Secondary battery, preparation method thereof and electronic equipment

Abstract

The invention discloses a secondary battery, a preparation method thereof and electronic equipment, a first current collector comprises a first main body part and a single first tab, and the first main body part and the first tab are integrally arranged. The first surface of the first main body part comprises a first area connected with the first tab, a first connecting position is arranged between the first main body part and the first tab, and the projection of the first area falls into the projection range of the first connecting position in the width direction of the first main body part. The width of the first body portion is W, the length of the first region is W1, W1 / W < = 8%, and the first region is provided with a first active material layer. The distances from the first tab to the two ends of the first main body part are L1 and L2 respectively, and L1-L2 is less than or equal to 100mm. The secondary battery further comprises a first adapter, one end of the first adapter is connected with the first tab, and the other end of the first adapter extends out of the shell. The charge-discharge rate of the secondary battery can be improved, and the energy density of the secondary battery can be improved.

Description

Technical Field

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

[0002] As a bridge for the electrical connection between the secondary battery and the external circuit, the tab is usually made of a metal material. The tab is welded to the current collector inside the secondary battery, so that the tab can be conducted with the electrode assembly inside the secondary battery, thereby achieving the purpose of transmitting current.

[0003] To facilitate the welding of the tab, double-sided empty foil areas are usually required to be provided on the current collector. The welding head and the welding seat are respectively in contact with the current collector at the empty foil areas on both sides for welding. When welding the tab to the empty foil area of the current collector, partial welding burrs usually appear. These burrs are likely to pierce the separator, easily causing the short-circuit failure of the positive and negative electrode plates inside the secondary battery. To reduce the risk of the burrs piercing the separator, an insulating adhesive layer is usually required to cover the welding area between the tab and the current collector to isolate the burrs.

[0004] However, the insulating adhesive layer occupies a certain space, and the insulating adhesive layer covers a part of the active material layer. It is difficult for this part of the active material layer to undergo an electrochemical reaction, resulting in a loss of the energy density of the secondary battery. Summary of the Invention

[0005] The present application aims to provide a secondary battery, a preparation method thereof, and an electronic device, aiming to improve the energy density of the secondary battery.

[0006] The embodiments of the present application adopt the following technical solutions to solve its technical problems:

[0007] In a first aspect, the present application provides a secondary battery, including a housing and an electrode assembly disposed within the housing. The electrode assembly includes a first electrode tab, a separator, and a second electrode tab that are stacked and wound. The first electrode tab includes a first current collector and a first active material layer. The first current collector includes a first main body portion and a single first tab. The first main body portion and the first tab are integrally provided, and the first tab extends from one side in the width direction of the first main body portion. The first main body portion includes a first surface on one side in the thickness direction of the first main body portion. The first surface includes a first region connected to the first tab. There is a first connection position between the first main body portion and the first tab. Along the width direction of the first main body portion, the projection of the first region falls within the projection range of the first connection position. Along the width direction of the first main body portion, the width of the first main body portion is W, the length of the first region is W1, and W1 / W ≤ 8%. The first active material layer is provided in the first region. Along the winding direction of the first electrode tab, the first main body portion includes a first end portion and a second end portion that are oppositely arranged. The length between the first tab and the first end portion is L1, and the length between the first tab and the second end portion is L2, and |L1 - L2| ≤ 100 mm. The secondary battery further includes a first adapter. One end of the first adapter is connected to the first tab, and the other end of the first adapter extends outside the housing.

[0008] In the above technical solution, by integrally providing the first main body portion and the first tab, potential risks such as poor soldering and defective soldering between the first tab and the first main body portion can be reduced. Secondly, the current conduction path between the first tab and the first main body portion is more direct and efficient, reducing energy loss and heat generation problems caused by contact resistance between the first tab and the first main body portion, which helps to improve the power performance and charge-discharge rate of the secondary battery. In addition, since the first tab and the first main body portion are integrally provided, there are no soldering burrs, and there is no need to provide an insulating adhesive layer to cover the soldering burrs. This not only reduces the risk of the separator being pierced but also makes full use of the space to improve the energy density of the secondary battery.

[0009] Due to the above-mentioned integral setting of the first tab and the first main body portion, there is no need to perform the operation of grooving and soldering the tab on the first active material layer of the first surface, and the proportion of the first active material layer is higher, which can improve the energy density of the secondary battery. There is also no need for an insulating adhesive layer to cover the soldering burrs, enabling the first active material layer originally covered by the insulating adhesive layer on the first surface to undergo an electrochemical reaction, which can further improve the energy density of the secondary battery; and it can reduce the contact resistance and improve the charge-discharge rate of the secondary battery.

[0010] At the same time, by limiting |L1 - L2| ≤ 100 mm, the first tab can be approximately located at the middle position in the length direction of the first electrode tab, thereby forming a middle-tab structure. Combining the setting of the first active material layer in the above-mentioned first region, the electron movement path between the first tab and the first active material layer is shortened, which can reduce the resistance of the secondary battery and improve the charge-discharge rate of the secondary battery.

[0011] Since the first tab and the first main body part are integrally provided, and due to the structure of the middle tab, the contact resistance between the first tab and the first main body part and between the first tab and the first active material layer is reduced, the conductivity is enhanced, and the charge and discharge rate of the secondary battery is improved. Therefore, a single first tab can be directly electrically connected to the first adapter, occupying less space, providing a larger welding space, improving the connection strength, and reducing the gap space between the electrode assembly and the housing, thereby improving the energy density of the secondary battery.

[0012] In some preferred embodiments, both the first tab and the first adapter extend along the width direction of the first main body part. The first tab and the first adapter directly extend out of the housing, which can reduce the influence on the dimensions of the secondary battery in the thickness direction due to the bending or turning of the first tab or the first adapter, and is applicable to ultra-thin secondary batteries. Moreover, the structure of the first tab and the first adapter directly extending out reduces the bending and turning during the current transmission process, reduces the resistance and energy loss, and improves the efficiency of current conduction.

[0013] In some preferred embodiments, along the extension direction of the first tab, the first tab includes a first connecting part and a first bending part connected in sequence. Along the extension direction of the first adapter, the first adapter includes a second connecting part and a second bending part connected in sequence. The first tab is bent through the first bending part, the first connecting part is connected to the second connecting part, and the first adapter extends out of the housing after being bent through the second bending part. The structure of the first tab and the first adapter being bent out can effectively utilize the space and improve the energy density of the secondary battery.

[0014] In some preferred embodiments, at least part of the surface of the first active material layer located in the first region is in direct contact with the separator. The first active material layer located in the first region can directly transfer lithium ions through the separator, and then the lithium ions can be deintercalated and intercalated, and an electrochemical reaction occurs, which can improve the energy density of the secondary battery.

[0015] In some preferred embodiments, |L1 - L2| ≤ 30 mm, the first tab is closer to the middle position of the first active material layer, the electron movement path between the first tab and the first active material layer is shortened, the resistance of the secondary battery can be further reduced, and the charge and discharge rate of the secondary battery can be improved.

[0016] In some preferred embodiments, the first main body portion further includes a second surface. Along the thickness direction of the first main body portion, the first surface and the second surface are oppositely arranged. The second surface includes a second region connected to the first tab. Along the width direction of the first main body portion, the projection of the second region falls within the projection range of the first connection position. Along the width direction of the first main body portion, the length of the second region is W2, and W2 / W ≤ 8%. The second region is provided with a first active material layer. There is no need to perform the operation of grooving and welding the tab on the first active material layer on the first surface, and a continuous first active material layer can be directly coated on the first surface a. The proportion of the first active material layer is higher, which can improve the energy density of the secondary battery.

[0017] In some preferred embodiments, in the second region, at least part of the surface of the first active material layer is in direct contact with the separator. The first active material layer located in the second region can directly transport lithium ions through the separator, and then the lithium ions can be extracted and inserted, and an electrochemical reaction occurs, which can improve the energy density of the secondary battery.

[0018] In some preferred embodiments, along the thickness direction of the first main body portion, the second electrode plate adjacent to the first region includes a third region oppositely arranged with respect to the first region. The third region is provided with a second active material layer, and the second active material layer located in the third region is in direct contact with the separator. There is no need to perform the operation of grooving and welding the tab on the second active material layer on the third surface, and the proportion of the second active material layer is higher, which can improve the energy density of the secondary battery.

[0019] In some preferred embodiments, along the thickness direction of the first main body portion, the second electrode plate adjacent to the second region includes a fourth region oppositely arranged with respect to the second region. The fourth region is provided with a second active material layer, and the second active material layer located in the fourth region is in direct contact with the separator. There is no need to perform the operation of grooving and welding the tab on the second active material layer on the fourth surface, and the proportion of the second active material layer is higher, which can improve the energy density of the secondary battery.

[0020] In some preferred embodiments, along the winding direction of the first electrode plate, the width of the first tab is W3, and 6 mm ≤ W3 ≤ 30 mm. While improving the current-carrying capacity of the first tab, the risk of breakage and tearing caused by the first tab passing through the corner can be reduced.

[0021] In some preferred embodiments, the first tab is a positive tab, and the thickness of the first tab is T1, and 8 μm ≤ T1 ≤ 20 μm; or, the first tab is a negative tab, and the thickness of the first tab is T1, and 5 μm ≤ T1 ≤ 15 μm. The thickness of the first adapter is T2, and 40 μm ≤ T2 ≤ 100 μm. While improving the current-carrying capacity of the secondary battery, the influence of the first adapter on the energy density of the secondary battery can be reduced.

[0022] In some preferred embodiments, the connection area between the first adapter and the first tab is S, 10 mm 2 ≤ S ≤ 140 mm 2 . While improving the current-carrying capacity and connection strength, the space occupied by the first tab and the first adapter can be reduced, and the breakage between the first tab and the first adapter can be reduced.

[0023] In some preferred embodiments, along the width direction of the first main body portion, the first main body portion includes a first edge on the side where the first tab protrudes. The first surface includes a first empty foil area, and along the width direction of the first main body portion, the first empty foil area is located between the first active material layer and the first edge. The secondary battery further includes a first insulating layer disposed in the first empty foil area. The first insulating layer can cover the first empty foil area and the partial trimming burrs of the first edge, thereby reducing the burrs from piercing the separator.

[0024] In some preferred embodiments, the secondary battery further includes a first adhesive layer that covers the connection between the first adapter and the first tab, and the first adhesive layer extends to the first active material layer. Along the width direction of the first main body portion, the width of the first adhesive layer covering the first active material layer is W4, 0 < W4 ≤ 1 mm, which can reduce the influence of the first adhesive layer 60 on the energy density of the secondary battery 1000.

[0025] In a second aspect, the present application also proposes an electronic device including the secondary battery according to any of the embodiments in the first aspect above.

[0026] In a third aspect, the present application also proposes a method for manufacturing a secondary battery, including the following steps:

[0027] Provide a first current collector, cut the first current collector to obtain an integrally formed first main body portion and a first tab, and the distances between the first tab and the two ends of the first main body portion in the length direction are L1 and L2 respectively, |L1 - L2| ≤ 100 mm.

[0028] Set a first active material layer on at least one surface in the thickness direction of the first main body portion to obtain a first electrode sheet; wherein, the first main body portion has a first region connected to the first tab, and there is a first connection position between the first main body portion and the first tab. Along the width direction of the first main body portion, the projection of the first region falls within the projection range of the first connection position; along the width direction of the first main body portion, the width of the first main body portion is W, the length of the first region is W1, W1 / W ≤ 8%, and the first region is provided with a first active material layer.

[0029] Provide a separator and a second electrode sheet, stack and wind the separator, the first electrode sheet, and the second electrode sheet in sequence to obtain an electrode assembly.

[0030] Provide a first adapter, and electrically connect one end of the first adapter to the first tab.

[0031] Provide a housing, dispose an electrode assembly within the housing, and extend the other end of the first adapter outside the housing.

[0032] Inject electrolyte into the housing and seal it to obtain a secondary battery.

[0033] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the following description, or through the implementation of the embodiments of the present application. Description of the Drawings

[0034] One or more embodiments are illustrated by corresponding drawings. These illustrative descriptions do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, unless otherwise stated. The drawings in the figures do not constitute a scale limitation.

[0035] Figure 1 Schematic diagram of the stacked structure of the positive and negative electrode plates and the separator in the prior art;

[0036] Figure 2 Schematic diagram of the structure of the secondary battery according to some embodiments of the present application;

[0037] Figure 3 Exploded view of the secondary battery according to some embodiments of the present application;

[0038] Figure 4 Schematic diagram of the winding structure of the electrode assembly according to some embodiments of the present application;

[0039] Figure 5 Structural view of the first electrode plate according to some embodiments of the present application;

[0040] Figure 6 Top view of the first current collector according to some embodiments of the present application;

[0041] Figure 7 Structural view of the first electrode plate according to some embodiments of the present application;

[0042] Figure 8 is Figure 4 Partial enlarged view at A in

[0043] Figure 9 is Figure 2 A-A sectional view of

[0044] Figure 10 For another embodiment of the present application Figure 2 A-A sectional view of

[0045] Figure 11 Bottom view of the first current collector according to some embodiments of the present application;

[0046] Figure 12 Structural view of the second pole piece according to some embodiments of the present application;

[0047] Figure 13 Top view of the first pole piece according to some embodiments of the present application;

[0048] Figure 14 Top view of the first pole piece according to some embodiments of the present application;

[0049] Figure 15 is Figure 9 Local enlarged view at position C in

[0050] Explanation of reference numerals in the drawings:

[0051] 1000, secondary battery;

[0052] 100, electrode assembly;

[0053] 10, first pole piece; 11, first current collector; 11a, first surface; 11b, second surface; 111, first main body; 111a, first end; 111b, second end; 1111, first region; 1112, second region; 112, first tab; 1121, first bent portion; 1122, first connecting portion; 1113, first edge; 1114, first empty foil area; 12, first active material layer; 13, first connection position;

[0054] 20, second pole piece; 21, second current collector; 22a, third surface; 22b, fourth surface; 211, second main body; 2111, third region; 2121, fourth region; 212, second tab; 22, second active material layer;

[0055] 30, separator;

[0056] 40, first adapter; 41, second connecting portion; 42, second bent portion;

[0057] 50, first insulating layer;

[0058] 60, first adhesive layer;

[0059] 200, housing;

[0060] 10a, positive electrode pole piece; 10a2, positive electrode current collector; 10a1, positive electrode tab; 10a3, positive electrode active material layer;

[0061] 20a, negative electrode pole piece; 20a2, negative electrode current collector; 20a1, negative electrode tab; 20a3, negative electrode active material layer;

[0062] 300, insulating adhesive layer; 400, pole piece adhesive;

[0063] X, the first direction; Y, the second direction; Z, the third direction. Detailed implementation manners

[0064] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application.

[0065] Referring to "embodiments" in the present application means that specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0066] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means two or more, unless otherwise specifically defined.

[0067] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0068] The technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0069] As a bridge for electrically connecting a secondary battery to an external circuit, the tab is usually made of a metal material. The tab is welded to the current collector inside the secondary battery, which can make the tab conduct with the electrode assembly inside the secondary battery, so as to achieve the purpose of transmitting current.

[0070] Please refer to Figure 1 , Figure 1The stacked structure of the positive electrode tab 10a, the separator 30, and the negative electrode tab 20a is shown. After stacking, it can be wound to form an electrode assembly. To facilitate the welding of the positive electrode tab 10a1, a double-sided empty foil area (the empty foil area is the area on the current collector where the active material layer is not provided) is usually required on the positive current collector 10a2. The welding seat contacts the positive current collector 10a2 in one empty foil area, and the positive electrode tab 10a1 contacts the positive current collector 10a2 in the other empty foil area. And the positive electrode tab 10a1 is welded to the positive current collector 10a2 through a welding head. The negative electrode tab 20a is usually arranged similarly.

[0071] However, when welding the positive electrode tab 10a1 to the positive current collector 10a2 and the negative electrode tab 20a1 to the negative current collector 20a2, welding burrs usually appear. These burrs are likely to pierce the separator 30, easily causing the short-circuit failure of the positive electrode tab 10a and the negative electrode tab 20a inside the secondary battery.

[0072] To reduce the risk of the separator 20 being pierced, as Figure 1 shown, it is usually necessary to set an insulating adhesive layer 300 at the position of the positive electrode tab 10a1, that is, to set an insulating adhesive layer 300 on one empty foil side of the positive current collector 10a2, and also set an insulating adhesive layer 300 on the other empty foil area. The same is true for the negative electrode tab 20a. The setting of the insulating adhesive layers 300 on both sides prevents the burrs from piercing the separator 30.

[0073] Moreover, to enable the negative electrode tab 20a to have sufficient margin to buffer the lithium dissolution, and to reduce the influence of the burrs at the position of the positive electrode tab 10a1 after winding on the negative active material layer 20a3, two electrode adhesives 400 need to be set on the negative electrode tab 20a. Similarly, two electrode adhesives 400 also need to be set on the positive electrode tab 10a to reduce the influence of the burrs at the position of the negative electrode tab 20a1 on the positive active material layer 10a3. However, the setting of multiple layers of adhesive occupies too much space, resulting in the loss of the energy density of the secondary battery. And the inventors of the present application also found that the active material layer covered by each adhesive layer is difficult to undergo an electrochemical reaction. This part of the active material layer occupies space and will also cause the loss of the energy density of the secondary battery. And during the welding process of the tab and the current collector, it may be difficult for the welding material to be in full contact with the tab and the current collector, and there will be a certain contact resistance, affecting the current-carrying capacity of the secondary battery.

[0074] To reduce the above problems, on the first hand, the present application proposes a secondary battery 1000. Please refer to Figures 2 to 4, the secondary battery 1000 includes a housing 200 and an electrode assembly 100, and the electrode assembly 100 is disposed within the housing 200. The electrode assembly 100 includes a first electrode tab 10, a separator 30, and a second electrode tab 20 that are stacked and wound. The polarities of the first electrode tab 10 and the second electrode tab 20 are opposite. For example, the first electrode tab 10 is a positive electrode tab and the second electrode tab 20 is a negative electrode tab, or the first electrode tab 10 is a negative electrode tab and the second electrode tab 20 is a positive electrode tab. The separator 30 is disposed between the first electrode tab 10 and the second electrode tab 20 for insulating and separating the first electrode tab 10 and the second electrode tab 20.

[0075] For the above-mentioned first electrode tab 10, please refer to Figure 5 , the first electrode tab 10 includes a first current collector 11 and a first active material layer 12. The first current collector 11 serves as the conductive substrate of the first electrode tab 10 and can be an aluminum foil, a copper foil, or other metal foils with an overall flat and strip-shaped structure. For example, both aluminum foil and copper foil have high electrical conductivity, which can effectively reduce the internal resistance of the secondary battery 1000, facilitate the improvement of the energy density and power density of the secondary battery 1000, and have good mechanical strength to withstand the expansion and contraction of the secondary battery 1000 during charge and discharge.

[0076] Please refer to Figure 6 , the first current collector 11 includes a first main body portion 111 and a single first electrode lug 112. The first main body portion 111 and the first electrode lug 112 are integrally provided, and the first electrode lug 112 extends from one side of the first main body portion 111 in the width direction (the first direction X). For example, the first electrode lug 112 is directly cut out on one side of the first current collector 11 in the width direction (the first direction X) by means of die cutting.

[0077] In the embodiments of the present application, by integrally providing the first main body portion 111 and the first electrode lug 112, the welding step of the first electrode lug 112 is not required, improving the production efficiency of the secondary battery 1000. Moreover, potential risks such as poor soldering and virtual soldering between the first electrode lug 112 and the first main body portion 111 can be reduced. At the same time, the integral setting reduces the possible loosening and falling off of the first electrode lug 112 during use, reducing the internal short circuit caused by the loosening of the first electrode lug 112.

[0078] Secondly, the current conduction path between the first electrode lug 112 and the first main body portion 111 is more direct and efficient, reducing the energy loss and heat generation problems caused by the contact resistance between the first electrode lug 112 and the first main body portion 111, which helps to improve the power performance and charge-discharge rate of the secondary battery 1000. Furthermore, since the current conduction is more uniform, the heat generation inside the secondary battery 1000 is also more uniform, reducing the phenomenon of local overheating, which helps to improve the safety and cycle life of the secondary battery 1000.

[0079] In addition, since the first tab 112 is integrally provided with the first main body portion 111, there are no welding burrs, and there is no need to provide an insulating adhesive layer to cover the welding burrs. This not only reduces the risk of the separator 30 being punctured, but also makes full use of the space and improves the energy density of the secondary battery 1000.

[0080] Please refer to Figure 5 and Figure 6 , along the thickness direction (the third direction Z) of the first main body portion 111, the first main body portion 111 includes a first surface 11a and a second surface 11b which are oppositely arranged, and the first active material layer 12 can be provided on the first surface 11a. The first active material layer 12 is the core for the occurrence of the electrochemical reaction, and the amount of its components directly affects the energy density of the secondary battery 1000. The first active material layer 12 includes an active material, a conductive agent, an adhesive, etc. After the above-mentioned various material components are mixed and stirred evenly, they are coated on the first surface 11a, and after drying, the first active material layer 12 can be formed on the first surface 11a.

[0081] The first surface 11a includes a first region 1111 connected to the first tab 112. There is a first connection position 13 between the first main body portion 111 and the first tab 112 (the first connection position 13 is the connection portion between the first tab 112 and the first main body portion 111). Along the width direction (the first direction X) of the first main body portion 111, the projection of the first region 1111 falls within the projection range of the first connection position 13. Along the width direction (the first direction X) of the first main body portion 111, the width of the first main body portion 111 is W, the length of the first region 1111 is W, and W1 / W≤8%. The first active material layer 12 is provided on the first region 1111. W1 / W can be any value within 8%, such as 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%, etc.

[0082] For the traditional welded tab structure, it is necessary to remove the first active material layer 12 in the first region 1111 to weld the first tab 112. In the present application, since the first tab 112 is integrally provided with the first main body portion 111, there is no need to perform the operation of grooving and welding the tab on the first active material layer 12 on the first surface 11a, and the continuous first active material layer 12 can be directly coated on the first surface 11a. Compared with the traditional grooved welded tab structure, in the present application, the proportion of the first active material layer 12 is higher, and the energy density of the secondary battery 1000 can be improved.

[0083] Moreover, in the traditional welding tab structure, the insulating adhesive layer covers part of the active material layer, and it is difficult for this part of the active material layer to undergo an electrochemical reaction. The current flowing through the tab first needs to pass through this part of the active material layer that does not undergo an electrochemical reaction, which results in a contact resistance between the tab and the active material layer that undergoes an electrochemical reaction. In the present application, there is no need for the insulating adhesive layer to cover the welding burrs, so that the first active material layer 12 that was originally covered by the insulating adhesive layer on the first surface 11a can undergo an electrochemical reaction, which can further improve the energy density of the secondary battery 1000 and reduce the contact resistance, thereby improving the charge-discharge rate of the secondary battery 1000.

[0084] For example, please further refer to Figure 7 and Figure 8 , at least part of the surface of the first active material layer 12 located in the first region 1111 is in direct contact with the separator 30 ( Figure 8 In order to facilitate the description of the positions of the components, there is a space between the components. After actual winding, direct contact is formed between the components, or there are some small gap spaces). The first active material layer 12 located in the first region 1111 can directly transfer lithium ions through the separator 30, and then the lithium ions can be extracted and inserted, and an electrochemical reaction occurs, which can improve the energy density of the secondary battery 1000.

[0085] Please refer to Figure 6 , in the present application, along the winding direction of the first electrode sheet 10 (the electrode sheet is wound along its length direction / second direction Y), the first main body portion 111 includes a first end portion 111a and a second end portion 111b that are oppositely arranged, and the first tab 112 is located between the first end portion 111a and the second end portion 111b. The length between the first tab 112 and the first end portion 111a is L1, and the length between the first tab 112 and the second end portion 111b is L2, and |L1 - L2| ≤ 100 mm, such as 100 mm, 90 mm, 80 mm, 70 mm, 60 mm, 50 mm, 40 mm, 30 mm, 20 mm, 10 mm, 5 mm, or 0 mm, etc. For the process of slotting and welding tabs on the electrode sheet, specific equipment is usually required to slot the active material layer of the electrode sheet. Limited by the size of traditional equipment, it is usually difficult to determine the intermediate position in the length direction / winding direction of the electrode sheet. In the present application, the method of die-cutting can be directly adopted. First, the intermediate position of the first electrode sheet 10 is directly measured, and then the first current collector 11 is die-cut to form the integrally formed first main body portion 111 and the first tab 112.

[0086] For the electrode tab of a consumer winding secondary battery, its length is usually 500 mm to 2500 mm. In this application, it is defined that |L1 - L2| ≤ 100 mm, which can make the first electrode tab 112 roughly located at the middle position in the length direction (the second direction Y) of the first electrode sheet 10, thus forming a middle-out electrode tab structure. Combining the above-mentioned first region 1111 to set the first active material layer 12, the electron movement path between the first electrode tab 112 and the first active material layer 12 is shortened, which can reduce the resistance of the secondary battery 1000 and improve the charge and discharge rate of the secondary battery 1000. Moreover, it helps the current to be more evenly distributed on the first electrode sheet 10, reduces local current concentration, and thus reduces the internal resistance and heat generation. At the same time, during the charge and discharge process of the secondary battery 1000, along the winding direction of the first electrode sheet 10, the first active material layers 12 on both sides of the first electrode tab 112 can react simultaneously, reducing the polarization phenomenon and making the charge and discharge process of the secondary battery 1000 more balanced.

[0087] In some other embodiments, |L1 - L2| ≤ 30 mm. The electron movement path between the first electrode tab 112 and the first active material layer 12 is shortened, further reducing local current concentration, reducing the resistance of the secondary battery 1000, and improving the charge and discharge rate of the secondary battery 1000.

[0088] Please refer to Figure 9 , the secondary battery 1000 further includes a first adapter 40. One end of the first adapter 40 is connected to the first electrode tab 112, and the other end of the first adapter 40 extends out of the housing 200. The first adapter 40 can conduct the electrode assembly 100 and an external circuit to facilitate charge and discharge.

[0089] In this application, due to the above-mentioned first electrode tab 112 being integrally provided with the first main body portion 111 and the middle-out electrode tab structure, the contact resistance between the first electrode tab 112 and the first main body portion 111 and the first active material layer 12 is reduced, the conductivity is enhanced, and the charge and discharge rate of the secondary battery 1000 is improved. Therefore, the single first electrode tab 112 can be directly electrically connected to the first adapter 40, occupying less space, providing a larger welding space, improving the connection strength, and reducing the gap space between the electrode assembly 100 and the housing 200, thereby improving the energy density of the secondary battery 1000.

[0090] Regarding the extension of the first adapter 40, please refer to Figure 9, both the first tab 112 and the first adapter 40 can extend along the width direction (the first direction X) of the first main body 111 and extend out of the housing 200. The first tab 112 and the first adapter 40 directly extend out of the housing 200, which can reduce the influence on the thickness dimension of the secondary battery 1000 due to the bending or turning of the first tab 112 or the first adapter 40, and is applicable to the ultra-thin secondary battery 1000. Moreover, the structure of the directly extending first tab 112 and the first adapter 40 reduces the bending and turning during the current transmission process, reduces the resistance and energy loss, and improves the efficiency of current conduction.

[0091] The first tab 112 and the first adapter 40 can also be bent and then extend out of the housing 200. Please refer to Figure 10 , along the extending direction of the first tab 112, the first tab 112 includes a first connecting portion 1122 and a first bending portion 1121 connected in sequence. Along the extending direction of the first adapter 40, the first adapter 40 includes a second connecting portion 41 and a second bending portion 42 connected in sequence. The first tab 112 is bent through the first bending portion 1121, the first connecting portion 1122 is connected to the second connecting portion 41, and the first adapter 40 extends out of the housing 200 after being bent through the second bending portion 42.

[0092] The structure of bending out the first tab 112 and the first adapter 40 can better adapt to the complex internal space layout of the secondary battery 1000. Especially in the case of limited or irregular space, the space can be effectively utilized. For example, after the first tab 112 and the first adapter 40 are bent, the clearance space between the main body part of the electrode assembly 100 and the housing 200 becomes smaller, thereby improving the energy density of the secondary battery 1000. Moreover, the bent structure can buffer external stress and vibration to a certain extent, reduce the direct impact on the first tab 112 and the first adapter 40, and improve its mechanical stability. At the same time, the bent structure can make the first tab 112 and the first adapter 40 longer, provide a larger connection area, and improve the connection strength between the first tab 112 and the first adapter 40.

[0093] Please refer to Figure 5 , a first active material layer 12 can also be provided on the second surface 11b of the first main body 111. The first electrode plate 10 with a double-layer active material layer can improve the energy density of the secondary battery 1000.

[0094] Please further refer to Figure 11, the second surface 11b includes a second region 1112 connected to the first tab 112. There is a first connection position 13 between the first main body portion 111 and the first tab 112. Along the width direction (the first direction X) of the first main body portion 111, the projection of the second region 1112 falls within the projection range of the first connection position 13. Along the width direction (the first direction X) of the first main body portion 111, the length of the second region 1112 is W2, and W2 / W≤8%. The first active material layer 12 is provided on the second region 1112.

[0095] In this application, since the above-mentioned first tab 112 and the first main body portion 111 are integrally provided, no additional tab welding step is required. Therefore, there is no need to groove the first active material layer 12 on the second surface 11b, and the proportion of the first active material layer 12 is higher, which can further improve the energy density of the secondary battery 1000.

[0096] Moreover, there is no need for the insulating adhesive layer to cover the welding burrs on the active material layer on the other side, so that the first active material layer 12 originally covered by the insulating adhesive layer on the second surface 11b can undergo an electrochemical reaction, reducing the contact resistance, which can further improve the energy density of the secondary battery 1000 and can improve the charge and discharge rate of the secondary battery 1000.

[0097] For example, please further refer to Figure 8 , at least part of the surface of the first active material layer 12 located in the second region 1112 is in direct contact with the separator 30. The first active material layer 12 located in the second region 1112 can directly transport lithium ions through the separator 30, and then the lithium ions can be extracted and inserted, and an electrochemical reaction occurs, which can improve the energy density of the secondary battery 1000.

[0098] In some other embodiments, the second electrode sheet 20 can also be arranged similarly to the first electrode sheet 10. For example, please refer to Figure 12 , the second electrode sheet 20 includes a second current collector 21 and a second active material layer 22. The second current collector 21 includes a second main body portion 211 and a single second tab 212. The second main body portion 211 and the second tab 212 are integrally provided, and the second tab 212 extends from one side in the width direction (the first direction X) of the second main body portion 211. For example, the second tab 212 is directly cut out on one side in the width direction (the first direction X) of the second current collector 21 by means of die cutting.

[0099] The welding step of the second tab 212 is not required, which can reduce potential risks such as poor soldering and defective soldering between the second tab 212 and the second main body 211, and can also reduce situations such as loosening and falling off of the second tab 212 that may occur during use, reducing the internal short circuit caused by the loosening of the second tab 212. The current conduction path between the second tab 212 and the second main body 211 is more direct and efficient, reducing the energy loss and heat generation problems caused by the contact resistance between the second tab 212 and the second main body 211. Since the current conduction is more uniform, the heat generation inside the secondary battery 1000 is also more uniform, reducing local overheating. There are no welding burrs, and there is no need to set an insulating glue layer to cover the welding burrs, which can not only reduce the risk of piercing the separator 30, but also make full use of the space and improve the energy density of the secondary battery 1000.

[0100] Along the thickness direction (the third direction Z) of the second main body 211, the second main body 211 includes a relatively arranged third surface 22a and a fourth surface 22b, and the second active material layer 22 can be arranged on the third surface 22a and / or the fourth surface 22b. The second active material layer 22 on the third surface 22a and the fourth surface 22b also does not need to be grooved. The proportion of the second active material layer 22 is higher, which can improve the energy density of the secondary battery 1000. Moreover, there is no need for an insulating glue layer to cover the welding burrs, so that the second active material layer 22 originally covered by the insulating glue layer on the third surface 22a and the fourth surface 22b can undergo an electrochemical reaction, reducing the contact resistance, further improving the energy density of the secondary battery 1000, and improving the charge-discharge rate of the secondary battery 1000.

[0101] In some embodiments, please refer to Figure 5 and Figure 8 , the second electrode sheet 20 adjacent to the first region 1111 includes a third region 2111 arranged opposite to the first region 1111. The second active material layer 22 is arranged in the third region 2111, and there is no need to groove and weld the tab on the second active material layer 22 on the third surface 22a. The proportion of the second active material layer 22 is higher, which can improve the energy density of the secondary battery 1000.

[0102] Moreover, there is no need for an insulating glue layer to cover the welding burrs, so that the second active material layer 22 originally covered by the insulating glue layer on the third surface 22a can undergo an electrochemical reaction, reducing the contact resistance, further improving the energy density of the secondary battery 1000, and improving the charge-discharge rate of the secondary battery 1000. For example, at least part of the surface of the second active material layer 22 located in the third region 2111 is in direct contact with the separator 30. The second active material layer 22 located in the third region 2111 can directly transmit lithium ions through the separator 30, and then the lithium ions are deintercalated and intercalated, undergoing an electrochemical reaction, which can improve the energy density of the secondary battery 1000.

[0103] In some other embodiments, along the thickness direction (the third direction Z) of the first main body portion 111, the second pole piece 20 adjacent to the second region 1112 includes a fourth region 2121 disposed opposite to the second region 1112. The fourth region 2121 is provided with a second active material layer 22. There is no need to perform the operation of grooving and welding the tab on the second active material layer 22 of the fourth surface 22b. The proportion of the second active material layer 22 is higher, which can improve the energy density of the secondary battery 1000.

[0104] Moreover, there is no need for an insulating adhesive layer to cover the welding burrs, so that the second active material layer 22 originally covered by the insulating adhesive layer on the fourth surface 22b can undergo an electrochemical reaction, reducing the contact resistance, which can further improve the energy density of the secondary battery 1000 and can improve the charge-discharge rate of the secondary battery 1000. For example, at least a part of the surface of the second active material layer 22 located in the fourth region 2121 is in direct contact with the separator 30. The second active material layer 22 located in the fourth region 2121 can directly transport lithium ions through the separator 30, and then the lithium ions are deintercalated and intercalated, and an electrochemical reaction occurs, which can improve the energy density of the secondary battery 1000.

[0105] In some embodiments, please refer to Figure 6 , along the winding direction of the first pole piece 10, the width of the first tab 112 is W3, and 6 mm ≤ W3 ≤ 30 mm. If the width of the first tab 112 is too small, the current-carrying capacity of the first tab 112 will be affected. If the width of the first tab 112 is too large, when winding, the first tab 112 may pass through the winding corner position (such as Figure 4 the bending positions of 100a and 100b in ), which is likely to cause the first tab 112 to be damaged and torn. By defining 6 mm ≤ W3 ≤ 30 mm, the current-carrying capacity of the first tab 112 can be improved while reducing the risk of the first tab 112 being damaged and torn when passing through the corner. Optionally, the second tab 212 can be set similarly.

[0106] In some embodiments, the thickness of the first tab 112 is T1, and 5 μm ≤ T1 ≤ 20 μm. For example, when the first tab 112 is a positive tab, the thickness of the first tab 112 is T1, and 8 μm ≤ T1 ≤ 20 μm; or when the first tab 112 is a negative tab, the thickness of the first tab 112 is T1, and 5 μm ≤ T1 ≤ 15 μm. The first adapter 40 can be welded to the first tab 112. In this application, the thickness of the first adapter 40 is T2, and 40 μm ≤ T2 ≤ 100 μm, which can improve the current-carrying capacity of the secondary battery 1000 while reducing the influence of the first adapter 40 on the energy density of the secondary battery 1000.

[0107] In some embodiments, the connection area between the first adapter 40 and the first tab 112 is S, 10 mm 2 ≤S≤140 mm 2 . If the welding area is too small, the current-carrying capacity is insufficient and the connection strength is low. If the welding area is too large, for the structure of the directly extending tab and the adapter, a large welding area means a large area of the first tab 112 and the first adapter 40, occupying the head space and affecting the energy density.

[0108] For the structure where the first tab 112 and the first adapter 40 are bent, when the welding area is too large, if the welding position is located in the straight section of the bend, the welding position occupies a large space in the thickness direction of the secondary battery 1000, which may cause the thickness to exceed that of the secondary battery 1000 after bending, resulting in a loss of energy density. If the welding position is located in the bent section, the bent position is prone to breakage. In this application, it is defined that 10 mm 2 ≤S≤140 mm 2 , which can improve the current-carrying capacity and connection strength while reducing the space occupied by the first tab 112 and the first adapter 40, and reducing the breakage of the first tab 112 and the first adapter 40. Optionally, the second tab 212 and the second adapter can be similarly arranged.

[0109] In some embodiments, please refer to Figure 13 and Figure 14 , along the width direction (the first direction X) of the first main body 111, the first main body 111 includes a first edge 1113 on the side where the first tab 112 extends. The first surface 11a includes a first empty foil area 1114. Along the width direction (the first direction X) of the first main body 111, the first empty foil area 1114 is located between the first active material layer 12 and the first edge 1113. The setting of the first empty foil area 1114 can adapt to the expansion and contraction of the first active material layer 12 during the charge and discharge of the secondary battery 1000. Among them, the first empty foil area 1114 can be 1% to 5% of the width of the first main body 111. The first area 1111 can include part of the first empty foil area 1114, or due to the presence of the first tab 112, the first area 1111 can also be entirely provided with the first active material layer 12.

[0110] In this application, the secondary battery 1000 further includes a first insulating layer 50, and the first insulating layer 50 is disposed in the first empty foil area 1114. The first insulating layer 50 can cover the first empty foil area 1114 and part of the trimming burrs of the first edge 1113, thereby reducing the burrs from piercing the separator 30. In some other embodiments, high-precision trimming can also be used to reduce the formation of burrs. Among them, the first insulating layer 50 can adopt an alumina ceramic layer, and the alumina ceramic layer can be directly coated in the first empty foil area 1114. Compared with the traditional glue layer, the thickness of the alumina ceramic layer is thinner, which is convenient for improving the energy density of the secondary battery 100.

[0111] In some embodiments, please refer to Figure 9 and Figure 15 , the secondary battery 1000 further includes a first adhesive layer 60. The first adhesive layer 60 covers the connection between the first adapter 40 and the first tab 112, and can cover the welding burrs of the first tab 112 and the first adapter 40, reducing the piercing of the separator film 30 by the burrs and reducing the scratching of the inner wall of the housing 200 by the burrs. And the first adhesive layer 60 extends to the first active material layer 12, which can isolate the first tab 112 from the second electrode plate 20 and reduce the occurrence of short circuits. Wherein, along the width direction (the first direction X) of the first main body portion 111, the width of the first adhesive layer 60 covering the first active material layer 12 is W4, and 0 < W4 ≤ 1 mm. This can reduce the influence of the first adhesive layer 60 on the energy density of the secondary battery 1000. The first adhesive layer can be made of materials such as polyimide (PI), polyester (PET), polypropylene (PP), and acrylate.

[0112] Second, the present application also proposes an electronic device, including the secondary battery 1000 described in any one of the above first aspects. The electronic device of the embodiments of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to Bluetooth headsets, mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecraft, and so on. Among them, the electric toy can include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric aircraft toys, etc., and the spacecraft can include airplanes, rockets, space shuttles, and spaceships, etc.

[0113] Third, the present application also proposes a method for manufacturing a secondary battery, including the following steps:

[0114] Provide a first current collector, cut the first current collector to obtain an integrally formed first main body portion and a first tab. The distances between the first tab and the two ends of the first main body portion in the length direction are L1 and L2 respectively, and |L1 - L2| ≤ 100 mm. Defining |L1 - L2| ≤ 100 mm can make the first tab approximately located at the middle position in the length direction of the first electrode plate, thereby forming a middle-out tab structure. This helps the current to be more evenly distributed on the first electrode plate, reduces local current concentration, and thus reduces the internal resistance and heat generation.

[0115] A first active material layer is provided on at least one surface in the thickness direction of the first main body portion to obtain a first electrode sheet. Wherein, the first main body portion has a first region connected to the first tab, and there is a first connection position between the first main body portion and the first tab. Along the width direction of the first main body portion, the projection of the first region falls within the projection range of the first connection position. Along the width direction of the first main body portion, the width of the first main body portion is W, the length of the first region is W1, and W1 / W≤8%. The first active material layer is provided in the first region. Since the above-mentioned first tab is integrally provided with the first main body portion, there is no need to perform the operation of grooving and welding the tab on the first active material layer, and a continuous first active material layer can be directly coated. Compared with the traditional grooving and welding tab structure, in the present application, the proportion of the first active material layer is higher, which can improve the energy density of the secondary battery.

[0116] A separator and a second electrode sheet are provided, and the separator, the first electrode sheet, and the second electrode sheet are stacked and wound in sequence to obtain an electrode assembly.

[0117] A first adapter is provided, and one end of the first adapter is electrically connected to the first tab. The single first tab can be directly electrically connected to the first adapter, which occupies less space, provides a larger welding space, can improve the connection strength, and can reduce the gap space between the electrode assembly and the housing, thereby improving the energy density of the secondary battery.

[0118] A housing is provided, the electrode assembly is disposed in the housing, and the other end of the first adapter extends out of the housing.

[0119] The housing is filled with liquid and encapsulated to obtain a secondary battery.

[0120] Experiment 1: Energy density test of lithium-ion battery

[0121] Example A1

[0122] <Preparation of positive electrode sheet>:

[0123] Aluminum foil with a thickness of 8 um and a length of ...... 5 ) are mixed in a mass ratio of 94:3:3, and N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred in a vacuum mixer until the solid content is 75 wt% and the positive electrode slurry is uniform. The positive electrode slurry is uniformly and continuously coated on one surface of the positive electrode current collector aluminum foil and dried at 110 °C to obtain a positive electrode sheet with a single-sided coated positive electrode active material layer. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode active material layer.

[0124] <Preparation of Negative Electrode Plate>

[0125] A copper foil with a thickness of 5 μm and a length of 1050 mm is selected as the negative electrode current collector, and a negative electrode tab integrally formed is cut out from the negative electrode current collector copper foil. The negative electrode tab is located at a position 5 mm offset from the middle of the negative electrode current collector towards the winding starting end. The negative electrode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) are mixed according to a weight ratio of 87:10.5:1:1.5, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 50 wt%, and it is stirred evenly. After the above steps are completed, the single-sided coating of the negative electrode plate is completed. Then, the above steps are repeated on the other surface of the negative electrode plate to obtain a negative electrode plate with a double-sided coated negative electrode active material layer.

[0126] <Preparation of Separator>

[0127] A polyethylene (PE) porous film with a thickness of 7 μm is used as the separator.

[0128] <Preparation of Electrolyte>

[0129] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt lithium hexafluorophosphate is added to the organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0130] <Preparation of Lithium-Ion Battery>

[0131] The above-prepared separator, positive electrode plate, separator, and negative electrode plate are stacked in sequence, wound to obtain an electrode assembly, and the electrode assembly is hot-pressed with a pressure of 5 MPa, a temperature of 65 °C, and a holding time of 10 s. The electrode assembly is placed in an aluminum-plastic film casing. A 50-μm-thick aluminum sheet is selected as the first adapter. After the positive electrode tab is bent, one end of the first adapter is welded to the positive electrode tab, and the other end of the first adapter is bent and extends out of the casing. A 40-μm-thick nickel sheet is selected as the second adapter. After the negative electrode tab is bent, one end of the second adapter is welded to the negative electrode tab, and the other end of the second adapter is bent and extends out of the casing. After the whole is dehydrated at 80 °C, the electrolyte is injected and sealed.

[0132] The relevant data in Comparative Example A1, Comparative Example A2, Example A1, and Example A2 are shown in Table 1 below. Among them, in Comparative Example A1, different from Example A1, by laser cleaning, a first groove was cleaned out on the active material layer on one side of the positive electrode tab, and a second groove was cleaned out on the other side. The aluminum positive electrode tab was welded to the positive current collector in the first groove. An epoxy resin insulating glue layer with a length, width, and thickness of 24 mm × 15 mm × 16 μm was used to cover the first groove on one side of the positive electrode tab, and an epoxy resin insulating glue layer with a length, width, and thickness of 24 mm × 15 mm × 16 μm was used to cover the second groove on the other side of the positive electrode tab.

[0133] By laser cleaning, a third groove was cleaned out on the active material layer on one side of the negative electrode tab, and a fourth groove was cleaned out on the other side. The nickel positive electrode tab was welded to the negative current collector in the third groove. An epoxy resin insulating glue layer with a length, width, and thickness of 28 mm × 20 mm × 16 μm was used to cover the third groove on one side of the negative electrode tab, and an epoxy resin insulating glue layer with a length, width, and thickness of 28 mm × 20 mm × 16 μm was used to cover the fourth groove on the other side of the negative electrode tab. An epoxy resin tab glue with a length, width, and thickness of 24 mm × 15 mm × 10 μm was set at the position of the positive electrode tab corresponding to the negative electrode tab in the positive active material layer, and an epoxy resin tab glue with a length, width, and thickness of 28 mm × 20 mm × 10 μm was set at the position of the negative electrode tab corresponding to the positive electrode tab in the negative active material layer.

[0134] Energy density test method: For the lithium-ion battery prepared by the above preparation method, the lithium-ion battery was charged to the cut-off voltage at a constant current of 1C, then charged at a constant voltage of the cut-off voltage until 0.05C, and then discharged at a constant current of 0.2C until 3V, and the discharge energy E was recorded; the external dimensions of the lithium-ion battery were measured, and its volume was calculated, which was V; then the energy density W = E / V.

[0135] Table 1

[0136]

[0137]

[0138] According to Table 1 above, in combination with Example A1 and Comparative Example A1, it can be seen that for lithium-ion batteries with bent tabs, when the tabs and current collectors are integrally formed, the energy density of the lithium-ion batteries can be effectively improved. For lithium-ion batteries with straight-out tabs, in combination with Example A2 and Comparative Example A2, when the tabs and current collectors are integrally formed, the energy density of the lithium-ion batteries can also be improved, which is applicable to ultra-thin lithium-ion batteries with a smaller thickness. This is because there is no need to perform the operation of grooving and welding the tabs on the active material layer, and the proportion of the active material layer is higher, which can improve the energy density of the secondary battery. There is also no need for various insulating glue layers and tab glue to cover the welding burrs, enabling the active material layer originally covered by the insulating glue layer and tab glue to undergo electrochemical reactions, which can further improve the energy density of the secondary battery.

[0139] Experiment 2: Charge-discharge rate test of lithium-ion batteries

[0140] In Example B1, different from Example A1, the positive tab is die-cut and cut out at a roughly middle position of the positive current collector aluminum foil. The distances between the positive tab and the two ends of the aluminum foil in the length direction are L1 and L2 respectively, and L1 - L2 = 100 mm. The negative tab is die-cut and cut out at a roughly middle position of the negative current collector copper foil. The distances between the negative tab and the two ends of the copper foil in the length direction are L3 and L4 respectively, and L3 - L4 = 95 mm.

[0141] Taking Example A1 as a reference, the relevant data in Examples B1 to B7 and Comparative Examples B1 to B4 are shown in Table 2 below.

[0142] Maximum charge-discharge rate test: At room temperature (25 °C), charge at a constant current of 5C to 4.2V, and then charge at a constant voltage of 4.2V to 4C, recording the current, voltage, capacity, and temperature of the lithium-ion battery. Each time, reduce the constant current by 0.2C and repeat the charge-discharge test. Then charge at a constant current of 4C to 4.3V, charge at a constant voltage of 4.3V to 3C, recording the current, voltage, capacity, and temperature of the lithium-ion battery. Each time, reduce the constant current by 0.2C and repeat the charge-discharge test. Then charge at a constant current of 3C to 4.45V, charge at a constant voltage of 4.45V to 2C, recording the current, voltage, capacity, and temperature of the lithium-ion battery. Each time, reduce the constant current by 0.2C and repeat the charge-discharge test. Finally, charge at a constant current of 2C to 4.5V, and then charge at a constant voltage of 4.5V to 0.02C, recording the current, voltage, capacity, and temperature of the lithium-ion battery.

[0143] Check whether the lithium-ion battery shows any abnormal phenomena such as bulging and overheating (above 60 °C). When the lithium-ion battery shows abnormal phenomena such as a serious decline in performance, damage, overheating, or inability to complete a normal charge-discharge cycle at a certain rate, the rate at which the previous problem did not occur is usually considered the maximum charge-discharge rate of the lithium-ion battery.

[0144] Table 2

[0145]

[0146] According to Table 2 above, in combination with Examples B1 to B7 and Comparative Examples B1 to B4, it can be seen that when the positive electrode tab and the positive electrode current collector are integrally formed and the negative electrode tab and the negative electrode current collector are integrally formed, the charge and discharge rate of the lithium-ion battery can be effectively improved. This is because the current conduction path between the tab and the current collector is more direct and efficient, reducing the energy loss and heat generation problems caused by the welding contact resistance between the tab and the current collector, which helps to improve the charge and discharge rate of the lithium-ion battery. Moreover, there is no need for an insulating adhesive layer to cover the welding burrs, enabling the active material layer originally covered by the insulating adhesive layer to undergo an electrochemical reaction, reducing the current concentration phenomenon and local overheating phenomenon, and improving the charge and discharge rate of the lithium-ion battery.

[0147] In combination with Examples B1 to B7 and Comparative Example B4, among Examples B1 to B7, the maximum charge and discharge rate is greater than that of Comparative Example B4. Among Examples B1 to B7, it is defined that |L1 - L2| ≤ 100 mm, which can make the tab roughly located at the middle position in the length direction of the electrode sheet, thereby forming a middle-out tab structure. Combining the integrally arranged tab and current collector above, the electron movement path between the tab and the active material layer is shortened, the resistance of the lithium-ion battery can be reduced, and the charge and discharge rate of the lithium-ion battery can be improved. Moreover, it helps the current to be more evenly distributed on the electrode sheet, reducing local current concentration, thereby reducing the internal resistance and heat generation. At the same time, during the charge and discharge process of the lithium-ion battery, along the winding direction of the electrode sheet, the active material layers on both sides of the tab can react simultaneously, reducing the polarization phenomenon and making the charge and discharge process of the lithium-ion battery more balanced. Therefore, in the examples of the present application, |L1 - L2| ≤ 100 mm can be selected. Similarly, |L3 - L4| ≤ 100 mm can also be selected.

[0148] In combination with Examples B1 to B7, among Examples B4 to B7, the maximum charge and discharge rate is greater than that of Examples B1 and B3, and among Examples B4 to B7, the maximum charge and discharge rate exceeds 4C. This is because the tab is closer to the middle position of the electrode sheet, the current is more evenly distributed on the electrode sheet, further reducing local current concentration, thereby reducing the internal resistance and heat generation, and improving the charge and discharge rate of the secondary battery. Therefore, in the present application, |L1 - L2| ≤ 30 mm can be selected. Similarly, |L3 - L4| ≤ 30 mm can be selected.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it; under the idea of the present application, 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 changes in different aspects of the present application as described above. For the sake of brevity, they are not provided in detail; although the present application 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 on 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 embodiments of the present application.

Claims

1. A secondary battery, comprising a housing and an electrode assembly disposed within the housing, the electrode assembly including a first electrode tab, a separator, and a second electrode tab that are stacked and wound, the first electrode tab including a first current collector and a first active material layer, characterized in that, The first current collector includes a first main body portion and a single first tab, the first main body portion and the first tab are integrally provided, and the first tab extends from one side in the width direction of the first main body portion; The first main body portion includes a first surface on one side in the thickness direction of the first main body portion, the first surface includes a first region connected to the first tab, and there is a first connection position between the first main body portion and the first tab. Along the width direction of the first main body portion, the projection of the first region falls within the projection range of the first connection position; along the width direction of the first main body portion, the width of the first main body portion is W, the length of the first region is W1, and W1 / W≤8%. The first active material layer is provided in the first region; Along the winding direction of the first electrode sheet, the first main body portion includes a first end portion and a second end portion arranged opposite to each other. The length between the first tab and the first end portion is L1, and the length between the first tab and the second end portion is L2, and |L1 - L2|≤100mm; The secondary battery further includes a first adapter, one end of the first adapter is connected to the first tab, and the other end of the first adapter extends out of the housing.

2. The secondary battery according to claim 1, wherein Both the first tab and the first adapter extend along the width direction of the first main body portion.

3. The secondary battery according to claim 1, wherein Along the extending direction of the first tab, the first tab includes a first connection portion and a first bending portion connected in sequence; Along the extending direction of the first adapter, the first adapter includes a second connection portion and a second bending portion connected in sequence; The first tab is bent through the first bending portion, the first connection portion is connected to the second connection portion, and the first adapter extends out of the housing after being bent through the second bending portion.

4. The secondary battery according to any one of claims 1 to 3, characterized in that |L1 - L2|≤30mm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, At least part of the surface of the first active material layer located in the first region is in direct contact with the separator.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The first main body portion further includes a second surface, and along the thickness direction of the first main body portion, the first surface and the second surface are arranged opposite to each other; The second surface includes a second region connected to the first tab. Along the width direction of the first main body portion, the projection of the second region falls within the projection range of the first connection position; Along the width direction of the first main body portion, the length of the second region is W2, and W2 / W≤8%; The second active material layer is provided in the second region.

7. The secondary battery according to claim 6, characterized in that, In the second region, at least part of the surface of the first active material layer is in direct contact with the separator.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, Along the thickness direction of the first main body portion, the second electrode sheet adjacent to the first region includes a third region arranged opposite to the first region; The second active material layer is provided in the third region, and the second active material layer located in the third region is in direct contact with the separator.

9. The secondary battery according to claim 6 or 7, characterized in that, Along the thickness direction of the first main body portion, the second electrode sheet adjacent to the second region includes a fourth region arranged opposite to the second region; The fourth region is provided with a second active material layer, and the second active material layer located in the fourth region is in direct contact with the separator film.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, Along the winding direction of the first electrode tab, the width of the first tab is W3, and 6 mm ≤ W3 ≤ 30 mm.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The first tab is a positive electrode tab, and the thickness of the first tab is T1, and 8 μm ≤ T1 ≤ 20 μm; or, the first tab is a negative electrode tab, and the thickness of the first tab is T1, and 5 μm ≤ T1 ≤ 15 μm; The thickness of the first adapter is T2, and 40 μm ≤ T2 ≤ 100 μm.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The connection area between the first adapter and the first tab is S, 10mm 2 ≤ S ≤ 140mm 2 .

13. The secondary battery according to any one of claims 1 to 12, characterized in that, Along the width direction of the first main body portion, the first main body portion includes a first edge on the side where the first tab extends; The first surface includes a first empty foil region, and along the width direction of the first main body portion, the first empty foil region is located between the first active material layer and the first edge; The secondary battery further includes a first insulating layer, and the first insulating layer is disposed in the first empty foil region.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, The secondary battery further includes a first adhesive layer, the first adhesive layer covers the connection between the first adapter and the first tab, and the first adhesive layer extends to the first active material layer; Along the width direction of the first main body portion, the width of the first adhesive layer covering the first active material layer is W4, and 0 < W4 ≤ 1 mm.

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

16. A method for preparing a secondary battery, characterized in that, Including: Providing a first current collector, cutting the first current collector to obtain an integrally formed first main body portion and a first tab, the distances between the first tab and the two ends of the first main body portion in the length direction are L1 and L2 respectively, and |L1 - L2| ≤ 100 mm; Providing a first active material layer on at least one surface in the thickness direction of the first main body portion to obtain a first electrode tab; wherein, the first main body portion has a first region connected to the first tab, there is a first connection position between the first main body portion and the first tab, and along the width direction of the first main body portion, the projection of the first region falls within the projection range of the first connection position; along the width direction of the first main body portion, the width of the first main body portion is W, and the length of the first region is W1, W1 / W ≤ 8%, and the first active material layer is provided in the first region; Providing a separator film and a second electrode tab, laminating and winding the separator film, the first electrode tab, and the second electrode tab in sequence to obtain an electrode assembly; Providing a first adapter, and electrically connecting one end of the first adapter to the first tab; Providing a housing, disposing the electrode assembly in the housing, and the other end of the first adapter extends out of the housing; Injecting electrolyte into the housing and encapsulating it to obtain the secondary battery.

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