Secondary battery and electrochemical device

Abstract

The present application discloses a secondary battery and an electrochemical device. The secondary battery comprises a cathode electrode sheet and an anode electrode sheet; the cathode electrode sheet comprises a first cathode layer; the first cathode layer comprises a cathode tab and a cathode current collector; a first cathode active material layer and a second cathode active material layer are respectively provided on two surfaces of the cathode current collector; the cathode tab is provided in a groove formed in the first cathode active material layer; the anode electrode sheet comprises a first anode layer; the first anode layer comprises an anode current collector; a first anode active material layer and a second anode active material layer are respectively provided on two surfaces of the anode current collector; the first anode active material layer is adjacent to the second anode active material layer; the first anode layer is provided with a second groove; and in the thickness direction of the cathode tab, the second groove covers the cathode tab. The present application can reduce the probability of a cathode tab coming into direct contact with a first anode layer, thereby significantly improving the safety performance of a battery.

Description

Secondary batteries and electrochemical devices Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a secondary battery and an electrochemical device. Background Technology

[0002] As a major product in the new energy field, secondary batteries mainly consist of cathode and anode plates stacked or wound together, with a separator placed between the cathode and anode plates.

[0003] To prevent lithium deposition on the cathode surface during recharge, an overhang structure is typically formed at the edges of the cathode and anode electrodes (the anode boundary dimension exceeds that of the cathode). This results in the cathode tab being directly opposite the first anode active material layer through the separator. When the rechargeable battery is subjected to special environments such as drops, rolling, or high temperatures, the cathode tab can easily penetrate the separator and directly contact the first anode active material layer. Direct contact between the cathode tab and the first anode active material layer is the most dangerous short circuit scenario for a rechargeable battery, generating a large current instantaneously, causing the cell to overheat and run away, leading to serious consequences such as explosion or combustion. Summary of the Invention

[0004] One objective of this application is to provide a secondary battery and an electrochemical device to solve the technical problem of internal short circuits caused by contact between the anode tab and the anode active material layer in existing secondary batteries.

[0005] According to a first aspect of this application, a secondary battery is disclosed, including an electrode assembly, the electrode assembly comprising:

[0006] The cathode electrode includes a first cathode layer, which includes a cathode current collector, a first cathode active material layer, and a second cathode active material layer. The cathode current collector includes a first surface and a second surface disposed opposite to each other. The first cathode active material layer is disposed on the first surface, and the second cathode active material layer is disposed on the second surface. The first cathode active material layer has a first groove for exposing the cathode current collector. The cathode electrode also includes a cathode tab, which is at least partially disposed in the first groove and electrically connected to the cathode current collector. Along a first direction, the second cathode active material layer overlaps with the cathode tab. The first direction is the thickness direction of the cathode electrode.

[0007] The anode electrode includes a first anode layer disposed adjacent to a first cathode layer. The first anode layer includes an anode current collector and a first anode active material layer. The anode current collector includes a third surface and a fourth surface disposed opposite to each other. The first anode active material layer is disposed on the third surface. Along a second direction, the edge of the first anode layer extends beyond the first cathode layer. The cathode tab includes a first segment extending beyond the first cathode layer and overlapping the first anode layer along the second direction, and a second segment in electrical contact with the cathode current collector. The second direction is the direction in which the second segment extends.

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

[0009] The first anode active material layer has a second groove, which exposes the anode current collector and covers the first section of the cathode tab along the first direction.

[0010] In this way, when the secondary battery is subjected to special environments such as drops, rolling, and high temperatures, and the cathode tab moves closer to the first anode layer, the first anode active material layer in the corresponding area of ​​the first anode layer has been cleared by the second groove. This helps to reduce the probability of direct contact between the cathode tab and the first anode active material layer, thereby greatly improving the safety performance of the battery.

[0011] In one or more of the above optional embodiments, the cathode tab is at least partially bent toward the second groove. In this way, since the cathode tab is welded to the first surface of the cathode current collector, the pulling force of the cathode tab on the cathode current collector can be partially converted into pressure on the first surface of the cathode current collector during a drop, thereby reducing the tearing of the cathode tab on the cathode current collector during a drop and reducing the cathode tab drop failure rate.

[0012] In one or more of the above optional embodiments, the edge of the first cathode layer is provided with a notch, and along the first direction, the first segment at least partially overlaps with the notch, that is, the cathode tab extends out of the first cathode layer from the notch.

[0013] This allows the cathode tab to be welded to the first surface of the cathode current collector closer to the inside of the electrode assembly. During a drop, the pulling force of the cathode tab on the cathode current collector can be further converted into pressure on the first surface in the first direction. On the other hand, the starting part of the cathode tab bending towards the second groove can also be closer to the inside of the electrode assembly. During a drop, the support point of the cathode tab pulling the current collector, i.e. the edge of the notch, is located inside the electrode assembly, resulting in higher stability and further reducing the cathode tab drop failure rate.

[0014] In one or more of the above optional embodiments, the first cathode layer further includes a first adhesive paper, which is disposed on the surface of the second cathode active material layer and covers the second groove along the first direction.

[0015] In this way, along the first direction, the first adhesive tape covers the second groove, that is, the orthogonal projection of the first adhesive tape onto the first anode layer covers the second groove, so that the boundary of the second groove exceeds the part of the second cathode active material layer that is not covered by the first adhesive tape, thereby satisfying the requirement of overhang (the boundary of the anode electrode exceeds the cathode electrode) and further reducing the risk of lithium plating.

[0016] In one or more of the above optional embodiments, the first anode layer further includes a second adhesive tape disposed on the surface of the first anode material layer, covering the second groove. Thus, the second adhesive tape covering the second groove reduces the risk of the first segment coming into contact with the first anode current collector, further improving the safety performance of the secondary battery.

[0017] In one or more of the above optional embodiments, the first anode layer further includes hot melt adhesive, which fills the second groove and at least partially covers the anode current collector exposed at the second groove.

[0018] In this way, the hot melt adhesive can reduce the risk of the first section coming into contact with the anode current collector, further improving the safety performance of the secondary battery. At the same time, the hot melt adhesive also has fluidity after being heated, allowing it to move and fill the second groove, thereby improving the flatness of the cell.

[0019] In one or more of the above optional embodiments, a second adhesive tape is provided while the second groove is filled with hot melt adhesive, and the second adhesive tape covers the second groove. In this way, the hot melt adhesive can also reduce the accumulation of electrolyte in the second groove and reduce the risk of the second adhesive tape falling off.

[0020] In one or more of the above optional embodiments, along the first direction, the first adhesive paper covers the second adhesive paper, that is, the orthogonal projection of the first adhesive paper onto the surface of the first anodic active material layer covers the second adhesive paper.

[0021] In this way, the area of ​​the second cathode active material layer covered by the first adhesive tape is covered by the second adhesive tape, so that the boundary of the area of ​​the first anode active material layer not covered by the second adhesive tape exceeds the first adhesive tape, thereby meeting the requirement of overhang (the boundary of the anode electrode exceeds the cathode electrode) and further reducing the risk of lithium plating.

[0022] In one or more of the above optional embodiments, along the second direction, the edge of the first adhesive tape extends beyond the first anode layer. In this way, the first adhesive tape isolates the portion of the cathode tab extending beyond the first cathode layer from the first anode layer, reducing the risk of the cathode tab coming into contact with the first anode active material layer and / or the anode current collector.

[0023] In one or more of the above optional embodiments, along the third direction, the width of the second groove is W1, the width of the notch is W2, and the width of the first segment is W3, wherein W3≤W1≤W2. The third direction is perpendicular to the first and second directions.

[0024] By controlling W3≤W1≤W2, the risk of the cathode tab directly contacting the first anode active material layer is further reduced, thereby improving the safety performance of the secondary battery and reducing the impact on the energy density of the secondary battery.

[0025] In one or more of the above optional embodiments, the distance between the centerline of the first segment along the second direction and the centerline of the notch along the second direction is H, where 0≤H≤0.45(W2-W3). In this way, the position of the first segment is not too far away from the centerline of the notch, which is beneficial for the cathode tab to be bent toward the second groove. At the same time, it can also reduce the risk of the first segment contacting the first cathode active material layer, thereby improving the stability and safety of the secondary battery.

[0026] In one or more of the above optional embodiments, 0≤H≤0.25(W2-W3). In this way, the first segment is positioned closer to the center line of the notch, making it easier for the cathode tab to be bent toward the second groove.

[0027] In one or more of the above optional embodiments, along the second direction, the length of the second groove is L1, and the length of the first segment is L2, wherein L2≤L1≤L2+0.5mm. By controlling L2≤L1≤L2+0.5mm, the risk of the cathode tab directly contacting the first anode active material layer is further reduced, thereby further improving the safety performance of the secondary battery and reducing the impact on the energy density of the secondary battery.

[0028] In one or more of the above optional embodiments, the cathode tab is at least partially bent toward the second groove, and the first adhesive tape adheres to the second cathode active material layer and the first separator layer. This ensures that the first adhesive tape adheres to both the second cathode active material layer and the first separator layer simultaneously, reducing the risk of the first adhesive tape detaching from the second cathode active material layer when it shifts due to the bending of the cathode tab, thus improving the stability and safety of the secondary battery. Furthermore, the first adhesive tape constrains the first separator layer, reducing the risk of the first separator layer shrinking, further enhancing safety performance.

[0029] In one or more of the above optional embodiments, the second adhesive tape adheres to the first anode active material layer and the first diaphragm layer. In this way, the second adhesive tape restrains the first diaphragm layer, reducing the risk of shrinkage and further improving safety performance.

[0030] According to a second aspect of this application, an electrochemical device is disclosed, including the aforementioned secondary battery. Attached Figure Description

[0031] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0032] Figure 1 is a front view of the electrode assembly in an embodiment of this application;

[0033] Figure 2 is a top view of the electrode assembly in an embodiment of this application;

[0034] Figure 3 is a magnified view of part A in Figure 2;

[0035] Figure 4 is an exploded view of Figure 3;

[0036] Figure 5 is a three-dimensional structural diagram of the first cathode layer in an embodiment of this application;

[0037] Figure 6 is a three-dimensional structural diagram of the first anode layer in an embodiment of this application;

[0038] Figure 7 is a rear view of the first cathode layer in an embodiment of this application;

[0039] Figure 8 is a rear view of the first anode layer in another embodiment of this application;

[0040] Figure 9 is a schematic diagram corresponding to the dimensioning in Figure 7;

[0041] Figure 10 is a three-dimensional structural diagram of the first cathode layer in another embodiment of this application;

[0042] Figure 11 is a three-dimensional structural diagram of the first anode layer in another embodiment of this application;

[0043] Figure 12 is a top view of the second cathode layer in another embodiment of this application;

[0044] Figure 13 is a top view of the second cathode layer in another embodiment of this application;

[0045] Figure 14 is a three-dimensional structural diagram of the first cathode layer in another embodiment of this application;

[0046] Figure 15 is a top view of the electrode assembly in Comparative Example 1 of this application;

[0047] Figure 16 is a top view of the electrode assembly in Comparative Example 2 of this application.

[0048] The following are the meanings of the reference numerals in the attached diagram: Cathode electrode 1, First cathode layer 1a, Cathode current collector 10, First cathode active material layer 11, Second cathode active material layer 12, First groove 13, Cathode tab 14, First segment 141, First sub-segment 1411, Second sub-segment 1412, Second segment 142, Notch 15; Anode electrode 2, First anode layer 2a, Anode current collector 20, First anode active material layer 21, Second anode active material layer 22, Second groove 23, Anode tab 24; Separator 3, First separator layer 3a; First adhesive tape 4; Second adhesive tape 5; Hot melt adhesive 6. Detailed Implementation

[0049] To facilitate understanding of this utility model, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as "connected to" another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them. 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 this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Words such as "comprising" or "including" mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, without excluding other elements or objects. The terms "connection" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Unless otherwise defined, the features "parallel," "perpendicular," and "identical" used in the embodiments of this utility model include strictly defined "parallel," "perpendicular," and "identical," as well as cases where there is a certain margin of error, such as "approximately parallel," "approximately perpendicular," and "approximately identical." For example, "approximately" could mean that the difference between the compared objects is within 10% or 5% of the average value of the compared objects. Unless otherwise specified in the following embodiments of this utility model, the quantity of a component or element is implied; 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 "more" means at least two.

[0050] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0051] Furthermore, the technical features involved in the different embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other. Obviously, the described embodiments are some, but not all, of the embodiments of this utility model.

[0052] An electrochemical device disclosed in this application includes a secondary battery. As shown in Figures 1-3, the secondary battery includes an electrode assembly 100, which includes a cathode electrode 1 and an anode electrode 2, with a separator 3 disposed between the cathode electrode 1 and the anode electrode 2. As shown in Figures 4 and 5, the cathode electrode 1 includes a first cathode layer 1a, which includes a cathode current collector 10, a first cathode active material layer 11, and a second cathode active material layer 12. The cathode current collector 10 includes a first surface and a second surface disposed opposite to each other. The first cathode active material layer 11 is disposed on the first surface of the cathode current collector 10, and the second cathode active material layer 12 is disposed on the second surface of the cathode current collector 10. The first cathode active material layer 11 has a first groove 13 for exposing the cathode current collector 10. The cathode electrode 1 also includes a cathode tab 14, which is at least partially disposed in the first groove 13 and electrically connected to the cathode current collector 10 (first surface). Along a first direction X, the second cathode active material layer 12 overlaps with the cathode tab 14, where the first direction X is the thickness direction of the cathode electrode 1. In this embodiment, the cathode current collector 10 is an aluminum foil, and the cathode tab 14 is an aluminum tab.

[0053] As shown in Figures 4 and 6, the anode electrode 2 includes a first anode layer 2a, which includes an anode current collector 20, a first anode active material layer 21, and a second anode active material layer 22. The anode current collector 20 includes a third surface and a fourth surface disposed opposite to each other. The first anode active material layer 21 is disposed on the third surface of the anode current collector 20, and the second anode active material layer 22 is disposed on the fourth surface of the anode current collector 20.

[0054] The diaphragm 3 includes a first diaphragm layer 3a, which is disposed between the first anode active material layer 21 and the second cathode active material layer 12. The first diaphragm layer 3a is connected to both the first anode active material layer 21 and the second cathode active material layer 12. One side of the first diaphragm layer 3a is connected to the first anode active material layer 21, and the other side is connected to the second cathode active material layer 12.

[0055] Along the second direction Y, the edge of the first anode layer 2a extends beyond the first cathode layer 1a. Therefore, along the second direction Y, there is a certain distance between the edges of the first anode layer 2a and the first cathode layer 1a. As shown in Figure 7, the cathode tab 14 includes a first segment 141 and a second segment 142. The first segment 141 extends beyond the first cathode layer 1a along the second direction Y and overlaps with the first anode layer 2a along the first direction X. The second segment 142 is in electrical contact with the cathode current collector 10. The second direction Y is the direction in which the second segment 142 extends toward the edge of the first cathode layer 2a.

[0056] As shown in Figures 4 and 6, a second groove 23 is provided at the edge of the first anode active material layer 21, exposing the anode current collector 20. Along the second direction Y, the second groove 23 covers the first section 141 of the cathode tab 14. The second direction Y is the thickness direction of the cathode electrode 1, that is, the direction perpendicular to the cathode electrode 1 and pointing from the cathode electrode 1 to the anode electrode 2.

[0057] Specifically, as shown in Figure 6, the second groove 23 is formed by removing the first anode active material layer 21 of the first anode layer 2a using a laser cleaning process. As shown in Figure 4, along the first direction X, the second groove 23 covers the first section 141 of the cathode tab 14. That is, in the second direction Y, the boundary of the second groove 23 partially coincides with the cathode tab 14, or the boundary of the cathode tab 14 may fall completely within the range of the second groove 23, and the two boundaries do not coincide.

[0058] In this way, when the cathode tab 14 moves closer to the first anode layer 2a due to special environment, the cathode tab 14 moves closer to the second groove 23. Under special environments such as drops, rolling, and high temperatures, this helps to reduce the probability of direct contact between the cathode tab 14 and the first anode active material layer 21, thereby greatly improving the safety performance of the battery.

[0059] In some embodiments, as shown in FIG14, the cathode tab 14 is bent toward the second groove 23.

[0060] In this way, since the cathode tab 14 is welded to the first surface of the cathode current collector 10, 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 when it falls, thus reducing the tearing of the cathode tab 14 on the cathode current collector 10 when it falls and reducing the drop failure rate of the cathode tab 14.

[0061] In some embodiments, as shown in FIG4 and FIG5, the edge of the first cathode layer 1a is provided with a notch 15, and the first segment 141 of the cathode tab 14 protrudes from the edge of the first cathode layer 1a at the notch 15. Therefore, along the second direction Y, the notch 15 and the first segment 141 partially overlap.

[0062] As shown in Figure 7, the first segment 141 includes a first sub-segment 1411 overlapping with the notch 15 and a second sub-segment 1412 extending beyond the notch 15. Because the first cathode layer 1a has the notch 15, the first sub-segment 1411 also risks contacting the first anode active material layer 21. Therefore, in this embodiment, along the first direction X, the second groove 23 covers the first sub-segment 1411 and the second sub-segment 1412, ensuring that both the first sub-segment 1411 and the second sub-segment 1412 are within the boundary of the second groove 23. The first anode active material layer 21 on the first anode layer 2a corresponding to the first segment 141 is cleared by the second groove 23, thereby reducing the probability of the cathode tab 14 contacting the first anode active material layer 21 and reducing the risk of internal short circuits in the secondary battery.

[0063] It should be noted that the size of the second groove 23 needs to be such that it can cover the first segment 141 along the first direction X, so as to reduce the risk of the cathode tab 14 coming into contact with the first anode active material layer 21.

[0064] However, the larger the second groove 23 is, the more of the first anode active material layer 21 needs to be removed from the first anode layer 2a. Therefore, while ensuring the size of the second groove 23 covers the first segment 141, controlling the size of the second groove 23 can improve the energy density of the secondary battery. To this end, in this embodiment, as shown in FIG8, the width of the second groove 23 along the third direction Z is W1; as shown in FIG9, the width of the notch 15 is W2; and the width of the first segment 141 of the cathode tab 14 is W3. Therefore, W3 ≤ W1 ≤ W2. That is, the maximum value of the width W1 of the second groove 23 in the third direction Z is the same as the width W2 of the notch 15. By controlling W3 ≤ W1 ≤ W2, the risk of the cathode tab 14 directly contacting the first anode active material layer 21 is further reduced, improving the safety performance of the secondary battery and reducing the impact on the energy density of the secondary battery.

[0065] As shown in Figure 9, the centerline of the first segment 141 along the second direction Y is N1, and the centerline of the notch 15 along the second direction Y is N2. The distance between N1 and N2 is H, where 0 ≤ H ≤ 0.45 (W2 - W3). This arrangement ensures a certain distance between the first segment 141 and both sides of the notch 15 (located in the third direction Z). The position of the first segment 141 is not too far from the centerline N2 of the notch 15 along the second direction Y, which is beneficial for the cathode tab 14 to be bent towards the second groove 23. Simultaneously, it reduces the risk of the first segment 141 contacting the first cathode active material layer 11, thereby improving the conductivity, mechanical stability, chemical compatibility, and safety of the secondary battery.

[0066] In some embodiments of this application, 0 ≤ H ≤ 0.25 (W2 - W3).

[0067] As shown in Figure 8, along the second direction Y, the length of the second groove 23 is L1, and the length of the first segment 141 of the cathode tab 14 is L2, where L2≤L1≤L2+0.5mm.

[0068] In this way, by controlling the length L1 of the second groove 23 along the second direction Y, the risk of the cathode tab 14 directly contacting the first anode active material layer 21 is further reduced, thereby improving the safety performance of the secondary battery and reducing the impact on the energy density of the secondary battery.

[0069] When the secondary battery is charged, lithium ions will pass through the first separator layer 3a from the second cathode active material layer 12 to the first anode active material layer 21. Therefore, the surface of the first anode active material layer 21 needs to have enough anode active material to absorb these lithium ions, so as to reduce the probability of lithium ions being deposited on the surface of the first anode active material layer 21, thereby reducing the risk of damaging the first separator layer 3a and causing a short circuit between the cathode electrode 1 and the anode electrode 2.

[0070] Therefore, in some embodiments of this application, as shown in Figures 4 and 10, the first cathode layer 1a further includes a first adhesive tape 4, which is disposed on the surface of the second cathode active material layer 12. Along the first direction X, the first adhesive tape 4 covers the second groove 23, that is, the first adhesive tape 4 covers the second groove 23 by its orthogonal projection onto the first anode layer 2a. The first adhesive tape 4 can be an adhesive tape with insulation and a high melting point, such as polyimide tape.

[0071] In this way, by setting the first adhesive tape 4 on the second cathode active material layer 12 and making the boundary of the first adhesive tape 4 extend beyond the second groove 23, the requirement of overhang (the boundary of the anode electrode extends beyond the cathode electrode) is met, and the risk of lithium plating is further reduced.

[0072] In some embodiments, as shown in Figures 4 and 11, the first anode layer 2a further includes a second adhesive tape 5, which is disposed on the surface of the first anode active material layer 21 and covers the second groove 23. The second adhesive tape 5 can be an adhesive tape with insulation and a high melting point, such as polyimide tape.

[0073] In another embodiment of this application, the first adhesive tape 4 and the second adhesive tape 5 can be insulating tapes, including but not limited to polyimide tape, polyester tape, non-woven tape, and fiberglass tape. Such adhesive tapes possess properties such as resistance to electrolyte corrosion, high adhesion, and softness, allowing them to function effectively in lithium batteries.

[0074] In another embodiment of this application, the second adhesive tape 5 bonds the first anode active material layer 21 and the first diaphragm layer 3a. Thus, when the first diaphragm layer 3a tends to shrink due to factors such as heat, the second adhesive tape 5 restrains the first diaphragm layer 3a, reducing the risk of shrinkage.

[0075] Furthermore, while the second adhesive tape 5 seals the second groove 23, it also covers the first anode active material layer 21 at the edge of the second groove 23. Therefore, in some embodiments, as shown in FIG4, the first adhesive tape 4 covers the second adhesive tape 5 along the first direction X; that is, the orthographic projection of the first adhesive tape 4 onto the surface of the first anode material layer 21 covers the second adhesive tape 5. In this way, the boundary of the first adhesive tape 4 extends beyond the second adhesive tape 5 along the first direction X, satisfying the overhang requirement (the anode electrode boundary extends beyond the cathode electrode), further reducing the risk of lithium plating.

[0076] Along the second direction Y, the edge of the first adhesive tape 4 extends beyond the first anode layer 1a. In this way, the first adhesive tape 4 separates the portion of the cathode tab 14 extending beyond the first cathode layer 1a from the first anode layer 2a, reducing the risk of the cathode tab 14 contacting the first anode active material layer 21 and / or the anode current collector 20. In some embodiments, the cathode tab 14 is at least partially bent towards the second groove 23, while the first adhesive tape 4 adheres to the second cathode active material layer 12 and the first separator layer 3a. On one hand, the first separator layer 3a increases the bonding area of ​​the first adhesive tape 4, allowing the first separator layer 3 to support the first adhesive tape 4, reducing the risk of the first adhesive tape 4 detaching from the second cathode active material layer 12 when it shifts due to the bending of the cathode tab 14, thus improving the stability and safety of the secondary battery. On the other hand, the first adhesive tape 4 constrains the first separator layer 3a, reducing the risk of the first separator layer 3a shrinking.

[0077] In another embodiment of this application, as shown in FIG12, the second groove 23 is filled with hot melt adhesive 6. In this way, the hot melt adhesive can reduce the risk of the first section 141 contacting the anode current collector 10, further improving the safety performance of the secondary battery. Furthermore, the hot melt adhesive can flow after being heated to fill the second groove 23, thereby improving the flatness of the secondary battery.

[0078] In another embodiment of this application, as shown in FIG13, the second groove 23 is further filled with hot melt adhesive 6, and the first anode active material layer 21 is provided with a second adhesive tape 5 covering the second groove 23. In this way, the hot melt adhesive 6 can reduce the accumulation of electrolyte in the second groove 23 and reduce the risk of the second adhesive tape 5 falling off.

[0079] Another embodiment of this application discloses an electrochemical device, including the secondary battery in the above embodiments.

[0080] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0081] Comparative Example 1:

[0082] A secondary battery, as shown in Figure 15, includes a cathode electrode 1 and an anode electrode 2, with a separator 3 disposed between the cathode electrode 1 and the anode electrode 2. The cathode electrode 1, the separator 3, and the anode electrode 2 are stacked and wound into shape.

[0083] The cathode electrode 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. The first surface has a first cathode active material layer 11, and the second surface has a second cathode active material layer 12. The anode electrode 2 includes an anode current collector 20. The anode current collector 20 includes a first surface and a second surface. The first surface has a first anode active material layer 21, and the second surface has a second anode active material layer 22. The separator 3 includes a first separator layer 3a, which is located between the first anode active material layer 21 and the second cathode active material layer 12.

[0084] Comparative Example 2:

[0085] Based on Comparative Example 1, as shown in Figure 16, a second groove 23 is formed on the surface of the first anode active material layer 21. Along the first direction X, the first segment 141 of the cathode tab 14 covers the second groove 23. Specifically, along the third direction Z, the width of the second groove 23 is W1, and the width of the first segment 141 of the cathode tab 14 is W3, where W1 < W3, and W1 = 5 mm; along the second direction Y, the length of the second groove 23 is L1, and the length of the first segment 141 of the cathode tab 14 is L2, where L1 = L2 = 3 mm.

[0086] Comparative Example 3:

[0087] Based on Comparative Example 2, in Comparative Example 3, the width of the second groove 23 is W1, and the width of the first segment 141 of the cathode tab 14 is W3, where W1 = W3 = 6 mm. Along the second direction Y, the length of the second groove 23 is L1, and the length of the first segment 141 of the cathode tab 14 is L2, where L1 < L2, and L1 = 2 mm.

[0088] Example 1:

[0089] A secondary battery, with an initial thickness of 4.8 mm, a length of 87 mm, and a width of 64 mm at 50% SOC, is assembled as follows:

[0090] (1) Preparation of anode sheet: Artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1.5:2.5, and deionized water was added as a solvent to prepare a slurry with a weight percentage of 50 wt%. The slurry was stirred evenly and uniformly coated on one surface of a copper foil. Then, it was dried at 110°C to obtain an anode sheet with a single-sided coating of anode active material layer. When preparing a double-sided coated anode sheet, the above steps were repeated on the other surface of the anode sheet to obtain an anode sheet with a double-sided coating of anode active material layer. The coated electrode sheet was then cold-pressed to a thickness of 105 μm, and grooves were set on the anode active material. The anode tabs were then welded to the copper foil exposed in the grooves. Then, the position of the second groove on the anode electrode sheet was determined by a laser positioning system, and laser cleaning was performed.

[0091] (2) Preparation of cathode sheet: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The slurry was uniformly coated on one surface of an aluminum foil and then dried at 90°C to obtain a cathode sheet with a single-sided coating of cathode active material. When preparing a double-sided coated cathode sheet, the above coating steps were repeated on the other surface of the aluminum foil. The coated electrode sheet was then cold-pressed to a thickness of 95 μm, grooves were formed on the cathode active material, and the cathode tabs were welded to the aluminum foil exposed in the grooves.

[0092] (3) Preparation of 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 to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0093] (4) Preparation of the diaphragm: A three-layer diaphragm is adopted, which includes an adhesive layer, a substrate layer and an adhesive layer stacked together. The first substrate layer is made of polyethylene (PE), the adhesive layer is made of PVDF, and the adhesive layer also contains inorganic boehmite particles.

[0094] (5) Electrode assembly preparation: The cathode electrode, diaphragm and anode electrode are stacked and then wound into shape.

[0095] (6) Secondary battery assembly: Place the dented aluminum-plastic film in the assembly fixture with the dent facing upwards, place the electrode assembly in the dent, and apply external force to press it firmly. Then cover the electrode assembly with another dented aluminum-plastic film with the dent facing downwards, and heat seal the two aluminum-plastic films around their perimeter by hot pressing to obtain the assembled electrode assembly.

[0096] (7) Electrolyte injection and encapsulation: Electrolyte is injected into the assembled electrode assembly, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, a secondary battery is obtained.

[0097] As shown in Figure 4, in Embodiment 1, along the first direction X, the second groove 23 covers the first segment 141 of the cathode tab 14. Along the third direction Z, the width of the second groove 23 is W1, and the width of the first segment 141 of the cathode tab 14 is W3, where W1 = W3 = 6 mm. Along the second direction Y, the length of the second groove 23 is L1, and the length of the first segment 141 of the cathode tab 14 is L2, where L1 = L2 = 3 mm.

[0098] Example 2:

[0099] Based on Example 1, Example 2 is an improvement. A notch 15 is provided in the cathode current collector along the third direction Z. The width of the notch 15 is W2 = 11 mm, where W3 < W1 < W2, and W1 = 8 mm is taken.

[0100] Example 3:

[0101] Based on Example 2, adjustments were made. In Example 3, W1 = W2 = 11 mm and L1 = L2 = 3 mm.

[0102] Example 4:

[0103] Based on Example 2, adjustments were made. In Example 4, W1 > W2, W1 = 12mm, and L1 = L2 = 3mm.

[0104] Example 5:

[0105] Based on Example 3, adjustments were made. In Example 5, W1 = W2 = 11 mm, L2 < L1 < L2 + 0.5 mm, and L1 = 3.2 mm.

[0106] Example 6:

[0107] Based on Example 5, in Example 6, W1 = W2 = 11 mm and L1 = L2 + 0.5 mm = 3.5 mm.

[0108] Example 7:

[0109] Based on Example 5, adjustments were made. In Example 6, W1 = W2 = 11 mm, L1 > L2 + 0.5 mm, and L1 = 3.7 mm.

[0110] 1. Secondary battery drop test

[0111] First, the secondary batteries to be tested were pretreated under the following conditions: temperature 20±5℃, standing for 60 minutes, then discharged at a constant current of 0.7C to 3.0V, and left to stand for 10 minutes; then charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage of 4.25V to 0.05C. After pretreatment, the secondary batteries were clamped in a fixture and dropped onto a floor from a height of 1.5m. Two rounds of testing were conducted, with the drop sequence as follows: forward direction: bottom right-bottom left-top right-top left; reverse direction: top left-top right-bottom left-bottom right (angle: 45±15 degrees). During the test, if the secondary battery did not catch fire, explode, or emit smoke, the drop test was considered passed; otherwise, the drop test failed. If 100 secondary batteries were tested, and the number of batteries that passed the test was X, the pass rate was X / 100.

[0112] 2. Secondary battery hot box test:

[0113] First, the secondary batteries to be tested undergo pretreatment. The pretreatment conditions are as follows: after standing at a test temperature of 20℃ (±5℃) for 60 minutes, they are discharged to 3.0V using a constant current of 0.7C and then stood for 10 minutes; then, they are charged to 4.25V using a constant current of 0.5C, and then charged to 0.05C using a constant voltage of 4.25V. After pretreatment, the secondary batteries are placed vertically in a hot chamber for hot chamber testing. The temperature in the hot chamber is increased to 130±2℃ at a rate of 5±2℃ / min and maintained for 60 minutes. During the test, if the secondary battery does not burn or explode, the hot chamber test is considered passed; otherwise, the hot chamber test is considered failed. If 100 secondary batteries are tested, the number of cells that pass the test is X, and the pass rate is X / 100.

[0114] Table 1 Note: In Table 1, "\" indicates that the parameter is not included.

[0115] The experimental data in Table 1 show that, according to proportions 1 to 3 and examples 1 to 7, when the first anode layer 2a does not have the second groove 23, or when the second groove 23 does not cover the first segment 141 of the cathode tab 14 along the second direction Y, the drop test pass rate and the hot box test pass rate are both below 78%. When the first anode layer 2a has the second groove 23, and the second groove 23 covers the first segment 141 of the cathode tab 14 along the first direction X, the drop test pass rate and the hot box test pass rate can both reach or exceed 90%. When L1 = L2, further increasing W1 to make W1 > W2 does not significantly change the drop test pass rate and the hot box test pass rate, indicating that further increasing the size of W1 does not significantly improve the safety performance of the secondary battery. Similarly, when W1 = W2, further increasing L1 to make L1 > L2 + 0.5 mm reaches the upper limit of both the drop test pass rate and the hot box test pass rate, and further increasing the size of L1 does not significantly improve the safety performance of the secondary battery.

[0116] Therefore, as can be seen from Examples 1 to 7 in Table 1, when W3≤W1≤W2 and / or L2≤L1≤L2+0.5mm, 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.

[0117] Example 6:

[0118] In Example 6, W2-W3 = 5mm, H = 0.

[0119] Example 8:

[0120] Based on Example 6, adjustments were made. In Example 8, H = 0.25(W2 - W3) = 1.25 mm.

[0121] Example 9:

[0122] Based on Example 6, adjustments were made. In Example 9, H = 0.45(W2 - W3) = 2.25 mm.

[0123] Example 10:

[0124] Based on Example 6, adjustments were made. In Example 10, H = 0.50(W2 - W3) = 2.50 mm.

[0125] Table 2

[0126] As can be seen from Examples 6 and 8-10, limiting 0≤H≤0.45(W2-W3) facilitates the bending of the cathode tab toward the second groove, thereby improving the drop test pass rate of the secondary battery. Furthermore, further limiting 0≤H≤0.25(W2-W3) facilitates better bending of the tab, further improving the drop test pass rate of the secondary battery.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; under the concept of the present invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of brevity; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A secondary battery characterized by comprising: Includes an electrode assembly, the electrode assembly comprising: A cathode electrode sheet includes a first cathode layer, which includes a cathode current collector, a first cathode active material layer, and a second cathode active material layer. The cathode current collector includes a first surface and a second surface disposed opposite to each other. The first cathode active material layer is disposed on the first surface, and the second cathode active material layer is disposed on the second surface. The first cathode active material layer has a first groove that exposes the cathode current collector. The cathode electrode sheet also includes a cathode tab, which is at least partially disposed in the first groove and electrically connected to the cathode current collector. Along a first direction, the second cathode active material layer overlaps with the cathode tab. The first direction is the thickness direction of the cathode electrode sheet. An anode electrode includes a first anode layer, the first anode layer including an anode current collector and a first anode active material layer, the anode current collector including a third surface and a fourth surface disposed opposite to each other, the first anode active material layer being disposed on the third surface; along a second direction, the edge of the first anode layer extends beyond a first cathode layer, the cathode tab includes a first segment and a second segment, the first segment extending beyond the first cathode layer along the second direction and overlapping the first anode layer along the first direction, the second segment being in electrical contact with the cathode current collector, the second direction being the direction in which the second segment extends; and The diaphragm includes a first diaphragm layer, which is disposed between the first anode active material layer and the second cathode active material layer, and is connected to both the first anode active material layer and the second cathode active material layer. The first anode active material layer is provided with a second groove, the second groove exposes the anode current collector, and along the first direction, the second groove covers the first segment.

2. The secondary battery according to claim 1, characterized by The cathode tab is bent toward the second groove.

3. The secondary battery according to claim 2, characterized by The first cathode layer has a notch at its edge, and along the first direction, the first segment at least partially overlaps with the notch.

4. The secondary battery according to claim 3, characterized by The first cathode layer further includes a first adhesive tape, which is disposed on the surface of the second cathode active material layer and covers the second groove along the first direction.

5. The secondary battery according to claim 4, characterized by The first anode layer further includes a second adhesive tape disposed on the surface of the first anode active material layer, and the second adhesive tape covers the second groove.

6. The secondary battery according to claim 4 or 5, characterized by The first anode layer also includes hot melt adhesive filled in the second groove, the hot melt adhesive at least partially covering the anode current collector exposed at the second groove.

7. The secondary battery according to claim 5, characterized by Along the first direction, the first adhesive tape covers the second adhesive tape.

8. The secondary battery according to claim 4 or 7, characterized by Along the second direction, the edge of the first adhesive tape extends beyond the first anode layer.

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

10. The secondary battery according to claim 9, characterized in that, The distance between the centerline of the first segment along the second direction and the centerline of the gap along the second direction is H, where 0 ≤ H ≤ 0.45 (W2 - W3).

11. The secondary battery according to claim 10, characterized in that, 0≤H≤0.25(W2-W3).

12. The secondary battery according to claim 3 or 9, characterized in that, Along the second direction, the length of the second groove is L1, and the length of the first segment is L2, wherein L2≤L1≤L2+0.5mm.

13. The secondary battery according to claim 4 or 8, characterized in that, The cathode tab is bent toward the second groove, and the first adhesive tape adheres to the second cathode active material layer and the first diaphragm layer.

14. The secondary battery according to claim 5, characterized in that, The second adhesive tape bonds the first anode active material layer and the first diaphragm layer.

15. An electrochemical device, characterized in that, Includes the secondary battery as described in any one of claims 1-14.

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