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

Abstract

The invention relates to a secondary battery, electronic equipment and a manufacturing method of the secondary battery, the secondary battery comprises a packaging film and an electrode assembly, and the packaging film wraps 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-weakening area is phi 1, and the tensile elongation at break of the packaging film in the weakening area is phi 2 and phi 2lt; phi 1. According to the secondary battery, the electronic equipment and the manufacturing method of the secondary battery, the problem of short circuit of the secondary battery can be solved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a secondary battery, an electronic device, and a manufacturing method of the secondary battery. Background Art

[0002] As the power source of an electronic device, a secondary battery is the key to ensuring the normal use of the electronic device. When the secondary battery is damaged by external force, it is likely to cause internal short circuit, leading to safety problems such as thermal runaway. Summary of the Invention

[0003] The inventors of the present application have found that when the secondary battery is damaged by external force, the packaging film is easily extended to the electrode plate by the external force, resulting in the contact between the aluminum layer of the packaging film and the electrode plate, thus causing a short circuit. By providing a weakening area on the outer surface of the packaging film, in the weakening area, the tensile fracture elongation rate of the packaging film is weakened by the weakening treatment, so that the tensile fracture elongation rate of the packaging film in the weakening area is less than that in the non-weakening area. When the secondary battery is damaged by external force, the packaging film can be broken in advance, and the extension of the aluminum layer in the packaging film is reduced when it breaks, thereby reducing the possibility of the aluminum layer being extended greatly to contact the electrode plate and causing a short circuit.

[0004] The purpose of the present application is to provide a secondary battery, an electronic device, and a manufacturing method of the secondary battery, aiming to improve the problem of short circuit of the secondary battery.

[0005] According to the first aspect of the present application, a secondary battery is provided, which includes a packaging film and an electrode assembly, and the packaging film wraps the outer surface of the electrode assembly. The packaging film includes a weakening area. The tensile fracture elongation rate of the packaging film in the non-weakening area is The tensile fracture elongation rate of the packaging film in the weakening area is

[0006] In the above technical solution, by providing that the packaging film includes a weakening area, in the weakening area, the tensile fracture elongation rate of the packaging film is weakened by the weakening treatment, so that the tensile fracture elongation rate of the packaging film in the weakening area is less than the tensile fracture elongation rate of the packaging film in the non-weakening area When the packaging film is damaged by external force, it will break in advance, and the extension of the packaging film is small, which is beneficial to reducing the possibility of the packaging film being extended to the electrode plate by external force, and further reducing the possibility of the aluminum layer of the packaging film contacting the electrode plate and causing a short circuit.

[0007] In some preferred embodiments, the weakening area includes a treatment area, and the treatment area is located on the surface of the packaging film facing away from the electrode assembly. In the treatment area, the tensile fracture elongation rate of the packaging film is weakened by the weakening treatment.

[0008] In some preferred embodiments, a polymer layer is provided in the processing area, and the tensile fracture elongation rate of the packaging film provided with the polymer layer is less than that of the packaging film without the polymer layer. The tensile fracture elongation rate of the polymer layer is less than that of the packaging film. By providing a polymer layer in the processing area, the tensile fracture elongation rate of the packaging film in the processing area can be reduced.

[0009] In some preferred embodiments, the polymer layer includes at least one of a silicone compound and a polyacrylic resin, which can reduce the tensile fracture elongation rate of the packaging film in the processing area.

[0010] In some preferred embodiments, the thickness of the polymer layer is H1, and 20 μm ≤ H1 ≤ 200 μm. The greater the thickness H1 of the polymer layer, the lower the tensile fracture elongation rate of the packaging film in the processing area. When the thickness H1 of the polymer layer is less than 20 μm, the tensile fracture elongation rate of the packaging film in the processing area is relatively high. By setting the thickness H1 of the polymer layer ≥ 20 μm, the tensile fracture elongation rate of the packaging film in the processing area can be reduced. When the thickness H1 of the polymer layer increases to 200 μm, if the thickness H1 of the polymer layer continues to increase, the reduction of the tensile fracture elongation rate of the packaging film in the processing area is not obvious, and it is easy to lose more energy density of the secondary battery. By setting the thickness H1 of the polymer layer ≤ 200 μm, the energy density of the secondary battery can be improved.

[0011] In some preferred embodiments, the packaging film includes a first polymer layer, an adhesive layer, a metal layer, and a second polymer layer that are laminated in sequence. The first polymer layer is disposed on the surface of the adhesive layer facing away from the electrode assembly. The processing area is located on the surface of the first polymer layer facing away from the adhesive layer. The tensile fracture elongation rate of the first polymer layer in the processing area is weakened through weakening treatment, which can reduce the tensile fracture elongation rate of the first polymer layer in the processing area, and further reduce the tensile fracture elongation rate of the packaging film in the processing area. The first polymer layer includes polyamide, which can improve the strength of the packaging film.

[0012] 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 area further includes a mesh area located in the adhesive layer. The mesh area is provided with a plurality of holes. Along the thickness direction of the adhesive layer, the mesh area is located between the first polymer layer and the metal layer, which can reduce the possibility that the first polymer layer with a high tensile fracture elongation rate acts on the metal layer at the mesh area, and can reduce the tensile fracture elongation rate of the packaging film at the mesh area.

[0013] 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 possibility that the first polymer layer at the holes exerts a high tensile fracture elongation rate on the metal layer. The area of the mesh region is S1, and the sum of the areas of all the holes is S2. The ratio of S2 to S1 is 50% to 90%. The larger the ratio of S2 to S1, the smaller the possibility that the first polymer layer at the mesh region exerts a high tensile fracture elongation rate on the metal layer, and the lower the tensile fracture elongation rate of the packaging film in the mesh region. When the ratio of S2 to S1 is less than 50%, the tensile fracture elongation rate of the packaging film in the mesh region is relatively high. By setting the ratio of S2 to S1 ≥ 50%, the tensile fracture elongation rate of the packaging film in the mesh region can be reduced. When the ratio of S2 to S1 is greater than 90%, the tensile fracture elongation rate of the packaging film in the mesh region is relatively low, and the packaging film is prone to breakage. By setting the ratio of S2 to S1 ≤ 90%, the possibility of the packaging film breaking can be reduced.

[0014] In some preferred embodiments, the width of the holes is 3 mm to 10 mm. The larger the width of the holes, the smaller the possibility that the first polymer layer at the mesh region exerts a high tensile fracture elongation rate on the metal layer, and the lower the tensile fracture elongation rate of the packaging film in the mesh region. When the width of the holes is less than 3 mm, the tensile fracture elongation rate of the packaging film in the mesh region is relatively high. By setting the width of the holes ≥ 3 mm, the tensile fracture elongation rate of the packaging film in the mesh region can be reduced. When the width of the holes is greater than 10 mm, the tensile fracture elongation rate of the packaging film in the mesh region is relatively low, and the packaging film is prone to breakage. By setting the width of the holes ≤ 10 mm, the possibility of the packaging film breaking can be reduced.

[0015] In some preferred embodiments, the length of the holes is the same as the width of the mesh region. The larger the length of the holes, the smaller the tensile fracture elongation rate of the packaging film in the mesh region. By setting the length of the holes to be the same as the width of the mesh region, it is beneficial to further reduce the tensile fracture elongation rate of the packaging film in the mesh region. It can be understood that due to processing errors, the length of the holes being the same as the width of the mesh region means that the length of the holes is approximately the same as the width of the mesh region. A difference between the length of the holes and the width of the mesh region that does not exceed 10% of the length of the holes can also meet the requirements.

[0016] In some preferred embodiments, in the length direction of the mesh region, the hole edges near the edge of the mesh region coincide with the edge of the mesh region, which is beneficial to increasing the area ratio of the holes in the mesh region and is beneficial to reducing the tensile fracture elongation rate of the packaging film in the mesh region. It can be understood that due to processing errors, the hole edges coinciding with the edge of the mesh region means that the hole edges approximately coincide with the edge of the mesh region. A distance between the hole edges and the edge of the mesh region that does not exceed 10% of the width of the holes can also meet the requirements.

[0017] In some preferred embodiments, along the length direction of the electrode assembly, the packaging film includes opposite first and second edges. The distance between the weakening area and the first edge is L1, and the distance between the weakening area and the second edge is L2, where 0.5 mm ≤ L1 ≤ 5 mm and 0.5 mm ≤ L2 ≤ 5 mm. Since the packaging film needs to be stamped and the first and second edges of the packaging film are prone to being collided and worn, if the tensile fracture elongation rates of the first and second edges are reduced, it is difficult for the packaging film to meet the stamping requirements, and the first and second edges are prone to breakage. By defining L1 ≥ 0.5 mm, the possibility that the mesh area affects the tensile fracture elongation rate of the first edge can be reduced, which is beneficial for the packaging film to meet the stamping requirements and can reduce the possibility of breakage of the first edge. By defining L1 ≤ 5 mm, it is beneficial to increase the area of the mesh area, and thus beneficial to further reduce the tensile fracture elongation rate of the packaging film. By defining L2 ≥ 0.5 mm, the possibility that the mesh area affects the tensile fracture elongation rate 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 breakage of the second edge. By defining L2 ≤ 5 mm, it is beneficial to increase the area of the mesh area, and thus beneficial to further reduce the tensile fracture elongation rate of the packaging film.

[0018] In some preferred embodiments, along the width direction of the electrode assembly, the packaging film includes opposite third and fourth edges. The distance between the weakening area and the third edge is L3, and the distance between the weakening area and the fourth edge is L4, where 0.5 mm ≤ L3 ≤ 5 mm and 0.5 mm ≤ L4 ≤ 5 mm. By defining L3 ≥ 0.5 mm, the possibility that the mesh area affects the tensile fracture elongation rate of the third edge can be reduced, and the possibility of breakage of the third edge can be reduced. By defining L3 ≤ 5 mm, it is beneficial to increase the area of the mesh area, and thus beneficial to further reduce the tensile fracture elongation rate of the packaging film. By defining L4 ≥ 0.5 mm, the possibility that the mesh area affects the tensile fracture elongation rate of the fourth edge can be reduced, and the possibility of breakage of the fourth edge can be reduced. By defining L4 ≤ 5 mm, it is beneficial to increase the area of the mesh area, and thus beneficial to further reduce the tensile fracture elongation rate of the packaging film.

[0019] In some preferred embodiments, the packaging film includes oppositely arranged first and second walls along the thickness direction of the electrode assembly, and the first wall includes a weakening area. Since the first wall of the electrode assembly in the thickness direction is more likely to come into contact with the pole piece and cause a short circuit, by providing a weakening area on the first wall, the possibility that the aluminum layer of the first wall extends to the pole piece under the action of external force can be reduced, and the possibility that the aluminum layer of the first wall comes into contact with the pole piece and causes a short circuit can be reduced.

[0020] In some preferred embodiments, the second wall includes a weakening region. Since the second wall of the electrode assembly in the thickness direction is more likely to come into contact with the electrode sheet and cause a short circuit, by providing a weakening region in the second wall, the possibility that the aluminum layer of the second wall extends to the electrode sheet under the action of an external force can be reduced, and the possibility that the aluminum layer of the second wall comes into contact with the electrode sheet and causes a short circuit can be reduced.

[0021] In some preferred embodiments, The greater the the smaller the tensile fracture elongation rate of the packaging film in the weakening region, and the better the effect of improving the short circuit caused by the contact between the aluminum layer of the packaging film and the electrode sheet. When it is less than 25%, the tensile fracture elongation rate of the packaging film in the weakening region is relatively high, and the effect of improving the short circuit caused by the contact between the aluminum layer of the packaging film and the electrode sheet is not obvious. By setting ≥25%, the tensile fracture elongation rate of the packaging film in the weakening region can be reduced, and the possibility of short circuit caused by the contact between the aluminum layer of the packaging film and the electrode sheet can be reduced. When it is greater than 36%, further increasing the improvement effect of the short circuit caused by the contact between the aluminum layer of the packaging film and the electrode sheet is not obvious, and it is easy to lose more energy density of the secondary battery or cause a decrease in the strength of the packaging film. By setting It is possible to ensure that the tensile fracture elongation rate of the packaging film meets the requirements while not excessively affecting other properties of the packaging film.

[0022] In a second aspect, the present application also provides an electronic device, including the secondary battery according to any one of the embodiments in the first aspect above.

[0023] In a third aspect, the present application also provides a manufacturing method of a secondary battery for preparing the secondary battery according to any one of the embodiments in the first aspect above, including: providing a packaging film, performing a weakening treatment on a partial region of the packaging film to form a weakening region, and the tensile fracture elongation rate of the packaging film in the non-weakening region is The tensile fracture elongation rate of the packaging film in the weakening region is So that when the packaging film is damaged by an external force, it will break in advance, and the extension of the packaging film is small, which is beneficial to reducing the possibility that the packaging film is extended to the electrode sheet by the external force, and further reducing the possibility of short circuit caused by the contact between the aluminum layer of the packaging film and the electrode sheet.

[0024] In some preferred embodiments, the weakening treatment includes an acid reagent treatment, and the acid reagent can partially corrode the packaging film in the weakening region, thereby reducing the tensile fracture elongation rate of the packaging film in the weakening region.

[0025] In some preferred embodiments, the acid reagent includes at least one of formic acid, acetic acid, and hydrofluoric acid, which can improve the corrosion effect of the acid reagent.

[0026] In some preferred embodiments, the weakening treatment includes atmospheric plasma treatment, and the atmospheric plasma can cause surface molecular cross-linking of the packaging film in the weakening area, thereby reducing the tensile fracture elongation rate of the packaging film in the weakening area.

[0027] In some preferred embodiments, the atmospheric plasma includes at least one of air, oxygen, nitrogen, and argon, which can improve the effect of surface molecular cross-linking of the packaging film in the weakening area by the atmospheric plasma.

[0028] In some preferred embodiments, the time for the weakening area to be treated by the atmospheric plasma is M, where M ≥ 10 min. The longer the atmospheric plasma treatment time, the lower the tensile fracture elongation rate of the packaging film in the weakening area. When M < 10 min, the tensile fracture elongation rate of the packaging film in the weakening area is relatively high. By setting M ≥ 10 min, the tensile fracture elongation rate of the packaging film in the weakening area can be reduced.

[0029] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the subsequent description, or through the implementation of the embodiments of the present application. Description of the Drawings

[0030] One or more embodiments are exemplarily illustrated by the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, unless otherwise stated, and the dimensions in the drawings do not constitute a proportional limitation.

[0031] Figure 1 Schematic diagram of the structure of a secondary battery according to some embodiments of the present application;

[0032] Figure 2 Schematic diagram of the structure of an electrode assembly according to some embodiments of the present application;

[0033] Figure 3 Schematic diagram of the structure of a secondary battery according to some embodiments of the present application;

[0034] Figure 4 Schematic diagram of the structure of a secondary battery according to some embodiments of the present application;

[0035] Figure 5 Schematic diagram of the structure of a secondary battery according to some embodiments of the present application;

[0036] Figure 6 Schematic diagram of the structure of a packaging film and a polymer layer according to some embodiments of the present application;

[0037] Figure 7 Schematic diagram of the structure of a packaging film according to some embodiments of the present application;

[0038] Figure 8 Schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0039] Figure 9 Schematic structural diagram of a secondary battery according to some embodiments of the present application.

[0040] Description of the reference numerals in the drawings:

[0041] 100, secondary battery;

[0042] 10, packaging film; 101, weakened area;

[0043] 11, first polymer layer; 111, treatment area; 12, adhesive layer; 121, mesh area; 1211, hole; 13, metal layer; 14, second polymer layer;

[0044] 151, first edge; 152, second edge; 153, third edge; 154, fourth edge;

[0045] 161, first wall; 162, second wall;

[0046] 17, polymer layer;

[0047] 20, electrode assembly; 20a, tab; 21, positive electrode sheet; 22, negative electrode sheet; 23, separator;

[0048] X, length direction of the electrode assembly; Y, width direction of the electrode assembly; Z, thickness direction of the electrode assembly. Detailed implementation manners

[0049] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0050] Referring to "embodiments" in the present application means that the specific features, structures or characteristics described in connection with the embodiments may be included in at least one embodiment of the present application. The phrase appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0051] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means two or more unless otherwise specifically defined.

[0052] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in this text, the character " / " generally represents an "or" relationship between the associated objects before and after.

[0053] The term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there can be a state approximately vertical between two components. For example, in combination with numerical descriptions, vertical can refer to the included angle range between two straight lines being within 90±10°, vertical can also refer to the dihedral angle range between two planes being within 90±10°, and vertical can also refer to the included angle range between a straight line and a plane being within 90±10°. The two components described as "vertical" may not be absolutely straight lines or planes, and may also be approximately straight lines or planes. From a macroscopic perspective, as long as the overall extension direction is a straight line or a plane, the components can be considered "straight lines" or "planes".

[0054] The technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0055] In a first aspect, an embodiment of the present application provides a secondary battery 100. Please refer to Figure 1 , the secondary battery 100 includes a packaging film 10, an electrode assembly 20, and an ear 20a. The packaging film 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), and the electrolyte infiltrates the electrode assembly 20 within the packaging film 10. The ear 20a is connected to the electrode assembly 20, and the ear 20a extends out of the packaging film 10 in the length direction X of the electrode assembly 20 to assist the electrode assembly 20 in performing energy transfer with an external electronic device.

[0056] Regarding the above electrode assembly 20, please refer to Figure 2 , Figure 2 shows the laminated structure of the electrode assembly 20. The electrode assembly 20 includes a negative electrode sheet 22, a positive electrode sheet 21, and a separator 23. The positive electrode sheet 21 and the negative electrode sheet 22 are alternately laminated, and a separator 23 is provided between adjacent positive electrode sheets 21 and negative electrode sheets 22. The separator 23 is used to insulate and separate the positive electrode sheet 21 and the negative electrode sheet 22. In the embodiment of the present application, the electrode assembly 20 is taken as an example of a laminated structure for description. In some other embodiments, the electrode assembly 20 can also be a wound structure or other structures. For example, after the positive electrode sheet 21, the separator 23, and the negative electrode sheet 22 are laminated in sequence, they are then wound to form a wound electrode assembly 20.

[0057] The inventors of the present application have found through research that when the secondary battery 100 is damaged by an external force, the packaging film 10 is easily extended to the electrode sheet by the external force, resulting in the contact between the aluminum layer of the packaging film 10 and the electrode sheet, thereby causing a short circuit.

[0058] To improve the above problems, in the embodiments of the present application, please refer to Figure 3 and Figure 4 , the packaging film 10 includes a weakening region 101. The tensile fracture elongation rate of the packaging film 10 in the non-weakening region 101 is The tensile fracture elongation rate of the packaging film 10 in the weakening region 101 is By setting the packaging film 10 to include the weakening region 101, in the weakening region 101, the tensile fracture elongation rate of the packaging film 10 is weakened through the weakening treatment, so that the tensile fracture elongation rate of the packaging film 10 in the weakening region 101 is less than the tensile fracture elongation rate of the packaging film 10 in the non-weakening region 101 When the packaging film 10 is damaged by an external force, it will break in advance, and the extension of the packaging film 10 is small, which is beneficial to reducing the possibility that the packaging film 10 is extended to the pole piece by the external force, and further can reduce the possibility of short circuit between the aluminum layer of the packaging film 10 and the pole piece.

[0059] In some embodiments, the weakening region 101 includes a treatment region 111, and the treatment region 111 is located on the surface of the packaging film 10 facing away from the electrode assembly 20. In the treatment region 111, the tensile fracture elongation rate of the packaging film 10 is weakened through the weakening treatment.

[0060] In some embodiments, please refer to Figure 5 , a polymer layer 17 is provided in the treatment region 111, and the tensile fracture elongation rate of the packaging film 10 provided with the polymer layer 17 is less than that of the packaging film 10 not provided with the polymer layer 17. The tensile fracture elongation rate of the polymer layer 17 is less than that of the packaging film 10. By providing the polymer layer 17 in the treatment region 111, the tensile fracture elongation rate of the packaging film 10 in the treatment region 111 can be reduced.

[0061] In some embodiments, the polymer layer 17 includes at least one of a silicone compound and a polyacrylic resin, which can reduce the tensile fracture elongation rate of the packaging film 10 in the treatment region 111.

[0062] 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, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, 200 μm, 205 μm, 210 μm, 215 μm, 220 μm, 225 μm, 230 μm, 235 μm, 240 μm, 245 μm, 250 μm, or a value within the range formed by any two of these values or a value within the range formed by any two of these values. The greater the thickness H1 of the polymer layer 17, the lower the tensile fracture elongation of the packaging film 10 in the treatment area 111. When the thickness H1 of the polymer layer 17 is less than 20 μm, the tensile fracture elongation of the packaging film 10 in the treatment area 111 is relatively high. By setting the thickness H1 of the polymer layer 17 ≥ 20 μm, the tensile fracture elongation of the packaging film 10 in the treatment area 111 can be reduced. When the thickness H1 of the polymer layer 17 increases to 200 μm, if the thickness H1 of the polymer layer 17 continues to increase, the reduction in the tensile fracture elongation of the packaging film 10 in the treatment area 111 is not obvious, and it is easy to lose more energy density of the secondary battery 100. By setting the thickness H1 of the polymer layer 17 ≤ 200 μm, the energy density of the secondary battery 100 can be improved.

[0063] In some embodiments, please refer to Figure 5 and Figure 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 that are stacked in sequence. The first polymer layer 11 is disposed on the surface of the adhesive layer 12 facing away from the electrode assembly 20. The treatment area 111 is located on the surface of the first polymer layer 11 facing away from the adhesive layer 12. The tensile fracture elongation of the first polymer layer 11 in the treatment area 111 is weakened through weakening treatment, which can reduce the tensile fracture elongation of the first polymer layer 11 in the treatment area 111, and further reduce the tensile fracture elongation of the packaging film 10 in the treatment area 111. The first polymer layer 11 includes polyamide, which can improve the strength of the packaging film 10.

[0064] In some embodiments, the adhesive layer 12 includes polyurethane, which can enhance the adhesive performance of the adhesive layer 12. The metal layer 13 includes aluminum, which can enhance the plasticity of the packaging film 10. The second polymer layer 14 includes polypropylene, which can make the packaging film 10 easy to encapsulate.

[0065] In some embodiments, please refer to Figure 7 and Figure 8 , the packaging film 10 includes a first polymer layer 11, an adhesive layer 12, and a metal layer 13. The opposite two surfaces of the adhesive layer 12 are respectively adhered to the first polymer layer 11 and the metal layer 13. The weakened area 101 further includes a mesh area 121 located in the adhesive layer 12. The mesh area 121 is provided with a plurality of holes 1211. Along the thickness direction of the adhesive layer 12, the mesh area 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 acts on the metal layer 13 with a high tensile fracture elongation rate at the mesh area 121, and can reduce the tensile fracture elongation rate of the packaging film 10 at the mesh area 121.

[0066] 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 acts on the metal layer 13 with a high tensile fracture elongation rate at the holes 1211. The area of the mesh area 121 is S1, and the sum of the areas of all the holes 1211 is S2. The ratio of S2 to S1 is 37.5% to 95%. Preferably, the ratio of S2 to S1 is 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 value within the range composed of any two of these values or a value within the range composed of any two of these values. The larger the ratio of S2 to S1, the smaller the possibility that the first polymer layer 11 acts on the metal layer 13 with a high tensile fracture elongation rate at the mesh area 121, and the lower the tensile fracture elongation rate of the packaging film 10 at the mesh area 121. When the ratio of S2 to S1 is less than 50%, the tensile fracture elongation rate of the packaging film 10 at the mesh area 121 is relatively high. By setting the ratio of S2 to S1 ≥ 50%, the tensile fracture elongation rate of the packaging film 10 at the mesh area 121 can be reduced. When the ratio of S2 to S1 is greater than 90%, the tensile fracture elongation rate of the packaging film 10 at the mesh area 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.

[0067] In some embodiments, the holes 1211 are rectangular holes 1211, which is beneficial to improving the convenience of production. In some other embodiments, the shape of the holes 1211 can be circular, triangular, fan-shaped, polygonal, and any irregular shape, which can meet different processing requirements.

[0068] 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 may 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 value within the range formed by any two of these values or a value within the range formed by any two of these values. The larger the width of the hole 1211, the smaller the possibility that the first polymer layer 11 acts on the metal layer 13 with a high tensile fracture elongation rate at the mesh region 121, and the lower the tensile fracture elongation rate of the packaging film 10 at the mesh region 121. When the width of the hole 1211 is less than 3 mm, the tensile fracture elongation rate of the packaging film 10 at the mesh region 121 is relatively high. By setting the width of the hole 1211 ≥ 3 mm, the tensile fracture elongation rate of the packaging film 10 at the mesh region 121 can be reduced. When the width of the hole 1211 is greater than 10 mm, the tensile fracture elongation rate of the packaging film 10 at the mesh region 121 is relatively low, and the packaging film 10 is prone to breakage. By setting the width of the hole 1211 ≤ 10 mm, the possibility of breakage of the packaging film 10 can be reduced.

[0069] 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 fracture elongation rate of the packaging film 10 at 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 fracture elongation rate of the packaging film 10 at the mesh region 121. It can be understood that due to processing errors, the length of the hole 1211 being 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, and a difference not exceeding 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.

[0070] In some embodiments, in the length T direction of the mesh region 121, the edge of the hole 1211 near the edge of the mesh region 121 coincides with the edge of the mesh region 121, which is beneficial to increasing the area ratio of the holes 1211 in the mesh region 121 and beneficial to reducing the tensile fracture elongation rate of the packaging film 10 at the mesh region 121. It can be understood that due to processing errors, the edge of the hole 1211 coinciding with the edge of the mesh region 121 means that the edge of the hole 1211 is approximately coincident with the edge of the mesh region 121, and a distance not exceeding 10% of the width of the hole 121 between the edge of the hole 1211 and the edge of the mesh region 121 can also meet the requirements.

[0071] In some embodiments, along the length direction X of the electrode assembly 20, the packaging film 10 includes opposite first edge 151 and second edge 152. The distance between the weakening region 101 and the first edge 151 is L1, and the distance between the weakening region 101 and the second edge 152 is L2, where 0.5 mm ≤ L1 ≤ 5 mm and 0.5 mm ≤ L2 ≤ 5 mm. Since the packaging film 10 needs to be stamped and the first edge 151 and the second edge 152 of the packaging film 10 are prone to being collided and worn, if the tensile fracture elongation rates of the first edge 151 and the second edge 152 are reduced, it is difficult for the packaging film 10 to meet the requirements of stamping, and the first edge 151 and the second edge 152 are prone to being damaged. By defining L1 ≥ 0.5 mm, the possibility that the mesh region 121 affects the tensile fracture elongation rate of the first edge 151 can be reduced, which is beneficial for the packaging film 10 to meet the requirements of stamping, and the possibility of damage to the first edge 151 can be reduced. By defining L1 ≤ 5 mm, it is beneficial to increase the area of the mesh region 121, and further beneficial to further reduce the tensile fracture elongation rate of the packaging film 10. By defining L2 ≥ 0.5 mm, the possibility that the mesh region 121 affects the tensile fracture elongation rate of the second edge 152 can be reduced, which is beneficial for the packaging film 10 to meet the requirements of stamping, and the possibility of damage to the second edge 152 can be reduced. By defining L2 ≤ 5 mm, it is beneficial to increase the area of the mesh region 121, and further beneficial to further reduce the tensile fracture elongation rate of the packaging film 10.

[0072] In some embodiments, please refer to Figure 3 , along the width direction Y of the electrode assembly 20, the packaging film 10 includes opposite third edge 153 and fourth edge 154. The distance between the weakening region 101 and the third edge 153 is L3, and the distance between the weakening region 101 and the fourth edge 154 is L4, where 0.5 mm ≤ L3 ≤ 5 mm and 0.5 mm ≤ L4 ≤ 5 mm. By defining L3 ≥ 0.5 mm, the possibility that the mesh region 121 affects the tensile fracture elongation rate of the third edge 153 can be reduced, and the possibility of damage to the third edge 153 can be reduced. By defining L3 ≤ 5 mm, it is beneficial to increase the area of the mesh region 121, and further beneficial to further reduce the tensile fracture elongation rate of the packaging film 10. By defining L4 ≥ 0.5 mm, the possibility that the mesh region 121 affects the tensile fracture elongation rate of the fourth edge 154 can be reduced, and the possibility of damage to the fourth edge 154 can be reduced. By defining L4 ≤ 5 mm, it is beneficial to increase the area of the mesh region 121, and further beneficial to further reduce the tensile fracture elongation rate of the packaging film 10.

[0073] In some embodiments, please refer to Figure 3 , Figure 4 and Figure 9, the packaging film 10 includes a first wall 161 and a second wall 162 which are oppositely arranged along the thickness direction Z of the electrode assembly 20, and the first wall 161 includes a weakening area 101. Since the first wall 161 of the electrode assembly 20 in the thickness direction is more likely to come into contact with the electrode tab and cause a short circuit, by providing the weakening area 101 on the first wall 161, the possibility that the aluminum layer of the first wall 161 extends to the electrode tab under the action of external force can be reduced, and the possibility that the aluminum layer of the first wall 161 comes into contact with the electrode tab and causes a short circuit can be reduced.

[0074] In some embodiments, the second wall 162 includes a weakening area 101. Since the second wall 162 of the electrode assembly 20 in the thickness direction is more likely to come into contact with the electrode tab and cause a short circuit, by providing the weakening area 101 on the second wall 162, the possibility that the aluminum layer of the second wall 162 extends to the electrode tab under the action of external force can be reduced, and the possibility that the aluminum layer of the second wall 162 comes into contact with the electrode tab and causes a short circuit can be reduced.

[0075] In some embodiments, Preferably, In some embodiments, It 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 value within the range formed by any two of these values or a value within the range formed by any two of these values. The greater the the smaller the tensile fracture elongation rate of the packaging film 10 in the weakening area 101, the better the effect of improving the short circuit caused by the contact between the aluminum layer of the packaging film 10 and the electrode tab. When the tensile fracture elongation rate of the packaging film 10 in the weakening area 101 is less than 25%, the effect of improving the short circuit caused by the contact between the aluminum layer of the packaging film 10 and the electrode tab is not obvious. By setting the tensile fracture elongation rate of the packaging film 10 in the weakening area 101 can be reduced, and the possibility of short circuit caused by the contact between the aluminum layer of the packaging film 10 and the electrode tab can be reduced. When it is greater than 36%, continuing to increase the effect of improving the short circuit caused by the contact between the aluminum layer of the packaging film 10 and the electrode tab is not significantly improved, and it is easy to lose more energy density of the secondary battery 100 or cause a decrease in the strength of the packaging film 10. By setting while ensuring that the tensile fracture elongation rate of the packaging film 10 meets the requirements, other properties of the packaging film 10 will not be overly affected.

[0076] In a second aspect of the present application, an electronic device is further provided, which includes the secondary battery 100 according to any one of the embodiments of the first aspect above. The electronic device in the embodiments of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to Bluetooth headsets, mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecraft, and so on. Among them, the electric toys can include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, etc., and the spacecraft can include airplanes, rockets, space shuttles, and spaceships, etc.

[0077] Please refer to Figure 3 , in a third aspect of the present application, a method for manufacturing a secondary battery is further provided, which is used to prepare the secondary battery 100 according to any one of the embodiments of the first aspect above, and includes: providing a packaging film 10, performing a weakening treatment on a partial area of the packaging film 10 to form a weakening area 101, and the tensile fracture elongation rate of the packaging film 10 in the non-weakening area 101 is The tensile fracture elongation rate of the packaging film 10 in the weakening area 101 is such that when the packaging film 10 is damaged by an external force, it will break in advance, and the extension of the packaging film 10 is small, which is beneficial to reducing the possibility that the packaging film 10 is extended to the pole piece by an external force, and further can reduce the possibility of short circuit between the aluminum layer of the packaging film 10 and the pole piece.

[0078] In some embodiments, the weakening treatment includes acid reagent treatment. Spraying the acid reagent can corrode the packaging film 10 in the weakening area 101, and further can reduce the tensile fracture elongation rate of the packaging film 10 in the weakening area 101.

[0079] In some embodiments, the acid reagent includes at least one of formic acid, acetic acid, and hydrofluoric acid, which can improve the corrosion effect of the acid reagent.

[0080] In some embodiments, the weakening treatment includes atmospheric plasma treatment. Spraying the atmospheric plasma can cause surface molecular cross-linking of the packaging film 10 in the weakening area 101, and further can reduce the tensile fracture elongation rate of the packaging film 10 in the weakening area 101.

[0081] In some embodiments, the atmospheric plasma includes at least one of air, oxygen, nitrogen, and argon, which can improve the effect of surface molecular cross-linking of the packaging film 10 in the weakening area 101 by the atmospheric plasma.

[0082] In some embodiments, the time for the atmospheric plasma treatment of the weakening region 101 is M, where M ≥ 8 min, and 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 value within the range formed by any two of these values or within the range formed by any two of these values. The longer the atmospheric plasma treatment time, the lower the elongation at break of the packaging film 10 in the weakening region 101. When M < 10 min, the elongation at break of the packaging film 10 in the weakening region 101 is relatively high. By setting M ≥ 10 min, the elongation at break of the packaging film 10 in the weakening region 101 can be reduced.

[0083] Test part:

[0084] 1. Tensile test of the packaging film in the weakening region:

[0085] Take the packaging film in the weakening region as a sample. Use a special cutting knife for tensile testing to make the sample into a test sample with a length of 70 mm and a width of 15 mm. Fix the test sample to the test fixture of a high-speed tensile testing machine, with a tensile speed of 50 ± 0.5 mm / min and a tensile distance of 50 mm. After the sample is broken, record the maximum tensile force and the sample length. The maximum tensile force is the breaking tensile force. The elongation at break of the packaging film in the weakening region = (sample length at break - initial sample length) / initial sample length.

[0086] 2. Tensile test of the packaging film in the non-weakening region:

[0087] Take the packaging film in the non-weakening region as a sample. Use a special cutting knife for tensile testing to make the sample into a test sample with a length of 70 mm and a width of 15 mm. Fix the test sample to the test fixture of a high-speed tensile testing machine, with a tensile speed of 50 ± 0.5 mm / min and a tensile distance of 50 mm. After the sample is broken, record the maximum tensile force and the sample length. The maximum tensile force is the breaking tensile force. The elongation at break of the packaging film in the non-weakening region = (sample length at break - initial sample length) / initial sample length.

[0088] 3. Nail test:

[0089] First, fully charge the sample secondary battery. Place the sample flat on the test table. Use a special nail with a diameter of 3 mm, a chamfer of 0.3, a nail tip length of 3 mm, and a nail body length ≥ 100 mm to test from the center position of the sample at a speed of 150 ± 1.5 mm / s. When the sample is completely pierced, the passing criterion is that after the test, the battery core does not catch fire or explode.

[0090] Example 1

[0091] <Preparation of the positive electrode sheet>:

[0092] The aluminum foil is used as the positive current collector, and a layer of lithium cobalt oxide slurry is evenly 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). It is dried at 85 °C and then cold-pressed, sliced, and slit to prepare the positive electrode sheet.

[0093] <Preparation of the negative electrode sheet>:

[0094] The copper foil is used as the negative current collector, and a layer of graphite slurry is evenly 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). It is dried at 85 °C and then cold-pressed, sliced, and slit to prepare the negative electrode sheet.

[0095] <Preparation of the electrolyte>:

[0096] 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): vinylene carbonate (VC) = 20:30:20:28:2, mass ratio) at a mass ratio of 8:92 is used as the electrolyte of the secondary battery.

[0097] <Preparation of the secondary battery>:

[0098] The positive electrode sheet and the negative electrode sheet are welded with electrode tabs, and then the positive electrode sheet and the negative electrode sheet are wound. The positive electrode sheet and the negative electrode sheet are separated by a polyethylene separator to prepare the electrode assembly.

[0099] The aluminum-plastic film with a thickness of 103 μm from Zijiang is used as the packaging film. The packaging film is wrapped around the outer surface of the electrode assembly. After top-side sealing, inkjet coding, vacuum drying, electrolyte injection, and high-temperature standing, formation and capacity measurement are carried out to obtain the preliminary secondary battery. The length of the secondary battery is 90 mm, and the width of the secondary battery is 60 mm.

[0100] The packaging film includes a weakening area, and the weakening area includes a treatment area. The packaging film includes a first wall in the thickness direction of the electrode assembly. The surface of the first wall facing away from the electrode assembly includes the treatment area. The packaging film includes opposite first and second edges in the length direction of the electrode assembly. The distance L1 between the treatment area and the first edge is 5 mm, and the distance L2 between the treatment area and the second edge is 5 mm. The packaging film includes opposite third and fourth edges in the width direction of the electrode assembly. The distance L3 between the treatment area and the third edge is 5 mm, and the distance L4 between the treatment area and the fourth edge is 5 mm. 1-2 ml of formic acid reagent is evenly coated on the treatment area and left standing for 10 min until the reaction is completed. Among them, the concentration of formic acid in the formic acid reagent is 98%.

[0101] The relevant parameters in Comparative Example 1 and Examples 1 to 4 are shown in Table 1 below.

[0102] Among them, the packaging film of Comparative Example 1 does not include a weakening area.

[0103] The weakening treatment method for the weakening area in Example 2 is atmospheric plasma treatment. The specific steps are as follows: Place the preliminary secondary battery in a plasma device. The distance between the nozzle of the plasma device and the first wall is 5-10 cm. Spray atmospheric plasma on the treatment area under the atmospheric environment for 15 min.

[0104] The weakening treatment method for the weakening area in Example 3 is to set a polymer layer. The specific steps are as follows: Spray polyacrylic acid resin evenly on the surface of the first wall facing away from the electrode assembly through an inkjet printing device, and irradiate it with ultraviolet light of 395 nm for ~10 s for curing to form a polymer layer with a thickness of 30 μm.

[0105] The weakening treatment method for the weakening area in Example 4 is to set a mesh area. 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 in sequence. The weakening area further includes a mesh area located in the adhesive layer. The mesh area is provided with a plurality of holes. Along the thickness direction of the adhesive layer, the mesh area is located between the first polymer layer and the metal layer. The first polymer layer is a polyamide layer, the adhesive layer is a polyurethane layer, the metal layer is an aluminum foil, and the second polymer layer is a polypropylene layer.

[0106] Table 1

[0107]

[0108] Note: In Table 1, "\ " means that the parameter is not included.

[0109] According to Table 1 above, combined with Comparative Example 1 and Examples 1 to 4, it can be seen that by setting the packaging film to include a weakening area, in the weakening area, the tensile fracture elongation rate of the packaging film is weakened through the weakening treatment, which can make the tensile fracture elongation rate of the packaging film in the weakening area Less than the tensile fracture elongation of the packaging film in the non-weakening area When the packaging film is damaged by an external force, it will break in advance, and the extension of the packaging film is small, which is beneficial to reducing the possibility that the packaging film is extended to the pole piece by the external force, and thus can reduce the possibility of short circuit between the aluminum layer of the packaging film and the pole piece. Therefore, the needle penetration rate of the secondary battery can be improved.

[0110] The relevant parameters in Example 1 and Examples 5 to 9 are shown in Table 2 below.

[0111] Among them, the acid reagent concentrations in Example 1 and Examples 5 to 9 are different.

[0112] Table 2

[0113]

[0114] Combined with Example 1 and Examples 5 to 9, it can be seen that The larger the The smaller the tensile fracture elongation of the packaging film in the weakening area, the better the effect of improving the short circuit between the aluminum layer of the packaging film and the pole piece, and the higher the needle penetration rate of the secondary battery. When it is less than 25%, the tensile fracture elongation of the packaging film in the weakening area is relatively high, and the effect of improving the short circuit between the aluminum layer of the packaging film and the pole piece is not obvious. By setting The tensile fracture elongation of the packaging film in the weakening area can be reduced, and the possibility of short circuit between the aluminum layer of the packaging film and the pole piece can be reduced. When it is greater than 36%, continuing to increase The effect of improving the short circuit between the aluminum layer of the packaging film and the pole piece is not significantly improved, and it is easy to reduce the strength of the packaging film. By setting The tensile fracture elongation of the packaging film can meet the requirements while not overly affecting other properties of the packaging film.

[0115] The relevant parameters in Example 2 and Examples 10 to 14 are shown in Table 3 below.

[0116] Among them, the atmospheric plasma treatment time M in Example 2 and Examples 10 to 14 is different.

[0117] Table 3

[0118]

[0119]

[0120] According to Table 3 above, in combination with Example 2 and Examples 10 to 14, it can be seen that the longer the atmospheric plasma treatment time, the lower the tensile fracture elongation of the packaging film in the weakening area, and the higher the needle penetration rate of the secondary battery. When M < 10 min, the tensile fracture elongation of the packaging film in the weakening area is relatively high, and the needle penetration rate of the secondary battery is relatively low. By setting M ≥ 10 min, the tensile fracture elongation of the packaging film in the weakening area can be reduced, and the needle penetration rate of the secondary battery can be increased.

[0121] The larger, the tensile fracture elongation of the packaging film in the weakening area The smaller, the better the effect of improving the contact short circuit between the aluminum layer of the packaging film and the pole piece, and the higher the needle penetration rate of the secondary battery. When it is less than 25%, the tensile fracture elongation of the packaging film in the weakening area is relatively high, and the effect of improving the contact short circuit between the aluminum layer of the packaging film and the pole piece is not obvious. By setting The tensile fracture elongation of the packaging film in the weakening area can be reduced, and the possibility of contact short circuit between the aluminum layer of the packaging film and the pole piece can be reduced. When it is greater than 36%, continuing to increase The effect of improving the contact short circuit between the aluminum layer of the packaging film and the pole piece is not significantly improved, and it is easy to reduce the strength of the packaging film. By setting The tensile fracture elongation of the packaging film can be ensured to meet the requirements while not overly affecting other properties of the packaging film.

[0122] The relevant parameters in Example 3 and Examples 15 to 20 are shown in Table 4 below.

[0123] Among them, the thicknesses of the polymer layers in Example 3 and Examples 15 to 20 are different.

[0124] Table 4

[0125]

[0126]

[0127] According to Table 4 above, in combination with Example 3 and Examples 15 to 20, it can be seen that the greater the thickness H1 of the polymer layer, the lower the tensile fracture elongation of the packaging film in the weakening area, and the higher the puncture passing rate of the secondary battery. When the thickness H1 of the polymer layer is less than 20 μm, the tensile fracture elongation of the packaging film in the weakening area is relatively high. By setting the thickness H1 of the polymer layer ≥ 20 μm, the tensile fracture elongation of the packaging film in the weakening area can be reduced. When the thickness H1 of the polymer layer increases to 200 μm, if the thickness H1 of the polymer layer continues to increase, the reduction in the tensile fracture elongation of the packaging film in the weakening area is not obvious, and it is easy to lose more energy density of the secondary battery. By setting the thickness H1 of the polymer layer ≤ 200 μm, the energy density of the secondary battery can be increased.

[0128] The greater, the tensile fracture elongation of the packaging film in the weakening area The smaller, the better the effect of improving the contact short circuit between the aluminum layer of the packaging film and the electrode sheet, and the higher the puncture passing rate of the secondary battery. When it is less than 25%, the tensile fracture elongation of the packaging film in the weakening area is relatively high, and the effect of improving the contact short circuit between the aluminum layer of the packaging film and the electrode sheet is not obvious. By setting The tensile fracture elongation of the packaging film in the weakening area can be reduced, and the possibility of contact short circuit between the aluminum layer of the packaging film and the electrode sheet can be reduced. When it is greater than 36%, if it continues to increase The improvement effect of the contact short circuit between the aluminum layer of the packaging film and the electrode sheet is not obvious, and it is easy to lose more energy density of the secondary battery. By setting The energy density of the secondary battery can be increased.

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

[0130] Among them, the ratio of S2 to S1 in Example 4 and Examples 21 to 23 is different. The widths of the holes in Example 4 and Examples 24 to 28 are different.

[0131] Table 5

[0132]

[0133]

[0134] According to Table 5 above, in combination with Example 4 and Examples 21 to 23, it can be seen that the area of the mesh region is S1, the sum of the areas of all the holes is S2, the larger the ratio of S2 to S1, the smaller the possibility that the first polymer layer in the mesh region acts on the metal layer with a high tensile fracture elongation rate, the lower the tensile fracture elongation rate of the packaging film in the weakening region, and the higher the needle penetration rate of the secondary battery. When the ratio of S2 to S1 is less than 50%, the tensile fracture elongation rate of the packaging film in the weakening region is relatively high. By setting the ratio of S2 to S1 ≥ 50%, the tensile fracture elongation rate of the packaging film in the weakening region can be reduced. When the ratio of S2 to S1 is greater than 90%, the tensile fracture elongation rate of the packaging film in the weakening region is relatively low, and the packaging film is prone to breakage. By setting the ratio of S2 to S1 ≤ 90%, the possibility of the packaging film breaking can be reduced.

[0135] In combination with Example 4 and Examples 24 to 28, it can be seen that the larger the width of the hole, the smaller the possibility that the first polymer layer in the mesh region acts on the metal layer with a high tensile fracture elongation rate, the lower the tensile fracture elongation rate of the packaging film in the weakening region, and the higher the needle penetration rate of the secondary battery. When the width of the hole is less than 3 mm, the tensile fracture elongation rate of the packaging film in the weakening region is relatively high. By setting the width of the hole ≥ 3 mm, the tensile fracture elongation rate of the packaging film in the weakening region can be reduced. When the width of the hole is greater than 10 mm, the tensile fracture elongation rate of the packaging film in the weakening region is relatively low, and the packaging film is prone to breakage. By setting the width of the hole ≤ 10 mm, the possibility of the packaging film breaking can be reduced.

[0136] In combination with Example 4 and Examples 21 to 28, it can be seen that the larger, the tensile fracture elongation rate of the packaging film in the weakening region the smaller, the better the effect of improving the short circuit of the aluminum layer of the packaging film in contact with the pole piece, and the higher the needle penetration rate of the secondary battery. When it is less than 25%, the tensile fracture elongation rate of the packaging film in the weakening region is relatively high, and the effect of improving the short circuit of the aluminum layer of the packaging film in contact with the pole piece is not obvious. By setting the tensile fracture elongation rate of the packaging film in the weakening region can be reduced, and the possibility of the short circuit of the aluminum layer of the packaging film in contact with the pole piece can be reduced. When it is greater than 36%, continuing to increase the effect of improving the short circuit of the aluminum layer of the packaging film in contact with the pole piece is not significantly improved, and it is easy to reduce the strength of the packaging film. By setting the tensile fracture elongation rate of the packaging film can meet the requirements while not overly affecting other properties of the packaging film.

[0137] The above are only embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present 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; It is characterized in that The packaging film comprises a weakened area; the tensile elongation at break of the packaging film in the non-weakened area is φ1, the tensile elongation at break of the packaging film in the weakened area is φ2, and φ2<φ1.

2. The secondary battery according to claim 1, characterized in that: The weakened region includes a treated region located on a surface of the packaging film facing away from the electrode assembly.

3. The secondary battery according to claim 2, characterized in that: The processed area is provided with a polymer layer, and the tensile elongation at break of the packaging film provided with the polymer layer is smaller than the tensile elongation at break of the packaging film not provided with the polymer layer.

4. The secondary battery according to claim 3, characterized in that: The polymer layer includes at least one of an organic silicon compound and a polyacrylic resin.

5. The secondary battery according to claim 3, characterized in that: The thickness of the polymer layer is H1, 20 μm≤H1≤200 μm.

6. The secondary battery according to claim 2, characterized in that: The packaging film includes a first polymer layer, an adhesive layer, a metal layer and a second polymer layer stacked in sequence, the first polymer layer is arranged on the surface of the adhesive layer away from the electrode assembly, the processing area is located on the surface of the first polymer layer away from the adhesive layer, and the first polymer layer includes polyamide.

7. The secondary battery according to claim 1, characterized in that: The packaging film includes a first polymer layer, an adhesive layer and a metal layer, wherein two opposite surfaces of the adhesive layer are respectively bonded to the first polymer layer and the metal layer, and the weakened area also includes a mesh area located in the adhesive layer, wherein the mesh area is provided with a plurality of holes, and along the thickness direction of the adhesive layer, the mesh area is located between the first polymer layer and the metal layer.

8. The secondary battery according to claim 7, characterized in that: Along the thickness direction of the adhesive layer, the holes 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 holes is S2, and the ratio of S2 to S1 is 50% to 90%.

9. The secondary battery according to claim 8, characterized in that: The width of the hole is 3 mm to 10 mm.

10. The secondary battery according to claim 7, characterized in that: The length of the hole is the same as the width of the mesh area; and / or, in the length direction of the mesh area, the edge of the hole close to the edge of the mesh area coincides with the edge of the mesh area.

11. The secondary battery according to claim 1, characterized in that: Along the length direction of the electrode assembly, the packaging film includes a first edge and a second edge opposite to each other, the distance between the weakened area and the first edge is L1, the distance between the weakened area and the second edge is L2, 0.5 mm≤L1≤5 mm, 0.5 mm≤L2≤5 mm; And / or, along the width direction of the electrode assembly, the packaging film includes a third edge and a fourth edge relative to each other, the distance between the weakened area and the third edge is L3, the distance between the weakened area and the fourth edge is L4, 0.5mm≤L3≤5mm, 0.5mm≤L4≤5mm.

12. The secondary battery according to claim 1, characterized in that: The packaging film includes a first wall and a second wall that are oppositely disposed along a thickness direction of the electrode assembly, and the first wall and / or the second wall includes the weakened area.

13. The secondary battery according to claim 1, characterized in that: 25%≤φ1-φ2≤36%.

14. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 13.

15. A method for manufacturing a secondary battery, for preparing the secondary battery according to any one of claims 1 to 13, characterized in that: include: The packaging film is provided, and a partial area of ​​the packaging film is weakened to form the weakened area. The tensile elongation at break of the packaging film in the non-weakened area is φ1, and the tensile elongation at break of the packaging film in the weakened area is φ2, and φ2<φ1.

16. The method for manufacturing a secondary battery according to claim 15, characterized in that: The weakening treatment includes an acid reagent treatment.

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

18. The method for manufacturing a secondary battery according to claim 15, characterized in that: The weakening treatment includes atmospheric plasma treatment.

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

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

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