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 shell and an electrode assembly, the shell comprises a packaging film, and the packaging film wraps the outer surface of the electrode assembly. The shell further comprises a first polymer layer, at least part of the surface, away from the electrode assembly, of the packaging film is provided with the first polymer layer, the first polymer layer comprises polyacrylic resin, and the tensile elongation at break of the part, provided with the first polymer layer, of the shell is smaller than that of the packaging film. 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 easy to cause internal short circuit, thus bringing safety problems such as thermal runaway. Summary of the Invention

[0003] The inventors of the present application have found through research that when the secondary battery is damaged by external force, the packaging film is easily extended to the pole piece fracture along with the external force, resulting in the contact between the aluminum interlayer of the packaging film and the pole piece, thus causing a short circuit. By coating a polymer coating with a tensile fracture elongation lower than that of the packaging film on the outer surface of the packaging film of the finished secondary battery, the polymer coating and the packaging film form a composite packaging film, so that the tensile fracture elongation of the part of the composite packaging film provided with the polymer coating is lower than that of the original packaging film, thereby reducing the possibility that the aluminum interlayer in the packaging film is extended by external force and contacts the pole piece to cause 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, including a housing and an electrode assembly. The housing includes a packaging film that wraps around the outer surface of the electrode assembly. The housing further includes a first polymer layer, and at least part of the surface of the packaging film facing away from the electrode assembly is provided with the first polymer layer. The first polymer layer includes polyacrylic acid resin, and the tensile fracture elongation of the packaging film is The tensile fracture elongation of the part of the housing provided with the first polymer layer is

[0006] In the above technical solution, by providing at least part of the surface of the packaging film facing away from the electrode assembly with the first polymer layer, the first polymer layer and the packaging film form the housing. The first polymer layer includes polyacrylic acid resin, and the tensile fracture elongation of the part of the housing provided with the first polymer layer is less than the tensile fracture elongation of the packaging film When the housing is damaged by external force, it will break in advance, which can reduce the possibility that the housing extends to the pole piece fracture along with the external force, and can reduce the possibility that the aluminum interlayer of the housing contacts the pole piece to cause a short circuit.

[0007] In some preferred embodiments, the first polymer layer comprises solid particles with a particle size of 2 μm to 5 μm to increase the strength of the first polymer layer. Herein, the particle size of the solid particles refers to the maximum length of the solid particles.

[0008] In some preferred embodiments, the mass percentage content of the solid particles in the first polymer layer does not exceed 5% so that the first polymer layer has good adhesiveness.

[0009] In some preferred embodiments, the Shore D hardness of the first polymer layer is 70 HS to 80 HS. The first polymer layer can be used as a protective layer on the surface of the secondary battery and can improve the appearance damage of the secondary battery during the manufacturing process and transportation.

[0010] In some preferred embodiments, the thickness of the first polymer layer is H1 and the thickness of the secondary battery is H2, and 0.4% ≤ H1 / H2 ≤ 4%. This can reduce the tensile fracture elongation rate of the part of the housing provided with the first polymer layer, and at the same time, the secondary battery has good energy density.

[0011] In some preferred embodiments, 20 μm ≤ H1 ≤ 200 μm. This can reduce the tensile fracture elongation rate of the part of the housing provided with the first polymer layer, and at the same time, the secondary battery has good energy density.

[0012] In some preferred embodiments, the elastic modulus of the first polymer layer is 0.5 Mpa to 3 Mpa. When the elastic modulus of the first polymer layer is greater than 0.5 Mpa, it can have good elasticity and flexibility. When the elastic modulus of the first polymer layer is greater than 3 Mpa, it will become brittle and prone to fragmentation.

[0013] In some preferred embodiments, the shear force between the first polymer layer and the packaging film is not less than 38 N / m, which can reduce the possibility of the first polymer layer peeling off from the packaging film.

[0014] In some preferred embodiments, the adhesion force between the first polymer layer and the packaging film is not less than 6 N / m, which can reduce the possibility of the first polymer layer peeling off from the packaging film.

[0015] In some preferred embodiments, along the thickness direction of the packaging film, the packaging film comprises a first polymer layer, a first metal layer, a second polymer layer, and a third polymer layer stacked in sequence, and at least part of the surface of the third polymer layer facing away from the second polymer layer is provided with the first polymer layer.

[0016] In some preferred embodiments, the packaging film satisfies at least one of the following characteristics: (1) The first polymer layer comprises polypropylene, so that the packaging film is easy to encapsulate. (2) The first metal layer comprises aluminum to enhance the plasticity of the packaging film. (3) The second polymer layer comprises polyurethane to enhance the adhesion performance of the second polymer layer. (4) The third polymer layer comprises polyamide to enhance the strength of the packaging film.

[0017] In some preferred embodiments, the packaging film includes a first portion, a second portion, and a third portion connected in sequence along a first direction. A first polymer layer is disposed on the surface of the second portion facing away from the electrode assembly. The length of the first portion in the first direction is L1, and the length of the third portion in the first direction is L2, where 0.5 mm ≤ L1 ≤ 5 mm and 0.5 mm ≤ L2 ≤ 5 mm. The second portion is the middle region of the packaging film, and the first portion and the third portion are the head and tail regions of the packaging film. Since the head and tail regions of the packaging film are easily collided and worn, if the tensile fracture elongation rate of the head and tail regions of the packaging film is reduced, the head and tail regions of the packaging film are easily damaged. The first polymer layer is not disposed on the surfaces of the first portion and the third portion facing away from the electrode assembly. Defining the length of the first portion in the first direction to be from 0.5 mm to 5 mm can reduce the possibility of the first polymer layer adhering to the first portion and can reduce the possibility of the first portion being damaged. Defining the length of the third portion in the first direction to be from 0.5 mm to 5 mm can reduce the possibility of the first polymer layer adhering to the third portion and can reduce the possibility of the third portion being damaged.

[0018] In some preferred embodiments, the first part includes a first corner portion, a first middle portion, and a second corner portion that are sequentially connected along a second direction perpendicular to the first direction. A second polymer layer is provided on the surface of the first middle portion facing away from the electrode assembly, and the elongation at break of the portion of the housing provided with the second polymer layer is less than that of the packaging film. And / or, the third part includes a third corner portion, a second middle portion, and a fourth corner portion that are sequentially connected along a second direction perpendicular to the first direction. A third polymer layer is provided on the surface of the second middle portion facing away from the electrode assembly, and the elongation at break of the portion of the housing provided with the third polymer layer is less than that of the packaging film. Since the corners of the packaging film are easily collided and worn, if the elongation at break of the corners of the packaging film is reduced, the corners of the packaging film are likely to be damaged. The second polymer layer is not provided on the surfaces of the first corner portion and the second corner portion facing away from the electrode assembly, which can reduce the possibility of damage to the first corner portion and the second corner portion. The third polymer layer is not provided on the surfaces of the third corner portion and the fourth corner portion facing away from the electrode assembly, which can reduce the possibility of damage to the third corner portion and the fourth corner portion. Herein, the corners of the packaging film refer to the regions near the intersections between adjacent sides of the packaging film. Since an angle is formed between two adjacent sides, the regions near the intersections are called corners. Taking a cuboid-shaped packaging film as an example, if the outer surface of the packaging film is rectangular, it has 4 corners, and the 4 corners are respectively located near the intersections of every two adjacent sides of the rectangle. The cuboid-shaped packaging film has a total of 8 corners.

[0019] In some preferred embodiments, the length of the first corner portion in the second direction is L3, and the length of the second corner portion in the second direction is L4, where 0.5 mm ≤ L3 ≤ 5 mm and 0.5 mm ≤ L4 ≤ 5 mm. Defining the length of the first corner portion in the second direction to be from 0.5 mm to 5 mm can reduce the possibility of the second polymer layer adhering to the first corner portion and can reduce the possibility of damage to the first corner portion. Defining the length of the second corner portion in the second direction to be from 0.5 mm to 5 mm can reduce the possibility of the second polymer layer adhering to the second corner portion and can reduce the possibility of damage to the second corner portion.

[0020] In some preferred embodiments, the length of the third corner portion in the second direction is L5, and the length of the fourth corner portion in the second direction is L6, where 0.5 mm ≤ L5 ≤ 5 mm and 0.5 mm ≤ L6 ≤ 5 mm. Defining the length of the third corner portion in the second direction to be from 0.5 mm to 5 mm can reduce the possibility of the third polymer layer adhering to the third corner portion and can reduce the possibility of damage to the third corner portion. Defining the length of the fourth corner portion in the second direction to be from 0.5 mm to 5 mm can reduce the possibility of the third polymer layer adhering to the fourth corner portion and can reduce the possibility of damage to the fourth corner portion.

[0021] In some preferred embodiments, the elongation at break of the part of the housing provided with the first polymer layer can be made less than that of the packaging film. When is greater than 36%, the thickness of the first polymer layer will be relatively large, and it is difficult to further improve the elongation at break of the part of the housing provided with the first polymer layer by continuing to increase the thickness of the first polymer layer, and the energy density of the secondary battery will be lost more. When is less than 15%, the thickness of the first polymer layer will be relatively small, and the improvement effect on the elongation at break of the part of the housing provided with the first polymer layer is not obvious.

[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 and an electrode assembly, and wrapping the packaging film around the outer surface of the electrode assembly. Providing a polyacrylic acid resin, and coating the polyacrylic acid resin on at least part of the surface of the packaging film wrapped with the electrode assembly facing away from the electrode assembly to form a first polymer layer. Since the packaging film needs to be punched before wrapping the electrode assembly, if the elongation at break of the packaging film is relatively low, the aluminum layer at the corner is likely to be damaged during punching, and the packaging requirements cannot be met. Therefore, the packaging film needs to have good elongation at break. By providing the first polymer layer after the packaging film wraps the electrode assembly, the elongation at break of the part of the composite packaging film (housing) formed by the packaging film and the first polymer layer provided with the first polymer layer can be reduced, without affecting the elongation at break of the packaging film before wrapping the electrode assembly, so that the packaging film can meet the punching requirements.

[0024] The additional aspects and advantages of the embodiments of the present application will be partly described, shown, or explained through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] One or more embodiments are illustrated by corresponding drawings. These illustrative descriptions do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, unless otherwise stated, and the dimensions in the drawings do not constitute a proportional limitation.

[0026] Figure 1 is a schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0027] Figure 2 is a schematic structural diagram of an electrode assembly according to some embodiments of the present application;

[0028] Figure 3Schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0029] Figure 4 Schematic cross-sectional view of a secondary battery according to some embodiments of the present application in the third direction;

[0030] Figure 5 Schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0031] Figure 6 Schematic cross-sectional view of a secondary battery according to some embodiments of the present application in the first direction;

[0032] Figure 7 Schematic cross-sectional view of a secondary battery according to some embodiments of the present application in the first direction;

[0033] Figure 8 Schematic diagram of the first polymer layer and the packaging film according to some embodiments of the present application.

[0034] Explanation of reference numerals:

[0035] 100, secondary battery;

[0036] 10, housing;

[0037] 11, packaging film; 111, first polymer layer; 112, first metal layer; 113, second polymer layer; 114, third polymer layer; 115, first part; 1151, first corner part; 1152, first middle part; 1153, second corner part; 116, second part; 117, third part; 1171, third corner part; 1172, second middle part; 1173, fourth corner part.

[0038] 12, first polymer layer; 13, second polymer layer; 14, third polymer layer;

[0039] 20, electrode assembly;

[0040] 20a, tab; 21, positive electrode sheet; 22, negative electrode sheet; 23, separator;

[0041] X, first direction; Y, second direction; Z, third direction. Detailed implementation manners

[0042] 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.

[0043] Reference to "embodiment" in this application means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of this application. The phrase appears in various positions in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0044] In the description of the embodiments of this 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 specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0045] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this text generally represents an "or" relationship between the associated objects before and after.

[0046] The term "vertical" is used to describe the ideal state between two components. In the actual production or use state, there may be a state approximately vertical between two components. For example, in combination with numerical description, vertical may refer to the included angle range between two straight lines being between 90±10°, vertical may also refer to the dihedral angle range between two planes being between 90±10°, and vertical may also refer to the included angle range between a straight line and a plane being between 90±10°. The two components described as "vertical" may not be absolute 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".

[0047] The first direction X, the second direction Y, and the third direction Z of this application are two-way directions, that is, the first direction X includes the direction indicated by the arrow in the drawing and its opposite direction, the second direction Y includes the direction indicated by the arrow in the drawing and its opposite direction, and the third direction Z includes the direction indicated by the arrow in the drawing and its opposite direction.

[0048] The technical features involved in different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0049] In a first aspect, an embodiment of this application provides a secondary battery 100. Please refer to Figure 1, the secondary battery 100 includes a housing 10, an electrode assembly 20, and a tab 20a. The housing 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 housing 10. The tab 20a is connected to the electrode assembly 20 and extends out of the housing 10 in the length direction (the first direction X) of the electrode assembly 20 to assist in energy transfer between the electrode assembly 20 and an external electronic device.

[0050] For the above electrode assembly 20, please refer to Figure 2 , Figure 2 which 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 embodiments of the present application, taking the electrode assembly 20 as a laminated structure as an example for illustration, in some other embodiments, the electrode assembly 20 can also be a wound structure. For example, after the positive electrode sheet 21, the separator 23, and the negative electrode sheet 22 are sequentially laminated, they are then wound to form a wound electrode assembly 20.

[0051] Please refer to Figure 3 and Figure 4 , the housing 10 includes a packaging film 11, and the packaging film 11 wraps around the outer surface of the electrode assembly 20. When the secondary battery 100 is damaged by an external force, the packaging film 11 is easily extended to the tab fracture along with the external force, resulting in contact between the aluminum interlayer of the packaging film 11 and the tab, thus causing a short circuit.

[0052] To improve the above problems, in the embodiments of the present application, the housing 10 further includes a first polymer layer 12. At least part of the surface of the packaging film 11 facing away from the electrode assembly 20 is provided with the first polymer layer 12. The first polymer layer 12 includes a polyacrylic acid resin, and the tensile fracture elongation rate of the first polymer layer 12 is less than that of the packaging film 11. By providing the first polymer layer 12 on at least part of the surface of the packaging film 11 facing away from the electrode assembly 20, the first polymer layer 12 and the packaging film 11 form the housing 10. Since the first polymer layer 12 includes a polyacrylic acid resin, the tensile fracture elongation rate of the part of the housing 10 provided with the first polymer layer 12 can be made less than that of the packaging film 11. When the housing 10 is damaged by an external force, it will break in advance, which can reduce the possibility of the housing 10 extending to the tab fracture along with the external force, and can reduce the possibility of contact short circuit between the aluminum interlayer of the housing 10 and the tab.

[0053] In some embodiments, the tensile fracture elongation rate of the part of the housing 10 provided with the first polymer layer 12 can be made less than that of the packaging film 11. When When it is greater than 36%, the thickness of the first polymer layer 12 will be relatively large. Continuing to increase the thickness of the first polymer layer 12 is difficult to further improve the tensile fracture elongation of the part of the housing 10 provided with the first polymer layer 12, and it will result in a relatively large loss of the energy density of the secondary battery 100. When When it is less than 15%, the thickness of the first polymer layer 12 will be relatively small, and the improvement effect on the tensile fracture elongation of the part of the housing 10 provided with the first polymer layer 12 is not obvious.

[0054] In some embodiments, the first polymer layer 12 includes solid particles, and the particle size of the solid particles is 2 μm to 5 μm to increase the strength of the first polymer layer 12. Among them, the particle size of the solid particles refers to the maximum length of the solid particles.

[0055] In some embodiments, the mass percentage content of the solid particles in the first polymer layer 12 does not exceed 5% so that the first polymer layer 12 has good adhesiveness.

[0056] In some embodiments, the solid particles can be alumina, zirconia, silica, calcium carbonate to further enhance the strength of the first polymer layer 12.

[0057] In some embodiments, the Shore D hardness of the first polymer layer 12 is 70 HS to 80 HS. The first polymer layer 12 can be used as a protective layer on the surface of the secondary battery 100, and it can improve the appearance damage of the secondary battery 100 during the manufacturing process and transportation.

[0058] In some embodiments, the elastic modulus of the first polymer layer 12 is 0.5 Mpa to 3 Mpa. When the elastic modulus of the first polymer layer 12 is greater than 0.5 Mpa, it can have good elasticity and flexibility.

[0059] When the elastic modulus of the first polymer layer 12 is greater than 3 Mpa, it will become brittle and easily break.

[0060] In some embodiments, the thickness of the first polymer layer 12 is H1, and the thickness of the secondary battery 100 is H2, and 0.4% ≤ H1 / H2 ≤ 4%. It can reduce the tensile fracture elongation of the part of the housing 10 provided with the first polymer layer 12, and at the same time, the secondary battery 100 has good energy density.

[0061] In some embodiments, 20 μm ≤ H1 ≤ 200 μm. It can reduce the tensile fracture elongation of the part of the housing 10 provided with the first polymer layer 12, and at the same time, the secondary battery 100 has good energy density.

[0062] In some embodiments, 20 μm ≤ H1 ≤ 40 μm, which can further reduce the tensile fracture elongation of the part of the housing 10 provided with the first polymer layer 12, while the secondary battery 100 has good energy density.

[0063] In some embodiments, the shear force between the first polymer layer 12 and the packaging film 11 is not less than 38 N / m, which can reduce the possibility of the first polymer layer 12 peeling off from the packaging film 11.

[0064] In some embodiments, the adhesion force between the first polymer layer 12 and the packaging film 11 is not less than 6 N / m, which can reduce the possibility of the first polymer layer 12 peeling off from the packaging film 11.

[0065] In some embodiments, the packaging film 11 includes a first part 115, a second part 116, and a third part 117 that are sequentially connected along the first direction X. The first polymer layer 12 is provided on the surface of the second part 116 facing away from the electrode assembly 20. The length of the first part 115 in the first direction X is L1, and the length of the third part 117 in the first direction X is L2, where 0.5 mm ≤ L1 ≤ 5 mm and 0.5 mm ≤ L2 ≤ 5 mm. The second part 116 is the middle region of the packaging film 11, and the first part 115 and the third part 117 are the head and tail regions of the packaging film 11. Since the head and tail regions of the packaging film 11 are easily collided and worn, if the tensile fracture elongation of the head and tail regions of the packaging film 11 is reduced, the head and tail regions of the packaging film 11 are easily damaged. The first polymer layer 12 is not provided on the surfaces of the first part 115 and the third part 117 facing away from the electrode assembly 20. Defining the length of the first part 115 in the first direction X to be 0.5 mm to 5 mm can reduce the possibility of the first polymer layer 12 adhering to the first part 115 and can reduce the possibility of the first part 115 being damaged. Defining the length of the third part 117 in the first direction X to be 0.5 mm to 5 mm can reduce the possibility of the first polymer layer 12 adhering to the third part 117 and can reduce the possibility of the third part 117 being damaged.

[0066] In some embodiments, please refer to Figure 5 and Figure 6, the first part 115 includes a first corner portion 1151, a first intermediate portion 1152, and a second corner portion 1153 that are sequentially connected along the second direction Y. The second direction Y is perpendicular to the first direction X. A second polymer layer 13 is provided on the surface of the first intermediate portion 1152 facing away from the electrode assembly 20. The tensile fracture elongation of the portion of the housing 10 provided with the second polymer layer 13 is less than that of the packaging film 11. Since the corners of the packaging film 11 are easily collided and worn, if the tensile fracture elongation of the corners of the packaging film 11 is reduced, the corners of the packaging film 11 are likely to be damaged. The second polymer layer 13 is not provided on the surfaces of the first corner portion 1151 and the second corner portion 1153 facing away from the electrode assembly 20, which can reduce the possibility of damage to the first corner portion 1151 and the second corner portion 1153. Among them, the corners of the packaging film 11 refer to the areas near the intersections between adjacent sides of the packaging film 11. Since an angle is formed between two adjacent sides, the area near the intersection is called a corner. Taking the packaging film 11 in the shape of a cuboid as an example, the outer surface of the packaging film 11 is rectangular, so it has 4 corners, and the 4 corners are respectively located near the intersections of every two adjacent sides of the rectangle. The cuboid-shaped packaging film 11 has a total of 8 corners.

[0067] In some embodiments, the length of the first corner portion 1151 in the second direction Y is L3, and the length of the second corner portion 1153 in the second direction Y is L4, where 0.5 mm ≤ L3 ≤ 5 mm and 0.5 mm ≤ L4 ≤ 5 mm. Defining the length of the first corner portion 1151 in the second direction Y to be from 0.5 mm to 5 mm can reduce the possibility of the second polymer layer 13 adhering to the first corner portion 1151 and can reduce the possibility of damage to the first corner portion 1151. Defining the length of the second corner portion 1153 in the second direction Y to be from 0.5 mm to 5 mm can reduce the possibility of the second polymer layer 13 adhering to the second corner portion 1153 and can reduce the possibility of damage to the second corner portion 1153.

[0068] In some embodiments, please refer to Figure 5 and Figure 7 , the third part 117 includes a third corner portion 1171, a second intermediate portion 1172, and a fourth corner portion 1173 that are sequentially connected along the second direction Y. The second direction Y is perpendicular to the first direction X. A third polymer layer 14 is provided on the surface of the second intermediate portion 1172 facing away from the electrode assembly 20. The tensile fracture elongation of the portion of the housing 10 provided with the third polymer layer 14 is less than that of the packaging film 11. The third polymer layer 14 is not provided on the surfaces of the third corner portion 1171 and the fourth corner portion 1173 facing away from the electrode assembly 20, which can reduce the possibility of damage to the third corner portion 1171 and the fourth corner portion 1173.

[0069] In some embodiments, the length of the third corner portion 1171 in the second direction Y is L5, and the length of the fourth corner portion 1173 in the second direction Y is L6, where 0.5 mm ≤ L5 ≤ 5 mm and 0.5 mm ≤ L6 ≤ 5 mm. Defining the length of the third corner portion 1171 in the second direction Y to be from 0.5 mm to 5 mm can reduce the possibility of the third polymer layer 14 adhering to the third corner portion 1171 and can reduce the possibility of the third corner portion 1171 being damaged. Defining the length of the fourth corner portion 1173 in the second direction Y to be from 0.5 mm to 5 mm can reduce the possibility of the third polymer layer 14 adhering to the fourth corner portion 1173 and can reduce the possibility of the fourth corner portion 1173 being damaged.

[0070] In some embodiments, the second polymer layer 13 comprises a polyacrylic acid resin such that the tensile fracture elongation of the portion of the housing 10 provided with the second polymer layer 13 is less than that of the packaging film 11. The second polymer layer 13 may further comprise solid particles to enhance the strength of the second polymer layer 13. The third polymer layer 14 comprises a polyacrylic acid resin such that the tensile fracture elongation of the portion of the housing 10 provided with the third polymer layer 14 is less than that of the packaging film 11. The third polymer layer 14 may further comprise solid particles to enhance the strength of the third polymer layer 14.

[0071] In some embodiments, the thickness, material, composition mass percentage, and properties of the second polymer layer 13 may be the same as those of the first polymer layer 12. The thickness, material, composition mass percentage, and properties of the third polymer layer 14 may be the same as those of the first polymer layer 12.

[0072] In some embodiments, please refer to Figure 8 , in the thickness direction (third direction Z) of the packaging film 11, the packaging film 11 includes a first polymer layer 111, a first metal layer 112, a second polymer layer 113, and a third polymer layer 114 stacked in sequence. At least a part of the surface of the third polymer layer 114 facing away from the second polymer layer 113 is provided with a first polymer layer 12. The tensile fracture elongation of the first polymer layer 12 is less than that of the third polymer layer 114. The first polymer layer 12 and the third polymer layer 114 form a composite layer, and the tensile fracture elongation of the composite layer may be less than that of the third polymer layer 114.

[0073] In some embodiments, the packaging film 11 satisfies at least one of the following characteristics: (1) The first polymer layer 111 includes polypropylene, so that the packaging film 11 is easy to encapsulate. (2) The first metal layer 112 includes aluminum to enhance the plasticity of the packaging film 11. (3) The second polymer layer 113 includes polyurethane to enhance the adhesion performance of the second polymer layer 113. (4) The third polymer layer 114 includes polyamide to enhance the strength of the packaging film 11.

[0074] In the second aspect of the present application, an electronic device is further proposed, including the secondary battery 100 of any embodiment of the first aspect as described above. The electronic device of 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 toy 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.

[0075] In the third aspect of the present application, a manufacturing method of the secondary battery 100 is further proposed, which is used to prepare the secondary battery 100 of any embodiment of the first aspect as described above, including: providing the packaging film 11 and the electrode assembly 20, and wrapping the packaging film 11 on the outer surface of the electrode assembly 20. Providing polyacrylic resin, and coating the polyacrylic resin on at least part of the surface of the packaging film 11 wrapped with the electrode assembly 20 facing away from the electrode assembly 20 to form the first polymer layer 12. Since the packaging film 11 needs to be punched before wrapping the electrode assembly 20, if the tensile fracture elongation rate of the packaging film 11 is low, the aluminum layer at the corner is easily damaged during punching and cannot meet the packaging requirements. Therefore, the packaging film 11 needs to have a good tensile fracture elongation rate. By setting the first polymer layer 12 after the packaging film 11 wraps the electrode assembly 20, the tensile fracture elongation rate of the part of the composite packaging film (the housing 10) formed by the packaging film 11 and the first polymer layer 12 provided with the first polymer layer 12 can be reduced, without affecting the tensile fracture elongation rate of the packaging film 11 before the packaging film 11 wraps the electrode assembly 20, so that the packaging film 11 can meet the punching requirements.

[0076] Test part:

[0077] 1. Tensile test:

[0078] The sample is made into a test sample with a length of 100 mm and a width of 15 mm using a special tensile cutting knife for the sample, and the test sample is fixed to the test fixture of the high-speed rail tensile machine, with a tensile speed of 50 ± 0.5 mm / min and a tensile spacing of 50 mm. When the sample is broken, the maximum value is taken as the breaking tensile force, and the length of the sample when it is broken is recorded.

[0079] Elongation at break in tension = (Length of the sample at break - Initial length of the sample) / Initial length of the sample.

[0080] Tensile strength = Breaking force / Initial cross-sectional area of the sample.

[0081] 2. Shore D hardness test:

[0082] Place the sample to be tested flat on the test bench, calibrate the hardness tester to the standard settings, place the hardness tester vertically on the surface of the sample, apply a uniform pressure of 1 Kg, and keep the indenter stationary on the sample surface. Immediately read the value on the hardness tester when the indenter is stable.

[0083] 3. Elastic modulus test:

[0084] Use a special cutting knife for tensile testing to cut the coating into test samples with a length of 100 mm and a width of 15 mm. Fix the test samples to the test fixture of the high-speed tensile machine, with a tensile speed of 50 ± 0.5 mm / min and a tensile spacing of 50 mm. After the sample is broken, obtain the stress / strain curve, and calculate the elastic modulus = stress / strain.

[0085] 4. Shearing force test:

[0086] Take a polymer and coat a bonding area of 25 mm * 100 mm on the packaging film. Place the cured composite sample between the upper and lower fixtures of the tensile machine, ensure that the bonding surface of the sample is parallel to the contact surface of the fixture, apply a loading force of 10 mm / min, keep the first polymer layer peeled off from the packaging film at 0°, and record the maximum force value during the peeling process as the shearing force.

[0087] 5. Adhesive force test:

[0088] Take a composite sample of the first polymer layer and the packaging film, use a special cutting knife for tensile testing to cut the sample into a sample with a length of 100 mm and a width of 15 mm. Fix the sample between the upper and lower fixtures of the tensile machine, make the coating peeled off from the packaging film at 90°, apply a loading force of 50 mm / min, and record the maximum force value during the peeling process as the adhesive force.

[0089] 6. Nail test:

[0090] First, fully charge the secondary battery. Place the sample flat on the test bench, and 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 of ≥ 100 mm to test from the center position of the sample at a speed of 150 ± 1.5 mm / s. The sample is completely pierced. The passing criterion is that after the test, the battery cell does not catch fire or explode.

[0091] Example 1

[0092] <Preparation of the positive electrode plate>

[0093] Use aluminum foil as the positive current collector, and evenly coat a layer of lithium cobalt oxide slurry 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). Dry it at 85 °C, and then perform cold pressing, slicing, and slitting to prepare the positive electrode sheet.

[0094] <Preparation of negative electrode sheet>:

[0095] Use copper foil as the negative current collector, and evenly coat a layer of graphite slurry 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). Dry it at 85 °C, and then perform cold pressing, slicing, and slitting to prepare the negative electrode sheet.

[0096] <Electrolyte preparation>:

[0097] Use a solution prepared by mixing lithium salt LiPF6 and non-aqueous organic solvents (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate (VC) = 20:30:20:28:2, by mass) at a mass ratio of 8:92 as the electrolyte of the secondary battery.

[0098] <Preparation of secondary battery>:

[0099] Weld the tabs of the positive electrode sheet and the negative electrode sheet, then wind the positive electrode sheet and the negative electrode sheet. The positive electrode sheet and the negative electrode sheet are separated by a polyethylene separator to prepare the electrode assembly.

[0100] Use Zijiang's 103 μm thick aluminum-plastic film as the packaging film, wrap the packaging film around the outer surface of the electrode assembly, and perform top-side sealing, inkjet coding, vacuum drying, electrolyte injection, and high-temperature standing, and then perform formation and capacity measurement to obtain the preliminary secondary battery.

[0101] The polyacrylic resin is evenly sprayed on the outer surface of the preliminary secondary battery through an inkjet printing device and cured by ultraviolet light of 395 nm for ~10 s to form a first polymer layer with a thickness of 30 μm. The ratio of the thickness of the first polymer layer to the thickness of the secondary battery is 0.6%. The packaging film includes a first part, a second part, and a third part connected in sequence along the first direction (the direction in which the tab extends out of the housing). The first polymer layer is provided on the surface of the second part facing away from the electrode assembly. The length of the first part in the first direction is 5 mm, and the length of the third part in the first direction is 5 mm. The Shore D hardness of the first polymer layer is 76 HS, the elastic modulus is 2 Mpa, the shear force between the first polymer layer and the packaging film is 38 N / m, and the adhesion between the first polymer layer and the packaging film is 6 N / m. The packaging film with the first polymer layer becomes a composite packaging film (housing).

[0102] The relevant parameters in Comparative Examples 1 to 3 and Examples 1 to 8 are shown in Table 1 below.

[0103] Among them, in Comparative Example 1 and Examples 1 to 6, a Zijiang aluminum-plastic film with a thickness of 103 μm is used as the packaging film. The first polymer layer is not provided on the surface of the packaging film in Comparative Example 1, and only the thickness of the first polymer layer is different in Examples 1 to 6.

[0104] In Comparative Example 2 and Example 7, a Showa aluminum-plastic film with a thickness of 96 μm is used as the packaging film. The first polymer layer is not provided on the surface of the packaging film in Comparative Example 2.

[0105] In Comparative Example 3 and Example 8, a DNP aluminum-plastic film with a thickness of 115 μm is used as the packaging film. The first polymer layer is not provided on the surface of the packaging film in Comparative Example 3.

[0106] Table 1

[0107]

[0108]

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

[0110] According to Table 1 above, combined with Comparative Examples 1 to 3 and Examples 1 to 8, it can be seen that by providing a first polymer layer containing polyacrylic resin on the surface of the packaging film facing away from the electrode assembly, the tensile fracture elongation of the part of the housing provided with the first polymer layer is less than the tensile fracture elongation of the packaging film, which can improve the Nail passing rate of the secondary battery, that is, the problem of secondary battery short circuit can be improved.

[0111] Combined with Examples 1 to 6, it can be seen that the ratio of the thickness of the first polymer layer to the thickness of the secondary battery is 0.4% to 4%, which can preferably reduce the elongation at break of the part of the housing provided with the first polymer layer, enabling the secondary battery to have a good Nail passing rate. When the ratio of the thickness of the first polymer layer to the thickness of the secondary battery exceeds 4%, the energy density of the secondary battery will be reduced. When the thickness of the first polymer layer is 20 μm to 200 μm, it can preferably reduce the elongation at break of the part of the housing provided with the first polymer layer, enabling the secondary battery to have a good Nail passing rate. When the thickness of the first polymer layer exceeds 200 μm, the energy density of the secondary battery will be reduced.

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

[0113] Among them, in Examples 1, 9 to 11, only the mass percentage content of the solid particles in the first polymer layer is different. In Examples 12 to 14, only the particle size of the solid particles in the first polymer layer is different. The solid particles in Examples 9 to 14 are alumina. In other examples, the solid particles can be zirconia, silica, or calcium carbonate.

[0114] Table 2

[0115]

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

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

[0118] Combined with Examples 10, 12 to 14, it can be seen that when the particle size of the solid particles in the first polymer layer is 2 μm to 5 μm, the first polymer layer has better tensile strength. When the particle size of the solid particles exceeds 5 μm, the solid particles will reduce the internal cohesion within the first polymer layer.

[0119] Table 3

[0120]

[0121] According to Table 3 above, combined with Examples 1, 2, 3, 5, and 6, the elongation at break of the packaging film is The elongation at break of the part of the housing provided with the first polymer layer is The tensile fracture elongation of the part of the housing provided with the first polymer layer can be made less than that of the packaging film, which can improve the Nail passing rate of the secondary battery, that is, the problem of short circuit of the secondary battery can be improved. The thicker the first polymer layer, the larger the dimension that can be extended, and the better the improvement effect on the tensile fracture elongation of the part of the housing provided with the first polymer layer. Therefore, the tensile fracture elongation of the part of the housing provided with the first polymer layer is smaller. When is greater than 36%, the thickness of the first polymer layer will be relatively large. Continuing to increase the thickness of the first polymer layer is difficult to further improve the tensile fracture elongation of the part of the housing provided with the first polymer layer, and a relatively large amount of energy density of the secondary battery will be lost. When is less than 15%, the thickness of the first polymer layer will be relatively small, and the improvement effect on the tensile fracture elongation of the part of the housing provided with the first polymer layer is not obvious.

[0122] The above are only the 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 equally included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising a housing and an electrode assembly, wherein the housing comprises a packaging film, and the packaging film is wrapped around the outer surface of the electrode assembly; It is characterized in that The shell also includes a first polymer layer, and the surface of the packaging film facing away from the electrode assembly is at least partially provided with the first polymer layer, the first polymer layer includes polyacrylic resin, the tensile elongation at break of the packaging film is φ1, and the tensile elongation at break of the portion of the shell provided with the first polymer layer is φ2, φ2<φ1.

2. The secondary battery according to claim 1, characterized in that: The first polymer layer includes solid particles, and the particle size of the solid particles is 2 μm to 5 μm.

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

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

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

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

7. The secondary battery according to claim 1, characterized in that: The elastic modulus of the first polymer layer is 0.5 MPa to 3 MPa.

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

9. The secondary battery according to claim 1, characterized in that: The bonding force between the first polymer layer and the packaging film is not less than 6 N / m.

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

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

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The electrode assembly is connected to a pole ear, and the pole ear extends out of the shell along a first direction. The packaging film includes a first part, a second part and a third part connected in sequence along the first direction. The surface of the second part facing away from the electrode assembly is provided with the first polymer layer, the length of the first part in the first direction is L1, the length of the third part in the first direction is L2, 0.5mm≤L1≤5mm, 0.5mm≤L2≤5mm.

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

14. The secondary battery according to claim 1, characterized in that: 15%≤φ1-φ2≤36%.

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

16. A method for manufacturing a secondary battery, for preparing the secondary battery according to any one of claims 1 to 14, characterized in that: include: Providing the packaging film and the electrode assembly, and wrapping the packaging film on the outer surface of the electrode assembly; The polyacrylic acid resin is provided and coated on at least a portion of a surface of the packaging film wrapping the electrode assembly that is away from the electrode assembly to form the first polymer layer.

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