Electrode assembly, battery monomer, extrusion structure and extrusion jig

Abstract

The utility model provides an electrode assembly, a battery cell, an extrusion structure and an extrusion jig, and aims to solve the technical problem that lithium precipitation is easy to occur in the middle part of the electrode assembly. The electrode assembly comprises an isolating membrane and a pole piece which are stacked, the electrode assembly is provided with a middle part and an edge part, and the orthographic projection of the edge part surrounds the orthographic projection of the middle part in the thickness direction of the electrode assembly; the stripping force of the isolating membrane on the middle part and the pole piece is F1; the stripping force of the isolating membrane on the edge part and the pole piece is F2; wherein F1 is less than F2.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to an electrode assembly, a battery cell, an extrusion structure, and an extrusion fixture. Background Technology

[0002] Lithium-ion batteries can be classified into prismatic batteries, cylindrical batteries, and pouch batteries based on their shape. Prismatic batteries, with their flexible size and unique structural features, are widely used in both power and energy storage fields.

[0003] During the manufacturing process of prismatic batteries, the electrode assembly (also known as the core pack) is typically hot-pressed to facilitate its insertion into a prismatic casing (such as a prismatic aluminum casing). The conventional operation during this hot-pressing process is to hot-press the entire electrode assembly to ensure uniform stress across the entire area. Analysis of the prismatic casing reveals that the area near the eight edges (referred to as the edge region) exhibits stronger resistance to deformation, while the larger surface areas are less resistant. During cycling, the SEI film on the negative electrode of the prismatic battery continuously reconstructs and thickens, causing outward expansion within the electrode assembly, particularly noticeable in the center area corresponding to the larger surface area of ​​the prismatic casing. Therefore, the center of the electrode assembly experiences greater compression than the edges corresponding to the edges of the prismatic casing, making it more susceptible to lithium plating failure during cycling and leading to accelerated battery degradation. Utility Model Content

[0004] The embodiments of this application provide an electrode assembly, a battery cell, an extrusion structure, and an extrusion fixture, which can improve the technical problem that lithium plating easily occurs in the middle part of the electrode assembly.

[0005] In a first aspect, embodiments of this application provide an electrode assembly including a stacked separator and an electrode sheet. The electrode assembly has a middle portion and an edge portion. Along the thickness direction of the electrode assembly, the orthographic projection of the edge portion surrounds the orthographic projection of the middle portion. The peel force between the separator and the electrode sheet on the middle portion is F1; the peel force between the separator and the electrode sheet on the edge portion is F2; ​​wherein, F1 < F2.

[0006] In one embodiment, the ratio of F1 to F2 is 0.3 to 0.9.

[0007] In one embodiment, F1 is 0.1N to 0.2N, and / or F2 is 0.2N to 0.3N.

[0008] In one embodiment, along the thickness direction of the electrode assembly, the percentage of the orthographic projection area of ​​the middle portion to the orthographic projection area of ​​the electrode assembly is 20% to 80%.

[0009] In one embodiment, the aspect ratio of the electrode assembly is 0.8 to 1.2; and / or, the length of the electrode assembly is 150 mm to 180 mm, the width of the electrode assembly is 150 mm to 180 mm; and / or, the thickness of the electrode assembly is 10 mm to 25 mm.

[0010] In one embodiment, the separator includes an adhesive-coated separator, which includes a base film and an adhesive layer, the adhesive layer being located on at least one side surface of the base film.

[0011] In one embodiment, the thickness of the base film is 5 mm to 10 mm, and the thickness of the adhesive layer is 1 mm to 5 mm; and / or, the ratio of the thickness of the base film to the thickness of the adhesive layer is 1 to 10.

[0012] In one embodiment, the separator and the electrode are stacked layer by layer; or, the separator and the electrode are stacked and wound together.

[0013] In one embodiment, the difference between the thickness of the middle portion and the thickness of the edge portion is greater than or equal to 50 μm.

[0014] Secondly, embodiments of this application provide a single battery cell, comprising:

[0015] A housing having a receiving cavity, the surface of the housing being divided into an edge region and a large surface region, and along the thickness direction of the housing, the orthographic projection of the edge region surrounds the orthographic projection of the large surface region;

[0016] An electrode assembly is disposed within the receiving cavity, with the middle portion corresponding to the large surface and the edge portion corresponding to the edge. The electrode assembly is the aforementioned electrode assembly.

[0017] Thirdly, embodiments of this application provide an extrusion structure for fabricating the electrode assembly provided in the first aspect. The extrusion structure includes a central extrusion portion and an edge extrusion portion disposed around the edge of the central extrusion portion. A first extrusion surface for extruding the edge portion is formed on the edge extrusion portion, and a second extrusion surface for extruding the central portion is formed on the central extrusion portion. The second extrusion surface is configured to form a discontinuity with the first extrusion surface and be farther away from the central axis of the electrode assembly than the first extrusion surface when the extrusion structure extrudes the electrode assembly.

[0018] In one embodiment, the edge extrusion portion is fixedly connected to the middle extrusion portion and together defines a groove, the second extrusion surface is formed as the inner bottom surface of the groove, and the first extrusion surface is located outside the groove and surrounds the opening of the groove.

[0019] In one embodiment, the depth of the groove is 0.005 mm to 0.1 mm.

[0020] In one embodiment, the edge extrusion portion is a rigid portion, the middle extrusion portion is a flexible portion, the rigid portion is connected to the flexible portion, and the flexible portion is used to deform in a direction away from the electrode assembly when the extrusion structure extrudes the electrode assembly.

[0021] In one embodiment, along the thickness direction of the extrusion structure, the intermediate extrusion portion is movably disposed relative to the edge extrusion portion, and the intermediate extrusion portion is used to move toward or away from the electrode assembly when the extrusion structure extrudes the electrode assembly.

[0022] In one embodiment, the edge pressing portion includes a first frame having a first through hole, and the middle pressing portion includes a slider located within the first through hole and slidably connected to the first frame.

[0023] In one embodiment, a groove is formed by a partial recess in the inner wall of the first through hole toward the interior of the first frame. The slider includes a body portion and a boss protruding from the circumferential surface of the body portion. The body portion is located inside the first through hole and is adapted to the first through hole. One end face of the body portion is formed as the second extrusion surface. The boss extends into the groove and slides in cooperation with the groove. In the thickness direction of the first frame, the thickness of the boss is less than the width of the groove, and the distance between the side surface of the boss away from the second extrusion surface and the second extrusion surface is greater than the width of the groove.

[0024] In one embodiment, the ratio of the area of ​​the second extrusion surface to the sum of the areas of the first extrusion surface and the second extrusion surface is 0.1 to 0.4.

[0025] Fourthly, embodiments of this application provide an extrusion structure for fabricating the electrode assembly provided in the first aspect. The extrusion structure includes an edge extrusion portion, which is a second frame having a second through hole. The second frame is configured to extrude the edge portion when the extrusion structure extrudes the electrode assembly, and the second through hole corresponds to the middle portion.

[0026] Fifthly, embodiments of this application provide an extrusion fixture, including the extrusion structure described above.

[0027] The beneficial effects of the embodiments of this application are as follows:

[0028] In the embodiments of this application, during the fabrication of the electrode assembly, the force exerted on the middle portion of the electrode assembly is greater than that on the edge portion. This not only reduces the peeling force between the separator and the electrode sheet in the middle portion and the peeling force between the separator and the electrode sheet in the edge portion, but also increases the porosity of the middle portion of the electrode assembly. As a result, when the electrode assembly is applied to a battery cell, the rate at which the middle portion of the electrode assembly is immersed in the electrolyte increases, thereby reducing the risk of lithium plating in the middle portion. In addition, during the cycling process, the middle portion undergoes greater SEI film reconstruction and proliferation than the edge portion. The compression process makes the porosity of the middle portion greater than that of the edge portion, which can alleviate the volume expansion of the middle portion to a certain extent and reduce the risk of lithium plating in the middle portion. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a top view of the electrode assembly provided in an embodiment of this application;

[0031] Figure 2 This is a schematic diagram of the front view structure of the electrode assembly provided in an embodiment of this application;

[0032] Figure 3 yes Figure 2 Enlarged view of section A in the middle;

[0033] Figure 4 This is a cross-sectional view of the separator in the electrode assembly provided in an embodiment of this application;

[0034] Figure 5 This is a cross-sectional view of the positive electrode sheet in the electrode assembly provided in the embodiments of this application;

[0035] Figure 6 This is a flowchart of a method for fabricating an electrode assembly provided in an embodiment of this application;

[0036] Figure 7 This describes the relationship between the pressure on the middle and edge portions of the electrode assembly over time during the extrusion process in the electrode assembly fabrication method provided in the embodiments of this application. Figure 1 ;

[0037] Figure 8This describes the relationship between the pressure on the middle and edge portions of the electrode assembly over time during the extrusion process in the electrode assembly fabrication method provided in the embodiments of this application. Figure 3 ;

[0038] Figure 9 This is a cross-sectional structural diagram of a battery cell provided in an embodiment of this application;

[0039] Figure 10 This is an exploded view of a single battery cell provided in an embodiment of this application;

[0040] Figure 11 This is a cross-sectional structural schematic diagram of the first extrusion fixture provided in the embodiments of this application;

[0041] Figure 12 This is a cross-sectional view of the second type of extrusion fixture provided in the embodiments of this application;

[0042] Figure 13 This is a cross-sectional view of the first extrusion structure provided in the embodiments of this application;

[0043] Figure 14 This is a cross-sectional view of the second extrusion structure provided in the embodiments of this application;

[0044] Figure 15 This is a schematic cross-sectional view of the third extrusion structure provided in the embodiments of this application. Figure 1 ;

[0045] Figure 16 This is a schematic cross-sectional view of the third extrusion structure provided in the embodiments of this application. Figure 2 ;

[0046] Figure 17 This is a three-dimensional structural diagram of the fourth extrusion structure provided in the embodiments of this application.

[0047] Figure label:

[0048] 1. Electrode assembly; 101. Middle part; 102. Edge part;

[0049] 11a, Separating membrane; 111a, Base membrane; 112a, Coating layer;

[0050] 12a, electrode; 121a, positive electrode; 1211, positive current collector; 1212, positive electrode film; 122a, negative electrode;

[0051] 10a. Battery cell;

[0052] 2. Shell; 2a. Large surface area; 2b. Edge area; 21. Receiving cavity;

[0053] 3. Cover;

[0054] 10. Extrusion structure;

[0055] 11. Intermediate extrusion section; 110. Second extrusion surface; 111. Flexible section; 112. Plate; 113. Slider; 1131. Boss; 1132. Main body;

[0056] 12. Edge extrusion section; 120. First extrusion surface; 121. Rigid section; 122. First frame; 1221. First through hole; 1222. Slide groove; 124. Second frame; 125. Second through hole;

[0057] 13. Groove; 131. Slot opening;

[0058] 100. Extrusion fixture;

[0059] 20. Substrate. Detailed Implementation

[0060] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0061] Furthermore, it should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operation, specifically the directions shown in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0062] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0063] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0064] The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0065] In the description of the embodiments of this application, the words "example" or "for example" are used to indicate exemplification, illustration, or description. Any embodiment or design described as "example" or "for example" in the embodiments of this application is not to be construed as being more preferred or having more advantages than another embodiment or design. The use of the words "example" or "for example" is intended to present relative concepts in a clear manner.

[0066] To facilitate understanding of the present application, the spline curves and arrows used in the reference numerals in the accompanying drawings are explained below: spline curves without arrows indicate solid parts, that is, parts with solid structures; spline curves with arrows indicate virtual parts, that is, parts without solid structures.

[0067] Firstly, please see Figures 1 to 10 This application provides an electrode assembly 1. Here, the electrode assembly 1 is also called a core pack, and the electrode assembly 1 is the core component constituting the battery cell 10a (also called a battery cell).

[0068] Specifically, the electrode assembly 1 includes a stacked separator 11a and an electrode 12a, i.e., the separator 11a and the electrode 12a are stacked together. More specifically, the electrode 12a includes a positive electrode 121a and a negative electrode 122a, which are stacked with the separator 11a. The separator 11a is located between the positive electrode 121a and the negative electrode 122a to separate them and prevent direct contact between the positive electrode 121a and the negative electrode 122a, thus preventing a short circuit. The number of separators 11a, positive electrodes 121a, and negative electrodes 122a in the electrode assembly 1 can be one or more.

[0069] Electrode assembly 1 can be a stacked structure or a wound structure.

[0070] When the electrode assembly 1 has a stacked structure, the separator 11a and the electrode 12a are stacked layer by layer in the electrode assembly 1. As an example, the electrode assembly 1 has one separator 11a and multiple electrode 12a. The separator 11a is continuously bent in a "Z" shape to be stacked with the electrode 12a layer by layer. As an example, the separator 11a in the electrode assembly 1 is a separate film. There are multiple separators 11a and multiple electrode 12a. The electrode assembly 1 is obtained by stacking one layer of separator 11a, one layer of electrode 12a (specifically, positive electrode 121a), one layer of separator 11a, and one layer of electrode 12a (specifically, negative electrode 122a).

[0071] When the electrode assembly 1 is a wound structure, the separator 11a and the electrode 12a are stacked and wound together. When manufacturing the wound structure electrode assembly 1, the separator 11a and the electrode 12a are first stacked sequentially and then wound together.

[0072] Electrode assembly 1 has a central portion 101 and an edge portion 102, wherein the central portion 101 refers to the portion constituting the central region of electrode assembly 1, and the edge portion 102 refers to the portion constituting the edge region of electrode assembly 1. To more clearly illustrate the central portion 101 and the edge portion 102, the projection relationship between the central portion 101 and the edge portion 102 will be explained. When projected along the thickness direction of electrode assembly 1, the orthographic projection of the edge portion 102 surrounds the orthographic projection of the central portion 101. It can be understood that, in the thickness direction of electrode assembly 1, the orthographic projection of the edge portion 102 is annular. Optionally, the central portion 101 and the edge portion 102 are disposed adjacent to each other, then, in the thickness direction of electrode assembly 1, the orthographic projection of the edge portion 102 and the orthographic projection of the central portion 101 are also adjacent. In the thickness direction of electrode assembly 1, the separator 11a and the electrode sheet 12a still satisfy the stacked arrangement relationship.

[0073] For example, see Figure 1 , Figure 1 This is a top view of the electrode assembly 1 along its thickness direction. The solid lines in the figure represent the boundary lines of the electrode assembly 1, and the dashed lines represent the boundary lines between the middle portion 101 and the edge portion 102. The area within the dashed lines is the middle portion 101, and the area between the dashed and solid lines is the edge portion 102. The middle portion 101 is square, and the edge portion 102 is rectangular. Of course, in other embodiments, the middle portion 101 can also be rectangular, rhomboid, circular, triangular, or other shapes. Optionally, in... Figure 1 In this process, the shape of the middle part 101 is a scaled-down version of the boundary line of the electrode assembly 1, and the geometric center of the middle part 101 coincides with the geometric center of the electrode assembly 1.

[0074] For example, see Figure 2 , Figure 2 The dashed line indicates the boundary between the middle part 101 and the edge part 102.

[0075] Understandably, please see Figure 10 When the electrode assembly 1 is installed into the square housing 2, the edge portion 102 is closer to the edge region 2b on the housing 2 than the middle portion 101.

[0076] Typically, to facilitate the insertion of the electrode assembly 1 into the housing 2, the electrode assembly 1 is shaped by extrusion during its fabrication process. During extrusion, the stacked separator 11a and electrode 12a deform and bond together. Generally, the tighter the bond between the separator 11a and the electrode 12a, the greater the bonding force, and the greater the peeling force required to separate them, and vice versa. To achieve a tighter bond between the separator 11a and the electrode 12a, the greater the deformation of both. This results in greater pressure on the separator 11a and the electrode 12a during extrusion, leading to a decrease in porosity within the electrode assembly 1, shortening the lithium ion diffusion distance, and reducing the internal resistance of the electrode assembly 1.

[0077] Since the separator 11a and the electrode 12a are stacked in the electrode assembly 1, the middle portion 101 contains the separator 11a and the electrode 12a, and the edge portion 102 also contains the separator 11a and the electrode 12a. The peel force between the separator 11a and the electrode 12a in the middle portion 101 is F1; the peel force between the separator 11a and the electrode 12a in the edge portion 102 is F2; ​​where F1 < F2. Here, the peel force can refer to the peel force between the separator 11a and the positive electrode 121a, or it can refer to the peel force between the separator 11a and the negative electrode 122a.

[0078] In other words, the bonding force between the separator 11a on the edge portion 102 and the electrode 12a is greater than that between the separator 11a on the middle portion 101 and the electrode 12a. The bonding between the separator 11a on the edge portion 102 and the electrode 12a is tighter than that between the separator 11a on the middle portion 101. Therefore, the porosity of the middle portion 101 is greater than that of the edge portion 102. Typically, when the electrode assembly 1 is applied to the battery cell 10a, the electrode assembly 1 is immersed in the electrolyte. The edge portion 102 is more easily wetted by the electrolyte than the middle portion 101. Increasing the porosity of the middle portion 101 can improve the rate at which the middle portion 101 is wetted by the electrolyte.

[0079] In this embodiment, during the fabrication of the electrode assembly 1, the force exerted on the middle portion 101 of the electrode assembly 1 is greater than that on the edge portion 102. This results in a smaller peel force between the separator 11a on the middle portion 101 and the electrode 12a on the edge portion 102. Consequently, the porosity of the middle portion 101 is greater than that of the edge portion 102. When the electrode assembly 1 is applied to the battery cell 10a, the rate at which the middle portion 101 is immersed in the electrolyte increases, thereby reducing the risk of lithium plating in the middle portion 101. Furthermore, during cycling, the middle portion 101 undergoes greater SEI film reconstruction and proliferation than the edge portion 102. The compression process further increases the porosity of the middle portion 101 compared to the edge portion 102, which to some extent alleviates the volume expansion of the middle portion 101 and reduces the risk of lithium plating in the middle portion 101.

[0080] Furthermore, when the electrode assembly 1 is applied to the battery cell 10a, the electrode assembly 1 is installed inside the housing 2. The edge portion 102 of the electrode assembly 1 corresponds to the edge region 2b on the housing 2, while the middle portion 101 of the electrode assembly 1 corresponds to the large surface region 2a of the housing 2. During the cycling process of the electrode assembly 1, the middle portion 101 expands more than the edge portion 102, and it fits more tightly with the housing 2. The edge portion 102 expands less during the cycling process, and the edge region 2b of the housing 2 itself has stronger resistance to deformation, so the edge portion 102 can also fit tightly with the housing 2. Therefore, the degree of constraint of the electrode assembly 1 by the housing 2 is almost uniform, which reduces the risk of lithium plating failure of the electrode assembly 1 during cycling.

[0081] In some embodiments, the ratio of F1 to F2 is 0.3 to 0.9. It can be understood that the closer F1 and F2 are, the larger the ratio of F1 to F2, and the smaller the porosity difference between the middle portion 101 and the edge portion 102. This makes it difficult to reduce the risk of lithium plating in the middle portion 101. Conversely, the smaller F1 or the larger F2, the smaller the ratio of F1 to F2, and the larger the porosity difference between the middle portion 101 and the edge portion 102, which helps reduce the risk of lithium plating in the middle portion 101. However, if F1 is too small, the middle portion 101 will be too loose, making it difficult to achieve the desired shaping effect, affecting the insertion of the electrode assembly 1 into the housing 2, and also affecting the internal resistance of the electrode assembly 1. Especially in the middle and later stages of cycling, the gap between the electrode 12a and the separator 11a increases, making it difficult for lithium ions to pass through, thus increasing the risk of lithium plating. If F2 is too large, the porosity of the edge portion 102 will be too small, affecting the wetting effect of the electrolyte in the edge portion 102, thereby increasing the risk of lithium plating in the edge portion 102. By controlling the ratio of F1 to F2 to 0.3 to 0.9, the porosity difference between the middle part 101 and the edge part 102 is controlled, thereby making the overall wetting effect of the electrode assembly 1 in the electrolyte more consistent and reducing the risk of lithium plating in local areas.

[0082] In some embodiments, F1 is 0.1N to 0.2N. Generally, a larger F1 results in lower porosity in the intermediate portion 101, increasing the risk of lithium plating. However, an excessively small F1 can negatively impact the shaping effect and internal resistance of the electrode assembly 1. By controlling the peel force between the separator 11a and the electrode 12a on the intermediate portion 101 to 0.1N to 0.2N, the electrode assembly 1 can achieve both better shaping effect and lower internal resistance while reducing the risk of localized lithium plating. As examples, F1 can be 0.1N, 0.11N, 0.12N, 0.13N, 0.14N, 0.15N, 0.16N, 0.17N, 0.18N, 0.19N, or 0.2N.

[0083] In some embodiments, F2 is 0.2N to 0.3N. Generally, a larger F2 results in lower porosity of the edge portion 102, increasing the risk of lithium plating. However, an excessively small F2 can negatively impact the shaping effect and internal resistance of the electrode assembly 1. By controlling the peel force between the separator 11a and the electrode 12a on the edge portion 102 to 0.2N to 0.3N, the electrode assembly 1 can achieve both better shaping effect and lower internal resistance while reducing the risk of localized lithium plating. As examples, F2 can be 0.2N, 0.21N, 0.22N, 0.23N, 0.24N, 0.25N, 0.26N, 0.27N, 0.28N, 0.29N, or 0.3N.

[0084] In some embodiments, the percentage of the projected area of ​​the middle portion 101 along the thickness direction of the electrode assembly 1 to the total projected area of ​​the electrode assembly 1 is 20% to 80%. A larger middle portion 101 results in a larger proportion of its projected area along the thickness direction of the electrode assembly 1. A larger middle portion 101 improves the overall electrolyte wetting effect of the electrode assembly 1, but it also tends to increase internal resistance. Typically, controlling the percentage of the projected area of ​​the middle portion 101 to the total projected area of ​​the electrode assembly 1 to 20% to 80% allows the electrode assembly 1 to achieve both good electrolyte wetting and shaping effects, while maintaining low internal resistance. Using the thickness direction of the electrode assembly 1 as the first direction, the projected area of ​​the middle portion 101 is adjacent to the projected area of ​​the edge portion 102, and the ratio of the area of ​​the projected area of ​​the middle portion 101 to the area of ​​the projected area of ​​the electrode assembly 1 is 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0085] In some embodiments, the difference between the thickness of the middle portion 101 and the thickness of the edge portion 102 is greater than or equal to 50 μm. Typically, the thickness of the electrode assembly 1 decreases to some extent during the compression process. Because the compressive force on the middle portion 101 differs from that on the edge portion 102, their thicknesses will differ. Since the edge portion 102 experiences a greater compressive force, it is easier to compress, resulting in a smaller thickness and lower porosity. Conversely, the middle portion 101 experiences a relatively smaller compressive force, resulting in a larger thickness and higher porosity, thus making it less prone to lithium deposition.

[0086] In some implementations, please refer to Figure 1 With the X direction as the width direction of electrode assembly 1, the width W of electrode assembly 1 in the X direction is 150mm to 180mm. As an example, L is 150mm, 155mm, 160mm, 165mm, 170mm, 175mm or 180mm.

[0087] In some implementations, please refer to Figure 1 With the Y direction as the length direction of electrode assembly 1, the length L of electrode assembly 1 in the Y direction is 150mm to 180mm. As an example, W is 150mm, 155mm, 160mm, 165mm, 170mm, 175mm, or 180mm. The length L of electrode assembly 1 here does not include the tab area size.

[0088] In some implementations, please refer to Figure 2The thickness direction of electrode assembly 1 is defined by the Z direction, and the thickness D of electrode assembly 1 is 10mm to 25mm. For example, D is 10mm, 13mm, 15mm, 18mm, 20mm, 23mm or 25mm.

[0089] In some embodiments, the aspect ratio of electrode assembly 1 is 0.8 to 1.2. As an example, the aspect ratio of electrode assembly 1 is 0.8, 0.9, 1.0, 1.1, or 1.2. When the length L of electrode assembly 1 is equal to its width W, electrode assembly 1 is square.

[0090] In some implementations, please refer to Figure 4 The separator 11a includes an adhesive-coated separator. By configuring the separator 11a to include an adhesive-coated separator, it is convenient to adjust the peel force between the middle portion 101 and the edge portion 102 of the electrode assembly 1 by extrusion during the fabrication of the electrode assembly 1. Specifically, the adhesive-coated separator includes a base film 111a and an adhesive layer 112a, with the adhesive layer 112a located on at least one side surface of the base film 111a. The base film 111a has two opposite sides in the thickness direction of the base film 111a; the adhesive layer 112a may be provided on one side surface of the base film 111a, or it may be provided on both sides of the base film 111a. As an example, the base film 111a is made of polypropylene (PP) or polyethylene (PE). As an example, the adhesive layer 112a contains polyvinylidene fluoride (PVDF).

[0091] In some embodiments, the thickness of the base film 111a is 5 mm to 10 mm, and the thickness of the adhesive layer 112a is 1 mm to 5 mm. As an example, the thickness of the base film 111a is 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm, and the thickness of the adhesive layer 112a is 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0092] In some embodiments, the thickness ratio between the base film 111a and the adhesive layer 112a is 1 to 10. As an example, the thickness ratio between the base film 111a and the adhesive layer 112a is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0093] In some implementations, please refer to Figure 5 The positive electrode 121a includes a positive current collector 1211 and a positive electrode film 1212, with the positive electrode film 1212 disposed on the positive current collector 1211. The positive electrode film 1212 includes a positive electrode active material, which includes at least one of lithium iron phosphate and lithium manganese iron phosphate. Furthermore, the positive electrode film 1212 may also include a conductive agent, a binder, and a dispersant.

[0094] Secondly, please see Figure 6This application provides a method for preparing an electrode assembly 1, comprising:

[0095] S1. The separator 11a and the electrode 12a are stacked together to obtain the electrode assembly 1. The electrode assembly 1 has a middle part 101 and an edge part 102. Along the thickness direction of the electrode assembly 1, the orthographic projection of the edge part 102 surrounds the orthographic projection of the middle part 101.

[0096] S2. Along the thickness direction of electrode assembly 1, the middle part 101 is subjected to a first extrusion treatment by a first pressure P1, and the edge part 102 is subjected to a second extrusion treatment by a second pressure P2; wherein, the first pressure P1 is less than or equal to the second pressure P2.

[0097] It should be noted that the first extrusion process is performed on the middle portion 101, and the second extrusion process is performed on the edge portion 102. The first extrusion process and the second extrusion process can be performed simultaneously or in stages. If the first extrusion process and the second extrusion process are performed in stages, the middle portion 101 can be subjected to the first extrusion process first, and then the edge portion 102 can be subjected to the second extrusion process; or the edge portion 102 can be subjected to the second extrusion process first, and then the middle portion 101 can be subjected to the first extrusion process.

[0098] During the first compression process on the middle portion 101, the first pressure P1 can be a constant force or a variable force. Similarly, during the second compression process on the edge portion 102, the second pressure P2 can be a constant force or a variable force. The first pressure P1 being less than or equal to the second pressure P2 can mean that the first pressure P1 is always less than the second pressure P2 during the first compression process, or that the first pressure P1 is less than the second pressure P2 within a certain segment during the first compression process.

[0099] The electrode assembly 1 preparation method provided in this application involves extruding the middle portion 101 and the edge portion 102 of the electrode assembly 1 to different degrees along the thickness direction (i.e., unevenly extruding the electrode assembly 1). Compared to the edge portion 102, a smaller extrusion force is applied to the middle portion 101, making the middle portion 101 more porous than the edge portion 102, i.e., the middle portion 101 has a higher porosity. Thus, when the electrode assembly 1 is applied to the battery cell 10a, the rate at which the middle portion 101 is immersed in the electrolyte increases, thereby reducing the risk of lithium plating in the middle portion 101. In addition, since the middle portion 101 undergoes greater SEI film reconstruction and proliferation than the edge portion 102 during cycling, the extrusion makes the porosity of the middle portion 101 greater than that of the edge portion 102, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium plating in the middle portion 101.

[0100] Furthermore, when the electrode assembly 1 is applied to the battery cell 10a, the electrode assembly 1 is installed inside the housing 2. The edge portion 102 of the electrode assembly 1 corresponds to the edge area on the housing 2, while the middle portion 101 of the electrode assembly 1 corresponds to the large surface area of ​​the housing 2. During the cycling process of the electrode assembly 1, the middle portion 101 expands more than the edge portion 102, and it fits more tightly with the housing 2. The edge portion 102 expands less during the cycling process, and the edge area of ​​the housing 2 itself has stronger resistance to deformation, so the edge portion 102 can also fit tightly with the housing 2. Therefore, the degree of constraint of the electrode assembly 1 by the housing 2 is almost uniform, which reduces the risk of lithium plating failure of the electrode assembly 1 during cycling.

[0101] In summary, the embodiments of this application use uneven extrusion to make the porosity of the middle part 101 greater than that of the edge part 102. In this way, during the cycling process of the electrode assembly 1, the outward expansion of the volume of the middle part 101 can be alleviated, thereby reducing the extrusion of the shell 2 on the middle part 101. This allows the middle part 101 to have a certain rate of electrolyte wetting, reducing the risk of lithium plating failure of the electrode assembly 1 during cycling and improving the cycle performance of the battery cell 10a.

[0102] In some embodiments, the extrusion time of the first extrusion treatment is a first time t1, and the extrusion time of the second extrusion treatment is a second time t2, wherein the first time t1 is less than or equal to the second time t2, and the product of the first pressure P1 and the first time t1, S1, is less than the product of the second pressure P2 and the second time t2, S2.

[0103] Understandably, the first pressure P1 is less than the second pressure P2, and the first time t1 is less than or equal to the second time t2. In order to make the product of the first pressure P1 and the first time t1 less than the product of the second pressure P2 and the second time t2, there are several possibilities for the relationship between the first pressure P1 and the first time t1 during the first extrusion process and the second pressure P2 and the second time t2 during the second extrusion process: the first pressure P1 is less than the second pressure P2, and the first time t1 is equal to the second time t2; or the first pressure P1 is less than the second pressure P2, and the first time t1 is less than the second time t2.

[0104] For example, see Figure 7 and Figure 8 In the coordinate system shown in the figure, the horizontal axis represents time t, the vertical axis represents pressure P, and the area S of the shaded region represents the product of pressure P and time t. Please refer to [link / reference]. Figure 7Both the first pressure P1 and the second pressure P2 are constant forces. The first pressure P1 is less than the second pressure P2. The first time t1 is equal to the second time t2. The area S1 is less than the area S2 (in the diagram, the shaded area covered by "+" represents S1, and the shaded area covered by the diagonal line represents S2, and so on). Please refer to [link / reference]. Figure 8 The first pressure P1 and the second pressure P2 are both constant forces. The first pressure P1 is less than the second pressure P2. The first time t1 is less than the second time t2. The area S1 is less than the area S2.

[0105] In some embodiments, the first time t1 is less than the second time t2; specifically, the ratio of the first time t1 to the second time t2 is 0.2 to 0.8. Within this range, the intermediate portion 101 can have a better electrolyte wetting effect during the cycling of the electrode assembly 1. As an example, the ratio of the first time t1 to the second time t2 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8.

[0106] In some embodiments, the first pressure P1 is less than the second pressure P2; specifically, the ratio of the first pressure P1 to the second pressure P2 is 0.2 to 0.8. Within this range, the intermediate portion 101 can have a better electrolyte wetting effect during the cycling of the electrode assembly 1. As an example, the ratio of the first pressure P1 to the second pressure P2 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8.

[0107] In some embodiments, the ratio of the first time t1 to the second time t2 is 0.2 to 0.8, and the ratio of the first pressure P1 to the second pressure P2 is 0.2 to 0.8. Within this range, the intermediate portion 101 can have a better electrolyte wetting effect during the cycling of the electrode assembly 1.

[0108] In some embodiments, the first pressure P1 is 1000N to 5000N. Within this range, the intermediate portion 101 can have a better electrolyte wetting effect during the cycling of the electrode assembly 1. As an example, the first pressure P1 is 1000N, 2000N, 3000N, 4000N, or 5000N.

[0109] In some embodiments, the first time t1 is 30s to 140s. Within this range, the middle portion 101 can have a better electrolyte wetting effect during the cycling of the electrode assembly 1. As an example, the first time t1 is 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, 130s, or 140s.

[0110] In some embodiments, the second pressure P2 is 3000N to 5000N. Within this range, the edge portion 102 maintains good contact with the housing 2 during the cycling of the electrode assembly 1. As examples, the second pressure P2 is 3000N, 3400N, 3500N, 3600N, 3800N, 4000N, 4200N, 4400N, 4500N, or 5000N. Optionally, the second pressure P2 is 3400N to 4500N.

[0111] In some embodiments, the second time t2 is 120s to 180s. Within this range, the edge portion 102 can maintain good contact with the housing 2 during the cycling of the electrode assembly 1. As an example, the second time t2 is 120s, 130s, 140s, 145s, 150s, 155s, 160s, 170s, or 180s. Optionally, the second time t2 is 140s to 160s.

[0112] In some embodiments, both the first extrusion process and the second extrusion process are hot-pressing processes, with the hot-pressing temperature being 80°C to 100°C. That is, the middle portion 101 is heated during the first extrusion process, and the edge portion 102 is heated during the second extrusion process. Specifically, the middle portion 101 is heated at a first temperature during the first extrusion process, and the edge portion 102 is heated at a second temperature during the second extrusion process. The first and second temperatures are also referred to as hot-pressing temperatures, where the first temperature is 80°C to 100°C, and the second temperature is 80°C to 100°C. It should be noted that the first and second temperatures may be equal or unequal. Typically, the hot-pressing temperature is related to the separator 11a. By setting the hot-pressing temperature to 80°C to 100°C, the separator 11a can be heated and deformed during the hot-pressing process to better bond with the electrode 12a, without causing the separator 11a to decompose. As an example, the hot-pressing temperature is 80°C, 85°C, 90°C, 95°C, or 100°C.

[0113] In some embodiments, an extrusion fixture 200 is used to extrude the electrode assembly 1. Specifically, the extrusion fixture 200 includes an extrusion structure 20 for extruding the electrode assembly 1. A description of the extrusion fixture 200 and the extrusion structure 20 is provided below.

[0114] In some embodiments, the method for preparing the electrode assembly 1 described above is used to prepare the electrode assembly 1 provided in the first aspect.

[0115] Thirdly, please see Figure 9 This application provides a battery cell 10a, comprising:

[0116] The shell 2 has a receiving cavity 21. The surface of the shell 2 is divided into a large surface region 2a and an edge region 2b. Along the thickness direction of the shell 2, the orthographic projection of the edge region 2b surrounds the orthographic projection of the large surface region 2a.

[0117] Electrode assembly 1 is disposed in receiving cavity 21, with middle part 101 corresponding to large surface area 2a and edge part 102 corresponding to edge area 2b. Electrode assembly 1 is the electrode assembly 1 described above or the electrode assembly 1 prepared by the preparation method described above.

[0118] The division of edges and surfaces of a typical 10a battery cell is mainly determined by its geometry and design. Please refer to [link / reference]. Figure 10 Taking a square battery cell 10a as an example, the casing 2 usually has multiple surfaces, including the side surface, top surface and bottom surface. The side surface of the battery can be further divided into the first side surface and the second side surface that are opposite each other along the Z-axis. The area of ​​these two side surfaces is larger than the area of ​​the other side surfaces. Therefore, these two side surfaces are the large surfaces of the casing 2, while the other two side surfaces, the third side surface and the fourth side surface, are considered to be small surfaces.

[0119] The surface of shell 2 is divided into a large surface region 2a and an edge region 2b, wherein the large surface region 2a is located on the large surface and close to the center of the large surface, such as... Figure 10 As shown by the dashed lines on the middle shell 2, the area inside the dashed lines is the large surface region 2a, and the area outside the dashed lines is the edge region 2b, which is close to the edge on the shell 2.

[0120] Please continue reading Figure 10 As shown by the dashed line on electrode assembly 1 in the figure, the area inside the dashed line is the middle part 101, and the area outside the dashed line is the edge part 102. The middle part 101 corresponds to the large surface area 2a, and the edge part 102 corresponds to the edge area 2b.

[0121] Specifically, the battery cell 10a is a square battery, and the casing 2 is rectangular, for example, square. As an example, the casing 2 is an aluminum casing.

[0122] The battery cell 10a provided in this application embodiment is less prone to lithium plating failure in the electrode assembly 1 during cycling, thus improving the cycling performance of the battery cell 10a.

[0123] In some embodiments, the battery cell 10a also includes a cover 3 disposed on the housing 2 to close the receiving cavity 21.

[0124] Fourthly, please refer to Figures 11 to 17 This application provides an extrusion structure 10 for extruding an electrode assembly 1.

[0125] Here, electrode assembly 1, also known as the core package, is the core component constituting the battery cell (also known as a single battery cell). Typically, electrode assembly 1 includes a positive electrode 11, a negative electrode 12a, and a separator 13. The separator 13 is located between the positive electrode 11 and the negative electrode 12a to separate them, preventing direct contact and short circuits. Electrode assembly 1 can be a stacked structure or a wound structure. The extrusion structure 10 is used to extrude electrode assembly 1, both to shape it for easy insertion into the housing to form a battery cell, and to ensure a tight fit between the separator 13 and the positive and negative electrode 11 and 12a, shortening the lithium-ion diffusion distance and reducing the internal resistance of electrode assembly 1. Optionally, the extrusion structure 10 is also used to heat the electrode assembly 1, that is, to hot press the electrode assembly 1. Hot pressing can eliminate wrinkles and air in the separator 13, so that the separator 13 is more tightly attached to the positive electrode 11 and the negative electrode 12a.

[0126] Typically, please see Figure 1 , Figure 2 and Figure 10 Using the dashed line in the figure as a virtual dividing line, the electrode assembly 1 includes an adjacent middle portion 101 and an edge portion 102, wherein the edge portion 102 is disposed around the edge of the middle portion 101. When the electrode assembly 1 is installed in a square housing, the middle portion 101 corresponds to the large surface area 2a of the housing 2, and the edge portion 102 corresponds to the edge area 2b of the housing 2. As an example, taking the thickness direction of the electrode assembly 1 as the first direction, the orthographic projection of the middle portion 101 is adjacent to the orthographic projection of the edge portion 102, and the ratio of the area of ​​the orthographic projection of the middle portion 101 to the area of ​​the orthographic projection of the electrode assembly 1 is 20% to 80%, for example, it can be 20%, 30%, 40%, 50%, 60%, 70%, or 80%. Along the first direction, in the electrode assembly 1, the positive electrode 11, the separator 13, and the negative electrode 12a are stacked.

[0127] Specifically, the extrusion structure 10 includes a central extrusion portion 11 and an edge extrusion portion 12, wherein the edge extrusion portion 12 is disposed around the edge of the central extrusion portion 11.

[0128] When the extrusion structure 10 extrudes the electrode assembly 1, the intermediate extrusion portion 11 corresponds to the intermediate portion 101 of the electrode assembly 1, and the edge extrusion portion 12 corresponds to the edge portion 102 of the electrode assembly 1. Furthermore, when the extrusion structure 10 extrudes the electrode assembly 1, the intermediate extrusion portion 11 applies a first extrusion force G1 to the intermediate portion 101, and the edge extrusion portion 12 applies a second extrusion force G2 to the edge portion 102, wherein G2 ≥ G1, G1 ≥ 0, and G2 > 0. Additionally, during at least a portion of the time period during which the extrusion structure 10 extrudes the electrode assembly 1, G1 < G2.

[0129] Understandably, the edge extrusion portion 12 and the middle extrusion portion 11 can be directly connected together, for example, the edge extrusion portion 12 and the middle extrusion portion 11 can be integrally formed, or they can be indirectly connected together, or they can be independent of each other.

[0130] When the extrusion structure 10 extrudes the electrode assembly 1, the magnitude of the first extrusion force G1 can be fixed or variable, and the magnitude of the second extrusion force G2 can also be fixed or variable. However, regardless of the type, the second extrusion force G2 must be greater than the first extrusion force G1, or the second extrusion force G2 must be equal to the first extrusion force G1, i.e., G2 ≥ G1. Where G2 > 0, this means that when the extrusion structure 10 extrudes the electrode assembly 1, at least the edge extrusion portion 12 applies the second extrusion force G2 to the edge portion 102 of the electrode assembly 1, i.e., the edge extrusion portion 12 always extrudes the electrode assembly 1. G1 ≥ 0, this means that when the extrusion structure 10 extrudes the electrode assembly 1, the intermediate extrusion portion 11 can extrude the middle portion 101 of the electrode assembly 1, or it can not extrude the electrode assembly 1. When the intermediate extrusion portion 11 extrudes the electrode assembly 1, G1 > 0; when the intermediate extrusion portion 11 does not extrude the electrode assembly 1, G1 = 0. Furthermore, G1 < G2 during at least a portion of the time period of the extrusion structure 10 extruding electrode assembly 1, which can be either during the entire time period (i.e. the entire process) of the extrusion structure 10 extruding electrode assembly 1 or during a portion of the process of the extrusion structure 10 extruding electrode assembly 1.

[0131] As an example, throughout the entire process of the extrusion structure 10 extruding the electrode assembly 1, G2 > G1 > 0, that is, the extrusion force of the edge extrusion part 12 on the edge part 102 of the electrode assembly 1 is always greater than the extrusion force of the middle extrusion part 11 on the middle part 101 of the electrode assembly 1.

[0132] As an example, during the entire process of the extrusion structure 10 extruding the electrode assembly 1, G2 > G1 = 0, that is, only the edge extrusion part 12 extrudes the edge part 102 of the electrode assembly 1, while the middle extrusion part 11 never extrudes the electrode assembly 1.

[0133] The extrusion structure 10 provided in this application embodiment includes a middle extrusion portion 11 and an edge extrusion portion 12, wherein the middle extrusion portion 11 is used to extrude the middle region 101 of the electrode assembly 1, and the edge extrusion portion 12 is used to extrude the edge portion 102 of the electrode assembly 1. When the extrusion structure 10 is used to extrude the electrode assembly 1, during at least a portion of the extrusion process, the intermediate extrusion section 11 does not apply extrusion force to the intermediate section 101 or the extrusion force is less than the extrusion force of the edge extrusion section 12 on the edge section 102. This results in the porosity of the intermediate section 101 of the electrode assembly 1 after extrusion by the extrusion structure 10 being greater than the porosity of the edge section 102. Thus, when the electrode assembly 1 is applied to the battery cell, the rate at which the intermediate section 101 of the electrode assembly 1 is immersed in the electrolyte is greater than that of the edge section 102, thereby reducing the risk of lithium plating in the intermediate section 101. In addition, since the intermediate section 101 is at greater risk of volume expansion than the edge section 102 during the cycling process, extrusion makes the porosity of the intermediate section 101 greater than that of the edge section 102, which can alleviate the volume expansion of the intermediate section 101 to a certain extent and reduce the risk of lithium plating in the intermediate section 101.

[0134] In some implementations, please refer to Figures 11 to 15 The extrusion structure 10 includes a central extrusion portion 11 and an edge extrusion portion 12, with the edge extrusion portion 12 surrounding the edge of the central extrusion portion 11. A first extrusion surface 120 is formed on the edge extrusion portion 12 for extruding the edge portion 102; a second extrusion surface 110 is formed on the central extrusion portion 11 for extruding the central portion 101. Furthermore, when the extrusion structure 10 extrudes the electrode assembly 1, the second extrusion surface 110 is configured to form a discontinuity with the first extrusion surface 120, and the second extrusion surface 110 is located further away from the central axis of the electrode assembly 1 than the first extrusion surface 120.

[0135] Understandably, since the edge extrusion portion 12 has a first extrusion surface 120 and the middle extrusion portion 11 has a second extrusion surface 110, both the edge extrusion portion 12 and the middle extrusion portion 11 are solid structures.

[0136] It should be noted that the first extrusion surface 120 can be independently planar or curved, and the second extrusion surface 110 can be independently planar or curved. Optionally, the first extrusion surface 120 is adapted to the outer surface of the edge portion 102 of the electrode assembly 1 to better extrude the edge portion 102; the first extrusion surface 120 is adapted to the outer surface of the middle portion 101 of the electrode assembly 1 to better extrude the middle portion 101. As an example, the electrode assembly 1 has a wound structure, the outer surface of the middle portion 101 is planar, the second extrusion surface 110 is also planar, the outer surface of the edge portion 102 is curved, and the first extrusion surface 120 is also curved; or the electrode assembly 1 has a wound structure, the outer surfaces of the middle portion 101 and the edge portion 102 are both planar, and the first extrusion surface 120 and the second extrusion surface 110 are both planar.

[0137] During at least a portion of the time period of the extrusion structure 10 extruding electrode assembly 1, the second extrusion surface 110 and the first extrusion surface 120 form a discontinuity. This discontinuity means that the second extrusion surface 110 and the first extrusion surface 120 are not coplanar. This discontinuity can be maintained throughout the entire time period (i.e., the entire process) of the extrusion structure 10 extruding electrode assembly 1, or it can exist only for a portion of the time period during the extrusion process.

[0138] Furthermore, when the second extrusion surface 110 and the first extrusion surface 120 are not coplanar, the second extrusion surface 110 is farther away from the central axis of the electrode assembly 1 compared to the first extrusion surface 120. In other words, the distance between the second extrusion surface 110 and the central axis of the electrode assembly 1 is greater than the distance between the first extrusion surface 120 and the central axis of the electrode assembly 1. When the distance between the second extrusion surface 110 and the central axis of the electrode assembly 1 increases, the force between the intermediate extrusion part 11 and the electrode assembly 1 (i.e., the first extrusion force G1) decreases, and the following different situations may occur: the intermediate extrusion part 11 continues to extrude force on the intermediate part 101 of the electrode assembly 1, but the first extrusion force G1 decreases; or the second extrusion surface 110 separates from the electrode assembly 1, and the first extrusion force G1 becomes zero. Here, the central axis of the electrode assembly 1 is perpendicular to the first direction.

[0139] During the extrusion process of the extrusion structure 10 extruding the electrode assembly 1, at least one of the second extrusion surface 110 and the first extrusion surface 120 remains in contact with the electrode assembly 1. It can be understood that during the extrusion process of the extrusion structure 10 extruding the electrode assembly 1, the first extrusion surface 120 always remains in contact with the edge portion 102 of the electrode assembly 1, while the second extrusion surface 11 may come into contact with or separate from the middle portion 101 of the electrode assembly 1. In this case, the first extrusion force G1 exerted by the middle extrusion portion 11 on the middle portion 101 of the electrode assembly 1 decreases or disappears.

[0140] To more clearly illustrate the compression of the electrode assembly 1 by the first extrusion surface 120 and the second extrusion surface 110 during the extrusion process of the extrusion structure 10, the following example is provided. The extrusion process of the electrode assembly 1 by the extrusion structure 10 is divided into three time periods, namely, the first time period T1, the second time period T2, and the third time period T3, from beginning to end. During the T1 to T3 period, the force applied by the first extrusion surface 120 to the edge portion 102 of the electrode assembly 1 is the second extrusion force G2, which remains constant and its magnitude is always G20. During the T1 to T3 period, the force applied by the second extrusion surface 110 to the middle portion 101 of the electrode assembly 1 is the first extrusion force G1. During the T1 period, the magnitude of G1 is G11, during the T2 period, the magnitude of G1 is G12, and during the T3 period, the magnitude of G1 is G13.

[0141] As an example, during the process T1 to T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 remains at D1, then 0 < G11 = G12 = G13 < G20. That is to say, the extrusion time of the second extrusion surface 110 on the middle part 101 of the electrode assembly 1 is the same as the extrusion time of the first extrusion surface 120 on the edge part 102 of the electrode assembly 1, but the extrusion force is smaller.

[0142] As an example, during processes T1 and T2, the second extrusion surface 110 is coplanar with the first extrusion surface 120. However, during process T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D3, so 0 < G13 < G12 = G11 = G20. That is, the extrusion time of the second extrusion surface 110 on the middle part 101 of the electrode assembly 1 is the same as the extrusion time of the first extrusion surface 120 on the edge part 102 of the electrode assembly 1, but the extrusion force decreases in the third time period T3.

[0143] As an example, during processes T1 and T3, the second extrusion surface 110 is coplanar with the first extrusion surface 120. However, during process T2, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D2, so 0 < G12 < G13 = G11 = G20. That is, the extrusion time of the second extrusion surface 110 on the middle part 101 of the electrode assembly 1 is the same as the extrusion time of the first extrusion surface 120 on the edge part 102 of the electrode assembly 1, but the extrusion force decreases in the second time period T2.

[0144] As an example, during processes T2 and T3, the second extrusion surface 110 is coplanar with the first extrusion surface 120. However, during process T1, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D1, so 0 < G11 < G12 = G13 = G20. That is, the extrusion time of the second extrusion surface 110 on the middle part 101 of the electrode assembly 1 is the same as the extrusion time of the first extrusion surface 120 on the edge part 102 of the electrode assembly 1, but the extrusion force decreases during the first time period T1.

[0145] As an example, in process T1, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D1; ​​in process T2, the step difference is D2; and in process T3, the step difference is D3. Since D1 < D2 < D3, then 0 < G13 < G12 < G11 < G20. That is, the extrusion time of the second extrusion surface 110 on the middle portion 101 of the electrode assembly 1 is the same as the extrusion time of the first extrusion surface 120 on the edge portion 102 of the electrode assembly 1, but the extrusion pressure decreases sequentially in each time period.

[0146] As an example, during processes T1 and T2, the second extrusion surface 110 is coplanar with the first extrusion surface 120. However, during process T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D4, and the second extrusion surface 110 separates from the electrode assembly 1. Therefore, 0 = G13 < G12 = G11 = G20. In other words, the extrusion time of the second extrusion surface 110 on the middle portion 101 of the electrode assembly 1 is the same as the extrusion time of the first extrusion surface 120 on the edge portion 102 of the electrode assembly 1, but the extrusion force decreases to zero in the third time period T3. Alternatively, the extrusion force of the second extrusion surface 110 on the middle portion 101 of the electrode assembly 1 is the same as the extrusion force of the first extrusion surface 120 on the edge portion 102 of the electrode assembly 1, but the extrusion time is shorter.

[0147] In summary, the extrusion structure 10 provided in this application embodiment includes a middle extrusion portion 11 and an edge extrusion portion 12. The edge extrusion portion 12 has a first extrusion surface 120 for extruding the edge portion 102 of the electrode assembly 1, and the middle extrusion portion 11 has a second extrusion surface 110 for extruding the middle portion 101 of the electrode assembly 1. When the extrusion structure 10 extrudes the electrode assembly 1, a discontinuity is formed between the second extrusion surface 110 and the first extrusion surface 120, and the second extrusion surface 110 is farther away from the central axis of the electrode assembly 1 than the first extrusion surface 120. Thus, during the process of the extrusion structure 10 extruding the electrode assembly 1, for at least a part of the time period, the extrusion force of the middle extrusion portion 11 on the middle portion 101 (i.e., the first extrusion force G1) is less than the extrusion force of the edge extrusion portion 12 on the edge portion 102 (i.e., the second extrusion force G2), thereby making the porosity of the middle portion 101 of the electrode assembly 1 after being extruded by the extrusion structure 10 greater than the porosity of the edge portion 102. Thus, when electrode assembly 1 is applied to the battery cell, the rate at which the middle portion 101 of electrode assembly 1 is immersed in the electrolyte is greater than that of the edge portion 102 of electrode assembly 1, thereby reducing the risk of lithium plating in the middle portion 101. In addition, since the middle portion 101 is at greater risk of volume expansion than the edge portion 102 during the cycling process, the porosity of the middle portion 101 is made greater than that of the edge portion 102 by compression, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium plating in the middle portion 101.

[0148] In some implementations, please refer to Figure 11 The edge extrusion portion 12 is fixedly connected to the middle extrusion portion 11 and together defines the groove 13. The second extrusion surface 110 is formed as the inner bottom surface of the groove 13, and the first extrusion surface 120 is located outside the groove 13 and surrounds the opening 131 of the groove 13. In this case, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is a fixed value and is equal to the depth of the groove 13.

[0149] As an example, the edge extrusion part 12 is a first frame 122, which has a first through hole 1221. The middle extrusion part 11 is a plate 112, which is located on one side of the first frame 122 and blocks one end opening of the first through hole 1221, thereby forming a groove 13. The other opening of the first through hole 1221 is formed as the slot 131 of the groove 13. The plate 112 is fixedly connected to the first frame 122 to form an extrusion structure 10.

[0150] When using the extrusion structure 10 to extrude the electrode assembly 1, the second extrusion force G2 can always be kept greater than the first extrusion force G1, thereby making the porosity of the middle part 101 greater than the porosity of the edge part 102.

[0151] In some embodiments, the depth of the groove 13 is 0.005 mm to 0.1 mm. The depth of the groove 13 represents the step difference between the second extrusion surface 110 and the first extrusion surface 120. The greater the depth of the groove 13, the greater the porosity difference between the edge portion 102 and the middle portion 101. However, if the depth of the groove 13 is too large, the second extrusion surface 110 will not be able to extrude the middle portion 101 of the electrode assembly 1, resulting in poor shaping effect of the electrode assembly 1, affecting the assembly of the electrode assembly 1 with the housing and the internal resistance of the electrode assembly 1. As an example, the depth of the groove 13 is any one of 0.005 mm, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, and 0.1 mm, or a range between any two.

[0152] In some implementations, please refer to Figure 12 The edge extrusion portion 12 is a rigid portion 121, and the middle extrusion portion 11 is a flexible portion 111. The rigid portion 121 is connected to the flexible portion 111, and the flexible portion 111 is used to deform in a direction away from the electrode assembly 1 when the extrusion structure 10 extrudes the electrode assembly 1. In this case, since the flexible portion 111 is a flexible portion 111, the characteristic that the flexible portion 111 will undergo elastic deformation when subjected to force is utilized to form a step difference between the second extrusion surface 110 and the first extrusion surface 120, thereby making the first extrusion force G1 of the middle extrusion portion 11 on the middle portion 101 less than the second extrusion force G2 of the edge extrusion portion 12 on the edge portion 102.

[0153] As an example, the flexible part 111 is made of a flexible resin. The flexible resin includes, but is not limited to, at least one of silicone and rubber. The rigid part 121 is a metal component, such as a stainless steel sheet.

[0154] As an example, the flexible part 111 is a capsule filled with a fluid medium. The deformation of the capsule can be adjusted by regulating the amount of fluid medium inside the capsule. Furthermore, the timing of the fluid medium filling the capsule can be adjusted to improve the formation time of the step difference.

[0155] In some implementations, please refer to Figure 13 and Figure 14Along the thickness direction of the extrusion structure 10, the intermediate extrusion section 11 is movably disposed relative to the edge extrusion section 12. The intermediate extrusion section 11 is used to move towards or away from the electrode assembly 1 when the extrusion structure 10 extrudes the electrode assembly 1. Since the intermediate extrusion section 11 can move relative to the edge extrusion section 12 along the thickness direction of the extrusion structure 10, the distance between the second extrusion surface 110 on the intermediate extrusion section 11 and the first extrusion surface 120 on the edge extrusion section 12 can be adjusted when the extrusion structure 10 extrudes the electrode assembly 1. This allows a step difference to be formed between the second extrusion surface 110 and the first extrusion surface 120 during at least a portion of the time period when the extrusion structure 10 extrudes the electrode assembly 1. As a result, the first extrusion force G1 of the intermediate extrusion section 11 on the intermediate portion 101 is less than the second extrusion force G2 of the edge extrusion section 12 on the edge portion 102.

[0156] As an example, the process of the extrusion structure 10 extruding the electrode assembly 1 is divided into three time periods, which are divided into the first time period T1, the second time period T2 and the third time period T3 from the beginning to the end. During the first time period T1 and the second time period T2, the second extrusion surface 110 and the first extrusion surface 120 are kept coplanar. Then, the intermediate extrusion part 11 is moved away from the electrode assembly 1, so that a step difference is formed between the second extrusion surface 110 and the first extrusion surface 120 during the third time period T3.

[0157] As an example, the process of extruding the electrode assembly 1 by the extrusion structure 10 is divided into three time periods, which are divided into the first time period T1, the second time period T2 and the third time period T3 from the beginning to the end. During the first time period T1 and the second time period T2, a step difference is maintained between the second extrusion surface 110 and the first extrusion surface 120. Then, the intermediate extrusion part 11 is moved towards the electrode assembly 1 so that the second extrusion surface 110 and the first extrusion surface 120 are coplanar during the third time period T3.

[0158] As an example, the process of extruding the electrode assembly 1 by the extrusion structure 10 is divided into three time periods, which are divided into the first time period T1, the second time period T2 and the third time period T3 from the beginning to the end. In the first time period T1, a step difference is maintained between the second extrusion surface 110 and the first extrusion surface 120. Then, the middle extrusion part 11 is moved towards the electrode assembly 1 so that the second extrusion surface 110 and the first extrusion surface 120 are coplanar in the second time period T2. Then, the middle extrusion part 11 is moved away from the electrode assembly 1 so that a step difference is formed between the second extrusion surface 110 and the first extrusion surface 120 in the third time period T3.

[0159] In some embodiments, the extrusion structure 10 further includes a drive member (not shown) connected to the intermediate extrusion section 11 and used to drive the intermediate extrusion section 11 to move. As an example, the drive member is a push rod motor.

[0160] In some implementations, please refer to Figure 13 and Figure 14 The edge extrusion part 12 includes a first frame 122 having a first through hole 1221, and the middle extrusion part 11 includes a slider 113, which is located inside the through hole 1221 and slidably connected to the first frame 122. The distance between the second extrusion surface 110 and the first extrusion surface 120 can be adjusted by sliding the first frame 122 and the slider 113.

[0161] In some implementations, please refer to Figure 13 and Figure 14 A groove 1222 is formed by a partial recess in the inner wall of the first through hole 1221 into the interior of the first frame 122. The slider 113 includes a boss 1131 and a body portion 1132. The boss 1131 protrudes from the circumferential surface of the body portion 1132. The body portion 1132 is located within and fits into the first through hole 1221, and one end face of the body portion 1132 is formed as a second pressing surface 110. The boss 1131 extends into the groove 1222 and slides within it. Please continue reading... Figure 14 When the boss 1131 slides to one end of the groove 1222, as shown in the figure, the second extrusion surface 110 is flush with the first extrusion surface 120, i.e., they are coplanar; please continue reading. Figure 13 When the boss 1131 slides to the other end of the groove 1222, as shown at the bottom end, there is a step difference between the second extrusion surface 110 and the first extrusion surface 120. Optionally, the length of the groove 1222 is less than the thickness of the first frame 122.

[0162] In some implementations, please refer to Figure 13 and Figure 14 In the thickness direction of the first frame 122, the thickness of the boss 1131 is less than the width of the groove 1222, and the distance between the side surface of the boss 1131 facing away from the second pressing surface 110 and the second pressing surface 110 is greater than the width of the groove 1222. Thus, when the side surface of the boss 1131 facing away from the second pressing surface 110 abuts against the side wall of the groove 1222, the body portion 1132 can seal the opening of the groove 1222, reducing the risk of foreign objects entering the groove 1222.

[0163] In some implementations, please refer to Figure 15 and Figure 16 The distance between the side surface of the boss 1131 near the second extrusion surface 110 and the end face of the body portion 1132 opposite to the second extrusion surface 110 is greater than the width of the groove 1222. Thus, when the side surface of the boss 1131 near the second extrusion surface 110 abuts against the side wall of the groove 1222, the body portion 1132 can seal the opening of the groove 1222, reducing the risk of foreign objects entering the groove 1222.

[0164] In some embodiments, the ratio of the area of ​​the second extrusion surface 110 to the sum of the areas of the first extrusion surface 120 and the second extrusion surface 110 is 0.1 to 0.4. As an example, the ratio of the area of ​​the second extrusion surface 110 to the sum of the areas of the first extrusion surface 120 and the second extrusion surface 110 is 0.1, 0.2, 0.3 or 0.4.

[0165] In some implementations, please refer to Figure 15 The extrusion structure 10 includes only the edge extrusion portion 12, eliminating the middle extrusion portion 11. Specifically, the edge extrusion portion 12 is a second frame 124 with a second through hole 125. The second frame 124 is configured to extrude the edge portion 102 when the extrusion structure 10 extrudes the electrode assembly 1. The second through hole 125 corresponds to the middle portion 101, i.e., the second through hole 125 is used to avoid the middle portion 101. In this case, when the extrusion structure 10 extrudes the electrode assembly 1, only the second frame 124 extrudes the edge portion 102 of the electrode assembly 1, while the extrusion force on the middle portion 101 of the electrode assembly 1 is zero, thereby making the porosity of the middle portion 101 greater than that of the edge portion 102. Thus, when electrode assembly 1 is applied to the battery cell, the rate at which the middle portion 101 of electrode assembly 1 is immersed in the electrolyte is greater than that of the edge portion 102 of electrode assembly 1, thereby reducing the risk of lithium plating in the middle portion 101. In addition, since the middle portion 101 is at greater risk of volume expansion than the edge portion 102 during the cycling process, the porosity of the middle portion 101 is made greater than that of the edge portion 102 by compression, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium plating in the middle portion 101.

[0166] In some embodiments, the extrusion structure 10 is used to prepare the electrode assembly 1 provided in the first aspect.

[0167] Additionally, please see Figures 16 to 17 This application embodiment also provides an extrusion fixture 100, including any of the extrusion structures 10 described above.

[0168] In some implementations, please refer to Figure 16 The extrusion fixture 100 has two extrusion structures 10, which are arranged facing each other. When using the extrusion fixture 100 to extrude the electrode assembly 1, the electrode assembly 1 is located between the two opposing extrusion structures 10.

[0169] In some implementations, please refer to Figure 17The extrusion fixture 100 includes one extrusion structure 10. The extrusion fixture 100 also includes a substrate 20, which is optionally a flat plate. The extrusion structure 10 and the substrate 20 are arranged face-to-face. When using the extrusion fixture 100 to extrude the electrode assembly 1, the electrode assembly 1 is located between the extrusion structure 10 and the substrate 20.

[0170] In some embodiments, the extrusion fixture 100 is a hot press fixture, and during the extrusion of the electrode assembly 1, at least one of the extrusion structure 10 and the substrate 20 can also heat the electrode assembly 1.

[0171] In some embodiments, the extrusion fixture 100 is used to prepare the electrode assembly 1 provided in the first aspect.

[0172] The following description is based on specific embodiments.

[0173] Example 1

[0174] This embodiment provides a battery cell, the preparation method of which is as follows:

[0175] S1. Preparation of positive electrode sheet: The positive electrode active material (lithium iron phosphate, LFP): positive electrode conductive agent (conductive graphite, SP): positive electrode conductive agent (carbon nanotube, CNT): positive electrode binder (polyvinylidene fluoride, PVDF) in a ratio of 97.4wt%:0.5wt%:0.4wt%:1.7wt% is mixed with solvent (N-methylpyrrolidone, NMP) to prepare a positive electrode slurry. Then, the positive electrode slurry is coated on both sides of the positive electrode current collector (12μm aluminum foil), dried, and cut to obtain the positive electrode sheet.

[0176] S2. Preparation of negative electrode sheet: A negative electrode slurry is prepared according to the following composition: negative electrode active material (artificial graphite, abbreviated as AG): negative electrode conductive agent (conductive graphite, SP): dispersant (carboxymethyl cellulose, CMC): negative electrode binder (styrene-butadiene rubber, SBR) in a ratio of 96.7wt%:0.6wt%:1.2wt%:1.5wt%. Then, the negative electrode slurry is coated on both sides of the negative electrode current collector (5μm copper foil), dried, and cut to obtain the negative electrode sheet.

[0177] S3. Core Packaging Preparation: The separator, positive electrode, separator, and negative electrode are stacked layer by layer to obtain the core packaging. The separator is a double-sided mixed-coating separator with a mixed-coating layer thickness of 2 μm and a base film thickness of 7 μm. The adhesive material in the mixed-coating layer is a mixture of polyvinylidene fluoride (PVDF) and ceramic. Figure 1 As shown, the core package is divided into a middle portion 101 and an edge portion 102. In the thickness direction of the core package, the ratio of the area of ​​the orthographic projection of the middle portion 101 to the area of ​​the orthographic projection of the core package (referred to as the area ratio) is 50%.

[0178] S4. Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 1000N, and the hot pressing time is 140s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 1300N, and the hot pressing time is 180s. The ratio of the hot pressing pressure between the middle part 101 and the edge part 102 (referred to as the pressure ratio) is 0.77, and the ratio of the hot pressing time between the middle part 101 and the edge part 102 (referred to as the time ratio) is 0.78.

[0179] S5. Assemble the battery cell: Pack the hot-pressed core into a square aluminum shell, inject electrolyte (lithium salt containing LiFSI and LiPF6 in a molar ratio of 1:1, lithium salt concentration of 1mol / L, solvent containing ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC and dimethyl carbonate DMC, EC:PC:EMC:DMC=30:5:25:40), the electrolyte injection coefficient is 3.1, then let it stand and form to obtain the battery cell.

[0180] Example 2

[0181] The difference from Example 1 is as follows:

[0182] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 1200N, and the hot pressing time is 140s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 1500N, and the hot pressing time is 180s. The pressure ratio between the middle part 101 and the edge part 102 is 0.8, and the time ratio between the middle part 101 and the edge part 102 is 0.78.

[0183] Example 3

[0184] The difference from Example 1 is as follows:

[0185] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 85s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 4000N, and the hot pressing time is 110s. The pressure ratio between the middle part 101 and the edge part 102 is 0.75, and the time ratio between the middle part 101 and the edge part 102 is 0.77.

[0186] Example 4

[0187] The difference from Example 3 is that the area ratio in S3 is 20%, that is, the middle part 101 is smaller.

[0188] Example 5

[0189] The difference from Example 3 is that the area ratio in S3 is 80%, that is, the middle part 101 is larger.

[0190] Example 6

[0191] The difference from Example 3 is that lithium iron phosphate in S1 is replaced with lithium manganese iron phosphate (LMFP), while everything else remains the same.

[0192] Example 7

[0193] The difference from Example 3 is that the hot pressing temperature of the middle part 101 of S4 is reduced to 80°C, and the hot pressing temperature of the edge part 102 is also reduced to 80°C, while the rest remains unchanged.

[0194] Example 8

[0195] The difference from Example 3 is that the hot pressing temperature of the middle part 101 of S4 is raised to 90°C, and the hot pressing temperature of the edge part 102 is also raised to 90°C, while the rest remains unchanged.

[0196] Example 9

[0197] The difference from Example 3 is that the hot pressing temperature of the middle part 101 of S4 is raised to 100°C, and the hot pressing temperature of the edge part 102 is also raised to 100°C, while the rest remains unchanged.

[0198] Comparative Example 1

[0199] The difference from Example 3 is as follows:

[0200] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to the same hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 4000N, and the hot pressing time is 110s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 4000N, and the hot pressing time is 110s. The pressure ratio between the middle part 101 and the edge part 102 is 1, and the time ratio between the middle part 101 and the edge part 102 is 1.

[0201] Comparative Example 2

[0202] The difference from Example 3 is as follows:

[0203] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to the same hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 85s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 85s. The pressure ratio between the middle part 101 and the edge part 102 is 1, and the time ratio between the middle part 101 and the edge part 102 is 1.

[0204] Comparative Example 3

[0205] The difference from Example 3 is as follows:

[0206] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 4000N, and the hot pressing time is 85s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 85s. The pressure ratio between the middle part 101 and the edge part 102 is 1.3, and the time ratio between the middle part 101 and the edge part 102 is 1.

[0207] Comparative Example 4

[0208] The difference from Example 3 is as follows:

[0209] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 110s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 85s. The pressure ratio between the middle part 101 and the edge part 102 is 1, and the time ratio between the middle part 101 and the edge part 102 is 1.3.

[0210] Comparative Example 5

[0211] The difference from Example 3 is as follows:

[0212] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 4000N, and the hot pressing time is 110s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 3000N, and the hot pressing time is 85s. The pressure ratio between the middle part 101 and the edge part 102 is 1.3, and the time ratio between the middle part 101 and the edge part 102 is 1.3.

[0213] The hot pressing parameters in Examples 1 to 9 and Comparative Examples 1 to 5 are recorded in Table 1.

[0214] Table 1

[0215]

[0216] Example 10

[0217] The difference from Example 1 is as follows:

[0218] S4: Core Packaging Hot Pressing: The middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters. The hot pressing temperature of the middle part 101 is 85℃, the hot pressing pressure is 500N, and the hot pressing time is 120s. The hot pressing temperature of the edge part 102 is 85℃, the hot pressing pressure is 5000N, and the hot pressing time is 120s. The pressure ratio between the middle part 101 and the edge part 102 is 0.1, and the time ratio between the middle part 101 and the edge part 102 is 1.

[0219] Example 11

[0220] The difference from Example 10 is that in S4, the hot pressing pressure of the middle part 101 is increased to 1000N, so the pressure ratio becomes 0.2, while the others remain unchanged.

[0221] Example 12

[0222] The difference from Example 10 is that in S4, the hot pressing pressure of the middle part 101 is increased to 2000N, so the pressure ratio becomes 0.4, while the others remain unchanged.

[0223] Example 13

[0224] The difference from Example 10 is that in S4, the hot pressing pressure of the middle part 101 is increased to 3000N, so the pressure ratio becomes 0.6, while the others remain unchanged.

[0225] Example 14

[0226] The difference from Example 10 is that in S4, the hot pressing pressure of the middle part 101 is increased to 4000N, so the pressure ratio becomes 0.8, while the others remain unchanged.

[0227] Comparative Example 6

[0228] The difference from Example 10 is that in S4, the hot pressing pressure of the middle part 101 is increased to 5000N, so the pressure ratio becomes 1, and the others remain unchanged.

[0229] Comparative Example 7

[0230] The difference from Example 10 is that in S4, the hot pressing pressure of the middle part 101 is increased to 6000N, so the pressure ratio becomes 1.2, while other aspects remain unchanged.

[0231] The hot pressing parameters in Examples 10 to 14 and Comparative Examples 6 to 7 are recorded in Table 2.

[0232] Table 2

[0233]

[0234]

[0235] The following tests were performed on the battery cells provided in all embodiments and comparative examples:

[0236] 1. Lithium plating detection:

[0237] After fully charging the battery cells, they were disassembled, and the lithium plating at the interface was observed and graded as follows: no lithium plating, slight lithium plating (lithium plating area less than 0.5 cm²). 2 Moderate lithium plating (lithium plating area 0.5 cm²) 2 ~1.0cm 2 Severe lithium plating (lithium plating area greater than 1 cm²) 2 The results are recorded in Table 3;

[0238] Full charge conditions for the battery cell: At a temperature of 25℃, charge at a constant current of 0.33C to the cutoff voltage (the cutoff voltage of the battery cell is 3.65V when the positive electrode active material is LFP, and 4.2V when the positive electrode active material is LMFP), then switch to constant voltage charging with a cutoff current of 0.05C.

[0239] 2. Peel force test:

[0240] After the battery cells were fully loaded, they were disassembled and the cell packs were removed. They were then vacuum dried in a vacuum oven at 30°C for 48 hours. The peel force between the positive electrode and the separator was tested according to the peel force test method of GB / T 2792-2014. The results are recorded in Table 3.

[0241] Full discharge conditions for the battery cell: at 25℃, discharge at 1C to 2.5V.

[0242] Table 3

[0243]

[0244] The results in Table 3 show that:

[0245] 1. Comparing Examples 1 to 3 and Comparative Examples 1 to 5, it can be seen that when the hot-pressing pressure of the middle portion 101 is less than that of the edge portion 102, and the hot-pressing time of the middle portion 101 is less than that of the edge portion 102, the peel force between the electrode and the separator in the middle portion 101 is less than that between the electrode and the separator in the edge portion 102, thus reducing the risk of lithium plating in the cell. When the hot-pressing pressure of the middle portion 101 is greater than or equal to that of the edge portion 102, the peel force between the electrode and the separator in the middle portion 101 is greater than that between the electrode and the separator in the edge portion 102, resulting in severe lithium plating in the cell. The peel force between the electrode and the separator in the middle portion 101 should not be too low. If the peel force is too low (below 0.1N), the gap between the electrode and the separator will increase in the middle and later stages of cell cycling, making it difficult for lithium ions to pass through, thus increasing the risk of lithium plating.

[0246] 2. Comparing Example 3 and Example 6, it was found that no lithium was deposited on the electrode after the positive electrode active material was replaced with LMFP, indicating that the same rule applies to the LMFP system.

[0247] 3. Comparing Examples 3, 4, and 5, the interface is optimal when the area of ​​the middle portion 101 and the edge portion 102 is controlled at around 50%. That is, the area of ​​the middle portion 101 should not be too large or too small, because lithium plating tends to concentrate in the middle portion 101. If the area of ​​the middle portion 101 is too large, it will reduce the peeling force of the originally normal area and accelerate the decay in later cycles. If the area of ​​the middle portion 101 is too small, it will make the middle portion 101 prone to lithium plating.

[0248] 4. Comparing Examples 7 to 9, as the hot pressing temperature increases, the peeling force between the positive electrode and the separator increases, and the lithium plating area at the cell interface gradually increases. This is because the separator is more easily deformed after the temperature rises, which makes the electrode and the separator bond more tightly, that is, the peeling force between the two increases. At the same time, the porosity inside the electrode assembly decreases, making it easier for lithium plating to occur.

[0249] 5. Comparing Examples 12 to 16 and Comparative Examples 6 and 7, as the hot-pressing pressure of the middle portion 101 increases, the peeling force between the positive electrode and the separator increases, the area of ​​lithium plating gradually increases, and the degree of lithium plating becomes more and more severe. After the hot-pressing pressure of the middle portion 101 is equal to or greater than the hot-pressing pressure of the edge portion 102, the area of ​​lithium plating increases significantly, and the degree of lithium plating becomes more and more severe. This indicates that reducing the hot-pressing pressure of the middle portion 101 is beneficial to controlling the degree of lithium plating. However, the hot-pressing pressure of the middle portion 101 should not be too low, otherwise the peeling force will be too low, which will lead to accelerated cell degradation in the later stages of cycling.

[0250] In summary, the factors affecting peeling force during hot-pressing of electrode assemblies mainly include hot-pressing pressure, hot-pressing temperature, and hot-pressing time. Therefore, the problem of lithium plating in battery cells can be improved by addressing the following three aspects:

[0251] The hot pressing pressure ratio between the middle part 101 and the edge part 102 can be controlled within a certain range to ensure that the hot pressing pressure of the middle part 102 is less than that of the edge part 102; the hot pressing time ratio between the middle part 101 and the edge part 102 can also be controlled within a certain range to ensure that the hot pressing time of the middle part 102 is shorter than that of the edge part 102; the hot pressing temperature needs to be controlled within a certain range to ensure that the peeling force meets the requirements.

[0252] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrode assembly, characterized in that, The electrode assembly includes a stacked separator and an electrode sheet. The electrode assembly has a middle portion and an edge portion. Along the thickness direction of the electrode assembly, the orthographic projection of the edge portion surrounds the orthographic projection of the middle portion. The peel force between the separator and the electrode sheet on the middle portion is F1. The peeling force between the separator and the electrode on the edge is F2; ​​where F1 < F2.

2. The electrode assembly according to claim 1, characterized in that, The ratio of F1 to F2 is 0.3 to 0.

9.

3. The electrode assembly according to claim 1, characterized in that, The F1 is 0.1N to 0.2N, and / or the F2 is 0.2N to 0.3N.

4. The electrode assembly according to claim 1, characterized in that, Along the thickness direction of the electrode assembly, the percentage of the orthographic projection area of ​​the middle portion to the orthographic projection area of ​​the electrode assembly is 20% to 80%.

5. The electrode assembly according to claim 1, characterized in that, The aspect ratio of the electrode assembly is 0.8 to 1.2; and / or, the length of the electrode assembly is 150 mm to 180 mm, the width of the electrode assembly is 150 mm to 180 mm; and / or, the thickness of the electrode assembly is 10 mm to 25 mm.

6. The electrode assembly according to claim 1, characterized in that, The separator includes an adhesive-coated separator, which includes a base film and an adhesive layer, wherein the adhesive layer is located on at least one side surface of the base film.

7. The electrode assembly according to claim 6, characterized in that, The thickness of the base film is 5mm to 10mm, and the thickness of the adhesive layer is 1mm to 5mm; and / or, the ratio of the thickness of the base film to the thickness of the adhesive layer is 1 to 10.

8. The electrode assembly according to any one of claims 1 to 7, characterized in that, The separator and the electrode are stacked layer by layer; or the separator and the electrode are stacked and wound together.

9. The electrode assembly according to any one of claims 1 to 7, characterized in that, The difference between the thickness of the middle portion and the thickness of the edge portion is greater than or equal to 50 μm.

10. A single battery cell, characterized in that, include: A housing having a receiving cavity, the surface of the housing being divided into an edge region and a large surface region, and along the thickness direction of the housing, the orthographic projection of the edge region surrounds the orthographic projection of the large surface region; An electrode assembly is disposed within the receiving cavity, wherein the middle portion corresponds to the large surface and the edge portion corresponds to the edge, and the electrode assembly is the electrode assembly as described in any one of claims 1 to 9.

11. An extrusion structure for fabricating an electrode assembly as described in any one of claims 1 to 9, characterized in that, The extrusion structure includes a central extrusion section and an edge extrusion section disposed around the edge of the central extrusion section. A first extrusion surface for extruding the edge section is formed on the edge extrusion section, and a second extrusion surface for extruding the central section is formed on the central extrusion section. The second extrusion surface is configured to form a discontinuity with the first extrusion surface and be farther away from the central axis of the electrode assembly than the first extrusion surface when the extrusion structure extrudes the electrode assembly.

12. The extrusion structure according to claim 11, characterized in that, The edge extrusion part is fixedly connected to the middle extrusion part and together defines the groove. The second extrusion surface is formed as the inner bottom surface of the groove, and the first extrusion surface is located outside the groove and surrounds the opening of the groove.

13. The extrusion structure according to claim 12, characterized in that, The depth of the groove is 0.005mm to 0.1mm.

14. The extrusion structure according to claim 11, characterized in that, The edge extrusion part is a rigid part, the middle extrusion part is a flexible part, the rigid part is connected to the flexible part, and the flexible part is used to deform in a direction away from the electrode assembly when the extrusion structure extrudes the electrode assembly.

15. The extrusion structure according to claim 11, characterized in that, Along the thickness direction of the extrusion structure, the intermediate extrusion portion is movably disposed relative to the edge extrusion portion, and the intermediate extrusion portion is used to move toward or away from the electrode assembly when the extrusion structure extrudes the electrode assembly.

16. The extrusion structure according to claim 15, characterized in that, The edge extrusion part includes a first frame having a first through hole, and the middle extrusion part includes a slider located in the first through hole and slidably connected to the first frame.

17. The extrusion structure according to claim 16, characterized in that, A groove is formed by a partial recess in the inner wall of the first through hole into the interior of the first frame. The slider includes a body and a boss protruding from the circumferential surface of the body. The body is located inside the first through hole and is adapted to the first through hole. One end face of the body is formed as the second extrusion surface. The boss extends into the groove and slides in cooperation with the groove. In the thickness direction of the first frame, the thickness of the boss is less than the width of the groove, and the distance between the side surface of the boss away from the second extrusion surface and the second extrusion surface is greater than the width of the groove.

18. The extrusion structure according to any one of claims 11 to 16, characterized in that, The ratio of the area of ​​the second extrusion surface to the sum of the areas of the first extrusion surface and the second extrusion surface is 0.1 to 0.

4.

19. An extrusion structure for fabricating an electrode assembly as described in any one of claims 1 to 9, characterized in that, The extrusion structure includes an edge extrusion portion, which is a second frame having a second through hole. The second frame is configured to extrude the edge portion when the extrusion structure extrudes the electrode assembly, and the second through hole corresponds to the middle portion.

20. An extrusion fixture, characterized in that, Includes the extrusion structure according to any one of claims 11 to 19.

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