Electrode assembly and preparation method thereof, battery monomer, extrusion structure and extrusion jig

Abstract

The invention provides an electrode assembly and a preparation method thereof, a battery monomer, 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] The present application relates to the field of battery technology, and in particular to an electrode assembly and a preparation method thereof, a battery cell, an extrusion structure and an extrusion jig. Background Art

[0002] Lithium-ion batteries can be divided into square batteries, cylindrical batteries and soft-pack batteries according to their different shapes. Square batteries are widely used in the fields of power and energy storage due to their flexible and changeable size and unique structural characteristics.

[0003] During the manufacturing process of square batteries, the electrode assembly (also known as the core pack) is usually hot-pressed and shaped to facilitate the installation of the electrode assembly into a square shell (such as a square aluminum shell). During the hot pressing process of the electrode assembly, the conventional operation is to hot-press the electrode assembly as a whole to ensure that the entire area of ​​the electrode assembly is evenly stressed. Through the analysis of the square shell, it is found that the area near the eight edges of the square shell (referred to as the edge area) has a strong ability to resist deformation, while the large surface area of ​​the square shell has a weaker ability to resist deformation; and in the process of cycling of the square battery, the SEI film on the negative electrode of the electrode assembly will continue to reconstruct and thicken, causing the inside of the electrode assembly to expand outward, especially the middle part of the electrode assembly corresponding to the large surface area of ​​the square shell. Therefore, the degree of compression of the middle part of the electrode assembly is greater than that of the edge part of the electrode assembly corresponding to the edge area of ​​the square shell. During the cycle, the middle part is more prone to lithium deposition failure, resulting in accelerated decay of the square battery cycle. Summary of the invention

[0004] The embodiments of the present application provide an electrode assembly and a method for preparing the same, a battery cell, an extrusion structure and an extrusion jig, which can improve the technical problem that lithium deposition is prone to occur in the middle portion of the electrode assembly.

[0005] In the first aspect, an embodiment of the present application provides an electrode assembly, comprising a stacked isolation membrane and a pole piece, the electrode assembly having 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 peeling force between the isolation membrane and the pole piece on the middle portion is F1; the peeling force between the isolation membrane and the pole piece on the edge portion is F2; ​​wherein, F1<F2.

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

[0007] In one embodiment, the F1 is 0.1N-0.2N, and / or the F2 is 0.2N-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 isolation film includes a glue-coated membrane, and the glue-coated membrane includes a base film and a glue-coated layer, and the glue-coated layer is 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 isolation film and the pole piece are stacked layer by layer; or, the isolation film and the pole piece are stacked and wound.

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

[0014] In a second aspect, an embodiment of the present application provides a method for preparing an electrode assembly, comprising:

[0015] The separator and the electrode sheet are stacked together to obtain an electrode assembly, wherein the electrode assembly has a middle portion and an edge portion, and along the thickness direction of the electrode assembly, the orthographic projection of the edge portion surrounds the orthographic projection of the middle portion;

[0016] Along the thickness direction of the electrode assembly, the middle portion is subjected to a first extrusion treatment at a first pressure, and the edge portion is subjected to a second extrusion treatment at a second pressure; wherein the first pressure is less than or equal to the second pressure.

[0017] In one embodiment, the ratio of the first time to the second time is 0.2-0.8; and / or the ratio of the first pressure to the second pressure is 0.2-0.8; and / or the difference between the second pressure and the first pressure is greater than or equal to 1000N.

[0018] In one embodiment, the first pressure is 1000N-5000N.

[0019] In one embodiment, the second pressure is 3000N-5000N.

[0020] In one embodiment, the second pressure is 3400N-4500N.

[0021] In one embodiment, the extrusion time of the first extrusion process is a first time, and the extrusion time of the second extrusion process is a second time, wherein the first time is less than or equal to the second time, and the product of the first pressure and the first time is less than the product of the second pressure and the second time.

[0022] In one embodiment, the first time is 30s to 140s, or the second time is 120s to 180s, or the second time is 140s to 160s.

[0023] In one embodiment, both the first extrusion process and the second extrusion process are hot pressing processes, and the hot pressing temperature of the hot pressing processes is 80° C. to 100° C.

[0024] In a third aspect, an embodiment of the present application provides a battery cell, including:

[0025] A shell having a receiving cavity, wherein the surface of the shell is divided into an edge region and a large surface region, and along the thickness direction of the shell, the orthographic projection of the edge region surrounds the orthographic projection of the large surface region;

[0026] The electrode assembly is arranged in the accommodating cavity, the middle portion corresponds to the large surface, the edge portion corresponds to the edge, and the electrode assembly is the above-mentioned electrode assembly or an electrode assembly prepared by the above-mentioned electrode assembly preparation method.

[0027] In a fourth aspect, an embodiment of the present application provides an extrusion structure for preparing the electrode assembly provided in the first aspect, the extrusion structure comprising a middle extrusion portion and an edge extrusion portion arranged around the edge of the middle extrusion portion, a first extrusion surface for extruding the edge portion being formed on the edge extrusion portion, a second extrusion surface for extruding the middle portion being formed on the middle extrusion portion, the second extrusion surface being configured to form a step difference with the first extrusion surface and to be farther away from the central axis of the electrode assembly than the first extrusion surface when the extrusion structure extrudes the electrode assembly.

[0028] In one embodiment, the edge extrusion portion is fixedly connected to the middle extrusion portion and jointly defines a groove, the second extrusion surface forms an inner bottom surface of the groove, and the first extrusion surface is located outside the groove and surrounds the notch of the groove.

[0029] In one embodiment, the depth of the groove is 0.005 mm to 0.1 mm.

[0030] 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.

[0031] In one embodiment, along the thickness direction of the extrusion structure, the middle extrusion portion is movably arranged relative to the edge extrusion portion, and the middle extrusion portion is used to move toward or away from the electrode assembly when the extrusion structure extrudes the electrode assembly.

[0032] In one embodiment, the edge extrusion portion includes a first frame body having a first through hole, and the middle extrusion portion includes a slider, and the slider is located in the first through hole and is slidably connected to the first frame body.

[0033] In one embodiment, the inner side wall of the first through hole is partially recessed into the interior of the first frame to form a slide groove, and the slider includes a main body and a boss protruding on the circumferential surface of the main body, the main body is located in the first through hole and adapted to the first through hole, an end surface of the main body is formed as the second extrusion surface, and the boss extends into the slide groove and slidably cooperates with the slide groove; in the thickness direction of the first frame, the thickness of the boss is smaller than the width of the slide groove, and the distance between the side surface of the boss facing away from the second extrusion surface and the second extrusion surface is greater than the width of the slide groove.

[0034] 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 0.1-0.4.

[0035] In the fifth aspect, an embodiment of the present application provides an extrusion structure for preparing the electrode assembly provided in the first aspect, the extrusion structure comprising an edge extrusion portion, the edge extrusion portion being a second frame having a second through hole, the second frame being configured to extrude the edge portion when the extrusion structure extrudes the electrode assembly, and the second through hole corresponds to the middle portion.

[0036] In a sixth aspect, an embodiment of the present application provides an extrusion jig, comprising the above-mentioned extrusion structure.

[0037] Beneficial effects of the embodiments of the present application:

[0038] In the embodiments of the present application, since the squeezing force on the middle portion of the electrode assembly is greater than the squeezing force on the edge portion of the electrode assembly during the preparation process of the electrode assembly, not only the peeling force between the isolation membrane and the electrode piece on the middle portion is smaller than the peeling force between the isolation membrane and the electrode piece on the edge portion, but also the porosity of the middle portion of the electrode assembly is greater than the porosity of the edge portion. In this way, when the electrode assembly is applied to a battery cell, the rate at which the middle portion of the electrode assembly is infiltrated with electrolyte increases, thereby helping to reduce the risk of lithium deposition in the middle portion. In addition, since the SEI film reconstruction and proliferation in the middle portion are greater than those in the edge portion during the circulation process of the electrode assembly, the porosity of the middle portion is made greater than that of the edge portion through extrusion. This can alleviate the volume expansion of the middle portion to a certain extent and reduce the risk of lithium deposition in the middle portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 is a schematic diagram of a top view of the electrode assembly provided in an embodiment of the present application;

[0041] Figure 2 is a schematic diagram of the main structure of an electrode assembly provided in an embodiment of the present application;

[0042] Figure 3 yes Figure 2 Enlarged view of part A in the middle;

[0043] Figure 4 is a schematic cross-sectional structural diagram of a separator in an electrode assembly provided in an embodiment of the present application;

[0044] Figure 5 is a schematic cross-sectional structural diagram of a positive electrode sheet in an electrode assembly provided in an embodiment of the present application;

[0045] Figure 6 is a flow chart of a method for preparing an electrode assembly provided in an embodiment of the present application;

[0046] Figure 7 The relationship between the pressure on the middle and edge of the electrode assembly and time during the extrusion of the electrode assembly in the preparation method of the electrode assembly provided in the embodiment of the present application is Figure 1 ;

[0047] Figure 8The relationship between the pressure on the middle and edge of the electrode assembly and time during the extrusion of the electrode assembly in the preparation method of the electrode assembly provided in the embodiment of the present application is Figure 3 ;

[0048] Fig. 9 is a schematic cross-sectional structural diagram of a battery cell provided in an embodiment of the present application;

[0049] Fig.10 is an exploded view of a battery cell provided in an embodiment of the present application;

[0050] Fig.11 is a schematic cross-sectional structural diagram of a first extrusion jig provided in an embodiment of the present application;

[0051] Fig.12 is a schematic cross-sectional structural diagram of a second extrusion jig provided in an embodiment of the present application;

[0052] Fig.13 is a schematic cross-sectional structural diagram of a first extrusion structure provided in an embodiment of the present application;

[0053] Fig.14 is a schematic cross-sectional structural diagram of a second extrusion structure provided in an embodiment of the present application;

[0054] Fig.15 The cross-sectional structure diagram of the third extrusion structure provided in the embodiment of the present application is Figure 1 ;

[0055] Fig.16 The cross-sectional structure diagram of the third extrusion structure provided in the embodiment of the present application is Figure 2 ;

[0056] Fig.17 It is a schematic diagram of the three-dimensional structure of the fourth extrusion structure provided in the embodiment of the present application.

[0057] Reference numerals:

[0058] 1. electrode assembly; 101. middle portion; 102. edge portion;

[0059] 11a, isolation film; 111a, base film; 112a, adhesive layer;

[0060] 12a, pole piece; 121a, positive pole piece; 1211, positive electrode current collector; 1212, positive electrode film layer; 122a, negative pole piece;

[0061] 10a, battery cell;

[0062] 2. Shell; 2a. Large surface area; 2b. Edge area; 21. Accommodation cavity;

[0063] 3. Cover body;

[0064] 10. Extrusion structure;

[0065] 11. middle extrusion part; 110. second extrusion surface; 111. flexible part; 112. plate body; 113. slider; 1131. boss; 1132. main body;

[0066] 12, edge extrusion portion; 120, first extrusion surface; 121, rigid portion; 122, first frame; 1221, first through hole; 1222, slide groove; 124, second frame; 125, second through hole;

[0067] 13. groove; 131. notch;

[0068] 100. Extrusion jig;

[0069] 20. Substrate. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0071] In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0072] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0073] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0074] The terms "comprises," "includes," or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0075] In the description of the embodiments of the present application, words such as "example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "example" or "for example" in the embodiments of the present application is not to be interpreted as being more preferred or having more advantages than another embodiment or design. The use of words such as "example" or "for example" is intended to present relative concepts in a clear manner.

[0076] To facilitate understanding of the scheme of the present application, the spline curves and arrows used in the drawings are explained here: the components indicated by the spline curves without arrows are solid components, that is, components with solid structures; the components indicated by the spline curves with arrows are virtual components, that is, components without solid structures.

[0077] First, see Figures 1 to 10 The embodiment of the present application provides an electrode assembly 1. The electrode assembly 1 is also called a core pack, and the electrode assembly 1 is a core component constituting a battery cell 10a (also called a battery cell).

[0078] Specifically, the electrode assembly 1 includes a stacked separator 11a and a pole piece 12a, that is, the separator 11a and the pole piece 12a are stacked. More specifically, the pole piece 12a includes a positive pole piece 121a and a negative pole piece 122a, and the positive pole piece 121a, the negative pole piece 122a and the separator 11a are stacked, wherein the separator 11a is located between the positive pole piece 121a and the negative pole piece 122a to separate the positive pole piece 121a and the negative pole piece 122a, and prevent the positive pole piece 121a and the negative pole piece 122a from directly contacting each other and causing a short circuit. The number of separators 11a in the electrode assembly 1 can be one or more, the number of positive pole pieces 121a can be one or more, and the number of negative pole pieces 122a can be one or more.

[0079] The electrode assembly 1 may be a laminated structure or a wound structure.

[0080] When the electrode assembly 1 is a laminated structure, the isolation membrane 11a and the pole piece 12a in the electrode assembly 1 are laminated layer by layer. As an example, the number of isolation membranes 11a in the electrode assembly 1 is 1, the number of pole pieces 12a is multiple, and the isolation membrane 11a is continuously bent in a "Z" shape to be stacked layer by layer with the pole piece 12a. As an example, the isolation membrane 11a in the electrode assembly 1 is a separate membrane, the number of isolation membranes 11a is multiple, the number of pole pieces 12a is multiple, and the electrode assembly 1 is obtained by laminating in the manner of one layer of isolation membrane 11a, one layer of pole piece 12a (specifically, the positive pole piece 121a), one layer of isolation membrane 11a, and one layer of pole piece 12a (specifically, the negative pole piece 122a).

[0081] When the electrode assembly 1 is a winding structure, the separator 11a and the pole piece 12a are stacked and wound. When manufacturing the electrode assembly 1 with a winding structure, the separator 11a and the pole piece 12a are first stacked and arranged in sequence and then wound together.

[0082] The electrode assembly 1 has a middle portion 101 and an edge portion 102, wherein the middle portion 101 refers to the portion constituting the middle area of ​​the electrode assembly 1, and the edge portion 102 refers to the portion constituting the edge area of ​​the electrode assembly 1. In order to more clearly explain the middle portion 101 and the edge portion 102, an explanation is given from the projection relationship between the middle portion 101 and the edge portion 102. When projected along the thickness direction of the electrode assembly 1, the orthographic projection of the edge portion 102 surrounds the orthographic projection of the middle portion 101. It can be understood that in the thickness direction of the electrode assembly 1, the orthographic projection of the edge portion 102 is annular. Optionally, the middle portion 101 and the edge portion 102 are arranged adjacent to each other, and the orthographic projection of the edge portion 102 and the orthographic projection of the middle portion 101 in the thickness direction of the electrode assembly 1 are also adjacent to each other. In the thickness direction of the electrode assembly 1, the isolation membrane 11a and the pole piece 12a still satisfy the relationship of stacking.

[0083] As an example, see Figure 1 , Figure 1 Schematic diagram of the top view of the electrode assembly 1 along the thickness direction of the electrode assembly 1. The solid line in the figure is the boundary line of the electrode assembly 1, and the dotted line in the figure is the boundary line between the middle part 101 and the edge part 102. The area within the dotted line is the middle part 101, and the area between the dotted line and the solid line is the edge part 102, wherein the middle part 101 is square and the edge part 102 is frame-shaped. Of course, in other embodiments, the middle part 101 can also be rectangular, diamond, circular, triangular or other shapes. Optionally, in Figure 1 In the figure, the middle portion 101 has a shape that is a proportionally reduced shape of the boundary line of the electrode assembly 1 , and the geometric center of the middle portion 101 coincides with the geometric center of the electrode assembly 1 .

[0084] As an example, see Figure 2 , Figure 2 The middle dotted line shows the boundary between the middle portion 101 and the edge portion 102 .

[0085] Understandably, see Fig.10 When the electrode assembly 1 is installed in the square housing 2 , the edge portion 102 is closer to the edge region 2 b on the housing 2 than the middle portion 101 .

[0086] Usually, in order to facilitate the installation of the electrode assembly 1 into the shell 2, the electrode assembly 1 is squeezed during the preparation process to achieve shaping, and during the squeezing process, the stacked isolation membrane 11a and the pole piece 12a will be deformed and further combined together. Generally, the tighter the isolation membrane 11a and the pole piece 12a are combined, the greater the bonding force, and the greater the peeling force required to separate the isolation membrane 11a from the pole piece 12a, and vice versa. The tighter the isolation membrane 11a and the pole piece 12a are combined, the greater the deformation of the isolation membrane 11a and the pole piece 12a. In this way, when the electrode assembly 1 is squeezed, the greater the pressure on the isolation membrane 11a and the pole piece 12a, which will reduce the porosity in the electrode assembly 1, shorten the diffusion distance of lithium ions, and reduce the internal resistance of the electrode assembly 1.

[0087] Since the separator 11a and the pole piece 12a in the electrode assembly 1 are stacked, the middle portion 101 includes the separator 11a and the pole piece 12a, and the edge portion 102 also includes the separator 11a and the pole piece 12a. The peeling force between the separator 11a and the pole piece 12a on the middle portion 101 is F1; the peeling force between the separator 11a and the pole piece 12a on the edge portion 102 is F2; ​​wherein F1<F2. The peeling force here may refer to the peeling force between the separator 11a and the positive pole piece 121a, or the peeling force between the separator 11a and the negative pole piece 122a.

[0088] That is to say, the bonding force between the separator 11a and the pole piece 12a on the edge portion 102 is greater than the bonding force between the separator 11a and the pole piece 12a on the middle portion 101, and the bonding between the separator 11a and the pole piece 12a on the edge portion 102 is tighter than the bonding between the separator 11a and the pole piece 12a on the middle portion 101. It can be known that the porosity of the middle portion 101 is greater than the porosity of the edge portion 102. Usually, when the electrode assembly 1 is applied to the battery cell 10a, the electrode assembly 1 is immersed in the electrolyte, and the edge portion 102 is more easily infiltrated by the electrolyte than the middle portion 101. By increasing the porosity of the middle portion 101, the rate at which the middle portion 101 is infiltrated by the electrolyte can be increased.

[0089] In the embodiment of the present application, since the squeezing force on the middle portion 101 of the electrode assembly 1 is greater than the squeezing force on the edge portion 102 of the electrode assembly 1 during the preparation process of the electrode assembly 1, not only the peeling force between the isolation film 11a and the pole piece 12a on the middle portion 101 is smaller than the peeling force between the isolation film 11a and the pole piece 12a on the edge portion 102, but also the porosity of the middle portion 101 of the electrode assembly 1 is greater than the porosity of the edge portion 102. In this way, when the electrode assembly 1 is applied to the battery cell 10a, the rate at which the middle portion 101 of the electrode assembly 1 is infiltrated with the electrolyte is increased, thereby helping to reduce the risk of lithium deposition in the middle portion 101. In addition, since the SEI film reconstruction and proliferation in the middle portion 101 are greater than those in the edge portion 102 during the circulation process of the electrode assembly 1, the porosity of the middle portion 101 is made greater than that of the edge portion 102 through extrusion, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium deposition in the middle portion 101.

[0090] In addition, when the electrode assembly 1 is applied to a battery cell 10a, the electrode assembly 1 is loaded in the shell 2, and the edge portion 102 of the electrode assembly 1 corresponds to the edge area 2b on the shell 2, and the middle portion 101 of the electrode assembly 1 corresponds to the large surface area 2a of the shell 2. During the cycle of the electrode assembly 1, the middle portion 101 expands more than the edge portion 102, and fits tightly with the shell 2; while the edge portion 102 expands less during the cycle, and the edge area 2b of the shell 2 itself has a stronger ability to resist deformation, so that the edge portion 102 can also fit tightly with the shell 2; therefore, the degree to which the electrode assembly 1 as a whole is constrained by the shell 2 is almost the same, reducing the risk of lithium deposition failure of the electrode assembly 1 during the cycle.

[0091] 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 greater the ratio of F1 to F2, and the smaller the porosity difference between the middle part 101 and the edge part 102, so that the risk of expansion and lithium precipitation in the middle part 101 is difficult to reduce; and the smaller F1 or the larger F2, the smaller the ratio of F1 to F2, the greater the porosity difference between the middle part 101 and the edge part 102, which is conducive to reducing the risk of lithium precipitation in the middle part 101, but F1 is too small, which will cause the middle part 101 to be too loose, and it is difficult to achieve the effect of shaping, which will affect the electrode assembly 1 to be loaded into the shell 2, and will affect the internal resistance of the electrode assembly 1, especially in the middle and late stages of the cycle, the gap between the pole piece 12a and the separator 11a increases, and lithium ions are difficult to pass through, but there is a higher risk of lithium precipitation; F2 is too large, which will cause the porosity of the edge part 102 to be too small, affecting the effect of the edge part 102 infiltrating the electrolyte, thereby increasing the risk of lithium precipitation in the edge part 102. By controlling the ratio of F1 to F2 to 0.3-0.9, the porosity difference between the middle portion 101 and the edge portion 102 is controlled, thereby making the overall electrolyte infiltration effect of the electrode assembly 1 more consistent, thereby reducing the risk of lithium deposition in local areas.

[0092] In some embodiments, F1 is 0.1N to 0.2N. Generally, the larger the F1, the smaller the porosity of the middle portion 101, and the greater the risk of lithium deposition. However, if F1 is too small, it will affect the shaping effect of the electrode assembly 1 and the internal resistance of the electrode assembly 1. By controlling the peeling force between the isolation film 11a and the pole piece 12a on the middle portion 101 to 0.1N to 0.2N, the electrode assembly 1 can have both better shaping effect and lower internal resistance and reduce the risk of lithium deposition in local areas. As an example, F1 is 0.1N, 0.11N, 0.12N, 0.13N, 0.14N, 0.15N, 0.16N, 0.17N, 0.18N, 0.19N or 0.2N.

[0093] In some embodiments, F2 is 0.2N to 0.3N. Generally, the larger the F2, the smaller the porosity of the edge portion 102, and the greater the risk of lithium deposition. However, if F2 is too small, it will affect the shaping effect of the electrode assembly 1 and the internal resistance of the electrode assembly 1. By controlling the peeling force between the isolation film 11a and the pole piece 12a on the edge portion 102 to 0.2N to 0.3N, the electrode assembly 1 can have both better shaping effect and lower internal resistance and reduce the risk of lithium deposition in local areas. As an example, F2 is 0.2N, 0.21N, 0.22N, 0.23N, 0.24N, 0.25N, 0.26N, 0.27N, 0.28N, 0.29N or 0.3N.

[0094] In some embodiments, along the thickness direction of the electrode assembly 1, the percentage of the orthogonal projection area of ​​the middle portion 101 to the orthogonal projection area of ​​the electrode assembly 1 is 20% to 80%. The larger the middle portion 101 is, the larger the proportion of the orthogonal projection area of ​​the middle portion 101 in the thickness direction of the electrode assembly 1, and the larger the middle portion 101 is, the better the effect of the electrode assembly 1 being infiltrated with the electrolyte as a whole, but the internal resistance is easy to increase. Usually, the percentage of the orthogonal projection area of ​​the middle portion 101 to the orthogonal projection area of ​​the electrode assembly 1 is controlled to be 20% to 80%, so that the electrode assembly 1 can have both better electrolyte infiltration effect and shaping effect, and lower internal resistance. Taking the thickness direction of the electrode assembly 1 as the first direction, projecting along the first direction, the orthogonal projection of the middle portion 101 is adjacent to the orthogonal projection of the edge portion 102, and the ratio of the area of ​​the orthogonal projection of the middle portion 101 to the area of ​​the orthogonal projection of the electrode assembly 1 is 20%, 30%, 40%, 50%, 60%, 70% or 80%.

[0095] 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. Usually, the thickness of the electrode assembly 1 will decrease to a certain extent during the extrusion process of the electrode assembly 1. Since the force of extrusion of the middle portion 101 is different from the force of extrusion of the edge portion 102, there will be a difference in the thickness of the two. Since the force of extrusion of the edge portion 102 is greater, the edge portion 102 is more easily compressed, has a smaller thickness, and has a smaller porosity, while the force of extrusion of the middle portion 101 is relatively small, the thickness of the middle portion 101 is larger, and the porosity is also larger, so that the middle portion 101 is not easy to precipitate lithium.

[0096] In some embodiments, see Figure 1 , taking the X direction as the width direction of the electrode assembly 1, in the X direction, the width W of the electrode assembly 1 is 150 mm to 180 mm. As an example, L is 150 mm, 155 mm, 160 mm, 165 mm, 170 mm, 175 mm or 180 mm.

[0097] In some embodiments, see Figure 1 , taking the Y direction as the length direction of the electrode assembly 1, in the Y direction, the length L of the electrode assembly 1 is 150 mm to 180 mm. As an example, W is 150 mm, 155 mm, 160 mm, 165 mm, 170 mm, 175 mm or 180 mm. The length L of the electrode assembly 1 here does not include the size of the tab area.

[0098] In some embodiments, see Figure 2, with the Z direction being the thickness direction of the electrode assembly 1 , the thickness D of the electrode assembly 1 is 10 mm to 25 mm. As an example, D is 10 mm, 13 mm, 15 mm, 18 mm, 20 mm, 23 mm or 25 mm.

[0099] In some embodiments, the aspect ratio of the electrode assembly 1 is 0.8 to 1.2. As an example, the aspect ratio of the electrode assembly 1 is 0.8, 0.9, 1.0, 1.1 or 1.2. When the length L and width W of the electrode assembly 1 are equal, the electrode assembly 1 is square.

[0100] In some embodiments, see Figure 4 , the isolation film 11a includes a rubber-coated diaphragm. By setting the isolation film 11a to include a rubber-coated diaphragm, it is convenient to adjust the peeling force between the middle part 101 and the edge part 102 of the electrode assembly 1 by extrusion when making the electrode assembly 1. Specifically, the rubber-coated diaphragm includes a base film 111a and a rubber-coated layer 112a, and the rubber-coated layer 112a is located on at least one side surface of the base film 111a. The base film 111a has two side surfaces opposite to each other in the thickness direction of the base film 111a. The rubber-coated layer 112a may be provided on one side surface of the base film 111a, or the rubber-coated layer 112a may be provided on both sides of the base film 111a. As an example, the material of the base film 111a is polypropylene (PP) or polyethylene (PE). As an example, the rubber-coated layer 112a contains polyvinylidene fluoride (PVDF).

[0101] 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.

[0102] 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.

[0103] In some embodiments, see Figure 5 The positive electrode sheet 121a includes a positive electrode current collector 1211 and a positive electrode film layer 1212, and the positive electrode film layer 1212 is disposed on the positive electrode current collector 1211. The positive electrode film layer 1212 includes a positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate. In addition, the positive electrode film layer 1212 may also include a conductive agent, a binder, a dispersant, and the like.

[0104] Second, see Figure 6, the present application embodiment provides a method for preparing an electrode assembly 1, comprising:

[0105] S1. Stacking the separator 11a and the electrode piece 12a together to obtain an electrode assembly 1, wherein the electrode assembly 1 has a middle portion 101 and an edge portion 102, and along the thickness direction of the electrode assembly 1, the orthographic projection of the edge portion 102 surrounds the orthographic projection of the middle portion 101;

[0106] S2. Along the thickness direction of the electrode assembly 1, the middle portion 101 is subjected to a first extrusion treatment at a first pressure P1, and the edge portion 102 is subjected to a second extrusion treatment at a second pressure P2; wherein the first pressure P1 is less than or equal to the second pressure P2.

[0107] 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 steps. Here, the first extrusion process and the second extrusion process are performed in steps, and the first extrusion process can be performed on the middle portion 101 first, and then the second extrusion process is performed on the edge portion 102; or the second extrusion process can be performed on the edge portion 102 first, and then the first extrusion process is performed on the middle portion 101.

[0108] During the first extrusion process of the middle portion 101, the first pressure P1 may be a constant force or a variable force. Similarly, during the second extrusion process of the edge portion 102, the second pressure P2 may be a constant force or a variable force. The first pressure P1 may be less than or equal to the second pressure P2, and the first pressure P1 may be always less than the second pressure P2 during the first extrusion process, or the first pressure P1 may be less than the second pressure P2 in a portion of the first extrusion process.

[0109] The preparation method of the electrode assembly 1 provided in the embodiment of the present application performs different degrees of extrusion on the middle portion 101 and the edge portion 102 of the electrode assembly 1 along the thickness direction of the electrode assembly 1 (that is, the electrode assembly 1 is unevenly extruded), and a smaller extrusion force is applied to the middle portion 101 than to the edge portion 102, so that the middle portion 101 is more fluffy than the edge portion 102, that is, the porosity of the middle portion 101 is higher, so that when the electrode assembly 1 is applied to the battery cell 10a, the rate at which the middle portion 101 of the electrode assembly 1 is infiltrated with the electrolyte is increased, thereby helping to reduce the risk of lithium deposition in the middle portion 101; in addition, since the SEI film reconstruction and proliferation of the middle portion 101 are greater than those of the edge portion 102 during the cycle of the electrode assembly 1, the porosity of the middle portion 101 is made greater than that of the edge portion 102 through extrusion, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium deposition in the middle portion 101.

[0110] In addition, when the electrode assembly 1 is applied to a battery cell 10a, the electrode assembly 1 is loaded in the shell 2, and the edge portion 102 of the electrode assembly 1 corresponds to the edge area on the shell 2, and the middle portion 101 of the electrode assembly 1 corresponds to the large surface area of ​​the shell 2. During the cycle of the electrode assembly 1, the middle portion 101 expands more than the edge portion 102, and fits tightly with the shell 2; while the edge portion 102 expands less during the cycle, and the edge area of ​​the shell 2 itself has a stronger ability to resist deformation, so that the edge portion 102 can also fit tightly with the shell 2; therefore, the degree to which the electrode assembly 1 as a whole is constrained by the shell 2 is almost the same, reducing the risk of lithium deposition failure of the electrode assembly 1 during the cycle.

[0111] In summary, the embodiment of the present application performs uneven extrusion on the electrode assembly 1 so that the porosity of the middle portion 101 is greater than the porosity of the edge portion 102. In this way, during the cycle of the electrode assembly 1, the outward expansion of the volume of the middle portion 101 can be alleviated and the extrusion of the middle portion 101 by the shell 2 can be increased, so that the middle portion 101 has a certain rate of infiltration of the electrolyte, thereby reducing the risk of lithium plating failure of the electrode assembly 1 during the cycle and improving the cycle performance of the battery cell 10a.

[0112] In some embodiments, the extrusion time of the first extrusion treatment is the first time t1, and the extrusion time of the second extrusion treatment is the second time t2, wherein the first time t1 is less than or equal to the second time t2, and the product S1 of the first pressure P1 and the first time t1 is less than the product S2 of the second pressure P2 and the second time t2.

[0113] It can be understood that 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 multiple possibilities for the relationship between the first pressure P1 and the first time t1 during the first extrusion treatment and the second pressure P2 and the second time t2 during the second extrusion treatment: the first pressure P1 is less than the second pressure P2, and the first time t1 is equal to the second time t2; the first pressure P1 is less than the second pressure P2, and the first time t1 is less than the second time t2.

[0114] As an example, see Figure 7 and Figure 8 , the horizontal axis in the coordinate system of the figure represents time t, the vertical axis represents pressure P, and the area S of the shaded area in the figure represents the product of pressure P and time t. Figure 7, 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 equal to the second time t2, and the area S1 is less than the area S2 (the shaded area covered by "+" in the figure represents S1, and the shaded area covered by the slash represents S2, the same below). Please refer to Figure 8 , the first pressure P1 and the second pressure P2 are both constant forces, the first pressure P1 is smaller than the second pressure P2, the first time t1 is smaller than the second time t2, and the area S1 is smaller than the area S2.

[0115] In some embodiments, the first time t1 is less than the second time t2, and specifically, the ratio of the first time t1 to the second time t2 is 0.2 to 0.8. Within this range, the middle portion 101 can have a better electrolyte infiltration effect during the cycle 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.

[0116] In some embodiments, the first pressure P1 is less than the second pressure P2, and specifically, the ratio of the first pressure P1 to the second pressure P2 is 0.2 to 0.8. Within this range, the middle portion 101 can have a better electrolyte infiltration effect during the cycle 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.

[0117] 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 middle portion 101 can have a better electrolyte infiltration effect during the cycle of the electrode assembly 1.

[0118] In some embodiments, the first pressure P1 is 1000N to 5000N. Within this range, the middle portion 101 can have a better electrolyte infiltration effect during the cycle of the electrode assembly 1. As an example, the first pressure P1 is 1000N, 2000N, 3000N, 4000N or 5000N.

[0119] In some embodiments, the first time t1 is 30s to 140s. Within this range, the middle portion 101 can have a better electrolyte infiltration effect during the cycle 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.

[0120] In some embodiments, the second pressure P2 is 3000N to 5000N. Within this range, the edge portion 102 can be well fitted with the shell 2 during the cycle of the electrode assembly 1. As an example, 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.

[0121] In some embodiments, the second time t2 is 120s to 180s. Within this range, the edge portion 102 can be well fitted with the housing 2 during the cycle 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.

[0122] In some embodiments, both the first extrusion process and the second extrusion process are hot pressing processes, and the hot pressing temperature of the hot pressing process is 80°C to 100°C. That is, the middle part 101 is also heated during the first extrusion process, and the edge part 102 is also heated during the second extrusion process. Specifically, the middle part 101 is heated at a first temperature during the first extrusion process, and the edge part 102 is heated at a second temperature during the second extrusion process. The first temperature and the second temperature are also called hot pressing temperatures, wherein 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 temperature and the second temperature may be equal or unequal. Usually, the size of the hot pressing temperature is related to the isolation film 11a. By setting the hot pressing temperature to 80°C to 100°C, the isolation film 11a can be deformed by heat during the hot pressing process to better combine with the pole piece 12a, but the isolation film 11a will not decompose. As an example, the hot pressing temperature is 80°C, 85°C, 90°C, 95°C or 100°C.

[0123] In some embodiments, an extrusion jig 200 is used to extrude the electrode assembly 1. Specifically, the extrusion jig 200 includes an extrusion structure 20, and the extrusion structure 20 is used to extrude the electrode assembly 1. For a description of the extrusion jig 200 and the extrusion structure 20, please refer to the following.

[0124] 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.

[0125] Third, see Fig. 9 , the embodiment of the present application provides a battery cell 10a, comprising:

[0126] The housing 2 has a receiving cavity 21, and the surface of the housing 2 is divided into a large area 2a and an edge area 2b; along the thickness direction of the housing 2, the orthographic projection of the edge area 2b surrounds the orthographic projection of the large area 2a;

[0127] The electrode assembly 1 is disposed in the accommodating cavity 21, the middle portion 101 corresponds to the large surface area 2a, and the edge portion 102 corresponds to the edge area 2b. The electrode assembly 1 is the above-mentioned electrode assembly 1 or the electrode assembly 1 prepared by the above-mentioned preparation method.

[0128] Usually, the division of the edges and large areas of the battery cell 10a is mainly based on the geometric shape and design of the battery cell 10a. Fig.10 Taking the square battery cell 10a as an example, the shell 2 usually has multiple surfaces, including side surfaces, a top surface and a bottom surface. The side surfaces of the battery can be divided into a first side surface and a second side surface opposite to each other along the Z axis. The areas of these two side surfaces are larger than those of other surfaces. Therefore, these two surfaces are large surfaces of the shell 2, and the other two sides, the third side surface and the fourth side surface are considered small surfaces.

[0129] The surface of the housing 2 is divided into a large area 2a and an edge area 2b, wherein the large area 2a is located on the large surface and close to the center of the large surface. Fig.10 As shown by the dotted line on the middle shell 2 , the area within the dotted line is the large surface area 2 a , and the area outside the dotted line is the edge area 2 b , which is close to the edge on the shell 2 .

[0130] Please continue to see Fig.10 As shown by the dotted line on the electrode assembly 1 in the figure, the area within the dotted line is the middle portion 101, and the area outside the dotted line is the edge portion 102. The middle portion 101 corresponds to the large surface area 2a, and the edge portion 102 corresponds to the edge area 2b.

[0131] In detail, the battery cell 10a is a square battery, and the housing 2 is rectangular, for example, square. As an example, the housing 2 is an aluminum shell.

[0132] The battery cell 10a provided in the embodiment of the present application is not prone to lithium plating failure in the electrode assembly 1 during the cycle process, and the cycle performance of the battery cell 10a is improved.

[0133] In some embodiments, the battery cell 10 a further includes a cover 3 , which is disposed on the housing 2 to close the accommodating cavity 21 .

[0134] For the fourth aspect, please see Figures 11 to 17 , an embodiment of the present application provides an extrusion structure 10, which is used to extrude an electrode assembly 1.

[0135] Here, the electrode assembly 1 is also called the core pack, which is the core component of the battery cell (also called a battery cell). Usually, the electrode assembly 1 includes a positive electrode sheet 11, a negative electrode sheet 12a and a separator 13. The separator 13 is located between the positive electrode sheet 11 and the negative electrode sheet 12a to separate the positive electrode sheet 11 and the negative electrode sheet 12a to prevent the positive electrode sheet 11 and the negative electrode sheet 12a from directly contacting each other and causing a short circuit. Here, the electrode assembly 1 can be a laminated structure or a winding structure. The extrusion structure 10 is used to extrude the electrode assembly 1. On the one hand, it is to shape the electrode assembly 1 to facilitate the installation of the electrode assembly 1 into the shell to obtain a battery cell; on the other hand, it is to make the separator 13 fit closely with the positive electrode sheet 11 and the negative electrode sheet 12a, shorten the diffusion distance of lithium ions, and reduce the internal resistance of the electrode assembly 1. Optionally, the extrusion structure 10 is also used to heat the electrode assembly 1, that is, to achieve hot pressing of the electrode assembly 1. Hot pressing can eliminate wrinkles and air in the isolation film 13, so that the isolation film 13 fits more closely with the positive electrode sheet 11 and the negative electrode sheet 12a.

[0136] Typically, see Figure 1 , Figure 2 and Fig.10 , with the dotted 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 arranged around the edge of the middle portion 101. When the electrode assembly 1 is placed in a square shell, the middle portion 101 corresponds to the large surface area 2a of the shell 2, and the edge portion 102 corresponds to the edge area 2b of the shell 2. As an example, taking the thickness direction of the electrode assembly 1 as the first direction, along the first direction projection, the orthographic projection of the middle portion 101 is adjacent to the orthographic projection of the edge portion 102, and the ratio of the orthographic projection area of ​​the middle portion 101 to the orthographic projection area 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 sheet 11, the separator 13 and the negative electrode sheet 12a are stacked.

[0137] Specifically, the extrusion structure 10 includes a middle extrusion portion 11 and an edge extrusion portion 12 , wherein the edge extrusion portion 12 is disposed around the edge of the middle extrusion portion 11 .

[0138] When the extrusion structure 10 extrudes the electrode assembly 1, the middle extrusion portion 11 corresponds to the middle portion 101 of the electrode assembly 1, and the edge extrusion portion 12 corresponds to the edge portion 102 of the electrode assembly 1. When the extrusion structure 10 extrudes the electrode assembly 1, the middle extrusion portion 11 is used to apply a first extrusion force G1 to the middle portion 101, and the edge extrusion portion 12 is used to apply a second extrusion force G2 to the edge portion 102, wherein G2≥G1, G1≥0, and G2>0. In addition, G1<G2 during at least part of the period when the extrusion structure 10 extrudes the electrode assembly 1.

[0139] It can be understood that 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 are integrally formed, or they can be indirectly connected together, or they can be independent of each other.

[0140] When the extrusion structure 10 extrude the electrode assembly 1, the magnitude of the first extrusion force G1 may be fixed or variable, and the magnitude of the second extrusion force G2 may be fixed or variable, but in any case, the second extrusion force G2 must be greater than the first extrusion force G1, or the second extrusion force G2 is equal to the first extrusion force G1, that is, G2≥G1. Where G2>0, which means that when the extrusion structure 10 extrude 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, that is, the edge extrusion portion 12 always extrude the electrode assembly 1. G1≥0, which means that when the extrusion structure 10 extrude the electrode assembly 1, the middle extrusion portion 11 may extrude the middle portion 101 of the electrode assembly 1, or may not extrude the electrode assembly 1. When the middle extrusion portion 11 extrudes the electrode assembly 1, G1>0, and when the middle extrusion portion 11 does not extrude the electrode assembly 1, G1=0. And G1<G2 during at least part of the time period when the extrusion structure 10 extrudes the electrode assembly 1. It can be that G1<G2 during the whole time period (i.e. the whole process) when the extrusion structure 10 extrudes the electrode assembly 1, or it can be that G1<G2 during part of the time period when the extrusion structure 10 extrudes the electrode assembly 1.

[0141] As an example, during 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 portion 12 on the edge portion 102 of the electrode assembly 1 is always greater than the extrusion force of the middle extrusion portion 11 on the middle portion 101 of the electrode assembly 1 .

[0142] As an example, during the whole process of the extrusion structure 10 extruding the electrode assembly 1 , G2 > G1 = 0, that is, only the edge extrusion portion 12 extrudes the edge portion 102 of the electrode assembly 1 , and the middle extrusion portion 11 never extrudes the electrode assembly 1 .

[0143] The extrusion structure 10 provided in the embodiment of the present application 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 part of the extrusion process, the middle extrusion portion 11 does not apply an extrusion force to the middle portion 101 or the extrusion force is less than the extrusion force of the edge extrusion portion 12 on the edge portion 102, so that the porosity of the middle portion 101 of the electrode assembly 1 extruded by the extrusion structure 10 is greater than the porosity of the edge portion 102. In this way, when the electrode assembly 1 is applied to a battery cell, the rate at which the middle portion 101 of the electrode assembly 1 is infiltrated into the electrolyte is greater than that of the edge portion 102 of the electrode assembly 1, thereby reducing the risk of lithium deposition in the middle portion 101. In addition, since the risk of volume expansion of the middle portion 101 is greater than that of the edge portion 102 during the circulation of the electrode assembly 1, the porosity of the middle portion 101 is made greater than that of the edge portion 102 by extrusion, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium deposition in the middle portion 101.

[0144] In some embodiments, see Figures 11 to 15 The extrusion structure 10 includes a middle extrusion portion 11 and an edge extrusion portion 12, wherein the edge extrusion portion 12 is arranged around the edge of the middle extrusion portion 11. A first extrusion surface 120 is formed on the edge extrusion portion 12, and the first extrusion surface 120 is used to extrude the edge portion 102; a second extrusion surface 110 is formed on the middle extrusion portion 11, and the second extrusion surface 110 is used to extrude the middle portion 101. In addition, when the extrusion structure 10 extrude the electrode assembly 1, the second extrusion surface 110 is configured to form a step difference with 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.

[0145] It can be understood that a first extrusion surface 120 is formed on the edge extrusion portion 12 , and a second extrusion surface 110 is formed on the middle extrusion portion 11 , and the edge extrusion portion 12 and the middle extrusion portion 11 are both solid structures.

[0146] It should be noted here that the first extrusion surface 120 can be independently a plane or a curved surface, and the second extrusion surface 110 can be independently a plane or a curved surface. 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 is a winding structure, the outer surface of the middle portion 101 is a plane, the second extrusion surface 110 is also a plane, the outer surface of the edge portion 102 is an arc surface, and the first extrusion surface 120 is also an arc surface; or the electrode assembly 1 is a winding structure, the outer surfaces of the middle portion 101 and the edge portion 102 are both planes, and the first extrusion surface 120 and the second extrusion surface 110 are both planes.

[0147] During at least part of the time period when the extrusion structure 10 extrudes the electrode assembly 1, the second extrusion surface 110 and the first extrusion surface 120 form a step difference, where the formation of the step difference means that the second extrusion surface 110 and the first extrusion surface 120 are not arranged coplanarly. Here, the second extrusion surface 110 and the first extrusion surface 120 form a step difference, which may be that the second extrusion surface 110 and the first extrusion surface 120 always maintain a step difference during the entire time period (i.e., the entire process) when the extrusion structure 10 extrudes the electrode assembly 1, or there may be a step difference between the second extrusion surface 110 and the first extrusion surface 120 during part of the time period when the extrusion structure 10 extrudes the electrode assembly 1.

[0148] In addition, when the second extrusion surface 110 and the first extrusion surface 120 are not arranged in the same plane, the second extrusion surface 110 is farther away from the central axis of the electrode assembly 1 than the first extrusion surface 120, that is, 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 middle extrusion portion 11 and the electrode assembly 1 (i.e., the first extrusion force G1) will decrease, and the following different situations may exist: the middle extrusion portion 11 continues to squeeze the middle portion 101 of the electrode assembly 1, but the first extrusion force G1 becomes smaller, or the second extrusion surface 110 is separated from the electrode assembly 1, and the first extrusion force G1 is zero. Here, the central axis of the electrode assembly 1 is perpendicular to the first direction.

[0149] During the 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 maintains contact with the electrode assembly 1. It can be understood that during the process of the extrusion structure 10 extruding the electrode assembly 1, the first extrusion surface 120 always maintains contact with the edge portion 102 of the electrode assembly 1, while the second extrusion surface 110 is in contact with or separated from the middle portion 101 of the electrode assembly 1. At this time, the first extrusion force G1 of the middle extrusion portion 11 on the middle portion 101 of the electrode assembly 1 is reduced or disappears.

[0150] In order to more clearly illustrate the extrusion of the electrode assembly 1 by the first extrusion surface 120 and the second extrusion surface 110 during the extrusion of the electrode assembly 1 by the extrusion structure 10, an example is given below. The process of the extrusion of the electrode assembly 1 by the extrusion structure 10 is subdivided 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 process of T1 to T3, 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, G2 remains unchanged, and the magnitude of G2 is always G20; during the process of T1 to T3, 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 T1, the magnitude of G1 is G11, during T2, the magnitude of G1 is G12, and during T3, the magnitude of G1 is G13.

[0151] As an example, during the process from T1 to T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is always maintained at D1, then 0<G11=G12=G13<G20. In other words, the second extrusion surface 110 extrudes the middle portion 101 of the electrode assembly 1 for the same time as the first extrusion surface 120 extrudes the edge portion 102 of the electrode assembly 1, but the extrusion force is smaller.

[0152] As an example, during T1 and T2, the second extrusion surface 110 is coplanar with the first extrusion surface 120, and during T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D3, then 0<G13<G12=G11=G20. That is, the second extrusion surface 110 extrudes the middle portion 101 of the electrode assembly 1 for the same time as the first extrusion surface 120 extrudes the edge portion 102 of the electrode assembly 1, but the extrusion force is reduced in the third period T3.

[0153] As an example, during T1 and T3, the second extrusion surface 110 is coplanar with the first extrusion surface 120, and during T2, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D2, then 0<G12<G13=G11=G20. That is, the second extrusion surface 110 extrudes the middle portion 101 of the electrode assembly 1 for the same time as the first extrusion surface 120 extrudes the edge portion 102 of the electrode assembly 1, but the extrusion force is reduced in the second period T2.

[0154] As an example, during T2 and T3, the second extrusion surface 110 is coplanar with the first extrusion surface 120, and during T1, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D1, then 0<G11<G12=G13=G20. That is, the second extrusion surface 110 extrudes the middle portion 101 of the electrode assembly 1 for the same time as the first extrusion surface 120 extrudes the edge portion 102 of the electrode assembly 1, but the extrusion force is reduced in the first period T1.

[0155] As an example, during T1, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D1, during T2, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D2, and during T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D3, D1<D2<D3, then 0<G13<G12<G11<G20. In other words, the second extrusion surface 110 extrudes the middle portion 101 of the electrode assembly 1 for the same time as the first extrusion surface 120 extrudes the edge portion 102 of the electrode assembly 1, but the extrusion force decreases successively in each time period.

[0156] As an example, during T1 and T2, the second extrusion surface 110 is coplanar with the first extrusion surface 120, and during T3, the step difference between the second extrusion surface 110 and the first extrusion surface 120 is D4, and the second extrusion surface 110 is separated from the electrode assembly 1, then 0=G13<G12=G11=G20. In other words, 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 reduced to zero in the third time period T3. In other words, the extrusion force of the second extrusion surface 110 on the middle part 101 of the electrode assembly 1 is the same as the extrusion force of the first extrusion surface 120 on the edge part 102 of the electrode assembly 1, but the extrusion time is shorter.

[0157] In summary, the extrusion structure 10 provided in the embodiment of the present application includes an intermediate extrusion portion 11 and an edge extrusion portion 12, and a first extrusion surface 120 for extruding the edge portion 102 of the electrode assembly 1 is formed on the edge extrusion portion 12, and a second extrusion surface 110 for extruding the middle portion 101 of the electrode assembly 1 is formed on the intermediate extrusion portion 11, and when the extrusion structure 10 extrudes the electrode assembly 1, a step 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. In this way, in the process of the extrusion structure 10 extruding the electrode assembly 1, in at least part of the time period, the extrusion force of the intermediate 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), so that the porosity of the middle portion 101 of the electrode assembly 1 extruded by the extrusion structure 10 is greater than the porosity of the edge portion 102. In this way, when the electrode assembly 1 is applied to a battery cell, the rate at which the middle portion 101 of the electrode assembly 1 is infiltrated with the electrolyte is greater than that of the edge portion 102 of the electrode assembly 1, thereby reducing the risk of lithium deposition in the middle portion 101; in addition, since the middle portion 101 is at a greater risk of volume expansion than the edge portion 102 during the circulation of the electrode assembly 1, the porosity of the middle portion 101 is made greater than the porosity of the edge portion 102 through extrusion, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium deposition in the middle portion 101.

[0158] In some embodiments, see Fig.11 , the edge extrusion portion 12 is fixedly connected to the middle extrusion portion 11 and defines a groove 13 together, 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 notch 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.

[0159] As an example, the edge extrusion portion 12 is a first frame body 122, which has a first through hole 1221. The middle extrusion portion 11 is a plate body 112. The plate body 112 is located on one side of the first frame body 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 a notch 131 of the groove 13. The plate body 112 is fixedly connected to the first frame body 122 to form an extrusion structure 10.

[0160] When the extrusion structure 10 is used to extrude the electrode assembly 1 , the second extrusion force G2 can always be kept greater than the first extrusion force G1 , so that the porosity of the middle portion 101 is greater than the porosity of the edge portion 102 .

[0161] 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 of the electrode assembly 1, affecting the assembly of the electrode assembly 1 with the shell 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 of any two thereof.

[0162] In some embodiments, see Fig.12 , the edge extrusion portion 12 is a rigid portion 121, 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 used to form a step difference between the second extrusion surface 110 and the first extrusion surface 120, so that the first extrusion force G1 of the middle extrusion portion 11 on the middle portion 101 is smaller than the second extrusion force G2 of the edge extrusion portion 12 on the edge portion 102.

[0163] 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 part, such as a stainless steel plate.

[0164] As an example, the flexible part 111 is a capsule filled with a flowing medium, and the deformation of the capsule can be adjusted by adjusting the amount of the flowing medium in the capsule. In addition, the time for the step difference to be formed can be adjusted by adjusting the timing of filling the flowing medium in the capsule.

[0165] In some embodiments, see Fig.13 and Fig.14, along the thickness direction of the extrusion structure 10, the middle extrusion part 11 is movably arranged relative to the edge extrusion part 12, and the middle extrusion part 11 is used to move in a direction close to or away from the electrode assembly 1 when the extrusion structure 10 extrudes the electrode assembly 1. Since the middle extrusion part 11 can move relative to the edge extrusion part 12 along the thickness direction of the extrusion structure 10, the distance between the second extrusion surface 110 on the middle extrusion part 11 and the first extrusion surface 120 on the edge extrusion part 12 can be adjusted when the extrusion structure 10 extrudes the electrode assembly 1, and a step difference is formed between the second extrusion surface 110 and the first extrusion surface 120 during at least a part of the time period when the extrusion structure 10 extrudes the electrode assembly 1, so that the first extrusion force G1 of the middle extrusion part 11 on the middle part 101 is smaller than the second extrusion force G2 of the edge extrusion part 12 on the edge part 102.

[0166] As an example, the process of extruding the electrode assembly 1 by the extrusion structure 10 is subdivided 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. The second extrusion surface 110 and the first extrusion surface 120 are kept coplanar in the first time period T1 and the second time period T2, and then the middle extrusion portion 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.

[0167] As an example, the process of extruding the electrode assembly 1 by the extrusion structure 10 is subdivided 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 and the second time period T2, a step difference is maintained between the second extrusion surface 110 and the first extrusion surface 120, and then the middle extrusion part 11 is moved toward the direction close to the electrode assembly 1, so that the second extrusion surface 110 and the first extrusion surface 120 are coplanar in the third time period T3.

[0168] As an example, the process of extruding the electrode assembly 1 by the extrusion structure 10 is subdivided into three time periods, which are divided into a first time period T1, a second time period T2 and a third time period T3 from the beginning to the end. In the first time period T1, a step difference is formed between the second extrusion surface 110 and the first extrusion surface 120, and then the middle extrusion portion 11 is moved toward the direction close to 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, and then the middle extrusion portion 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.

[0169] In some embodiments, the extrusion structure 10 further includes a driving member (not shown), which is connected to the middle extrusion portion 11 and is used to drive the middle extrusion portion 11 to move. As an example, the driving member is a push rod motor.

[0170] In some embodiments, see Fig.13 and Fig.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 in the through hole 1221 and is 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 slidably connecting the first frame 122 and the slider 113.

[0171] In some embodiments, see Fig.13 and Fig.14 The inner wall of the first through hole 1221 is partially recessed into the first frame 122 to form a slide groove 1222. The slider 113 includes a boss 1131 and a body 1132. The boss 1131 is convexly arranged on the circumference of the body 1132. The body 1132 is located in the first through hole 1221 and matches the first through hole 1221. One end surface of the body 1132 forms the second extrusion surface 110. The boss 1131 extends into the slide groove 1222 and slidably matches the slide groove 1222. Please continue to refer to Fig.14 When the boss 1131 slides to one end of the slide groove 1222, as shown in the figure, the second extrusion surface 110 is flush with the first extrusion surface 120, that is, the two are coplanar; please continue to refer to Fig.13 When the boss 1131 slides to the other end of the slide groove 1222, as shown in 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 slide groove 1222 is less than the thickness of the first frame 122.

[0172] In some embodiments, see Fig.13 and Fig.14 In the thickness direction of the first frame 122, the thickness of the boss 1131 is smaller than the width of the slide groove 1222, and the distance between the side surface of the boss 1131 away from the second extrusion surface 110 and the second extrusion surface 110 is greater than the width of the slide groove 1222. In this way, when the side surface of the boss 1131 away from the second extrusion surface 110 abuts against the side wall of the slide groove 1222, the main body 1132 can close the notch of the slide groove 1222, reducing the risk of foreign matter entering the slide groove 1222.

[0173] In some embodiments, see Fig.15 and Fig.16 , the distance between the side surface of the boss 1131 close to the second extrusion surface 110 and the end surface of the body 1132 opposite to the second extrusion surface 110 is greater than the width of the slide groove 1222. In this way, when the side surface of the boss 1131 close to the second extrusion surface 110 abuts against the side wall of the slide groove 1222, the body 1132 can close the notch of the slide groove 1222, reducing the risk of foreign matter entering the slide groove 1222.

[0174] 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 0.1-0.4. 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.

[0175] In some embodiments, see Fig.15 , the extrusion structure 10 only includes the edge extrusion portion 12, and the middle extrusion portion 11 is cancelled. Specifically, the edge extrusion portion 12 is a second frame 124 having a second through hole 125, and the second frame 124 is configured to squeeze the edge portion 102 when the extrusion structure 10 squeezes the electrode assembly 1, and the second through hole 125 corresponds to the middle portion 101, that is, the second through hole 125 is used to avoid the middle portion 101. In this case, when the extrusion structure 10 squeezes the electrode assembly 1, only the second frame 124 squeezes the edge portion 102 of the electrode assembly 1, and the squeezing force on the middle portion 101 of the electrode assembly 1 is zero, so that the porosity of the middle portion 101 is greater than the porosity of the edge portion 102. In this way, when the electrode assembly 1 is applied to a battery cell, the rate at which the middle portion 101 of the electrode assembly 1 is infiltrated with the electrolyte is greater than that of the edge portion 102 of the electrode assembly 1, thereby reducing the risk of lithium deposition in the middle portion 101; in addition, since the middle portion 101 is at a greater risk of volume expansion than the edge portion 102 during the circulation of the electrode assembly 1, the porosity of the middle portion 101 is made greater than the porosity of the edge portion 102 through extrusion, which can alleviate the volume expansion of the middle portion 101 to a certain extent and reduce the risk of lithium deposition in the middle portion 101.

[0176] In some embodiments, the extruded structure 10 is used to prepare the electrode assembly 1 provided in the first aspect.

[0177] Also, see Figure 16 to Figure 17 The embodiment of the present application also provides an extrusion jig 100 , comprising any one of the extrusion structures 10 described above.

[0178] In some embodiments, see Fig.16 The number of the extrusion structures 10 in the extrusion jig 100 is two, and the two extrusion structures 10 are disposed face to face. When the extrusion jig 100 is used to extrude the electrode assembly 1, the electrode assembly 1 is located between the two extrusion structures 10 disposed face to face.

[0179] In some embodiments, see Fig.17The number of the extrusion structure 10 in the extrusion jig 100 is one, and the extrusion jig 100 further includes a substrate 20. Optionally, the substrate 20 is a flat plate, and the extrusion structure 10 is disposed face to face with the substrate 20. When the extrusion jig 100 is used to extrude the electrode assembly 1, the electrode assembly 1 is located between the extrusion structure 10 and the substrate 20.

[0180] In some embodiments, the extrusion jig 100 is a hot pressing jig, and during the process of extruding the electrode assembly 1 , at least one of the extrusion structure 10 and the substrate 20 can also heat the electrode assembly 1 .

[0181] In some embodiments, the extrusion jig 100 is used to prepare the electrode assembly 1 provided in the first aspect.

[0182] The following is a description with reference to specific embodiments.

[0183] Example 1

[0184] This embodiment provides a battery cell, and the preparation method of the battery cell is as follows:

[0185] S1. Preparation of positive electrode sheet: According to 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 the ratio of 97.4wt%: 0.5wt%: 0.4wt%: 1.7wt%, mixed with solvent (N-methylpyrrolidone, NMP) to prepare positive electrode slurry, and then coated the positive electrode slurry on both sides of the positive electrode collector (12μm aluminum foil), and cut to obtain positive electrode sheet after drying;

[0186] S2. Preparation of negative electrode sheet: prepare negative electrode slurry according to the negative electrode active material (artificial graphite, referred to as AG): negative electrode conductive agent (conductive graphite, SP): dispersant (carboxymethyl cellulose, CMC): negative electrode binder (styrene butadiene rubber, SBR) at 96.7wt%: 0.6wt%: 1.2wt%: 1.5wt%, then apply the negative electrode slurry on both sides of the negative electrode collector (5μm copper foil), dry and cut to obtain negative electrode sheet;

[0187] S3, core package preparation: stack the separator, positive electrode sheet, separator, and negative electrode sheet layer by layer to obtain a core package. The separator is a double-sided mixed-coated separator, the mixed coating thickness of the double-sided mixed-coated separator is 2μm, the base film thickness is 7μm, and the coating material in the mixed coating 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 orthographic projection area of ​​the middle portion 101 to the orthographic projection area of ​​the core package (hereinafter referred to as the area ratio) is 50%.

[0188] S4. Core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 1000N, and the hot pressing time is 140s; the hot pressing temperature of the edge part 102 is 85°C, 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 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 time ratio) is 0.78.

[0189] S5. Assemble battery cells: pack the hot-pressed core into a square aluminum shell, inject electrolyte (lithium salt comprises LiFSI and LiPF6 in a molar ratio of 1:1, lithium salt concentration is 1 mol / L, solvent comprises ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC and dimethyl carbonate DMC, EC: PC: EMC: DMC = 30:5:25:40), injection coefficient is 3.1, then let stand and form to obtain battery cells.

[0190] Example 2

[0191] The difference from Example 1 is:

[0192] S4: core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 1200N, and the hot pressing time is 140s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0193] Example 3

[0194] The difference from Example 1 is:

[0195] S4: core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 3000N, and the hot pressing time is 85s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0196] Example 4

[0197] The difference from the third embodiment is that the area ratio in S3 is 20%, that is, the middle portion 101 becomes smaller.

[0198] Example 5

[0199] The difference from the third embodiment is that the area ratio in S3 is 80%, that is, the middle part 101 is enlarged.

[0200] Example 6

[0201] The difference from Example 3 is that the lithium iron phosphate in S1 is replaced with lithium manganese iron phosphate (LMFP), and the other parts remain unchanged.

[0202] Example 7

[0203] The difference from Example 3 is that the hot pressing temperature of the middle part 101 in S4 is reduced to 80° C., the hot pressing temperature of the edge part 102 is also reduced to 80° C., and the other parts remain unchanged.

[0204] Example 8

[0205] The difference from Example 3 is that the hot pressing temperature of the middle part 101 in S4 is increased to 90° C., the hot pressing temperature of the edge part 102 is also increased to 90° C., and the other parts remain unchanged.

[0206] Example 9

[0207] The difference from Example 3 is that the hot pressing temperature of the middle part 101 in S4 is increased to 100° C., the hot pressing temperature of the edge part 102 is also increased to 100° C., and the other steps remain unchanged.

[0208] Comparative Example 1

[0209] The difference from Example 3 is:

[0210] S4: core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to the same hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 4000N, and the hot pressing time is 110s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0211] Comparative Example 2

[0212] The difference from Example 3 is:

[0213] S4: hot pressing of the core package: the middle part 101 and the edge part 102 are hot pressed according to the same hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 3000N, and the hot pressing time is 85s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0214] Comparative Example 3

[0215] The difference from Example 3 is:

[0216] S4: hot pressing of the core package: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 4000N, and the hot pressing time is 85s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0217] Comparative Example 4

[0218] The difference from Example 3 is:

[0219] S4: core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 3000N, and the hot pressing time is 110s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0220] Comparative Example 5

[0221] The difference from Example 3 is:

[0222] S4: core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 4000N, and the hot pressing time is 110s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0223] The hot pressing parameters in Examples 1 to 9 and Comparative Examples 1 to 5 are recorded in Table 1.

[0224] Table 1

[0225]

[0226] Example 10

[0227] The difference from Example 1 is:

[0228] S4: core package hot pressing: the middle part 101 and the edge part 102 are hot pressed according to different hot pressing parameters, wherein the hot pressing temperature of the middle part 101 is 85°C, the hot pressing pressure is 500N, and the hot pressing time is 120s; the hot pressing temperature of the edge part 102 is 85°C, 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.

[0229] Embodiment 11

[0230] The difference from Example 10 is that in S4 the hot pressing pressure of the middle part 101 is increased to 1000N, the pressure ratio becomes 0.2, and the others remain unchanged.

[0231] Example 12

[0232] The difference from Example 10 is that in S4 the hot pressing pressure of the middle part 101 is increased to 2000N, the pressure ratio becomes 0.4, and the others remain unchanged.

[0233] Embodiment 13

[0234] The difference from Example 10 is that in S4 the hot pressing pressure of the middle part 101 is increased to 3000N, the pressure ratio becomes 0.6, and the others remain unchanged.

[0235] Embodiment 14

[0236] The difference from Example 10 is that in S4 the hot pressing pressure of the middle part 101 is increased to 4000N, the pressure ratio becomes 0.8, and the others remain unchanged.

[0237] Comparative Example 6

[0238] The difference from Example 10 is that in S4 the hot pressing pressure of the middle part 101 is increased to 5000N, the pressure ratio becomes 1, and the others remain unchanged.

[0239] Comparative Example 7

[0240] The difference from Example 10 is that in S4 the hot pressing pressure of the middle part 101 is increased to 6000N, the pressure ratio becomes 1.2, and the others remain unchanged.

[0241] The hot pressing parameters in Examples 10 to 14 and Comparative Examples 6 to 7 are recorded in Table 2.

[0242] Table 2

[0243]

[0244] The following tests were performed on the cells provided in all embodiments and comparative examples:

[0245] 1. Lithium deposition detection:

[0246] After fully charging, the battery cell is disassembled and the lithium deposition on the interface is observed and graded into: no lithium deposition, slight lithium deposition (lithium deposition area is less than 0.5cm 2 ), moderate lithium deposition (lithium deposition area 0.5cm 2 ~1.0cm 2 ), severe lithium deposition (lithium deposition area is greater than 1cm 2 ), the results are recorded in Table 3;

[0247] Full charging conditions of the battery cell: At a temperature of 25°C, charge at a constant current of 0.33C to the cut-off voltage (when the positive electrode active material is LFP, the cut-off voltage of the battery cell is 3.65V, and when the positive electrode active material is LMFP, the cut-off voltage of the battery cell is 4.2V), then change to constant voltage charging with a cut-off current of 0.05C.

[0248] 2. Peel force test:

[0249] After the battery cell is fully discharged, it is disassembled, the core package is taken out, and vacuum dried in a vacuum oven at 30°C for 48 hours. The peeling force between the positive electrode and the separator is tested according to the peeling force test method of GB / T 2792-2014, and the results are recorded in Table 3;

[0250] Battery full discharge condition: discharge to 2.5V at 1C at 25℃.

[0251] Table 3

[0252]

[0253] From the results in Table 3, we can see that:

[0254] 1. It can be seen from the comparison of Examples 1 to 3 and Comparative Examples 1 to 5 that when the hot pressing pressure of the middle part 101 is less than the hot pressing pressure of the edge part 102, and the hot pressing time of the middle part 101 is less than the hot pressing time of the edge part 102, the peeling force between the pole piece and the isolation film in the middle part 101 is less than the peeling force between the pole piece and the isolation film in the edge part 102, so that the risk of lithium precipitation of the battery cell is small. When the hot pressing pressure of the middle part 101 is greater than or equal to the hot pressing pressure of the edge part 102, the peeling force between the pole piece and the isolation film in the middle part 101 is greater than the peeling force between the pole piece and the isolation film in the edge part 102, and the lithium precipitation of the battery cell is serious. The peeling force between the pole piece and the isolation film in the middle part 101 should not be too low. If the peeling force is too low (less than 0.1N), the gap between the pole piece and the isolation film will increase in the middle and late stages of the battery cell cycle, making it difficult for lithium ions to pass through, but there is a higher risk of lithium precipitation.

[0255] 2. Comparing Example 3 with Example 6, when the positive electrode active material is replaced with LMFP, no lithium deposition occurs on the electrode sheet, which indicates that the rule is also applicable to the LMFP system.

[0256] 3. Comparing Example 3, Example 4 and Example 5, when the area of ​​the middle part 101 and the edge part 102 is controlled at about 50%, the interface is optimal. That is, the area of ​​the middle part 101 should not be too large or too small, because lithium deposition is easily concentrated in the middle part 101. If the area of ​​the middle part 101 is too large, the peeling force of the original non-abnormal area will be reduced, and the later cycle will be accelerated. Attenuation, while the area of ​​the middle part 101 is too small, it will make the middle part 101 easy to deposit lithium.

[0257] 4. Comparing Examples 7 to 9, as the hot pressing temperature increases, the peeling force between the positive electrode and the isolation membrane increases, and the lithium deposition area of ​​the interface of the battery cell gradually increases. This is because the isolation membrane is easier to deform after the temperature increases, which makes the electrode and the diaphragm bonded more tightly, that is, the peeling force between the two increases. At the same time, the porosity inside the electrode assembly decreases, making lithium deposition more likely to occur.

[0258] 5. Comparing Examples 12 to 16 and Comparative Examples 6 and 7, as the hot pressing pressure of the middle part 101 increases, the peeling force between the positive electrode and the separator becomes larger and larger, the area of ​​lithium deposition gradually increases, and the degree of lithium deposition becomes more and more serious. After the hot pressing pressure of the middle part 101 is equal to and greater than the hot pressing pressure of the edge part 102, the area of ​​lithium deposition increases significantly, and the degree of lithium deposition becomes more and more serious. It is shown that reducing the hot pressing pressure of the middle part 101 is conducive to controlling the degree of lithium deposition, but the hot pressing pressure of the middle part 101 should not be too small, otherwise the peeling force is too low, which will cause the battery cell to decay faster in the later stage of the cycle.

[0259] In summary, when hot pressing electrode components, the factors affecting the peeling force mainly include hot pressing pressure, hot pressing temperature, and hot pressing time. Therefore, the problem of lithium deposition in the battery cell can be improved from the following three points:

[0260] 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 smaller 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.

[0261] The embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrode assembly, characterized in that: The electrode assembly comprises a stacked isolation film and an electrode piece, wherein the electrode assembly has a middle portion and an edge portion, and along the thickness direction of the electrode assembly, the orthographic projection of the edge portion surrounds the orthographic projection of the middle portion; the peeling force between the isolation film and the electrode piece on the middle portion is F1; The peeling force between the isolation film and the electrode sheet on the edge portion is F2, wherein F1<F2.

2. The electrode assembly according to claim 1, characterized in that: The ratio of the F1 to the 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 isolation film includes a glue-coated diaphragm, and the glue-coated diaphragm includes a base film and a glue-coated layer, and the glue-coated 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 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.

8. The electrode assembly according to any one of claims 1 to 7, characterized in that: The isolation film and the pole piece are stacked layer by layer; or, the isolation film and the pole piece are stacked and wound.

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

10. A method for preparing an electrode assembly, characterized in that: include: The separator and the electrode sheet are stacked together to obtain an electrode assembly, wherein the electrode assembly has a middle portion and an edge portion, and along the thickness direction of the electrode assembly, the orthographic projection of the edge portion surrounds the orthographic projection of the middle portion; Along the thickness direction of the electrode assembly, the middle portion is subjected to a first extrusion treatment at a first pressure, and the edge portion is subjected to a second extrusion treatment at a second pressure; wherein the first pressure is less than or equal to the second pressure.

11. The method for preparing an electrode assembly according to claim 10, characterized in that: The ratio of the first time to the second time is 0.2 to 0.8; and / or, the ratio of the first pressure to the second pressure is 0.2 to 0.8; and / or, the difference between the second pressure and the first pressure is greater than or equal to 1000N.

12. The method for preparing an electrode assembly according to claim 10, characterized in that: The first pressure is 500N-5000N; or, the second pressure is 3000N-5000N; or, the second pressure is 3400N-4500N.

13. The method for preparing an electrode assembly according to any one of claims 10 to 12, characterized in that: The extrusion time of the first extrusion process is a first time, and the extrusion time of the second extrusion process is a second time, wherein the first time is less than or equal to the second time, and the product of the first pressure and the first time is less than the product of the second pressure and the second time.

14. The method for preparing an electrode assembly according to claim 13, characterized in that: The first time is 30s to 140s, or the second time is 120s to 180s, or the second time is 140s to 160s.

15. The method for preparing an electrode assembly according to any one of claims 10 to 12, characterized in that: The first extrusion process and the second extrusion process are both hot pressing processes, and the hot pressing temperature of the hot pressing process is 80° C. to 100° C.

16. A battery cell, characterized in that: include: A shell having a receiving cavity, wherein the surface of the shell is divided into an edge region and a large surface region, and along the thickness direction of the shell, the orthographic projection of the edge region surrounds the orthographic projection of the large surface region; An electrode assembly is arranged in the accommodating cavity, the middle portion corresponds to the large surface, and the edge portion corresponds to the edge. The electrode assembly is an electrode assembly as described in any one of claims 1 to 9 or an electrode assembly prepared by the preparation method of the electrode assembly as described in any one of claims 10 to 15.

17. An extruded structure for preparing an electrode assembly as claimed in any one of claims 1 to 9, characterized in that: The extrusion structure includes a middle extrusion portion and an edge extrusion portion arranged around the edge of the middle 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 middle portion is formed on the middle extrusion portion, and the second extrusion surface is configured to form a step difference 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.

18. The extruded structure according to claim 17, characterized in that The edge extrusion portion is fixedly connected to the middle extrusion portion and defines a groove together. The second extrusion surface is formed as an inner bottom surface of the groove. The first extrusion surface is located outside the groove and surrounds the notch of the groove.

19. The extruded structure according to claim 18, characterized in that The depth of the groove is 0.005 mm to 0.1 mm.

20. The extruded structure of claim 17, wherein: 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.

21. The extruded structure of claim 17, wherein: Along the thickness direction of the extrusion structure, the middle extrusion portion is movably arranged relative to the edge extrusion portion, and the middle extrusion portion is used to move toward or away from the electrode assembly when the extrusion structure extrudes the electrode assembly.

22. The extruded structure according to claim 21, characterized in that The edge extrusion portion includes a first frame body having a first through hole, and the middle extrusion portion includes a slider, which is located in the first through hole and is slidably connected to the first frame body.

23. The extruded structure according to claim 22, characterized in that The inner side wall of the first through hole is partially recessed into the interior of the first frame to form a slide groove, and the slider includes a main body and a boss protruding on the circumferential surface of the main body, the main body is located in the first through hole and adapted to the first through hole, and one end surface of the main body is formed as the second extrusion surface, and the boss extends into the slide groove and slidably cooperates with the slide groove; in the thickness direction of the first frame, the thickness of the boss is smaller than the width of the slide groove, and the distance between the side surface of the boss facing away from the second extrusion surface and the second extrusion surface is greater than the width of the slide groove.

24. An extruded structure according to any one of claims 17 to 23, 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.

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

26. An extrusion jig, characterized in that: Comprising an extruded structure according to any one of claims 17 to 25.

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