Secondary battery, electronic device, and manufacturing method for secondary battery

Abstract

The present application relates to a secondary battery, an electronic device, and a manufacturing method for the secondary battery. The secondary battery comprises a housing and an electrode assembly, wherein the housing comprises a packaging film, and the packaging film is wrapped around the outer surface of the electrode assembly. The housing further comprises a first polymer layer; the surface of the packaging film facing away from the electrode assembly is at least partially provided with the first polymer layer; the first polymer layer comprises a polyacrylic resin; the tensile elongation at break of the portion of the housing provided with the first polymer layer is less than the tensile elongation at break of the packaging film. With respect to the secondary battery, the electronic device, and the manufacturing method for the secondary battery of the present application, the problem of short circuit of the secondary battery can be ameliorated.

Description

Secondary batteries, electronic devices, and methods for manufacturing secondary batteries

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510341778.7, filed on March 21, 2025, entitled "Secondary Battery, Electronic Device and Method for Manufacturing a Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a secondary battery, an electronic device, and a method for manufacturing a secondary battery. Background Technology

[0004] Secondary batteries, as the power source for electronic devices, are crucial for ensuring their normal operation. Damage to secondary batteries from external forces can easily lead to internal short circuits, resulting in safety issues such as thermal runaway. Summary of the Invention

[0005] The inventors of this application have discovered that when a secondary battery is damaged by external force, the packaging film is easily stretched to the electrode breakage point, causing the aluminum interlayer of the packaging film to come into contact with the electrode and thus short-circuit. By coating the outer surface of the packaging film of the finished secondary battery with a polymer coating whose tensile elongation at break is lower than that of the packaging film, the polymer coating and the packaging film form a composite packaging film. This allows the tensile elongation at break of the portion of the composite packaging film with the polymer coating to be lower than that of the original packaging film, thereby reducing the possibility that the aluminum interlayer in the packaging film will be stretched by external force and come into contact with the electrode and short-circuit.

[0006] The purpose of this application is to provide a secondary battery, an electronic device, and a method for manufacturing a secondary battery, with the aim of improving the problem of short circuits in secondary batteries.

[0007] According to a first aspect of this application, a secondary battery is provided, including a housing and an electrode assembly. The housing includes a packaging film that wraps around the outer surface of the electrode assembly. The housing also includes a first polymer layer, wherein the packaging film is disposed at least partially away from the surface of the electrode assembly. The first polymer layer includes polyacrylic acid resin. The tensile elongation at break of the packaging film is φ1, and the tensile elongation at break of the portion of the housing disposed of the first polymer layer is φ2, where φ2 < φ1.

[0008] In the above technical solution, by providing at least a first polymer layer on the surface of the packaging film away from the electrode assembly, the first polymer layer and the packaging film form a shell. The first polymer layer includes polyacrylic acid resin. The tensile elongation at break φ2 of the portion of the shell where the first polymer layer is provided is less than the tensile elongation at break φ1 of the packaging film. When the shell is damaged by external force, it will break in advance, which can reduce the possibility that the shell will extend to the electrode breakage point with the external force, and reduce the possibility that the aluminum interlayer of the shell will short-circuit with the electrode.

[0009] In some preferred embodiments, the first polymer layer comprises solid particles with a particle size of 2 μm to 5 μm to increase the strength of the first polymer layer. The particle size refers to the maximum length of the solid particles.

[0010] In some preferred embodiments, the mass percentage of solid particles in the first polymer layer does not exceed 5% to ensure good adhesion of the first polymer layer.

[0011] In some preferred embodiments, the first polymer layer has a Shore D hardness of 70HS to 80HS. The first polymer layer can serve as a protective layer on the surface of the secondary battery, which can improve the appearance damage of the secondary battery during manufacturing and transportation.

[0012] In some preferred embodiments, the thickness of the first polymer layer is H1, and the thickness of the secondary battery is H2, with 0.4% ≤ H1 / H2 ≤ 4%. This can reduce the tensile elongation at break of the portion of the casing where the first polymer layer is located, while the secondary battery has good energy density.

[0013] In some preferred embodiments, 20μm≤H1≤200μm can reduce the tensile elongation at break of the portion of the casing where the first polymer layer is provided, while the secondary battery has good energy density.

[0014] In some preferred embodiments, the elastic modulus of the first polymer layer is between 0.5 MPa and 3 MPa. An elastic modulus greater than 0.5 MPa provides good elasticity and flexibility. An elastic modulus greater than 3 MPa makes the first polymer layer brittle and prone to breakage.

[0015] In some preferred embodiments, the shear force between the first polymer layer and the packaging film is not less than 38 N / m, which can reduce the possibility of the first polymer layer falling off the packaging film.

[0016] In some preferred embodiments, the adhesive force between the first polymer layer and the packaging film is not less than 6 N / m, which can reduce the possibility of the first polymer layer falling off the packaging film.

[0017] In some preferred embodiments, along the thickness direction of the packaging film, the packaging film includes a first polymer layer, a first metal layer, a second polymer layer and a third polymer layer stacked sequentially, wherein the surface of the third polymer layer facing away from the second polymer layer is at least partially provided with the first polymer layer.

[0018] In some preferred embodiments, the packaging film satisfies at least one of the following characteristics: (1) the first polymer layer comprises polypropylene to facilitate sealing; (2) the first metal layer comprises aluminum to enhance the plasticity of the packaging film; (3) the second polymer layer comprises polyurethane to enhance the adhesive properties of the second polymer layer; and (4) the third polymer layer comprises polyamide to improve the strength of the packaging film.

[0019] In some preferred embodiments, the packaging film includes a first portion, a second portion, and a third portion connected sequentially along a first direction. A first polymer layer is disposed on the surface of the second portion facing away from the electrode assembly. The length of the first portion in the first direction is L1, and the length of the third portion in the first direction is L2, where 0.5mm ≤ L1 ≤ 5mm and 0.5mm ≤ L2 ≤ 5mm. The second portion is the middle region of the packaging film, and the first and third portions are the beginning and end regions of the packaging film. Since the beginning and end regions of the packaging film are easily damaged by impact, reducing the tensile elongation at break of these regions can easily lead to breakage. The first polymer layer is not disposed on the surface of the first and third portions facing away from the electrode assembly. Limiting the length of the first portion in the first direction to 0.5mm to 5mm reduces the likelihood of the first polymer layer adhering to the first portion and thus reduces the likelihood of breakage. Limiting the length of the third portion in the first direction to 0.5mm to 5mm also reduces the likelihood of the first polymer layer adhering to the third portion and thus reduces the likelihood of breakage.

[0020] In some preferred embodiments, the first portion includes a first corner portion, a first intermediate portion, and a second corner portion connected sequentially along a second direction, the second direction being perpendicular to the first direction. A second polymer layer is disposed on the surface of the first intermediate portion facing away from the electrode assembly. The tensile elongation at break of the portion of the housing with the second polymer layer is less than the tensile elongation at break of the packaging film. And / or, the third portion includes a third corner portion, a second intermediate portion, and a fourth corner portion connected sequentially along the second direction, the second direction being perpendicular to the first direction. A third polymer layer is disposed on the surface of the second intermediate portion facing away from the electrode assembly. The tensile elongation at break of the portion of the housing with the third polymer layer is less than the tensile elongation at break of the packaging film. Since the corners of the packaging film are easily damaged by impact, reducing the tensile elongation at break of the corners of the packaging film makes them prone to breakage. The first and second corner portions do not have a second polymer layer disposed on the surface facing away from the electrode assembly, which reduces the possibility of breakage of the first and second corner portions. The third and fourth corner portions do not have a third polymer layer disposed on the surface facing away from the electrode assembly, which reduces the possibility of breakage of the third and fourth corner portions. In this context, the corner area of ​​a packaging film refers to the region near the intersection of each adjacent side of the film. Since an angle is formed between two adjacent sides, the region near the intersection is called the corner area. Taking a cuboid-shaped packaging film as an example, the outer surface of the film is rectangular, so it has four corner areas. These four corner areas are located near the intersection of each pair of adjacent sides of the rectangle, resulting in a total of eight corner areas for a cuboid-shaped packaging film.

[0021] In some preferred embodiments, the length of the first corner portion in the second direction is L3, and the length of the second corner portion in the second direction is L4, where 0.5mm ≤ L3 ≤ 5mm and 0.5mm ≤ L4 ≤ 5mm. Limiting the length of the first corner portion in the second direction to 0.5mm to 5mm reduces the likelihood of the second polymer layer adhering to the first corner portion and reduces the likelihood of damage to the first corner portion. Similarly, limiting the length of the second corner portion in the second direction to 0.5mm to 5mm reduces the likelihood of the second polymer layer adhering to the second corner portion and reduces the likelihood of damage to the second corner portion.

[0022] In some preferred embodiments, the length of the third corner portion in the second direction is L5, and the length of the fourth corner portion in the second direction is L6, where 0.5mm ≤ L5 ≤ 5mm and 0.5mm ≤ L6 ≤ 5mm. Limiting the length of the third corner portion in the second direction to 0.5mm to 5mm reduces the likelihood of the third polymer layer adhering to the third corner portion and reduces the likelihood of damage to the third corner portion. Similarly, limiting the length of the fourth corner portion in the second direction to 0.5mm to 5mm reduces the likelihood of the third polymer layer adhering to the fourth corner portion and reduces the likelihood of damage to the fourth corner portion.

[0023] In some preferred embodiments, 15% ≤ φ1-φ2 ​​≤ 36% ensures that the tensile elongation at break of the portion of the casing with the first polymer layer is less than that of the packaging film. When φ1-φ2 ​​is greater than 36%, the thickness of the first polymer layer becomes too large, and further increasing the thickness of the first polymer layer makes it difficult to further improve the tensile elongation at break of the portion of the casing with the first polymer layer, and will result in a significant loss of energy density in the secondary battery. When φ1-φ2 ​​is less than 15%, the thickness of the first polymer layer becomes too small, and the improvement effect on the tensile elongation at break of the portion of the casing with the first polymer layer is not significant.

[0024] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0025] Thirdly, this application also proposes a method for manufacturing a secondary battery, used to prepare a secondary battery as described in any of the embodiments of the first aspect above, comprising: providing a packaging film and an electrode assembly, and wrapping the packaging film around the outer surface of the electrode assembly. Providing polyacrylic acid resin, and coating the polyacrylic acid resin onto at least a portion of the surface of the packaging film wrapping the electrode assembly away from the electrode assembly to form a first polymer layer. Since the packaging film needs to be perforated before wrapping the electrode assembly, if the tensile elongation at break of the packaging film is low, the corner aluminum layer is easily damaged during perforation, failing to meet packaging requirements. Therefore, the packaging film needs a good tensile elongation at break. By providing the first polymer layer after the packaging film wraps the electrode assembly, the tensile elongation at break of the portion of the composite packaging film (shell) formed by the packaging film and the first polymer layer where the first polymer layer is provided can be reduced without affecting the tensile elongation at break of the packaging film before wrapping the electrode assembly, allowing the packaging film to meet the perforation requirements.

[0026] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0027] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the dimensions in the drawings do not constitute a limitation on scale.

[0028] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0029] Figure 2 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0030] Figure 3 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0031] Figure 4 is a cross-sectional view of a secondary battery in some embodiments of this application in the third direction;

[0032] Figure 5 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0033] Figure 6 is a cross-sectional schematic diagram of a secondary battery according to some embodiments of this application in a first direction;

[0034] Figure 7 is a cross-sectional schematic diagram of a secondary battery according to some embodiments of this application in a first direction;

[0035] Figure 8 is a simplified schematic diagram of the first polymer layer and packaging film of some embodiments of this application.

[0036] Explanation of reference numerals in the attached figures:

[0037] 100. Secondary batteries;

[0038] 10. Shell;

[0039] 11. Packaging film; 111. First polymer layer; 112. First metal layer; 113. Second polymer layer; 114. Third polymer layer; 115. First part; 1151. First corner part; 1152. First middle part; 1153. Second corner part; 116. Second part; 117. Third part; 1171. Third corner part; 1172. Second middle part; 1173. Fourth corner part;

[0040] 12. First polymer layer; 13. Second polymer layer; 14. Third polymer layer;

[0041] 20. Electrode assembly;

[0042] 20a. Tab; 21. Positive electrode plate; 22. Negative electrode plate; 23. Separator;

[0043] X, first direction; Y, second direction; Z, third direction. Embodiments of the present invention

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0045] 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.

[0046] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0047] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0048] The term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular. For example, in numerical terms, perpendicularity can refer to the angle between two straight lines within the range of 90 ± 10°, the dihedral angle between two planes within the range of 90 ± 10°, or the angle between a straight line and a plane within the range of 90 ± 10°. The two components described as "perpendicular" do not have to be absolutely straight lines or planes; they can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is straight or plane, the component can be considered a "straight line" or "plane".

[0049] The first direction X, the second direction Y, and the third direction Z of this application are bidirectional directions. That is, the first direction X includes the direction shown by the arrow in the figure and the opposite direction thereto, the second direction Y includes the direction shown by the arrow in the figure and the opposite direction thereto, and the third direction Z includes the direction shown by the arrow in the figure and the opposite direction thereto.

[0050] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0051] In a first aspect, embodiments of this application provide a secondary battery 100. Referring to Figure 1, the secondary battery 100 includes a housing 10, an electrode assembly 20, and tabs 20a. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), and the electrolyte wets the electrode assembly 20 within the housing 10. The tabs 20a are connected to the electrode assembly 20 and extend out of the housing 10 in the longitudinal direction (first direction X) of the electrode assembly 20 to assist the electrode assembly 20 in energy transfer with external electronic devices.

[0052] Referring to Figure 2, which shows the stacked structure of the electrode assembly 20, the electrode assembly 20 includes a negative electrode 22, a positive electrode 21, and a separator 23. The positive electrode 21 and the negative electrode 22 are stacked alternately, and a separator 23 is disposed between adjacent positive electrode 21 and negative electrode 22 to insulate and separate them. In the embodiments of this application, the electrode assembly 20 is described as a stacked structure. In other embodiments, the electrode assembly 20 may also be a wound structure. For example, the positive electrode 21, the separator 23, and the negative electrode 22 are stacked sequentially and then wound to form a wound electrode assembly 20.

[0053] Referring to Figures 3 and 4, the housing 10 includes a packaging film 11, which wraps around the outer surface of the electrode assembly 20. When the secondary battery 100 is damaged by external force, the packaging film 11 can easily extend to the electrode break, causing the aluminum interlayer of the packaging film 11 to come into contact with the electrode, resulting in a short circuit.

[0054] To address the aforementioned issues, in embodiments of this application, the housing 10 further includes a first polymer layer 12. The packaging film 11, at least partially on the surface facing away from the electrode assembly 20, is provided with the first polymer layer 12. The first polymer layer 12 comprises polyacrylic acid resin, and its tensile elongation at break is less than that of the packaging film 11. By providing the first polymer layer 12 at least partially on the surface of the packaging film 11 facing away from the electrode assembly 20, the first polymer layer 12 and the packaging film 11 form the housing 10. The first polymer layer 12 comprises polyacrylic acid resin, which ensures that the tensile elongation at break of the portion of the housing 10 with the first polymer layer 12 is less than that of the packaging film 11. This causes the housing 10 to fracture prematurely when subjected to external force, reducing the likelihood of the housing 10 extending to the electrode breakage point and reducing the possibility of a short circuit between the aluminum interlayer of the housing 10 and the electrode.

[0055] In some embodiments, 15% ≤ φ1-φ2 ​​≤ 36% ensures that the tensile elongation at break of the portion of the housing 10 with the first polymer layer 12 is less than that of the packaging film 11. When φ1-φ2 ​​is greater than 36%, the thickness of the first polymer layer 12 becomes too large, and further increasing the thickness of the first polymer layer 12 makes it difficult to further improve the tensile elongation at break of the portion of the housing 10 with the first polymer layer 12, and will result in a significant loss of energy density of the secondary battery 100. When φ1-φ2 ​​is less than 15%, the thickness of the first polymer layer 12 becomes too small, and the improvement effect on the tensile elongation at break of the portion of the housing 10 with the first polymer layer 12 is not significant.

[0056] In some embodiments, the first polymer layer 12 includes solid particles with a particle size of 2 μm to 5 μm to increase the strength of the first polymer layer 12. The particle size refers to the maximum length of the solid particles.

[0057] In some embodiments, the mass percentage of solid particles in the first polymer layer 12 does not exceed 5% to ensure good adhesion of the first polymer layer 12.

[0058] In some embodiments, the solid particles may be alumina, zirconium oxide, silicon dioxide, or calcium carbonate to further enhance the strength of the first polymer layer 12.

[0059] In some embodiments, the first polymer layer 12 has a Shore D hardness of 70HS to 80HS. The first polymer layer 12 can serve as a protective layer on the surface of the secondary battery 100, which can improve the appearance damage of the secondary battery 100 during manufacturing and transportation.

[0060] In some embodiments, the elastic modulus of the first polymer layer 12 is between 0.5 MPa and 3 MPa. An elastic modulus greater than 0.5 MPa in the first polymer layer 12 provides good elasticity and flexibility. An elastic modulus greater than 3 MPa in the first polymer layer 12 makes it brittle and prone to breakage.

[0061] In some embodiments, the thickness of the first polymer layer 12 is H1, and the thickness of the secondary battery 100 is H2, with 0.4% ≤ H1 / H2 ≤ 4%, which can reduce the tensile elongation at break of the portion of the housing 10 where the first polymer layer 12 is provided, while the secondary battery 100 has good energy density.

[0062] In some embodiments, 20μm≤H1≤200μm can reduce the tensile elongation at break of the portion of the housing 10 where the first polymer layer 12 is provided, while the secondary battery 100 has good energy density.

[0063] In some embodiments, 20μm≤H1≤40μm can further reduce the tensile elongation at break of the portion of the housing 10 where the first polymer layer 12 is provided, while the secondary battery 100 has good energy density.

[0064] In some embodiments, the shear force between the first polymer layer 12 and the packaging film 11 is not less than 38 N / m, which can reduce the possibility of the first polymer layer 12 falling off the packaging film 11.

[0065] In some embodiments, the adhesive force between the first polymer layer 12 and the packaging film 11 is not less than 6 N / m, which can reduce the possibility of the first polymer layer 12 falling off the packaging film 11.

[0066] In some embodiments, the packaging film 11 includes a first portion 115, a second portion 116, and a third portion 117 connected sequentially along a first direction X. A first polymer layer 12 is disposed on the surface of the second portion 116 facing away from the electrode assembly 20. The length of the first portion 115 in the first direction X is L1, and the length of the third portion 117 in the first direction X is L2, where 0.5mm ≤ L1 ≤ 5mm and 0.5mm ≤ L2 ≤ 5mm. The second portion 116 is the middle region of the packaging film 11, and the first portion 115 and the third portion 117 are the beginning and end regions of the packaging film 11. Since the beginning and end regions of the packaging film 11 are easily damaged by impact and wear, reducing the tensile elongation at break of the beginning and end regions of the packaging film 11 will easily lead to breakage of these regions. The first polymer layer 12 is not disposed on the surface of the first portion 115 and the third portion 117 facing away from the electrode assembly 20. The length of the first portion 115 in the first direction X is limited to 0.5 mm to 5 mm, which reduces the possibility of the first polymer layer 12 adhering to the first portion 115 and the possibility of damage to the first portion 115. Similarly, the length of the third portion 117 in the first direction X is limited to 0.5 mm to 5 mm, which reduces the possibility of the first polymer layer 12 adhering to the third portion 117 and the possibility of damage to the third portion 117.

[0067] In some embodiments, referring to Figures 5 and 6, the first portion 115 includes a first corner portion 1151, a first intermediate portion 1152, and a second corner portion 1153 connected sequentially along the second direction Y. The second direction Y is perpendicular to the first direction X. A second polymer layer 13 is disposed on the surface of the first intermediate portion 1152 facing away from the electrode assembly 20. The tensile elongation at break of the portion of the housing 10 with the second polymer layer 13 is less than the tensile elongation at break of the packaging film 11. Since the corners of the packaging film 11 are easily worn by impact, reducing the tensile elongation at break of the corners of the packaging film 11 would make the corners of the packaging film 11 more prone to breakage. The second polymer layer 13 is not disposed on the surface of the first corner portion 1151 and the second corner portion 1153 facing away from the electrode assembly 20, which can reduce the possibility of breakage of the first corner portion 1151 and the second corner portion 1153. Herein, the corner of the packaging film 11 refers to the area near the intersection of each adjacent side of the packaging film 11. Since an angle is formed between two adjacent sides, the area near the intersection is called the corner. Taking a cuboid-shaped packaging film 11 as an example, the outer surface of the packaging film 11 is rectangular, so it has 4 corners. The 4 corners are located near the intersection of each pair of adjacent sides of the rectangle. The cuboid-shaped packaging film 11 has a total of 8 corners.

[0068] In some embodiments, the length of the first corner portion 1151 in the second direction Y is L3, and the length of the second corner portion 1153 in the second direction Y is L4, where 0.5mm ≤ L3 ≤ 5mm and 0.5mm ≤ L4 ≤ 5mm. Limiting the length of the first corner portion 1151 in the second direction Y to 0.5mm to 5mm reduces the likelihood of the second polymer layer 13 adhering to the first corner portion 1151 and reduces the likelihood of damage to the first corner portion 1151. Similarly, limiting the length of the second corner portion 1153 in the second direction Y to 0.5mm to 5mm reduces the likelihood of the second polymer layer 13 adhering to the second corner portion 1153 and reduces the likelihood of damage to the second corner portion 1153.

[0069] In some embodiments, referring to Figures 5 and 7, the third portion 117 includes a third corner portion 1171, a second intermediate portion 1172, and a fourth corner portion 1173 connected sequentially along the second direction Y. The second direction Y is perpendicular to the first direction X. A third polymer layer 14 is disposed on the surface of the second intermediate portion 1172 facing away from the electrode assembly 20. The tensile elongation at break of the portion of the housing 10 disposed of the third polymer layer 14 is less than the tensile elongation at break of the packaging film 11. The third polymer layer 14 is not disposed on the surface of the third corner portion 1171 and the fourth corner portion 1173 facing away from the electrode assembly 20, which can reduce the possibility of damage to the third corner portion 1171 and the fourth corner portion 1173.

[0070] In some embodiments, the length of the third corner portion 1171 in the second direction Y is L5, and the length of the fourth corner portion 1173 in the second direction Y is L6, where 0.5mm ≤ L5 ≤ 5mm and 0.5mm ≤ L6 ≤ 5mm. Limiting the length of the third corner portion 1171 in the second direction Y to 0.5mm to 5mm reduces the likelihood of the third polymer layer 14 adhering to the third corner portion 1171 and reduces the likelihood of damage to the third corner portion 1171. Similarly, limiting the length of the fourth corner portion 1173 in the second direction Y to 0.5mm to 5mm reduces the likelihood of the third polymer layer 14 adhering to the fourth corner portion 1173 and reduces the likelihood of damage to the fourth corner portion 1173.

[0071] In some embodiments, the second polymer layer 13 comprises polyacrylic acid resin such that the elongation at break of the portion of the housing 10 provided with the second polymer layer 13 is less than the elongation at break of the packaging film 11. The second polymer layer 13 may also comprise solid particles to enhance its strength. The third polymer layer 14 comprises polyacrylic acid resin such that the elongation at break of the portion of the housing 10 provided with the third polymer layer 14 is less than the elongation at break of the packaging film 11. The third polymer layer 14 may also comprise solid particles to enhance its strength.

[0072] In some embodiments, the thickness, material, component mass percentage, and properties of the second polymer layer 13 may be the same as those of the first polymer layer 12. The thickness, material, component mass percentage, and properties of the third polymer layer 14 may be the same as those of the first polymer layer 12.

[0073] In some embodiments, referring to FIG8, along the thickness direction (third direction Z) of the packaging film 11, the packaging film 11 includes a first polymer layer 111, a first metal layer 112, a second polymer layer 113 and a third polymer layer 114 stacked sequentially. At least a portion of the surface of the third polymer layer 114 facing away from the second polymer layer 113 is provided with a first polymer layer 12. The tensile elongation at break of the first polymer layer 12 is less than the tensile elongation at break of the third polymer layer 114. The first polymer layer 12 and the third polymer layer 114 form a composite layer. The tensile elongation at break of the composite layer may be less than the tensile elongation at break of the third polymer layer 114.

[0074] In some embodiments, the packaging film 11 satisfies at least one of the following characteristics: (1) a first polymer layer 111 comprises polypropylene to facilitate sealing of the packaging film 11; (2) a first metal layer 112 comprises aluminum to enhance the plasticity of the packaging film 11; (3) a second polymer layer 113 comprises polyurethane to enhance the adhesive properties of the second polymer layer 113; and (4) a third polymer layer 114 comprises polyamide to improve the strength of the packaging film 11.

[0075] A second aspect of this application also provides an electronic device including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0076] In a third aspect, this application also proposes a method for manufacturing a secondary battery 100, used to prepare a secondary battery 100 as described in any embodiment of the first aspect above, comprising: providing a packaging film 11 and an electrode assembly 20, and wrapping the packaging film 11 around the outer surface of the electrode assembly 20. Providing polyacrylic acid resin, and coating the polyacrylic acid resin onto at least a portion of the surface of the packaging film 11 covering the electrode assembly 20 away from the electrode assembly 20 to form a first polymer layer 12. Since the packaging film 11 needs to be perforated before wrapping the electrode assembly 20, if the tensile elongation at break of the packaging film 11 is low, the corner aluminum layer is easily damaged during perforation, failing to meet packaging requirements. Therefore, the packaging film 11 needs a good tensile elongation at break. By providing the first polymer layer 12 after the packaging film 11 wraps the electrode assembly 20, the tensile elongation at break of the portion of the composite packaging film (shell 10) formed by the packaging film 11 and the first polymer layer 12 where the first polymer layer 12 is provided can be reduced, without affecting the tensile elongation at break of the packaging film 11 before wrapping the electrode assembly 20, thus enabling the packaging film 11 to meet the perforation requirements.

[0077] Test section:

[0078] 1. Tensile test:

[0079] The sample was cut into 100mm long and 15mm wide test specimens using a special tensile cutting tool. The test specimens were then fixed onto the test fixture of the high-speed rail tensile testing machine. The tensile speed was 50±0.5mm / min, and the tensile spacing was 50mm. The maximum value after the sample broke was recorded as the breaking tensile force, and the length of the sample at the point of breakage was also recorded.

[0080] Tensile elongation at break = (length of sample at break - initial length of sample) / initial length of sample.

[0081] Tensile strength = breaking tensile force / initial cross-sectional area of ​​sample.

[0082] 2. Shore D hardness test:

[0083] Place the sample to be tested flat on the testing table. Calibrate the hardness tester to the standard settings. Place the hardness tester vertically on the surface of the sample and apply a uniform pressure of 1 kg to make the indenter stationary on the sample surface. Once the indenter has stabilized, immediately read the value on the hardness tester.

[0084] 3. Elastic modulus test:

[0085] The coating was cut into 100mm long and 15mm wide test samples using a special tensile cutting tool. The test samples were then fixed onto the test fixture of a high-speed rail tensile testing machine. The tensile speed was 50±0.5mm / min, and the tensile spacing was 50mm. After the sample was broken, the stress / strain curve was obtained, and the elastic modulus was calculated as stress / strain.

[0086] 4. Shear force test:

[0087] Apply a 25mm × 100mm bonding area to the packaging film using polymer. Place the cured composite sample between the upper and lower clamps of the tensile testing machine, ensuring that the bonding surface of the sample is parallel to the contact surface of the clamps. Apply a loading force of 10mm / min to peel the first polymer layer from the packaging film at 0°. Record the maximum force value during the peeling process as shear force.

[0088] 5. Adhesion test:

[0089] Take a composite sample of the first polymer layer and the packaging film, and use a special tensile test cutter to make the sample 100mm long and 15mm wide. Fix the sample between the upper and lower clamps of the tensile testing machine, peel the coating and the packaging film at a 90° angle, apply a loading force of 50mm / min, and record the maximum force value during the peeling process as the adhesive force.

[0090] 6. Nail test:

[0091] The secondary battery is first fully charged. The sample is placed flat on the test platform. A special nail with a diameter of 3mm, a chamfer of 0.3, a tip length of 3mm, and a body length of ≥100mm is used to test from the center of the sample at a speed of 150±1.5mm / s. The sample is completely pierced. The judgment criterion is that the battery cell does not catch fire or explode after the test is completed.

[0092] Example 1

[0093] <Preparation of the positive electrode>:

[0094] Aluminum foil is used as the positive electrode current collector. A layer of lithium cobalt oxide slurry is uniformly coated on the surface of the aluminum foil. The slurry composition is a combination of 97.5 wt% lithium cobalt oxide (LiCoO2), 1.0 wt% carbon black (Super P) and 1.5 wt% polyvinylidene fluoride (PVDF). The slurry is dried at 85°C and then cold-pressed, cut, and slit to prepare the positive electrode sheet.

[0095] <Preparation of negative electrode sheet>:

[0096] Copper foil is used as the negative electrode current collector. A layer of graphite slurry is uniformly coated on the surface of the copper foil. The slurry composition is a combination of 97.7 wt% artificial graphite, 1.3 wt% sodium carboxymethyl cellulose (CMC) and 1.0 wt% styrene-butadiene rubber (SBR). The slurry is dried at 85°C and then cold-pressed, cut, and slit to prepare the negative electrode sheet.

[0097] <Electrolyte Preparation>:

[0098] A solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): ethylene carbonate (VC) = 20:30:20:28:2, mass ratio) at a mass ratio of 8:92 was used as the electrolyte for the secondary battery.

[0099] <Preparation of Secondary Batteries>:

[0100] The positive and negative electrode sheets are welded together with tabs, and then the positive and negative electrode sheets are wound together. The positive and negative electrode sheets are separated by a polyethylene separator to prepare the electrode assembly.

[0101] Using Zijiang's 103μm thick aluminum-plastic film as the packaging film, the packaging film is wrapped around the outer surface of the electrode assembly. After top and side sealing, inkjet printing, vacuum drying, electrolyte injection, and high-temperature standing, formation and capacity testing are carried out to obtain a preliminary secondary battery.

[0102] Polyacrylic resin is uniformly sprayed onto the outer surface of the initial secondary battery using an inkjet printer. After curing under 395nm ultraviolet light for ~10s, a first polymer layer with a thickness of 30μm is formed. The thickness of the first polymer layer is 0.6% of the thickness of the secondary battery. The packaging film includes a first part, a second part, and a third part connected sequentially along a first direction (the direction in which the electrode tabs extend from the housing). The second part has the first polymer layer disposed on the surface opposite to the electrode assembly. The length of the first part in the first direction is 5mm, and the length of the third part in the first direction is 5mm. The Shore D hardness of the first polymer layer is 76HS, the elastic modulus is 2MPa, the shear force between the first polymer layer and the packaging film is 38N / m, and the adhesive force between the first polymer layer and the packaging film is 6N / m. The packaging film with the first polymer layer becomes a composite packaging film (housing).

[0103] The relevant parameters in Comparative Examples 1 to 3 and Examples 1 to 8 are shown in Table 1 below.

[0104] In Comparative Example 1 and Examples 1 to 6, a 103μm thick Zijiang aluminum-plastic film was used as the packaging film. In Comparative Example 1, the surface of the packaging film did not have a first polymer layer, while in Examples 1 to 6, only the thickness of the first polymer layer was different.

[0105] Both Comparative Example 2 and Example 7 used 96μm thick Showa aluminum-plastic film as packaging film. In Comparative Example 2, the surface of the packaging film did not have a first polymer layer.

[0106] Both Comparative Example 3 and Example 8 used a 115μm thick DNP aluminum-plastic film as the packaging film. In Comparative Example 3, the surface of the packaging film did not have a first polymer layer.

[0107] Table 1

[0108]

[0109] Note: In Table 1, "\" indicates that the parameter is not included.

[0110] According to Table 1 above, and in conjunction with Comparative Examples 1 to 3 and Examples 1 to 8, it can be seen that by providing a first polymer layer comprising polyacrylic acid resin on the surface of the packaging film away from the electrode assembly, the tensile elongation at break of the portion of the housing with the first polymer layer is less than the tensile elongation at break of the packaging film, which can improve the Nail pass rate of the secondary battery, that is, can improve the problem of short circuit in the secondary battery.

[0111] As can be seen from Examples 1 to 6, a ratio of the thickness of the first polymer layer to the thickness of the secondary battery of 0.4% to 4% can effectively reduce the tensile elongation at break of the portion of the casing where the first polymer layer is located, resulting in a good Nail throughput for the secondary battery. A ratio exceeding 4% will reduce the energy density of the secondary battery. A first polymer layer thickness of 20 μm to 200 μm can effectively reduce the tensile elongation at break of the portion of the casing where the first polymer layer is located, resulting in a good Nail throughput for the secondary battery. A first polymer layer thickness exceeding 200 μm will reduce the energy density of the secondary battery.

[0112] The relevant parameters in Examples 9 to 14 are shown in Table 2 below.

[0113] In Examples 1 and 9 to 11, the only difference is the mass percentage of solid particles in the first polymer layer. In Examples 12 to 14, the only difference is the particle size of the solid particles in the first polymer layer. In Examples 9 to 14, the solid particles are alumina. In other examples, the solid particles can be zirconium oxide, silicon dioxide, or calcium carbonate.

[0114] Table 2

[0115]

[0116] Note: In Table 2, "\" indicates that the parameter is not included.

[0117] According to Table 2 above, and in conjunction with Examples 1 and 9 to 11, it can be seen that when the mass percentage of solid particles in the first polymer layer is ≤5%, the tensile strength of the first polymer layer can be increased. When the mass percentage of solid particles in the first polymer layer exceeds 5%, it will affect the uniformity of the coating of the first polymer layer.

[0118] As can be seen from Examples 10, 12 to 14, when the particle size of the solid particles in the first polymer layer is 2 μm to 5 μm, the first polymer layer has good tensile strength. When the particle size of the solid particles exceeds 5 μm, the solid particles will reduce the cohesive force inside the first polymer layer.

[0119] Table 3

[0120]

[0121] According to Table 3 above, and in conjunction with Examples 1, 2, 3, 5, and 6, the tensile elongation at break of the packaging film is φ1, and the tensile elongation at break of the portion of the shell with the first polymer layer is φ2. Since 15% ≤ φ1 - φ2 ≤ 36%, the tensile elongation at break of the portion of the shell with the first polymer layer is less than that of the packaging film, which can improve the nail pass rate of the secondary battery, thus mitigating the short-circuit problem. A thicker first polymer layer allows for greater extensibility, resulting in a better improvement in the tensile elongation at break of the portion of the shell with the first polymer layer; therefore, a smaller tensile elongation at break of the portion of the shell with the first polymer layer is preferable. When φ1 - φ2 is greater than 36%, the thickness of the first polymer layer becomes too large, making it difficult to further improve the tensile elongation at break of the portion of the shell with the first polymer layer, and resulting in a significant loss of energy density in the secondary battery. When φ1 - φ2 is less than 15%, the thickness of the first polymer layer becomes too small, and the improvement effect on the tensile elongation at break of the portion of the shell with the first polymer layer is not significant.

[0122] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A secondary battery, comprising a casing and an electrode assembly, the casing including a packaging film wrapped around the outer surface of the electrode assembly; Its features are, The housing further includes a first polymer layer, and the packaging film is at least partially disposed on the surface opposite to the electrode assembly. The first polymer layer comprises polyacrylic acid resin. The tensile elongation at break of the packaging film is φ1, and the tensile elongation at break of the portion of the housing disposed of the first polymer layer is φ2, where φ2 < φ1.

2. The secondary battery according to claim 1, characterized in that, The first polymer layer comprises solid particles with a particle size of 2 μm to 5 μm.

3. The secondary battery according to claim 2, characterized in that, The mass percentage of solid particles in the first polymer layer does not exceed 5%.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The Shore D hardness of the first polymer layer is 70HS to 80HS.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the first polymer layer is H1, and the thickness of the secondary battery is H2, with 0.4% ≤ H1 / H2 ≤ 4%.

6. The secondary battery according to claim 5, characterized in that, 20μm≤H1≤200μm.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The elastic modulus of the first polymer layer is 0.5 MPa to 3 MPa.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The shear force between the first polymer layer and the packaging film is not less than 38 N / m.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The adhesive force between the first polymer layer and the packaging film is not less than 6 N / m.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, Along the thickness direction of the packaging film, the packaging film includes a first polymer layer, a first metal layer, a second polymer layer and a third polymer layer stacked sequentially, wherein the first polymer layer is at least partially disposed on the surface of the third polymer layer facing away from the second polymer layer.

11. The secondary battery according to claim 10, characterized in that, The packaging film satisfies at least one of the following characteristics: (1) The first polymer layer comprises polypropylene; (2) The first metal layer comprises aluminum; (3) The second polymer layer includes polyurethane; (4) The third polymer layer comprises polyamide.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The electrode assembly is connected to a tab, which extends out of the housing along a first direction. The packaging film includes a first part, a second part, and a third part connected in sequence along the first direction. The second part is provided with the first polymer layer on the surface opposite to the electrode assembly. The length of the first part in the first direction is L1, and the length of the third part in the first direction is L2, where 0.5mm≤L1≤5mm and 0.5mm≤L2≤5mm.

13. The secondary battery according to claim 12, characterized in that, The first part includes a first corner portion, a first middle portion and a second corner portion connected in sequence along the second direction. The second direction is perpendicular to the first direction. The first middle portion is provided with a second polymer layer on the surface away from the electrode assembly. The tensile elongation at break of the portion of the housing provided with the second polymer layer is less than the tensile elongation at break of the packaging film. And / or, the third part includes a third corner portion, a second intermediate portion and a fourth corner portion connected in sequence along the second direction, the second direction being perpendicular to the first direction, the second intermediate portion having a third polymer layer disposed on the surface opposite to the electrode assembly, and the tensile elongation at break of the portion of the housing having the third polymer layer being less than the tensile elongation at break of the packaging film.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, 15%≤φ1-φ2≤36%.

15. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 14.

16. A method for manufacturing a secondary battery, used to prepare a secondary battery as described in any one of claims 1 to 14, characterized in that, include: The packaging film and the electrode assembly are provided, wherein the packaging film is wrapped around the outer surface of the electrode assembly; The polyacrylic resin is provided, and the polyacrylic resin is coated onto at least a portion of the surface of the packaging film encapsulating the electrode assembly away from the electrode assembly to form the first polymer layer.

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