

[0126] (3) Using tweezers, gently separate the stacked sample from the second electrode closest to the second electrode assembly at the edge. Lift the separated layers (current collector and diaphragm) 5 mm and fold them upward (starting from the tab edge).

[0127] (4) Use tape to attach the polyester film to the folded layer as an extension of the clamping.

[0128] (5) Cut a piece of double-sided tape that is 10mm shorter and 20mm wider than the current collector and stick it on the current collector (the side opposite to the current collector + diaphragm peeled off in step 3).

[0129] (6) Adhere the current collector to the steel plate substrate and place the steel plate on the peel tester.

[0130] (7) On the peel tester, clamp the polyester film on the folded layer and adjust the position of the clamp so that the clamped layer is perpendicular to the substrate.

[0131] (8) Set the peeling speed to 50 mm / min and start the test. During the test, the fixture should move upward while the substrate moves forward to maintain a peeling angle of 90°.

[0132] (9) Save the test data in force-displacement format.

[0133] The method for detecting the porosity of the diaphragm is as follows:

[0134] (1) Remove the diaphragm from the electrode and soak it in toluene solvent at 45°C for 10 hours. Repeat this process twice to obtain the base sample of the diaphragm.

[0135] (2) Calculate the porosity of the base layer φ=[1-m / (s×h×ρ)]×100%, where m is the mass of the base layer sample, s is the area of ​​the base layer sample, h is the thickness of the base layer sample, and ρ is the true density of the base layer material.

[0136] The test methods for adhesive coating weight include:

[0137] (1) After discharging the secondary battery to 3.0V at 0.5C, the separator was disassembled. The impurities on the surface of the separator were cleaned with DMC (dimethyl carbonate), and then dried at 60℃ to obtain a test sample of the separator.

[0138] (2) Punch an area of ​​S mm onto the test sample of the diaphragm. 2 Weigh the small disc and record its mass as m1; then peel off the adhesive layer on the small disc to obtain the mass of the small disc after peeling off the adhesive layer, which is recorded as m2; the coating weight of the adhesive layer = (m1-m2) / S.

[0139] Table 1. Interfacial black spot rate test of secondary batteries

[0140] Methods for testing the rate of black spots on the interface include:

[0141] (1) Take 10 finished secondary batteries after formation, fully charge them at 0.5C and disassemble them to observe whether black spots are generated on the interface of the first end electrode due to lithium plating, and take pictures to record the results.

[0142] (2) Interface black spot rate = number of secondary cells with obvious black spots / total number of secondary cells.

[0143] Based on Table 1, the following conclusions can be drawn:

[0144] 1. Referring to Comparative Examples 1-2 and Examples 1-10, when F1 / F2 is less than 1.2, the adhesion force F1 between the first sub-separator and the first end electrode is small, the risk of separation between the first sub-separator and the first end electrode is high, and metal ion precipitation of the first end electrode is easily caused, resulting in a high interface black spot rate. When F1 / F2 is greater than 3, the adhesion force F1 between the first sub-separator and the first end electrode is large, but the risk of pore blockage of the first sub-separator is high when the first electrode assembly is subjected to heat and pressure, which also causes metal ion precipitation and a high interface black spot rate. When 1.2≤F1 / F2≤3, the risk of separation between the first sub-separator and the first end electrode can be reduced when the first electrode assembly is subjected to uneven force, thereby reducing the generation of metal ion precipitation in the secondary battery and resulting in a lower interface black spot rate. It can also reduce the risk of pore blockage of the first sub-separator when the first electrode assembly is subjected to heat and pressure, thereby facilitating the passage of metal ions through the first sub-separator, resulting in better internal circulation of the secondary battery and a lower interface black spot rate.

[0145] 2. Referring to Examples 1-4, when 1.2≤F1 / F2≤3, the interface black spot rate is relatively low. When 1.2≤F1 / F2≤2, the risk of pore blockage in the first sub-diaphragm can be further reduced, resulting in an even lower interface black spot rate.

[0146] 3. Referring to Examples 1-7, when 10N≤F1≤24N, the interface black spot rate is relatively low. When 10N≤F1≤18N, the risk of pore blockage in the first sub-diaphragm can be further reduced, resulting in an even lower interface black spot rate.

[0147] 4. Referring to Comparative Example 1, Example 1, and Examples 8-10, when K1 / K2 is less than 1.04, the porosity K1 of the first sub-diaphragm is relatively small, and the risk of pore blockage in the first sub-diaphragm is higher when the first electrode assembly is subjected to hot pressing, resulting in a higher rate of interface black spots. When 1.04 ≤ K1 / K2 ≤ 1.5, the porosity K1 of the first sub-diaphragm is relatively large, and the risk of pore blockage in the first sub-diaphragm is lower when the first electrode assembly is subjected to hot pressing, resulting in a lower rate of interface black spots.

[0148] 5. Referring to Examples 1 and 8-10, when K1 is less than 50%, the porosity of the first sub-separator is low, and the risk of pore blockage in the first sub-separator is high when the first electrode assembly is subjected to heat and pressure, resulting in a high rate of interface black spots. When 50% ≤ K1 ≤ 60%, the risk of pore blockage in the first sub-separator when the first electrode assembly is subjected to heat and pressure can be reduced, thereby facilitating the passage of metal ions through the first sub-separator, resulting in better internal circulation of the secondary battery and a lower rate of interface black spots.

[0149] 6. Referring to Comparative Examples 1-2 and Examples 1-7, when M1 is less than 0.0004 mg / mm 2A smaller coating weight of the first adhesive layer results in a weaker adhesion force (F1) between the first sub-diaphragm and the first end electrode, increasing the risk of separation between them and potentially causing metal ion deposition and a higher rate of interface black spots. When M1 is greater than 0.002 mg / mm², further issues arise. 2 The coating weight of the first adhesive layer is relatively large, resulting in a large adhesion force F1 between the first sub-diaphragm and the first end electrode. However, when the first electrode assembly is subjected to heat and pressure, the risk of pore blockage in the first sub-diaphragm is high, which can also cause metal ion precipitation and a high rate of interface black spots. (When 0.0004 mg / mm...) 2 ≤M1≤0.002mg / mm 2 The coating weight of the first adhesive layer is relatively large, and the adhesion force F1 between the first sub-separator and the first end electrode is relatively large. This can reduce the risk of separation between the first sub-separator and the first end electrode when the first electrode assembly is subjected to uneven force, thereby reducing the precipitation of metal ions in the secondary battery and resulting in a lower interface black spot rate.

[0150] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0151] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, It includes a first electrode assembly and a second electrode assembly, which are stacked along a first direction. The dimension of the first electrode assembly along a second direction is larger than the dimension of the second electrode assembly along the second direction. The first direction is perpendicular to the second direction. The first electrode assembly includes a plurality of first electrodes, a plurality of second electrodes, and a plurality of first diaphragms. The first electrodes and the second electrodes have opposite polarities, and the first diaphragms are disposed between the first electrodes and the second electrodes. The plurality of first electrode plates include a first end electrode plate, wherein the first end electrode plate is the electrode plate in the first electrode assembly that is closest to the second electrode assembly; The plurality of first diaphragms include a first sub-diaphragm and a second sub-diaphragm, the first sub-diaphragm being bonded to the side of the first end electrode facing away from the second electrode assembly, and the second sub-diaphragm being bonded to any of the first electrodes except the first end electrode; Wherein, the adhesive force between the first sub-diaphragm and the first end electrode is F1, and the adhesive force between the second sub-diaphragm and the adjacent first electrode is F2, satisfying 1.2F2≤F1≤3F2.

2. The secondary battery according to claim 1, characterized in that, 1.2F2≤F1≤2F2.

3. The secondary battery according to claim 1, characterized in that, 10N≤F1≤24N.

4. The secondary battery according to claim 3, characterized in that, 10N≤F1≤18N.

5. The secondary battery according to claim 1, characterized in that, The porosity of the first sub-membrane is K1, and the porosity of the second sub-membrane is K2, satisfying 1.04K2≤K1≤1.5K2.

6. The secondary battery according to claim 5, characterized in that, 1.1K2≤K1≤1.5K2.

7. The secondary battery according to claim 1, characterized in that, The porosity of the first sub-membrane is K1, which satisfies 50% ≤ K1 ≤ 60%.

8. The secondary battery according to claim 1, characterized in that, The first sub-diaphragm includes a first base layer and a first adhesive layer, the first adhesive layer being disposed on the side of the first base layer facing the first end electrode; the second sub-diaphragm includes a second base layer and a second adhesive layer, the second adhesive layer being disposed on the side of the second base layer facing the first electrode; the coating weight of the first adhesive layer is greater than the coating weight of the second adhesive layer, and the coating weight of the first adhesive layer is 0.0004 mg / mm². 2 Up to 0.002 mg / mm 2 The coating weight of the second adhesive layer is 0.0001 mg / mm². 2 Up to 0.0006 mg / mm 2 .

9. The secondary battery according to claim 8, characterized in that, The first adhesive layer comprises at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide, and the second adhesive layer comprises at least one of polyvinylidene fluoride, polyacrylate, polyvinyl alcohol, and polyimide.

10. The secondary battery according to claim 1, characterized in that, The first electrode is the negative electrode, and the second electrode is the positive electrode.

11. The secondary battery according to claim 1, characterized in that, The thickness of the first sub-diaphragm is H, which satisfies 10μm≤H≤14μm.

12. An electrical appliance, characterized in that, Includes a secondary battery as described in any one of claims 1-11, wherein the secondary battery is used to provide electrical energy.

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