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 comprising 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, the negative electrode sheet and the separator are wound to form a flat area and a bending area; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer comprises a first active material layer located on a first surface of the positive electrode current collector; the first surface is a surface of two surfaces of the positive electrode current collector along a thickness direction and away from a winding center of the electrode assembly; the first active material layer has a first groove located at the bending area; the first groove is filled with a first solid-state electrolyte; and the maximum thickness of the first solid-state electrolyte in the thickness direction of the positive electrode current collector is greater than the depth of the first groove. In this way, the electrode interface electrolyte wetting effect can be improved through the first solid-state electrolyte, the lithium intercalation kinetics of the negative electrode sheet at the bending area is improved, and lithium precipitation of the negative electrode is inhibited.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrode assembly, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, and high power output, and are widely used in new energy vehicles, energy storage power stations, and base station backup power supplies. The electrode components inside lithium-ion batteries include wound electrode components and stacked electrode components. Wound electrode components are formed by sequentially stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet, typically including a flat region and bending regions on both sides of the flat region. Wound electrode components are widely used due to their simple manufacturing process and high production efficiency.

[0003] However, after the wound electrode assembly is pressed and formed, the electrode in the bending area is squeezed and undergoes asynchronous deformation and non-proportional shrinkage, which increases the gap between adjacent electrodes in this area and makes the adhesion between the electrode and the separator less tight. This affects the electrolyte wetting at the electrode interface, easily causes uneven lithium intercalation in the negative electrode, and thus easily induces lithium plating, lowers the temperature threshold for thermal runaway of the battery, and threatens the safety performance of the battery. Summary of the Invention

[0004] In view of this, embodiments of this application provide an electrode assembly, a method for preparing the same, and a battery to solve at least one problem existing in the prior art.

[0005] In a first aspect, embodiments of this application provide an electrode assembly, including a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet, the negative electrode sheet, and the separator are wound to form a straight region and a bent region;

[0006] The positive electrode sheet includes a positive current collector and a positive active material layer located on the positive current collector. The positive active material layer includes a first active material layer located on a first surface of the positive current collector. The first surface is the surface of the positive current collector that is away from the winding center of the electrode assembly among two surfaces along the thickness direction. The first active material layer has a first groove located in the bending region. The first groove is filled with a first solid electrolyte. The maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector is greater than the depth of the first groove.

[0007] In conjunction with the first aspect of this application, in an optional embodiment, the areal density of the first active material layer located in the flat region is C1, and the areal density of the first active material layer located in the bent region is C2, wherein C1 is greater than C2; optionally, C1 is 300 g / m³. 2 ~450g / m 2The C2 is 150 g / m³ 2 ~405g / m 2 .

[0008] In conjunction with the first aspect of this application, in an optional embodiment, the depth of the first groove is Q, where Q = (1-a) × d1; and,

[0009] a = C2 / C1, where a ranges from 0.5 to 0.9; d1 is the maximum thickness of the first active material layer.

[0010] In conjunction with the first aspect of this application, in an optional embodiment, the maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is P. n P n =ΔW-d total -Δd neg +Q; where,

[0011] Q is the depth of the first groove;

[0012] d total The total thickness of the single-layer positive electrode, the single-layer negative electrode, and the two-layer separator located in the bending region;

[0013] ΔW is the spacing between adjacent negative electrode plates in the bending region, ΔW=d total ×(1+μ*ξ bluk ), where μ is the radius compression sensitivity coefficient of the bending region, and its value ranges from 0.65 to 0.85, ξ bluk The total thickness compression ratio of the electrode assembly before and after pressing is 0.2 to 0.3.

[0014] Δd neg Δd represents the fully charged expansion thickness of the single-layer negative electrode sheet. neg =υ×d2, where υ is the coefficient of thermal expansion at full charge, and its value ranges from 18% to 25%, and d2 is the thickness of the negative electrode active material layer in the negative electrode sheet.

[0015] In conjunction with the first aspect of this application, in an alternative embodiment,

[0016] The first solid electrolyte includes a polymer electrolyte and / or a sulfide electrolyte;

[0017] And / or, the positive electrode active material layer further includes a second active material layer located on the second surface of the positive electrode current collector, the second surface being the surface opposite to the first surface; the second active material layer has a second groove located in the bending region; optionally, the second groove is filled with a second solid electrolyte.

[0018] Secondly, embodiments of this application provide a method for preparing an electrode assembly, the method comprising:

[0019] A positive electrode, a separator, and a negative electrode are provided; the positive electrode includes a positive current collector and a positive active material layer located on the positive current collector, the positive active material layer including a first active material layer located on a first surface of the positive current collector, the first active material layer having a first groove; the first groove is filled with a first solid electrolyte, the maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector being greater than the depth of the first groove;

[0020] The positive electrode, separator, and negative electrode are stacked in sequence and wound along a first direction. After being pressed, the electrode assembly is formed. The electrode assembly includes a flat region and a bent region. The first surface is the surface of the positive current collector that is away from the winding center of the electrode assembly among the two surfaces along the thickness direction. The first groove is located in the bent region.

[0021] In conjunction with a second aspect of this application, in an optional embodiment, the positive electrode includes:

[0022] The positive electrode active material, positive electrode conductive agent and positive electrode binder are mixed in a solvent and stirred evenly to obtain a positive electrode slurry;

[0023] The positive electrode current collector includes a first segment and a second segment arranged alternately along the first direction. The positive electrode slurry is coated on the surface of the first segment and the second segment respectively. After drying and rolling, the first active material layer is formed on the first surface. The areal density of the first active material layer located in the first segment is C1, and the areal density of the first active material layer located in the second segment is C2, wherein C1 is greater than C2. The first segment is located in the straight region of the electrode assembly, and the second segment is located in the bent region of the electrode assembly.

[0024] The first solid electrolyte is filled into the first groove.

[0025] In conjunction with the second aspect of this application, in an alternative embodiment,

[0026] The C1 is 300g / m 2 ~450g / m 2 The C2 is 150 g / m³ 2 ~405g / m 2 ;

[0027] And / or, the depth of the first groove is Q, Q=(1-a)×d1; where a=C2 / C1, the value of a ranges from 0.5 to 0.9; d1 is the maximum thickness of the first active material layer;

[0028] And / or, the feed flow rates for coating the positive electrode slurry on the first section and the second section are V1 and V2, respectively; V2 and V1 satisfy:

[0029] ;

[0030] And / or, if the dimension of the portion of the first active material layer in the bending region in the first direction is smaller than the minimum coating gap in the coating process, then the length of the second segment is set as the minimum coating gap.

[0031] In conjunction with the second aspect of this application, in an alternative embodiment,

[0032] The maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is P. n P n =ΔW-d total -Δd neg +Q; where,

[0033] Q is the depth of the first groove;

[0034] d total The total thickness of the single-layer positive electrode, the single-layer negative electrode, and the two-layer separator located in the bending region;

[0035] ΔW is the spacing between adjacent negative electrode plates in the bending region, ΔW=d total ×(1+μ*ξ bluk ), where μ is the radius compression sensitivity coefficient of the bending region, and its value ranges from 0.65 to 0.85, ξ bluk The total thickness compression ratio of the electrode assembly before and after pressing is 0.2 to 0.3.

[0036] Δd neg Δd represents the fully charged expansion thickness of the single-layer negative electrode sheet. neg =υ×d2, where υ is the coefficient of thermal expansion at full charge, and its value ranges from 18% to 25%, and d2 is the thickness of the negative electrode active material layer in the negative electrode sheet;

[0037] And / or, the first solid electrolyte includes a polymer electrolyte and / or a sulfide electrolyte;

[0038] And / or, the positive electrode active material layer further includes a second active material layer located on the second surface of the positive electrode current collector, the second surface being the surface opposite to the first surface; the second active material layer has a second groove located in the bending region; optionally, the second groove is filled with a second solid electrolyte.

[0039] Thirdly, embodiments of this application provide a battery comprising the electrode assembly described in any one of the first aspects, or an electrode assembly prepared by a method comprising the electrode assembly described in any one of the second aspects.

[0040] Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0041] The electrode assembly provided in this application embodiment includes a positive electrode sheet comprising a first active material layer on a first surface of a positive electrode current collector. The first active material layer has a first groove located in the bending region, which helps to improve the N / P value of the bending region, thereby reducing the risk of lithium plating on the negative electrode sheet in the bending region. At the same time, the first groove is filled with a first solid electrolyte, and the maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is greater than the depth of the first groove. Thus, the first solid electrolyte can not only store electrolyte and construct a continuous active ion transport channel, but its protruding part can also fill the increased gap between adjacent negative electrodes in the bending region of the pressed electrode assembly, improve the electrolyte wetting effect at the electrode interface, improve the lithium intercalation kinetics of the negative electrode sheet in the bending region, thereby suppressing lithium plating on the negative electrode, and thus improving the cycle performance and safety performance of the battery.

[0042] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0043] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0044] Figure 1 A schematic flowchart illustrating a method for fabricating an electrode assembly according to an embodiment of this application;

[0045] Figure 2 This is a schematic diagram of the structure of a positive electrode sheet during the preparation process in an embodiment of this application;

[0046] Figure 3 For along Figure 2 A schematic diagram of a cross-sectional structure of line A-A' in the middle;

[0047] Figure 4 for Figure 3 The diagram shown illustrates the structure of the positive electrode area after rolling.

[0048] Figure 5 For along Figure 2 Another cross-sectional view of line A-A';

[0049] Figure 6 for Figure 5 The diagram shown illustrates the structure of the positive electrode area after rolling.

[0050] Figure 7 This is a schematic diagram of the structure of a positive electrode sheet provided in an embodiment of this application;

[0051] Figure 8 This is a schematic diagram of the structure of an electrode assembly provided in an embodiment of this application;

[0052] Figure 9 For along Figure 8 A schematic diagram of the cross-sectional structure of line B-B' in the middle section;

[0053] Figure 10 for Figure 9 A magnified view of the middle bend area. Detailed Implementation

[0054] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0055] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0056] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify 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. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0057] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0058] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0059] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0060] The inventors discovered that after the wound electrode assembly is formed by pressing (e.g., cold pressing or hot pressing), the electrode sheet located in the bending area (also known in the industry as the R-angle) is compressed, causing the gap between adjacent electrode sheets in this area to increase. This easily leads to uneven lithium intercalation in the negative electrode, which in turn induces lithium plating. Moreover, this phenomenon is more likely to occur at the interface of the negative electrode sheet on the side of the positive electrode sheet away from the winding center at the bending area. It can be understood that lithium plating is more likely to occur in the negative-wrapped-positive structure where the negative electrode sheet covers the positive electrode sheet. With the development and application of fast charging technology, under high-rate charging conditions, the problem of uneven lithium intercalation and lithium plating on the surface of the negative electrode sheet facing the winding center in the above-mentioned negative-wrapped-positive structure becomes more serious.

[0061] Based on this, embodiments of this application provide an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet, the negative electrode sheet, and the separator are wound to form a straight region and a bent region; the positive electrode sheet includes a positive current collector and a positive active material layer located on the positive current collector, the positive active material layer including a first active material layer located on a first surface of the positive current collector, the first surface being the surface of the positive current collector away from the winding center of the electrode assembly among two surfaces along the thickness direction; the first active material layer has a first groove located in the bent region, the first groove being filled with a first solid electrolyte, the maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector being greater than the depth of the first groove.

[0062] In the electrode assembly of this application embodiment, the positive electrode includes a first active material layer on the first surface of the positive current collector. The first active material layer has a first groove in the bending region, which helps to improve the N / P value of the bending region, thereby reducing the risk of lithium plating of the negative electrode in the bending region. At the same time, the first groove is filled with a first solid electrolyte, and the maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector is greater than the depth of the first groove. Thus, the first solid electrolyte can not only store electrolyte and construct a continuous active ion (e.g., lithium ion or sodium ion) transport channel, but its protruding part can also fill the increased gap between adjacent negative electrodes in the bending region of the pressed electrode assembly, improve the electrolyte wetting effect at the electrode interface, improve the lithium intercalation kinetics of the negative electrode in the bending region, thereby suppressing lithium plating of the negative electrode, and thus improving the cycle performance and safety performance of the battery.

[0063] In this embodiment, the negative electrode may include a negative current collector and a negative active layer located on at least one surface (typically two surfaces in a wound electrode) of the negative current collector along the thickness direction. The positive electrode may include a positive current collector and a positive active layer located on at least one surface (typically two surfaces in a wound electrode) of the positive current collector along the thickness direction. The N / P value of the bending region can be understood as the ratio of the areal capacity of the adjacent bending segment of the negative electrode to that of the bending segment of the positive electrode at the bending region.

[0064] In some embodiments, the size of the first groove in the electrode assembly winding direction is less than or equal to the size of the bent section of the first active material layer in the electrode assembly winding direction where the first groove is located.

[0065] In some embodiments, the areal density of the first active material layer located in the flat region is C1, and the areal density of the first active material layer located in the bent region is C2, wherein C1 can be greater than C2. Thus, in the actual fabrication process of the positive electrode sheet, the positive current collector has a first segment located in the flat region and a second segment located in the bent region. By controlling the coating areal density of the positive electrode slurry on the first segment to be less than the coating areal density on the second segment (i.e., the coating thickness on the first segment is less than the coating thickness on the second segment), C1 can be made greater than C2. Ultimately, the thickness of the first active material layer located in the bent region can be made less than the thickness of the first active material layer located in the flat region, thereby directly forming the first groove in the first active material layer without secondary processing, simplifying the process. It can be understood that, in this case, the dimension of the first groove in the electrode assembly winding direction is substantially equal to the dimension of the bent segment of the first active material layer containing the first groove in the electrode assembly winding direction.

[0066] Of course, in the embodiments of this application, it is not excluded that other processes (such as laser etching) may be used to form the first groove in the bending area of ​​the first active material layer.

[0067] Optionally, C1 is 300g / m 2 ~450g / m 2 For example, it can be 300g / m 2 350g / m 2 400g / m 2 450g / m 2 Or any value between any two of the above ranges; C2 is 150 g / m 2 ~405g / m 2 For example, it can be 150g / m 2 200g / m 2 250g / m 2 300g / m 2 350g / m 2 405g / m 2 Or any value between any two of the above ranges.

[0068] In some embodiments, the depth of the first groove is Q, Q = (1-a) × d1; where a = C2 / C1, and the value of a ranges from 0.5 to 0.9; d1 is the maximum thickness of the first active material layer (here, it refers to the thickness of the portion of the first active material layer that does not have the first groove).

[0069] In this embodiment, with the maximum thickness d1 of the first active material layer remaining constant, the smaller the value of a (i.e., the larger the value of C1 exceeding C2), the larger the depth Q of the first groove. Controlling the value of a within the range of 0.5 to 0.9, for example, 0.5, 0.6, 0.7, 0.8, 0.9, or any value between any two of the above ranges, allows the depth of the first groove to be adapted to the thickness of the first active material layer. This can appropriately increase the N / P value of the bending region to reduce the overall lithium plating risk in the bending region, while avoiding excessive reduction of the first active material layer in the positive electrode, thus balancing the energy density of the battery. Furthermore, it can better ensure that an appropriate amount of the first solid electrolyte is filled in the first groove, ensuring the effectiveness of storing the electrolyte and constructing a channel for continuous and rapid transport of active ions. This can better suppress lithium plating in the negative electrode of the negative-to-positive structure in the bending region, thereby better improving the cycle performance and safety performance of the battery.

[0070] In some embodiments, the maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is P. n P n =ΔW-d total -Δd neg +Q; where Q is the depth of the first groove; d totalΔW represents the total thickness of the single-layer positive electrode, single-layer negative electrode, and two-layer separator located in the bending region; ΔW is the spacing between adjacent negative electrode sheets in the bending region, ΔW=d total ×(1+μ*ξ bluk ), where μ is the radius compression sensitivity coefficient of the bending region, which is related to the positive electrode active material, and its value ranges from 0.65 to 0.85. For example, it can be 0.65, 0.75, 0.85, or any value between any two of the above ranges, and ξ bluk ξ represents the total thickness compression ratio of the electrode assembly before and after pressing. bluk =(H0-H1) / H0, where H0 is the thickness of the entire electrode assembly before pressing, and H1 is the thickness of the entire electrode assembly after pressing. ξ bluk The value range is 0.2 to 0.3, for example, it can be 0.2, 0.25, 0.3, or any value between any two of the above ranges; Δd neg Δd represents the fully charged expansion thickness of a single-layer negative electrode. neg =υ×d2, where υ is the coefficient of thermal expansion at full charge, and its value ranges from 18% to 25%. For example, it can be 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value between any two of the above ranges. d2 is the thickness of the negative electrode active material layer in the negative electrode sheet.

[0071] In the manufacturing process of electrode components, the negative electrode sheet, separator, positive electrode sheet, and separator are typically stacked in that order and then wound. After winding, both the positive and negative electrode sheets are bonded to the adjacent separator. The spacing between adjacent negative electrode sheets in the bending region (e.g., the spacing between the outer contours of adjacent negative electrode sheets away from the winding center) is the total thickness d of the single-layer positive electrode sheet, single-layer negative electrode sheet, and two-layer separator located in the bending region. total d here total This can also be understood as the thickness of the electrode assembly after it has been unfolded. After the wound assembly is pressed and formed, the spacing ΔW between adjacent negative electrode sheets in the bending area increases due to the compression effect. The magnitude of this increase is related to the radius of the bending area, the compression sensitivity coefficient μ, and the total thickness compression ratio ξ of the electrode assembly before and after pressing. bluk It is directly proportional. In this embodiment, ΔW is based on d. total μ and ξ bluk Based on the actual process, the spacing between adjacent negative electrode sheets in the bending area of ​​the electrode assembly after pressing and forming can be estimated relatively accurately. Furthermore, considering that the negative electrode sheets generally expand during cycling, the maximum thickness of the portion of the first solid electrolyte protruding from the first groove in the direction of the positive electrode current collector thickness is based on ΔW-d. totalIt is confirmed that the first solid electrolyte will essentially come into contact with the negative electrode. If the negative electrode expands, the two will compress each other, potentially causing localized stress concentration and affecting the battery's cycle stability. Therefore, in this embodiment, P is controlled... n =ΔW-d total -Δd neg +Q, that is, based on the first solid electrolyte filling the first groove and protruding from the first groove, a certain gap is reserved between the first solid electrolyte and the negative electrode plate. This gap is based on the fully charged expansion thickness Δd of the single-layer negative electrode plate. neg Determined, Δd neg Based on the full-charge expansion coefficient υ and the thickness d2 of the negative electrode active material layer in the negative electrode sheet, this can better ensure the adhesion between the electrode sheet and the separator during battery cycling, ensure the electrolyte wetting effect at the electrode interface, and thus ensure the continuous and rapid transport of active ions, suppress lithium plating at the negative electrode, and at the same time, better avoid the stress concentration problem that may be caused by the mutual compression between the first solid electrolyte and the negative electrode sheet.

[0072] It should be noted that, in this embodiment, the above-mentioned P is set. n When formulating the formula, the thickness changes of the single-layer electrode (including positive and negative electrode) and the separator before and after pressing are both regarded as zero, that is, the thickness is regarded as basically unchanged before and after pressing.

[0073] In some embodiments, the first solid electrolyte may include a polymer electrolyte and / or a sulfide electrolyte. Specifically, the first solid electrolyte is a polymer electrolyte and / or a sulfide electrolyte.

[0074] Preferably, the first solid electrolyte is a polymer electrolyte, which has excellent flexibility, bendability and deformation adaptability, better interface adhesion, and can better adapt to the shape of the bending area.

[0075] For example, the material of the polymer electrolyte matrix may be one or more of polyethylene oxide (PEO), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF).

[0076] The polymer electrolyte also includes a lithium salt, which may be one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium di(oxalato)borate (LiBOB), and lithium di(fluorooxalato)borate (LiDFOB). In practical applications, the lithium salt in the polymer electrolyte may be the same as the lithium salt in the electrolyte.

[0077] In some specific embodiments, the mass ratio of the polymer electrolyte matrix to the lithium salt can be 100:(8~36), for example, 100:8, 100:12, 100:16, 100:20, 100:24, 100:28, 100:32, 100:36 or any other ratio within the above mass ratio range.

[0078] For example, the sulfide electrolyte can be Li 10 GeP2S 12 (LGPS), Li 4-x Ge 1-x P x One or more of S4 (0 < x < 1).

[0079] In some embodiments, the positive electrode active material layer further includes a second active material layer located on the second surface of the positive electrode current collector, the second surface being the surface opposite to the first surface; the second active material layer has a second groove located in the bending region.

[0080] In the bending region of the electrode assembly, where the positive electrode is located on the side furthest from the winding center of the adjacent negative electrode (the positive electrode covers the negative electrode), after the electrode assembly is unrolled, the projected area of ​​the positive electrode in the stacking direction is larger than that of the negative electrode. This results in a smaller N / P ratio between the negative and positive electrode segments, making lithium plating more likely in the later stages of battery cycling due to insufficient N / P. In this embodiment, the second active material layer has a second groove located in the bending region, which can improve the N / P ratio of the positive electrode covering the negative electrode in the bending region, thereby effectively improving the lithium plating problem caused by insufficient N / P ratio in the later stages of battery cycling.

[0081] In some embodiments, the second groove may be filled with a second solid electrolyte. This allows the second solid electrolyte to store the electrolyte and create a continuous active ion transport channel, thereby further improving the lithium intercalation kinetics of the negative electrode at the bending region and suppressing lithium plating at the negative electrode.

[0082] The type of the second solid electrolyte can be understood with reference to the type of the first solid electrolyte, and will not be repeated here. The second solid electrolyte may be the same as or different from the first solid electrolyte.

[0083] In some specific embodiments, the thickness of the second solid electrolyte in the thickness direction of the positive electrode current collector can be less than or equal to the depth of the second groove.

[0084] In this embodiment, the second solid electrolyte is located on the side of the positive electrode current collector near the winding center. The thickness of the second solid electrolyte in the thickness direction of the positive electrode current collector is less than or equal to the depth of the second groove, that is, the second solid electrolyte fills part of the second groove, or the second solid electrolyte just fills the second groove. In this way, the second solid electrolyte can be avoided from being excessively compressed in the bending area, resulting in excessive local stress.

[0085] This application also provides a method for preparing an electrode assembly; please refer to [reference needed]. Figure 1 The method for preparing the electrode assembly provided in this application includes the following steps:

[0086] S1: Provides a positive electrode sheet, a separator, and a negative electrode sheet; the positive electrode sheet includes a positive current collector and a positive active material layer located on the positive current collector, the positive active material layer includes a first active material layer located on a first surface of the positive current collector, the first active material layer has a first groove; the first groove is filled with a first solid electrolyte, the maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector is greater than the depth of the first groove;

[0087] S2: The positive electrode sheet, separator and negative electrode sheet are stacked in sequence and wound along the first direction. After being pressed, an electrode assembly is formed. The electrode assembly includes a flat area and a bent area. The first surface is the surface of the positive electrode current collector that is away from the winding center of the electrode assembly among the two surfaces along the thickness direction. The first groove is located in the bent area.

[0088] In this embodiment, the positive electrode sheet provided in step S1 includes a first active material layer on the first surface of the positive current collector, and the first active material layer has a first groove. In the electrode assembly obtained in step S2, the first surface is the surface of the positive current collector away from the winding center of the electrode assembly, and the first groove is located in the bending region. This is beneficial to improve the N / P value of the bending region, thereby reducing the risk of lithium plating of the negative electrode sheet in the bending region. At the same time, the first groove is filled with a first solid electrolyte, and the maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector is greater than the depth of the first groove. Thus, the first solid electrolyte can not only store electrolyte and construct a continuous active ion transport channel, but its part protruding from the first groove can also fill the increased gap between adjacent negative electrode sheets in the bending region of the pressed electrode assembly, improve the electrolyte wetting effect at the electrode interface, thereby improving the lithium intercalation kinetics of the negative electrode sheet in the bending region, suppressing lithium plating of the negative electrode, and thus improving the cycle performance and safety performance of the battery.

[0089] In step S1, providing the positive electrode may include the following steps:

[0090] Step S11: Mix the positive electrode active material, positive electrode conductive agent and positive electrode binder in a solvent, and stir evenly to obtain a positive electrode slurry.

[0091] The types of positive electrode active materials, positive electrode conductive agents, positive electrode binders, and solvents are not specifically limited herein; any positive electrode active material, positive electrode conductive agent, positive electrode binder, and solvent well known to those skilled in the art can be used. For example, the positive electrode active material can be one or more of lithium iron phosphate, ternary materials, and lithium manganese iron phosphate. The positive electrode conductive agent can be one or more of conductive carbon black, carbon nanotubes, and graphene. The positive electrode binder can be one or more of polyvinylidene fluoride, polyacrylic acid, and polymethyl methacrylate. The solvent can be N-methylpyrrolidone.

[0092] Step S12: Please refer to Figures 2 to 4 The positive electrode current collector 10 includes a first section 101 and a second section 102 arranged alternately along a first direction. Positive electrode slurry is coated on the surfaces of the first section 101 and the second section 102 respectively. After drying and rolling, a first active material layer 21 is formed on the first surface 1011 of the positive electrode current collector 10. The areal density of the first active material layer 21 located in the first section 101 is C1, and the areal density of the first active material layer 21 located in the second section 102 is C2, wherein C1 is greater than C2. The first section 101 is located in the straight region in the electrode assembly, and the second section 102 is located in the bent region in the electrode assembly.

[0093] In the actual manufacturing process, a positive electrode slurry is coated on the first surface 1011 of the positive electrode current collector 10 along the thickness direction. The coating thickness of the positive electrode slurry on the second section 102 is less than the coating thickness of the positive electrode slurry on the first section 101 (e.g., ...). Figure 3 (As shown in the dashed box), thus a groove can be directly formed in the corresponding area of ​​the second section 102. After drying and rolling, a first active material layer 21 is formed, which can make C1 greater than C2. The groove is then transformed into the first groove 211 in the first active material layer 21 (as shown in the dashed box). Figure 4 (As shown within the dashed box), thus, a first groove 211 can be formed in the portion of the first active material layer 21 located in the bending region, eliminating the need for secondary processing to form the first groove 211, simplifying the process, and ensuring uniform composition of the positive electrode active layer in the positive electrode sheet, resulting in high performance consistency of the positive electrode sheet. In this case, the dimension of the first groove 211 in the first direction is approximately equal to the dimension of the second segment 102 in the first direction.

[0094] In some embodiments, please refer to Figures 2 to 4 The method for preparing the positive electrode sheet may further include: coating a positive electrode slurry on the second surface 1021 (the surface opposite to the first surface 1011) of the positive electrode current collector 10 along the thickness direction, wherein the coating thickness of the positive electrode slurry on the second section 102 may be the same as the coating thickness of the positive electrode slurry on the first section 101 (e.g., ...). Figure 3 As shown), after drying and rolling, a second active material layer 22 is formed (as shown). Figure 4 (As shown).

[0095] In some embodiments, please refer to Figure 5 and Figure 6 The method for preparing the positive electrode sheet may further include: coating a positive electrode slurry on the second surface 1021 of the positive electrode current collector 10 along the thickness direction, wherein the coating thickness of the positive electrode slurry on the second section 102 is less than the coating thickness of the positive electrode slurry on the first section 101 (e.g., ...). Figure 5 (As shown in the dashed box), after drying and rolling, a second active material layer 22 is formed, thereby enabling the second active material layer 22 to have a second groove 221 located in the bending area (as shown in the dashed box). Figure 6 (As shown within the dashed box).

[0096] In the bending region of the electrode assembly, where the positive electrode is located on the side furthest from the winding center of the adjacent negative electrode (the positive electrode covers the negative electrode), when the electrode assembly is unrolled, the projected area of ​​the positive electrode in the stacking direction is larger than that of the negative electrode. This results in a smaller N / P ratio between the negative and positive electrode segments, making lithium plating more likely in the later stages of battery cycling due to insufficient N / P. In this embodiment, the second active material layer 22 of the fabricated positive electrode has a second groove 221 located in the bending region, which can improve the N / P ratio of the positive electrode covering the negative electrode in the bending region, thereby effectively improving the lithium plating problem caused by insufficient N / P ratio in the later stages of battery cycling.

[0097] Optionally, the areal density C1 of the first active material layer 21 located in the first section 101 is 300 g / m². 2 ~450g / m 2 For example, it can be 300g / m 2 350g / m 2 400g / m 2 450g / m 2 Or any value between any two of the above-mentioned numerical ranges; the areal density C2 of the first active material layer 21 located in the second segment 102 is 150 g / m². 2 ~405g / m 2 For example, it can be 150g / m 2 200g / m 2 250g / m 2 300g / m 2 350g / m 2 405g / m 2 Or any value between any two of the above ranges.

[0098] In some embodiments, the depth of the first groove 211 is Q, Q = (1-a) × d1; where a = C2 / C1, and the value of a ranges from 0.5 to 0.9; d1 is the maximum thickness of the first active material layer 21 (here, it refers to the thickness of the portion of the first active material layer 21 that does not have the first groove 211).

[0099] In this embodiment, with the maximum thickness d1 of the first active material layer 21 remaining constant, the smaller the value of a (i.e., the larger the value of C1 exceeding C2), the larger the depth Q of the first groove 211. Controlling the value of a within the range of 0.5 to 0.9, for example, 0.5, 0.6, 0.7, 0.8, 0.9, or any value between any two of the above ranges, allows the depth of the first groove 211 to be adapted to the thickness of the first active material layer 21. This can appropriately increase the N / P value of the bending region to reduce the overall lithium plating risk in the bending region, while avoiding excessive reduction of the first active material layer 21 in the positive electrode, thus balancing the energy density of the battery. Furthermore, it can better ensure that an appropriate amount of the first solid electrolyte is filled in the first groove 211, ensuring the effect of using the first solid electrolyte to store the electrolyte and construct a channel for continuous and rapid transport of active ions. This can better suppress lithium plating in the negative electrode of the negative-to-positive structure in the bending region, thereby better improving the cycle performance and safety performance of the battery.

[0100] In some embodiments, the areal density of the first active material layer 21 located in the first section 101 is C1, the areal density of the first active material layer 21 located in the second section 102 is C2, and the feed flow rates of the positive electrode slurry coated on the first section 101 and the second section 102 are V1 and V2, respectively; V2 and V1 satisfy:

[0101] .

[0102] In this embodiment, based on the target values ​​of C1 and C2, and combined with the feed flow rate of the positive electrode slurry coated on the first section 101, the feed flow rate of the positive electrode slurry coated on the second section 102 is determined. In this way, the areal density of the first active material layer 21 in different sections can be better controlled by the process to achieve the target value.

[0103] Optionally, V1 can be 10 mL / min to 60 mL / min, for example, it can be 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, 50 mL / min, 60 mL / min or any value between any two of the above ranges.

[0104] In actual manufacturing processes, the cathode slurry can be coated using an extrusion coating process, specifically, an extrusion coater. The feed flow rate of the cathode slurry can also be referred to as the coating pump speed. In the coating process, the coating conveyor speed can be from 1 mm / s to 10 mm / s, for example, 1 mm / s, 2 mm / s, 3 mm / s, 4 mm / s, 5 mm / s, 6 mm / s, 7 mm / s, 8 mm / s, 9 mm / s, 10 mm / s, or any value within any two of these ranges.

[0105] In the electrode assembly formed by winding, the sections of the positive and negative electrode sheets located in the bending region are the positive electrode bending section and the negative electrode bending section, respectively. The shape of each positive and negative electrode bending section is semi-circular or approximately semi-circular. The dimension Ln of any positive electrode bending section along the first direction can be calculated using the formula: Ln = πr, where r is the radius of each positive electrode bending section. It can be seen that as the number of winding layers increases, r increases, and Ln increases. Therefore, from the starting end to the ending end of the winding of the positive electrode sheet, the values ​​of L1 to Ln show an increasing trend. Accordingly, please refer to... Figure 2 From the starting end to the ending end of the winding of the positive electrode sheet, the size of the second segment 102 of the positive electrode current collector 10 increases in the first direction (corresponding to L1~Ln in the figure), while the size of the first segment 101 in the first direction (corresponding to L in the figure) remains unchanged. The positive electrode slurry is continuously coated in the first direction, and the coating size in the width direction of the positive electrode current collector 10 can remain unchanged.

[0106] For one or more positive electrode bending sections closest to the straight region, Ln is also small due to the small size of r. In the actual preparation process, if the dimension of the portion of the first active material layer 21 in the bending region in the first direction is smaller than the minimum coating gap in the coating process, then the length of the second section 102 is set as the minimum coating gap.

[0107] The minimum coating gap here can be 5mm to 10mm, for example, it can be 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or any value between any two of the above ranges.

[0108] Of course, in this embodiment, it is not excluded that the same surface density positive electrode paste is coated on the surfaces of the first section 101 and the second section 102. After drying and rolling, an active material layer with a consistent surface density is formed. Then, other processes (such as laser etching) can be used to form a first groove in the portion of the active material layer located in the bending region. The size of the first groove in the first direction can be less than or equal to the size of the bending section of the first active material layer where the first groove is located in the electrode assembly winding direction.

[0109] Step S13: Please refer to Figure 7The first solid electrolyte 212 is filled in the first groove 211.

[0110] In the actual manufacturing process, the position of the first groove 211 can be identified using a CCD camera, and then the first solid electrolyte 212 can be sprayed. During the coating of the positive electrode slurry, since the coating thickness of the positive electrode slurry on the second section 102 is less than that on the first section 101, the positive electrode slurry on the first section 101 will flow onto the positive electrode slurry on the second section 102, resulting in a sloping sidewall of the final formed first groove 211. The opening area of ​​the first groove 211 is larger than the bottom area of ​​the first groove 211, meaning the longitudinal section of the first groove 211 presents an inverted trapezoidal shape. This facilitates the filling of the first solid electrolyte 212 and increases the contact area between the first solid electrolyte 212 and the first active material layer 21, improving the stability of their adhesion.

[0111] In some embodiments, the maximum thickness of the first solid electrolyte 212 in the thickness direction of the positive electrode current collector 10 is P. n P n =ΔW-d total -Δd neg +Q; where Q is the depth of the first groove 211; d total ΔW represents the total thickness of the single-layer positive electrode, single-layer negative electrode, and two-layer separator located in the bending region; ΔW is the spacing between adjacent negative electrode sheets in the bending region, ΔW=d total ×(1+μ*ξ bluk ), where μ is the radius compression sensitivity coefficient of the bending region, and its value ranges from 0.65 to 0.85. For example, it can be 0.65, 0.75, 0.85, or any value between any two of the above ranges. ξ bluk The total thickness compression ratio of the electrode assembly before and after pressing, with a value ranging from 0.2 to 0.3, for example, can be 0.2, 0.25, 0.3, or any value between any two of the above ranges; Δd neg Δd represents the fully charged expansion thickness of a single-layer negative electrode. neg =υ×d2, where υ is the coefficient of thermal expansion at full charge, and its value ranges from 18% to 25%. For example, it can be 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value between any two of the above ranges. d2 is the thickness of the negative electrode active material layer in the negative electrode sheet.

[0112] In the manufacturing process of electrode components, the negative electrode sheet, separator, positive electrode sheet, and separator are typically stacked in that order and then wound. After winding, both the positive and negative electrode sheets are bonded to the adjacent separator. The spacing between adjacent negative electrode sheets in the bending region (e.g., the spacing between the outer contours of adjacent negative electrode sheets away from the winding center) is the total thickness d of the single-layer positive electrode sheet, single-layer negative electrode sheet, and two-layer separator located in the bending region. total d here total This can also be understood as the thickness of the electrode assembly after it has been unfolded. After the wound assembly is pressed and formed, the spacing ΔW between adjacent negative electrode sheets in the bending area increases due to compression. The magnitude of this increase is related to the radius of the bending area, the compression sensitivity coefficient μ, and the total thickness compression ratio ξ of the electrode assembly before and after pressing. bluk It is directly proportional. In this embodiment, ΔW is based on d. total μ and ξ bluk Based on the actual process, the spacing between adjacent negative electrode sheets in the bending area of ​​the electrode assembly after pressing and forming can be estimated relatively accurately. Furthermore, considering that the negative electrode sheets generally expand during cycling, the maximum thickness of the portion of the first solid electrolyte protruding from the first groove in the direction of the positive electrode current collector thickness is based on ΔW-d. total It is confirmed that the first solid electrolyte will essentially come into contact with the negative electrode. If the negative electrode expands, the two will compress each other, potentially causing localized stress concentration and affecting the battery's cycle stability. Therefore, in this embodiment, P is controlled... n =ΔW-d total -Δd neg +Q, that is, based on the first solid electrolyte 212 filling the first groove 211 and protruding from the first groove 211, a certain gap is reserved between the first solid electrolyte 212 and the negative electrode sheet. This gap is based on the fully charged expansion thickness Δd of the single-layer negative electrode sheet. neg Determined, Δd neg Based on the full-charge expansion coefficient υ and the thickness d2 of the negative electrode active material layer in the negative electrode sheet, this can better ensure the adhesion between the electrode sheet and the separator during battery cycling, ensure the electrolyte wetting effect at the electrode interface, and thus ensure the continuous and rapid transport of active ions, suppress lithium plating on the negative electrode, and at the same time, better avoid the stress concentration problem that may be caused by the mutual compression between the first solid electrolyte 212 and the negative electrode sheet.

[0113] It should be noted that, in this embodiment, the above-mentioned P is set. n When formulating the formula, the thickness changes of the single-layer electrode (including positive and negative electrode) and the separator before and after pressing are basically regarded as zero, that is, the thickness before and after pressing is regarded as basically unchanged.

[0114] In some embodiments, the first solid electrolyte 212 may include a polymer electrolyte and / or a sulfide electrolyte. Specifically, the first solid electrolyte is a polymer electrolyte and / or a sulfide electrolyte.

[0115] Preferably, the first solid electrolyte is a polymer electrolyte, which has excellent flexibility, bendability and deformation adaptability, better interface adhesion, and can better adapt to the shape of the bending area.

[0116] For example, the material of the polymer electrolyte matrix may be one or more of polyethylene oxide (PEO), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF).

[0117] The polymer electrolyte also includes a lithium salt, which may be one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium di(oxalato)borate (LiBOB), and lithium di(fluorooxalato)borate (LiDFOB). In practical applications, the lithium salt in the polymer electrolyte may be the same as the lithium salt in the electrolyte.

[0118] In some specific embodiments, the mass ratio of the polymer electrolyte matrix to the lithium salt can be 100:(8~36), for example, 100:8, 100:12, 100:16, 100:20, 100:24, 100:28, 100:32, 100:36 or any other ratio within the above mass ratio range.

[0119] For example, the sulfide electrolyte can be Li 10 GeP2S 12 (LGPS), Li 4-x Ge 1-x P x One or more of S4 (0 < x < 1).

[0120] In embodiments where the second active material layer 22 has a second groove 221, step S13 may further include filling the second groove 221 with a second solid electrolyte (not shown). This allows the second solid electrolyte to store the electrolyte and construct a continuous active ion transport channel, thereby further improving the lithium intercalation kinetics of the negative electrode at the bending region and suppressing lithium plating at the negative electrode.

[0121] The type and filling process of the second solid electrolyte can be understood by referring to the type and filling process of the first solid electrolyte, and will not be repeated here. The second solid electrolyte can be the same as or different from the first solid electrolyte.

[0122] In some specific embodiments, the thickness of the second solid electrolyte in the thickness direction of the positive electrode current collector can be less than or equal to the depth of the second groove.

[0123] In this embodiment, the second solid electrolyte is located on the side of the positive electrode current collector near the winding center. The thickness of the second solid electrolyte in the thickness direction of the positive electrode current collector is less than or equal to the depth of the second groove, that is, the second solid electrolyte fills part of the second groove, or the second solid electrolyte just fills the second groove. In this way, the second solid electrolyte can be avoided from being excessively compressed in the bending area, resulting in excessive local stress.

[0124] The preparation of the negative electrode sheet is not limited in the embodiments of this application. For example, the preparation method commonly used in the art can be used. First, the negative electrode active material, negative electrode conductive agent and negative electrode binder are mixed in a solvent and stirred evenly to obtain a negative electrode slurry. Then, the negative electrode slurry is coated on at least one surface of the negative electrode current collector along the thickness direction (in a wound electrode assembly, it is generally coated on two surfaces of the negative electrode current collector along the thickness direction). After drying and rolling, the negative electrode sheet is obtained.

[0125] The type of diaphragm is not limited in the embodiments of this application, and any diaphragm type known to those skilled in the art can be used.

[0126] In step S2, the positive electrode sheet, separator and negative electrode sheet are stacked in sequence and wound along the first direction. After being pressed, an electrode assembly is formed. The electrode assembly includes a flat area and a bent area. The first surface is the surface of the positive electrode current collector that is away from the winding center of the electrode assembly among the two surfaces along the thickness direction. The first groove is located in the bent area.

[0127] The first direction here is usually the length direction of the positive electrode, separator, and negative electrode.

[0128] In the actual manufacturing process, the electrode assembly can be obtained by stacking the negative electrode, separator, positive electrode, and separator in that order, then winding them along the first direction, and pressing them (cold pressing or hot pressing).

[0129] Figure 8 and Figure 9 An electrode assembly 400 prepared according to an embodiment of this application is shown. Figure 9 For along Figure 8 A vertical cross-sectional view along line B-B'. Electrode assembly 400 includes a straight region 401 and bent regions 402 located on both sides of the straight region 401. Separator 300 is located between positive electrode 100 and negative electrode 200.

[0130] In some embodiments, please refer to Figure 8 The electrode assembly 400 may further include a positive electrode tab 110 electrically connected to the positive electrode 100 and a negative electrode tab 210 electrically connected to the negative electrode 200.

[0131] certainly, Figure 8 The fact that the positive electrode tab 110 and the negative electrode tab 210 are located on one side of the electrode assembly 400 is only one example. In some other embodiments of this application, the positive electrode tab 110 and the negative electrode tab 210 may also be located on both sides of the electrode assembly 400.

[0132] Figure 10 for Figure 9 A magnified view of a section at point 402 in the middle bend area. Figure 10 It can be seen that the first solid electrolyte 212 is formed on the side of the positive electrode 100 away from the winding center. Figure 10 The positive electrode 100 corresponds to Figure 7 In the structure shown, the size of the first groove 211 in the first direction is basically equal to the size of the positive electrode bending section in the first direction. Therefore, in the bending region 402, the first solid electrolyte 212 completely covers the positive electrode bending section.

[0133] This application also provides a battery, which includes the electrode assembly described in any of the foregoing embodiments or the electrode assembly prepared by the method described in any of the foregoing embodiments.

[0134] It is understood that the beneficial effects of the electrode assembly described in any of the above embodiments also apply to the battery.

[0135] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0136] The methods for preparing the electrode assembly are basically the same in all embodiments, specifically including: coating a positive electrode paste on the first surface 1011 and the second surface 1021 of the positive electrode current collector 10 (aluminum foil), wherein the coating thickness of the positive electrode paste on the first surface 1011 in the first section 101 is greater than the coating thickness in the second section 1021 (see reference). Figure 2 On the second surface 1021, the coating thickness of the positive electrode slurry is the same. After drying and rolling, a first active material layer 21 with a first groove 211 is formed on the first surface 1011, and a second active material layer 22 is formed on the second surface 1021 (see reference). Figure 4 The thickness of the second active material layer 22 is the same as the maximum thickness of the first active material layer 21, that is, the same as the thickness of the portion of the first active material layer 21 that does not have the first groove 211; the position of the first groove 211 is identified using a CCD camera, and a solid electrolyte slurry (the mass ratio of polyacrylonitrile to lithium hexafluorophosphate in the slurry is 100:16) is sprayed into the first groove 211. After drying, the first solid electrolyte 212 is formed, and the positive electrode sheet is obtained (reference). Figure 7The negative electrode slurry is coated onto both surfaces of the negative electrode current collector copper foil along its thickness direction. After drying and rolling, a negative electrode active layer is formed, resulting in a negative electrode sheet. The negative electrode sheet, PE separator, positive electrode sheet, and PE separator are then stacked in that order, wound, and hot-pressed to produce the desired product. Figure 9 The electrode assembly shown has 36 winding layers, meaning that both the positive and negative electrode layers in the bending area on one side of the electrode assembly have 36 layers. The minimum coating gap Lmin of the slurry coating machine is 5mm, and the coating speed is 5mm / s; the thickness d of the PE separator... 隔 =16μm. The specific parameters of the positive and negative electrodes in each embodiment are as follows.

[0137] Example 1

[0138] Based on the mass of the positive electrode active layer as 100%, the positive electrode active layer comprises: 97.5% positive electrode active material (lithium iron phosphate), 0.7% positive electrode conductive agent (conductive carbon black SP), and 1.8% positive electrode binder (PVDF); wherein, the specific capacity of lithium iron phosphate is 145 mAh / g, and the areal density C1 of the first active material layer located in the flat region is 300 g / m³. 2 The areal density C2 of the first active material layer located in the bending region is 270 g / m². 2 ,refer to Figure 2 The coating pump speed of the positive electrode slurry on the first section 101 of the positive electrode current collector 10 is V1 = 20 mL / min, and the coating pump speed of the positive electrode slurry on the second section 102 of the positive electrode current collector 10 is V2 = C2 * V1 / C1 = 18 mL / min. The radius of each positive electrode bending section is r = nd. 正 +nd 负 +(2n+1)d 隔 (n=1~36), the dimension Ln=πr of each positive electrode bending segment along the first direction is used to determine the dimension of the second segment 102 along the first direction (i.e., the slurry coating dimension). If the calculated Ln is less than Lmin, then the dimension of the second segment 102 along the first direction is determined to be Lmin. The thickness d of the positive electrode in the straight region. 正 =144μm, the thickness of the aluminum foil is 12μm, that is, the maximum thickness of the first active material layer d1=(144-12) / 2=66μm; a=C2 / C1=0.9, the depth of the first groove Q=(1-a)×d1=0.1*66=6.6μm.

[0139] Based on the mass of the negative electrode active layer as 100%, the negative electrode active layer comprises: 96.5% negative electrode active material (graphite), 0.5% negative electrode conductive agent (conductive carbon black SP), 1.2% negative electrode binder (CMC), and 1.8% negative electrode binder (SBR); wherein the specific capacity of graphite is 345 mAh / g, and the areal density of the negative electrode sheet is 144 g / m². 2 The thickness d of the negative electrode 负 =100μm, the thickness of the copper foil for the negative electrode current collector is 6μm, and the thickness of the negative electrode active material layer is d2=100-6=94μm. The full-charge expansion thickness of a single-layer negative electrode sheet is Δdneg=υ×d2=0.25*94=23.5μm (υ=25%).

[0140] The total thickness d of the single-layer positive electrode, single-layer negative electrode, and two-layer separator located in the bending region total =d 正 +d 负 +2d 隔 =144+100+2*16=276μm; the spacing ΔW between adjacent negative electrodes in the bending region is d. total ×(1+μ*ξ bluk )=276*(1+0.75*0.2)=317.4μm (μ=0.75,ξ bluk =0.2); the maximum thickness of the first solid electrolyte in the direction of the positive electrode current collector is P. n =ΔW-d total -Δd neg +Q=317.4-276-23.5+6.6=24.5μm.

[0141] It should be noted that the electrode thickness mentioned in this application refers to the thickness after roll forming. The calculation formula for r above is based on... Figure 9 The electrode assembly is fixed. When the structure of the electrode assembly changes (e.g., adjusting the number of diaphragm layers, adjusting the number of turns of the diaphragm at the winding start point excluding the electrode sheet), the formula for calculating r needs to be adjusted accordingly based on the actual structure of the electrode assembly. Furthermore, the areal density is tested using the punching weight method: a standard-sized sample (geometric area 1540.25 mm²) is cut from the electrode sheet to be tested. 2 The total mass of the disc (a circular piece) was measured using a high-precision electronic balance (0.01 mg resolution) and denoted as m. total The active layer is removed by solvent immersion followed by ultrasonic peeling or pyrolysis, leaving only the foil. The mass of the foil is weighed and recorded as m. foil ; Surface density = (m total -m foil ) / sample area.

[0142] Example 2

[0143] Based on the mass of the positive electrode active layer as 100%, the positive electrode active layer comprises: 97.5% positive electrode active material (lithium iron phosphate), 0.7% positive electrode conductive agent (conductive carbon black SP), and 1.8% positive electrode binder (PVDF); wherein, the specific capacity of lithium iron phosphate is 145 mAh / g, and the areal density C1 of the first active material layer located in the flat region is 300 g / m³. 2 The areal density C2 of the first active material layer located in the bending region is 150 g / m². 2 ,refer to Figure 2 The coating pump speed of the positive electrode slurry on the first section 101 of the positive electrode current collector 10 is V1 = 20 mL / min, and the coating pump speed of the positive electrode slurry on the second section 102 of the positive electrode current collector 10 is V2 = C2 * V1 / C1 = 10 mL / min. The radius of each positive electrode bending section is r = nd. 正 +nd 负 +(2n+1)d 隔 (n=1~36), the dimension Ln=πr of each positive electrode bending segment along the first direction is used to determine the dimension of the second segment 102 along the first direction (i.e., the slurry coating dimension). If the calculated Ln is less than Lmin, then the dimension of the second segment 102 along the first direction is determined to be Lmin. The thickness d of the positive electrode. 正 =144μm, the thickness of the aluminum foil is 12μm, that is, the maximum thickness of the first active material layer d1=(144-12) / 2=66μm; a=C2 / C1=0.5, the depth of the first groove Q=(1-a)×d1=0.5*66=33μm.

[0144] Based on the mass of the negative electrode active layer as 100%, the negative electrode active layer comprises: 96.5% negative electrode active material (graphite), 0.5% negative electrode conductive agent (conductive carbon black SP), 1.2% negative electrode binder (CMC), and 1.8% negative electrode binder (SBR); wherein the specific capacity of graphite is 345 mAh / g, and the areal density of the negative electrode sheet is 144 g / m². 2 The thickness d of the negative electrode 负 =100μm, the thickness of the copper foil for the negative electrode current collector is 6μm, and the thickness of the negative electrode active material layer is d2=100-6=94μm. The full-charge expansion thickness of a single-layer negative electrode sheet is Δdneg=υ×d2=0.25*94=23.5μm (υ=25%).

[0145] The total thickness d of the single-layer positive electrode, single-layer negative electrode, and two-layer separator located in the bending region total =d 正 +d 负 +2d 隔=144+100+2*16=276μm; the spacing between adjacent negative electrode plates in the bending region, ΔW=d total ×(1+μ*ξ bluk )=276*(1+0.75*0.3)=338.1μm (μ=0.75,ξ bluk =0.3); the maximum thickness of the first solid electrolyte in the direction of the positive electrode current collector is P. n =ΔW-d total -Δd neg +Q=338.1-276-23.5+33=71.6μm.

[0146] Example 3

[0147] Based on the mass of the positive electrode active layer as 100%, the positive electrode active layer comprises: 97.5% positive electrode active material (lithium iron phosphate), 0.7% positive electrode conductive agent (conductive carbon black SP), and 1.8% positive electrode binder (PVDF); wherein, the specific capacity of lithium iron phosphate is 145 mAh / g, and the areal density C1 of the first active material layer located in the flat region is 300 g / m³. 2 The areal density C2 of the first active material layer located in the bending region is 210 g / m². 2 ,refer to Figure 2 The coating pump speed of the positive electrode slurry on the first section 101 of the positive electrode current collector 10 is V1 = 20 mL / min, and the coating pump speed of the positive electrode slurry on the second section 102 of the positive electrode current collector 10 is V2 = C2 * V1 / C1 = 14 mL / min. The radius of each positive electrode bending section is r = nd. 正 +nd 负 +(2n+1)d 隔 (n=1~36), the dimension Ln=πr of each positive electrode bending segment along the first direction is used to determine the dimension of the second segment 102 along the first direction (i.e., the slurry coating dimension). If the calculated Ln is less than Lmin, then the dimension of the second segment 102 along the first direction is determined to be Lmin. The thickness d of the positive electrode. 正 =144μm, the thickness of the aluminum foil is 12μm, that is, the maximum thickness of the first active material layer d1=(144-12) / 2=66μm; a=C2 / C1=0.7, the depth of the first groove Q=(1-a)×d1=0.3*66=19.8μm.

[0148] Based on the mass of the negative electrode active layer as 100%, the negative electrode active layer comprises: 96.5% negative electrode active material (graphite), 0.5% negative electrode conductive agent (conductive carbon black SP), 1.2% negative electrode binder (CMC), and 1.8% negative electrode binder (SBR); wherein the specific capacity of graphite is 345 mAh / g, and the areal density of the negative electrode sheet is 144 g / m². 2 The thickness d of the negative electrode 负 =100μm, the thickness of the copper foil for the negative electrode current collector is 6μm, and the thickness of the negative electrode active material layer is d2=100-6=94μm. The full-charge expansion thickness of a single-layer negative electrode sheet is Δdneg=υ×d2=0.25*94=23.5μm (υ=25%).

[0149] The total thickness d of the single-layer positive electrode, single-layer negative electrode, and two-layer separator located in the bending region total =d 正 +d 负 +2d 隔 =144+100+2*16=276μm; the spacing between adjacent negative electrode plates in the bending region, ΔW=d total ×(1+μ*ξ bluk )=276*(1+0.75*0.3)=338.1μm (μ=0.75,ξ bluk =0.3); the maximum thickness of the first solid electrolyte in the direction of the positive electrode current collector is P. n =ΔW-d total -Δd neg +Q=338.1-276-23.5+19.8=58.4μm.

[0150] Comparative Example 1

[0151] The difference between the preparation method of the electrode assembly in this comparative example and that in Example 3 is that the first solid electrolyte is not filled in the first groove, while the other steps are the same as in Example 3.

[0152] Comparative Example 2

[0153] The first active material layer in the positive electrode does not have a first groove, and the areal density of the first active material layer is 300 g / m³. 2 Based on the mass of the positive electrode active layer as 100%, the positive electrode active layer includes: 97.5% positive electrode active material (lithium iron phosphate), 0.7% positive electrode conductive agent (conductive carbon black SP), and 1.8% positive electrode binder (PVDF). Other aspects are the same as in Example 1.

[0154] Batteries were fabricated using the same assembly method for the electrode assemblies prepared in the above embodiments and comparative examples. Fast-charge cycle tests were performed on the batteries: the batteries were charged to 3.65V using a peak 4C rate stepped constant current method, allowed to stand for 30 minutes, and then discharged to 2.0V using a 1C rate. This cycle was repeated 500 times. The batteries were then disassembled, and the presence of lithium plating at the negative electrode interface in the bending area of ​​the electrode assembly was observed. Lithium plating was categorized into three levels: no lithium plating, slight lithium plating, and severe lithium plating. Slight and severe lithium plating were judged according to the following criteria:

[0155] 1) Slight lithium plating, meeting at least one of the following conditions:

[0156] • The deposited lithium only appears in localized areas: at the base of the tab, at the corners, at the winding head, and in areas where the coating is thinned;

[0157] • Color: Light gray, grayish white, local spots / stripes, not continuous patches;

[0158] •Thickness: Extremely thin layer, no grainy feel or bumps to the touch;

[0159] • No obvious dendrites, no powder shedding, and no risk of puncturing the diaphragm;

[0160] • The surface of the negative electrode is mostly still golden yellow / grayish black (normal lithium intercalation).

[0161] 2) Severe lithium plating, meeting at least one of the following conditions:

[0162] • The deposited lithium covers a large area, a whole sheet, and continuously on the surface of the negative electrode;

[0163] • Color: Bright silver-white, strong metallic luster, even white and shiny;

[0164] • Significantly increased thickness: raised, bulging, and feels granular / moss-like to the touch;

[0165] • Dendritic, needle-like, and whisker-like lithium crystals appear;

[0166] • The lithium plating layer is prone to peeling off, powdering, and friction against the diaphragm;

[0167] • Lithium buildup occurs at the edges / head of the negative electrode.

[0168] The test results are shown in Table 1.

[0169] Table 1

[0170] After fast-charge cycle testing, the batteries in Examples 1 to 3 showed no lithium plating at the negative electrode interface in the bending area of ​​the electrode assembly, especially at the interface of the negative electrode covering the positive electrode sheet in the bending area, where there was virtually no uneven lithium intercalation or lithium plating. However, after fast-charge cycle testing, the batteries in Comparative Examples 1 and 2 showed uneven lithium intercalation and severe lithium plating at the negative electrode interface in the bending area of ​​the electrode assembly. This indicates that in the electrode assembly provided in this application, the first active material layer of the positive electrode sheet has a first groove located in the bending region. This is beneficial to improving the N / P value of the bending region, thereby reducing the risk of lithium plating on the negative electrode sheet in the bending region. At the same time, the first groove is filled with a first solid electrolyte, and the maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is greater than the depth of the first groove. Thus, the first solid electrolyte can not only store electrolyte and construct a continuous active ion transport channel, but its part protruding from the first groove can also fill the increased gap between adjacent negative electrodes in the bending region of the pressed electrode assembly, improve the electrolyte wetting effect at the electrode interface, thereby improving the lithium intercalation kinetics of the negative electrode sheet in the bending region, suppressing lithium plating on the negative electrode, and thus improving the cycle performance and safety performance of the battery.

[0171] It should be noted that the electrode assembly embodiments, electrode assembly preparation method embodiments, and battery embodiments provided in this application belong to the same concept; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0172] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

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 positive electrode, the negative electrode, and the separator are wound to form a straight region and a bent region; The positive electrode sheet includes a positive current collector and a positive active material layer located on the positive current collector. The positive active material layer includes a first active material layer located on a first surface of the positive current collector. The first surface is the surface of the positive current collector that is away from the winding center of the electrode assembly among two surfaces along the thickness direction. The first active material layer has a first groove located in the bending region. The first groove is filled with a first solid electrolyte. The maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector is greater than the depth of the first groove.

2. The electrode assembly according to claim 1, characterized in that, The areal density of the first active material layer located in the straight region is C1, and the areal density of the first active material layer located in the bent region is C2, wherein C1 is greater than C2; optionally, C1 is 300 g / m³. 2 ~450g / m 2 The C2 is 150 g / m³ 2 ~405g / m 2 .

3. The electrode assembly according to claim 2, characterized in that, The depth of the first groove is Q, where Q = (1-a) × d1; a = C2 / C1, where a ranges from 0.5 to 0.9; d1 is the maximum thickness of the first active material layer.

4. The electrode assembly according to claim 1, characterized in that, The maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is P. n P n =ΔW-d total -Δd neg +Q; where, Q is the depth of the first groove; d total The total thickness of the single-layer positive electrode, the single-layer negative electrode, and the two-layer separator located in the bending region; ΔW is the spacing between adjacent negative electrode plates in the bending region, ΔW=d total ×(1+μ*ξ bluk ), where μ is the radius compression sensitivity coefficient of the bending region, and its value ranges from 0.65 to 0.85, ξ bluk The total thickness compression ratio of the electrode assembly before and after pressing is 0.2 to 0.

3. Δd neg Δd represents the fully charged expansion thickness of the single-layer negative electrode sheet. neg =υ×d2, where υ is the coefficient of thermal expansion at full charge, and its value ranges from 18% to 25%, and d2 is the thickness of the negative electrode active material layer in the negative electrode sheet.

5. The electrode assembly according to claim 1, characterized in that, The first solid electrolyte includes a polymer electrolyte and / or a sulfide electrolyte; And / or, the positive electrode active material layer further includes a second active material layer located on the second surface of the positive electrode current collector, the second surface being the surface opposite to the first surface; the second active material layer has a second groove located in the bending region; optionally, the second groove is filled with a second solid electrolyte.

6. A method for preparing an electrode assembly, characterized in that, The method includes: A positive electrode, a separator, and a negative electrode are provided; the positive electrode includes a positive current collector and a positive active material layer located on the positive current collector, the positive active material layer including a first active material layer located on a first surface of the positive current collector, the first active material layer having a first groove; the first groove is filled with a first solid electrolyte, the maximum thickness of the first solid electrolyte in the thickness direction of the positive current collector being greater than the depth of the first groove; The positive electrode, separator, and negative electrode are stacked in sequence and wound along a first direction. After being pressed, the electrode assembly is formed. The electrode assembly includes a flat region and a bent region. The first surface is the surface of the positive current collector that is away from the winding center of the electrode assembly among the two surfaces along the thickness direction. The first groove is located in the bent region.

7. The method for preparing the electrode assembly according to claim 6, characterized in that, The positive electrode plate includes: The positive electrode active material, positive electrode conductive agent and positive electrode binder are mixed in a solvent and stirred evenly to obtain a positive electrode slurry; The positive electrode current collector includes a first segment and a second segment arranged alternately along the first direction. The positive electrode slurry is coated on the surface of the first segment and the second segment respectively. After drying and rolling, the first active material layer is formed on the first surface. The areal density of the first active material layer located in the first segment is C1, and the areal density of the first active material layer located in the second segment is C2, wherein C1 is greater than C2. The first segment is located in the straight region of the electrode assembly, and the second segment is located in the bent region of the electrode assembly. The first solid electrolyte is filled into the first groove.

8. The method for preparing the electrode assembly according to claim 7, characterized in that, The C1 is 300g / m 2 ~450g / m 2 The C2 is 150 g / m³ 2 ~405g / m 2 ; And / or, the depth of the first groove is Q, Q=(1-a)×d1; where a=C2 / C1, the value of a ranges from 0.5 to 0.9; d1 is the maximum thickness of the first active material layer; And / or, the feed flow rates for coating the positive electrode slurry on the first section and the second section are V1 and V2, respectively; V2 and V1 satisfy: ； And / or, if the dimension of the portion of the first active material layer in the bending region in the first direction is smaller than the minimum coating gap in the coating process, then the length of the second segment is set as the minimum coating gap.

9. The method for preparing the electrode assembly according to claim 6, characterized in that, The maximum thickness of the first solid electrolyte in the thickness direction of the positive electrode current collector is P. n P n =ΔW-d total -Δd neg +Q; where, Q is the depth of the first groove; d total The total thickness of the single-layer positive electrode, the single-layer negative electrode, and the two-layer separator located in the bending region; ΔW is the spacing between adjacent negative electrode plates in the bending region, ΔW=d total ×(1+μ*ξ bluk ), where μ is the radius compression sensitivity coefficient of the bending region, and its value ranges from 0.65 to 0.85, ξ bluk The total thickness compression ratio of the electrode assembly before and after pressing is 0.2 to 0.

3. Δd neg Δd represents the fully charged expansion thickness of the single-layer negative electrode sheet. neg =υ×d2, where υ is the coefficient of thermal expansion at full charge, and its value ranges from 18% to 25%, and d2 is the thickness of the negative electrode active material layer in the negative electrode sheet; And / or, the first solid electrolyte includes a polymer electrolyte and / or a sulfide electrolyte; And / or, the positive electrode active material layer further includes a second active material layer located on the second surface of the positive electrode current collector, the second surface being the surface opposite to the first surface; the second active material layer has a second groove located in the bending region; optionally, the second groove is filled with a second solid electrolyte.

10. A battery, characterized in that, The electrode assembly includes the electrode assembly according to any one of claims 1 to 5, or the electrode assembly prepared by the method of the electrode assembly according to any one of claims 6 to 9.

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