Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrode assembly and a shell, the electrode assembly comprises multiple layers of first electrode plates and multiple layers of second electrode plates, the polarities of the first electrode plates and the second electrode plates are opposite, the first electrode plates comprise first current collectors, and the second electrode plates comprise second current collectors; a protruding first foil lug is arranged on one side of each layer of first current collector, the multiple first foil lugs are overlapped in the direction perpendicular to the electrode pole piece, and the multiple first foil lugs are welded together in a first welding area to form a first welding foil lug; the first welding area comprises a first surface and a second surface which are opposite in the thickness direction, the height difference between the highest point and the lowest point on the first surface is smaller than 8 micrometers, and the height difference between the highest point and the lowest point on the second surface is smaller than 8 micrometers. Through the arrangement, the manufacturing process can be simplified, the manufacturing yield can be improved, the secondary battery can be compatible with a use environment with a smaller size, the energy density of the secondary battery is favorably improved, and the use performance and the safety performance of the secondary battery are favorably improved.

Description

Technical Field

[0001] This application relates to the field of electrochemistry technology, and particularly to a secondary battery and an electronic device. Background Art

[0002] Common multi-layer pole piece electrode assemblies are divided into soft-pack batteries and steel-shell batteries according to the type of packaging bag. In soft-pack batteries, the multi-layer pole piece extends out the multi-layer pole ears for transfer welding with a transfer piece. After welding, the transferred part is placed inside the soft-pack battery case, and the remaining part of the transfer piece extends out of the soft-pack battery case; in steel-shell batteries, the multi-layer pole ears are subjected to transfer welding with a transfer piece. After welding, the positive transfer piece is welded to the pole column, and the negative transfer piece is welded to the case cover.

[0003] During the welding process of the transfer pole ears, there is a relatively high risk of over-welding and virtual welding, which also increases the risk of damage to the multi-layer pole ears, resulting in a decrease in the yield and quality of the secondary battery. Moreover, the transfer pole ears occupy the space at the end and in the thickness direction of the electrode assembly, leading to a decrease in energy density. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to solve at least one of the above problems. The specific technical solutions are as follows:

[0005] The present application provides a secondary battery, comprising an electrode assembly and a housing. The electrode assembly includes multiple layers of first electrode tabs and multiple layers of second electrode tabs, with opposite polarities between the first electrode tabs and the second electrode tabs. The first electrode tab includes a first current collector, and one side of each first current collector has a protruding first foil tab. A plurality of first foil tabs overlap in a direction perpendicular to the electrode tab, and the plurality of first foil tabs are welded together in a first welding area to form a first welded foil tab. The first welding area includes a first surface and a second surface opposite to each other in the thickness direction. The height difference between the highest point and the lowest point on the first surface is less than 8 μm, and the height difference between the highest point and the lowest point on the second surface is less than 8 μm. Preferably, the height difference between the highest point and the lowest point on the first surface is less than 5 μm. By controlling the height differences between the highest point and the lowest point on the first surface and the second surface within the scope of the present application, the flatness of the first welded foil tab is relatively high, and there is no need to additionally transfer the connection piece within the housing. That is, in a soft-pack battery, during the sealing of the housing, it can be directly carried out on the first welded foil tab, and the risk of liquid leakage after sealing is relatively small; in a steel-shell battery, the first welded foil tab can be directly used to connect with the pole column. The above settings can simplify the manufacturing process of the secondary battery, and can also avoid the problems of over-welding or false welding during the welding of the connection piece, reduce the risk of damage to multiple layers of pole ears, thereby improving the manufacturing yield, and at the same time is beneficial to improving the safety performance of the secondary battery. Setting a connection piece within the housing will occupy the space in the length direction and the thickness direction within the housing. Through the above settings, there is no need to set a connection piece within the housing. On the one hand, the secondary battery can be compatible with usage environments with smaller dimensions in the length direction and / or the width direction, and on the other hand, it is beneficial to improve the energy density of the secondary battery, thereby being beneficial to improving the usage performance of the secondary battery.

[0006] In an implementation scheme of the present application, the housing is an aluminum-plastic film, and the first welded foil tab is connected to the aluminum-plastic film through a sealing part. The first welded foil tab extends out of the housing, and the sealing part covers at least part of the first welding area. The first welded foil tab includes a first extension part and a second extension part. The first extension part is the part extending from the sealing part to the inside of the housing, and the second extension part is the part extending from the sealing part to the outside of the housing. By directly arranging the sealing part on the first welded foil tab, the manufacturing process of the secondary battery can be simplified and the manufacturing yield can be improved. At the same time, compared with setting a connection piece inside the housing, the first extension part occupies less space inside the housing, which is beneficial to improving the energy density of the secondary battery.

[0007] In an embodiment of the present application, the first welding tab and the first adapter are welded in the second welding area, the first welding area and the second welding area at least partially overlap, the sealing portion covers at least a part of the second welding area, and the second welding area is the junction area between the first welding tab and the first adapter. By sealing the housing at the junction of the first welding area and the second welding area, that is, at the connection between the first welding tab and the first adapter, the occupation of the overall size of the secondary battery by the connection between the first welding tab and the first adapter can be reduced, which is beneficial to improving the energy density of the secondary battery.

[0008] In an embodiment of the present application, multiple first tabs are welded to form the first welding tab by pressure fusion welding or molecular diffusion welding, and the first welding tab is connected to the first adapter by pressure fusion welding or molecular diffusion welding. Both pressure fusion welding and molecular diffusion welding require pressure for welding and do not require additional welding materials. At the same time, both have the characteristics of high precision, high welding strength, small welding defects, and small heat influence. Due to the small welding defects and small heat influence of pressure fusion welding and molecular diffusion welding, the flatness of the first welding area and the second welding area is relatively high, and the housing can be sealed at the junction of the first welding area and the second welding area, that is, at the connection between the first welding tab and the first adapter. At this time, the risk of damage to the sealing portion and the risk of leakage of the secondary battery are relatively small, which is beneficial to improving the safety performance of the secondary battery while improving the manufacturing yield.

[0009] In an embodiment of the present application, the first welding tab and the first adapter are welded in the second welding area, and the second welding area is provided on the second extension portion. By providing the second welding area on the second extension portion, the manufacturing process of the secondary battery can be simplified.

[0010] In an embodiment of the present application, the first welding tab and the first adapter are connected by ultrasonic welding. Ultrasonic welding has the characteristic of simple process, but compared with pressure fusion welding and molecular diffusion welding, the surface flatness is relatively poor. Therefore, when the sealing portion does not cover the connection between the first welding tab and the first adapter, using ultrasonic welding can simplify the manufacturing process of the secondary battery and improve the manufacturing yield.

[0011] In an embodiment of the present application, the sealing portion includes a first sealing layer and a second sealing layer covering both sides of the first welding tab in the thickness direction, and the thickness of the first sealing layer and the second sealing layer is 80 μm to 100 μm. If the thickness of the first sealing layer and the second sealing layer is too small, the sealing effect of the sealing portion will be reduced, thereby reducing the production yield of the secondary battery. If the first sealing layer and the second sealing layer are too large, the proportion of the sealing layer in the overall quality of the secondary battery will be increased, thereby reducing the energy density of the secondary battery. Therefore, by controlling the thickness of the first sealing layer and the second sealing layer within the scope of this application, it is beneficial to improve the production yield of the secondary battery while taking into account the energy density of the secondary battery.

[0012] In an embodiment of the present application, the length of the sealing portion is 4 mm to 4.5 mm, the length of the first extension portion is greater than 0.4 mm, and the length of the second extension portion is 1 mm to 3 mm. The upper limit of the length of the first extension portion is related to the thickness of the electrode assembly. The first extension portion can reduce the risk that the force generated by the thickness expansion of the electrode assembly during charge and discharge is concentrated at the connection position of the first welding foil tab and the sealing portion. The greater the thickness of the electrode assembly, the greater the force generated by the thickness expansion during charge and discharge, and the longer the length of the first extension portion that needs to be reserved. However, if the length of the first extension portion is too long, resulting in an overly long size of the first foil tab, it will increase the risk of the first foil tab being folded or broken before forming the first welding foil tab. On the other hand, if the first extension portion is too short, there is a higher risk of liquid leakage due to deviation of the sealing position during sealing. Therefore, by controlling the length of the first extension portion within the scope of the present application, the production yield of the secondary battery can be improved, and at the same time, it is beneficial to improve the safety performance of the secondary battery. By controlling the lengths of the sealing portion and the second extension portion within the scope of the present application, the sealing portion and the second extension portion occupy a relatively small length dimension of the secondary battery, which is beneficial to improving the energy density of the secondary battery and is also beneficial for the secondary battery to be compatible with a smaller-length usage environment, thereby being beneficial to improving the usage performance of the secondary battery.

[0013] When the housing is an aluminum plastic film, the first welding foil tab extends out of the housing, and there are two setting methods for the second welding foil tab.

[0014] When the housing is made of an aluminum-plastic film, the first setting method of the second welding tab is that the second welding tab is bent and disposed inside the housing. The second electrode tab includes a second current collector. One side of each layer of the second current collector has a protruding second tab. A plurality of second tabs overlap in a direction perpendicular to the electrode tab. The plurality of second tabs are welded together to form a second welding tab. The second electrode tab is a positive electrode tab. The second welding tab is bent and placed inside the housing. The outermost layer of the electrode assembly is the second current collector. The aluminum-plastic film includes a polypropylene layer, a metal layer, and a nylon layer arranged in sequence from the inside to the outside in the thickness direction. The polypropylene layer in the first area of the aluminum-plastic film is removed to expose the metal layer. The second current collector on the outermost layer of the electrode assembly is connected to the first area through a conductive adhesive. Through the above settings, the manufacturing process of the secondary battery can be simplified, and the use of welding in the manufacturing process can be reduced, which is beneficial to improving the manufacturing yield. The conductive adhesive is disposed on one side where the first welding tab extends out of the housing and one side of the bending point of the second welding tab, which can reduce the relative displacement between the first welding tab and the housing when the secondary battery drops, thereby reducing the risk of the housing being damaged at the sealing part due to excessive displacement of the first welding tab when the secondary battery drops. It can also reduce the relative displacement between the first welding tab and the electrode assembly when the secondary battery drops, and at the same time reduce the relative displacement between the second welding tab and the electrode assembly when the secondary battery drops, reducing the risk of fracture at the bending part of the multi-layer tabs and the second welding tab, which is beneficial to improving the safety performance of the secondary battery. Moreover, since the conductive adhesive is connected after the polypropylene layer of the aluminum-plastic film is removed, it occupies less space in the thickness direction of the secondary battery, which is beneficial to improving the energy density of the secondary battery.

[0015] A preparation method of the above embodiments, preparing an electrode assembly; stacking a plurality of first tab ears of the electrode assembly; welding the plurality of first tab ears together in a first welding area to form a first welded tab ear, and the welding is carried out by pressure fusion welding or molecular diffusion welding; welding a plurality of second tab ears together to form a second welded tab ear; connecting the first welded tab ear with a first adapter in a second welding area; bending the second welded tab ear inside the housing, and the length of the second welded tab ear after bending does not exceed the thickness of the electrode assembly to reduce the risk of the second welded tab ear piercing the housing; after bending the second welded tab ear, adhesive tape can be used for fixation to limit the movement space of the second welded tab ear and further reduce the risk of the second welded tab ear piercing the housing; removing the polypropylene layer in the first area of the housing, coating conductive adhesive in the first area, and connecting the outermost second current collector of the electrode assembly close to the first welded tab ear with the first area of the housing through the conductive adhesive; extending the first welded tab ear out of the housing and sealing it with the housing in the first welding area to form a sealing part, and the sealing part covers the first welding area. Conducting the second electrode tab of the electrode assembly with conductive adhesive can simplify the manufacturing process. Using pressure fusion welding or molecular diffusion welding makes the height difference between the highest point and the lowest point of the first surface and the height difference between the highest point and the lowest point of the second surface of the first welded tab ear within the scope of this application. At this time, the flatness of the first welded tab ear is relatively high, and the risk of the first welded tab ear piercing the sealing part is small, and the housing can be directly sealed on the first welded tab ear, and the risk of liquid leakage after sealing is small. This application has no special limitation on the welding formation method of the second welded tab ear in the above preparation method, as long as the purpose of this application can be achieved. For example, one of pressure fusion welding, molecular diffusion welding, resistance welding, ultrasonic welding and laser welding can be used. This application has no special limitation on the electrical connection method between the housing and the outside after connecting the housing with conductive adhesive, as long as the purpose of this application can be achieved. For example, a connecting piece can be led out by laser welding on the outside of the housing for electrical connection.

[0016] When the housing is made of an aluminum-plastic film, the second setting method of the second welding tab is that the second welding tab extends out of the housing. The second electrode tab includes a second current collector, and one side of each layer of the second current collector has a protruding second tab. A plurality of second tabs overlap in a direction perpendicular to the electrode tab, and the plurality of second tabs are welded together in a third welding area to form a second welding tab; the third welding area includes a third surface and a fourth surface opposite to each other in the thickness direction. The height difference between the highest point and the lowest point on the third surface is less than 8 μm, and the height difference between the highest point and the lowest point on the fourth surface is less than 8 μm. By controlling the height difference between the highest point and the lowest point on the third surface and the height difference between the highest point and the lowest point on the fourth surface, the second welding tab has a relatively high flatness. In a soft-pack battery, sealing can be directly performed on the second welding tab when the housing is sealed, and the risk of liquid leakage after sealing is relatively small. There is no need to additionally transfer the connector inside the housing, and the risk of liquid leakage after sealing is relatively small. The above setting can simplify the manufacturing process of the secondary battery, and can also avoid problems such as over-welding or false-welding when welding the connector, reduce the risk of damage to the multi-layer tabs, thereby improving the manufacturing yield, and at the same time is beneficial to improving the safety performance of the secondary battery. Setting a connector inside the housing will occupy the space in the length direction and the thickness direction inside the housing. Through the above setting, there is no need to set a connector inside the housing. On the one hand, the secondary battery can be compatible with a usage environment with smaller dimensions in the length direction and / or the width direction, and on the other hand, it is beneficial to improve the energy density of the secondary battery, thereby being beneficial to improving the usage performance of the secondary battery.

[0017] After the second welding tab is formed, the second welding tab is connected to the aluminum-plastic film through a sealing portion. The second welding tab extends out of the housing, and the sealing portion covers at least a part of the third welding area. Compared with Method 1, the processing methods of the first welding tab and the second welding tab in Method 2 are the same, and the manufacturing process is more unified, which can further simplify the manufacturing process of the secondary battery.

[0018] A preparation method of the above embodiments, preparing an electrode assembly; stacking a plurality of first tab ears of the electrode assembly; welding the plurality of first tab ears together at a first welding area to form a first welded tab ear, and the welding is performed by pressure fusion welding or molecular diffusion welding; extending the first welded tab ear out of the housing and sealing it with the housing at the first welding area to form a first sealing portion, and the first sealing portion covers the first welding area; connecting the first welded tab ear with a first adapter at a second welding area; welding a plurality of second tab ears together at a third welding area to form a second welded tab ear, and the welding is performed by pressure fusion welding or molecular diffusion welding; extending the second welded tab ear out of the housing and sealing it with the housing at the third welding area to form a second sealing portion, and the second sealing portion covers the third welding area. By using pressure fusion welding or molecular diffusion welding, the height difference between the highest point and the lowest point on the first surface and the second surface of the first welded tab ear and the height difference between the highest point and the lowest point on the third surface and the fourth surface of the second welded tab ear are within the scope of this application. At this time, the flatness of the first welded tab ear and the second welded tab ear is relatively high, and the risk of piercing the sealing portion is small. The housing can be directly sealed on the first welded tab ear, and the risk of liquid leakage after sealing is small. While simplifying the production process, it is beneficial to improve the safety performance of the secondary battery.

[0019] In an embodiment of the present application, the secondary battery is a steel shell battery, and the secondary battery includes a pole column, and the first welding area is directly connected to the pole column. By directly connecting the first welding area of the first welded tab ear to the pole column, the manufacturing process can be simplified, and the size of the secondary battery in the length direction can be reduced, which is beneficial to improving the energy density of the secondary battery.

[0020] The secondary battery is a steel shell battery, the first welded tab ear is directly connected to the pole column, and there are two setting methods for the second welded tab ear.

[0021] When the secondary battery is a steel shell battery, the setting method A of the second welded tab ear is that the second welded tab ear is directly connected to the cell cover without being connected after being transferred, which can simplify the manufacturing process.

[0022] When the secondary battery is a steel shell battery, the setting method B of the second welding foil tab is that the second welding foil tab is bent and placed inside the shell. The outermost layer of the battery assembly is the second current collector, and the outermost second current collector is connected to the steel shell through conductive adhesive. By setting the conductive adhesive to conduct the second electrode tab of the electrode assembly, the manufacturing process of the secondary battery can be simplified, and the use of welding in the manufacturing process can be reduced, which is beneficial to improving the manufacturing yield. The conductive adhesive is set on one side of the bending point of the second welding foil tab, which can reduce the relative displacement between the second welding foil tab and the shell when the secondary battery drops, thereby reducing the risk of the shell being damaged due to excessive displacement of the second welding foil tab when the secondary battery drops. It is beneficial to reduce the risk of fracture at the bending part of the multi-layer tabs and the second welding foil tab, and is beneficial to improving the safety performance of the secondary battery. Compared with method A, method B uses conductive adhesive to achieve the conduction of the second tab, which can further simplify the manufacturing process, and the thickness of the conductive adhesive occupies less dimension in the thickness direction of the inside of the shell than the connection between the second welding foil tab and the shell cover, which is beneficial to improving the energy density of the secondary battery.

[0023] A preparation method of the above embodiments is as follows: prepare an electrode assembly; stack multiple first foil tabs of the electrode assembly; weld the multiple first foil tabs together in the first welding area to form a first welding foil tab, and the welding is carried out by pressure fusion welding or molecular diffusion welding; weld multiple second foil tabs together to form a second welding foil tab; directly connect the first welding area to the pole column; bend the second welding foil tab inside the shell, and the length of the second welding foil tab after bending does not exceed the thickness of the electrode assembly to reduce the occupation of the internal space of the shell by the second welding foil tab; after the second welding foil tab is bent, adhesive tape can be used for fixation to limit the movement space of the second welding foil tab; connect the outermost second current collector of the electrode assembly near the bending part of the second welding foil tab to the shell through conductive adhesive. By using pressure fusion welding or molecular diffusion welding, the height difference between the highest point and the lowest point on the first surface and the height difference between the highest point and the lowest point on the second surface of the first welding foil tab are within the scope of this application. At this time, the flatness of the first welding foil tab is relatively high, and the first welding foil tab can be directly used to connect to the pole column without considering the risk of poor contact between the first welding foil tab and the pole column due to the rough surface of the first welding foil tab. There is no special limitation on the welding method of the second welding foil tab in the above preparation method in this application, as long as the purpose of this application can be achieved. For example, one of ultrasonic welding and laser welding can be used.

[0024] In an embodiment of the present application, the thickness of the conductive adhesive is 5 μm to 10 μm. The conductive adhesive includes a conductive binder and conductive fillers. The conductive binder is selected from thermosetting adhesives, hot-melt adhesives or metal adhesives; based on the mass of the conductive adhesive, the content of the conductive fillers is 50% to 80%, and the conductive fillers are conductive particles with a diameter greater than 5 μm and less than 10 μm. The present application has no special restrictions on the conductive particles, as long as the purpose of the present application can be achieved. If the thickness of the conductive adhesive is too small, the adhesive force of the conductive adhesive will be reduced, increasing the risk of peeling of the conductive adhesive. The peeling of the conductive adhesive will cause a short circuit in the secondary battery. If the thickness of the conductive adhesive is too large, the energy density of the secondary battery will be reduced. If the content of the conductive fillers is too low, the conductive effect of the conductive adhesive will be reduced. If the content of the conductive fillers is too high, the content of the conductive binder will be insufficient, thus reducing the adhesive force of the conductive adhesive. The diameter of the conductive fillers should not be greater than the thickness of the conductive adhesive. If it is greater than the thickness of the conductive adhesive, the current collector connected to the conductive adhesive will be damaged. Therefore, through the above settings, while taking into account the energy density of the secondary battery, it is beneficial to improve the secondary safety performance.

[0025] In an embodiment of the present application, the peeling force between the multiple first foil ears in the first welded foil ear is greater than 1.5 N / mm. For a welded part, the peeling force refers to the force required to separate the welded part. Therefore, by controlling the peeling force between the multiple foil ears within the scope of the present application, the risk of short circuit caused by the separation of the welded part when the first welded foil ear is stressed can be reduced, which is beneficial to improving the safety performance of the secondary battery.

[0026] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has good use performance and safety performance.

[0027] Advantages of the present application:

[0028] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly and a housing. The electrode assembly includes multiple layers of first electrode tabs and multiple layers of second electrode tabs. The first electrode tabs and the second electrode tabs have opposite polarities. The first electrode tab includes a first current collector. One side of each first current collector has a protruding first foil tab. Multiple first foil tabs overlap along a direction perpendicular to the electrode tab. Multiple first foil tabs are welded together at a first welding area to form a first welded foil tab. The first welding area includes a first surface and a second surface opposite to each other in the thickness direction. The height difference between the highest point and the lowest point on the first surface is less than 8 μm, and the height difference between the highest point and the lowest point on the second surface is less than 8 μm. By controlling the height differences between the highest point and the lowest point on the first surface and the second surface within the scope of the present application, the flatness of the first welded foil tab is relatively high, and there is no need to additionally transfer through a transfer member within the housing. That is, in a soft-pack battery, when the housing is sealed, it can be directly carried out on the first welded foil tab, and the risk of liquid leakage after sealing is relatively small. In a steel-shell battery, the first welded foil tab can be directly used to connect with the pole column. The above settings can simplify the manufacturing process of the secondary battery, and can also avoid the problems of over-welding or false welding when welding the transfer member, reduce the risk of damage to multiple layers of pole ears, thereby improving the manufacturing yield, and at the same time is beneficial to improving the safety performance of the secondary battery. Setting a transfer member within the housing will occupy the space in the length direction and the thickness direction within the housing. Through the above settings, there is no need to set a transfer member within the housing. On the one hand, the secondary battery can be compatible with usage environments with smaller dimensions in the length direction and / or the width direction. On the other hand, it is beneficial to improve the energy density of the secondary battery, thereby being beneficial to improving the usage performance of the secondary battery.

[0029] Of course, it is not necessary for any product or method implementing the present application to simultaneously achieve all the above-mentioned advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0031] Figure 1 Schematic diagram of the structure of the first electrode tab in an implementation solution of the present application;

[0032] Figure 2 For Figure 1 Partial view of P of

[0033] Figure 3 Schematic diagram of the structure of the second electrode tab in another implementation solution of the present application;

[0034] Figure 4Schematic diagram of the first electrode tab structure in the third implementation of this application;

[0035] Figure 5 is Figure 4 a partial view of Q of;

[0036] Figure 6 Schematic diagram of the second electrode tab structure in the fourth implementation of this application;

[0037] Figure 7 Schematic diagram of the first electrode tab structure in the fifth implementation of this application;

[0038] Figure 8 Schematic diagram of the second electrode tab structure in the sixth implementation of this application.

[0039] The reference numerals are as follows:

[0040] Electrode assembly 10; First electrode tab 11; First current collector 111; First tab ear 1111; First welded tab ear 1112; First welding area 1112A; Second welding area 1112E; First surface 1112A1; Second surface 1112A2; First extension 1112B; Sealing part 1112C; First sealing layer 1112C1; Second sealing layer 1112C2; Second extension 1112D; Second electrode tab 12; Second current collector 121; Second tab ear 1211; Second welded tab ear 1212; Third welding area 1212A; Third surface 1212A1; Fourth surface 1212A2; Housing 13; Polypropylene layer 131; Metal layer 132; Nylon layer 133; Terminal 134; First area 135; First adapter 14; Conductive adhesive 16. Detailed implementation

[0041] Next, the technical solutions in this application will be clearly and completely described in conjunction with the embodiments of this application and the drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application belong to the scope of protection of this application.

[0042] This application provides a secondary battery, including an electrode assembly 10 and a housing 13, as Figure 1As shown, the electrode assembly 10 includes multiple layers of first electrode plates 11 and multiple layers of second electrode plates 12. The first electrode plates 11 and the second electrode plates 12 have opposite polarities. The first electrode plate 11 includes a first current collector 111. On one side of each first current collector 111, there is a protruding first tab 1111. Multiple first tabs 1111 overlap along the direction (Y direction) perpendicular to the electrode plate. Multiple first tabs are welded together in the first welding area 1112A to form a first welded tab 1112. The first welding area 1112A includes a first surface 1112A1 and a second surface 1112A2 that are opposite to each other in the thickness direction (Y direction). The height difference between the highest point and the lowest point on the first surface 1112A1 is less than 8 μm, and the height difference between the highest point and the lowest point on the second surface 1112A2 is less than 8 μm. Preferably, the height difference between the highest point and the lowest point on the first surface 1112A1 is less than 5 μm. By controlling the height differences between the highest point and the lowest point on the first surface 1112A1 and the second surface 1112A2 within the scope of this application, the flatness of the first welded tab 1112 is relatively high, and there is no need for additional transfer of the transfer piece within the housing 13. That is, as Figure 1 shown, in a soft-pack battery, when the housing 13 is sealed, it can be directly carried out on the first welded tab 1112, and the risk of liquid leakage after sealing is relatively small; as Figure 7 shown, in a steel-shell battery, the first welded tab 1112 can be directly used to connect with the terminal 134. The above settings can simplify the manufacturing process of the secondary battery, and can also avoid problems such as over-welding or false welding when welding the transfer piece, reduce the risk of damage to multiple layers of tabs, thereby improving the manufacturing yield, and at the same time is beneficial to improving the safety performance of the secondary battery. Setting a transfer piece within the housing 13 will occupy the space in the length direction and thickness direction within the housing. Through the above settings, there is no need to set a transfer piece within the housing 13. On the one hand, the secondary battery can be compatible with usage environments with smaller dimensions in the length direction and / or width direction, and on the other hand, it is beneficial to improve the energy density of the secondary battery, thereby being beneficial to improving the usage performance of the secondary battery.

[0043] In an implementation scheme of this application, as Figure 4 shown, the housing 13 is an aluminum-plastic film. The first welded tab 1112 is connected to the aluminum-plastic film (i.e., Figure 4 the housing 13 in Figure 5As shown, the first welding foil ear 1112 includes a first extension portion 1112B and a second extension portion 1112D, wherein the first extension portion 1112B is a portion extending from the sealing portion 1112C to the inside of the housing 13; and the second extension portion 1112D is a portion extending from the sealing portion 1112C to the outside of the housing 13. By directly arranging the sealing portion 1112C on the first welding foil ear 1112, the manufacturing process of the secondary battery can be simplified and the manufacturing rate can be improved. At the same time, compared with arranging the adapter inside the housing 13, the first extension portion 1112B occupies less space inside the housing 13, which is conducive to improving the energy density of the secondary battery.

[0044] In one embodiment of the present application, Figure 2 As shown, the first welding foil ear 1112 is welded to the first adapter 14 at the second welding area 1112E, the first welding area 1112A and the second welding area 1112E at least partially overlap, the sealing portion 1112C covers at least a portion of the second welding area 1112E, and the second welding area 1112E is the junction area between the first welding foil ear 1112 and the first adapter 14. By sealing the housing 13 at the junction of the first welding area 1112A and the second welding area 1112E, that is, at the connection between the first welding foil ear 1112 and the first adapter 14, the occupation of the overall size of the secondary battery by the connection between the first welding foil ear 1112 and the first adapter 14 can be reduced, which is conducive to improving the energy density of the secondary battery.

[0045] In one embodiment of the present application, a plurality of first foil ears 1111 are welded by pressure fusion welding or molecular diffusion welding to form a first welding foil ear 1112, and the first welding foil ear 1112 is connected to the first adapter 14 by pressure fusion welding or molecular diffusion welding. Both pressure fusion welding and molecular diffusion welding require pressurization for welding and do not require additional welding materials. At the same time, both have the characteristics of high precision, high welding strength, small welding defects and small thermal impact. Due to the small welding defects and small thermal impact of pressure fusion welding and molecular diffusion welding, the flatness of the first welding area 1112A and the second welding area 1112E is relatively high, and the shell can be sealed at the junction of the first welding area 1112A and the second welding area 1112E, that is, the connection between the first welding foil ear 1112 and the first adapter 14. At this time, the risk of damage to the sealing portion 1112C and the risk of leakage of the secondary battery are relatively small, thereby improving the manufacturing rate while improving the safety performance of the secondary battery.

[0046] In one embodiment of the present application, Figure 5As shown, the first welding tab 1112 and the first adapter 14 are welded at the second welding area 1112E, and the second welding area 1112E is provided on the second extension 1112D. By providing the second welding area 1112E on the second extension 1112D, the manufacturing process of the secondary battery can be simplified.

[0047] In an embodiment of the present application, the first welding tab 1112 and the first adapter 14 are connected by ultrasonic welding. Ultrasonic welding features a simple process, but has a relatively poor surface flatness compared to pressure fusion welding and molecular diffusion welding. Therefore, when the sealing portion 1112C does not cover the connection between the first welding tab 1112 and the first adapter 14, using ultrasonic welding can simplify the manufacturing process of the secondary battery and improve the manufacturing yield.

[0048] In an embodiment of the present application, as Figure 5 shown, the sealing portion 1112C includes a first sealing layer 1112C1 and a second sealing layer 1112C2 that cover both sides of the first welding tab 1112 in the thickness direction (Y direction). The thickness of the first sealing layer 1112C1 and the second sealing layer 1112C2 is 80 μm to 100 μm. If the thickness of the first sealing layer 1112C1 and the second sealing layer 1112C2 is too small, the sealing effect of the sealing portion 1112C will be reduced, thereby reducing the production yield of the secondary battery. If the first sealing layer 1112C1 and the second sealing layer 1112C2 are too large, the proportion of the sealing layer 1112C in the overall mass of the secondary battery will increase, thereby reducing the energy density of the secondary battery. Therefore, by controlling the thickness of the first sealing layer 1112C1 and the second sealing layer 1112C2 within the scope of this application, it is beneficial to improve the production yield of the secondary battery while taking into account the energy density of the secondary battery.

[0049] In an embodiment of the present application, as Figure 5As shown, the length A1 of the sealing part 1112C is 4 mm to 4.5 mm, the length A2 of the first extension part 1112B is greater than 0.4 mm, and the length A3 of the second extension part 1112D is 1 mm to 3 mm. For example, the length of the sealing part can be 4 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, 4.5 mm or a range composed of any two of these values. For example, the length of the second extension part can be 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm or a range composed of any two of these values. The upper limit of the length of the first extension part 1112B is related to the thickness of the electrode assembly 10. The first extension part 1112B can reduce the risk that the force generated by the thickness expansion of the electrode assembly 10 during charge and discharge is concentrated at the connection position of the first welding foil tab 1112 and the sealing part 1112C. The greater the thickness of the electrode assembly, the greater the force generated by the thickness expansion during charge and discharge, and the longer the length of the first extension part 1112B that needs to be reserved. However, if the reserved dimension of the first extension part 1112B is too long, resulting in too long a dimension of the first foil tab 1111, it will increase the risk of the first foil tab 1111 being folded or broken before forming the first welding foil tab 1112. If the first extension part 1112B is too short, the risk of liquid leakage due to the deviation of the sealing position during sealing is higher. Therefore, by controlling the length of the first extension part 1112B within the scope of this application, the production yield of the secondary battery can be improved, and at the same time, it is beneficial to improve the safety performance of the secondary battery. By controlling the lengths of the sealing part 1112C and the second extension part 1112D within the scope of this application, the sealing part 1112C and the second extension part 1112D occupy a relatively small length dimension of the secondary battery, which is beneficial to improving the energy density of the secondary battery and is also beneficial to the secondary battery being compatible with a smaller length usage environment, thereby being beneficial to improving the usage performance of the secondary battery.

[0050] When the housing 13 is an aluminum plastic film, the first welding foil tab 1112 extends out of the housing 13, and there are two setting methods for the second welding foil tab 1212.

[0051] When the housing 13 is an aluminum plastic film, the first setting method of the second welding foil tab 1212 is that the second welding foil tab 1212 is bent and arranged inside the housing 13. As Figure 6As shown, the second electrode tab 12 includes a second current collector 121. One side of each layer of the second current collector 121 has a protruding second tab ear 1211. A plurality of second tab ears 1211 overlap in a direction (Y direction) perpendicular to the electrode tab. The plurality of second tab ears 1211 are welded together to form a second welded tab ear 1212. The second electrode tab 12 is a positive electrode tab. The second welded tab ear 1212 is bent and placed inside the housing 13. The outermost layer of the electrode assembly 10 is the second current collector 121. The aluminum-plastic film includes a polypropylene layer 131, a metal layer 132, and a nylon layer 133 arranged in sequence from the inside to the outside in the thickness direction. The polypropylene layer 131 of the first region 135 of the aluminum-plastic film is removed to expose the metal layer 132. The outermost second current collector 121 is connected to the first region 135 through a conductive adhesive 16. Through the above arrangement, the manufacturing process of the secondary battery can be simplified, and the use of welding in the manufacturing process can be reduced, which is beneficial to improving the manufacturing yield. As Figure 1 shown, the conductive adhesive 16 is disposed on one side of the first welded tab ear 1112 extending out of the housing 13, as Figure 6 shown, the conductive adhesive 16 is disposed on one side of the bending point of the second welded tab ear 1212, which can reduce the relative displacement between the first welded tab ear 1112 and the housing 13 when the secondary battery drops, thereby reducing the risk of the housing 13 being damaged at the sealing portion 1112C due to excessive displacement of the first welded tab ear 1112 when the secondary battery drops. It can also reduce the relative displacement between the first welded tab ear 1112 and the electrode assembly 10 when the secondary battery drops, and at the same time reduce the relative displacement between the second welded tab ear 1212 and the electrode assembly 10 when the secondary battery drops, reducing the risk of breakage at the bending portion of the multi-layer tab ears 111 and the second welded tab ear 1212, which is beneficial to improving the safety performance of the secondary battery. Moreover, since the conductive adhesive 16 is connected after the polypropylene layer 131 of the aluminum-plastic film is removed, it occupies less space in the thickness direction of the secondary battery, which is beneficial to improving the energy density of the secondary battery.

[0052] A preparation method of the above-described implementation scheme, preparing the electrode assembly 10; laminating a plurality of first tab ears 1111 of the electrode assembly 10; welding the plurality of first tab ears 1111 together at the first welding area 1112A to form a first welded tab ear 1112, and the welding is carried out by pressure fusion welding or molecular diffusion welding; welding a plurality of second tab ears 1211 together to form a second welded tab ear 1212; connecting the first welded tab ear 1112 to the first adapter 14 at the second welding area 1112E; bending the second welded tab ear 1212 inside the housing 13, and the length of the second welded tab ear 1212 after bending does not exceed the thickness of the electrode assembly 10 to reduce the risk of the second welded tab ear 1212 piercing the housing 13; after bending the second welded tab ear 1212, adhesive tape can be used for fixation to limit the movement space of the second welded tab ear 1212 and further reduce the risk of the second welded tab ear 1212 piercing the housing 13; removing the polypropylene layer 131 in the first area 135 of the housing 13, coating conductive adhesive 16 in the first area 135, and connecting the outermost second current collector 121 of the electrode assembly 10 close to the first welded tab ear to the first area 135 of the housing 13 through the conductive adhesive 16; extending the first welded tab ear 1112 out of the housing 13 and sealing it with the housing 13 at the first welding area 1112A to form a sealing part 1112C, and the sealing part 1112C covers the first welding area 1112A. Conducting the second electrode tab 12 of the electrode assembly 10 by using the conductive adhesive 16 can simplify the manufacturing process. Using pressure fusion welding or molecular diffusion welding makes the height difference between the highest point and the lowest point of the first surface 1112A1 of the first welded tab ear 1112 and the height difference between the highest point and the lowest point of the second surface 1112A2 within the scope of this application. At this time, the flatness of the first welded tab ear 1112 is relatively high, and the risk of the first welded tab ear 1112 piercing the sealing part 1112C is small, so the housing 13 can be directly sealed on the first welded tab ear 1112, and the risk of liquid leakage after sealing is small. This application does not particularly limit the welding formation method of the second welded tab ear 1212 in the above preparation method, as long as the purpose of this application can be achieved. For example, one of pressure fusion welding, molecular diffusion welding, resistance welding, ultrasonic welding, and laser welding can be used. This application does not particularly limit the electrical connection method between the housing 13 and the outside after connecting the housing 13 with the conductive adhesive 16, as long as the purpose of this application can be achieved. For example, a connection piece can be led out by laser welding on the outside of the housing for electrical connection.

[0053] When the housing 13 is an aluminum plastic film, the setting method 2 of the second welded tab ear 1212 is that the second welded tab ear 1212 extends out of the housing 13. As Figure 3As shown in the figure, the second electrode tab 12 includes a second current collector 121. One side of each layer of the second current collector 121 has a protruding second foil tab 1211. A plurality of second foil tabs 1211 overlap along the direction (Y direction) perpendicular to the electrode tab. A plurality of second foil tabs 1211 are welded together at the third welding area 1212A to form a second welded foil tab 1212. The third welding area 1212A includes a third surface 1212A1 and a fourth surface 1212A2 that are opposite to each other in the thickness direction (Y direction). The height difference between the highest point and the lowest point on the third surface 1212A1 is less than 8 μm, and the height difference between the highest point and the lowest point on the fourth surface 1212A2 is less than 8 μm. By controlling the height difference between the highest point and the lowest point on the third surface 1212A1 and the height difference between the highest point and the lowest point on the fourth surface 1212A2, the second welded foil tab 1212 has a relatively high flatness. As Figure 3 shown, in a soft-pack battery, when the housing 13 is sealed, it can be directly performed on the second welded foil tab 1212, and the risk of liquid leakage after sealing is relatively small. There is no need to additionally transfer components inside the housing 13, and the risk of liquid leakage after sealing is relatively small. The above settings can simplify the manufacturing process of the secondary battery, and can also avoid problems such as over-welding or false welding when welding the transfer component, reduce the risk of damage to the multi-layer tabs, thereby improving the manufacturing yield, and at the same time is beneficial to improving the safety performance of the secondary battery. Setting a transfer component inside the housing will occupy the space in the length direction and thickness direction of the housing 13. Through the above settings, there is no need to set a transfer component inside the housing 13. On the one hand, the secondary battery can be compatible with a usage environment with smaller dimensions in the length direction and / or width direction, and on the other hand, it is beneficial to improve the energy density of the secondary battery, thereby being beneficial to improving the usage performance of the secondary battery.

[0054] After the second welded foil tab 1212 is formed, as Figure 3 shown, the housing 13 is an aluminum-plastic film. The second welded foil tab 1212 is connected to the aluminum-plastic film through the sealing part 1112C. The second welded foil tab 1212 extends out of the housing, and the sealing part 1112C covers at least part of the third welding area 1212A. Compared with Method 1, the processing methods of the first welded foil tab 1112 and the second welded foil tab 1212 are the same, and the manufacturing process is more unified, which can further simplify the manufacturing process of the secondary battery.

[0055] A preparation method of the above embodiment comprises preparing an electrode assembly 10; overlapping a plurality of first foil ears 1111 of the electrode assembly 10; welding the plurality of first foil ears 1111 together in a first welding region 1112A to form a first welded foil ear 1112, wherein the welding is performed by pressure fusion welding or molecular diffusion welding; extending the first welded foil ear 1112 out of the shell 13, and sealing the first welded foil ear 1112A with the shell 13 to form a first sealing portion, wherein the first sealing portion covers the first welded foil ear 1112A; connecting the first welded foil ear 1112 with the first adapter 14 in a second welded foil region 1112E; welding a plurality of second foil ears 1211 together in a third welded foil region 1212A to form a second welded foil ear 1212, wherein the welding is performed by pressure fusion welding or molecular diffusion welding; extending the second welded foil ear 1212 out of the shell 13, and sealing the second welded foil ear 1212 with the shell 13 in a third welded foil region 1212A to form a second sealing portion, wherein the second sealing portion covers the third welded foil region 1212A. By using pressure fusion welding or molecular diffusion welding, the height difference between the highest point and the lowest point on the first surface 1112A1 of the first welding foil ear 1112 and the height difference between the highest point and the lowest point on the second surface 1112A2, as well as the height difference between the highest point and the lowest point on the third surface 1212A1 of the second welding foil ear 1212 and the height difference between the highest point and the lowest point on the fourth surface 1212A2 are within the scope of the present application. At this time, the first welding foil ear 1112 and the second welding foil ear 1212 have higher flatness and lower risk of puncturing the sealing part. The shell 13 can be sealed directly on the first welding foil ear 1112, and the risk of leakage after sealing is lower. While simplifying the production process, it is beneficial to improve the safety performance of the secondary battery.

[0056] In one embodiment of the present application, Figure 7 As shown, the secondary battery is a steel shell battery, the secondary battery includes a pole 134, and the first welding area 1112A is directly connected to the pole 134. By directly connecting the first welding area 1112A of the first welding foil ear 1112 to the pole 134, the manufacturing process can be simplified, and the size of the secondary battery in the length direction can be reduced, which is conducive to improving the energy density of the secondary battery.

[0057] The secondary battery is a steel shell battery, the first welding foil ear 1112 is directly connected to the pole 134, and the second welding foil ear 1212 has two configuration modes.

[0058] When the secondary battery is a steel shell battery, the arrangement mode A of the second welding foil ear 1212 is that the second welding foil ear 1212 is directly connected to the shell cover without the need for switching and then connecting, which can simplify the manufacturing process.

[0059] When the secondary battery is a steel shell battery, the arrangement mode B of the second welding foil ear 1212 is that the second welding foil ear 1212 is bent and placed inside the shell 13. Figure 8As shown, the second welding tab 1212 is bent and placed inside the steel shell 13. The outermost layer of the battery assembly is the second current collector 121, and the outermost second current collector 121 is connected to the steel shell 13 through the conductive adhesive 16. By providing the conductive adhesive 16 to conduct the second electrode tab of the electrode assembly, the manufacturing process of the secondary battery can be simplified, and the use of welding in the manufacturing process can be reduced, which is beneficial to improving the manufacturing yield. As Figure 8 shown, the conductive adhesive 16 is provided on one side of the bending point of the second welding tab 1212, which can reduce the relative displacement between the second welding tab 1212 and the shell 13 when the secondary battery drops, which is beneficial to reducing the risk of fracture at the bending part of the multi-layer tabs 111 and the second welding tab 1212, and is beneficial to improving the safety performance of the secondary battery. Compared with Method A, using the conductive adhesive 16 to achieve the conduction of the second tab 12 can further simplify the manufacturing process, and the thickness of the conductive adhesive 16 occupies less dimension in the thickness direction of the interior of the shell than the connection between the second welding tab 1212 and the cover, which is beneficial to improving the energy density of the secondary battery.

[0060] A preparation method of the above-mentioned implementation scheme is as follows: prepare the electrode assembly 10; stack a plurality of first tabs 1111 of the electrode assembly 10; weld the plurality of first tabs 1111 together at the first welding area 1112A to form the first welding tab 1112, and the welding is carried out by pressure fusion welding or molecular diffusion welding; weld a plurality of second tabs 1211 together to form the second welding tab 1212; directly connect the first welding area 1112A to the terminal 134; bend the second welding tab 1212 inside the shell 13, and the length of the second welding tab 1212 after bending does not exceed the thickness of the electrode assembly 10 to reduce the occupation of the interior space of the shell 13 by the second welding tab 1212; after the second welding tab 1212 is bent, adhesive tape can be used for fixation to limit the movement space of the second welding tab 1212; connect the outermost second current collector 121 of the electrode assembly 10 near the bending part of the second welding tab 1212 to the shell 13 through the conductive adhesive 16. By using pressure fusion welding or molecular diffusion welding, the height difference between the highest point and the lowest point of the first surface 1112A1 of the first welding tab 1112 and the height difference between the highest point and the lowest point of the second surface 1112A2 are within the scope of this application. At this time, the flatness of the first welding tab 1112 is relatively high, and the first welding tab 1112 can be directly connected to the terminal 134 without considering the risk of poor contact between the first welding tab 1112 and the terminal 134 due to the rough surface of the first welding tab 1112. There is no special limitation on the welding method of the second welding tab 1212 in the above preparation method of this application, as long as the purpose of this application can be achieved. For example, one of ultrasonic welding and laser welding can be used.

[0061] In an embodiment of the present application, the thickness of the conductive adhesive is 5 μm to 10 μm. The conductive adhesive includes a conductive binder and conductive fillers. The conductive binder is selected from thermosetting adhesives, hot-melt adhesives or metal adhesives; based on the mass of the conductive adhesive, the content of the conductive fillers is 50% to 80%, and the conductive fillers are conductive particles with a diameter greater than 5 μm and less than 10 μm. For example, the value of the thickness of the conductive adhesive can be 5, 6, 7, 8, 9, 10 or a range composed of any two of these values. For example, the content of the conductive fillers can be 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range composed of any two of these values. For example, the value of the diameter of the conductive fillers can be 5, 6, 7, 8, 9, 10 or a range composed of any two of these values. The present application has no particular limitation on the conductive particles, as long as the purpose of the present application can be achieved. For example, the conductive particles can be selected from one of silver, copper or carbon. If the thickness of the conductive adhesive is too small, the adhesion of the conductive adhesive will be reduced, increasing the risk of peeling of the conductive adhesive. The peeling of the conductive adhesive will cause a short circuit in the secondary battery. If the thickness of the conductive adhesive is too large, the energy density of the secondary battery will be reduced. If the content of the conductive fillers is too low, the conductivity of the conductive adhesive will be reduced. If the content of the conductive fillers is too high, the content of the conductive binder will be insufficient, thus reducing the adhesion of the conductive adhesive. The diameter of the conductive fillers should not be greater than the thickness of the conductive adhesive. If it is greater than the thickness of the conductive adhesive, the current collector connected to the conductive adhesive will be damaged. Therefore, through the above settings, while taking into account the energy density of the secondary battery, it is beneficial to improve the secondary safety performance.

[0062] In an embodiment of the present application, the peeling force between the multiple first foil ears 1111 in the first welded foil ear 1112 is greater than 1.5 N / mm. For a welded part, the peeling force refers to the force required to separate the welded part. Therefore, by controlling the peeling force between the multiple foil ears within the scope of the present application, the risk of short circuit caused by the separation of the welded part when the first welded foil ear is stressed can be reduced, which is beneficial to improving the safety performance of the secondary battery.

[0063] The present application has no particular limitation on the secondary battery, and it can be any secondary battery well-known in the art. For example, it can be a lithium-ion battery.

[0064] The present application has no particular limitation on the electrode assembly, and it can be any electrode assembly well-known in the art. For example, it can be a laminated or wound electrode assembly.

[0065] The housing is used to accommodate the first electrode plate, the separator, the second electrode plate and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above other components.

[0066] In the second aspect of the present application, an electronic device is provided, which includes the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has good use performance and safety performance.

[0067] The electronic device 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 may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor.

[0068] Example

[0069] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0070] Testing method and equipment:

[0071] Height difference test:

[0072] Disassemble the secondary battery in an environment of normal temperature and humidity less than 20%, and cut off the first welded foil tab; paste the first welded foil tab onto a glass plate or a bakelite plate with double-sided tape to make a sample; place the sample on the stage of a 3D profile measuring instrument VR-3000. Under the 5X lens, move the sample into the field of view and preliminarily adjust the sample angle. Switch to the 20X lens and adjust the sample angle so that the horizontal row points of the sample are parallel to the upper part of the field of view; rotate the XY direction knob of the platform to move the measurement position to the upper left corner, avoiding the first row and the first column; select the laser confocal mode, perform measurement and collect images; after the image collection is completed, use the analysis software to select the just-collected image and perform multi-point processing to obtain the result.

[0073] Red ink penetration test:

[0074] Directly apply red ink on the surface of the secondary battery and let it stand for 1 to 2 hours to penetrate by capillary action. If the color of the externally coated area fades, it may be due to leakage and the ink is sucked in. Then disassemble the secondary battery in an environment of humidity less than 1% and observe. If the separator and the electrode sheet are stained after disassembly, it indicates that the red ink has penetrated into the interior of the housing, that is, there is a liquid leakage channel.

[0075] Measure 10 samples in each group, calculate the red ink penetration situation, and the red ink penetration situation = the number of batteries without red ink penetration / 10.

[0076] Example 1-1

[0077] <Preparation of the positive electrode sheet>

[0078] The positive active material LiCoO2, the conductive agent Super P, and the binder polyvinylidene fluoride are mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75 wt%. After vacuum stirring evenly, a positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm and dried at 120 °C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. The coating weight of the positive electrode material layer is 267.8 mg / 1540 mm 2 。Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. After drying at 120 °C, it is cold-pressed, and then a second tab is formed by cutting to obtain a positive electrode sheet with a specification of 74 mm × 867 mm for use. Among them, the thickness of the single-sided positive electrode material layer is 42 μm.

[0079] <Preparation of the negative electrode sheet>

[0080] The negative active material artificial graphite, the binder styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97.4:1.4:1.2, and deionized water is added as a solvent to prepare a slurry with a solid content of 45 wt%. After being stirred evenly by a vacuum mixer, a negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm and dried at 120 °C to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. The coating weight of the negative electrode material layer is 142 mg / 1540 mm 2 。Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode material layer. After drying at 120 °C, it is cold-pressed, and then a first tab is formed by cutting to obtain a negative electrode sheet with a specification of 78 mm × 875 mm for use. Among them, the thickness of the single-sided negative electrode material layer is 54.5 μm.

[0081] <Preparation of the electrolyte>

[0082] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then the electrolyte salt LiPF6 is added to the organic solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content of the electrolyte salt is 12.5%, and the rest is the organic solvent.

[0083] <Separator>

[0084] A porous polyethylene film with a thickness of 7 μm (provided by Celgard) is used as the separator.

[0085] <Preparation of Conductive Adhesive>

[0086] Add 60% conductive filler to the epoxy resin thermosetting adhesive and stir at low speed (500 - 1000 rpm) for preliminary mixing. Then use a high-speed homogenizer (2000 - 5000 rpm) for forced dispersion to avoid filler agglomeration. Among them, the conductive filler is copper particles with a diameter of 8 μm.

[0087] <Preparation of Lithium-Ion Battery>

[0088] Stack the positive electrode plate, separator, and negative electrode plate prepared above in sequence, with the separator placed between the positive electrode plate and the negative electrode plate to play an isolation role, and the positive electrode plate is located on the outermost layer. There is no positive electrode material layer on the outer side of the outermost positive electrode plate. Wind it to obtain an electrode assembly. Stack multiple first foil ears of the electrode assembly and then weld them together in the first welding area to form a first welded foil ear. The welding is carried out by pressure fusion welding or molecular diffusion welding. Weld multiple second foil ears together to form a second welded foil ear. Place the electrode assembly into an aluminum-plastic film packaging bag, extend the first welded foil ear out of the packaging bag, and bend the second welded foil ear inside the packaging bag. Remove the polypropylene layer from the first area of the aluminum-plastic film, and connect the outermost positive electrode plate of the electrode assembly to the first area through a 9-μm-thick conductive adhesive. Remove moisture at 80°C, inject the electrolyte prepared above, seal it at the first welding area of the first welded foil ear, and then obtain a lithium-ion battery through processes such as standing, formation, degassing, and trimming. Among them, the upper limit voltage of formation is 4.15 V, the formation temperature is 70°C, and the formation standing time is 2 h.

[0089] Examples 1 - 2

[0090] Except for the different preparation methods of the lithium-ion battery, the rest are the same as in Example 1 - 1. The preparation method of the lithium-ion battery is as follows.

[0091] <Preparation of Lithium-Ion Battery>

[0092] Stack the above-prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an insulating role, and the positive electrode sheet located on the outermost layer, and wind them to obtain an electrode assembly. Stack multiple first foil tabs of the electrode assembly, and then weld them together in the first welding area to form a first welded foil tab, and the welding is carried out by pressure fusion welding or molecular diffusion welding. Stack multiple second foil tabs of the electrode assembly, and then weld them together in the third welding area to form a second welded foil tab, and the welding is carried out by pressure fusion welding or molecular diffusion welding. Place the electrode assembly into an aluminum-plastic film packaging bag, with the first welded foil tab and the second welded foil tab protruding from the packaging bag, remove moisture at 80°C, inject the above-prepared electrolyte, seal at the first welding area of the first welded foil tab and the third welding area of the second welded foil tab, and then obtain a lithium-ion battery through processes such as standing, formation, degassing, and trimming. Among them, the upper limit voltage of formation is 4.15V, the formation temperature is 70°C, and the formation standing time is 2h.

[0093] Examples 1 - 3

[0094] Except for the different preparation methods of the lithium-ion battery, the rest are the same as in Examples 1 - 1. The preparation method of the lithium-ion battery is as follows.

[0095] <Preparation of Lithium-Ion Battery>

[0096] Stack the above-prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an insulating role, and the positive electrode sheet located on the outermost layer. There is no positive electrode material layer on the outer side of the outermost positive electrode sheet, and wind them to obtain an electrode assembly. Stack multiple first foil tabs of the electrode assembly, and then weld them together in the first welding area to form a first welded foil tab, and the welding is carried out by pressure fusion welding or molecular diffusion welding. Weld multiple second foil tabs together to form a second welded foil tab. Place the electrode assembly into a steel shell, connect the first welded foil tab to the pole column, and bend the second welded foil tab inside the shell. Connect the outermost positive electrode sheet of the electrode assembly to the steel shell through a 9μm conductive adhesive. Remove moisture at 80°C, inject the above-prepared electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, degassing, and trimming. Among them, the upper limit voltage of formation is 4.15V, the formation temperature is 70°C, and the formation standing time is 2h.

[0097] Comparative Example 1

[0098] Except that ultrasonic welding is used for welding, the rest are the same as in Examples 1 - 1.

[0099] Comparative Example 2

[0100] Except that ultrasonic welding is used for welding the first welded foil tab, the rest are the same as in Example 1 - 2.

[0101] The performance parameters of each example and comparative example are shown in Table 1.

[0102] Table 1

[0103] Height difference (μm) Red ink penetration (%) Example 1-1 3μm 0％ Example 1-2 5μm 0％ Example 1-3 8μm 0％ Comparative example 1 9μm 20％ Comparative example 2 10μm 30％

[0104] It can be seen from Example 1-1 to Example 1-3 and Comparative Example 1 to Comparative Example 2 that by welding a plurality of first foil tabs of the multi-layer first electrode sheet in the first welding area to form a first welded foil tab, and controlling the height difference between the highest point and the lowest point of the first surface and the second surface of the first welded foil tab within the scope of this application, the manufacturing yield can be improved. In Comparative Example 1 to Comparative Example 2, the number of batteries with red ink infiltrating into the housing is relatively large, indicating that the sealing performance of the battery is poor.

[0105] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery, comprising an electrode assembly and a housing, characterized in that, The electrode assembly includes multiple layers of first electrode plates and multiple layers of second electrode plates. The first electrode plates and the second electrode plates have opposite polarities. The first electrode plate includes a first current collector. On one side of each first current collector, there is a protruding first tab. A plurality of the first tabs overlap along a direction perpendicular to the electrode plate, and the plurality of first tabs are welded together in a first welding area to form a first welded tab. The first welding area includes a first surface and a second surface opposite to each other in the thickness direction. The height difference between the highest point and the lowest point on the first surface is less than 8 μm, and the height difference between the highest point and the lowest point on the second surface is less than 8 μm.

2. The secondary battery according to claim 1, characterized in that, The housing is an aluminum-plastic film. The first welded tab is connected to the aluminum-plastic film through a sealing part. The first welded tab extends out of the housing. The sealing part covers at least part of the first welding area. The first welded tab includes a first extension part and a second extension part. The first extension part is the part extending from the sealing part into the housing, and the second extension part is the part extending from the sealing part out of the housing.

3. The secondary battery according to claim 2, wherein The first welded tab is welded to the first adapter in a second welding area. The first welding area and the second welding area at least partially overlap, and the sealing part covers at least part of the second welding area.

4. The secondary battery according to claim 3, characterized in that, A plurality of the first tabs are welded to form the first welded tab by pressure fusion welding or molecular diffusion welding, and the first welded tab is connected to the first adapter by pressure fusion welding or molecular diffusion welding.

5. The secondary battery according to claim 2, wherein The first welded tab is welded to the first adapter in a second welding area, and the second welding area is arranged on the second extension part.

6. The secondary battery according to claim 5, wherein The first welded tab is connected to the first adapter by ultrasonic welding.

7. The secondary battery according to claim 2, characterized in that, The sealing part includes a first sealing layer and a second sealing layer covering both sides of the first welded tab in the thickness direction. The thickness of the first sealing layer and the second sealing layer is 80 μm to 100 μm.

8. The secondary battery according to claim 2, wherein The length of the sealing part is 4 mm to 4.5 mm, the length of the first extension part is greater than 0.4 mm, and the length of the second extension part is 1 mm to 3 mm.

9. The secondary battery according to any one of claims 2 to 8, characterized in that, The second electrode plate includes a second current collector. On one side of each second current collector, there is a protruding second tab. A plurality of the second tabs overlap along a direction perpendicular to the electrode plate, and the plurality of second tabs are welded together to form a second welded tab. The second electrode plate is a positive electrode plate. The second welded tab is bent and placed inside the housing. The outermost layer of the electrode assembly is the second current collector. The aluminum-plastic film includes a polypropylene layer, a metal layer, and a nylon layer arranged in sequence from the inside to the outside in the thickness direction. The polypropylene layer in a first area of the aluminum-plastic film is removed to expose the metal layer. The second current collector of the outermost layer of the electrode assembly is connected to the first area through a conductive adhesive.

10. The secondary battery according to claim 1, characterized in that, The secondary battery is a steel shell battery. The secondary battery includes a terminal post, and the first welding area is directly connected to the terminal post.

11. The secondary battery according to claim 10, wherein The second welded tab is bent and placed inside the steel shell housing. The outermost layer of the battery assembly is the second current collector, and the outermost second current collector is connected to the steel shell housing through a conductive adhesive.

12. The secondary battery according to claim 11, wherein The thickness of the conductive adhesive is 5 μm to 10 μm. The conductive adhesive includes a conductive binder and a conductive filler. The conductive binder is selected from thermosetting glue, hot-melt glue or metal adhesive; based on the mass of the conductive adhesive, the content of the conductive filler is 50% to 80%, and the conductive filler is a conductive particle with a diameter greater than 5 μm and less than 10 μm.

13. The secondary battery according to claim 1, characterized in that, The second electrode tab includes a second current collector. One side of each layer of the second current collector has a protruding second tab. A plurality of the second tabs overlap in a direction perpendicular to the electrode tab, and a plurality of the second tabs are welded together in a third welding area to form a second welded tab; the third welding area includes a third surface and a fourth surface opposite to each other in the thickness direction. The height difference between the highest point and the lowest point on the third surface is less than 8 μm, and the height difference between the highest point and the lowest point on the fourth surface is less than 8 μm.

14. The secondary battery according to claim 13, wherein The housing is an aluminum-plastic film. The second welded tab is connected to the aluminum-plastic film through a sealing part. The second welded tab extends out of the housing, and the sealing part covers at least part of the third welding area.

15. The secondary battery according to claim 1, wherein The peeling force between multiple layers of the first tabs in the first welded tab is greater than 1.5 N / mm.

16. The secondary battery according to claim 1, wherein The height difference between the highest point and the lowest point on the first surface is less than 5 μm.

17. An electronic device, which includes the secondary battery according to any one of claims 1 to 16.

18. A method for preparing a secondary battery according to claim 9, characterized in that, Prepare an electrode assembly; Stack a plurality of first tabs of the electrode assembly; Weld a plurality of the first tabs together in the first welding area to form the first welded tab. The welding is performed by pressure fusion welding or molecular diffusion welding; Weld a plurality of the second tabs together to form the second welded tab; Extend the first welded tab out of the housing and seal it with the housing in the first welding area to form a sealing part. The sealing part covers the first welding area; Connect the first welded tab to the first adapter in the second welding area.

19. The preparation method according to claim 18, characterized in that: The preparation method further includes bending the second welded tab inside the housing; removing the polypropylene layer in the first area inside the housing, and connecting the second current collector on the outermost layer of the electrode assembly to the first area of the housing through a conductive adhesive.

20. A method for preparing a secondary battery according to claim 10, characterized in that, Prepare an electrode assembly; Stack a plurality of first tabs of the electrode assembly; Weld a plurality of the first tabs together in the first welding area to form the first welded tab. The welding is performed by pressure fusion welding or molecular diffusion welding; Weld a plurality of the second tabs together to form the second welded tab; Directly connect the first welding area to the pole post; Bend the second welded tab inside the housing; Connect the second current collector on the outermost layer of the electrode assembly to the housing through a conductive adhesive.

21. A method for manufacturing a secondary battery according to claim 14, characterized in that Manufacture an electrode assembly; Stack multiple first foil tabs of the electrode assembly; Weld the multiple first foil tabs together in the first welding area to form the first welded foil tab, and the welding is performed by pressure fusion welding or molecular diffusion welding; Extend the first welded foil tab out of the housing and seal it with the housing in the first welding area to form a first sealing portion, and the first sealing portion covers the first welding area; Connect the first welded foil tab to the first adapter in the second welding area; Weld multiple second foil tabs together in the third welding area to form the second welded foil tab, and the welding is performed by pressure fusion welding or molecular diffusion welding; Extend the second welded foil tab out of the housing and seal it with the housing in the third welding area to form a second sealing portion, and the second sealing portion covers the third welding area.

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