Pole piece structure and preparation method thereof, battery cell, and secondary battery

Abstract

This application relates to an electrode structure in which the areal load ratio CB1 of the second cathode material layer to the first anode material layer is controlled to be 1:(1.01-1.3), and the areal load ratio CB2 of the first cathode material layer to the second anode material layer is controlled to be 1:(1.03-1.4). This ensures that the areal loads of both the first and second anode material layers are slightly higher than their corresponding areal loads of the second and first cathode material layers. Therefore, during cycling, especially under high-rate conditions, the first and second anode material layers can provide sufficient lithium intercalation capacity, preventing lithium plating on the anode. This application also differentiates the material layers on both sides of the electrode, making CB1 different from CB2, avoiding the energy density loss caused by excessively high CB values ​​on both sides of the electrode, thereby improving the energy density of the cell. This application also relates to a method for fabricating the electrode structure, achieving differentiation on both sides of the electrode and preventing assembly errors.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to an electrode structure and its preparation method, a battery cell, and a secondary battery. Background Technology

[0002] Lithium-ion batteries have become the most popular energy storage system due to their low cost, long lifespan, and high safety, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. Lithium-ion battery cells are mainly manufactured using a winding method, where they are hot-pressed after winding to form a wound bare cell. However, current wound bare cells pose a risk of lithium plating at the anode during cycling, especially under high-rate conditions, which can lead to puncture of the battery separator and cause safety accidents. To avoid lithium plating at the anode, researchers have proposed a series of improvements to the cells. While these measures have prevented lithium plating at the anode to some extent, they have significantly reduced the energy density of the cells.

[0003] Therefore, there is an urgent need to develop an electrode structure that can both prevent lithium plating at the anode and improve the energy density of the battery cell. Summary of the Invention

[0004] In view of the problems existing in the background technology, this application provides an electrode structure that can both avoid lithium plating at the anode and improve the energy density of the battery cell.

[0005] The electrode structure provided in the first aspect of this application includes: a cathode electrode and an anode electrode; the cathode electrode and the anode electrode are wound to form part of a battery cell;

[0006] The cathode electrode includes: a first cathode material layer located near the center of the battery cell; and a second cathode material layer located away from the center of the battery cell;

[0007] The anode electrode includes: a first anode material layer located near the center of the battery cell; and a second anode material layer located away from the center of the battery cell;

[0008] Wherein, the second cathode material layer is disposed opposite to the first anode material layer, and the first cathode material layer is disposed opposite to the first anode material layer;

[0009] The ratio of the areal load of the second cathode material layer to the areal load of the first anode material layer, CB1, is 1:(1.01-1.3).

[0010] The ratio of the areal load of the first cathode material layer to the areal load of the second anode material layer, CB2, is 1:(1.03-1.4), and CB2 is different from CB1.

[0011] A second aspect of this application provides a method for preparing an electrode structure, comprising:

[0012] The preparation methods for the first cathode material layer and the second cathode material layer are different; and / or

[0013] The preparation methods for the first anode material layer and the second anode material layer are different.

[0014] A third aspect of this application provides a battery cell including the electrode structure described in the first aspect of this application.

[0015] A fourth aspect of this application provides a secondary battery, including the cell described in the third aspect of this application.

[0016] Compared with the prior art, this application has at least the following beneficial effects:

[0017] This application provides an electrode structure comprising a cathode electrode and an anode electrode. By controlling the ratio CB1 of the areal load of the second cathode material layer to the areal load of the first anode material layer to be 1:(1.01-1.3), and controlling the ratio CB2 of the areal load of the first cathode material layer to the areal load of the second anode material layer to be 1:(1.03-1.4), the areal loads of both the first and second anode material layers are slightly higher than their corresponding areal loads of the second and first cathode material layers. Therefore, during cycling, especially under high-rate conditions, the first and second anode material layers can provide sufficient lithium intercalation capacity, preventing lithium plating on the anode. Simultaneously, the inventors have differentiated the material layers on both sides of the electrode, making CB1 different from CB2, avoiding the energy density loss caused by excessively high CB values ​​on both sides of the electrode, thereby improving the energy density of the battery cell.

[0018] Furthermore, this application provides a method for fabricating an electrode structure, wherein the fabrication methods for the first cathode material layer and the second cathode material layer are different; and / or the fabrication methods for the first anode material layer and the second anode material layer are different. After the electrode fabrication process, the material layer loading on both sides of the electrode has only a slight difference, making it difficult to distinguish. Therefore, a significant difference is needed to facilitate the differentiation of different corresponding sides during the winding process. To address this problem, this application employs different fabrication methods to achieve a difference between the two sides of the electrode. Before winding, the two sides of the electrode can be clearly distinguished by simple CCD (charge-coupled device) observation or laser thickness measurement, preventing assembly errors. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a wound bare cell including the electrode structure of this application.

[0021] Explanation of reference numerals in the attached figures:

[0022] 100 is the first cathode material layer, 200 is the second cathode material layer, 300 is the first anode material layer, 400 is the second anode material layer, 500 is the separator, and R is the innermost corner angle of the bare cell. Detailed Implementation

[0023] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0024] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0025] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more (including two).

[0026] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0027] Lithium-ion batteries have become the most popular energy storage system due to their low cost, long lifespan, and high safety, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. Lithium-ion battery cells are mainly manufactured using a winding method. After winding, they are hot-pressed to form a wound bare cell. The bare cell has corners on both sides. During the electrode winding process, as the winding becomes thicker, the cathode surface load may exceed the anode surface load at the corners. This can lead to lithium deposition at the anode during cycling, especially under high-rate conditions. Once lithium dendrites form, they can pierce the battery separator, causing a short circuit between the anode and cathode. This results in a sudden temperature rise inside the cell, the electrolyte reaching its ignition point, or a flash of lightning, causing the cell to burn and explode, leading to a safety accident.

[0028] To avoid lithium plating at the anode, researchers designed a capacity ratio (CB) of 40% higher for the anode and cathode active materials, making the anode capacity higher than the cathode capacity, for example. This design ensures that the anode provides sufficient lithium intercalation capacity at the corner of the bare cell, preventing lithium plating. However, this design results in wasted capacity on the side of the anode electrode with a smaller radius of curvature, reducing the cell's energy density.

[0029] To avoid lithium plating at the anode and simultaneously improve the cell's energy density, the inventors, through in-depth research, designed an electrode structure comprising a cathode electrode and an anode electrode. By controlling the ratio of the areal load of the second cathode material layer to the areal load of the first anode material layer (CB1) to 1:(1.01-1.3), and controlling the ratio of the areal load of the first cathode material layer to the areal load of the second anode material layer (CB2) to 1:(1.03-1.4), the areal loads of both the first and second anode material layers are slightly higher than their corresponding areal loads of the second and first cathode material layers. This ensures that during cycling, especially under high-rate conditions, the first and second anode material layers can provide sufficient lithium intercalation capacity, preventing lithium plating at the anode. Simultaneously, the inventors differentiated the material layers on both sides of the electrode, making CB1 different from CB2, avoiding the energy density loss caused by excessively high CB values ​​on both sides of the electrode, thereby improving the cell's energy density.

[0030] Specifically, the first aspect of this application provides an electrode structure, including: a cathode electrode and an anode electrode; the cathode electrode and the anode electrode are wound to form part of a battery cell;

[0031] The cathode electrode includes: a first cathode material layer located near the center of the battery cell; and a second cathode material layer located away from the center of the battery cell;

[0032] The anode electrode includes: a first anode material layer located near the center of the battery cell; and a second anode material layer located away from the center of the battery cell;

[0033] Wherein, the second cathode material layer is disposed opposite to the first anode material layer, and the first cathode material layer is disposed opposite to the first anode material layer;

[0034] The ratio of the areal load of the second cathode material layer to the areal load of the first anode material layer, CB1, is 1:(1.01-1.3).

[0035] The ratio of the areal load of the first cathode material layer to the areal load of the second anode material layer, CB2, is 1:(1.03-1.4), and CB2 is different from CB1.

[0036] In this application, "area loading" refers to the mass of active material loaded per unit area on one surface of the current collector. "Area loading of the first cathode material layer" refers to the mass of cathode active material loaded per unit area on the surface of the cathode current collector closest to the cell center. "Area loading of the second cathode material layer" refers to the mass of cathode active material loaded per unit area on the surface of the cathode current collector furthest from the cell center. "Area loading of the first anode material layer" refers to the mass of anode active material loaded per unit area on the surface of the anode current collector closest to the cell center. "Area loading of the second anode material layer" refers to the mass of anode active material loaded per unit area on the surface of the anode current collector furthest from the cell center.

[0037] In some embodiments of this application, the cathode electrode includes: a cathode current collector and cathode material layers disposed on two surfaces of the cathode current collector, namely, a first cathode material layer and a second cathode material layer. The battery cell of this application is a wound battery cell. The first cathode material layer is located near the center of the battery cell, while the second cathode material layer is located away from the center of the battery cell.

[0038] In some embodiments of this application, both the first cathode material layer and the second cathode material layer include cathode active materials. This application does not impose any particular limitation on the type of cathode active material; commonly used cathode active materials in the art can be used in this application. The first cathode material layer and the second cathode material layer may also include conductive agents and binders, wherein the type and content of the conductive agents and binders are not specifically limited and can be selected according to actual needs.

[0039] In some embodiments of this application, the second cathode material layer can be prepared by a quasi-dry process. The quasi-dry process is described in detail below. The second cathode material layer may include a mixture of a fibrillable binder and a soluble, highly polar binder.

[0040] Preferably, the fibrillable adhesive may be one or more of polytetrafluoroethylene, polyethylene, polypropylene, and polyacrylonitrile, with polytetrafluoroethylene being the most preferred. Preferably, the soluble strong polar adhesive may be polyvinylidene fluoride. Preferably, the mass ratio of the fibrillable adhesive to the soluble strong polar adhesive may be 1:(1-10), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10, with 1:(3-7) being the most preferred.

[0041] Through extensive experimentation, the inventors discovered that when using a fibrillable binder alone, the materials do not self-adhere, making it difficult to form a complete membrane. While using a soluble, highly polar binder alone produces a membrane with very strong adhesion but insufficient strength, and it easily adheres to the rollers, leading to high process difficulty. Therefore, this application uses a mixture of a fibrillable binder and a soluble, highly polar binder to prepare the second cathode material layer. This ensures both material self-adhesion to form a complete membrane with sufficient strength and avoids adhesion to the rollers, simplifying the process.

[0042] In some embodiments of this application, the anode electrode includes: an anode current collector and anode material layers disposed on two surfaces of the anode current collector, namely, a first anode material layer and a second anode material layer. The battery cell of this application is a wound battery cell. The first anode material layer is located near the center of the battery cell, while the second anode material layer is located away from the center of the battery cell. Corresponding to the first anode material layer is the second cathode material layer, and corresponding to the second anode layer is the first cathode material layer.

[0043] In some embodiments of this application, both the first anode material layer and the second anode material layer include an anode active material. This application does not impose any particular limitation on the type of anode active material; commonly used anode active materials in the art can be used in this application. The first anode material layer and the second anode material layer may also include a conductive agent and a binder, wherein the type and content of the conductive agent and the binder are not specifically limited and can be selected according to actual needs.

[0044] In some embodiments of this application, the second anode material layer can be prepared by a quasi-dry process. The quasi-dry process is described in detail below. The second anode material layer comprises a mixture of a fibrillable adhesive and a self-adhesive adhesive.

[0045] Preferably, the fibrillable adhesive is one or more of polytetrafluoroethylene, polyethylene, polypropylene, and polyacrylonitrile, with polytetrafluoroethylene being the most preferred. Preferably, the self-adhesive adhesive is a high-strength self-adhesive adhesive. Preferably, the self-adhesive adhesive is one or more of polyacrylic acid resin, polyacrylic acid-acrylonitrile copolymer, polyacrylic acid-acrylate copolymer, and polypropylene-butadiene copolymer. Preferably, the viscosity of the self-adhesive adhesive is 50,000 to 200,000 Pa·s. Preferably, the mass ratio of the fibrillable adhesive to the self-adhesive adhesive can be 1:(1-20), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20, preferably 1:(5-18).

[0046] Through extensive experimentation, the inventors discovered that when using a fibrillable binder alone, the materials do not self-adhere, making it difficult to form a complete membrane. Conversely, when using a self-adhesive binder alone, the resulting membrane exhibits very strong adhesion but insufficient strength and is prone to sticking to the rollers, leading to complex manufacturing processes. Therefore, this application employs a mixture of a fibrillable binder and a self-adhesive binder to prepare the second anode material layer. This ensures both material self-adhesion for forming a complete membrane with sufficient strength and avoids sticking to the rollers, simplifying the manufacturing process.

[0047] In some embodiments of this application, the ratio CB1 of the areal load of the second cathode material layer to the areal load of the first anode material layer can be 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1, 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1: The ratios are 1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19, 1:1.2, 1:1.21, 1:1.22, 1:1.23, 1:1.24, 1:1.25, 1:1.26, 1:1.27, 1:1.28, 1:1.29, or 1:1.3, preferably 1:(1.03-1.2), and more preferably 1:(1.03-1.07). If CB1 is too large, the anode material layer cannot provide sufficient lithium intercalation capacity, which may lead to lithium plating on the anode and cause a safety accident. If CB1 is too small, it will result in wasted capacity of the anode material layer and reduce the energy density of the cell.

[0048] In some embodiments of this application, the ratio CB2 of the areal load of the first cathode material layer to the areal load of the second anode material layer can be 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1, 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19, 1:1.2, 1:1.21, 1:1.22, 1:1.23, 1:1.24, 1:1.25, 1:1.26, 1:1.27, 1:1.28, 1:1.29 or 1:1.3, preferably 1:(1.05-1.3), more preferably 1:(1.06-1.1). If CB2 is too large, the anode material layer cannot provide sufficient lithium intercalation capacity, which may lead to lithium plating on the anode and cause safety accidents. If CB2 is too small, it will result in wasted capacity of the anode material layer and reduce the energy density of the cell.

[0049] In some embodiments of this application, CB1 can be 1:(1.03-1.2), and CB2 can be 1:(1.05-1.3). Preferably, CB1 can be 1:(1.03-1.07), and CB2 can be 1:(1.06-1.1). Within the range of CB1 and CB2 in this application, lithium plating will not occur on the anode of the bare cell, even during high-rate cycling. Furthermore, the differentiated design of CB1 and CB2 in this application avoids the energy density loss caused by excessively high CB values ​​on both sides of the electrode, thus improving the energy density of the cell.

[0050] In some embodiments of this application, CB1 is preferably larger than CB2. This design avoids lithium plating on the anode and prevents capacity waste on the side of the anode electrode with a smaller radius of curvature, thereby improving the energy density of the cell.

[0051] In some embodiments of this application, the difference between CB1 and CB2 may be 0.02-0.1, preferably 0.02-0.05.

[0052] The electrode structure of this application is as follows: Figure 1 As shown. Figure 1The innermost corner R of the battery cell is shown, and the value of corner R is related to the values ​​of CB1 and CB2. For example, when the angle range of the innermost corner R of the battery cell is 5°-45°, CB1 can be 1:(1.06-1.3), preferably 1:(1.06-1.2); CB2 can be 1:(1.08-1.4), preferably 1:(1.08-1.3). For example, when the angle range of the innermost corner R of the battery cell is 45°-90°, CB1 can be 1:(1.01-1.06), preferably 1:(1.03-1.04); CB2 can be 1:(1.03-1.08), preferably 1:(1.06-1.07).

[0053] In some embodiments of this application, both CB1 and CB2 increase with the increase of the innermost bend angle R of the cell.

[0054] Based on the variation of the innermost bend R of the cell, this application rationally designs the value range of CB1 and CB2. While avoiding lithium plating at the anode, it also effectively avoids the capacity waste on the side with a smaller radius of curvature of the anode electrode, further improving the energy density of the cell.

[0055] In this application, the areal load of the first cathode material layer may be lower than that of the second cathode material layer, and / or, the areal load of the first anode material layer may be lower than that of the second anode material layer.

[0056] For example, in some embodiments of this application, the areal load of the first cathode material layer is lower than that of the second cathode material layer, and the areal load of the first anode material layer is equal to that of the second anode material layer. In other embodiments of this application, the areal load of the first cathode material layer is equal to that of the second cathode material layer, and the areal load of the first anode material layer is lower than that of the second anode material layer. This setting of the areal load ensures that the values ​​of CB1 and CB2 meet the aforementioned ranges, while also simplifying the fabrication of the material layers and simplifying the process.

[0057] This application does not impose any particular restrictions on the areal load of the first cathode material layer, the second cathode material layer, the first anode material layer, and the second anode material layer, as long as CB1 and CB2 meet the aforementioned ranges. However, to optimize cell performance, especially cycle performance, it is preferable that the areal load of both the first cathode material layer and the second cathode material layer is 75-200 mg / 1000 mm². 2 Preferably 85-180mg / 1000mm 2 Similarly, preferably, the areal loading of both the first anode material layer and the second anode material layer is 125-525 mg / 1000 mm. 2 The preferred concentration is 150-450 mg / 1000 mg. 2 .

[0058] Since the material load on both sides of the electrode is only slightly different after the electrode manufacturing process, making it difficult to distinguish them, a clear difference is needed to facilitate the differentiation of different corresponding sides during the winding process.

[0059] Therefore, to address this problem, a second aspect of this application provides a method for preparing an electrode structure, comprising:

[0060] The preparation methods for the first cathode material layer and the second cathode material layer are different; and / or

[0061] The preparation methods for the first anode material layer and the second anode material layer are different.

[0062] This application employs a different preparation method to achieve double-sided difference in the electrode sheet. Before winding, the two sides of the electrode sheet can be clearly distinguished by simple CCD observation or laser thickness measurement, and assembly errors will not occur.

[0063] This application does not impose any particular restrictions on the preparation methods of the first cathode material layer, the second cathode material layer, the first anode material layer, and the second anode material layer, as long as the two sides of the electrode can be differentiated, thereby enabling the distinction between the two sides.

[0064] In some embodiments of this application, the preparation methods of the first cathode material layer, the second cathode material layer, the first anode material layer, and the second anode material layer can each be independently one of dry method, quasi-dry method, and wet method, preferably one of quasi-dry method and wet method.

[0065] In this application, when the above electrode material layer is prepared using a wet coating process, the surface loading of the electrode material layer can be controlled by controlling the distance between the extruder (Die) and the current collector.

[0066] In this application, when preparing the above electrode material layer using the quasi-dry method, it is necessary to perform roll pressing to thin it. By controlling the gap between the two rollers used during roll pressing, the surface load of the electrode material layer can be controlled.

[0067] In this application, CB1 and CB2 can be controlled by controlling the areal load of each electrode material layer.

[0068] In this application, the term "quasi-dry method" refers to a preparation method comprising: mixing an active material, a conductive agent, a binder, and a solvent to form a granular material; extruding and thinning the granular material to obtain a membrane; and combining the membrane with a current collector. The active material refers to a cathode active material or an anode active material.

[0069] In some embodiments of this application, the material layer on the side with higher areal loading of the cathode and anode electrodes is prepared using a quasi-dry method, while the material layer on the side with lower areal loading is prepared using a conventional wet coating process. The angle between the edge of the material layer prepared using the quasi-dry method and the current collector can be 60°–90°, preferably 75°–90°. The angle between the edge of the material layer prepared using the wet method and the current collector can be 10°–60°, preferably 30°–45°.

[0070] For example, in some embodiments of this application, the second cathode material layer is prepared using a quasi-dry method, while the first cathode material layer is prepared using a wet method. When preparing the second cathode material layer using the quasi-dry method, the binder used is preferably a mixture of a fibrillable binder and a soluble, highly polar binder. For details regarding the specific types and mass ratios of the fibrillable binder and the soluble, highly polar binder, please refer to the description above.

[0071] Specifically, the preparation of the second cathode material layer using a quasi-dry method includes: dry mixing a cathode active material, a fiberizable binder, and a conductive agent to obtain a mixed powder; adding a soluble, highly polar binder solution to the mixed powder and mixing to obtain a clump-like material; extruding and thinning the clump-like material to obtain a membrane; and combining the membrane with a cathode current collector. The solid content of the clump-like material can be 65%–98%, preferably 70%–85%.

[0072] In some other embodiments of this application, the second anode material layer is prepared using a quasi-dry method, while the first anode material layer is prepared using a wet method. When preparing the second anode material layer using the quasi-dry method, the binder used is a mixture of a fibrillable binder and a self-adhesive binder. For details regarding the specific types and mass ratios of the fibrillable binder and the self-adhesive binder, please refer to the above description.

[0073] Specifically, the preparation of the second anode material layer using a quasi-dry method includes: dry mixing an anode active material, a fiberizable binder, and a conductive agent to obtain a mixed powder; adding a self-adhesive binder to the mixed powder and injecting solvent to adjust the solid content, resulting in a clump-like material; extruding and thinning the clump-like material to obtain a membrane; and composite the membrane with an anode current collector. The solid content of the clump-like material can be 63%–97%, preferably 70%–85%.

[0074] Extensive experimental research has shown that using a mixture of fibrillable binders and soluble strong polar binders, or a mixture of fibrillable binders and self-adhesive binders, as the adhesive allows for simultaneous feeding of powder and binder. The resulting thick film is extruded through a die, then thinned by rolling. During thinning, edges are removed by a cutter, ensuring a high degree of perpendicularity between the film transferred to the current collector surface. The composite electrode is then dried in an oven to obtain the final electrode sheet. This highly integrated process, coupled with a significantly higher solids content compared to wet coating processes, results in a substantial reduction in equipment footprint, overall energy consumption, and material costs.

[0075] A third aspect of this application provides a battery cell including the electrode structure described in the first aspect of this application.

[0076] Because of the electrode structure of the first aspect of this application, the battery cell of this application can avoid lithium plating at the anode and has improved energy density.

[0077] A fourth aspect of this application provides a secondary battery, including the cell described in the third aspect of this application.

[0078] Because of the electrode structure of the first aspect of this application, the secondary battery of this application can avoid lithium plating at the anode and has improved energy density.

[0079] The present invention will be further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0080] The cathode, anode, and battery cells in Examples 1-8 and Comparative Examples 1-3 were prepared according to the following general preparation method.

[0081] Preparation of cathode electrode

[0082] 1. Preparation of cathode electrode sheets using traditional wet coating method

[0083] The cathode active material (lithium iron phosphate or lithium nickel cobalt manganese oxide NCM 532), polyvinylidene fluoride (PVDF), and conductive carbon black SP are dispersed in an N-methylpyrrolidone (NMP) solvent system and thoroughly mixed. The mixture is then applied to an Al foil using extrusion coating. After drying, cold pressing, and slitting, the cathode electrode is obtained.

[0084] 2. Preparation of cathode electrode sheets using a combination of quasi-dry coating and traditional wet coating.

[0085] First, dry powder is prepared, specifically by mixing three dry powders—cathode active material (lithium iron phosphate or lithium nickel cobalt manganese oxide NCM 532), fibrillable binder polytetrafluoroethylene (PTFE), and conductive carbon black SP—in a ribbon mixer to obtain a mixed powder.

[0086] Then, a highly polar adhesive solution is prepared, specifically by dissolving PVDF in NMP.

[0087] Next, the cathode electrode is prepared, specifically including: using a twin-screw extruder, the first section feeds powder (i.e., the prepared mixed powder), the second section injects the prepared strong polar binder solution, and after several subsequent sections of stirring and mixing, a thick film is extruded through an extrusion die. The thick film is thinned to the designed thickness by roller pressing, the edges of the film are cut off by a cutter, and the film is transferred onto one surface of an Al foil by pressure and dried to obtain the second cathode material layer.

[0088] Finally, the cathode active material (lithium iron phosphate or lithium nickel cobalt manganese oxide NCM 532, the same cathode active material used in the dry powder preparation step), PVDF, and conductive carbon black SP are dispersed in an NMP solvent system and thoroughly mixed. This mixture is then applied to the other surface of the Al foil using extrusion coating to obtain the first cathode material layer. After drying, cold pressing, and slitting, a cathode electrode sheet is obtained. This cathode electrode sheet comprises a second cathode material layer prepared by the aforementioned quasi-dry method and a first cathode material layer prepared by the aforementioned wet coating method.

[0089] Preparation of anode plates

[0090] 1. Preparation of anode plates using traditional wet coating method

[0091] The anode active material, artificial graphite, the conductive agent, acetylene black, styrene-butadiene copolymer (SBR), and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in deionized water and then coated onto Cu foil. After drying, cold pressing, and slitting, the anode electrode was obtained.

[0092] 2. Anode plates were prepared using a combination of quasi-dry coating and traditional wet coating.

[0093] First, dry powder is prepared, specifically by dry mixing three dry powders: artificial graphite (anodic active material), polytetrafluoroethylene (PTFE) (a filamentizable binder), and conductive carbon black SP, in a ribbon mixer to obtain a mixed powder.

[0094] Then, a high-strength self-adhesive adhesive solution is provided, namely, an aqueous solution of polyacrylic acid resin with an adhesive viscosity of 50,000 Pa·s.

[0095] Next, the anode electrode is prepared, specifically including: using a twin-screw extruder, the first section feeds powder (i.e., the prepared mixed powder), the second section injects adhesive (i.e., the above-mentioned polyacrylic acid resin aqueous solution), the third section injects deionized water to adjust the solid content, and after the subsequent sections are stirred and mixed evenly, a thick film is extruded through an extrusion die. The thick film is thinned to the designed thickness by roller pressing, the edge of the film is cut off by a cutter, and the film is transferred onto a surface of Cu foil by pressure to obtain the second anode material layer.

[0096] Finally, the anolyte active material artificial graphite, the conductive agent acetylene black, styrene-butadiene copolymer (SBR), and sodium carboxymethyl cellulose (CMC) are thoroughly stirred in deionized water and then coated onto the other surface of a Cu foil to obtain the first anode material layer. After drying, cold pressing, and slitting, the anode electrode sheet is obtained. This anode electrode sheet includes a second anode material layer prepared by the above-described quasi-dry method and a first anode material layer prepared by the above-described wet coating method.

[0097] Cell manufacturing

[0098] The cathode electrode, separator, and anode electrode are stacked in sequence, with the separator positioned between the anode and cathode for isolation. They are then wound and hot-pressed to obtain a bare battery cell, with the innermost corner R of the bare cell forming a specific angle. The bare cell is placed in an outer package, filled with prepared electrolyte, and sealed to obtain the battery. The electrolyte uses ethylene carbonate and dimethyl carbonate as solvents, and lithium hexafluorophosphate as the lithium salt. A porous polyethylene polymer film is used as the separator.

[0099] Example 1

[0100] The innermost corner radius (R) of the bare battery cell is 15°.

[0101] The cathode active material is lithium iron phosphate.

[0102] Cathode plates were prepared using a combination of quasi-dry coating and traditional wet coating. Anode plates were prepared using traditional wet coating.

[0103] Example 2

[0104] The innermost corner radius (R) of the bare battery cell is 15°.

[0105] The cathode active material is lithium iron phosphate.

[0106] The cathode electrode was prepared using a traditional wet coating process.

[0107] Anode plates were prepared using a combination of quasi-dry coating and traditional wet coating.

[0108] Comparative Example 1

[0109] The innermost corner radius (R) of the bare battery cell is 15°.

[0110] The cathode active material is lithium iron phosphate.

[0111] The cathode electrode was prepared using a traditional wet coating process.

[0112] Anode plates were prepared using a traditional wet coating process.

[0113] Example 3

[0114] The innermost corner radius (R) of the bare battery cell is 15°.

[0115] The cathode active material is lithium nickel cobalt manganese oxide (NCM 532). The cathode electrode was prepared using a combination of a quasi-dry coating process and a conventional wet coating process. The anode electrode was prepared using a conventional wet coating process.

[0116] Example 4

[0117] The innermost corner radius (R) of the bare battery cell is 15°.

[0118] The cathode active material is lithium nickel cobalt manganese oxide (NCM 532).

[0119] The cathode electrode was prepared using a traditional wet coating process.

[0120] Anode plates were prepared using a combination of quasi-dry coating and traditional wet coating.

[0121] Example 5

[0122] The innermost corner radius (R) of the bare battery cell is 15°.

[0123] The cathode active material is lithium nickel cobalt manganese oxide (NCM 532).

[0124] Cathode plates were prepared using a combination of quasi-dry coating and traditional wet coating. Anode plates were prepared using traditional wet coating.

[0125] Example 6

[0126] The innermost corner radius (R) of the bare battery cell is 15°.

[0127] The cathode active material is lithium nickel cobalt manganese oxide (NCM 532).

[0128] The cathode electrode was prepared using a traditional wet coating process.

[0129] Anode plates were prepared using a combination of quasi-dry coating and traditional wet coating.

[0130] Comparative Example 2

[0131] The innermost corner radius (R) of the bare battery cell is 15°.

[0132] The cathode active material is lithium nickel cobalt manganese oxide (NCM 532).

[0133] The cathode electrode was prepared using a traditional wet coating process.

[0134] Anode plates were prepared using a traditional wet coating process.

[0135] Example 7

[0136] The innermost bend angle R of the bare battery cell is 60°.

[0137] The cathode active material is lithium iron phosphate.

[0138] Cathode plates were prepared using a combination of quasi-dry coating and traditional wet coating. Anode plates were prepared using traditional wet coating.

[0139] Example 8

[0140] The innermost bend angle R of the bare battery cell is 60°.

[0141] The cathode active material is lithium iron phosphate.

[0142] The cathode electrode was prepared using a traditional wet coating process.

[0143] Anode plates were prepared using a combination of quasi-dry coating and traditional wet coating.

[0144] Comparative Example 3

[0145] The innermost bend angle R of the bare battery cell is 60°.

[0146] The cathode active material is lithium iron phosphate.

[0147] The cathode electrode was prepared using a traditional wet coating process.

[0148] Anode plates were prepared using a traditional wet coating process.

[0149] The relevant parameters of the cathode electrode, anode electrode, and battery cell in Examples 1-8 and Comparative Examples 1-3 are shown in Table 1 below.

[0150] Performance testing methods

[0151] Characterization of lithium deposition on electrodes:

[0152] After cycling under different rate conditions, the batteries were disassembled, and the morphology at the corners was observed to see if any silvery-white substance was produced. The test results obtained from each embodiment and comparative example are shown in Table 1 below.

[0153]

[0154]

[0155] Comparing Examples 1-2 with Comparative Example 1, it can be seen that the lithium iron phosphate battery of this application does not exhibit lithium plating, even under high-rate 2C conditions; while the lithium iron phosphate battery of Comparative Example 1 already exhibits lithium plating at a rate of 1.5C. Furthermore, compared to the lithium iron phosphate battery of Comparative Example 1, the lithium iron phosphate battery of this application has smaller CB1 and CB2 values, resulting in less energy density waste and thus improved battery energy density.

[0156] Comparing Examples 3-6 with Comparative Example 2, it can be seen that the nickel-cobalt-manganese lithium oxide NCM 532 battery of this application does not exhibit lithium plating, even under high-rate 3C conditions; while the lithium iron phosphate battery of Comparative Example 2 already exhibits lithium plating at 2C rate. Furthermore, compared to the lithium iron phosphate battery of Comparative Example 2, the nickel-cobalt-manganese lithium oxide NCM 532 battery of this application has smaller CB1 and CB2 values, resulting in less energy density waste and thus improved battery energy density.

[0157] Comparing Examples 7-8 with Comparative Example 3, it can be seen that the lithium iron phosphate battery of this application does not exhibit lithium plating, even under high-rate 4C conditions; while the lithium iron phosphate battery of Comparative Example 3 already exhibits lithium plating at 2C rate. Furthermore, compared to the lithium iron phosphate battery of Comparative Example 3, the lithium iron phosphate battery of this application has smaller CB1 and CB2 values, resulting in less energy density waste and thus improved battery energy density.

[0158] By comparing Examples 1 and 7, it can be seen that the larger the innermost corner R of the bare cell, the smaller CB1 and CB2 can be, further reducing energy density waste and thus improving battery energy density.

[0159] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An electrode structure, characterized in that, include: Cathode and anode plates; The cathode electrode and the anode electrode are wound together to form part of the battery cell; The cathode electrode includes: a first cathode material layer located near the center of the battery cell; and a second cathode material layer located away from the center of the battery cell. The anode electrode includes: a first anode material layer located near the center of the battery cell; and a second anode material layer located away from the center of the battery cell; Wherein, the second cathode material layer is disposed opposite to the first anode material layer, and the first cathode material layer is disposed opposite to the first anode material layer; The ratio of the areal load of the second cathode material layer to the areal load of the first anode material layer is CB1; The ratio of the areal load of the first cathode material layer to the areal load of the second anode material layer is CB2, and CB2 is different from CB1; Among them, the angle range of the innermost corner R of the battery cell satisfies: when 5°≤R<45°, CB1 and CB2 satisfy (1:1.06)<CB1≤(1:1.3), (1:1.08)<CB2≤(1:1.4). When the angle range of the innermost corner R of the battery cell is 45°≤R≤90°, CB1 and CB2 satisfy (1:1.01)<CB1≤(1:1.06), (1:1.03)≤CB2≤(1:1.08).

2. The electrode structure according to claim 1, characterized in that, CB1 is greater than CB2.

3. The electrode structure according to claim 2, characterized in that, CB1 is 1: (1.03-1.2); CB2 is 1: (1.05-1.3).

4. The electrode structure according to claim 3, characterized in that, CB1 is 1: (1.03-1.07); CB2 is 1: (1.06-1.1).

5. The electrode structure according to claim 2, characterized in that, Both CB1 and CB2 increase with the increase of the innermost bend angle R of the cell.

6. The electrode structure according to claim 2, characterized in that, CB1 is 1: (1.06-1.2), CB2 is 1: (1.08-1.3).

7. The electrode structure according to claim 2, characterized in that, CB1 is 1: (1.03-1.04), CB2 is 1: (1.06-1.07).

8. The electrode structure according to claim 2, characterized in that, The areal load of the first cathode material layer is lower than that of the second cathode material layer, and / or the areal load of the first anode material layer is lower than that of the second anode material layer.

9. The electrode structure according to claim 8, characterized in that, The areal load of the first cathode material layer is lower than that of the second cathode material layer, and the areal load of the first anode material layer is equal to that of the second anode material layer. Alternatively, the areal load of the first cathode material layer is equal to the areal load of the second cathode material layer, and the areal load of the first anode material layer is lower than the areal load of the second anode material layer.

10. A method for preparing an electrode structure, characterized in that, include: The electrode structure includes a cathode electrode and an anode electrode; The cathode electrode and the anode electrode are wound together to form part of the battery cell; The cathode electrode includes: a first cathode material layer located near the center of the battery cell; and a second cathode material layer located away from the center of the battery cell. The anode electrode includes: a first anode material layer located near the center of the battery cell; and a second anode material layer located away from the center of the battery cell; Wherein, the second cathode material layer is disposed opposite to the first anode material layer, and the first cathode material layer is disposed opposite to the first anode material layer; The ratio of the areal load of the second cathode material layer to the areal load of the first anode material layer is CB1; The ratio of the areal load of the first cathode material layer to the areal load of the second anode material layer is CB2, and CB2 is different from CB1; Wherein, when the angle range of the innermost corner R of the battery cell is 5°≤R<45°, CB1 and CB2 satisfy (1:1.06)<CB1≤(1:1.3), (1:1.08)<CB2≤(1:1.4). When the angle range of the innermost corner R of the battery cell is 45°≤R≤90°, CB1 and CB2 satisfy (1:1.01)<CB1≤(1:1.06), (1:1.03)≤CB2≤(1:1.08). The preparation methods of the first cathode material layer and the second cathode material layer are different; and / or The preparation methods for the first anode material layer and the second anode material layer are different.

11. The preparation method according to claim 10, characterized in that, The second cathode material layer is prepared using a quasi-dry method, and the first cathode material layer is prepared using a wet method.

12. The preparation method according to claim 11, characterized in that, When the second cathode material layer is prepared using the quasi-dry method, the binder used is a mixture of a fibrillable binder and a soluble strong polar binder.

13. The preparation method according to claim 12, characterized in that, When the second cathode material layer is prepared using a quasi-dry method, the solid content of the mixture is 65% to 98%.

14. The preparation method according to claim 10, characterized in that, The second anode material layer is prepared using a quasi-dry method, and the first anode material layer is prepared using a wet method.

15. The preparation method according to claim 14, characterized in that, When the second anode material layer is prepared using the quasi-dry method, the binder used is a mixture of a fibrillable binder and a self-adhesive binder.

16. The preparation method according to claim 15, characterized in that, When the second anode material layer is prepared using a quasi-dry method, the solid content of the mixture is 63% to 97%.

17. A battery cell, characterized in that, The electrode structure includes any one of claims 1-16.

18. A secondary battery, characterized in that, Includes the battery cell as described in claim 17.

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