Electrode assembly, method of manufacturing the same, and battery

Abstract

The application relates to an electrode assembly, a preparation method thereof and a battery. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector in a first direction. In a second direction, the edge of the negative electrode sheet is closer to the edge of the separator than the edge of the positive electrode active material layer. The separator comprises a base material and a first adhesive layer and a second adhesive layer located on a first surface of the base material, and the second adhesive layer is located on at least one side of the first adhesive layer in the second direction. In the first direction, the projection of the first adhesive layer covers the projection of the positive electrode active material layer, the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet and does not overlap with the projection of the positive electrode active material layer. The peeling strength between the second adhesive layer and the negative electrode sheet is greater than the peeling strength between the first adhesive layer and the negative electrode sheet. Thus, the problem that the edge of the separator is prone to wrinkles and folding can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrode assembly, a preparation method thereof and a battery. BACKGROUND

[0002] In the production process of a battery, after the core (which can also be referred to as an electrode assembly) is subjected to a hot pressing process, it will be subjected to subsequent processes such as transfer and overwelding, which can cause the separator at the top and bottom (both ends in the width direction of the core) of the core to be folded. In addition, during the negative pressure liquid injection process after the core is loaded into the shell, the separator at the top of the core is also prone to folding under the action of the electrolyte.

[0003] HiPot test (dielectric withstand voltage test) can detect the core with a severely folded separator, but it is not easy to detect the core with a relatively slightly folded separator. The slight folding of the separator will cause the overhang (which can be understood as the reserved area of the separator beyond the positive and negative electrode sheets) of the positive and negative electrode sheets to be too small, and the short-circuit phenomenon may not be detected by detection means in the short term. However, during the long-term operation of the vehicle after packaging, the separator is prone to further deformation (such as wrinkling and further folding) due to the bumps during driving and the charge and discharge cycles, which can cause micro-short circuits of the positive and negative electrode sheets, thereby causing self-discharge and other problems, and eventually leading to a differential pressure alarm of the vehicle terminal. SUMMARY

[0004] Therefore, the present application provides an electrode assembly, a preparation method thereof and a battery to solve at least one problem in the background art.

[0005] In a first aspect, the present application provides an electrode assembly, comprising a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the thickness direction of the separator is defined as a first direction, and the width direction of the separator is defined as a second direction.

[0006] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector along the first direction; in the second direction, the edge of the negative electrode sheet is closer to the edge of the separator than the edge of the positive electrode active material layer.

[0007] The separator comprises a substrate and a first adhesive layer and a second adhesive layer located on a first surface of the substrate, the second adhesive layer being located on at least one side of the first adhesive layer along the second direction; the first surface is the surface of the substrate facing the negative electrode sheet.

[0008] In the first direction, a projection of the first adhesive layer covers a projection of the positive active material layer, a projection of the second adhesive layer overlaps with a projection of the negative electrode sheet and does not overlap with the projection of the positive active material layer; a peeling strength between the second adhesive layer and the negative electrode sheet is greater than a peeling strength between the first adhesive layer and the negative electrode sheet.

[0009] In combination with the first aspect of the present application, in an optional embodiment, the electrode assembly satisfies at least one of the following features:

[0010] (1) a difference between the peeling strength between the second adhesive layer and the negative electrode sheet and the peeling strength between the first adhesive layer and the negative electrode sheet is greater than or equal to 1 N / m;

[0011] (2) a size of the second adhesive layer in the second direction is greater than or equal to 1 mm;

[0012] (3) a thickness of the second adhesive layer is 1 μm to 5 μm;

[0013] (4) an edge of the second adhesive layer away from the positive active material layer extends to at least an edge of the negative electrode sheet;

[0014] (5) a thickness of the first adhesive layer is the same as a thickness of the second adhesive layer;

[0015] (6) a material of the first adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, and polyvinylidene fluoride-hexafluoropropylene;

[0016] (7) a material of the second adhesive layer includes an acrylate-based adhesive and / or polyimide-polyvinylpyrrolidone; the acrylate-based adhesive is generated by an esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic acid monomer and sodium carboxymethyl cellulose;

[0017] (8) the separator further includes a third adhesive layer on a second surface of the base material, the second surface being a surface of the base material facing the positive electrode sheet; a material of the third adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, and polyvinylidene fluoride-hexafluoropropylene.

[0018] In combination with the first aspect of the present application, in an optional embodiment, the negative electrode sheet includes a negative current collector and a negative active material layer on at least one side surface of the negative current collector in the first direction; a negative active material in the negative active material layer includes graphite and / or silicon-carbon material;

[0019] The material of the second adhesive layer comprises an acrylate-based adhesive; the acrylate-based adhesive is generated by an esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic acid monomer and sodium carboxymethyl cellulose; in the first direction, the second adhesive layer overlaps with the projection of the negative active material layer.

[0020] In combination with the first aspect of the present application, in an optional embodiment,

[0021] The edge of the second adhesive layer away from the positive active material layer coincides with the projection of the edge of the negative active material layer in the first direction; and / or,

[0022] In the second direction, the second adhesive layer is arranged to be spaced apart from the positive active material layer, and the distance between the second adhesive layer and the positive active material layer is greater than 0 and less than or equal to 1 mm.

[0023] In a second aspect, the embodiments of the present application provide a preparation method of an electrode assembly, the method comprising:

[0024] forming a first adhesive layer and a second adhesive layer on a first surface of a substrate in a first direction, the second adhesive layer being located on at least one side of the first adhesive layer in a second direction, to obtain a separator; the first surface is the surface of the substrate facing the negative electrode sheet side;

[0025] forming a positive active material layer on at least one side surface of a positive current collector in the first direction, to obtain a positive electrode sheet;

[0026] forming a negative active material layer on at least one side surface of a negative current collector in the first direction, to obtain a negative electrode sheet;

[0027] placing the separator between the positive electrode sheet and the negative electrode sheet, after lamination or winding, performing a pressing treatment to form the electrode assembly; in the second direction, the edge of the negative electrode sheet is closer to the edge of the separator relative to the edge of the positive active material layer; in the first direction, the projection of the first adhesive layer covers the projection of the positive active material layer, the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet and does not overlap with the projection of the positive active material layer; the peeling strength between the second adhesive layer and the negative electrode sheet is greater than the peeling strength between the first adhesive layer and the negative electrode sheet;

[0028] The first direction is the thickness direction of the substrate, and the second direction is the width direction of the substrate.

[0029] In combination with the second aspect of the present application, in an optional embodiment, the electrode assembly satisfies at least one of the following characteristics:

[0030] (1) the difference between the peeling strength between the second adhesive layer and the negative electrode sheet and the peeling strength between the first adhesive layer and the negative electrode sheet is greater than or equal to 1 N / m;

[0031] (2) the size of the second adhesive layer in the second direction is greater than or equal to 1 mm;

[0032] (3) the thickness of the second adhesive layer is 1 μm to 5 μm;

[0033] (4) the edge of the second adhesive layer away from the positive electrode active material layer extends to at least the edge of the negative electrode sheet;

[0034] (5) the thickness of the first adhesive layer is the same as the thickness of the second adhesive layer;

[0035] (6) the material of the first adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, and polyvinylidene fluoride-hexafluoropropylene;

[0036] (7) the material of the second adhesive layer includes an acrylate-based adhesive and / or polyimide-polyvinylpyrrolidone; the acrylate-based adhesive is generated by esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer, and acrylic acid monomer and sodium carboxymethyl cellulose;

[0037] (8) the step of preparing the separator further includes: forming a third adhesive layer on the second surface of the base material, the second surface being the surface of the base material facing the positive electrode sheet; the material of the third adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, and polyvinylidene fluoride-hexafluoropropylene.

[0038] In combination with the second aspect of the present application, in an optional implementation, the negative electrode active material in the negative electrode active material layer includes graphite and / or silicon-carbon material; and the pressing treatment is a hot pressing treatment.

[0039] The material of the second adhesive layer includes an acrylate-based adhesive; the acrylate-based adhesive is generated by esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer, and acrylic acid monomer and sodium carboxymethyl cellulose; and in the first direction, the projection of the second adhesive layer and the negative electrode active material layer overlap.

[0040] In combination with the second aspect of the present application, in an optional implementation,

[0041] The edge of the second adhesive layer away from the positive electrode active material layer coincides with the projection of the edge of the negative electrode active material layer in the first direction; and / or,

[0042] In the second direction, the second bonding layer is arranged apart from the positive active material layer, and the distance between the second bonding layer and the positive active material layer is greater than 0 and less than or equal to 1 mm; and / or,

[0043] The temperature of the hot-pressing treatment is 60-100℃, the pressure of the hot-pressing treatment is 1.5-4 MPa, and the time of the hot-pressing treatment is 25-240 s.

[0044] In combination with the second aspect of the present application, in an optional implementation, forming the second bonding layer on the first surface comprises:

[0045] After the butyl acrylate monomer, the acrylonitrile monomer and the acrylic acid monomer are uniformly mixed, the pre-emulsion is obtained by mixing with the emulsifier solution;

[0046] After the initiator is mixed and stirred with part of the pre-emulsion, the remaining pre-emulsion is added, and after the stirring reaction is completed, the polymeric emulsion is obtained by filtration;

[0047] The polymeric emulsion is mixed with sodium carboxymethyl cellulose to stir and react, and the acrylate-based adhesive glue solution is obtained.

[0048] The acrylate-based adhesive glue solution is coated on the first surface, and the second bonding layer is formed after drying.

[0049] In a third aspect, the embodiments of the present application provide a battery, which comprises the electrode assembly of any one of the first aspect or the electrode assembly prepared by the preparation method of any one of the second aspect.

[0050] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0051] The electrode assembly provided by the embodiment of the present application, the preparation method of the electrode assembly and the battery, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the thickness direction of the separator is defined as a first direction, and the width direction of the separator is defined as a second direction; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector in the first direction; in the second direction, the edge of the negative electrode sheet is closer to the edge of the separator than the edge of the positive electrode active material layer; the separator comprises a base material and a first adhesive layer and a second adhesive layer located on a first surface of the base material, and the second adhesive layer is located on at least one side of the first adhesive layer in the second direction; the first surface is the surface of the base material facing the negative electrode sheet; in the first direction, the projection of the first adhesive layer covers the projection of the positive electrode active material layer, and the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet and does not overlap with the projection of the positive electrode active material layer; the peeling strength between the second adhesive layer and the negative electrode sheet is greater than the peeling strength between the first adhesive layer and the negative electrode sheet. In the embodiment of the present application, the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet and does not overlap with the projection of the positive electrode active material layer, and the peeling strength between the second adhesive layer and the negative electrode sheet is greater than the peeling strength between the first adhesive layer and the negative electrode sheet. In this way, on the one hand, the second adhesive layer can improve the bonding strength between the edge of the negative electrode sheet and the separator, and enhance the supporting effect of the negative electrode sheet on the separator, thereby effectively improving the problem that the edge of the separator is prone to wrinkle and folding, and further avoiding the problems of self-discharge and pressure difference alarm of the battery caused by micro-short circuit of the positive and negative electrode sheets, and improving the yield rate of the production line; on the other hand, the active ion transmission in the main area of the electrode assembly (the area where the projection of the positive electrode active material layer in the first direction is located) can be avoided, thereby being conducive to reducing the internal resistance of the battery and protecting the electrochemical performance of the battery.

[0052] Additional aspects and advantages of the present application will be made apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0053] The accompanying drawings, which are included to provide a further understanding of the present application, constitute a part of the present application, and the illustrative embodiments of the present application and their description serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0054] Figure 1 A structural schematic diagram of an electrode assembly provided by the embodiment of the present application;

[0055] Figure 2 A structural schematic diagram of another electrode assembly provided by the embodiment of the present application;

[0056] Figure 3 A structural schematic diagram of another electrode assembly provided by the embodiment of the present application;

[0057] Figure 4 Schematic diagram of cross-linking between acrylate-based binder and negative active material;

[0058] Figure 5 Flowchart of a preparation method of an electrode assembly provided by an embodiment of the present application. DETAILED DESCRIPTION

[0059] In order to make the technical solutions and beneficial effects of the present application more obvious and easy to understand, the following will be described in detail by combining the drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not used to limit the scope of the present application. The experimental methods not specified in the following embodiments are generally carried out according to the conventional experimental conditions. The reagents and raw materials used in the present application are commercially available unless otherwise specified.

[0060] In the following description, a large number of specific details are given in order to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid obscuring the present application, some technical features known in the art are not described; that is, not all features of the actual embodiments are described here, and well-known functions and steps are not described in detail.

[0061] The terms used herein are only for the purpose of describing specific embodiments and not as a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the terms "comprise" and / or "comprising", when used in this specification, determine the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0062] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description in order to explain the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows, however, in addition to these detailed descriptions, the present application can also have other implementation manners.

[0063] Unless otherwise defined, the technical and scientific terms used in the present application have the same meaning as the technical and scientific terms in the technical field to which the present application belongs.

[0064] The specific techniques or conditions not specified in the following examples are generally carried out according to the conventional techniques or conditions described in the literature in the art, or according to the product instructions and manufacturer's recommended conditions. The numerical ranges in the following examples include the end point values.

[0065] In related technologies, although an adhesive layer is provided on the surface of the separator, the main function of the adhesive layer is to improve the problem of hot pressing of the core. The adhesive layer usually has poor adhesion, resulting in poor adhesion between the separator and the electrode. It is difficult for the electrode to provide stable support for the separator. Therefore, during the battery production process, wrinkles and folds are likely to occur at the edges of the separator.

[0066] Based on this, embodiments of this application provide an electrode assembly, such as... Figures 1 to 3 As shown, the electrode assembly includes a positive electrode 100, a negative electrode 200, and a separator 300 disposed between the positive and negative electrode sheets. The thickness direction of the separator 300 is defined as a first direction, and the width direction of the separator 300 is defined as a second direction. The positive electrode 100 includes a positive current collector (not shown) and a positive active material layer 110 located on at least one side surface of the positive current collector along the first direction. In the second direction, the edge of the negative electrode 200 is closer to the edge of the separator 300 than the edge of the positive active material layer 110. The separator 300 includes a substrate (not shown) and a membrane located on the substrate. A first adhesive layer 310 and a second adhesive layer 320 are on the first surface, the second adhesive layer 320 being located on at least one side of the first adhesive layer 310 along a second direction; the first surface is the surface of the substrate facing the negative electrode 200; in the first direction, the projection of the first adhesive layer 310 covers the projection of the positive electrode active material layer 110, the projection of the second adhesive layer 320 overlaps with the projection of the negative electrode 200 but does not overlap with the projection of the positive electrode active material layer 110; the peel strength between the second adhesive layer 320 and the negative electrode 200 is greater than the peel strength between the first adhesive layer 310 and the negative electrode 200.

[0067] For wound electrode assemblies, the structure of the electrode assembly can be referenced. Figure 1 Before winding, the separator 300, negative electrode 200, and positive electrode 100 are stacked in sequence. After winding, they form a structure as shown in the figure. Figure 1 In the structure shown, multiple positive tabs 400 are connected to the positive electrode plate 100, and multiple negative tabs 500 are connected to the negative electrode plate 200. Figure 2 and Figure 3 The electrode assembly in the image can be considered as a combination of adjacent positive electrode plates 100 and negative electrode plates 200 and a separator 300 located between adjacent positive electrode plates 100 and negative electrode plates 200 in the first direction. For a stacked electrode assembly, Figure 2 and Figure 3 The electrode assembly can be considered as a combination of the positive electrode 100, the separator 300 and the negative electrode 200 stacked on top. Figures 1 to 3The first direction in the electrode assembly can also be referred to as the thickness direction of the electrode assembly, and the second direction can also be referred to as the width direction of the electrode assembly. For a wound electrode assembly, the third direction can be regarded as the winding direction, and for a stacked electrode assembly, the third direction can be regarded as a direction perpendicular to both the first direction and the second direction.

[0068] It should be noted that, as shown in Figure 1 , a plurality of positive tabs 400 and a plurality of negative tabs 500 can be arranged in the electrode assembly, the plurality of positive tabs 400 are arranged in a column in the first direction, and the plurality of negative tabs 500 are arranged in a column in the thickness direction of the electrode assembly, and therefore, Figure 2 , and Figure 3 , only one positive tab 400 and one negative tab 500 are shown. Of course, Figure 1 , only one example of the arrangement of positive and negative tabs is shown in

[0069] As shown in Figure 2 , and Figure 3 , in the electrode assembly, in order to ensure safety, the edge of the separator 300 is usually arranged to protrude from the edge of the positive plate 100 and the negative plate 200, so that the separator 300 can reliably isolate the positive plate 100 and the negative plate 200. Because the edge of the separator 300 protrudes from the edge of the positive plate 100 and the negative plate 200, and the separator 300 itself has a relatively thin thickness and relatively low mechanical strength, the edge of the separator 300 is prone to wrinkling and folding during the production process of the battery and the subsequent use process. In the embodiment of the present application, the projection of the second adhesive layer 320 overlaps the projection of the negative plate 200 and does not overlap the projection of the positive active material layer 110, and the peeling strength between the second adhesive layer 320 and the negative plate 200 is greater than the peeling strength between the first adhesive layer 310 and the negative plate 200. In this way, on the one hand, the second adhesive layer 320 can improve the adhesion strength between the edge of the negative plate 200 and the separator 300, and enhance the support of the negative plate 200 to the separator 300, thereby effectively improving the problem that the edge of the separator 300 is prone to wrinkling and folding, and further avoiding the problems of self-discharge and pressure difference alarm of the battery caused by micro-short circuit of the positive and negative plates, and improving the yield rate of the production line; on the other hand, it can avoid hindering the transmission of active ions in the main area of the electrode assembly (the area where the projection of the positive active material layer 110 in the first direction is located), thereby being conducive to ensuring the electrochemical performance of the battery.

[0070] It should be noted that, Figure 2 , and Figure 3 , the second adhesive layer 320 is located on both sides of the first adhesive layer 310 in the second direction, which is only one example. In some other embodiments of the present application, the second adhesive layer 320 can be located on any one side of the first adhesive layer 310 in the second direction.

[0071] In some embodiments, referring to Figure 2 and Figure 3 The positive electrode sheet 100 can further include an insulating layer 120 located on at least one side surface of the positive current collector along the first direction, the insulating layer 120 being located on at least one side of the positive active material layer 110 along the second direction. The insulating layer 120 can play a better insulation and anti-spiking role, thereby improving the safety performance of the battery.

[0072] Generally, the peeling strength between the first bonding layer 310 and the negative electrode sheet 200 is low. In some embodiments, the difference between the peeling strength between the second bonding layer 320 and the negative electrode sheet 200 and the peeling strength between the first bonding layer 310 and the negative electrode sheet 200 is greater than or equal to 1 N / m. In this way, the bonding between the edge of the negative electrode sheet 200 and the separator 300 is more stable, the entire electrode assembly is in a better sealed state at one end or both ends provided with the second bonding layer 320 in the second direction, and the negative electrode sheet 200 can provide more stable support to the separator 300, thereby better improving the problem of easy folding and wrinkling of the edge of the separator 300.

[0073] It can be understood that the size of the second bonding layer 320 in the second direction is too small, which has a limited effect on improving the folding and wrinkling of the edge of the separator 300. Therefore, in some embodiments, the size of the second bonding layer 320 in the second direction is greater than or equal to 1 mm. In this way, it is beneficial to ensure that the bonding between the edge of the negative electrode sheet 200 and the separator 300 is more stable, thereby better improving the problem of easy folding and wrinkling of the edge of the separator 300.

[0074] When the thickness of the second bonding layer 320 is too thin, the bonding stability between the second bonding layer 320 and the negative electrode sheet 200 is affected; when the thickness of the second bonding layer 320 is too thick, not only the cost is increased, but also the different thicknesses of the second bonding layer 320 and the first bonding layer 310 will affect the bonding effect between the separator 300 and the negative electrode sheet 200 after pressing. Therefore, in some embodiments, the thickness of the second bonding layer 320 can be 1 μm to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range between any two of the above values.

[0075] In some embodiments, the thickness of the first bonding layer 310 is the same as the thickness of the second bonding layer 320. In this way, the surfaces of the first bonding layer 310 and the second bonding layer 320 close to the negative electrode sheet 200 are flush, the interface between the separator 300 and the negative electrode sheet 200 is flat, which is beneficial to improve the effect of the pressing process, thereby improving the performance of the electrode assembly.

[0076] In some embodiments, the first bonding layer 310 is adjacent to the second bonding layer 320 in the second direction. This is advantageous for ensuring that the separator 300 is tightly attached to the negative electrode sheet 200, thereby improving the electrical performance of the battery.

[0077] In some embodiments, referring to Figure 2 and Figure 3 , the edge of the second bonding layer 320 away from the positive active material layer 110 extends at least to the edge of the negative electrode sheet 200.

[0078] Specifically, the edge of the second bonding layer 320 away from the positive active material layer 110 can extend to the edge of the negative electrode sheet 200 (as shown in Figure 3 ). This can reduce the cost while ensuring that the separator 300 is stably attached to the negative electrode sheet 200. Of course, the edge of the second bonding layer 320 away from the positive active material layer 110 can extend beyond the edge of the negative electrode sheet 200, for example, to the edge of the separator 300 (as shown in Figure 2 ). This can further improve the mechanical strength of the edge of the separator 300, thereby better solving the problem of wrinkles and folds at the edge of the separator 300.

[0079] In some embodiments, the material of the first bonding layer 310 can include at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR, i.e., a copolymer of sodium carboxymethyl cellulose and styrene butadiene rubber), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, i.e., a copolymer of polyvinylidene fluoride and hexafluoropropylene). Specifically, the material of the first bonding layer 310 can be at least one of PVDF, PAA, CMC, CMC-SBR, and PVDF-HFP.

[0080] The above-mentioned type of bonding agent has good chemical stability and is less likely to react with negative active materials (e.g., graphite, etc.), thereby being advantageous for ensuring the reaction kinetics of the negative active materials.

[0081] In some embodiments, the material of the second bonding layer 320 can include an acrylate-based bonding agent and / or polyimide-polyvinylpyrrolidone (PI-PVP, i.e., a copolymer of polyimide and polyvinylpyrrolidone); wherein the acrylate-based bonding agent is generated by an esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer, and acrylic acid monomer and sodium carboxymethyl cellulose. Specifically, the material of the second bonding layer 320 can be the acrylate-based bonding agent and / or PI-PVP.

[0082] Compared with conventional binders (e.g., PVDF, etc.), the binder of the above type has better high-temperature stability and stronger adhesion, so that a stronger interfacial bonding between the separator 300 and the negative electrode sheet 200 can be formed, thereby better improving the problem of wrinkles and folding of the edges of the separator 300.

[0083] In some embodiments, the separator 300 further includes a third adhesive layer (not shown in the figure) on a second surface of the substrate, the second surface being a surface of the substrate facing the positive electrode sheet 100; the material of the third adhesive layer can include at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, polyvinylidene fluoride-hexafluoropropylene. Specifically, the material of the third adhesive layer can be at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, polyvinylidene fluoride-hexafluoropropylene.

[0084] In the embodiments of the present application, the third adhesive layer can enhance the adhesion stability between the separator 300 and the positive electrode sheet 100, thereby facilitating the improvement of the overall performance of the electrode assembly.

[0085] In some embodiments, the substrate of the separator 300 can be a polyethylene film and / or a polypropylene film. The first adhesive layer 310 and the second adhesive layer 320 are arranged on the surface of the polyethylene film and / or the polypropylene film.

[0086] In some embodiments, the substrate of the separator 300 can include a base film and a ceramic coating layer on at least one surface of the base film in the thickness direction, and the base film can be a polyethylene film and / or a polypropylene film. Accordingly, the first adhesive layer 310 and the second adhesive layer 320 are arranged on the surface of the ceramic coating layer.

[0087] In some embodiments, the negative electrode sheet 200 includes a negative electrode current collector (not shown in the figure) and a negative electrode active material layer 210 on at least one side surface of the negative electrode current collector in the first direction; the negative electrode active material in the negative electrode active material layer 210 includes graphite and / or silicon-carbon material; the material of the second adhesive layer 320 includes an acrylate-based adhesive; in the first direction, the projection of the second adhesive layer 320 and the negative electrode active material layer 210 overlap.

[0088] In the embodiments of the present application, the acrylate-based binder is generated by esterification cross-linking reaction of the copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic acid monomer and sodium carboxymethyl cellulose, and therefore the acrylate-based binder contains carboxyl and hydroxyl groups. The second bonding layer 320 overlaps with the projection of the negative active material layer 210, so that in the hot-pressing process for preparing the electrode assembly, the second bonding layer 320 can cross-link with the negative active material (graphite and / or silicon-carbon material) under high temperature and pressure conditions. Specifically, the carboxyl and hydroxyl groups of the acrylate-based binder can be tightly combined with the oxidized and hydrolyzed layer on the surface of the graphite and / or silicon-carbon material through hydrogen bonding, thereby enhancing the adhesion between the second bonding layer 320 and the negative active material layer 210, i.e., the peeling strength between the second bonding layer 320 and the negative plate 200 can be enhanced, so as to better improve the problem that the edge of the separator 300 is prone to wrinkle and fold.

[0089] The copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic acid monomer can also be referred to as a polyacrylate copolymer. In the preparation process of the polyacrylate copolymer, the three monomers are usually mixed with an emulsifier to obtain a pre-emulsion, and then an initiator is added to initiate the polymerization reaction to obtain the polyacrylate copolymer. In some embodiments, the emulsifier includes a benzene ring, and the emulsifier includes, for example, 1-alkenyl oxy-3-(4-nonyl phenol)-2-propanol polyoxyethylene (10) ether (DP-10) and / or nonylphenol polyoxyethylene ether (OP-10). In this case, the benzene ring is introduced into the polyacrylate copolymer, and further, the benzene ring is introduced into the acrylate-based binder finally prepared. The π-π conjugation of the benzene ring can make it stably adhere to the six-membered carbon ring porous layer on the surface of the carbon particles (graphite and / or silicon-carbon material), so as to further enhance the adhesion between the second bonding layer 320 and the negative active material layer 210. For details, please refer to Figure 4 The schematic diagram of the cross-linking between the acrylate-based binder and the negative active material is shown. The carboxyl and hydroxyl groups in the acrylate-based binder can be tightly combined with the oxidized and hydrolyzed layer on the surface of the graphite and / or silicon-carbon material through hydrogen bonding, and at the same time, the π-π conjugation of the benzene ring in the acrylate-based binder can make it stably adhere to the six-membered carbon ring porous layer on the surface of the carbon particles. Therefore, after the hot-pressing process, a stronger interface bonding can be formed between the edge of the negative plate 200 and the separator 300 in the electrode assembly, so that the negative plate 200 can play a more stable supporting role on the separator 300, thereby better improving the problem that the edge of the separator 300 is prone to wrinkle and fold.

[0090] In some embodiments, please refer to Figure 3, the edge of the second bonding layer 320 away from the positive active material layer 110 coincides with the projection of the edge of the negative active material layer 210 in the first direction. In this way, the adhesion between the negative plate 200 and the separator 300 can be further enhanced through the cross-linking between the material of the second bonding layer 320 and the graphite and / or silicon-carbon material in the negative active material layer 210, and the cost can be better controlled.

[0091] In some embodiments, please refer to Figure 2 In the second direction, the second bonding layer 320 is spaced apart from the positive active material layer 110, and the spacing between the second bonding layer 320 and the positive active material layer 110 is greater than 0 and less than or equal to 1 mm.

[0092] In the actual preparation process of the electrode assembly, the relative positions of the positive plate 100, the negative plate 200 and the separator 300 may be offset, and when the positions of the positive plate 100 and / or the negative plate 200 relative to the separator 300 are offset, the negative active material in the negative active material layer 210 directly opposite the positive active material layer 110 in the second direction may be bonded with the second bonding layer 320, thereby affecting the electrochemical reaction between the positive active material and the negative active material. In the embodiments of the present application, in the second direction, the second bonding layer 320 is spaced apart from the positive active material layer 110, and when the spacing between the second bonding layer 320 and the positive active material layer 110 is too large, under the condition that the size of the separator 300 is fixed, the size of the second bonding layer 320 in the second direction will be significantly reduced, making it difficult to form a stable bond with the negative plate 200, thereby making it difficult to improve the problem of wrinkles and folding at the edge of the separator 300. If the size of the second bonding layer 320 in the second direction is kept unchanged, the size of the separator 300 in the second direction needs to be increased accordingly, i.e. the width of the electrode assembly is larger, which will affect the energy density of the battery. Therefore, in the second direction, the spacing between the second bonding layer 320 and the positive active material layer 110 is set to be greater than 0 and less than or equal to 1 mm, which can not only provide a suitable margin for the offset of the positive and negative plates, but also ensure that the second bonding layer has a relatively wide size in the second direction, thereby forming a stable bond with the negative plate and further improving the problem of wrinkles and folding at the edge of the separator 300.

[0093] The embodiments of the present application also provide a preparation method of an electrode assembly, please refer to Figure 5 The preparation method of the electrode assembly provided by the embodiments of the present application comprises the following steps:

[0094] S1: forming a first bonding layer and a second bonding layer on a first surface of a substrate along a first direction, the second bonding layer being located on at least one side of the first bonding layer along a second direction, to obtain a separator; the first surface is the surface of the substrate facing the negative plate side;

[0095] S2: forming a positive active material layer on at least one side surface of the positive current collector along the first direction to obtain a positive electrode sheet;

[0096] S3: forming a negative active material layer on at least one side surface of the negative current collector along the first direction to obtain a negative electrode sheet;

[0097] S4: placing the separator between the positive electrode sheet and the negative electrode sheet, and performing a pressing treatment after stacking or winding to form an electrode assembly; in the second direction, the edge of the negative electrode sheet is closer to the edge of the separator than the edge of the positive active material layer; in the first direction, the projection of the first adhesive layer covers the projection of the positive active material layer, and the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet and does not overlap with the projection of the positive active material layer; the peeling strength between the second adhesive layer and the negative electrode sheet is greater than the peeling strength between the first adhesive layer and the negative electrode sheet; the first direction is the thickness direction of the substrate, and the second direction is the width direction of the substrate.

[0098] In the electrode assembly prepared by the embodiments of the present application, the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet and does not overlap with the projection of the positive active material layer, and the peeling strength between the second adhesive layer and the negative electrode sheet is greater than the peeling strength between the first adhesive layer and the negative electrode sheet. In this way, on the one hand, the second adhesive layer can improve the adhesion strength of the edge of the negative electrode sheet and the separator, and enhance the support of the negative electrode sheet to the separator, thereby effectively improving the problem that the edge of the separator is prone to wrinkle and folding, and further avoiding the problems of self-discharge and pressure difference alarm of the battery caused by micro-short circuit of the positive and negative electrode sheets, and improving the yield rate of the production line; on the other hand, the active ion transmission in the main body region of the electrode assembly (the region where the projection of the positive active material layer in the first direction is located) can be avoided, thereby being conducive to reducing the internal resistance of the battery and protecting the electrochemical performance of the battery.

[0099] It should be noted that although each step in the above flowchart is displayed in sequence according to the direction of the arrow, these steps are not necessarily executed in the order indicated by the arrow. Moreover, at least part of the steps in the above flowchart can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time or in sequence.

[0100] In step S1, the first adhesive layer and the second adhesive layer are formed on the first surface of the substrate along the first direction, and the second adhesive layer is located on at least one side of the first adhesive layer along the second direction to obtain the separator.

[0101] In some embodiments, the substrate can be a polyethylene film and / or a polypropylene film. In some other embodiments of the present application, the substrate can include a base film and a ceramic coating layer located on at least one surface of the base film along the thickness direction, and the base film can be a polyethylene film and / or a polypropylene film.

[0102] In the actual preparation process, the first surface of the substrate is provided with regions corresponding to the first adhesive layer and the second adhesive layer, respectively, and the first adhesive layer and the second adhesive layer can be formed by using a coating process well known to those skilled in the art, which is not limited herein. In addition, the order of forming the first adhesive layer and the second adhesive layer is not limited in the embodiments of the present application.

[0103] In some embodiments, the difference between the peeling strength between the second adhesive layer and the negative electrode tab and the peeling strength between the first adhesive layer and the negative electrode tab is greater than or equal to 1 N / m. In this way, the adhesion between the edge of the negative electrode tab and the separator can be more stable, the entire electrode assembly can be in a better sealed state, and the negative electrode tab can provide more stable support to the separator, thereby better improving the problem that the edge of the separator is prone to wrinkle and folding.

[0104] It can be understood that if the size of the second adhesive layer in the second direction is too small, the effect of improving the wrinkle and folding of the edge of the separator is limited. Therefore, in some embodiments, the size of the second adhesive layer in the second direction is greater than or equal to 1 mm. In this way, the adhesion between the edge of the negative electrode tab and the separator can be more stable, thereby better improving the problem that the edge of the separator is prone to wrinkle and folding.

[0105] When the thickness of the second adhesive layer is too thin, the adhesion stability between the second adhesive layer and the negative electrode tab is affected; when the thickness of the second adhesive layer is too thick, not only the cost is increased, but also the thickness difference between the second adhesive layer and the first adhesive layer affects the adhesion effect between the separator and the negative electrode tab after pressing. Therefore, in some embodiments, the thickness of the second adhesive layer can be 1 μm to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range between any two of the above values.

[0106] In some embodiments, the thickness of the first adhesive layer is the same as the thickness of the second adhesive layer. In this way, the surfaces of the first adhesive layer and the second adhesive layer close to the surface of the negative electrode tab can be flush, the interface between the separator and the negative electrode tab is flat, which is conducive to improving the effect of the pressing process, thereby improving the performance of the electrode assembly.

[0107] In some embodiments, in the second direction, the first adhesive layer and the second adhesive layer are adjacent to each other. In this way, the close fit between the separator and the negative electrode tab can be ensured, thereby improving the electrical performance of the battery.

[0108] In some embodiments, the second adhesive layer extends beyond the edge of the positive active material layer to at least the edge of the negative sheet.

[0109] Specifically, the second adhesive layer can extend beyond the edge of the positive active material layer to the edge of the negative sheet. In this way, the cost can be reduced while ensuring stable adhesion of the separator to the negative sheet. Of course, the second adhesive layer can extend beyond the edge of the negative sheet, for example, to the edge of the separator, so as to further improve the mechanical strength of the edge of the separator, thereby better solving the problem of wrinkles and folding at the edge of the separator.

[0110] In some embodiments, the material of the first adhesive layer can include at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, and polyvinylidene fluoride-hexafluoropropylene. Specifically, the material of the first adhesive layer can be at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, and polyvinylidene fluoride-hexafluoropropylene. The above types of adhesives have good chemical stability and are less likely to react with negative active materials (such as graphite, etc.), thereby facilitating the protection of the reaction kinetics of the negative material.

[0111] In some embodiments, the material of the second adhesive layer can include an acrylate-based adhesive and / or polyimide-polyvinylpyrrolidone; wherein the acrylate-based adhesive is generated by esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer, and acrylic acid monomer and sodium carboxymethyl cellulose. Specifically, the material of the second adhesive layer can be an acrylate-based adhesive and / or PI-PVP. The above types of adhesives have better high-temperature stability and stronger adhesion than traditional adhesives (such as PVDF, etc.), so as to form a stronger interfacial bond between the separator and the negative sheet, thereby better solving the problem of wrinkles and folding at the edge of the separator.

[0112] When the material of the second adhesive layer is an acrylate-based adhesive, forming the second adhesive layer on the first surface can include the following steps:

[0113] Step one: uniformly mix butyl acrylate monomer, acrylonitrile monomer, and acrylic acid monomer, and then mix with an emulsifier solution to obtain a pre-emulsion.

[0114] Specifically, the mass ratio of the butyl acrylate monomer, the acrylonitrile monomer and the acrylic acid monomer can be (4-6):(1-3):(2-3), for example, can be 4:1:2, 4:2:2, 4:3:3, 5:1:2, 5:2:3, 5:3:2, 6:1:2, 6:2:2.5, 6:3:3, or any other ratio within the above range. In this way, the quality of the polyacrylate copolymer obtained after polymerization of the three monomers is improved.

[0115] The emulsifier in the emulsifier solution can be at least one of 1-alkyleneoxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether (DP-10), 3-alkyleneoxy-2-hydroxy-1-propanesulfonic acid sodium salt (HAPS), sodium dodecyl sulfate (SDS), and nonylphenol polyoxyethylene ether (OP-10). In a specific example, the emulsifier solution is a solution of equal mass of DP-10 and HAPS. The polyoxyethylene chain in the DP-10 molecule stretches to form a hydration layer in water, preventing monomer droplets from colliding and aggregating through entropy repulsion effect, can reduce the oil-water interfacial tension, promote the dispersion of monomer into small droplets, the sulfonic acid group in HAPS ionizes to generate negative charge, making the double electric layer between the droplets repulsive, inhibiting the aggregation of droplets, and can neutralize the metal ion impurities in the monomer, prevent demulsification caused by charge shielding, thereby significantly improving the stability of the pre-emulsion.

[0116] Step two: mix part of the pre-emulsion with the initiator and stir, then add the remaining pre-emulsion, stir to complete the reaction, and then filter to obtain the polymerization emulsion.

[0117] In actual preparation, half of the pre-emulsion prepared in step one can be mixed with the initiator, then stirred at a temperature of 70-85°C for 30-60 minutes, then the remaining pre-emulsion is added, and uniform stirring is performed at 85-95°C for 2-3 hours, and then the polymerization emulsion is obtained by filtering. The initiator can be ammonium persulfate and / or potassium persulfate.

[0118] Step three: mix the polymerization emulsion with sodium carboxymethyl cellulose and stir to react to obtain the acrylate-based adhesive sizing liquid.

[0119] In actual preparation, the polymerization emulsion and sodium carboxymethyl cellulose can be mixed in a mass ratio of 2:1 and stirred for about 2 hours to obtain the acrylate-based adhesive sizing liquid.

[0120] Step four: coat the acrylate-based adhesive sizing liquid on the first surface to form a second bonding layer after drying.

[0121] In actual preparation, the acrylate-based adhesive sizing liquid is coated on the region of the first surface corresponding to the second bonding layer. The coating process is not limited in the embodiments of the present application.

[0122] In some embodiments, the step of preparing the separator can further include: forming a third adhesive layer on the second surface of the substrate, the second surface being the surface of the substrate facing the positive electrode sheet; the material of the third adhesive layer can include at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, polyvinylidene fluoride-hexafluoropropylene. Specifically, the material of the third adhesive layer can be at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butyl rubber, polyvinylidene fluoride-hexafluoropropylene.

[0123] In the embodiments of the present application, the third adhesive layer can enhance the bonding stability between the separator and the positive electrode sheet, thereby facilitating the improvement of the overall performance of the electrode assembly.

[0124] In step S2, a positive electrode active material layer is formed on at least one side surface of the positive electrode current collector in the first direction, to obtain a positive electrode sheet.

[0125] In the actual preparation process, the positive electrode active material (specifically, for example, lithium iron phosphate), the dispersing agent (specifically, for example, polyethylene glycol phosphate), and the positive electrode binder (specifically, for example, PVDF) can be added into the first solvent (specifically, for example, N-methyl pyrrolidone), stirred uniformly, to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the surface of the positive electrode current collector (specifically, for example, aluminum foil), to form the positive electrode active material layer after drying, to obtain the positive electrode sheet.

[0126] In step S3, a negative electrode active material layer is formed on at least one side surface of the negative electrode current collector in the first direction, to obtain a negative electrode sheet.

[0127] In the actual preparation process, the negative electrode active material (specifically, for example, graphite and / or silicon-carbon material), the negative electrode conductive agent (specifically, for example, conductive carbon black), and the negative electrode binder (specifically, for example, PVDF) can be added into the second solvent (specifically, for example, water), stirred uniformly, to obtain a negative electrode slurry, and then the negative electrode slurry is coated on the surface of the negative electrode current collector (specifically, for example, copper foil), to form the negative electrode active material layer after drying, to obtain the negative electrode sheet.

[0128] In some embodiments, the negative electrode active material in the negative electrode active material layer includes graphite and / or silicon-carbon material; the material of the second adhesive layer includes an acrylate-based binder; in the first direction, the projection of the second adhesive layer and the negative electrode active material layer overlap.

[0129] As described in the above embodiments, the acrylate-based binder is generated by esterification cross-linking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic acid monomer and sodium carboxymethyl cellulose, and thus the acrylate-based binder contains carboxyl and hydroxyl groups. The second binder layer overlaps with the projection of the negative active material layer, so that in the hot-pressing process for preparing the electrode assembly, the second binder layer can cross-link with the negative active material (graphite and / or silicon-carbon material), and specifically, the carboxyl and hydroxyl groups of the acrylate-based binder can be tightly combined with the oxidized and hydrolyzed layer on the surface of the graphite and / or silicon-carbon material through hydrogen bonding, thereby enhancing the adhesion between the second binder layer and the negative active material layer, i.e., the peeling strength between the second binder layer and the negative sheet, so as to better improve the problem of easy wrinkling and folding of the edges of the separator.

[0130] In step S4, the separator is placed between the positive sheet and the negative sheet, and after the lamination or winding, a pressing treatment is performed to form the electrode assembly.

[0131] Specifically, the lamination treatment includes sequentially laminating in the order of positive sheet-separator-negative sheet-separator to a set number of layers, i.e., obtaining the electrode assembly. The winding treatment includes sequentially laminating in the order of positive sheet-separator-negative sheet-separator to obtain an initial electrode assembly, and then winding along the length direction of the separator to obtain the electrode assembly. The shape of the electrode assembly formed after winding is not limited in the present application.

[0132] In some embodiments, the pressing treatment can be a hot-pressing treatment. The temperature of the hot-pressing treatment can be 60-100°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, or any value within any two of the above-mentioned value ranges. The pressure of the hot-pressing treatment can be 1.5-4 MPa, for example, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, or any value within any two of the above-mentioned value ranges. The time of the hot-pressing treatment can be 25-240 s, for example, 25 s, 50 s, 75 s, 100 s, 125 s, 150 s, 175 s, 200 s, 225 s, 240 s, or any value within any two of the above-mentioned value ranges.

[0133] In the hot-pressing process, the binder in the pole piece is softened by heating, which can enhance the bonding strength of the active material and the interface contact, thereby reducing the internal resistance of the pole piece, improving the compaction density and the stability of the pole piece structure. In addition, the negative active material in the negative active material layer includes graphite and / or silicon-carbon material, the material of the second bonding layer includes an acrylate-based binder, and when the projection of the second bonding layer on the negative active material layer in the first direction overlaps, the second bonding layer can cross-link with the graphite and / or silicon-carbon material through the hot-pressing process, thereby enhancing the bonding force between the second bonding layer and the negative active material layer, and further better improving the problem of easy wrinkles and folding of the edge of the separator. Controlling the temperature, pressure and time of the hot-pressing process in the above range can better combine the interfaces between the positive pole piece, the separator and the negative pole piece, and fully exert the strong bonding effect of the second bonding layer to better improve the problem of easy wrinkles and folding of the edge of the separator.

[0134] In some embodiments, the pressing process can be cold pressing. In this way, the difficulty of the pressing process can be reduced, the production efficiency can be improved, and the production energy consumption can be reduced, thereby facilitating cost reduction.

[0135] The structure of the electrode assembly prepared by the embodiments of the present application is shown in Figures 1 to 3 . For a wound electrode assembly, the structure of the electrode assembly can refer to Figure 1 . Before winding, the separator 300, the negative pole piece 200, the separator 300 and the positive pole piece 100 are sequentially stacked, and after winding, the structure shown in Figure 1 is formed, a plurality of positive tabs 400 are connected to the positive pole piece 100, a plurality of negative tabs 500 are connected to the negative pole piece 200, Figure 2 and Figure 3 The electrode assembly in the electrode assembly can be regarded as the combined state of the adjacent positive pole piece 100 and negative pole piece 200 and the separator 300 located between the adjacent positive pole piece 100 and negative pole piece 200 in the first direction. For a stacked electrode assembly, Figure 2 and Figure 3 The electrode assembly in the electrode assembly can be regarded as the combined state of the uppermost positive pole piece 100, the separator 300 and the negative pole piece 200 after stacking.

[0136] In some embodiments, please refer to Figure 3 , the edge of the second bonding layer 320 away from the positive active material layer 110 coincides with the projection of the edge of the negative active material layer 210 in the first direction. In this way, the bonding force between the negative pole piece 200 and the separator 300 can be further enhanced by the cross-linking between the material of the second bonding layer 320 and the graphite and / or silicon-carbon material in the negative active material layer 210, and the cost can be better controlled.

[0137] In some embodiments, please refer to Figure 2In the second direction, the second bonding layer 320 can be spaced apart from the positive active material layer 110, and the spacing between the second bonding layer 320 and the positive active material layer 110 is greater than 0 and less than or equal to 1 mm. In this way, a suitable margin can be reserved for the offset of the positive and negative electrode sheets, and the second bonding layer 320 can have a relatively wide size in the second direction, thereby forming a stable bond with the negative electrode sheet 200, and thus better improving the problem of wrinkles and folding of the edges of the separator 300.

[0138] The application also provides a battery including the electrode assembly of any of the above embodiments or the electrode assembly prepared by the preparation method of any of the above embodiments.

[0139] It can be understood that the beneficial effects of the electrode assembly of any of the above embodiments or the electrode assembly prepared by the preparation method of any of the above embodiments are applicable to the battery in the application. The battery in the application has higher safety and electrochemical performance.

[0140] In some embodiments, the battery further includes:

[0141] The shell has an accommodation cavity with an open end; the electrode assembly is located in the accommodation cavity;

[0142] The top cover covers the opening of the accommodation cavity, and the top cover includes a liquid injection hole. One end surface of the electrode assembly perpendicular to the second direction is arranged towards the liquid injection hole.

[0143] In the electrode assembly of the above embodiments, the second bonding layer is located on at least one side of the first bonding layer in the second direction. The second bonding layer can effectively improve the bonding strength between the edge of the negative electrode sheet and the separator and enhance the support of the negative electrode sheet on the separator. Therefore, the problem of wrinkles and folding of the edges of the separator that can be caused during the liquid injection process can be better avoided. It can be understood that when the second bonding layer is located on both sides of the first bonding layer in the second direction, either of the two end surfaces of the electrode assembly perpendicular to the second direction can be arranged towards the liquid injection hole; when the second bonding layer is located on one side of the first bonding layer in the second direction, one of the two end surfaces of the electrode assembly perpendicular to the second direction close to the second bonding layer is arranged towards the liquid injection hole.

[0144] In the application, the types of the shell and the top cover are not particularly limited, and battery shells and top covers known in the art can be used.

[0145] The technical solutions of the application will be further described below in combination with multiple embodiments and comparative examples.

[0146] Embodiment 1

[0147] The preparation method of the electrode assembly in this embodiment includes the following steps:

[0148] Step S101: First, butyl acrylate (BA), acrylonitrile (AN) and acrylic acid (AA) monomers were uniformly mixed in a mass ratio of 5:2:3, then 1-alkyleneoxy-3-(4-nonyl phenol)-2-propanol polyoxyethylene (10) ether (DP-10) and 3-alkyleneoxy-2-hydroxy-1-propane sulfonate sodium salt (HAPS) were mixed in the same mass ratio and stirred for 20 min, then the mixed monomers were added and stirred uniformly to obtain a pre-emulsion; secondly, half of the pre-emulsion was mixed with its initiator ammonium persulfate, stirred at 80℃ for 30 min, then the remaining pre-emulsion was added and stirred uniformly at 90℃ for 2h, and then filtered to obtain a polymerization emulsion; thirdly, the polymerization emulsion and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 2:1 and stirred for 2h to prepare an acrylate-based adhesive glue solution;

[0149] Step S102: A PE base film with a thickness of 7μm was used, and a ceramic coating (including Al2O3 and PVDF, the mass ratio of Al2O3 to PVDF was 97:3) with a thickness of 2μm and a PVDF glue layer (third adhesive layer) with a thickness of 3μm were coated on the surface of the base film facing the positive plate in sequence, a PVDF glue layer (first adhesive layer) with a thickness of 3μm was coated on the first area of the other side surface of the PE base film (surface facing the negative plate), and an acrylate-based adhesive glue solution was coated on the second area to form an acrylate-based adhesive glue layer (second adhesive layer) with a thickness of 3μm, thereby obtaining a separator; the second adhesive layer was located on both sides of the first adhesive layer in the second direction (the width direction of the PE base film), and in the second direction, the size of the second adhesive layer was 1mm, and the distance between the edge of the second adhesive layer away from the first adhesive layer and the edge of the PE base film was 2mm;

[0150] Step S103: Lithium iron phosphate (positive active material), polyethylene glycol phosphate (dispersant) and PVDF (positive electrode binder) were added to N-methyl pyrrolidone in a mass ratio of 98.2:0.1:1.7, and stirred uniformly to obtain a positive electrode slurry, which was coated on an aluminum foil to form a positive active material layer after drying, thereby obtaining a positive electrode plate;

[0151] Step S104: Artificial graphite (negative active material), conductive carbon black (negative electrode conductive agent) and polyacrylic acid (negative electrode binder) were added to pure water in a mass ratio of 96.6:1:1.5, and stirred uniformly to obtain a negative electrode slurry, which was coated on a copper foil to form a negative active material layer after drying, thereby obtaining a negative electrode plate;

[0152] Step S105: stacking the positive electrode sheet, the negative electrode sheet and the separator, the separator being between the positive electrode sheet and the negative electrode sheet, in the second direction, the size of the negative electrode sheet beyond the positive active material layer is 1.3 mm, and the size of the separator beyond the negative electrode sheet is 2.5 mm; obtaining a rolled electrode assembly by rolling; and obtaining a final electrode assembly by hot pressing (temperature: 90℃, surface pressure: 2.5Mpa, time: 50s) on the rolled electrode assembly.

[0153] Example 2

[0154] The preparation method of the electrode assembly in this example is basically the same as that in Example 1, and the difference lies in that:

[0155] Step S101 is omitted, and in step S102, a PI-PVP adhesive layer (second adhesive layer) with a thickness of 3μm is formed on the second area of the surface of the PE base film facing the negative electrode sheet; the preparation method of the PI-PVP adhesive layer is: slowly dropping the PI solution into the PVP solution, stirring for 9h to obtain a uniform PI-PVP blended adhesive solution, coating the PI-PVP blended adhesive solution on the second area of the surface of the PE base film facing the negative electrode sheet, and forming a PI-PVP adhesive layer after drying, wherein the mass ratio of PI to PVP is 9:1.

[0156] Example 3

[0157] The preparation method of the electrode assembly in this example is basically the same as that in Example 1, and the difference lies in that:

[0158] In step S102, the size of the second adhesive layer is adjusted to 1.5mm in the second direction, and the distance between the edge of the second adhesive layer away from the first adhesive layer and the edge of the PE base film is 2mm.

[0159] Example 4

[0160] The preparation method of the electrode assembly in this example is basically the same as that in Example 1, and the difference lies in that:

[0161] In step S102, the size of the second adhesive layer is adjusted to 0.8mm in the second direction, and the distance between the edge of the second adhesive layer away from the first adhesive layer and the edge of the PE base film is 2mm.

[0162] Example 5

[0163] The preparation method of the electrode assembly in this example is basically the same as that in Example 1, and the difference lies in that:

[0164] In step S102, the thickness of the second adhesive layer is adjusted to 5μm.

[0165] Comparative Example 1

[0166] The preparation method of the electrode assembly in this example is basically the same as that in Example 1, and the difference lies in that:

[0167] Step S101 was omitted, and in step S102, the surface of the PE-based film facing the negative electrode sheet was entirely coated with a PVDF adhesive layer having a thickness of 3 μm.

[0168] Comparative Example 2

[0169] The method for preparing the electrode assembly in this comparative example was basically the same as that in Example 1, except that:

[0170] Step S101 was omitted, and in step S102, the surface of the PE-based film facing the negative electrode sheet was entirely coated with a PAA adhesive layer having a thickness of 3 μm.

[0171] Comparative Example 3

[0172] The method for preparing the electrode assembly in this comparative example was basically the same as that in Example 1, except that:

[0173] In step S102, the first area of the surface of the PE-based film facing the negative electrode side was coated with an acrylate-based adhesive solution to form an acrylate-based adhesive layer having a thickness of 3 μm, and the second area was coated with a PVDF adhesive layer having a thickness of 3 μm. That is, the positions of the first adhesive layer and the second adhesive layer were interchanged relative to Example 1.

[0174] The peeling strength of the electrode assembly prepared in each of the above examples and comparative examples was tested. The specific test procedure was as follows: the negative electrode sheet and the separator at both ends of the electrode assembly in the second direction were cut into a long strip having a size of 10 cm (size in the third direction) x 1 cm (size in the second direction) as the sample to be tested, one side of the negative electrode sheet of the sample to be tested was attached to a stainless steel plate, and the sample to be tested was placed in the clamps of a tensile testing machine so that the peeling direction of the separator was perpendicular to the surface of the negative electrode sheet; then, the sample to be tested was loaded at 20 mm / min until the separator and the coating layer on the surface of the negative electrode sheet were completely separated. According to the tensile testing machine, the peeling force and the peeling width during the loading process were recorded to obtain the peeling force and the peeling strength between the separator and the surface of the negative electrode coating layer, wherein the peeling strength = peeling force / peeling width.

[0175] The electrode assemblies prepared in each of the above examples and comparative examples were loaded into a shell, and sequentially subjected to processes such as baking, liquid injection, high-temperature storage, formation, aging, and capacity distribution to obtain a battery. The direct current resistance (DCR) of the battery was tested, and the folding of the separator was detected.

[0176] The steps for testing the direct current resistance of the battery were as follows:

[0177] (1) The battery was charged at 0.33C constant current and constant voltage to 3.65V, and then stored for 30 min. The battery was discharged at 1C to 2.5V, and the process was repeated twice. The second discharge capacity was recorded as C0.

[0178] (2) 0.33C0 constant current constant voltage to 3.65V, stand for 30min, 1C0 constant current discharge for 30min, stand for 1h, 4C0 discharge for 10s, the direct current internal resistance of the battery is measured.

[0179] The step of detecting the folding of the separator is: disassembling the battery prepared above (which can be regarded as a normal offline battery), taking out the electrode assembly, and observing whether the separator is folded.

[0180] The test results are shown in Table 1.

[0181] Table 1

[0182]

[0183] As can be seen from the data in Table 1, in Comparative Example 1, the PE-based film surface facing the negative electrode side is entirely coated with a PVDF adhesive layer (equivalent to the first adhesive layer) with a thickness of 3μm, that is, no second adhesive layer is provided on at least one side of the first adhesive layer along the width direction of the separator, and the peeling strength between the negative electrode tab edge and the separator is very low, thereby causing the separator to fold. In Comparative Example 2, the PVDF adhesive layer is replaced by a PAA adhesive layer (also equivalent to the first adhesive layer), and similarly, the peeling strength between the negative electrode tab edge and the separator is very low, thereby causing the separator to fold. In Comparative Example 3, the positions of the first adhesive layer and the second adhesive layer are interchanged relative to Example 1, which not only fails to improve the adhesion strength between the negative electrode tab edge and the separator, causing the separator to fold, but also hinders the transmission of active ions in the main body region of the electrode assembly, thereby increasing the direct current internal resistance of the battery and reducing the electrochemical performance of the battery.

[0184] As can be seen from the data in Table 1, in the electrode assemblies of Examples 1 to 5, the strong adhesion effect of the second adhesive layer significantly improves the peeling strength between the negative electrode tab edge and the separator, effectively enhances the support of the negative electrode tab to the separator, and avoids the folding of the separator; at the same time, the second adhesive layer is provided on both sides of the first adhesive layer along the width direction of the separator, which does not hinder the transmission of active ions in the main body region of the electrode assembly, so that the direct current internal resistance of the battery is at a low level, which can guarantee the electrochemical performance of the battery.

[0185] As can be seen from the data of Examples 1, 3 and 4, the larger the size of the second adhesive layer in the width direction of the separator, the better the adhesion effect, which increases the peeling strength between the negative electrode tab edge and the separator, but slightly increases the direct current internal resistance of the battery. As can be seen from the data of Examples 1 and 5, the larger the thickness of the second adhesive layer, the better the adhesion effect, which increases the peeling strength between the negative electrode tab edge and the separator, but also slightly increases the direct current internal resistance of the battery. Therefore, the size of the second adhesive layer can be adjusted comprehensively to meet the needs of actual products.

[0186] In addition, in Embodiment 5, the thickness of the second adhesive layer is greater than the thickness of the first adhesive layer, which not only increases the cost, but also the second adhesive layer and the first adhesive layer are not flush to the surface of the negative plate, which affects the bonding effect after pressing, and easily leads to uneven pressing interface between the separator and the negative plate, which also affects the electrochemical performance of the battery. Therefore, the thickness of the first adhesive layer and the second adhesive layer is the same is a more optimal technical solution.

[0187] It should be noted that the electrode assembly embodiments, the preparation method of the electrode assembly embodiments and the battery embodiments provided in the present application belong to the same concept. In the technical solutions disclosed in each embodiment, each technical feature can be combined arbitrarily without conflict.

[0188] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations. Various modifications and changes can also be made to the above embodiments without departing from the scope of the present disclosure. Similarly, each technical feature of the above embodiments can be combined arbitrarily to form additional embodiments of the present application that have not been explicitly described. Therefore, the above embodiments only express several implementation manners of the present application, and do not limit the protection scope of the patent of the present application.

Claims

1. An electrode assembly, characterized in that, It includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the thickness direction of the separator is defined as a first direction, and the width direction of the separator is defined as a second direction; The positive electrode includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector along the first direction; in the second direction, the edge of the negative electrode is closer to the edge of the separator than the edge of the positive active material layer. The separator includes a substrate and a first adhesive layer and a second adhesive layer located on a first surface of the substrate, wherein the second adhesive layer is located on at least one side of the first adhesive layer along a second direction; the first surface is the surface of the substrate facing the negative electrode sheet; In the first direction, the projection of the first adhesive layer covers the projection of the positive electrode active material layer, the projection of the second adhesive layer overlaps with the projection of the negative electrode sheet but does not overlap with the projection of the positive electrode active material layer; the peel strength between the second adhesive layer and the negative electrode sheet is greater than the peel strength between the first adhesive layer and the negative electrode sheet.

2. The electrode assembly according to claim 1, characterized in that, The electrode assembly satisfies at least one of the following characteristics: (1) The difference between the peel strength between the second adhesive layer and the negative electrode sheet and the peel strength between the first adhesive layer and the negative electrode sheet is greater than or equal to 1 N / m; (2) The dimension of the second adhesive layer in the second direction is greater than or equal to 1 mm; (3) The thickness of the second adhesive layer is 1μm~5μm; (4) The edge of the second adhesive layer away from the positive electrode active material layer extends at least to the edge of the negative electrode sheet; (5) The thickness of the first adhesive layer is the same as the thickness of the second adhesive layer; (6) The material of the first adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butadiene rubber, and polyvinylidene fluoride-hexafluoropropylene; (7) The material of the second adhesive layer includes an acrylate-based adhesive and / or polyimide-polyvinylpyrrolidone; the acrylate-based adhesive is generated by a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic monomer with sodium carboxymethyl cellulose through an esterification crosslinking reaction; (8) The separator further includes a third adhesive layer on a second surface of the substrate, the second surface being the surface of the substrate facing the positive electrode; the material of the third adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butadiene rubber, and polyvinylidene fluoride-hexafluoropropylene.

3. The electrode assembly according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector along the first direction; the negative electrode active material in the negative electrode active material layer includes graphite and / or silicon-carbon material; The material of the second adhesive layer includes an acrylate-based adhesive; the acrylate-based adhesive is generated by esterification crosslinking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic monomer with sodium carboxymethyl cellulose; in the first direction, the projection of the second adhesive layer overlaps with that of the negative electrode active material layer.

4. The electrode assembly according to claim 3, characterized in that, The edge of the second adhesive layer away from the positive electrode active material layer coincides with the projection of the edge of the negative electrode active material layer in the first direction; and / or, In the second direction, the second adhesive layer and the positive electrode active material layer are spaced apart, and the distance between the second adhesive layer and the positive electrode active material layer is greater than 0 and less than or equal to 1 mm.

5. A method for preparing an electrode assembly, characterized in that, The method includes: A first adhesive layer and a second adhesive layer are formed on a first surface of a substrate along a first direction, the second adhesive layer being located on at least one side of the first adhesive layer along a second direction, to obtain a separator; the first surface is the surface of the substrate facing the negative electrode sheet. A positive electrode active material layer is formed on at least one side surface of the positive electrode current collector along the first direction to obtain a positive electrode sheet; A negative electrode active material layer is formed on at least one side surface of the negative electrode current collector along the first direction to obtain a negative electrode sheet; The separator is placed between the positive electrode and the negative electrode, and after stacking or winding, it is pressed to form the electrode assembly; in the second direction, the edge of the negative electrode is closer to the edge of the separator than the edge of the positive electrode active material layer; in the first direction, the projection of the first adhesive layer covers the projection of the positive electrode active material layer, the projection of the second adhesive layer overlaps with the projection of the negative electrode but does not overlap with the projection of the positive electrode active material layer; the peel strength between the second adhesive layer and the negative electrode is greater than the peel strength between the first adhesive layer and the negative electrode; The first direction is the thickness direction of the substrate, and the second direction is the width direction of the substrate.

6. The method for preparing the electrode assembly according to claim 5, characterized in that, The electrode assembly satisfies at least one of the following characteristics: (1) The difference between the peel strength between the second adhesive layer and the negative electrode sheet and the peel strength between the first adhesive layer and the negative electrode sheet is greater than or equal to 1 N / m; (2) The dimension of the second adhesive layer in the second direction is greater than or equal to 1 mm; (3) The thickness of the second adhesive layer is 1μm~5μm; (4) The edge of the second adhesive layer away from the positive electrode active material layer extends at least to the edge of the negative electrode sheet; (5) The thickness of the first adhesive layer is the same as the thickness of the second adhesive layer; (6) The material of the first adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butadiene rubber, and polyvinylidene fluoride-hexafluoropropylene; (7) The material of the second adhesive layer includes an acrylate-based adhesive and / or polyimide-polyvinylpyrrolidone; the acrylate-based adhesive is generated by a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic monomer with sodium carboxymethyl cellulose through an esterification crosslinking reaction; (8) The step of preparing the separator further includes: forming a third adhesive layer on the second surface of the substrate, wherein the second surface is the surface of the substrate facing the positive electrode sheet; The material of the third adhesive layer includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose-butadiene rubber, and polyvinylidene fluoride-hexafluoropropylene.

7. The method for preparing the electrode assembly according to claim 5, characterized in that, The negative electrode active material in the negative electrode active material layer includes graphite and / or silicon-carbon materials; the pressing process is a hot pressing process; The material of the second adhesive layer includes an acrylate-based adhesive; the acrylate-based adhesive is generated by esterification crosslinking reaction of a copolymer of butyl acrylate monomer, acrylonitrile monomer and acrylic monomer with sodium carboxymethyl cellulose; in the first direction, the projection of the second adhesive layer overlaps with that of the negative electrode active material layer.

8. The method for preparing the electrode assembly according to claim 7, characterized in that, The edge of the second adhesive layer away from the positive electrode active material layer coincides with the projection of the edge of the negative electrode active material layer in the first direction; and / or, In the second direction, the second adhesive layer and the positive electrode active material layer are spaced apart, and the distance between the second adhesive layer and the positive electrode active material layer is greater than 0 and less than or equal to 1 mm; and / or, The hot pressing temperature is 60℃~100℃, the hot pressing pressure is 1.5MPa~4MPa, and the hot pressing time is 25s~240s.

9. The method for preparing the electrode assembly according to claim 7 or 8, characterized in that, Forming the second adhesive layer on the first surface includes: After uniformly mixing butyl acrylate monomer, acrylonitrile monomer and acrylic monomer, they are mixed with emulsifier solution to obtain pre-emulsion; A portion of the pre-emulsion was mixed with the initiator and stirred, then the remaining pre-emulsion was added. After stirring to complete the reaction, the mixture was filtered to obtain a polymer emulsion. The polymer emulsion was mixed with sodium carboxymethyl cellulose and stirred to react, resulting in an acrylate-based adhesive solution. The acrylate-based adhesive solution is applied to the first surface and dried to form the second adhesive layer.

10. A battery, characterized in that, The electrode assembly includes the electrode assembly according to any one of claims 1 to 4, or the electrode assembly prepared by the method of the electrode assembly according to any one of claims 5 to 9.

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