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 packaging film and an electrode assembly, wherein the packaging film wraps an outer surface of the electrode assembly. The packaging film comprises a weakened region. The tensile elongation at break of the packaging film in a non-weakened region is φ 1, the tensile elongation at break of the packaging film in the weakened region is φ 2, and φ 2<φ 1. The secondary battery, the electronic device, and the method for manufacturing the secondary battery of the present application can improve the problem of short circuit of the secondary battery.

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. 202510341799.9, 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, causing the aluminum layer of the packaging film to come into contact with the electrode and thus short-circuit. By setting a weakened region on the outer surface of the packaging film, the tensile elongation at break of the packaging film is weakened through the weakening treatment. This makes the tensile elongation at break of the packaging film in the weakened region less than that in the non-weakened region. When the secondary battery is damaged by external force, the packaging film can break earlier, and the stretching of the aluminum layer in the packaging film is reduced upon breakage, thereby reducing the possibility of the aluminum layer stretching excessively and coming into contact with the electrode for a 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 packaging film and an electrode assembly, wherein the packaging film is wrapped around the outer surface of the electrode assembly. The packaging film includes a weakened region. The tensile elongation at break of the packaging film in the non-weakened region is φ1, and the tensile elongation at break of the packaging film in the weakened region is φ2, where φ2 < φ1.

[0008] In the above technical solution, by setting the packaging film to include a weakened region, the tensile elongation at break of the packaging film is weakened through the weakening treatment in the weakened region. This makes the tensile elongation at break φ2 of the packaging film in the weakened region less than the tensile elongation at break φ1 of the packaging film in the non-weakened region. When the packaging film is damaged by external force, it will break earlier. The smaller elongation of the packaging film helps to reduce the possibility of the packaging film being extended to the electrode by external force, thereby reducing the possibility of short circuit between the aluminum layer of the packaging film and the electrode.

[0009] In some preferred embodiments, the weakening region includes a treatment region located on the surface of the packaging film opposite to the electrode assembly. In the treatment region, the tensile elongation at break of the packaging film is weakened by the weakening treatment.

[0010] In some preferred embodiments, the processing area is provided with a polymer layer, and the tensile elongation at break of the packaging film with the polymer layer is lower than that of the packaging film without the polymer layer. Since the tensile elongation at break of the polymer layer is lower than that of the packaging film, providing a polymer layer in the processing area can reduce the tensile elongation at break of the packaging film in the processing area.

[0011] In some preferred embodiments, the polymer layer includes at least one of an organosilicon compound and a polyacrylic resin, which can reduce the tensile elongation at break of the packaging film in the treated area.

[0012] In some preferred embodiments, the thickness of the polymer layer is H1, where 20 μm ≤ H1 ≤ 200 μm. A larger polymer layer thickness H1 results in a lower elongation at break of the packaging film in the treated area. When the polymer layer thickness H1 is less than 20 μm, the elongation at break of the packaging film in the treated area is relatively high. By setting the polymer layer thickness H1 ≥ 20 μm, the elongation at break of the packaging film in the treated area can be reduced. When the polymer layer thickness H1 is increased to 200 μm, further increasing the polymer layer thickness H1 does not significantly reduce the elongation at break of the packaging film in the treated area and easily leads to a significant loss of energy density in the secondary battery. By setting the polymer layer thickness H1 ≤ 200 μm, the energy density of the secondary battery can be improved.

[0013] In some preferred embodiments, the packaging film includes a first polymer layer, an adhesive layer, a metal layer, and a second polymer layer stacked sequentially. The first polymer layer is disposed on the surface of the adhesive layer facing away from the electrode assembly. The treatment area is located on the surface of the first polymer layer facing away from the adhesive layer. The tensile elongation at break of the first polymer layer in the treatment area is weakened by a weakening treatment, which can reduce the tensile elongation at break of the first polymer layer in the treatment area, thereby reducing the tensile elongation at break of the packaging film in the treatment area. The first polymer layer includes polyamide, which can improve the strength of the packaging film.

[0014] In some preferred embodiments, the packaging film includes a first polymer layer, an adhesive layer, and a metal layer. The two opposite surfaces of the adhesive layer are respectively adhered to the first polymer layer and the metal layer. The weakening region also includes a mesh region located in the adhesive layer. The mesh region has a plurality of holes. Along the thickness direction of the adhesive layer, the mesh region is located between the first polymer layer and the metal layer. This can reduce the possibility that the first polymer layer in the mesh region will exert a high tensile elongation at break on the metal layer, and can reduce the tensile elongation at break of the packaging film in the mesh region.

[0015] In some preferred embodiments, along the thickness direction of the adhesive layer, the holes are located between the first polymer layer and the metal layer, which can reduce the likelihood that the first polymer layer at the hole will exert a high tensile elongation at break on the metal layer. The area of ​​the mesh region is S1, and the sum of the areas of all holes is S2, with the ratio of S2 to S1 being 50% to 90%. The larger the ratio of S2 to S1, the smaller the likelihood that the first polymer layer at the mesh region will exert a high tensile elongation at break on the metal layer, and the lower the tensile elongation at break of the packaging film in the mesh region. When the ratio of S2 to S1 is less than 50%, the tensile elongation at break of the packaging film in the mesh region is relatively high. By setting the ratio of S2 to S1 ≥ 50%, the tensile elongation at break of the packaging film in the mesh region can be reduced. When the ratio of S2 to S1 is greater than 90%, the tensile elongation at break of the packaging film in the mesh region is relatively low, and the packaging film is easily damaged. By setting the ratio of S2 to S1 ≤ 90%, the possibility of packaging film damage can be reduced.

[0016] In some preferred embodiments, the width of the holes is between 3 mm and 10 mm. The larger the hole width, the less likely the first polymer layer in the mesh area will exert a high tensile elongation at break on the metal layer, resulting in a lower tensile elongation at break of the packaging film in the mesh area. When the hole width is less than 3 mm, the tensile elongation at break of the packaging film in the mesh area is relatively high; by setting the hole width ≥ 3 mm, the tensile elongation at break of the packaging film in the mesh area can be reduced. When the hole width is greater than 10 mm, the tensile elongation at break of the packaging film in the mesh area is relatively low, and the packaging film is easily damaged; by setting the hole width ≤ 10 mm, the possibility of packaging film damage can be reduced.

[0017] In some preferred embodiments, the length of the hole is the same as the width of the mesh area. A larger hole length results in a lower elongation at break of the packaging film in the mesh area. By setting the hole length to be the same as the width of the mesh area, it is beneficial to further reduce the elongation at break of the packaging film in the mesh area. It is understood that due to processing errors, "the length of the hole is the same as the width of the mesh area" means that the length of the hole and the width of the mesh area are approximately the same; a difference of no more than 10% of the hole length between the hole length and the width of the mesh area is also acceptable.

[0018] In some preferred embodiments, along the length of the mesh area, the edge of the hole near the edge of the mesh area coincides with the edge of the mesh area. This is beneficial for increasing the area ratio of the holes in the mesh area and for reducing the tensile elongation at break of the packaging film in the mesh area. It is understood that due to processing errors, the coincidence of the hole edge with the edge of the mesh area means that the hole edge and the edge of the mesh area roughly coincide; a distance of no more than 10% of the hole width between the hole edge and the edge of the mesh area is also acceptable.

[0019] In some preferred embodiments, along the length of the electrode assembly, the packaging film includes opposing first and second edges. The distance between the weakened region and the first edge is L1, and the distance between the weakened region and the second edge is L2, where 0.5mm ≤ L1 ≤ 5mm and 0.5mm ≤ L2 ≤ 5mm. Since the packaging film requires stamping, and the first and second edges are easily damaged by impact, reducing the tensile elongation at break of the first and second edges would make it difficult for the packaging film to meet stamping requirements, and the first and second edges would be prone to breakage. By limiting L1 to ≥ 0.5mm, the possibility of the mesh area affecting the tensile elongation at break of the first edge can be reduced, which is beneficial for the packaging film to meet stamping requirements and can reduce the possibility of breakage of the first edge. By limiting L1 to ≤ 5mm, the area of ​​the mesh area can be increased, which further helps to reduce the tensile elongation at break of the packaging film. By limiting L2 to ≥ 0.5 mm, the possibility of the mesh area affecting the tensile elongation at break of the second edge can be reduced, which is beneficial for the packaging film to meet the stamping requirements and can reduce the possibility of damage to the second edge. By limiting L2 to ≤ 5 mm, the area of ​​the mesh area can be increased, which in turn helps to further reduce the tensile elongation at break of the packaging film.

[0020] In some preferred embodiments, along the width direction of the electrode assembly, the packaging film includes opposing third and fourth edges. The distance between the weakened region and the third edge is L3, and the distance between the weakened region and the fourth edge is L4, where 0.5mm ≤ L3 ≤ 5mm and 0.5mm ≤ L4 ≤ 5mm. By limiting L3 to ≥ 0.5mm, the possibility of the mesh area affecting the tensile elongation at break of the third edge can be reduced, thus reducing the possibility of breakage of the third edge. By limiting L3 to ≤ 5mm, the area of ​​the mesh area can be increased, which further helps to reduce the tensile elongation at break of the packaging film. Similarly, by limiting L4 to ≥ 0.5mm, the possibility of the mesh area affecting the tensile elongation at break of the fourth edge can be reduced, thus reducing the possibility of breakage of the fourth edge. By limiting L4 to ≤ 5mm, the area of ​​the mesh area can be increased, which further helps to reduce the tensile elongation at break of the packaging film.

[0021] In some preferred embodiments, the packaging film includes a first wall and a second wall disposed opposite each other along the thickness direction of the electrode assembly, the first wall including a weakened region. Since the first wall of the electrode assembly is more likely to contact the electrode sheet and short-circuit in the thickness direction, by providing a weakened region in the first wall, the possibility of the aluminum layer of the first wall extending to the electrode sheet under external force can be reduced, thereby reducing the possibility of a short circuit between the aluminum layer of the first wall and the electrode sheet.

[0022] In some preferred embodiments, the second wall includes a weakened region. Since the second wall of the electrode assembly is more likely to short-circuit with the electrode in the thickness direction, by providing a weakened region in the second wall, the possibility of the aluminum layer of the second wall extending to the electrode under external force can be reduced, thereby reducing the possibility of a short circuit between the aluminum layer of the second wall and the electrode.

[0023] In some preferred embodiments, 25% ≤ φ1-φ2 ​​≤ 36%. The larger φ1-φ2 ​​is, the smaller the tensile elongation at break φ2 of the packaging film in the weakened region, and the better the effect of improving the short circuit between the aluminum layer and the electrode. When φ1-φ2 ​​is less than 25%, the tensile elongation at break of the packaging film in the weakened region is relatively high, and the effect of improving the short circuit between the aluminum layer and the electrode is not significant. By setting φ1-φ2 ​​≥ 25%, the tensile elongation at break of the packaging film in the weakened region can be reduced, thus reducing the possibility of a short circuit between the aluminum layer and the electrode. When φ1-φ2 ​​is greater than 36%, further increasing φ1-φ2 ​​does not significantly improve the effect of improving the short circuit between the aluminum layer and the electrode, and it is easy to lose a significant amount of energy density of the secondary battery or cause a decrease in the strength of the packaging film. By setting φ1-φ2 ​​≤ 36%, the tensile elongation at break of the packaging film can be guaranteed to meet the requirements without excessively affecting other properties of the packaging film.

[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 embodiment of the first aspect above, comprising: providing a packaging film; weakening a portion of the packaging film to form a weakened region; the tensile elongation at break of the packaging film in the non-weakened region being φ1; and the tensile elongation at break of the packaging film in the weakened region being φ2, where φ2 < φ1. This causes the packaging film to break prematurely when subjected to external force, and the smaller elongation of the packaging film helps reduce the possibility of the packaging film being extended to the electrode by external force, thereby reducing the possibility of a short circuit between the aluminum layer of the packaging film and the electrode.

[0026] In some preferred embodiments, the weakening treatment includes acid treatment, which can partially corrode the packaging film in the weakened area, thereby reducing the tensile elongation at break of the packaging film in the weakened area.

[0027] In some preferred embodiments, the acid reagent includes at least one of formic acid, acetic acid, and hydrofluoric acid, which can enhance the corrosive effect of the acid reagent.

[0028] In some preferred embodiments, the weakening treatment includes atmospheric plasma treatment, which can cause surface molecular cross-linking of the packaging film in the weakened area, thereby reducing the tensile elongation at break of the packaging film in the weakened area.

[0029] In some preferred embodiments, the atmospheric plasma includes at least one of air, oxygen, nitrogen, and argon, which can enhance the effect of atmospheric plasma on the surface molecular cross-linking of the packaging film in the weakened area.

[0030] In some preferred embodiments, the weakened region is treated with atmospheric plasma for a time M, where M ≥ 10 min. The longer the atmospheric plasma treatment time, the lower the tensile elongation at break of the packaging film in the weakened region. When M < 10 min, the tensile elongation at break of the packaging film in the weakened region is relatively high. By setting M ≥ 10 min, the tensile elongation at break of the packaging film in the weakened region can be reduced.

[0031] 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

[0032] 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.

[0033] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0034] Figure 2 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0035] Figure 3 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0036] Figure 4 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0037] Figure 5 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0038] Figure 6 is a schematic diagram of the structure of the packaging film and polymer layer in some embodiments of this application;

[0039] Figure 7 is a schematic diagram of the structure of the packaging film according to some embodiments of this application;

[0040] Figure 8 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0041] Figure 9 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application.

[0042] Explanation of reference numerals in the attached figures:

[0043] 100. Secondary batteries;

[0044] 10. Packaging film; 101. Weakened area;

[0045] 11. First polymer layer; 111. Processed area; 12. Adhesive layer; 121. Mesh area; 1211. Hole; 13. Metal layer; 14. Second polymer layer;

[0046] 151. First edge; 152. Second edge; 153. Third edge; 154. Fourth edge;

[0047] 161. First wall; 162. Second wall;

[0048] 17. Polymer layer;

[0049] 20. Electrode assembly; 20a. Tab; 21. Positive electrode plate; 22. Negative electrode plate; 23. Separator;

[0050] X: Length direction of the electrode assembly; Y: Width direction of the electrode assembly; Z: Thickness direction of the electrode assembly. Embodiments of the present invention

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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".

[0056] 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.

[0057] In a first aspect, embodiments of this application provide a secondary battery 100. Referring to Figure 1, the secondary battery 100 includes a packaging film 10, an electrode assembly 20, and tabs 20a. The packaging film 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 packaging film 10. The tabs 20a are connected to the electrode assembly 20 and extend from the packaging film 10 in the longitudinal direction X of the electrode assembly 20 to assist the electrode assembly 20 in energy transfer with external electronic devices.

[0058] 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 or other structures. 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.

[0059] The inventors of this application have discovered that when the secondary battery 100 is damaged by external force, the packaging film 10 is easily stretched to the electrode by the external force, causing the aluminum layer of the packaging film 10 to come into contact with the electrode and thus causing a short circuit.

[0060] To address the aforementioned issues, in the embodiments of this application, referring to Figures 3 and 4, the packaging film 10 includes a weakened region 101. The tensile elongation at break of the packaging film 10 in the non-weakened region 101 is φ1, and the tensile elongation at break of the packaging film 10 in the weakened region 101 is φ2, where φ2 < φ1. By including the weakened region 101 in the packaging film 10, the tensile elongation at break of the packaging film 10 is weakened through the weakening process. This allows the tensile elongation at break φ2 in the weakened region 101 to be less than the tensile elongation at break φ1 in the non-weakened region 101. Consequently, the packaging film 10 will break prematurely when subjected to external force, resulting in less elongation. This reduces the likelihood of the packaging film 10 being extended to the electrode by external force, thereby reducing the possibility of a short circuit between the aluminum layer of the packaging film 10 and the electrode.

[0061] In some embodiments, the weakening region 101 includes a processing region 111 located on the surface of the packaging film 10 opposite to the electrode assembly 20. In the processing region 111, the tensile elongation at break of the packaging film 10 is weakened by the weakening process.

[0062] In some embodiments, referring to FIG5, the processing area 111 is provided with a polymer layer 17, and the tensile elongation at break of the packaging film 10 provided with the polymer layer 17 is less than the tensile elongation at break of the packaging film 10 without the polymer layer 17. Since the tensile elongation at break of the polymer layer 17 is less than the tensile elongation at break of the packaging film 10, the provision of the polymer layer 17 in the processing area 111 can reduce the tensile elongation at break of the packaging film 10 in the processing area 111.

[0063] In some embodiments, the polymer layer 17 includes at least one of an organosilicon compound and a polyacrylic resin, which can reduce the tensile elongation at break of the packaging film 10 in the treated area 111.

[0064] In some embodiments, the thickness of the polymer layer 17 is H1, where 10 μm ≤ H1 ≤ 250 μm, preferably 20 μm ≤ H1 ≤ 200 μm. In some embodiments, H1 can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm. The thickness H1 of the polymer layer 17 is 150μm, 155μm, 160μm, 165μm, 170μm, 175μm, 180μm, 185μm, 190μm, 195μm, 200μm, 205μm, 210μm, 215μm, 220μm, 225μm, 230μm, 235μm, 240μm, 245μm, 250μm, or a range of any two of these values. The greater the thickness H1 of the polymer layer 17, the lower the elongation at break of the packaging film 10 in the treated area 111. When the thickness H1 of the polymer layer 17 is less than 20μm, the elongation at break of the packaging film 10 in the treated area 111 is relatively high. By setting the thickness H1 of the polymer layer 17 to ≥ 20μm, the elongation at break of the packaging film 10 in the treated area 111 can be reduced. When the thickness H1 of polymer layer 17 is increased to 200 μm, further increasing the thickness H1 of polymer layer 17 does not significantly reduce the tensile elongation at break of packaging film 10 in the treated area 111, and easily results in a significant loss of energy density of secondary battery 100. By setting the thickness H1 of polymer layer 17 to ≤ 200 μm, the energy density of secondary battery 100 can be improved.

[0065] In some embodiments, referring to Figures 5 and 6, the packaging film 10 includes a first polymer layer 11, an adhesive layer 12, a metal layer 13, and a second polymer layer 14 stacked sequentially. The first polymer layer 11 is disposed on the surface of the adhesive layer 12 facing away from the electrode assembly 20. The processing region 111 is located on the surface of the first polymer layer 11 facing away from the adhesive layer 12. The tensile elongation at break of the first polymer layer 11 in the processing region 111 is weakened by a weakening treatment, which can reduce the tensile elongation at break of the first polymer layer 11 in the processing region 111, thereby reducing the tensile elongation at break of the packaging film 10 in the processing region 111. The first polymer layer 11 includes polyamide, which can improve the strength of the packaging film 10.

[0066] In some embodiments, the adhesive layer 12 comprises polyurethane, which can enhance the adhesive properties of the adhesive layer 12. The metal layer 13 comprises aluminum, which can enhance the plasticity of the packaging film 10. The second polymer layer 14 comprises polypropylene, which can facilitate the sealing of the packaging film 10.

[0067] In some embodiments, referring to Figures 7 and 8, the packaging film 10 includes a first polymer layer 11, an adhesive layer 12, and a metal layer 13. The two opposite surfaces of the adhesive layer 12 are respectively bonded to the first polymer layer 11 and the metal layer 13. The weakening region 101 also includes a mesh region 121 located in the adhesive layer 12. The mesh region 121 is provided with a plurality of holes 1211. Along the thickness direction of the adhesive layer 12, the mesh region 121 is located between the first polymer layer 11 and the metal layer 13, which can reduce the possibility that the first polymer layer 11 at the mesh region 121 will exert a high tensile elongation at break on the metal layer 13, and can reduce the tensile elongation at break of the packaging film 10 in the mesh region 121.

[0068] In some embodiments, along the thickness direction of the adhesive layer 12, the holes 1211 are located between the first polymer layer 11 and the metal layer 13, which can reduce the possibility that the first polymer layer 11 at the holes 1211 will exert a high tensile elongation at break on the metal layer 13. The area of ​​the mesh region 121 is S1, and the sum of the areas of all holes 1211 is S2. The ratio of S2 to S1 is 37.5% to 95%, preferably 50% to 90%. In some embodiments, the ratio of S2 to S1 can be 37.5%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range of any two of these values. The higher the ratio of S2 to S1, the less likely the first polymer layer 11 in the mesh region 121 will exert a high tensile elongation at break on the metal layer 13, and the lower the tensile elongation at break of the packaging film 10 in the mesh region 121. When the ratio of S2 to S1 is less than 50%, the tensile elongation at break of the packaging film 10 in the mesh region 121 is relatively high. By setting the ratio of S2 to S1 ≥ 50%, the tensile elongation at break of the packaging film 10 in the mesh region 121 can be reduced. When the ratio of S2 to S1 is greater than 90%, the tensile elongation at break of the packaging film 10 in the mesh region 121 is relatively low, and the packaging film 10 is easily damaged. By setting the ratio of S2 to S1 ≤ 90%, the possibility of damage to the packaging film 10 can be reduced.

[0069] In some embodiments, the hole 1211 is a rectangular hole, which improves production convenience. In other embodiments, the shape of the hole 1211 can be circular, triangular, sector-shaped, polygonal, or any irregular shape, which can meet different processing requirements.

[0070] In some embodiments, the width W1 of the hole 1211 is 1 mm to 15 mm, preferably 3 mm to 10 mm. In some embodiments, W1 can be 1 mm, 2 mm, 2.9 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, or a range of any two of these values. The larger the width of the hole 1211, the less likely the first polymer layer 11 at the mesh region 121 will exert a high tensile elongation at break on the metal layer 13, and the lower the tensile elongation at break of the packaging film 10 at the mesh region 121. When the width of the hole 1211 is less than 3 mm, the tensile elongation at break of the packaging film 10 at the mesh region 121 is relatively high. By setting the width of the hole 1211 to be ≥3 mm, the tensile elongation at break of the packaging film 10 at the mesh region 121 can be reduced. When the width of hole 1211 is greater than 10mm, the tensile breaking elongation of the packaging film 10 in the mesh area 121 is low, and the packaging film 10 is easily damaged. By setting the width of hole 1211 to ≤10mm, the possibility of damage to the packaging film 10 can be reduced.

[0071] In some embodiments, the length T1 of the hole 1211 is the same as the width W of the mesh region 121. The larger the length of the hole 1211, the smaller the tensile elongation at break of the packaging film 10 in the mesh region 121. By setting the length of the hole 1211 to be the same as the width of the mesh region 121, it is beneficial to further reduce the tensile elongation at break of the packaging film 10 in the mesh region 121. It is understood that due to processing errors, the statement that the length of the hole 1211 is the same as the width of the mesh region 121 means that the length of the hole 1211 is approximately the same as the width of the mesh region 121. A difference of no more than 10% of the length of the hole 1211 between the length of the hole 1211 and the width of the mesh region 121 can also meet the requirements.

[0072] In some embodiments, along the length T of the mesh region 121, the edges of the holes 1211 near the edge of the mesh region 121 coincide with the edge of the mesh region 121. This is beneficial for increasing the area ratio of the holes 1211 in the mesh region 121 and for reducing the tensile elongation at break of the packaging film 10 in the mesh region 121. It is understood that due to processing errors, the coincidence of the hole 1211 edge with the edge of the mesh region 121 means that the hole 1211 edge roughly coincides with the edge of the mesh region 121. A distance of no more than 10% of the hole 121 width between the hole 1211 edge and the edge of the mesh region 121 is also acceptable.

[0073] In some embodiments, along the length direction X of the electrode assembly 20, the packaging film 10 includes opposing first edges 151 and second edges 152. The distance between the weakened region 101 and the first edge 151 is L1, and the distance between the weakened region 101 and the second edge 152 is L2, where 0.5mm ≤ L1 ≤ 5mm and 0.5mm ≤ L2 ≤ 5mm. Since the packaging film 10 requires stamping, and the first edges 151 and second edges 152 of the packaging film 10 are easily damaged by impact, reducing the tensile elongation at break of the first edges 151 and second edges 152 would make it difficult for the packaging film 10 to meet stamping requirements, and the first edges 151 and second edges 152 would be prone to breakage. By limiting L1 ≥ 0.5mm, the possibility of the mesh region 121 affecting the tensile elongation at break of the first edge 151 can be reduced, which is beneficial for the packaging film 10 to meet stamping requirements and can reduce the possibility of breakage of the first edge 151. By limiting L1 ≤ 5mm, the area of ​​the mesh region 121 can be increased, which further helps to reduce the tensile elongation at break of the packaging film 10. By limiting L2 to ≥ 0.5 mm, the possibility of the mesh area 121 affecting the tensile elongation at break of the second edge 152 can be reduced, which is beneficial for the packaging film 10 to meet the stamping requirements and can reduce the possibility of damage to the second edge 152. By limiting L2 to ≤ 5 mm, the area of ​​the mesh area 121 can be increased, which is beneficial for further reducing the tensile elongation at break of the packaging film 10.

[0074] In some embodiments, referring to FIG3, along the width direction Y of the electrode assembly 20, the packaging film 10 includes opposing third edges 153 and fourth edges 154. The distance between the weakened region 101 and the third edge 153 is L3, and the distance between the weakened region 101 and the fourth edge 154 is L4, where 0.5mm ≤ L3 ≤ 5mm and 0.5mm ≤ L4 ≤ 5mm. By limiting L3 ≥ 0.5mm, the possibility of the mesh region 121 affecting the tensile elongation at break of the third edge 153 can be reduced, and the possibility of the third edge 153 breaking can be reduced. By limiting L3 ≤ 5mm, it is beneficial to increase the area of ​​the mesh region 121, which in turn is beneficial to further reduce the tensile elongation at break of the packaging film 10. Similarly, by limiting L4 ≥ 0.5mm, the possibility of the mesh region 121 affecting the tensile elongation at break of the fourth edge 154 can be reduced, and the possibility of the fourth edge 154 breaking can be reduced. By limiting L4 ≤ 5mm, it is beneficial to increase the area of ​​the mesh region 121, which in turn is beneficial to further reduce the tensile elongation at break of the packaging film 10.

[0075] In some embodiments, referring to Figures 3, 4, and 9, the packaging film 10 includes a first wall 161 and a second wall 162 disposed opposite each other along the thickness direction Z of the electrode assembly 20. The first wall 161 includes a weakening region 101. Since the first wall 161 of the electrode assembly 20 is more likely to contact the electrode sheet and cause a short circuit in the thickness direction, by providing the weakening region 101 in the first wall 161, the possibility that the aluminum layer of the first wall 161 extends to the electrode sheet under the action of external force can be reduced, and the possibility that the aluminum layer of the first wall 161 will contact the electrode sheet and cause a short circuit can be reduced.

[0076] In some embodiments, the second wall 162 includes a weakening region 101. Since the second wall 162 of the electrode assembly 20 is more likely to short-circuit with the electrode in the thickness direction, by providing the weakening region 101 in the second wall 162, the possibility that the aluminum layer of the second wall 162 may extend to the electrode under the action of external force can be reduced, and the possibility that the aluminum layer of the second wall 162 may short-circuit with the electrode can be reduced.

[0077] In some embodiments, 12% ≤ φ1-φ2 ​​≤ 91%, preferably, 25% ≤ φ1-φ2 ​​≤ 36%. In some embodiments, φ1-φ2 ​​can be 12%, 13%, 15%, 20%, 25%, 30%, 31%, 35%, 36%, 37%, 40%, 45%, 50%, 55%, 59%, 60%, 64%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, or a range of any two of these values, or a value within a range of any two of these values. The larger φ1-φ2 ​​is, the smaller the tensile elongation at break φ2 of the packaging film 10 in the weakened region 101, and the better the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film 10. When φ1-φ2 ​​is less than 25%, the tensile elongation at break of the packaging film 10 in the weakened region 101 is relatively high, and the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film 10 is not obvious. By setting φ1-φ2 ​​≥ 25%, the tensile elongation at break of the packaging film 10 in the weakened region 101 can be reduced, and the possibility of short circuit between the aluminum layer and the electrode of the packaging film 10 can be reduced. When φ1-φ2 ​​is greater than 36%, further increasing φ1-φ2 ​​does not significantly improve the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film 10, and it is easy to lose a lot of energy density of the secondary battery 100 or cause a decrease in the strength of the packaging film 10. By setting φ1-φ2 ​​≤ 36%, the tensile elongation at break of the packaging film 10 can be guaranteed to meet the requirements without excessively affecting other properties of the packaging film 10.

[0078] 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.

[0079] Referring to Figure 3, a third aspect of this application also proposes a method for manufacturing a secondary battery, used to prepare a secondary battery 100 as described in any embodiment of the first aspect above, comprising: providing a packaging film 10; weakening a portion of the packaging film 10 to form a weakened region 101; the tensile elongation at break of the packaging film 10 in the non-weakened region 101 being φ1; and the tensile elongation at break of the packaging film 10 in the weakened region 101 being φ2, where φ2 < φ1. This causes the packaging film 10 to break prematurely when subjected to external force, and the smaller elongation of the packaging film 10 reduces the possibility that the packaging film 10 will be extended to the electrode by external force, thereby reducing the possibility of a short circuit between the aluminum layer of the packaging film 10 and the electrode.

[0080] In some embodiments, the weakening treatment includes acid treatment, in which spraying acid can corrode the packaging film 10 in the weakened region 101, thereby reducing the tensile elongation at break of the packaging film 10 in the weakened region 101.

[0081] In some embodiments, the acid reagent includes at least one of formic acid, acetic acid, and hydrofluoric acid, which can enhance the corrosive effect of the acid reagent.

[0082] In some embodiments, the weakening treatment includes atmospheric plasma treatment, in which atmospheric plasma is sprayed to cause surface molecular cross-linking of the packaging film 10 in the weakened region 101, thereby reducing the tensile elongation at break of the packaging film 10 in the weakened region 101.

[0083] In some embodiments, atmospheric plasma includes at least one of air, oxygen, nitrogen, and argon, which can enhance the effect of atmospheric plasma on the surface molecular cross-linking of the packaging film 10 in the weakened region 101.

[0084] In some embodiments, the weakened region 101 is treated with atmospheric plasma for a time M, where M ≥ 8 min, preferably M ≥ 10 min. In some embodiments, M can be 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 30 min, or a range of any two of these values. The longer the atmospheric plasma treatment time, the lower the tensile elongation at break of the packaging film 10 in the weakened region 101. When M < 10 min, the tensile elongation at break of the packaging film 10 in the weakened region 101 is relatively high. By setting M ≥ 10 min, the tensile elongation at break of the packaging film 10 in the weakened region 101 can be reduced.

[0085] Test section:

[0086] 1. Tensile test of packaging film in weakened areas:

[0087] The weakened area of ​​the packaging film was used as a sample. The sample was cut into 70mm long and 15mm wide test specimens using a special tensile cutter. The test specimens were then fixed onto the testing fixture of a high-speed rail tensile testing machine. The tensile speed was 50±0.5mm / min, and the tensile spacing was 50mm. The maximum tensile force and sample length were recorded after the sample broke. The maximum tensile force is the breaking tensile force. The tensile elongation at break of the weakened area packaging film = (sample length at break - initial sample length) / initial sample length.

[0088] 2. Tensile test of packaging film in non-weakened areas:

[0089] Using the packaging film from the non-weakened area as a sample, cut it into test specimens 70mm long and 15mm wide using a special tensile cutter. Fix the test specimen onto the testing fixture of a high-speed rail tensile testing machine. The tensile speed is 50±0.5mm / min, and the tensile spacing is 50mm. Record the maximum tensile force and sample length after the sample breaks. The maximum tensile force is the breaking tensile force. The tensile elongation at break of the packaging film in the non-weakened area = (sample length at break - initial sample length) / initial sample length.

[0090] 3. Nail test:

[0091] The sample 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 nail tip length of 3mm, and a nail 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 the negative electrode>:

[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] <Preparation of Electrolyte>:

[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 plates are welded together with tabs, and then the positive and negative electrode plates are wound together. The positive and negative electrode plates are separated by a polyethylene separator, thereby preparing the electrode assembly.

[0101] A 103μm thick aluminum-plastic film from Zijiang was used as the packaging film. The film was wrapped around the outer surface of the electrode assembly. After top and side sealing, coding, vacuum drying, electrolyte injection, and high-temperature settling, formation and capacity testing were performed to obtain a preliminary secondary battery. The secondary battery is 90mm long and 60mm wide.

[0102] The packaging film includes a weakened region, which in turn includes a treatment region. The packaging film includes a first wall in the thickness direction of the electrode assembly. The first wall, facing away from the surface of the electrode assembly, includes the treatment region. The packaging film includes opposing first and second edges in the length direction of the electrode assembly. The distance L1 between the treatment region and the first edge is 5 mm, and the distance L2 between the treatment region and the second edge is 5 mm. The packaging film includes opposing third and fourth edges in the width direction of the electrode assembly. The distance L3 between the treatment region and the third edge is 5 mm, and the distance L4 between the treatment region and the fourth edge is 5 mm. 1-2 ml of formic acid reagent is uniformly coated onto the treatment region, and the reaction is completed after standing for 10 minutes. The concentration of formic acid in the formic acid reagent is 98%.

[0103] The relevant parameters in Comparative Example 1 and Examples 1 to 4 are shown in Table 1 below.

[0104] In Comparative Example 1, the packaging film did not include the weakened area.

[0105] The weakening treatment method for the weakened area in Example 2 is atmospheric plasma treatment. The specific steps are as follows: the initial secondary battery is placed in the plasma device, the distance between the nozzle of the plasma device and the first wall is 5-10cm, and atmospheric plasma is sprayed onto the treatment area in an atmospheric environment for 15 minutes.

[0106] The weakening treatment method of the weakened area in Example 3 is to set a polymer layer. The specific steps are as follows: polyacrylic acid resin is uniformly sprayed onto the surface of the first wall away from the electrode assembly by inkjet printing equipment, and cured by irradiation with 395nm ultraviolet light for ~10s to form a polymer layer with a thickness of 30μm.

[0107] The weakening treatment method for the weakened region in Example 4 involves setting a mesh region. The specific steps are as follows: The packaging film includes a first polymer layer, an adhesive layer, a metal layer, and a second polymer layer stacked sequentially. The weakened region also includes a mesh region located in the adhesive layer. The mesh region has several holes and is located between the first polymer layer and the metal layer along the thickness direction of the adhesive layer. The first polymer layer is a polyamide layer, the adhesive layer is a polyurethane layer, the metal layer is aluminum foil, and the second polymer layer is a polypropylene layer.

[0108] Table 1

[0109]

[0110] Note: In Table 1, "\" indicates that the parameter is not included.

[0111] According to Table 1 above, and in conjunction with Comparative Example 1 and Examples 1 to 4, it can be seen that by setting the packaging film to include a weakened region, the tensile elongation at break of the packaging film is weakened by the weakening treatment in the weakened region. This makes the tensile elongation at break φ2 of the packaging film in the weakened region smaller than the tensile elongation at break φ1 of the packaging film in the non-weakened region. When the packaging film is damaged by external force, it will break earlier. The smaller elongation of the packaging film helps to reduce the possibility of the packaging film being extended to the electrode by external force, thereby reducing the possibility of short circuit between the aluminum layer of the packaging film and the electrode. Therefore, the needle penetration pass rate of the secondary battery can be improved.

[0112] The relevant parameters in Examples 1 and 5 to 9 are shown in Table 2 below.

[0113] The acid reagent concentrations in Examples 1 and 5 to 9 are different.

[0114] Table 2

[0115]

[0116] Based on Examples 1 and 5 to 9, it can be seen that the larger φ1-φ2 ​​is, the smaller the tensile elongation at break φ2 of the packaging film in the weakened region, the better the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film, and the higher the needle penetration pass rate of the secondary battery. When φ1-φ2 ​​is less than 25%, the tensile elongation at break of the packaging film in the weakened region is relatively high, and the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film is not obvious. By setting φ1-φ2 ​​≥ 25%, the tensile elongation at break of the packaging film in the weakened region can be reduced, and the possibility of short circuit between the aluminum layer and the electrode of the packaging film can be reduced. When φ1-φ2 ​​is greater than 36%, further increasing φ1-φ2 ​​does not significantly improve the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film, and it is easy to reduce the strength of the packaging film. By setting φ1-φ2 ​​≤ 36%, the tensile elongation at break of the packaging film can be guaranteed to meet the requirements without excessively affecting other properties of the packaging film.

[0117] The relevant parameters in Example 2 and Examples 10 to 14 are shown in Table 3 below.

[0118] The atmospheric plasma treatment time M is different in Examples 2 and Examples 10 to 14.

[0119] Table 3

[0120]

[0121] According to Table 3 above, and in conjunction with Examples 2 and 10 to 14, it can be seen that the longer the atmospheric plasma treatment time, the lower the tensile elongation at break of the packaging film in the weakened area, and the higher the needle penetration rate of the secondary battery. When M < 10 min, the tensile elongation at break of the packaging film in the weakened area is relatively high, and the needle penetration rate of the secondary battery is relatively low. By setting M ≥ 10 min, the tensile elongation at break of the packaging film in the weakened area can be reduced, and the needle penetration rate of the secondary battery can be improved.

[0122] The larger φ1-φ2 ​​is, the smaller the tensile elongation at break φ2 of the packaging film in the weakened region, the better the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film, and the higher the needle penetration pass rate of the secondary battery. When φ1-φ2 ​​is less than 25%, the tensile elongation at break of the packaging film in the weakened region is relatively high, and the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film is not obvious. By setting φ1-φ2 ​​≥ 25%, the tensile elongation at break of the packaging film in the weakened region can be reduced, which can reduce the possibility of short circuit between the aluminum layer and the electrode of the packaging film. When φ1-φ2 ​​is greater than 36%, further increasing φ1-φ2 ​​will not significantly improve the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film, and it is easy to reduce the strength of the packaging film. By setting φ1-φ2 ​​≤ 36%, the tensile elongation at break of the packaging film can be guaranteed to meet the requirements without excessively affecting other properties of the packaging film.

[0123] The relevant parameters in Example 3 and Examples 15 to 20 are shown in Table 4 below.

[0124] The thickness of the polymer layer in Example 3 and Examples 15 to 20 is different.

[0125] Table 4

[0126]

[0127] According to Table 4 above, and in conjunction with Examples 3 and 15 to 20, it can be seen that the larger the polymer layer thickness H1, the lower the tensile elongation at break of the packaging film in the weakened area, and the higher the needle penetration rate of the secondary battery. When the polymer layer thickness H1 is less than 20 μm, the tensile elongation at break of the packaging film in the weakened area is relatively high. By setting the polymer layer thickness H1 ≥ 20 μm, the tensile elongation at break of the packaging film in the weakened area can be reduced. When the polymer layer thickness H1 is increased to 200 μm, further increasing the polymer layer thickness H1 does not significantly reduce the tensile elongation at break of the packaging film in the weakened area, and it is easy to lose a lot of energy density of the secondary battery. By setting the polymer layer thickness H1 ≤ 200 μm, the energy density of the secondary battery can be improved.

[0128] The larger φ1-φ2 ​​is, the smaller the tensile elongation at break φ2 of the packaging film in the weakened region, resulting in a better effect on improving the short circuit between the aluminum layer and the electrode of the packaging film, and a higher needle penetration rate of the secondary battery. When φ1-φ2 ​​is less than 25%, the tensile elongation at break of the packaging film in the weakened region is relatively high, and the effect on improving the short circuit between the aluminum layer and the electrode of the packaging film is not significant. By setting φ1-φ2 ​​≥ 25%, the tensile elongation at break of the packaging film in the weakened region can be reduced, thus reducing the possibility of a short circuit between the aluminum layer and the electrode of the packaging film. When φ1-φ2 ​​is greater than 36%, further increasing φ1-φ2 ​​does not significantly improve the effect on improving the short circuit between the aluminum layer and the electrode of the packaging film, and it is easy to lose a lot of energy density of the secondary battery. By setting φ1-φ2 ​​≤ 36%, the energy density of the secondary battery can be improved.

[0129] The relevant parameters in Example 4 and Examples 21 to 28 are shown in Table 5 below.

[0130] The ratio of S2 to S1 differs in Examples 4 and Examples 21 to 23. The width of the holes differs in Examples 4 and Examples 24 to 28.

[0131] Table 5

[0132]

[0133] According to Table 5 above, and in conjunction with Examples 4 and 21 to 23, the area of ​​the mesh region is S1, and the sum of the areas of all holes is S2. The larger the ratio of S2 to S1, the less likely the first polymer layer in the mesh region will exert a high tensile elongation at break on the metal layer, resulting in a lower tensile elongation at break of the packaging film in the weakened region and a higher needle penetration rate of the secondary battery. When the ratio of S2 to S1 is less than 50%, the tensile elongation at break of the packaging film in the weakened region is relatively high. By setting the ratio of S2 to S1 ≥ 50%, the tensile elongation at break of the packaging film in the weakened region can be reduced. When the ratio of S2 to S1 is greater than 90%, the tensile elongation at break of the packaging film in the weakened region is relatively low, and the packaging film is easily damaged. By setting the ratio of S2 to S1 ≤ 90%, the possibility of packaging film damage can be reduced.

[0134] Based on Examples 4 and 24 to 28, it can be seen that the larger the hole width, the less likely the first polymer layer in the mesh area will exert a high tensile elongation at break on the metal layer, resulting in a lower tensile elongation at break of the packaging film in the weakened area and a higher needle penetration rate of the secondary battery. When the hole width is less than 3 mm, the tensile elongation at break of the packaging film in the weakened area is relatively high. By setting the hole width ≥ 3 mm, the tensile elongation at break of the packaging film in the weakened area can be reduced. When the hole width is greater than 10 mm, the tensile elongation at break of the packaging film in the weakened area is relatively low, and the packaging film is easily damaged. By setting the hole width ≤ 10 mm, the possibility of packaging film damage can be reduced.

[0135] Based on Examples 4 and 21 to 28, it can be seen that the larger φ1-φ2 ​​is, the smaller the tensile elongation at break φ2 of the packaging film in the weakened region, the better the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film, and the higher the needle penetration pass rate of the secondary battery. When φ1-φ2 ​​is less than 25%, the tensile elongation at break of the packaging film in the weakened region is relatively high, and the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film is not obvious. By setting φ1-φ2 ​​≥ 25%, the tensile elongation at break of the packaging film in the weakened region can be reduced, and the possibility of short circuit between the aluminum layer and the electrode of the packaging film can be reduced. When φ1-φ2 ​​is greater than 36%, further increasing φ1-φ2 ​​does not significantly improve the effect of improving the short circuit between the aluminum layer and the electrode of the packaging film, and it is easy to reduce the strength of the packaging film. By setting φ1-φ2 ​​≤ 36%, the tensile elongation at break of the packaging film can be guaranteed to meet the requirements without excessively affecting other properties of the packaging film.

[0136] 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 packaging film and an electrode assembly, wherein the packaging film is wrapped around the outer surface of the electrode assembly; characterized in that The packaging film includes a weakened region; the tensile elongation at break of the packaging film outside the weakened region is φ1, and the tensile elongation at break of the packaging film in the weakened region is φ2, where φ2 < φ1.

2. The secondary battery according to claim 1, characterized by The weakened region includes a processing region located on the surface of the packaging film opposite to the electrode assembly.

3. The secondary battery according to claim 2, characterized by The processing area is provided with a polymer layer, and the tensile elongation at break of the packaging film provided with the polymer layer is less than that of the packaging film without the polymer layer.

4. The secondary battery according to claim 3, characterized by The polymer layer includes at least one of an organosilicon compound and a polyacrylic resin.

5. The secondary battery according to claim 3 or 4, characterized by The thickness of the polymer layer is H1, where 20μm≤H1≤200μm.

6. The secondary battery according to any one of claims 2 to 5, characterized by The packaging film comprises a first polymer layer, an adhesive layer, a metal layer, and a second polymer layer stacked sequentially. The first polymer layer is disposed on the surface of the adhesive layer opposite to the electrode assembly. The processing area is located on the surface of the first polymer layer opposite to the adhesive layer. The first polymer layer comprises polyamide.

7. The secondary battery according to claim 1, characterized by The packaging film includes a first polymer layer, an adhesive layer, and a metal layer. The two opposite surfaces of the adhesive layer are respectively adhered to the first polymer layer and the metal layer. The weakened region also includes a mesh region located in the adhesive layer. The mesh region has a plurality of holes and is located between the first polymer layer and the metal layer along the thickness direction of the adhesive layer.

8. The secondary battery according to claim 7, characterized by Along the thickness direction of the adhesive layer, the pores are located between the first polymer layer and the metal layer, the area of ​​the mesh region is S1, the sum of the areas of all the pores is S2, and the ratio of S2 to S1 is 50% to 90%.

9. The secondary battery according to claim 7 or 8, characterized by The width of the hole is 3mm to 10mm.

10. The secondary battery according to any one of claims 7 to 9, characterized by The length of the hole is the same as the width of the mesh region; and / or, in the length direction of the mesh region, the edge of the hole near the edge of the mesh region coincides with the edge of the mesh region.

11. The secondary battery according to any one of claims 1 to 10, characterized by Along the length of the electrode assembly, the packaging film includes a first edge and a second edge opposite to each other, the distance between the weakened region and the first edge is L1, the distance between the weakened region and the second edge is L2, 0.5mm≤L1≤5mm, 0.5mm≤L2≤5mm; And / or, along the width direction of the electrode assembly, the packaging film includes opposing third and fourth edges, the distance between the weakened region and the third edge is L3, the distance between the weakened region and the fourth edge is L4, 0.5mm≤L3≤5mm, 0.5mm≤L4≤5mm.

12. The secondary battery according to any one of claims 1 to 11, characterized by The packaging film includes a first wall and a second wall disposed opposite to each other along the thickness direction of the electrode assembly, the first wall and / or the second wall including the weakened region.

13. The secondary battery according to any one of claims 1 to 12, characterized by 25%≤φ1-φ2≤36%.

14. An electronic device, comprising: Includes the secondary battery as described in any one of claims 1 to 13.

15. A manufacturing method of a secondary battery for producing the secondary battery according to any one of claims 1 to 13, characterized by, include: The packaging film is provided, and a portion of the packaging film is weakened to form the weakened region. The tensile elongation at break of the packaging film outside the weakened region is φ1, and the tensile elongation at break of the packaging film in the weakened region is φ2, where φ2 < φ1.

16. The method of manufacturing a secondary battery according to claim 15, wherein The weakening treatment includes acid reagent treatment.

17. The method of manufacturing a secondary battery according to claim 16, wherein The acid reagent includes at least one of formic acid, acetic acid, and hydrofluoric acid.

18. The method of manufacturing a secondary battery according to claim 15, wherein The weakening process includes atmospheric plasma treatment.

19. The method of manufacturing a secondary battery according to claim 18, wherein The atmospheric plasma includes at least one of air, oxygen, nitrogen, and argon.

20. The method of manufacturing a secondary battery according to claim 18 or 19, characterized in that, The weakened region is treated by the atmospheric plasma for a time of M, where M ≥ 10 min.

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