Secondary battery, electronic device, and secondary battery manufacturing method

Abstract

The present application provides a secondary battery, an electronic device, and a secondary battery manufacturing method. The secondary battery comprises a negative electrode sheet. The negative electrode sheet comprises a first current collector, a first coating layer, and a second coating layer. In a first direction, the first coating layer is disposed between the first current collector and the second coating layer, and the first coating layer is separately bonded and fixed to the first current collector and the second coating layer. The second coating layer comprises a negative electrode active material. The first current collector comprises a main body portion and an uncoated foil portion which are integrally arranged. The first coating layer is disposed on the main body portion. A second direction is perpendicular to the first direction. In the second direction, the first coating layer comprises a second edge and a first edge that are arranged opposite to each other, and the second coating layer comprises a fourth edge and a third edge that are arranged opposite to each other. In the second direction, the first edge extends beyond the third edge by a width of L, wherein L≥0. In the secondary battery, the first coating layer is disposed between the second coating layer and the first current collector, and the second coating layer is not in contact with the first current collector, thereby reducing the risk of detachment of the second coating layer.

Description

Secondary batteries, electronic devices, and methods for preparing secondary batteries Technical Field

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

[0002] A rechargeable battery is a device that converts external energy into electrical energy and stores it internally, providing power to external electronic devices (such as portable electronic devices) when needed. Rechargeable batteries are widely used in daily life, greatly enhancing convenience and enriching people's lives. The negative electrode of a rechargeable battery typically includes a negative current collector, a base coating, and a negative active material layer. The base coating is located between the negative current collector and the negative active material layer, used to increase the peel strength between them. Summary of the Invention

[0003] Currently, the negative electrode sheet of a secondary battery typically includes a negative current collector, a base coating, and a negative active material layer. The base coating is located between the negative current collector and the negative active material layer to increase the peel strength between them. For negative electrode sheets with die-cut tabs, the manufacturing process involves first attaching adhesive tape to the negative current collector, then applying the base coating and the negative active material layer, then peeling off the adhesive tape to form a blank foil area, and finally die-cutting the blank foil area to obtain the tabs. Due to the thickness of the adhesive tape, during the base coating process, some surfaces of the negative current collector at the edges of the adhesive tape cannot be covered by the base coating. These uncoated surfaces of the negative current collector adhere directly to the negative active material layer. Compared to areas with a base coating, the peel strength between the negative current collector and the negative active material layer is lower, and the negative active material layer is prone to detachment. This can lead to a decrease in the energy density of the secondary battery, and the detached negative active material poses a risk of causing an internal short circuit in the secondary battery. The embodiments of this application aim to provide a secondary battery, an electronic device, and a method for preparing a secondary battery, so as to solve the problem that the negative electrode active material layer is easy to fall off in the prior art.

[0004] According to one aspect of the embodiments of this application, a secondary battery is provided, comprising a negative electrode sheet, the negative electrode sheet comprising a first current collector, a first coating, and a second coating. Along a first direction, the first coating is disposed between the first current collector and the second coating, and the first coating is bonded and fixed to both the first current collector and the second coating. The second coating comprises a negative electrode active material. The first direction is the thickness direction of the negative electrode sheet. Along the first direction, the first current collector comprises a second surface and a first surface disposed opposite to each other. The first current collector comprises a main body portion and a hollow foil portion integrally disposed, the surface of the hollow foil portion not having the first coating and the second coating disposed, and the hollow foil portion being used for electrical connection with an external circuit. The hollow foil portion is located on one side of the main body portion along a second direction, and the first coating is disposed on the main body portion, the second direction being perpendicular to the first direction. Along the second direction, the first coating comprises a second edge and a first edge disposed opposite to each other, and the second coating comprises a fourth edge and a third edge disposed opposite to each other, the first edge and the third edge being located on the same side of the secondary battery along the second direction. Along the second direction, the width of the first edge extending beyond the third edge is L, where L≥0. With this secondary battery, since the width of the first edge of the first coating extending beyond the third edge of the second coating along the second direction is greater than or equal to zero, and since the second coating is adhered to the first coating and the first current collector, that is, the second coating and the first current collector are spaced apart by the first coating, the peel strength between the second coating and the first current collector is small, the peel strength between the second coating and the first coating is large, and the peel strength between the first current collector and the first coating is large, the first coating respectively bonds and fixes the first current collector and the second coating, reducing the risk of the second coating falling off and failing.

[0005] In one or more alternative embodiments, L ≥ 0.01 mm. Further defining the first edge of the first coating extending beyond the third edge of the second coating by a width L ≥ 0.01 mm along the second direction, i.e., the third edge of the second coating adheres to the first coating, further reducing the risk of the second coating detaching and failing.

[0006] In one or more alternative embodiments, 0.1mm ≤ L ≤ 3mm. This not only improves manufacturability but also ensures the adhesion strength between the second coating and the first coating, the reliability of the connection between the empty foil portion of the first current collector and the external circuit, and the energy density of the secondary battery.

[0007] In one or more alternative embodiments, 0.5mm ≤ L ≤ 2mm. As described above, this further improves manufacturability, further ensures the adhesion strength between the second coating and the first coating, further ensures the reliability of the connection between the empty foil portion of the first current collector and the external circuit, and further ensures the energy density of the secondary battery.

[0008] In one or more alternative embodiments, the secondary battery includes a plurality of negative electrode plates. The secondary battery also includes an adapter that connects to a plurality of empty foil portions via a connecting area. Along a third direction, the width of the connecting area is M, where 1mm ≤ M ≤ 9mm, and the third direction is perpendicular to both the first and second directions. Limiting the width to 1mm ≤ M ≤ 9mm ensures both the reliability of the connection between the empty foil portions of the first current collector and the adapter, and also guarantees the energy density and charge / discharge efficiency of the secondary battery.

[0009] In one or more alternative embodiments, the thickness of the first coating is T1 along the first direction, where 0.1 μm ≤ T1 ≤ 5 μm. And / or, the thickness of the second coating is T2 along the first direction, where 10 μm ≤ T2 ≤ 300 μm. Limiting the thickness to 0.1 μm ≤ T1 ≤ 5 μm ensures the adhesion stability between the first coating and the first current collector while reducing the impact of the first coating on the energy density of the secondary battery. Limiting the thickness to 10 μm ≤ T2 ≤ 300 μm ensures both the capacity of the secondary battery and the adhesion stability between the second coating, the first coating, and the first current collector, while also meeting the performance and lightweight development requirements of the secondary battery.

[0010] In one or more alternative embodiments, along a first direction, the second coating has a first surface and a second surface disposed opposite to each other, with any point on the first surface being equidistant from the second surface. The second coating is uniformly distributed along the first direction, reducing the risk of localized defects, such as the risk of localized lithium plating, when interacting with the positive electrode active material of the secondary battery.

[0011] The phrase "the vertical distance from any point on the first surface to the second surface is the same" means that the difference between the vertical distances from any point on the first surface to the second surface is within 5% of the maximum vertical distance.

[0012] In one or more optional embodiments, the secondary battery further includes a separator and a positive electrode, with the negative electrode, separator, and positive electrode stacked sequentially. The positive electrode includes a second current collector, a positive active material, and a second tab, the second tab being integrally formed with the second current collector, and an insulating layer disposed on the second tab. Along a second direction, the insulating layer includes a sixth edge and a fifth edge disposed opposite to each other, the first edge, third edge, and fifth edge being located on the same side of the secondary battery in the second direction. Along the second direction, the third edge extends beyond the sixth edge. This insulating layer covers the cutting burrs used when forming the second tab, reducing the risk of short circuits caused by these burrs piercing the separator. Furthermore, by extending the third edge of the second coating beyond the sixth edge of the insulating layer—that is, along the second direction, the third edge of the second coating extends beyond the positive active material—the risk of lithium plating is reduced.

[0013] In one or more alternative embodiments, the first coating includes a conductive agent and a first adhesive. The conductive agent includes one or more of carbon nanotubes, graphene, graphene oxide, and conductive carbon black. The first adhesive includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, and polyacrylonitrile. By limiting the material of the first coating, on the one hand, the adhesion and fixation of the first coating to the first current collector and the second coating are ensured, reducing the risk of the second coating or the first coating and the second coating detaching from the first current collector; on the other hand, the overall impedance of the negative electrode sheet is guaranteed, improving the overall performance of the secondary battery.

[0014] In one or more optional embodiments, the second coating further includes a second adhesive, which includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, and polyacrylonitrile; the negative electrode active material includes one or more of graphite, silicon-based, tin-based, and metal oxides. By limiting the material of the second coating, the interaction function between the second coating and the positive electrode active material of the secondary battery is ensured, thereby ensuring the charge and discharge performance of the secondary battery.

[0015] In one or more alternative embodiments, the mass percentage of the negative electrode active material is m, based on the mass of the second coating, where 92% ≤ m ≤ 99.5%. By limiting the value of m to 92% ≤ m ≤ 99.5%, both the high energy density of the secondary battery and the adhesion reliability between the second coating and the first coating are ensured, reducing the risk of the second coating falling off.

[0016] According to one aspect of the embodiments of this application, an electronic device is provided, including any of the above-described secondary batteries.

[0017] According to one aspect of the embodiments of this application, a method for preparing a secondary battery is provided, for preparing a secondary battery according to any one of the above, comprising the following steps: taking a current collector substrate, the current collector substrate including a third surface and a fourth surface disposed opposite to each other along its thickness direction, and an eighth edge and a seventh edge disposed opposite to each other along its width direction. Applying a first adhesive tape to the third surface, one edge of the first adhesive tape being flush with the seventh edge, the portion of the current collector substrate not covered by the first adhesive tape being a coating area. Applying a first coating layer to the coating area. Removing the first adhesive tape, applying a second adhesive tape to the third surface, the width of the second adhesive tape being greater than the width of the first adhesive tape along the width direction of the current collector substrate, one edge of the second adhesive tape being flush with the seventh edge. Applying a second coating layer on the first coating layer and the second adhesive tape. Removing the second adhesive tape, the area of ​​the current collector substrate exposed between the first coating layer and the second coating layer being an empty foil area, cutting the current collector substrate to obtain a first current collector, and cutting the empty foil area to form an empty foil portion. In this secondary battery preparation method, since the width of the second adhesive paper is greater than the width of the first adhesive paper along the width direction of the current collector substrate, after removing the second adhesive paper, the first coating extends beyond the second coating along the width direction of the current collector substrate. That is, the first coating is provided between the second coating and the first current collector. Since the peel strength between the second coating and the first current collector is small, the peel strength between the second coating and the first coating is large, and the peel strength between the first current collector and the first coating is large, the first coating bonds and fixes the first current collector and the second coating respectively, reducing the risk of the second coating falling off and failing.

[0018] In one or more alternative embodiments, the width of the second adhesive tape is between 8 mm and 40 mm along the width direction of the current collector substrate. When the width of the second adhesive tape is small, for example, less than 8 mm, manufacturability is poor; when the width of the second adhesive tape is large, for example, greater than 40 mm, the width of the first coating will be much larger than the width of the second coating, and the width of the second coating will be smaller, affecting the energy density of the secondary battery.

[0019] In one or more alternative embodiments, the width of the first adhesive tape is between 7 mm and 40 mm along the width direction of the current collector substrate. By limiting the width of the first adhesive tape, both manufacturability and the energy density of the secondary battery can be guaranteed.

[0020] In one or more alternative embodiments, the peel strength between the first adhesive tape and the current collector substrate is between 1 mN / mm and 7 mN / mm. By limiting the peel strength between the first adhesive tape and the current collector substrate, the adhesion reliability between the first adhesive tape and the current collector substrate is ensured, the coating effect of the first coating is ensured, the operability of removing the first adhesive tape is ensured, and the welding efficiency of the subsequent welding adapter is ensured.

[0021] In one or more alternative embodiments, the peel strength between the first coating and the current collector substrate is greater than the peel strength between the first coating and the second adhesive tape. This arrangement ensures that when the second adhesive tape is removed, the first coating covered by the second adhesive tape remains on the current collector substrate, guaranteeing adhesion of the first coating to both the second coating and the current collector substrate.

[0022] In one or more alternative embodiments, the peel strength between the second adhesive tape and the current collector substrate is between 1 mN / mm and 7 mN / mm. The peel strength between the second adhesive tape and the first coating is also between 1 mN / mm and 7 mN / mm. By limiting the peel strength between the second adhesive tape and the current collector substrate, the welding yield of the subsequent welding adapter is ensured. By limiting the peel strength between the second adhesive tape and the first coating, the adhesion reliability between the second adhesive tape and the first coating is ensured, the coating effect of the second coating is ensured, the operability of removing the second adhesive tape is ensured, and the first coating is retained on the current collector substrate when the second adhesive tape is removed, ensuring the adhesion and fixation of the first coating to the second coating and the current collector substrate, and reducing the risk of the second coating falling off.

[0023] According to one aspect of the embodiments of this application, a method for preparing a secondary battery is provided, comprising the following steps: taking a current collector substrate, the current collector substrate including a third surface and a fourth surface disposed opposite to each other along its thickness direction, and an eighth edge and a seventh edge disposed opposite to each other along its width direction. A first coating is applied to the third surface. A second adhesive tape is applied to the first coating, one edge of the second adhesive tape being flush with the seventh edge. A second coating is applied to the first coating and the second adhesive tape. The second adhesive tape is removed, and the current collector substrate is cut to obtain a first current collector. Through this method for preparing a secondary battery, when the second adhesive tape is removed, the second coating on the second adhesive tape is removed, while the first coating covered by the second adhesive tape remains on the current collector substrate. Along the width direction of the current collector substrate, the first coating extends beyond the second coating, that is, the second coating is spaced apart from the first current collector, and the second coating does not contact the first current collector, reducing the risk of the second coating detaching and failing.

[0024] In one or more alternative embodiments, the third surface of the first current collector has an empty foil area without the first and second coatings, one edge of which is flush with the seventh edge. The empty foil area is cut to form an empty foil portion. This method of preparing a secondary battery facilitates the cutting and formation of an empty foil portion that is electrically connected to an external circuit.

[0025] In one or more alternative embodiments, the first coating completely covers the third surface. The first current collector is cut, and laser cleaning is performed to remove part of the first coating to form an empty foil portion. Through this secondary battery fabrication method, when the second adhesive tape is removed, the second coating on the second adhesive tape is removed, while the first coating covered by the second adhesive tape remains on the current collector substrate. Subsequent cleaning of part of the first coating can form an empty foil portion electrically connected to an external circuit. Furthermore, since the first coating covered by the second adhesive tape remains on the current collector substrate, and the first coating extends beyond the second coating along the width direction of the current collector substrate (i.e., the second coating is spaced apart from the first current collector), the peel strength between the second coating and the first current collector is relatively low, while the peel strength between the second coating and the first coating is relatively high. The first coating effectively bonds and fixes both the first current collector and the second coating, reducing the risk of the second coating detaching and failing.

[0026] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0028] Figure 1 is a schematic diagram of a secondary battery provided in an embodiment of this application;

[0029] Figure 2 is a schematic diagram of the negative electrode sheet in the prior art;

[0030] Figure 3 is a cross-sectional view of one implementation of the negative electrode sheet provided in the embodiment of this application;

[0031] Figure 4 is a cross-sectional view of another implementation of the negative electrode sheet provided in the embodiments of this application;

[0032] Figure 5 is a front view of one implementation of the negative electrode sheet provided in the embodiments of this application;

[0033] Figure 6 is a front view of another implementation of the negative electrode provided in the embodiments of this application;

[0034] Figure 7 is a front view of another implementation of the negative electrode provided in the embodiments of this application;

[0035] Figure 8 is a cross-sectional view of the secondary battery provided in an embodiment of this application;

[0036] Figure 9 is a front view of the negative electrode sheet provided in an embodiment of this application;

[0037] Figure 10 is a flowchart of one implementation of the secondary battery preparation method provided in the embodiments of this application;

[0038] Figure 11 is a flowchart illustrating one implementation of the secondary battery preparation method provided in this application embodiment;

[0039] Figure 12 is a flowchart of another implementation of the secondary battery preparation method provided in the embodiments of this application;

[0040] Figure 13 is a flowchart illustrating another implementation of the secondary battery preparation method provided in this application embodiment.

[0041] The reference numerals in the attached drawings are as follows: Secondary battery 100; First direction D1, Second direction D2, Third direction D3; Negative electrode 10, Separator 20, Positive electrode 30, Adapter 40; First current collector 11, First coating 12, Second coating 13; First part 11a; First tab 11b; First surface 111, Second surface 112; Main body 1111, Empty foil part 1112; First edge 121, Second edge 122; First surface 123, Second surface 124; Third edge 131, Fourth edge 132; First part 1301, Second part 1302; Second current collector 31, Positive active material 32, Second tab 33, Insulating layer 34; Fifth edge 341, Sixth edge 342; Connection area 41; Thickness direction D4 of current collector substrate, Width direction D5 of current collector substrate; Current collector substrate 1, First adhesive tape 2, Second adhesive tape 3; Third surface 101, fourth surface 102, seventh edge 103, eighth edge 104, coating area 105, empty foil area 106. Detailed Implementation

[0042] To facilitate understanding of this application, 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 being "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 being "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 to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this application 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 application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0043] 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 application belongs. 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 application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0044] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0045] Example 1

[0046] Please refer to Figure 1. This application embodiment provides a secondary battery 100. The secondary battery 100 includes a negative electrode 10, a separator 20 and a positive electrode 30. The negative electrode 10, the separator 20 and the positive electrode 30 are stacked sequentially along a first direction D1, that is, the first direction D1 is the vector direction from the negative electrode 10 to the positive electrode 30.

[0047] The negative electrode 10 includes a first current collector 11, a first coating 12, and a second coating 13. Along a first direction D1, the first coating 12 is disposed between the first current collector 11 and the second coating 13, and is bonded and fixed to both the first current collector 11 and the second coating 13. That is, the first direction D1 is also the vector direction from the first coating 12 to the second coating 13. The second coating 13 includes a negative electrode active material. The first direction D1 is also the thickness direction of the negative electrode 10. Along the first direction D1, the first current collector 11 includes a second surface 112 and a first surface 111 disposed opposite to each other. The first coating 12 is attached to the first surface 111.

[0048] The positive electrode 30 includes a second current collector 31, a positive active material 32, and a second tab 33, wherein the second tab 33 is integrally disposed with the second current collector 31.

[0049] The inventors of this application have discovered that, in the prior art, as shown in Figures 1 and 2, when the second coating 13 of the negative electrode sheet 10 extends beyond the first coating 12 along the second direction D2, forming a first portion 1301 of the second coating 13 attached to the first current collector 11, the first portion 1301 of the second coating 13 is easily detached from the first current collector 11. This results in the detachment of negative electrode active material from the second coating 13, creating bumps. When the negative electrode active material interacts with the positive electrode active material 32, the detached negative electrode active material can easily puncture the separator 20, causing a short circuit between the positive and negative electrodes and affecting the performance of the secondary battery 100. The second direction D2 is perpendicular to the first direction D1.

[0050] In embodiments of this application, referring to Figures 3 or 4, the first current collector 11 includes an integrally formed main body 1111 and an empty foil portion 1112. The surface of the empty foil portion 1112 is not provided with a first coating 12 and a second coating 13. The empty foil portion 1112 is used for electrical connection with an external circuit. The empty foil portion 1112 is located on one side of the main body 1111 along the second direction D2. The first coating 12 is disposed on the area of ​​the first surface 111 located in the main body 1111. The second direction D2 is perpendicular to the first direction D1, and is the vector direction from the main body 1111 to the empty foil portion 1112. Along the second direction D2, the first coating 12 includes a second edge 122 and a first edge 121 disposed opposite to each other, and the second coating 13 includes a fourth edge 132 and a third edge 131 disposed opposite to each other. The first edge 121 and the third edge 131 are located on the same side of the secondary battery 100 in the second direction D2. Along the second direction D2, the width of the first edge 121 extending beyond the third edge 131 is L, where L ≥ 0. Through this secondary battery 100, since the width of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 along the second direction D2 is greater than or equal to zero, and since the second coating 13 is adhered to the first coating 12, and the first coating 12 is adhered to the first current collector 11, that is, the second coating 13 and the first current collector 11 are spaced apart by the first coating 12, since the peel strength between the second coating 13 and the first current collector 11 is small, the peel strength between the second coating 13 and the first coating 12 is large, and the peel strength between the first current collector 11 and the first coating 121 is large, the first coating 12 bonds and fixes the first current collector 11 and the second coating 13 respectively, reducing the risk of the second coating 13 falling off and failing.

[0051] The number of empty foil sections 1112 can be one or more. When there are multiple empty foil sections 1112, each empty foil section 1112 is integrally connected to the main body section 1111 along the second direction D2, which can increase the connection points between the secondary battery 100 and the external circuit, thereby improving the current transmission capability of the secondary battery 100.

[0052] The inventors of this application have discovered that when the value of L is small, for example, when L is less than 0.01 mm, there may be a higher risk of the second coating 13 peeling off due to manufacturing tolerances.

[0053] In some embodiments of this application, the width L of the first edge 121 extending beyond the third edge 131 satisfies: L ≥ 0.01 mm. For example, L can be selected as 0.01 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, or 3 mm, etc. Further defining the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 along the second direction D2 by a width L ≥ 0.01 mm, that is, the third edge 131 of the second coating 13 adheres to the first coating 12, further reducing the risk of the second coating 13 detaching and failing.

[0054] The inventors of this application have discovered that when the value of L is small, for example, when L is less than 0.1 mm, processing and molding are inconvenient, manufacturability is poor, and the adhesion strength between the second coating 13 and the first coating 12 may be affected, potentially leading to the risk of the second coating 13 detaching. When the value of L is large, for example, when L is greater than 3 mm, along the second direction D2, if the width of the first current collector 11 remains unchanged, the width of the empty foil portion 1112 of the first current collector 11 used for electrical connection with the external circuit is small, affecting the reliability of the connection between the first current collector 11 and the external circuit. Along the second direction D2, if the width of the first current collector 11 is increased to ensure the width of the empty foil portion 1112, the energy density of the secondary battery 100 is affected. In some embodiments of this application, the width L of the first edge 121 extending beyond the third edge 131 is limited to satisfy: 0.1mm≤L≤3mm. For example, L can be selected as 0.1mm, 0.5mm, 1mm, 1.5mm, 2mm or 3mm, which can not only improve manufacturability, but also ensure the bonding strength between the second coating 13 and the first coating 12, as well as ensure the reliability of the connection between the empty foil portion 1112 of the first current collector 11 and the external circuit, and ensure the energy density of the secondary battery 100.

[0055] In some embodiments of this application, 0.5mm ≤ L ≤ 2mm. For example, L can be selected as 0.5mm, 1mm, 1.5mm, or 2mm. As mentioned above, when the value of L is small, such as less than 0.5mm, it may cause inconvenience in processing and molding, and may also affect the bonding strength between the second coating 13 and the first coating 12. When the value of L is large, such as greater than 2mm, if the width of the first current collector 11 remains unchanged, it will affect the reliability of the connection between the first current collector 11 and the external circuit. Along the second direction D2, if the width of the first current collector 11 is increased to ensure the width of the empty foil portion 1112, it will affect the energy density of the secondary battery 100. The optimal value of L is 0.5mm ≤ L ≤ 2mm, which ensures manufacturability, the bonding strength between the second coating 13 and the first coating 12, the reliability of the connection between the first current collector 11 and the external circuit, and the energy density of the secondary battery 100.

[0056] Regarding the empty foil portion 1112 of the first current collector 11 described above, the empty foil portion 1112 is not equivalent to the negative electrode tab as understood by those skilled in the art. Referring to Figure 5, the first current collector 11 includes a first portion 11a and a first electrode tab 11b extending from the first portion 11a along the second direction D2. The first electrode tab 11b is the negative electrode tab. The first portion 11a and the first electrode tab 11b are integrally molded. There are various relative positional relationships between the first coating 12, the second coating 13, the first part 11a, and the first tab 11b. For example, as shown in Figure 5, the first coating 12 and the second coating 13 are both located in the first part 11a. In this case, the first tab 11b is equivalent to the empty foil part 1112, and the first part 11a is equivalent to the main body part 1111. As another example, as shown in Figure 6, a part of the first coating 12 is located in the first part 11a, and another part of the first coating 12 is located in the first tab 11b. The area of ​​the first tab 11b not covered by the first coating 12 is the empty foil part 1112, and the second coating 13 is located in the first part 11a. As yet another example, as shown in Figure 7, a part of the first coating 12 is located in the first part 11a, and another part of the first coating 12 is located in the first tab 11b. The area of ​​the first tab 11b not covered by the first coating 12 is the empty foil part 1112, a part of the second coating 13 corresponds to the first part 11a, and the other part of the second coating 13 corresponds to the first tab 11b.

[0057] The inventors of this application have discovered that the secondary battery 100 includes multiple negative electrode plates 10. The secondary battery 100 also includes an adapter 40, which is connected to multiple empty foil portions 1112 via a connection area 41. Referring to Figures 4 and 9, the empty foil portions 1112 of the first current collector 11 are electrically connected to an external circuit via the connection area 41 of the adapter 40. Along the third direction D3, the value range of the width M of the connection area 41 is crucial, where the third direction D3 is perpendicular to the first direction D1 and the second direction D2, respectively. When the value of M is small, for example, when M is less than 1 mm, there is a risk of unstable connection between the adapter 40 and the empty foil portions 1112; when the value of M is large, for example, when M is greater than 9 mm, the width of the empty foil portions 1112 of the first current collector 11 also needs to be correspondingly large, resulting in lower space utilization of the secondary battery 100 and affecting the energy density of the secondary battery 100. Furthermore, when the value of M is large, a large contact resistance will be generated between the empty foil portion 1112 of the first current collector 11 and the adapter 40, affecting the charging and discharging efficiency of the secondary battery 100. In some embodiments of this application, the width M of the connection area 41 along the third direction D3 is limited to satisfy: 1mm ≤ M ≤ 9mm. For example, M can be selected as 1mm, 1.2mm, 1.5mm, 2mm, 4mm, 6mm, 8mm, or 9mm, which not only ensures the connection reliability between the empty foil portion 1112 of the first current collector 11 and the adapter 40, but also ensures the energy density and charging and discharging efficiency of the secondary battery 100.

[0058] In some embodiments of this application, there are multiple negative electrode plates 10, multiple positive electrode plates 30, and multiple separators 20. The negative electrode plates 10, separators 20, and positive electrode plates 30 are stacked along a first direction D1. When there are multiple negative electrode plates 10, there are multiple empty foil portions 1112 for electrical connection with external circuits. The number of empty foil portions 1112 for each negative electrode plate 10 can be one or multiple, which can increase the connection points between the secondary battery 100 and the external circuit, thereby improving the current transmission capability of the secondary battery 100.

[0059] The inventors of this application have discovered, as shown in Figure 4, that along the first direction D1, a smaller thickness T1 of the first coating 12, for example, when T1 is less than 0.1 μm, may affect the adhesion stability between the first coating 12 and the first current collector 11, and there is a high risk that the first coating 12, along with the second coating 13, will detach from the first current collector 11. Conversely, along the first direction D1, a larger thickness T1 of the first coating 12, for example, when T1 is greater than 5 μm, results in the first coating 12 occupying a larger space, affecting the energy density of the secondary battery 100. In some embodiments of this application, the thickness of the first coating 12 along the first direction D1 is limited to T1, where 0.1 μm ≤ T1 ≤ 5 μm. For example, T1 can be selected as 0.1 μm, 0.5 μm, 1 μm, 2 μm, or 5 μm, thereby ensuring both the adhesion stability between the first coating 12 and the first current collector 11 and reducing the impact of the first coating 12 on the energy density of the secondary battery 100.

[0060] The inventors of this application have discovered that, along the first direction D1, when the thickness T2 of the second coating 13 is small, for example, when T2 is less than 10 μm, the thickness of the negative electrode active material included in the second coating 13 is small, making it difficult to provide sufficient space for interaction with the positive electrode active material 32 of the secondary battery 100, thus affecting the capacity of the secondary battery 100; along the second direction D2, when the thickness T2 of the second coating 13 is large, for example, when T2 is greater than 300 μm, the thickness of the negative electrode active material included in the second coating 13 is large, which may pose a risk that the second coating 13 and the first coating 12 may detach together from the first current collector 11; especially when the mass ratio of the adhesive material in the active material is small, the second coating 13 is easily detached from the first coating 12 due to the weight of the thick second coating 13, and may even easily detach from the first current collector 11 along with the first coating 12.

[0061] Furthermore, the inventors of this application have also discovered that a larger thickness of the second coating 13 increases the diffusion path of the positive electrode active material 32 in the secondary battery 100, affecting the performance of the secondary battery 100. In addition, a larger thickness of the second coating 13 may also increase the weight and volume of the secondary battery 100, which is not conducive to the miniaturization and lightweight development of the secondary battery 100.

[0062] Based on research on the thickness of the second coating 13, the inventors of this application have defined the thickness of the second coating 13 along the first direction D1 as T2, where 10μm≤T2≤300μm. For example, T2 can be selected as 10μm, 50μm, 100μm, 200μm, or 300μm, thereby ensuring both the capacity of the secondary battery 100 and the adhesion stability between the second coating 13, the first coating 12, and the first current collector 11, while also ensuring the performance of the secondary battery 100 and meeting the development requirements for lightweight design.

[0063] The inventors of this application have discovered that, in the prior art, referring to Figure 2, the second coating 13 includes a second portion 1302 and a first portion 1301 connected along a second direction D2. The second portion 1302 is located in the first coating 12, and the first portion 1301 is attached to the first current collector 11. After the second coating 13 is formed, the thickness of the first portion 1301 gradually decreases along the second direction D2, forming a "thinning region." The thickness of the first portion 1301 is the thickness of the first portion 1301 along the first direction D1. Because the thickness of the first portion 1301 gradually decreases along the second direction D2, local defects, such as local lithium plating, are easily generated in the "thinning region" when interacting with the positive electrode active material of the secondary battery 100. In this embodiment, the first portion 1301 of the second coating 13 is defined to not only adhere to the first current collector 11, but also, along the first direction D1, the second coating 13 has a first surface 123 and a second surface 124 disposed opposite to each other, with any point on the first surface 123 having the same vertical distance from the second surface 124. The second coating 13 is uniformly distributed along the first direction D1, reducing the risk of localized defects, such as the risk of localized lithium plating, when interacting with the positive electrode active material of the secondary battery 100.

[0064] The phrase "the vertical distance from any point on the first surface 123 to the second surface 124 is the same" means that the maximum vertical distance from any point on the first surface 123 to the second surface 124 is within 5% of the maximum value.

[0065] The inventors of this application discovered that during the cutting process to form the second tab 33, the cutting burrs pose a risk of piercing the separator 20. Therefore, an insulating layer 34 can be provided on the second tab 33, as shown in FIG1. ​​Along the second direction D2, the insulating layer 34 includes a sixth edge 342 and a fifth edge 341 disposed opposite to each other, wherein, in some embodiments of this application, the sixth edge 342 is connected to the positive electrode active material 32. The first edge 121 of the first coating 12 of the negative electrode 10, the third edge 131 of the second coating 13 of the negative electrode 10, and the aforementioned fifth edge 341 are located on the same side of the secondary battery 100 in the second direction D2. Along the second direction D2, the third edge 131 extends beyond the sixth edge 342. By providing this insulating layer 34, the insulating layer 34 covers the cutting burrs during the formation of the second tab 33, reducing the risk of short circuit caused by the cutting burrs piercing the separator 20. In addition, the third edge 131 of the second coating 13 extends beyond the sixth edge 342 of the insulating layer 34, that is, along the second direction D2, the third edge 131 of the second coating 13 extends beyond the positive electrode active material 32, thereby reducing the risk of lithium plating.

[0066] In some embodiments of this application, the first coating 12 of the negative electrode 10 includes a conductive agent and a first adhesive. The conductive agent includes one or more of carbon nanotubes, graphene, graphene oxide, and conductive carbon black. The first adhesive includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, and polyacrylonitrile. By limiting the material of the first coating 12, on the one hand, the adhesion and fixation of the first coating 12 to the first current collector 11 and the second coating 13 are ensured, reducing the risk of the second coating 13 or the first coating 12 together with the second coating 13 detaching from the first current collector 11; on the other hand, the overall impedance of the negative electrode 10 is guaranteed, improving the overall performance of the secondary battery 100.

[0067] In some embodiments of this application, the second coating 13 of the negative electrode sheet 10, in addition to the aforementioned negative electrode active material, also includes a second adhesive. The second adhesive includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, and polyacrylonitrile. The negative electrode active material includes one or more of graphite, silicon-based, tin-based, and metal oxides. By limiting the material of the second coating 13, the interaction function between the second coating 13 and the positive electrode active material 32 of the secondary battery 100 is ensured, thereby ensuring the charge and discharge performance of the secondary battery 100.

[0068] The inventors of this application have discovered that, based on the mass of the second coating 13, the mass percentage of the negative electrode active material is m. When the value of m is small, for example, less than 92%, it affects the energy density of the secondary battery 100; when the value of m is large, for example, greater than 99.5%, it affects the adhesion between the second coating 13 and the first coating 12. In the embodiments of this application, 92% ≤ m ≤ 99.5%. By limiting the value of m, both a high energy density of the secondary battery 100 and reliable adhesion between the second coating 13 and the first coating 12 are ensured, reducing the risk of the second coating 13 detaching.

[0069]

Example 2

[0070] This application provides an electronic device including a secondary battery 100 as described in any of the embodiments above. The secondary battery 100 is an important component of the electronic device, providing stable power support. The electronic device can be a portable device, such as a smartphone, tablet computer, laptop computer, smartwatch, digital camera, etc., or a stationary device, such as an electric vehicle, electric bicycle, power tool, energy storage system, etc.

[0071]

Example 3

[0072] This application provides a method for preparing a secondary battery 100, used to prepare any of the above-mentioned secondary battery 100. Please refer to Figures 10, 11 and 3. The method for preparing the secondary battery 100 includes the following steps:

[0073] Step S10: Take the current collector substrate 1. The current collector substrate 1 includes a third surface 101 and a fourth surface 102 disposed opposite to each other along its thickness direction. The current collector substrate 1 also includes an eighth edge 104 and a seventh edge 103 disposed opposite to each other along its width direction.

[0074] Here, the thickness direction D4 of the current collector substrate is defined as a vector direction opposite to the first direction D1 mentioned above.

[0075] In this context, the width direction D5 of the current collector substrate is defined to correspond to the second direction D2 mentioned above.

[0076] In step S20, a first adhesive tape 2 is applied to the third surface 101. One edge of the first adhesive tape 2 is flush with the seventh edge 103. The portion of the current collector substrate 1 not covered by the first adhesive tape 2 is the coating area 105.

[0077] The coating area 105 is a part of the third surface 101, and the coating area 105 is the part of the third surface 101 that is not covered by the first adhesive tape 2.

[0078] Step S30: Apply a first coating 12 to the coating area 105.

[0079] The first coating 12 can be provided in the coating area 105 in two ways: either in the coating area 105 and the first adhesive tape 2, or in the coating area 105 only, avoiding the first adhesive tape 2.

[0080] Step S40: Remove the first adhesive tape 2, and attach the second adhesive tape 3 to the third surface 101. Along the width direction D5 of the current collector substrate, the width w2 of the second adhesive tape 3 is greater than the width w1 of the first adhesive tape 2, and one edge of the second adhesive tape 3 is flush with the seventh edge 103.

[0081] Since the width of the second adhesive tape 3 is greater than the width of the first adhesive tape 2 along the width direction D5 of the current collector substrate, and one edge of the second adhesive tape 3 is flush with the seventh edge 103, the second adhesive tape 3 is partially attached to the first coating layer 12.

[0082] Step S50: Apply a second coating 13 to the first coating 12 and the second adhesive tape 3.

[0083] In step S60, the second adhesive tape 3 is removed, and the area of ​​the current collector substrate 1 exposed in the first coating 12 and the second coating 13 is the empty foil area 106. The current collector substrate 1 is cut to obtain the first current collector 11, and the empty foil area 106 is cut to form the empty foil portion 1112.

[0084] The empty foil section 1112 is used for electrical connection with an external circuit.

[0085] By means of the preparation method of the secondary battery 100, since the width of the second adhesive tape 3 is greater than the width of the first adhesive tape 2 along the width direction D5 of the current collector substrate, after removing the second adhesive tape 3, the first coating 12 extends beyond the second coating 13 along the width direction of the current collector substrate 1. That is, the first coating 12 is provided between the second coating 13 and the first current collector 11. Since the peel strength between the second coating 13 and the first current collector 11 is small, the peel strength between the second coating 13 and the first coating 12 is large, and the peel strength between the first current collector 11 and the first coating 121 is large, the first coating 12 bonds and fixes the first current collector 11 and the second coating 13 respectively, reducing the risk of the second coating 13 falling off and failing.

[0086] The inventors of this application have discovered that when the width of the second adhesive tape 3 is small, for example, less than 8 mm, manufacturability is poor; when the width w2 of the second adhesive tape 3 is large, for example, greater than 40 mm, the first coating 12 will exceed the width w2 of the second coating 13, resulting in a smaller width of the second coating 13, which affects the energy density of the secondary battery 100. In the embodiments of this application, the width w2 of the second adhesive tape 3 is limited to between 8 mm and 40 mm along the width direction D5 of the current collector substrate. For example, the width w2 of the second adhesive tape 3 can be 8 mm, 10 mm, 20 mm, 30 mm, or 40 mm, which ensures both manufacturability and the energy density of the secondary battery 100.

[0087] The inventors of this application have discovered that when the width w1 of the first adhesive tape 2 is small, for example, less than 7.9 mm, manufacturability is poor; when the width w1 of the first adhesive tape 2 is large, for example, greater than 38 mm, the width of the empty foil portion 1112 on the first current collector 11 for electrical connection with external circuits is larger along the second direction D2, occupying space and affecting the energy density of the secondary battery 100. In the embodiments of this application, the width w1 of the first adhesive tape 2 is limited to between 7 mm and 40 mm along the width direction D5 of the current collector substrate 1. For example, the width w1 of the first adhesive tape 2 can be 7 mm, 7.9 mm, 10 mm, 20 mm, 30 mm, 38 mm, or 40 mm, which can ensure both manufacturability and the energy density of the secondary battery 100.

[0088] The inventors of this application have discovered that when the peel strength between the first adhesive tape 2 and the current collector substrate 1 is low, for example, less than 1 mN / mm, it affects the bonding reliability between the first adhesive tape 2 and the current collector substrate 1. When the first adhesive tape 2 bulges or the bonding is unreliable, it may affect the coating effect of the first coating 12 and increase the risk of the second coating 13 falling off and failing. When the peel strength between the first adhesive tape 2 and the current collector substrate 1 is high, for example, greater than 7 mN / mm, it affects the ease of removing the first adhesive tape 2 and the welding yield of the subsequent welding adapter 40. In the embodiments of this application, the peel strength between the first adhesive tape 2 and the current collector substrate 1 is limited to between 1 mN / mm and 7 mN / mm. For example, the peel strength between the first adhesive tape 2 and the current collector substrate 1 is 1mN / mm, 4mN / mm, 6mN / mm or 7mN / mm. By limiting the peel strength between the first adhesive tape 2 and the current collector substrate 1, the bonding reliability between the first adhesive tape 2 and the current collector substrate 1 is ensured, the coating effect of the first coating 12 is ensured, the operability of removing the first adhesive tape 2 is ensured, and the welding efficiency of the subsequent welding adapter 40 is ensured.

[0089] The peel strength test method for the first adhesive tape 2 and the current collector substrate 1 can be a peel strength test. The first adhesive tape 2 is adhered to a standard test plate, and then peeled off at a certain angle (usually 180 degrees or 90 degrees) and a constant speed. The required force is recorded. The equipment used is a peel strength tester, and the reference standards are ASTM D903, ISO 8295, etc.

[0090] In some embodiments, the first adhesive tape 2 includes a substrate layer (not shown) and an adhesive (not shown) disposed on the substrate layer. The substrate layer may be selected from polyethylene terephthalate, co-extruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, and polyolefin. The adhesive may be selected from one or a combination of acrylic resin, polypropylene, or rubber. By selecting different material types and / or qualities to adjust the adhesive strength of the adhesive, the peel strength between the first adhesive tape 2 and the current collector substrate 1 can be adjusted.

[0091] It should be noted that the peel strength between the first adhesive tape 2 and the current collector substrate 1 before immersion in the electrolyte affects the peel strength between the first adhesive tape 2 and the current collector substrate 1 after immersion in the electrolyte. Therefore, by selecting different types and / or qualities of materials to adjust the adhesive strength, the bonding strength between the first adhesive tape 2 and the current collector substrate 1 can be adjusted.

[0092] The inventors of this application discovered that when the peel strength between the first coating 12 and the current collector substrate 1 is less than or equal to the peel strength between the first coating 12 and the second adhesive tape 3, the first coating 12 covered by the second adhesive tape 3 easily detaches from the current collector substrate 1 when the second adhesive tape 3 is removed, affecting the adhesion of the second coating 13 to the current collector electrode through the first coating 12. In the embodiments of this application, the peel strength between the first coating 12 and the current collector substrate 1 is limited to be greater than the peel strength between the first coating 12 and the second adhesive tape 3. With this setting, when the second adhesive tape 3 is removed, the first coating 12 covered by the second adhesive tape 3 remains on the current collector substrate 1, ensuring the adhesion of the first coating 12 to the second coating 13 and the current collector substrate 1.

[0093] The inventors of this application have discovered that when the peel strength between the second adhesive tape 3 and the current collector substrate 1 is low, for example, less than 1 mN / mm, the second coating 13 can easily penetrate between the second adhesive tape 3 and the current collector electrode 1 during the coating process, affecting the subsequent welding effect on the adapter 40. Conversely, when the peel strength between the second adhesive tape 3 and the current collector substrate 1 is high, for example, greater than 7 mN / mm, it affects the ease of removing the second adhesive tape 3 and also impacts the subsequent welding effect on the adapter 40. In some embodiments of this application, the peel strength between the second adhesive tape 3 and the current collector substrate 1 is limited to between 1 mN / mm and 7 mN / mm, for example, 1 mN / mm, 4 mN / mm, 6 mN / mm, or 7 mN / mm. By limiting the peel strength between the second adhesive tape 3 and the current collector substrate 1, the subsequent welding effect on the adapter 40 is ensured.

[0094] The peel strength test method for the second adhesive tape 3 and the current collector substrate 1 can be the peel strength test. For details, please refer to the above-mentioned test method for the peel strength test of the first adhesive tape 2 and the current collector substrate 1. It will not be repeated here.

[0095] It should be noted that the peel strength between the second adhesive tape 3 and the current collector substrate 1 before immersion in the electrolyte affects the peel strength between the second adhesive tape 3 and the current collector substrate 1 after immersion in the electrolyte. Therefore, by selecting different types and / or qualities of materials to adjust the adhesive strength, the bonding strength between the second adhesive tape 3 and the current collector substrate 1 can be adjusted. The principle and method of adjusting the bonding strength between the second adhesive tape 3 and the current collector substrate 1 can be referred to the adjustment of the first adhesive tape 2 and the current collector substrate 1, and will not be repeated here.

[0096] The inventors of this application have discovered that when the peel strength between the second adhesive tape 3 and the first coating 12 is low, for example, less than 1 mN / mm, it affects the adhesion reliability between the second adhesive tape 3 and the first coating 12. If the second adhesive tape 3 bulges or the adhesion is unreliable, it may affect the coating effect of the second coating 13 and increase the risk of the second coating 13 detaching. When the peel strength between the second adhesive tape 3 and the first coating 12 is high, for example, greater than 7 mN / mm, it affects the ease of removing the second adhesive tape 3. Furthermore, during removal, due to the high peel strength between the second adhesive tape 3 and the first coating 12, there is a risk that the second adhesive tape 3 may peel the first coating 12 off the current collector substrate 1, thus increasing the risk that the second coating 13 will adhere to the current collector substrate 1 and detach from it. In some embodiments of this application, the peel strength between the second adhesive tape 3 and the first coating 12 is limited to between 1 mN / mm and 7 mN / mm. By limiting the peel strength between the second adhesive tape 3 and the first coating 12, the adhesion reliability between the second adhesive tape 3 and the first coating 12 is ensured, the coating effect of the second coating 13 is ensured, the operability of removing the second adhesive tape 3 is ensured, and the first coating 12 is retained on the current collector substrate 1 when the second adhesive tape 3 is removed. This ensures the adhesion and fixation of the first coating 12 between the second coating 13 and the current collector substrate 1, and reduces the risk of the second coating 13 falling off.

[0097] The peel strength between the second adhesive tape 3 and the first coating 12 can be tested by peel strength test. For details, please refer to the above test method for the peel strength between the first adhesive tape 2 and the current collector substrate 1. It will not be repeated here.

[0098] It should be noted that the peel strength between the second adhesive tape 3 and the first coating 12 before immersion in the electrolyte affects the peel strength between the second adhesive tape 3 and the first coating 12 after immersion in the electrolyte. Therefore, by selecting different material types and / or qualities to adjust the adhesive strength, the peel strength between the second adhesive tape 3 and the first coating 12 can be adjusted. The principle and method for adjusting the peel strength between the second adhesive tape 3 and the first coating 12 can refer to the adjustment of the first adhesive tape 2 and the current collector substrate 1, and will not be repeated here.

[0099]

Example 4

[0100] This application provides a method for preparing a secondary battery 100. Referring to Figures 12, 13, and 4, the method for preparing the secondary battery 100 includes the following steps:

[0101] Step S1: Take the current collector substrate 1. The current collector substrate 1 includes a third surface 101 and a fourth surface 102 disposed opposite to each other along its thickness direction. The current collector substrate 1 also includes an eighth edge 104 and a seventh edge 103 disposed opposite to each other along its width direction.

[0102] Here, the thickness direction D4 of the current collector substrate is defined as a vector direction opposite to the first direction D1 mentioned above.

[0103] In this context, the width direction D5 of the current collector substrate is defined to correspond to the second direction D2 mentioned above.

[0104] Step S2: Apply a first coating 12 to the third surface 101.

[0105] The first coating 12 can completely cover the third surface 101; or the first coating 12 can cover only a portion of the third surface 101, in which case the area on the third surface 101 covered by the first layer is the coating area 105.

[0106] Step S3: Apply a second adhesive tape 3 to the first coating 12, with one edge of the second adhesive tape 3 flush with the seventh edge 103.

[0107] When the first coating 12 completely covers the third surface 101, one edge of the first coating 12 and one edge of the second adhesive tape 3 are flush with the seventh edge 103.

[0108] When the first coating 12 only covers the coating area 105 of the third surface 101, one edge of the second adhesive tape 3 is flush with the seventh edge 103, and the other edge of the second edge 122 is attached to the first coating 12.

[0109] Step S4: Apply a second coating 13 to the first coating 12 and the second adhesive tape 3.

[0110] Step S5: Remove the second adhesive tape 3 and cut the current collector substrate 1 to obtain the first current collector 11.

[0111] By means of the preparation method of the secondary battery 100, when the second adhesive tape 3 is removed, the second coating 13 on the second adhesive tape 3 is removed, and the first coating 12 covered by the second adhesive tape 3 remains on the current collector substrate 1. Along the width direction of the current collector substrate 1, the first coating 12 extends beyond the second coating 13. That is, the first coating 12 is provided between the second coating 13 and the first current collector 11, and the second coating 13 does not contact the first current collector 11, thereby reducing the risk of the second coating 13 falling off and failing.

[0112] In some embodiments of this application, the third surface 101 of the first current collector 11 has an empty foil area 106 without the first coating 12 and the second coating 13. One edge of the empty foil area 106 is flush with the seventh edge 103. The empty foil area 106 is cut to form an empty foil portion 1112. This method of preparing the secondary battery 100 facilitates subsequent cutting to form the empty foil portion 1112 that is electrically connected to an external circuit.

[0113] In some embodiments of this application, the first coating 12 completely covers the third surface 101. The first current collector 11 is cut, and laser cleaning is performed to remove part of the first coating 12 to form an empty foil portion 1112. Through this method of preparing the secondary battery 100, when the second adhesive tape 3 is removed, the second coating 13 on the second adhesive tape 3 is removed, and the first coating 12 covered by the second adhesive tape 3 remains on the current collector substrate 1. Subsequent cleaning of part of the first coating 12 can form an empty foil portion 1112 that is electrically connected to an external circuit. In addition, since the first coating 12 covered by the second adhesive tape 3 remains on the current collector substrate 1, the first coating 12 extends beyond the second coating 13 along the width direction of the current collector substrate 1. That is, the first coating 12 is provided between the second coating 13 and the first current collector 11. Since the peel strength between the second coating 13 and the first current collector 11 is small, the peel strength between the second coating 13 and the first coating 12 is large, and the peel strength between the first current collector 11 and the first coating 121 is large, the first coating 12 bonds and fixes the first current collector 11 and the second coating 13 respectively, reducing the risk of the second coating 13 falling off and failing.

[0114] To evaluate the beneficial effects of the secondary battery 100 and its preparation method, the prepared secondary battery 100 was tested. The test results evaluating the beneficial effects of the secondary battery 100 are recorded in Table 1 below, and the test results evaluating the preparation method of the secondary battery 100 are recorded in Table 2 below. Unless otherwise specified, all reagents, materials, and instruments used in the following examples and comparative examples are commercially available.

[0115]

Example 1

[0116] <Preparation of Positive Electrode 30>

[0117] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (weight average molecular weight is 5×10). 5The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and stirred evenly under vacuum. An aluminum foil with a thickness of 12 μm, a length of 358 mm, and a width of 3.5 mm was used as the positive electrode current collector (corresponding to the second current collector 31 mentioned above). The positive electrode slurry was uniformly coated on one surface of the aluminum foil, leaving an uncoated portion at one end. The foil was dried at 110°C to obtain a positive electrode sheet 30 with a single-sided coating of 32 layers of positive active material. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet 30 with a double-sided coating of 32 layers of positive active material. The single-sided coating weight of the positive electrode sheet 30 was 17 mg / cm³. 2 The positive electrode sheet 30 is die-cut and slit to obtain multiple second electrode tabs 33.

[0118] <Preparation of negative electrode sheet 10>

[0119] A copper foil with a thickness of 10 μm, a width of 394 mm, and a length of 100 mm was selected as the negative electrode current collector (corresponding to the current collector substrate 1 mentioned above). The first current collector 11, the first coating 12, the second coating 13, and the empty foil portion 1112 for electrical connection with an external circuit were prepared using the scheme described in Example 3 above. After completing the above steps, the single-sided coating of the negative electrode 10 is complete. Then, the above steps are repeated on the other surface of the negative electrode 10 to obtain a negative electrode 10 with double-sided coating of negative electrode active material. The single-sided coating weight of the negative electrode 10 is 8 mg / cm³. 2 .

[0120] The preparation method of the first slurry used in the first coating 12 is as follows: room temperature water, adhesive, and conductive agent are mixed in a weight ratio of 55:20:25. The mixture is first initially stirred at low speed (200-400 rpm, 30 min) for preliminary mixing, and then stirred at high speed (1000 rpm, 30 min) to prepare a first slurry with a solid content of 40 wt%. After coating with the first slurry, it is dried at 110°C to obtain the first coating 12.

[0121] The second slurry used in the second coating 13 is prepared by mixing graphite powder (anode active material), sodium carboxymethyl cellulose, conductive carbon black (Super P), and styrene-butadiene rubber (binder) in a weight ratio of 98:0.6:0.6:0.8. Deionized water is then added as a solvent to prepare a second slurry with a solid content of 50 wt%, and the mixture is stirred evenly. After coating with the second slurry, the mixture is dried at 110°C to obtain the second coating 13.

[0122] <Preparation of diaphragm 20>

[0123] A porous membrane with a thickness of 7 μm polyethylene and a 2 μm alumina coating was used as the diaphragm 20.

[0124] <Electrolyte Preparation>

[0125] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate was added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0126] <Preparation of Secondary Battery 100>

[0127] A 3mm wide aluminum sheet is used as the positive electrode adapter, and the positive electrode adapter is welded to multiple positive electrode tabs 33. A 3mm wide nickel sheet is used as the negative electrode adapter 40, and the adapter 40 is welded to the empty foil portions 1112 of multiple negative electrode sheets 10. The separator 20, positive electrode sheet 30, separator 20, and negative electrode sheet 10 prepared above are stacked in sequence to obtain an electrode assembly. The electrode assembly is placed in a packaging bag with dimensions of 40mm × 20mm × 2mm, with the positive electrode adapter and the negative electrode adapter 40 extending out of the packaging bag. After removing moisture at 80°C, electrolyte is injected, and after processes such as encapsulation, electrolyte injection, formation, capacity testing, and voltage and internal resistance testing, a secondary battery 100 is obtained.

[0128] The difference between Examples 1 to 25 and Comparative Example 1 lies in the different relevant parameters, as shown in Table 1 below.

[0129] In Comparative Example 1 (Prior Art), the second coating 13 extends beyond the first coating 12 along the second direction D2. In Comparative Example 1, the negative electrode sheet 10 is prepared by selecting a copper foil with a thickness of 10μm, a width of 394mm, and a length of 100mm as the negative electrode current collector. Adhesive paper is attached to the negative electrode current collector, with one edge of the adhesive paper flush with one edge of the negative electrode current collector. A first slurry and a second slurry are sequentially coated on the area of ​​the negative electrode current collector without adhesive paper and on the adhesive paper. After removing the adhesive paper, the undried second slurry flows to the negative electrode current collector and is dried at 110°C, resulting in a situation where the second coating 13 extends beyond the first coating 12 along the second direction D2. That is, the width L corresponding to the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 along the second direction D2 is a negative value.

[0130] All electrode components in each experimental group underwent a withstand voltage test (Hi-pot test), which included the following steps:

[0131] Connect the electrode assembly to the high voltage output device, detect the leakage current generated by the secondary battery 100 under the 100KV test voltage output by the high voltage device, and then calculate the resistance value: resistance value = test voltage / leakage current.

[0132] The calculated resistance value is compared with the set judgment resistor. In this application, the preset value of the judgment resistor is 1 Mohm (megaohm).

[0133] If the detected resistance value is greater than or equal to the preset value of 1 Mohm, the product under test is deemed to have passed the test (OK).

[0134] If the detected resistance value is less than the preset value of 1 Mohm, the test voltage is cut off instantly and the product under test is judged to fail the test (NG);

[0135] The number of secondary batteries that passed the test is X1, and the test pass rate = X1 / 100 × 100%, which is also known as the Hi-pot success rate.

[0136] The principle of the Hi-pot test is that if the second coating 13 does not peel off or the amount of peeling off is not significant, the positive electrode 30 and the negative electrode 10 are in an insulating state due to the electrode assembly, and the detected resistance value is greater than or equal to the preset value. If the amount of peeling off the second coating 13 is too large, causing an internal short circuit in the electrode assembly, the detected resistance value is less than the preset value. Therefore, the peeling situation of the second coating 13 can be reflected by testing the resistance value.

[0137] After the Hi-pot test, 20 secondary batteries were randomly selected from each experimental group for the peel test.

[0138] The peel test process includes the following steps:

[0139] The negative electrode tab 50, together with the negative electrode adapter 40, can be cut off from the negative electrode sheet 10 as a sample. Select two adjacent layers from the sample (which can be the empty foil part 1112, or the negative electrode adapter 40 and the empty foil part 1112), and label them as sample 1 and sample 2. Use double-sided tape to stick sample 1 to the steel plate substrate, and place the steel plate on a high-speed rail tensile testing machine. Use a clamp to hold one end of sample 2 and peel it off at a tensile speed of 10 mm / min until the weld position is detached. Record the area of ​​sample 2 remaining on the surface of sample 1 after peeling. If the remaining area is less than 10% of the overall weld, it is considered a cold weld. Repeat the above steps six times by selecting different adjacent layers. Randomly select adjacent empty foil parts 1112 for testing five times, and adapter 40 and adjacent empty foil parts 1112 for testing once. If a cold weld occurs in any of the six tests, the secondary battery 100 will be judged as failing the test (NG).

[0140] The number of secondary batteries that passed the test was X2, and the pass rate was X2 / 20, which is also the welding quality rate.

[0141] The energy density ratio of the secondary batteries in each experimental group was tested. The test steps were as follows:

[0142] Place the secondary battery 100 in a constant temperature chamber at 25℃±2℃ and let it stand for 30 minutes to allow it to reach a constant temperature. Charge the secondary battery 100 at a constant current of 0.5C until it reaches the full charge voltage, then charge it at a constant voltage of 0.05C until the current reaches 0.2C, and discharge it at 0.2C until the voltage reaches 3.0V. Record the discharge energy.

[0143] Volumetric energy density = Discharge energy / (Length of secondary battery 100 × Width of secondary battery 100 × Thickness of secondary battery 100).

[0144] Energy density ratio = Volumetric energy density of secondary battery 100 in the embodiment / Volumetric energy density of secondary battery 100 in Comparative Example 1.

[0145] The difference between Examples 1 to 20 and Comparative Example 1 lies in the different relevant parameters, as shown in Table 1 below.

[0146] Table 1

[0147] According to Table 1 above, in Example 1, when the width L of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 along the second direction D2 is zero, the Hi-pot pass rate increases from 75 / 100 to 96 / 100 compared to Comparative Example 1, meaning the risk of the second coating 13 detaching is reduced. Furthermore, combining the welding yield and energy density ratio data from Example 1 and Comparative Example 1, this application, while reducing the risk of the second coating 13 detaching, also ensures the welding yield and the energy density ratio of the secondary battery 100.

[0148] In Example 2, when the width L of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 along the second direction D2 is 0.01 mm, the Hi-pot pass rate is further improved compared to Example 1, increasing from 96 / 100 to 98 / 100, meaning the risk of the second coating 13 detaching is further reduced. Furthermore, combining the welding yield and energy density ratio data from Examples 2 and 1, this application further reduces the risk of the second coating 13 detaching while ensuring both welding yield and the energy density ratio of the secondary battery 100.

[0149] From Examples 3 to 9, along the second direction D2, the width L of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 satisfies 0.1mm ≤ L ≤ 3mm. Compared to Examples 2 and 10, the Hi-pot throughput is improved, further reducing the risk of the second coating 13 peeling off. It can be seen that setting 0.1mm ≤ L ensures that the width of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 is not too small, thus ensuring that the Hi-pot throughput is not too low. Setting L ≤ 3mm ensures that the portion of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 does not occupy too much space, thus ensuring that the energy density ratio is not too low.

[0150] In Examples 4, 5, 6, and 7, along the second direction D2, the width L of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 satisfies 0.5mm ≤ L ≤ 2mm. Compared to Examples 3 and 8, this is beneficial for further ensuring the Hi-pot throughput and the energy density of the secondary battery 100. It can be seen that setting 0.5mm ≤ L ensures that the width of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 is not too small, thus ensuring that the Hi-pot throughput is not too low. Setting L ≤ 2mm ensures that the portion of the first edge 121 of the first coating 12 extending beyond the third edge 131 of the second coating 13 does not occupy too much space, thus ensuring that the energy density ratio is not too low.

[0151] The differences between Examples 21 to 45 lie in the different related parameters, as shown in Table 2 below. In Examples A1 to A20, L is the same (1 mm); M is the same (5 mm); T1 is the same (1 μm); T2 is the same (100 μm); and m is the same (95%). F1 represents the peel strength between the first adhesive tape 2 and the current collector substrate 1; F2 represents the peel strength between the second adhesive tape 3 and the current collector substrate 1; and F3 represents the peel strength between the second adhesive tape 3 and the first coating 12.

[0152] Table 2

[0153] According to Table 2 above, from Examples 22 to 28, the peel strength F1 between the first adhesive tape 2 and the current collector substrate 1 is between 1 mN / mm and 7 mN / mm. Compared with Examples 22 and 29, this not only ensures the Hi-pot pass rate but also the welding quality rate. It can be seen that when the peel strength F1 between the first adhesive tape 2 and the current collector substrate 1 is greater than 1 mN / mm, the peel strength F1 between the first adhesive tape 2 and the current collector substrate 1 is not too low, ensuring the bonding reliability between the first adhesive tape 2 and the current collector substrate 1, ensuring the coating effect of the first coating 12, and reducing the risk of subsequent second coating 13 applied to the first coating 12 falling off and failing, resulting in a higher Hi-pot pass rate. When the peel strength F1 between the first adhesive tape 2 and the current collector substrate 1 is less than 7 mN / mm, it does not affect the ease of removing the first adhesive tape 2, ensuring the welding quality rate.

[0154] In conjunction with Examples 31 to 36 and Example 25, the peel strength F2 between the second adhesive tape 3 and the current collector substrate 1 is between 1 mN / mm and 7 mN / mm. Compared to Examples 30 and 37, this not only ensures the Hi-pot pass rate but also guarantees the welding yield. It is evident that when the peel strength F2 between the second adhesive tape 3 and the current collector substrate 1 is greater than 1 mN / mm, the peel strength is appropriate, preventing the second slurry from easily entering between the second adhesive tape 3 and the current collector electrode 1 during coating, thus avoiding affecting the subsequent welding effect on the adapter 40 and resulting in a good welding yield. When the peel strength F2 between the second adhesive tape 3 and the current collector substrate 1 is less than 7 mN / mm, the ease of removing the second adhesive tape 3 is not affected, ensuring a good welding yield.

[0155] In conjunction with Examples 39 to 44 and Example 25, the peel strength F3 between the second adhesive tape 3 and the first coating 12 is between 1 mN / mm and 7 mN / mm. Compared to Examples 38 and 45, this not only ensures the Hi-pot pass rate but also the welding quality rate. It is evident that the peel strength F3 between the second adhesive tape 3 and the first coating 12 is greater than 1 mN / mm, ensuring an appropriate peel strength that does not affect the bonding reliability between the second adhesive tape 3 and the first coating 12, does not affect the coating effect of the second coating 13, and does not cause a high risk of detachment of the second coating 13, thus ensuring the Hi-pot pass rate. Furthermore, the peel strength F3 between the second adhesive tape 3 and the first coating 12 is less than 7 mN / mm, ensuring that removing the second adhesive tape 3 does not remove the first coating 12, does not affect the bonding stability of the second coating 13, does not cause a high risk of detachment of the second coating 13, does not affect the Hi-pot pass rate, and does not affect the welding quality rate.

[0156] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A secondary battery, characterized in that, include: The negative electrode sheet includes a first current collector, a first coating, and a second coating. Along a first direction, the first coating is disposed between the first current collector and the second coating, and the first coating is bonded and fixed to the first current collector and the second coating, respectively. The second coating includes a negative electrode active material. The first current collector includes an integrally formed main body and an empty foil portion. The surface of the empty foil portion is not provided with a first coating and a second coating. The empty foil portion is used for electrical connection with an external circuit. The empty foil portion is located on one side of the main body portion along a second direction. The first coating is provided on the main body portion. The second direction is perpendicular to the first direction. Along the second direction, the first coating includes a second edge and a first edge disposed opposite to each other, and the second coating includes a fourth edge and a third edge disposed opposite to each other, wherein the first edge and the third edge are located on the same side of the secondary battery in the second direction; Along the second direction, the first edge extends beyond the third edge by a width of L, where L ≥ 0.

2. The secondary battery according to claim 1, characterized in that, L≥0.01mm.

3. The secondary battery according to claim 2, characterized in that, 0.1mm≤L≤3mm.

4. The secondary battery according to claim 3, characterized in that, 0.5mm≤L≤2mm.

5. The secondary battery according to any one of claims 1-4, characterized in that, The secondary battery includes a plurality of the negative electrode plates; The secondary battery also includes an adapter, which is connected to a plurality of empty foil portions via a connecting area; along a third direction, the width of the connecting area is M, 1mm≤M≤9mm, and the third direction is perpendicular to the first direction and the second direction respectively.

6. The secondary battery according to any one of claims 1-5, characterized in that, Along the first direction, the thickness of the first coating is T1, 0.1μm≤T1≤5μm; And / or, Along the first direction, the thickness of the second coating is T2, 10μm≤T2≤300μm.

7. The secondary battery according to any one of claims 1-6, characterized in that, Along the first direction, the second coating has a first surface and a second surface disposed opposite to each other, and any point on the first surface is equidistant from the second surface.

8. The secondary battery according to any one of claims 1-7, characterized in that, The secondary battery also includes a separator and a positive electrode, wherein the negative electrode, separator and positive electrode are stacked in sequence. The positive electrode includes a second current collector, a positive active material, and a second tab. The second tab is integrally formed with the second current collector and has an insulating layer. Along the second direction, the insulating layer includes a sixth edge and a fifth edge disposed opposite to each other, wherein the first edge, the third edge, and the fifth edge are located on the same side of the secondary battery in the second direction; Along the second direction, the third edge extends beyond the sixth edge.

9. The secondary battery according to any one of claims 1-8, characterized in that, The first coating comprises a conductive agent and a first adhesive; the conductive agent comprises one or more of carbon nanotubes, graphene, graphene oxide, and conductive carbon black; the first adhesive comprises one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyimide, polyaniline, and polyacrylonitrile.

10. The secondary battery according to any one of claims 1-9, characterized in that, Based on the quality of the second coating, the mass percentage of the negative electrode active material is m, where 92% ≤ m ≤ 99.5%.

11. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1-10.

12. A method for preparing a secondary battery, used to prepare a secondary battery as described in any one of claims 1-11, characterized in that, Includes the following steps: A current collector substrate is taken, the current collector substrate includes a third surface and a fourth surface disposed opposite to each other along its thickness direction, and the current collector substrate includes an eighth edge and a seventh edge disposed opposite to each other along its width direction; A first adhesive tape is applied to the third surface, with one edge of the first adhesive tape flush with the seventh edge. The portion of the current collector substrate not covered by the first adhesive tape is the coating area. The first coating is applied to the coating area; Remove the first adhesive tape and apply a second adhesive tape to the third surface. Along the width direction of the current collector substrate, the width of the second adhesive tape is greater than the width of the first adhesive tape, and one edge of the second adhesive tape is flush with the seventh edge. The second coating is applied to the first coating and the second adhesive tape; Remove the second adhesive tape. The area of ​​the current collector substrate exposed between the first coating and the second coating is the empty foil area. Cut the current collector substrate to obtain the first current collector, and cut the empty foil area to form the empty foil portion.

13. The method for preparing a secondary battery according to claim 12, characterized in that, Along the width direction of the current collector substrate, the width of the second adhesive tape is between 8 mm and 40 mm.

14. The method for preparing a secondary battery according to claim 12, characterized in that, The peel strength between the first adhesive tape and the current collector substrate is between 1 mN / mm and 7 mN / mm.

15. The method for preparing a secondary battery according to any one of claims 12-14, characterized in that, The peel strength between the first coating and the current collector substrate is greater than the peel strength between the first coating and the second adhesive paper.

16. The method for preparing a secondary battery according to any one of claims 12-15, characterized in that, The peel strength between the second adhesive tape and the current collector substrate is between 1 mN / mm and 7 mN / mm; The peel strength between the second adhesive tape and the first coating is between 1 mN / mm and 7 mN / mm.

17. A method for preparing a secondary battery, used to prepare a secondary battery as described in any one of claims 1-11, characterized in that, Includes the following steps: A current collector substrate is taken, the current collector substrate includes a third surface and a fourth surface disposed opposite to each other along its thickness direction, and the current collector substrate includes an eighth edge and a seventh edge disposed opposite to each other along its width direction; A first coating is applied to the third surface; A second adhesive tape is applied to the first coating, with one edge of the second adhesive tape flush with the seventh edge; The second coating is applied to the first coating and the second adhesive tape; Remove the second adhesive tape and cut the current collector substrate to obtain the first current collector.

18. The method for preparing a secondary battery according to claim 17, characterized in that, The third surface of the first current collector has an empty foil area without the first and second coatings. One edge of the empty foil area is flush with the seventh edge. The empty foil area is cut to form the empty foil portion.

19. The method for preparing a secondary battery according to claim 17, characterized in that, The first coating completely covers the third surface, the first current collector is cut, and a portion of the first coating is removed by laser cleaning to form the empty foil portion.

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