Secondary battery and electrochemical device

Abstract

The invention discloses a secondary battery and an electrochemical device, the secondary battery comprises a cathode pole piece, an anode pole piece and a diaphragm, the cathode pole piece comprises a first cathode layer, the first cathode layer comprises a cathode tab and a cathode current collector, two sides of the anode current collector are respectively provided with a first cathode active material layer and a second cathode active material layer, and the first cathode active material layer and the second cathode active material layer are arranged on the first cathode pole piece and the second cathode pole piece respectively. The cathode tab is arranged in a groove in the first cathode active material layer; the anode pole piece comprises a first anode layer, the first anode layer comprises an anode current collector, and a first anode active material layer and a second anode active material layer are respectively arranged on two surfaces of the anode current collector; the edge of the first anode layer exceeds the first cathode layer, and the cathode tab comprises a first section positioned between the first cathode layer and the first anode layer along the extension direction of the cathode pole piece; the first anode layer is provided with a first gap, and the first gap covers the first section in the thickness direction of the cathode tab. Therefore, the contact probability of the cathode tab and the first anode layer is reduced, and the safety performance of the battery is improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of batteries, and in particular, to a secondary battery and an electrochemical device Background Art

[0002] As a main product in the new energy field, the secondary battery mainly includes a cathode electrode sheet and an anode electrode sheet that are stacked or wound on top of each other, and a separator is provided between the cathode electrode sheet and the anode electrode sheet

[0003] In order to avoid lithium plating on the surface of the cathode electrode sheet during the charging process, the secondary battery usually forms an overhang structure (the boundary size of the anode electrode sheet exceeds that of the cathode electrode sheet) at the edges of the cathode electrode sheet and the anode electrode sheet. In this way, the cathode tab directly faces the first anode material layer across the separator. When the secondary battery is in special environments such as dropping, rolling, or high temperature, it is easy for the cathode tab to penetrate the separator and directly contact the first anode material layer. The direct contact between the cathode tab and the first anode material layer is the most dangerous short-circuit situation for the secondary battery, which will generate a large current instantaneously, causing the battery cell to get out of control due to heat and resulting in serious consequences such as explosion or combustion Summary of the Invention

[0004] An object of the embodiments of the present application is to provide a battery pack and an electrical device using the same, so as to improve the technical problem that the existing battery pack is not suitable for lightweight applications

[0005] According to a first aspect of the present application, a secondary battery is disclosed, including an electrode assembly, and the electrode assembly includes

[0006] A cathode electrode sheet, the cathode electrode sheet includes a first cathode layer, the first cathode layer includes a cathode current collector, the cathode current collector includes a first surface and a second surface arranged opposite to each other, the first surface is provided with a first cathode active material layer, the second surface is provided with a second cathode active material layer, the first cathode active material layer is provided with a groove for exposing the cathode current collector, the cathode electrode sheet further includes a cathode tab, and the cathode tab is electrically connected to the cathode current collector in the groove

[0007] An anode electrode sheet, the first anode layer includes an anode current collector, the anode current collector includes a third surface and a fourth surface arranged opposite to each other, the third surface is provided with a first anode active material layer, the fourth surface is provided with a second anode active material layer, along a first direction, the edge of the first anode layer exceeds the first cathode layer, the cathode tab includes a first section located between the first cathode layer and the first anode layer along the first direction, and a second section in electrical contact with the cathode current collector, and the first direction is the extending direction of the second section; and

[0008] The separator includes a first separator layer disposed between the first anode active material layer and the second cathode active material layer, and the first separator layer is connected to both the first anode active material layer and the second cathode active material layer.

[0009] The first anode layer is provided with a first notch penetrating through the anode current collector, the first anode active material layer, and the second anode active material layer. Along the second direction, which is the thickness direction of the cathode electrode tab, the first notch covers the first section.

[0010] In this way, when the secondary battery is in special environments such as dropping, rolling, and high temperature, when the cathode electrode tab approaches the first anode layer, the corresponding area of the first anode layer has been cleared by the first notch, which is beneficial to reducing the probability of direct contact between the cathode electrode tab and the first anode active material layer and the anode current collector, thereby greatly improving the safety performance of the battery.

[0011] In one or more of the above optional embodiments, the edge of the first cathode layer is provided with a second notch, and the cathode electrode tab extends out of the first cathode layer from the second notch. Along the second direction, the second notch at least partially overlaps with the first section.

[0012] In this way, the first anode active material layer and the anode current collector corresponding to the first section in the first anode layer along the second direction have been cleared by the first notch. When the cathode electrode tab approaches the first anode layer, it is beneficial to reducing the probability of direct contact between the cathode electrode tab and the first anode active material layer and the anode current collector, thereby greatly improving the safety performance of the battery.

[0013] In one or more of the above optional embodiments, along the third direction, the width of the first notch is W1, the width of the second notch is W2, and the width of the first section is W3, where W3 ≤ W1 ≤ W2.

[0014] By controlling W3 ≤ W1 ≤ W2, the risk of the cathode electrode tab directly contacting the first anode active material layer is further reduced, the safety performance of the secondary battery is further improved, and the impact on the energy density of the secondary battery is reduced simultaneously.

[0015] In one or more of the above optional embodiments, along the first direction, the length of the first notch is L1, and the length of the first section is L2, where L2 ≤ L1 ≤ L2 + 0.5 mm. By controlling L2 ≤ L1 ≤ L2 + 0.5 mm, the risk of the cathode electrode tab directly contacting the first anode active material layer is further reduced, the safety performance of the secondary battery is further improved, and the impact on the energy density of the secondary battery is reduced simultaneously.

[0016] In one or more of the above optional embodiments, the second cathode active material layer is provided with a first adhesive tape, and along the second direction, the orthographic projection of the first adhesive tape on the first anode layer covers the first notch.

[0017] By setting a first adhesive tape on the second cathode active material layer and making the partial boundary of the second cathode active material layer covered by the first adhesive tape exceed the first notch, the requirement of overhang (the boundary of the anode tab exceeds that of the cathode tab) is satisfied, and the risk of lithium plating is further reduced.

[0018] In one or more of the above optional embodiments, a second cathode layer is further included. The first anode layer is located between the first cathode layer and the second cathode layer. The second cathode layer includes a third cathode active material layer. The separator further includes a second separator layer. The second separator layer is disposed between the third cathode active material layer and the second anode active material layer. The second separator layer is connected to both the second anode active material layer and the third cathode active material layer. A second adhesive tape is further provided on the surface of the third cathode active material layer. Along the opposite direction of the second direction, the orthographic projection of the second adhesive tape on the second anode material layer covers the first notch.

[0019] By setting a second adhesive tape on the first anode active material layer and making the partial boundary of the third cathode active material layer covered by the second adhesive tape exceed the first notch, the requirement of overhang (the boundary of the anode tab exceeds that of the cathode tab) is satisfied, and the risk of lithium plating is further reduced.

[0020] In one or more of the above optional embodiments, a third adhesive tape is further provided on the second anode active material layer, and the third adhesive tape covers the first notch.

[0021] In this way, the coverage of the third adhesive tape can block the burrs around the first notch from facing the second cathode active material layer, reducing the risk of the burrs piercing the separator and causing an internal short circuit of the battery.

[0022] In one or more of the above optional embodiments, along the opposite direction of the second direction, the orthographic projection of the second adhesive tape covers the third adhesive tape.

[0023] In this way, the area of the third cathode active material layer covered by the second adhesive tape covers the third adhesive tape, so that the boundary of the area of the first anode active material layer not covered by the third adhesive tape exceeds the second adhesive tape, satisfying the requirement of overhang (the boundary of the anode tab exceeds that of the cathode tab), and further reducing the risk of lithium plating.

[0024] In one or more of the above optional embodiments, a fourth adhesive tape is provided on the first anode active material layer, and the fourth adhesive tape covers the first notch.

[0025] In this way, the fourth adhesive tape covers the first notch, which can block the burrs around the first notch from facing the third cathode active material layer, reducing the risk of the burrs piercing the separator and causing an internal short circuit of the battery.

[0026] In one or more of the above optional embodiments, along the second direction, the first adhesive tape covers the orthographic projection of the fourth adhesive tape.

[0027] In this way, the area of the second cathode active material layer covered by the first adhesive tape covers the fourth adhesive tape, so that the boundary of the area where the first anode active material layer is not covered by the fourth adhesive tape exceeds the first adhesive tape, meeting the requirement of overhang (the boundary of the anode tab exceeds the cathode tab), and further reducing the risk of lithium plating.

[0028] In one or more of the above optional embodiments, along the second direction, the second cathode material layer overlaps with the second section. That is, the second surface of the cathode current collector corresponding to the groove covers the second cathode active material layer, which can increase the content of the active material in the first cathode layer, thereby improving the energy density of the secondary battery.

[0029] In one or more of the above optional embodiments, the cathode tab is bent at least partially along the second direction towards the first notch. In this way, during a drop, part of the pulling force of the cathode tab on the cathode current collector can be converted into pressure on the first surface of the cathode current collector, thus reducing the tearing effect of the cathode tab on the cathode current collector during a drop and lowering the failure rate of the tab during a drop.

[0030] According to the second aspect of the present application, the present application discloses an electrochemical device including the above secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations are not intended to limit the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements.

[0032] Figure 1 It is the front view of the electrode assembly in the embodiment of the present application;

[0033] Figure 2 It is the top view of the electrode assembly in the embodiment of the present application;

[0034] Figure 3 It is Figure 2 the partial enlarged view at A in

[0035] Figure 4 It is Figure 3 the exploded view of

[0036] Figure 5 It is the three-dimensional structure schematic diagram of the first cathode layer in the embodiment of the present application;

[0037] Figure 6 It is the three-dimensional structure schematic diagram of the first anode layer in the embodiment of the present application;

[0038] Figure 7 It is the rear view of the first cathode layer in the embodiment of the present application;

[0039] Figure 8 In another embodiment of the present application, it is a schematic three-dimensional structure diagram of the first cathode layer;

[0040] Figure 9 Corresponding to Figure 8 is a schematic diagram of dimension markings in;

[0041] Figure 10 In an embodiment of the present application, it is a rear view of the first anode layer;

[0042] Figure 11 In another embodiment of the present application, it is a schematic three-dimensional structure diagram of the first cathode layer;

[0043] Figure 12 In another embodiment of the present application, it is a schematic three-dimensional structure diagram of the first anode layer;

[0044] Figure 13 In another embodiment of the present application, it is a top view of the second cathode layer;

[0045] Figure 14 In Comparative Example 1 of the present application, it is a top view of the electrode assembly;

[0046] Figure 15 In Comparative Example 2 of the present application, it is a top view of the electrode assembly.

[0047] The meanings of the reference numerals in the drawings:

[0048] Cathode plate 1, first cathode layer 1a, second cathode layer 1b, cathode current collector 10, first cathode material layer 11, second cathode material layer 12, groove 13, cathode tab 14, first section 141, first sub-section 1411, second sub-section 1412, second section 142, second notch 15, third cathode material layer 16;

[0049] Anode plate 2, first anode layer 2a, anode current collector 20, first anode material layer 21, second anode material layer 22, first notch 23, anode tab 24;

[0050] Separator 3, first separator layer 3a, second separator layer 3b;

[0051] First adhesive tape 4;

[0052] Second adhesive tape 5, adhesive tape groove 50;

[0053] Third adhesive tape 6;

[0054] Fourth adhesive tape 7. Detailed implementation manners

[0055] For the convenience of understanding the present invention, the present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is expressed as "fixed to" another element, it can be directly on the other element, or there can be one or more intermediate elements therebetween. When an element is expressed as "connected to" another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween. The terms "upper", "lower", "inner", "outer", "vertical", "horizontal", etc. used in this specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Including" or "comprising" and other similar words mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. "Connection" or "connected" and other similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Unless otherwise defined, the features such as "parallel", "perpendicular", and "same" used in the embodiments of the present invention include the strict sense of "parallel", "perpendicular", "same", etc., as well as the cases with certain errors such as "substantially parallel", "substantially perpendicular", "substantially the same", etc. For example, the above "substantially" can mean that the difference between the compared objects is within 10% or 5% of the average value of the compared objects. When the number of a component or element is not specifically pointed out in the following text of the embodiments of the present invention, it means that the component or element can be one or more, or can be understood as at least one. "At least one" means one or more, and "a plurality" means at least two.

[0056] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not used to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0057] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments.

[0058] An electrochemical device disclosed in an embodiment of the present application includes a secondary battery. As Figures 1 - 3As shown, the secondary battery includes an electrode assembly 100, the electrode assembly 100 includes a cathode electrode sheet 1 and an anode electrode sheet 2, and a separator 3 is disposed between the cathode electrode sheet 1 and the anode electrode sheet 2. As Figure 4 and Figure 5 shown, the cathode electrode sheet 1 includes a first cathode layer 1a, the first cathode layer 1a includes a cathode current collector 10, the cathode current collector 10 includes a first surface and a second surface disposed opposite to each other, a first cathode active material layer 11 is provided on the first surface, a second cathode active material layer 12 is provided on the second surface, a groove 13 for exposing the first surface of the (cathode current collector 10) is provided in the first cathode active material layer 11, the cathode electrode sheet 1 further includes a cathode tab 14, and the cathode tab 14 is electrically connected to the first surface in the groove 13 (of the cathode current collector 10). In this embodiment, the cathode current collector 10 is an aluminum foil, and the cathode tab 14 is an aluminum tab.

[0059] As Figure 4 and Figure 6 shown, the anode electrode sheet 2 includes a first anode layer 2a. The first anode layer 2a includes an anode current collector 20, the anode current collector 20 includes a third surface and a fourth surface disposed opposite to each other, a first anode material layer 21 is provided on the third surface, and a second anode material layer 22 is provided on the fourth surface.

[0060] The separator 3 includes a first separator layer 3a, the first separator layer 3a is disposed between the first anode active material layer 21 and the second cathode active material layer 12, and the first separator layer 3a is connected to both the first anode active material layer 21 and the second cathode active material layer 12. Among them, one surface of the first separator layer 3a is connected to the first anode active material layer 21, and the other surface is connected to the second cathode active material layer 12.

[0061] Along the first direction X, the edge of the first anode layer 2a exceeds the first cathode layer 1a. Thus, along the first direction X, there is a certain distance between the edges of the first anode layer 2a and the first cathode layer 1a on the side where the cathode tab 14 is located. As Figure 7 shown, the cathode tab (14) includes a first section 141 located between the first cathode layer 1a and the first anode layer 2a along the first direction X, and a second section 142 in electrical contact with the cathode current collector 10. The first direction X is the direction in which the second section 142 extends toward the edge of the first cathode layer 2a.

[0062] As Figure 4 and Figure 6 shown, a first notch 23 is provided at the edge of the first anode layer 2a corresponding to the cathode tab 14, and the first notch 23 sequentially penetrates through the anode current collector 20, the first anode active material layer 21, and the second anode active material layer 22 along the second direction Y. The anode electrode sheet 2 further includes an anode tab 24 electrically connected to the anode current collector 20 (refer to Figure 1)。And along the second direction Y, the first notch 23 covers the first section 141 of the cathode tab 14, that is, along the second direction Y, the boundary of the first notch 23 coincides with or exceeds the first section 141 of the cathode tab 14. Wherein, the second direction Y is the thickness direction of the first cathode layer 1a, and the first direction X and the second direction Y are perpendicular. That is, the second direction Y is perpendicular to the first cathode layer 1a.

[0063] Specifically, as Figure 6 shown, the first notch 23 is formed by die-cutting the corresponding regions of the first anode active material layer 21, the anode current collector 20, and the second anode active material layer 22 of the first anode layer 2a. The first notch 23 penetrates the first anode active material layer 21, the anode current collector 20, and the second anode active material layer 22 along the second direction Y. As Figure 4 shown, along the second direction Y, the first notch 23 covers the first section 141 of the cathode tab 14, that is, along the first direction X or the third direction Z, the boundary of the first notch 23 partially coincides with the first section 141, or the boundary of the first notch 23 exceeds the first section 141, such that the edge of the first section 141 completely falls within the range of the first notch 23, and their boundaries do not coincide.

[0064] In this way, when the secondary battery causes the cathode tab 14 to approach the first anode layer 2a due to a special environment, the cathode tab 14 approaches the first notch 23. In special environments such as dropping, rolling, and high temperature, it is beneficial to reduce the probability of direct contact between the cathode tab 14 and the anode material on the surface of the first anode layer 2a, thereby greatly improving the safety performance of the battery.

[0065] In some embodiments, along the second direction Y, the second cathode material layer 12 overlaps with the second section (142) of the cathode tab 14. That is, the second surface of the cathode current collector 10 corresponding to the groove 13 covers the second cathode active material layer 12, thereby increasing the content of the active material in the first cathode layer 1a and thus improving the energy density of the secondary battery.

[0066] In some embodiments, as Figure 4 and Figure 5 shown, a second notch 15 is provided at the edge of the first cathode layer 1a. The first section 141 of the cathode tab 14 protrudes from the edge of the first cathode layer 1a at the second notch 15, and along the second direction Y, the second notch 15 partially overlaps with the first section 141.

[0067] Wherein, as Figure 7As shown, the first section 141 includes a first sub-section 1411 that overlaps with the second notch 15 in the second direction Y, and a second sub-section 1412 that extends beyond the second notch 15. Since the first cathode layer 1a is provided with the second notch 15, there is also a risk that the first sub-section 1411 comes into contact with the first anode active material layer 21. For this reason, in this embodiment, along the second direction Y, the first notch 23 covers both the first sub-section 1411 and the second sub-section 1412 in the second direction Y, so that both the first sub-section 1411 and the second sub-section 1412 are within the boundary range of the first notch 23, ensuring that the first anode active material layer 21, the second anode active material layer 22, and the anode current collector 20 corresponding to the entire first section 141 on the first anode layer 2a are all removed by the first notch 23, thereby reducing the risk of short circuit between the cathode tab 14 and the first anode layer 2a.

[0068] In some embodiments, as Figure 8 shown, the cathode tab 14 is bent at least partially along the second direction Y towards the first notch 23.

[0069] In this way, since the cathode tab 14 is welded to the first surface of the cathode current collector 10, during a drop, it can convert part of the pulling force of the cathode tab 14 on the cathode current collector 10 into pressure on the first surface of the cathode current collector 10, thus reducing the tearing of the cathode tab 14 on the cathode current collector 10 during a drop and lowering the failure rate of the cathode tab during a drop.

[0070] In addition, the second notch 15 makes the second section 142 closer to the inside of the electrode assembly 100, that is, it can make the welded part of the cathode tab 14 closer to the inside of the electrode assembly 100. In this way, the starting position of the bending of the cathode tab 14 towards the first notch 23 is closer to the inside of the electrode assembly 100, and the support point where the cathode tab 14 pulls the cathode current collector 10 during a drop is closer to the inside of the electrode assembly 100, so as to improve the stability of the cathode tab 14.

[0071] It should be noted that the size of the first notch 23 needs to satisfy covering the first section 141 along the second direction Y to reduce the risk of the cathode tab 14 coming into contact with the first anode active material layer 21. However, the larger the first notch 23 is, the more of the first anode active material layer 21 and the second anode active material layer 22 need to be removed from the first anode layer 2a. Therefore, on the premise of satisfying that the size of the first notch 23 covers the first section 141 along the second direction Y, controlling the size of the first notch 23 can improve the energy density of the secondary battery.

[0072] For this reason, in this embodiment, as Figure 9As shown, along the third direction Z, the width of the first notch 23 is W1, the width of the second notch 15 is W2, and the width of the first section 141 of the cathode tab 14 is W3, and W3 ≤ W1 ≤ W2 is satisfied. Among them, the third direction Z is perpendicular to the first direction X and the second direction Y.

[0073] By controlling W3 ≤ W1 ≤ W2, the risk of the cathode tab 14 directly contacting the first anode active material layer 21 is further reduced, the safety performance of the secondary battery is improved, and the impact on the energy density of the secondary battery is reduced.

[0074] As Figure 10 shown, along the first direction X, the length of the first notch 23 is L1, and the length of the first section 141 of the cathode tab 14 is L2, where L2 ≤ L1 ≤ L2 + 0.5 mm.

[0075] In this way, by controlling the dimension of the length L1 of the first notch 23 along the first direction X, the risk of the cathode tab 14 directly contacting the first anode active material layer 21 is further reduced, the safety performance of the secondary battery is improved, and the impact on the energy density of the secondary battery is reduced.

[0076] When the secondary battery is charged, lithium ions will pass through the separator 3 from the second cathode active material layer 12 to the first anode material layer 21. Therefore, there needs to be enough anode active material on the surface of the first anode active material layer 21 to absorb this part of lithium ions, so as to reduce the probability of lithium ions precipitating on the surface of the second anode material layer 22, thereby reducing the risk of short circuit between the cathode electrode sheet 1 and the anode electrode sheet 2 caused by damage to the separator 3.

[0077] For this reason, in some embodiments of the present application, as Figure 4 and Figure 11 shown, a first adhesive tape 4 is provided on the surface of the second cathode active material layer 12. Along the first direction X, the orthographic projection of the first adhesive tape 4 on the first anode layer 2a covers the first notch 23. The first adhesive tape 4 can be an adhesive tape with a high melting point, such as a polyimide tape.

[0078] In this way, by providing the first adhesive tape 4 on the second cathode active material layer 12 and making the boundary of the first adhesive tape 4 exceed the first notch 23 to meet the overhang requirement, the risk of lithium plating is further reduced.

[0079] As Figure 4As shown, the secondary battery includes a second cathode layer 1b, a first anode layer 2a located between the first cathode layer 1a and the second cathode layer 1b. The second cathode layer 1b includes a cathode current collector 10, the cathode current collector 10 includes a fifth surface opposite to the fourth surface, and a third cathode active material layer 16 is provided on the fifth surface. The separator 3 also includes a second separator layer 3b, the second separator layer 3b is disposed between the third cathode active material layer 16 and the second anode active material layer 22, and one side of the second separator layer 3b is connected to the third cathode active material layer 16 and the other side is connected to the second anode active material layer 22. Among them, the second cathode layer 1b and the first cathode layer 1a are both part of the cathode electrode sheet 1. After the cathode electrode sheet 1 and the anode electrode sheet 2 are wound and formed, the layers where they are located are different; the first separator layer 3a and the second separator layer 3b are both part of the separator 3. After winding and forming, the layers where they are located are different. A second adhesive tape 5 is also provided on the surface of the third cathode active material layer 16. Along the reverse direction of the second direction Y, the orthographic projection of the second adhesive tape 5 on the surface of the second anode active material layer 22 covers the first notch 23. Among them, the second adhesive tape 5 can be an adhesive tape with a high melting point, such as a polyimide tape.

[0080] In this way, along the second direction Y, the second adhesive tape 5 covers the first notch 23 to meet the requirement of overhang (the boundary of the anode electrode sheet exceeds the cathode electrode sheet), and further reduces the risk of lithium plating.

[0081] In some embodiments, as Figure 4 and Figure 12 shown, a third adhesive tape 6 is provided on the second anode active material layer 22, and the third adhesive tape 6 covers the first notch 23. The third adhesive tape 6 is an adhesive tape with insulation and a high melting point, such as a polyimide tape.

[0082] When the first notch 23 is processed by a die-cutting process, burrs are likely to be generated at the edge of the first notch 23. The third adhesive tape 6 covering the first notch 23 can block the burrs around the first notch 23 and reduce the risk of short circuit caused by the burrs piercing the separator 3.

[0083] In addition, while the third adhesive tape 6 covers the first notch 23, it also covers the second anode material layer 22 at the edge of the first notch 23. For this reason, in some embodiments, as Figure 4 shown, along the reverse direction of the second direction Y, the second adhesive tape 5 covers the orthographic projection of the third adhesive tape 6.

[0084] In this way, along the reverse direction of the second direction Y, the second adhesive tape 5 covers the third adhesive tape 6, so that the boundary of the area where the first anode active material layer 21 is not covered by the third adhesive tape 6 exceeds the second adhesive tape 5 to meet the requirement of overhang and further reduce the risk of lithium plating.

[0085] In some embodiments, as Figure 4 and Figure 12As shown, a fourth adhesive tape 7 is provided on the first anode active material layer 21, and the fourth adhesive tape 7 covers the first notch 23. The fourth adhesive tape 7 is an adhesive tape with insulation and high melting point, such as a polyimide tape.

[0086] When processing the first notch 23 through a die-cutting process, burrs are likely to be generated at the edge of the first notch 23. The fourth adhesive tape 7 covering the first notch 23 can block the burrs and reduce the risk of the burrs piercing the separator 3 and causing a short circuit.

[0087] In addition, while the fourth adhesive tape 7 covers the first notch 23, it also covers the first anode material layer 21 at the edge of the first notch 23. Therefore, in some embodiments, as Figure 4 shown, along the second direction Y, the first adhesive tape 4 covers the orthographic projection of the fourth adhesive tape 7. In this way, the boundary of the area where the second cathode active material layer 12 is covered by the first adhesive tape 4 exceeds the fourth adhesive tape 7 to meet the requirement of overhang (the boundary of the anode electrode tab exceeds the cathode electrode tab), and further reduces the risk of lithium plating.

[0088] In another embodiment of the present application, the first adhesive tape 4, the second adhesive tape 5, the third adhesive tape 6, and the fourth adhesive tape 7 can be insulating tapes, including but not limited to polyimide tapes, polyester tapes, non-woven fabric tapes, and fiberglass tapes. Such adhesive tapes have characteristics such as resistance to electrolyte corrosion, high adhesion, and soft conformability, and can play their due roles in lithium batteries.

[0089] In another embodiment of the present application, as Figure 13 shown, a tape groove 50 is provided on the surface of the third cathode material layer 16, and the second adhesive tape 5 is disposed in the tape groove 50. The tape groove 50 can reduce the space occupied by the second adhesive tape 5 and reduce the overall thickness of the electrode tab assembly 100, thereby improving the energy density of the battery.

[0090] Another embodiment of the present application also discloses an electrical device including the secondary battery in the above embodiment.

[0091] Hereinafter, examples and comparative examples are given to more specifically illustrate the implementation manners 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.

[0092] Comparative Example 1:

[0093] A secondary battery, as Figure 14 shown, includes a cathode electrode tab 1 and an anode electrode tab 2. A separator 3 is disposed between the cathode electrode tab 1 and the anode electrode tab 2. The cathode electrode tab 1, the separator 3, and the anode electrode tab 2 are stacked and wound into a shape.

[0094] Among them, the cathode electrode sheet 1 includes a cathode current collector 10 and a cathode tab 14 electrically connected to the cathode current collector 10. The cathode current collector 10 includes a first surface and a second surface. A first cathode active material layer 11 is provided on the first surface, and a second cathode active material layer 12 is provided on the second surface. The anode electrode sheet 2 includes an anode current collector 20. The anode current collector 20 includes a first surface and a second surface. A first anode active material layer 21 is provided on the first surface, and a second anode active material layer 22 is provided on the second surface. A separator 3 is provided between the first anode active material layer 21 and the second cathode active material layer 12.

[0095] Comparative Example 2:

[0096] Based on Comparative Example 1, as Figure 15 shown, a first notch 23 is formed in the anode electrode sheet 2. Along the second direction Y, the first section 141 of the cathode tab 14 covers the first notch 23. Specifically, along the third direction Z, the width of the first notch 23 is W1, and the width of the first section 141 of the cathode tab 14 is W3, where W1 < W3; along the first direction X, the length of the first notch 23 is L1, and the length of the first section 141 of the cathode tab 14 is L2, where L1 = L2.

[0097] Comparative Example 3:

[0098] Based on Comparative Example 2, in Comparative Example 3, the width of the first notch 23 is W1, and the width of the first section 141 of the cathode tab 14 is W3, where W1 = W3. Along the first direction X, the length of the first notch 23 is L1, and the length of the first section 141 of the cathode tab 14 is L2, where L1 < L2.

[0099] Example 1:

[0100] A secondary battery, with an initial thickness of 4.8 mm at 50% SOC, a length of 87 mm, and a width of 64 mm. The assembly process is as follows:

[0101] (1) Preparation of the anode sheet: The anode active material artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:1.5:2.5. Deionized water is added as a solvent to prepare a slurry with a weight percentage of 50 wt%. The slurry is stirred evenly and then uniformly coated on one surface of the copper foil. Then it is dried at 110 °C to obtain an anode sheet with an anode active material layer coated on one side. When preparing an anode sheet with double-sided coating, repeat the above steps on the other surface of the anode sheet to obtain an anode sheet with an anode active material layer coated on both sides. Then the coated electrode sheet is cold-pressed to a thickness of 105 μm, grooves are set on the anode active material, and the anode tab is welded to the copper foil exposed in the grooves. Then, the position of the first notch is determined on the anode sheet through a laser positioning system and die-cutting is performed to control the first notch to cover the first section of the cathode tab.

[0102] (2) Preparation of the cathode sheet: The cathode active material lithium cobalt oxide (LiCoO₂), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75 wt%. The slurry is stirred evenly and then uniformly coated on one surface of the aluminum foil. Then it is dried at 90 °C to obtain a cathode sheet with a cathode active material coated on one side. When preparing a cathode sheet with double-sided coating, repeat the above coating steps on the other surface of the aluminum foil. Then the coated electrode sheet is cold-pressed to a thickness of 95 μm, grooves are set on the cathode active material, and the cathode tab is welded to the aluminum foil exposed in the grooves.

[0103] (3) Preparation of the electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then lithium salt lithium hexafluorophosphate (LiPF₆) is added to the basic organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0104] (4) Preparation of the separator: A separator with a three-layer structure is used, which includes an adhesive layer, a base material layer, and an adhesive layer arranged in a stacked manner. The first base material layer is made of polyethylene (PE), the binder in the adhesive layer is PVDF, and the adhesive layer also contains inorganic particles boehmite.

[0105] (5) Preparation of the electrode assembly: The cathode sheet, the separator, and the anode sheet are stacked and then wound into a shape, ensuring that the first notch covers the cathode tab.

[0106] (6) Secondary battery assembly: Place the formed aluminum-plastic film with indentations in the assembly fixture with the indented surface facing up, place the electrode assembly in the indentation, and apply an external force to press it tightly. Then, cover the electrode assembly with another formed aluminum-plastic film with the indented surface facing down, and heat-seal the peripheries of the two aluminum-plastic films by hot pressing to obtain the assembled electrode assembly.

[0107] (7) Electrolyte injection and encapsulation: Inject electrolyte into the assembled electrode assembly, and through processes such as vacuum encapsulation, standing, hot pressing formation, and shaping, the secondary battery is obtained.

[0108] As Figure 4 shown, in Example 1, along the second direction Y, the first notch 23 covers the first section 141 of the cathode tab 14. Among them, the width of the first notch 23 is W1, the width of the first section 141 of the cathode tab 14 is W3, and W1 = W3. Along the first direction X, the length of the first notch 23 is L1, and the length of the first section 141 of the cathode tab 14 is L2, where L1 = L2.

[0109] Example 2:

[0110] Based on the improvement of Example 1, in Example 2, a second notch 15 is provided on the cathode current collector. Along the third direction Z, the width of the second notch 15 is W2, where W3 < W1 < W2.

[0111] Example 3:

[0112] Based on the adjustment of Example 2, in Example 3, W1 = W3 and L1 = L2.

[0113] Example 4:

[0114] Based on the adjustment of Example 3, in Example 4, W1 > W2 and L1 = L2.

[0115] Example 5:

[0116] Based on the adjustment of Example 3, in Example 5, W1 = W2 and L2 < L1 < L2 + 0.5 mm.

[0117] Example 6:

[0118] Based on the adjustment of Example 5, in Example 6, W1 = W2 and L1 = L2 + 0.5 mm.

[0119] Example 7:

[0120] Based on the adjustment of Example 5, in Example 6, W1 = W2 and L1 > L2 + 0.5 mm.

[0121] 1. Secondary battery drop test

[0122] First, pre-treat the secondary battery to be tested. The treatment conditions are as follows: at a temperature of 20 ± 5°C, after standing for 60 min, discharge at a constant current of 0.7C until 3.0V, and then stand for 10 min; then charge at a constant current of 0.5C rate to 4.25V, and then charge at a constant voltage of 4.25V to 0.05C. After the pre-treatment is completed, clamp the secondary battery with a fixture and drop it onto a metal floor from a height of 1.5m. A total of 2 rounds of tests are carried out. The dropping sequence in the positive direction is: bottom right - bottom left - top right - top left; the reverse direction is: top left - top right - bottom left - bottom right (angle: 45 ± 15 degrees). During the test, if the secondary battery does not catch fire, explode, or emit smoke, it means the drop test is passed; otherwise, the drop test is not passed. Test 100 secondary batteries, and the number of secondary batteries passing the test is X, and the test passing rate is X / 100.

[0123] 2. Thermal box test of secondary battery:

[0124] First, pre-treat the secondary battery to be tested. The pre-treatment conditions are as follows: after standing for 60 min at a test temperature of 20°C (±5°C), discharge at a constant current of 0.7C until 3.0V, and then stand for 10 min; then charge at a constant current of 0.5C rate to 4.25V, and then charge at a constant voltage of 4.25V to 0.05C. After the pre-treatment is completed, place the secondary battery vertically in the thermal box for the thermal box test. Among them, the temperature in the thermal box is raised to 130 ± 2°C at a rate of 5 ± 2°C / min and maintained for 60 min. During the test, if the secondary battery does not burn or explode, it means the thermal box test is passed; otherwise, the thermal box test is not passed. Test 100 secondary batteries, and the number of cells passing the test is X, and the test passing rate is X / 100.

[0125] Table 1

[0126]

[0127] Note: In Table 1, "\ " means that the parameter is not included.

[0128] It can be seen from Comparative Examples 1 to 3 and Examples 1 to 7 in the experimental results of Table 1 that when the first anode layer 2a does not have a first notch 23 die-cut, or along the second direction Y, the first notch 23 does not cover the first section 141 of the cathode tab 14, the passing rates of the drop test and the hot box test are both lower than 78%. When the first anode layer 2a has a first notch 23 and, along the second direction Y, the first notch 23 covers the first section 141 of the cathode tab 14, the passing rates of the drop test and the hot box test can both reach or exceed 90%. When L1 = L2 and then W1 is further increased such that W1 > W2, the passing rates of the drop test and the hot box test do not change significantly. It can be seen that further increasing the size of W1 does not significantly improve the safety performance of the secondary battery. Similarly, when W1 = W2 and then L1 is further increased such that L1 > L2 + 0.5 mm, the passing rates of the drop test and the hot box test have both reached the upper limit, and further increasing the size of L1 does not significantly improve the safety performance of the secondary battery either.

[0129] Therefore, it can be seen from Examples 1 to 7 in Table 1 that when W3 ≤ W1 ≤ W2 and / or L2 ≤ L1 ≤ L2 + 0.5 mm, the risk of the cathode tab 14 directly contacting the first anode active material layer 21 can be further reduced, and the safety performance of the secondary battery can be further improved.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above. For the sake of brevity, they are not provided in detail; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A secondary battery, characterized in that: include: An electrode assembly, comprising: A cathode plate, comprising a first cathode layer, the first cathode layer comprising a cathode current collector, the cathode current collector comprising a first surface and a second surface arranged opposite to each other, the first surface being provided with a first cathode active material layer, the second surface being provided with a second cathode active material layer, the first cathode active material layer being provided with a groove for exposing the cathode current collector, the cathode plate further comprising a cathode tab, the cathode tab being electrically connected to the cathode current collector exposed by the groove; An anode electrode sheet, comprising a first anode layer, the first anode layer comprising an anode current collector, the anode current collector comprising a third surface and a fourth surface arranged opposite to each other, the third surface being provided with a first anode active material layer, and the fourth surface being provided with a second anode active material layer; along a first direction, an edge of the first anode layer exceeds the first cathode layer, the cathode electrode tab comprising a first section located between the first cathode layer and the first anode layer along the first direction, and a second section electrically contacting the cathode current collector, the first direction being a direction in which the second section extends; and A separator, comprising a first separator layer, the first separator layer being disposed between the first anode active material layer and the second cathode active material layer, the first separator layer being connected to both the first anode active material layer and the second cathode active material layer; The first anode layer is provided with a first notch penetrating the anode current collector, the first anode active material layer and the second anode active material layer. The first notch covers the first segment along a second direction, and the second direction is the thickness direction of the first cathode layer.

2. The secondary battery according to claim 1, characterized in that: A second notch is provided at the edge of the first cathode layer, and the cathode tab extends out of the first cathode layer from the second notch. Along the second direction, the first section at least partially overlaps with the second notch.

3. The secondary battery according to claim 2, characterized in that: Along the third direction, the width of the first notch is W1, the width of the second notch is W2, and the width of the first section is W3, wherein W3≤W1≤W2, and the third direction is perpendicular to the first direction and the second direction.

4. The secondary battery according to claim 3, characterized in that: Along the first direction, the length of the first notch is L1, and the length of the first section is L2, wherein L2≤L1≤L2+0.5 mm.

5. The secondary battery according to claim 1, characterized in that: The second cathode active material layer is provided with a first adhesive tape, and along the second direction, the orthographic projection of the first adhesive tape on the first anode layer covers the first gap.

6. The secondary battery according to claim 1 or 5, characterized in that: It also includes a second cathode layer, the first anode layer is located between the first cathode layer and the second cathode layer, the second cathode layer includes a third cathode active material layer, the diaphragm also includes a second diaphragm layer, the second diaphragm layer is arranged between the third cathode active material layer and the second anode active material layer, the second diaphragm layer is connected to both the second anode active material layer and the third cathode active material layer, and a second adhesive tape is also provided on the surface of the third cathode active material layer, and along the opposite direction of the second direction, the second adhesive tape covers the first gap on the positive projection of the second anode material layer.

7. The secondary battery according to claim 6, characterized in that: The second anode active material layer is further provided with a third adhesive tape, and the third adhesive tape covers the first gap.

8. The secondary battery according to claim 7, characterized in that: Along the direction opposite to the second direction, the orthographic projection of the second adhesive tape covers the third adhesive tape.

9. The secondary battery according to claim 5, characterized in that: The first anode active material layer is provided with a fourth adhesive tape, and the fourth adhesive tape covers the first gap.

10. The secondary battery according to claim 9, characterized in that: Along the second direction, the first adhesive tape covers the orthographic projection of the fourth adhesive tape.

11. The secondary battery according to claim 1, characterized in that: Along the second direction, the second cathode material layer overlaps the second segment.

12. The secondary battery according to claim 2, characterized in that: At least a portion of the cathode tab is bent toward the first notch along the second direction.

13. An electrochemical device, characterized in that: A secondary battery comprising any one of claims 1 to 12.

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