Electrode assembly, method of manufacturing the same, and battery
Patent Information
- Application Number
- CN202611000796.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-07
- Publication Date
- 2026-09-22
AI Technical Summary
在电池充放电循环过程中，尤其是在循环末期，电极组件弯折区处易出现析锂现象，该区域的容量衰减速度显著快于平直区，并导致电池发生热失控的温度阈值降低，成为制约电池循环寿命和安全性能的关键薄弱环节
[0030]本申请实施例提供的电极组件，负极弯折段与位于该负极弯折段的远离平直区一侧的最邻近的正极弯折段的面容量之比为第一N/P，负极平直段与正极平直段的面容量之比为第二N/P，第一N/P大于第二N/P，如此，能够有效解决电极组件弯折区处在电池循环末期容易因第一N/P不足而引发的析锂问题，从而提高循环末期电池的整体动力学性能，进而提高电池的循环性能和安全性能。同时，考虑到自弯折区靠近平直区的一侧至远离平直区的一侧，正负极片的曲率逐渐降低，负极弯折段与位于该负极弯折段的远离平直区一侧的最邻近的正极弯折段的正对面积差值逐渐缩小，弯折区处的析锂风险逐渐降低，因此，本申请实施例中同时设置自弯折区靠近平直区的一侧至远离平直区的一侧，第一N/P呈现减小的趋势，如此可以减少负极弯折段容量的过剩程度，从而有利于在有效改善弯折区处析锂问题的同时兼顾电池的能量密度。
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Abstract
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 high energy density, long cycle life, and excellent rate performance, and are widely used in new energy vehicles, energy storage power stations, and backup power supplies for communication base stations. The electrode components inside lithium-ion batteries include wound electrode components and stacked electrode components. Among them, wound electrode components are widely used due to their simple manufacturing process and high production efficiency.
[0003] A wound electrode assembly is formed by sequentially stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet. It typically includes a flat region and bending regions located on both sides of the flat region. During battery charge-discharge cycles, especially towards the end of the cycle, lithium plating is prone to occur in the bending regions of the electrode assembly. The capacity decay rate in this region is significantly faster than in the flat region, and it also lowers the temperature threshold for thermal runaway, becoming a key weak point that restricts the battery's cycle life and safety performance. 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; the portions of the positive electrode sheet located in the straight region and the bent region are respectively a positive electrode straight section and a positive electrode bent section; the portions of the negative electrode sheet located in the straight region and the bent region are respectively a negative electrode straight section and a negative electrode bent section;
[0006] The ratio of the surface area of the negative electrode bending section to that of the nearest positive electrode bending section on the side of the negative electrode bending section away from the straight region is a first N / P, and the ratio of the surface area of the negative electrode straight section to that of the positive electrode straight section is a second N / P. The first N / P is greater than the second N / P, and the first N / P tends to decrease from the side of the bending section closer to the straight region to the side farther away from the straight region.
[0007] In conjunction with the first aspect of this application, in an optional embodiment, the areal density of the positive electrode bending segment is less than the areal density of the positive electrode straight segment.
[0008] In conjunction with the first aspect of this application, in an optional embodiment, the type and mass percentage of the positive electrode active material are the same in the positive electrode active layer of both the straight positive electrode section and the bent positive electrode section; the areal density C1 of the straight positive electrode section and the areal density C2 of the bent positive electrode section satisfy the following relationship:
[0009] ;
[0010] Where k is a correction coefficient, with a value of 2 to 3; d1 is the thickness of the positive electrode bending section; and r is the radius of each positive electrode bending section.
[0011] In conjunction with the first aspect of this application, in an alternative embodiment, the thickness of the straight section of the positive electrode is the same as that of the bent section of the positive electrode.
[0012] Secondly, embodiments of this application provide a method for preparing an electrode assembly, the method comprising:
[0013] A positive electrode, a negative electrode, and a separator are provided; the positive electrode includes a straight positive electrode section and a bent positive electrode section arranged alternately along a first direction; the negative electrode includes a straight negative electrode section and a bent negative electrode section arranged alternately along the first direction.
[0014] The positive electrode, the separator, and the negative electrode are stacked in sequence and then wound along the first direction to form the electrode assembly. The electrode assembly includes a flat region and a bent region. The positive electrode flat section and the negative electrode flat section are located in the flat region, and the positive electrode bent section and the negative electrode bent section are located in the bent region. The ratio of the areal capacity of the negative electrode bent section to the nearest positive electrode bent section on the side of the negative electrode bent section away from the flat region is a first N / P, and the ratio of the areal capacity of the negative electrode flat section to the positive electrode flat section is a second N / P. The first N / P is greater than the second N / P, and the first N / P decreases from the side of the bent region closer to the flat region to the side away from the flat region.
[0015] The first direction is the winding direction of the positive electrode sheet.
[0016] In conjunction with a second aspect of this application, in an optional embodiment, the positive electrode includes:
[0017] 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;
[0018] The positive current collector includes a first section and a second section arranged alternately along the first direction. The positive electrode slurry is coated on the surface of the first section and the second section respectively. After drying and rolling, a positive electrode sheet is obtained. The first section corresponds to the straight section of the positive electrode, and the second section corresponds to the bent section of the positive electrode. The coating surface density of the positive electrode slurry on the second section is less than the coating surface density on the first section.
[0019] In conjunction with the second aspect of this application, in an optional embodiment, the areal density C1 of the straight section of the positive electrode and the areal density C2 of the bent section of the positive electrode satisfy the following relationship:
[0020] ;
[0021] Where, k is a correction coefficient, taking a value of 2~3; d1 is the thickness of the straight section of the positive electrode; r is the radius of any of the bent sections of the positive electrode; and / or,
[0022] The straight section of the positive electrode has the same thickness as the bent section of the positive electrode.
[0023] In conjunction with the second aspect of this application, in an alternative embodiment,
[0024] The areal densities of the straight section and the bent section of the positive electrode are C1 and C2, respectively, and the feed flow rates of the positive electrode slurry coated on the first section and the second section are V1 and V2, respectively; V2 and V1 satisfy:
[0025] ;
[0026] Optionally, C1 is 300g / m 2 ~450g / m 2 V1 is 10 mL / min to 60 mL / min.
[0027] In conjunction with a second aspect of this application, in an optional embodiment, if the dimension of the positive electrode bending section in the first direction is less than the minimum coating gap in the coating process, then the length of the second section is set to the minimum coating gap.
[0028] 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.
[0029] Compared with the prior art, the embodiments of this application have the following beneficial effects:
[0030] The electrode assembly provided in this application has a first N / P ratio between the areal capacity of the negative electrode bending section and the nearest positive electrode bending section located on the side of the negative electrode bending section away from the straight area, and a second N / P ratio between the areal capacity of the negative electrode straight section and the positive electrode straight section. The first N / P is greater than the second N / P. In this way, the lithium plating problem caused by insufficient first N / P at the end of the battery cycle can be effectively solved, thereby improving the overall dynamic performance of the battery at the end of the cycle, and thus improving the cycle performance and safety performance of the battery. Meanwhile, considering that the curvature of the positive and negative electrode sheets gradually decreases from the side of the bending region closer to the straight region to the side farther from the straight region, the area difference between the negative electrode bending section and the nearest positive electrode bending section on the side of the negative electrode bending section farther from the straight region gradually decreases, and the risk of lithium plating at the bending region gradually decreases, this embodiment of the application also sets the first N / P ratio to decrease from the side of the bending region closer to the straight region to the side farther from the straight region. This can reduce the excess capacity of the negative electrode bending section, thereby helping to effectively improve the lithium plating problem at the bending region while taking into account the energy density of the battery.
[0031] 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
[0032] 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:
[0033] Figure 1 This is a schematic diagram showing the area comparison of adjacent positive and negative electrode plates located in the bending region of a wound electrode assembly after the electrode assembly is unfolded.
[0034] Figure 2 A schematic flowchart illustrating a method for fabricating an electrode assembly according to an embodiment of this application;
[0035] Figure 3 This is a schematic diagram of the structure of a positive electrode sheet during the preparation process in an embodiment of this application;
[0036] Figure 4 For along Figure 3 Schematic diagram of the cross-sectional structure of line A-A' in the middle;
[0037] Figure 5 for Figure 4 The diagram shown illustrates the structure of the positive electrode area after rolling.
[0038] Figure 6 This is a schematic diagram of the structure of an electrode assembly provided in an embodiment of this application;
[0039] Figure 7 For along Figure 6 A schematic diagram of the cross-sectional structure of line B-B' in the middle. Detailed Implementation
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] For wound electrode assemblies, please refer to Figure 1In the bending area of the electrode assembly (also known in the industry as the R-angle), when the positive electrode is located on the side of the adjacent negative electrode away from the winding center, 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 positive and negative electrode segments, making lithium plating more likely in the later stages of battery cycling due to insufficient N / P. The radius of the R-angle increases with the number of winding layers, and therefore the curvature of the R-angle also changes. According to the curvature formula of a circle, φ=1 / r, the larger the radius r of the R-angle, the smaller the curvature φ, and the less bent the electrode. The radius r of the R-angle is smallest and the curvature φ is largest on the side of the bending area closer to the winding center. Therefore, in the above case, the area difference between the positive and negative electrodes is the largest, the corresponding N / P ratio is the smallest, and the risk of lithium plating is the highest. As the number of winding layers increases, the radius of the R-angle r increases, the curvature φ gradually decreases, and the degree of bending of the electrode becomes smaller. Under the above conditions, the area difference between the positive and negative electrodes gradually decreases, and the corresponding N / P ratio gradually increases.
[0047] 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 portions of the positive electrode sheet located in the straight region and the bent region are respectively a positive electrode straight section and a positive electrode bent section; the portions of the negative electrode sheet located in the straight region and the bent region are respectively a negative electrode straight section and a negative electrode bent section; the ratio of the areal capacity of the negative electrode bent section to the nearest positive electrode bent section located on the side of the negative electrode bent section away from the straight region is a first N / P, and the ratio of the areal capacity of the negative electrode straight section to the positive electrode straight section is a second N / P, the first N / P is greater than the second N / P, and the first N / P shows a decreasing trend from the side of the bent region close to the straight region to the side away from the straight region.
[0048] In the electrode assembly of this application embodiment, the ratio of the areal capacity of the negative electrode bending section to the nearest positive electrode bending section located on the side of the negative electrode bending section away from the straight area is a first N / P, and the ratio of the areal capacity of the negative electrode straight section to the positive electrode straight section is a second N / P. The first N / P is greater than the second N / P. In this way, the lithium plating problem caused by insufficient first N / P at the end of the battery cycle can be effectively solved, thereby improving the overall dynamic performance of the battery at the end of the cycle, and thus improving the cycle performance and safety performance of the battery. Meanwhile, considering that the curvature of the positive and negative electrode sheets gradually decreases from the side of the bending region closer to the straight region to the side farther from the straight region, the area difference between the negative electrode bending section and the nearest positive electrode bending section on the side of the negative electrode bending section farther from the straight region gradually decreases, and the risk of lithium plating at the bending region gradually decreases, this embodiment of the application also sets the first N / P ratio to decrease from the side of the bending region closer to the straight region to the side farther from the straight region. This can reduce the excess capacity of the negative electrode bending section, which is beneficial to effectively improve the lithium plating problem at the bending region while taking into account the energy density of the battery.
[0049] In this embodiment, the negative electrode sheet may include a negative current collector and a negative active layer located on at least one surface (usually two surfaces in a wound electrode) of the negative current collector along the thickness direction. The negative active layer includes a negative active material, a negative conductive agent, and a negative binder. The positive electrode sheet may include a positive current collector and a positive active layer located on at least one surface (usually two surfaces in a wound electrode) of the positive current collector along the thickness direction. The positive active layer includes a positive active material, a positive conductive agent, and a positive binder.
[0050] The areal capacity of different sections of the negative and positive electrode sheets can be calculated as follows: Areal capacity = Active layer density * Mass percentage of active material in the active layer * Specific capacity of active material * Area of the active layer coated in that section. Here, the active layer corresponds to either the negative or positive active layer, and the active material corresponds to either the negative or positive active material. The ratio of the areal capacity of any negative electrode bend to the nearest positive electrode bend located on the side of the negative electrode bend furthest from the straight section is denoted as the first N / P. Therefore, given a fixed negative and positive electrode sheet, the first N / P varies, while the ratio of the areal capacity of the straight negative electrode section to the straight positive electrode section (the second N / P) remains constant.
[0051] In some embodiments, the areal density of the bent section of the positive electrode can be less than that of the straight section. Thus, in the actual manufacturing process of the positive electrode sheet, the straight section and the bent section of the positive electrode can be coated with the same positive electrode slurry. The first N / P ratio can be controlled to be greater than the second N / P simply by controlling the coating areal density, which simplifies the manufacturing process. Moreover, the composition of the positive electrode active layer in the positive electrode sheet is uniform, resulting in high performance consistency of the positive electrode sheet.
[0052] Here, the areal density of the positive electrode bending section can be regarded as the areal density of the positive electrode active layer in the positive electrode bending section, and the areal density of the negative electrode bending section can be regarded as the areal density of the negative electrode active layer in the negative electrode bending section.
[0053] In some embodiments, the type and mass percentage of the positive electrode active material are the same in both the straight section and the bent section of the positive electrode active layer; the areal density C1 of the straight section and the areal density C2 of the bent section of the positive electrode satisfy the following relationship:
[0054] ;
[0055] Where k is a correction factor, with a value of 2 to 3; d1 is the thickness of the positive electrode bending section; and r is the radius of each positive electrode bending section.
[0056] Here, r can be determined, for example, based on the outer contour of each positive electrode bending segment away from the straight region, i.e., the outer perimeter of each positive electrode bending segment. Of course, this application does not exclude the possibility of determining r based on the inner contour of each positive electrode bending segment near the straight region.
[0057] The cross-sectional shape of each positive and negative electrode bending segment located in the bending region is semi-circular or approximately semi-circular. The dimension Ln of any positive electrode bending segment along the winding direction of the positive electrode sheet (hereinafter referred to as the first direction) can be calculated using the formula: Ln = πr. The dimension Pn of the nearest negative electrode bending segment located on the side of any positive electrode bending segment closest to the straight region along the first direction is: Pn = π[r - (d1 + d3)] = Ln - π(d1 + d3); where d3 is the thickness of the separator. The first N / P and the second N / P can be calculated using the following formula:
[0058] ;
[0059] ;
[0060] In the above formula, C 负 x is the areal density of the negative electrode active layer. 负 Q represents the mass percentage of the negative electrode active material in the negative electrode active layer. 负 m is the specific capacity of the negative electrode active material. 负 P represents the dimension of the negative electrode active layer in the width direction of the negative electrode current collector (this dimension is the same for the negative electrode active layer in both the straight and bent sections of the negative electrode). 负 x is the dimension of the straight section of the negative electrode along the first direction; 正 Q represents the mass percentage of the positive electrode active material in the negative electrode active layer. 正 m is the specific capacity of the positive electrode active material. 正 P represents the dimension of the positive electrode active layer in the width direction of the positive electrode current collector (this dimension is the same for the positive electrode active layer in both the straight and bent sections of the positive electrode).正 P is the dimension of the straight section of the positive electrode along the first direction. 正 =P 负 Combining the relationship between C2 and C1 above, we can obtain:
[0061] .
[0062] Since k takes the value of 2 to 3, it is well known to those skilled in the art that the thickness d3 of the separator (typically 7 μm to 25 μm) is much smaller than the thickness d1 of the positive electrode bending section (typically 100 μm to 200 μm). Therefore... It must be less than ,Right now That is, the first N / P is greater than the second N / P.
[0063] As shown above, the surface density C1 of the straight section of the positive electrode and the surface density C2 of the bent section of the positive electrode satisfy the following relationship: When r increases, the first N / P ratio can be made greater than the second N / P ratio, thus effectively improving the lithium plating problem at the bending region. At the same time, as r increases, C2 gradually increases, so the first N / P ratio tends to decrease from the side of the bending region closer to the flat region to the side farther away from the flat region. This allows for effective improvement of the lithium plating problem at the bending region while maintaining the battery's energy density.
[0064] In some embodiments, the thickness of the straight section and the bent section of the positive electrode can be the same. This avoids the difference in kinetic performance caused by the different lengths of the lithium insertion / extraction paths between the straight section and the bent section of the positive electrode and the opposite negative electrode sheet, thereby better avoiding the problem of local lithium plating.
[0065] When the surface density C1 of the straight section of the positive electrode is greater than the surface density C2 of the bent section of the positive electrode, the thickness of the straight section and the bent section can be made the same by adjusting their compaction densities.
[0066] This application also provides a method for preparing an electrode assembly; please refer to [reference needed]. Figure 2 The method for preparing the electrode assembly provided in this application includes the following steps:
[0067] S1: Provides a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet includes a straight positive electrode section and a bent positive electrode section arranged alternately along a first direction; the negative electrode sheet includes a straight negative electrode section and a bent negative electrode section arranged alternately along the first direction;
[0068] S2: The separator is placed between the positive electrode and the negative electrode, and wound along the first direction to form an electrode assembly; the electrode assembly includes a flat region and a bent region, the positive electrode flat section and the negative electrode flat section are located in the flat region, and the positive electrode bent section and the negative electrode bent section are located in the bent region; the ratio of the areal capacity of the negative electrode bent section to the nearest positive electrode bent section located on the side of the negative electrode bent section away from the flat region is the first N / P, and the ratio of the areal capacity of the negative electrode flat section to the positive electrode flat section is the second N / P, the first N / P is greater than the second N / P, and the first N / P shows a decreasing trend from the side of the bent region close to the flat region to the side away from the flat region; the first direction is the winding direction of the positive electrode.
[0069] In this embodiment, the provided positive electrode sheet includes a straight positive electrode section and a bent positive electrode section, and the negative electrode sheet includes a straight negative electrode section and a bent negative electrode section. In the obtained electrode assembly, by making the first N / P ratio of the areal capacity of the bent negative electrode section to the nearest positive electrode bent section located on the side of the bent negative electrode section away from the straight region greater than the second N / P ratio of the areal capacity of the straight negative electrode section to the straight positive electrode section, the lithium plating problem caused by insufficient first N / P at the end of the battery cycle can be effectively solved, thereby improving the overall dynamic performance of the battery at the end of the cycle, and thus improving the cycle performance and safety performance of the battery. Moreover, from the side of the bent region close to the straight region to the side away from the straight region, the first N / P shows a decreasing trend. In this way, the excess capacity of the bent negative electrode section can be reduced, which is beneficial to effectively improve the lithium plating problem at the bent region while taking into account the energy density of the battery.
[0070] In step S1, providing the positive electrode may include the following steps:
[0071] 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;
[0072] S12: Please refer to Figure 3 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 positive electrode sheet is obtained. The first section 101 corresponds to the straight section of the positive electrode, and the second section 102 corresponds to the bent section of the positive electrode. The coating surface density of the positive electrode slurry on the second section 102 is less than the coating surface density on the first section 101.
[0073] In this embodiment, the same positive electrode slurry is coated on the first section 101 and the second section 102 of the positive electrode current collector 10. The coating surface density of the positive electrode slurry on the second section 102 is controlled to be less than the coating surface density on the first section 101 (i.e.,...). Figure 4The 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. This allows the areal density of the positive electrode active layer in the bent section to be less than that in the straight section, thus making the areal density of the bent section less than that of the straight section. This facilitates control of the first N / P ratio being greater than the second N / P ratio, simplifies the manufacturing process, and ensures uniform composition of the positive electrode active layer in the positive electrode sheet, resulting in high performance consistency of the positive electrode sheet.
[0074] In some embodiments, the type and mass percentage of the positive electrode active material are the same in both the straight section and the bent section of the positive electrode (e.g., the same positive electrode slurry is used for coating in the above embodiments), and the areal density C1 of the straight section and the areal density C2 of the bent section of the positive electrode satisfy the following relationship:
[0075] ;
[0076] Where k is a correction factor, with a value of 2 to 3; d1 is the thickness of the straight section of the positive electrode; and r is the radius of any bent section of the positive electrode.
[0077] In the electrode assembly formed by winding, each positive electrode bending segment and each negative electrode bending segment located in the bending region are semi-circular or approximately semi-circular. The dimension Ln of any positive electrode bending segment along the first direction can be calculated using the formula: Ln = πr. The dimension Pn of the nearest negative electrode bending segment located on the side of any positive electrode bending segment closest to the straight region along the first direction is Pn = π[r - (d1 + d3)] = Ln - π(d1 + d3); where d3 is the thickness of the separator. Combining the calculation formulas for the first N / P and the second N / P (see the calculation formulas in the aforementioned embodiments, which will not be repeated here) and the above-mentioned relationship between C2 and C1, we can obtain:
[0078] .
[0079] Since k takes the value of 2 to 3, it is well known to those skilled in the art that the thickness d3 of the separator (typically 7 μm to 25 μm) is much smaller than the thickness d1 of the positive electrode bending section (typically 100 μm to 200 μm). Therefore... It must be less than ,Right now, That is, the first N / P is greater than the second N / P.
[0080] As shown above, the surface density C1 of the straight section of the positive electrode and the surface density C2 of the bent section of the positive electrode satisfy the following relationship: When r increases, the first N / P ratio can be made greater than the second N / P ratio, thus effectively improving the lithium plating problem at the bending region. At the same time, as r increases, C2 gradually increases, so the first N / P ratio tends to decrease from the side of the bending region closer to the flat region to the side farther away from the flat region. This allows for effective improvement of the lithium plating problem at the bending region while maintaining the battery's energy density.
[0081] In some embodiments, the thickness of the straight section and the bent section of the positive electrode can be the same. This avoids the difference in kinetic performance caused by the different lengths of the lithium insertion / extraction paths between the straight section and the bent section of the positive electrode and the opposite negative electrode sheet, thereby better avoiding the problem of local lithium plating.
[0082] When the surface density C1 of the straight section of the positive electrode is greater than the surface density C2 of the bent section of the positive electrode, the thickness of the straight section and the bent section can be made the same by adjusting their compaction densities.
[0083] In the actual preparation process, please refer to... Figure 4 and Figure 5 The coating thickness of the positive electrode slurry on the second section 102 of the positive electrode current collector 10 is less than the coating thickness of the positive electrode slurry on the first section 101 (e.g., Figure 4 (As shown in the dashed box), after drying and rolling, the thickness of the straight section and the bent section of the positive electrode can be the same (e.g., Figure 5 (As shown in the dashed box), it also allows the surface density C1 of the straight section of the positive electrode to be greater than the surface density C2 of the bent section of the positive electrode.
[0084] In some embodiments, the areal densities of the straight section and the bent section of the positive electrode are C1 and C2, respectively, 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:
[0085] .
[0086] In this embodiment, based on the target areal density of the straight section and the bent section of the positive electrode, 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 straight section and the bent section of the positive electrode in the prepared positive electrode sheet can be better controlled by the process to achieve the target value.
[0087] 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 2Or any value between any two of the above ranges. 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.
[0088] 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.
[0089] As mentioned above, the dimension Ln of any positive electrode bending segment along the first direction can be calculated using the formula: Ln = πr. Therefore, the values of L1 to Ln gradually increase from the starting end to the ending end of the positive electrode winding. Please refer to [reference needed]. Figure 3 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 gradually 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 remains unchanged. That is, in the obtained positive electrode sheet, the portion of the positive electrode active layer located in the positive electrode bending section and the portion located in the positive electrode straight section have the same size in the width direction of the positive electrode current collector 10.
[0090] For one or more positive electrode bending segments closest to the straight region, Ln is also small due to the small size of r. In the actual manufacturing process, if the dimension Ln of the positive electrode bending segment in the first direction is smaller than the minimum coating gap in the coating process, the length of the second segment 102 is set as the minimum coating gap.
[0091] 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.
[0092] 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.
[0093] Step S2: After stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, they are wound along the first direction to form an electrode assembly. The electrode assembly includes a flat region and a bent region. The positive electrode flat section and the negative electrode flat section are located in the flat region, and the positive electrode bent section and the negative electrode bent section are located in the bent region.
[0094] In the actual manufacturing process, the electrode assembly can be obtained by stacking the positive electrode, separator, negative electrode and separator in that order, and then winding them along the first direction.
[0095] Figure 6 and Figure 7 An electrode assembly 400 prepared according to an embodiment of this application is shown. Figure 7 For along Figure 6 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.
[0096] In some embodiments, please refer to Figure 6 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.
[0097] certainly, Figure 6 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.
[0098] 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.
[0099] It is understood that the beneficial effects of the electrode assembly described in any of the above embodiments also apply to the battery.
[0100] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.
[0101] The methods for preparing the electrode assembly are basically the same in all embodiments, specifically including: coating the positive electrode slurry with different coating density on the first and second sections of the positive electrode current collector (see reference). Figure 3 After drying and rolling, a positive electrode active layer of uniform thickness is formed, resulting in a positive electrode sheet. A negative electrode slurry is coated onto the negative electrode current collector, and after drying and rolling, a negative electrode active layer is formed, resulting in a negative electrode sheet. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and wound to obtain the desired product. Figure 7 The electrode assembly is shown. The minimum coating gap Lmin of the slurry coating machine is 5 mm, and the coating speed is 5 mm / s; the thickness of the separator is d3 = 16 μm. The specific parameters of the positive and negative electrode sheets in each embodiment are as follows.
[0102] Example 1
[0103] 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 straight section of the positive electrode sheet is 300 g / m². 2 (The coating pump speed of the positive electrode slurry on the first section of the positive electrode current collector is V1 = 20 mL / min), and the thickness of the positive electrode sheet is d1 = 123 μm;
[0104] 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 of the negative electrode is d2=100μm.
[0105] Second N / P = =1.13, number of winding layers n=36 layers, from the 1st layer closest to the flat region to the 36th layer furthest from the flat region, the areal density C2 of each positive electrode bending segment located in the bending region of the electrode assembly is calculated according to the formula The calculation yields a value of k equal to 2, and the radius of each positive electrode bending segment is r = nd1 + nd2 + (2n + 1)d3, where r is in mm. The pumping speed for coating the positive electrode slurry on the second section of the positive electrode current collector is determined according to the formula... The calculated value is Ln = πr, the dimension of each positive electrode bending segment along the first direction. According to the formula... The first N / P is calculated. The values of C2, r, Ln, V2 and the first N / P are shown in Table 1.
[0106] 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 7 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.
[0107] Example 2
[0108] Based on the mass of the positive electrode active layer as 100%, the positive electrode active layer comprises: 97.5% positive electrode active material (NCM), 0.7% positive electrode conductive agent (conductive carbon black SP), and 1.8% positive electrode binder (PVDF); wherein, the specific capacity of NCM is 187 mAh / g, and the areal density C1 of the straight section of the positive electrode is 300 g / m³. 2 (The coating pump speed of the positive electrode slurry on the first section of the positive electrode current collector is V1 = 20 mL / min), and the thickness of the positive electrode sheet is d1 = 95 μm;
[0109] 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 186 g / m². 2 The thickness of the negative electrode is d2=127μm.
[0110] Second N / P = =1.13. Referring to the method of calculating r, Ln, C2, V2 and the first N / P in Example 1, the values of r, Ln, C2, V2 and the first N / P in this example are calculated, and the values are shown in Table 2.
[0111] Example 3
[0112] 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 and NCM, with a mass ratio of lithium iron phosphate to NCM of 3:7), 0.7% positive electrode conductive agent (conductive carbon black SP), and 1.8% positive electrode binder (PVDF); wherein, the specific capacity of the mixed positive electrode active material of lithium iron phosphate and NCM is 174.4 mAh / g, and the areal density C1 of the straight section of the positive electrode is 300 g / m². 2 (The coating pump speed of the positive electrode slurry on the first section of the positive electrode current collector is V1=20mL / min), and the thickness of the positive electrode sheet is d1=106μm;
[0113] 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 173 g / m². 2 The thickness of the negative electrode is d2=119μm.
[0114] Second N / P = =1.13. Referring to the method of calculating r, Ln, C2, V2 and the first N / P in Example 1, the values of r, Ln, C2, V2 and the first N / P in this example are calculated, and the values are shown in Table 3.
[0115] Comparative Example 1
[0116] The difference between the preparation method of the electrode assembly in this comparative example and that in Example 1 is:
[0117] The positive electrode sheet does not distinguish between a straight section and a bent section; the areal density of the positive electrode sheet is 300 g / m³. 2 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). Everything else is the same as in Example 1. The N / P ratio in the flat region of the electrode assembly is 1.13.
[0118] Table 1
[0119]
[0120] Table 2
[0121]
[0122] Table 3
[0123]
[0124] 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 1000 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:
[0125] 1) Slight lithium plating, meeting at least one of the following conditions:
[0126] • 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;
[0127] • Color: Light gray, grayish white, local spots / stripes, not continuous patches;
[0128] •Thickness: Extremely thin layer, no grainy feel or bumps to the touch;
[0129] • No obvious dendrites, no powder shedding, and no risk of puncturing the diaphragm;
[0130] • The surface of the negative electrode is mostly still golden yellow / grayish black (normal lithium intercalation).
[0131] 2) Severe lithium plating, meeting at least one of the following conditions:
[0132] • The deposited lithium covers a large area, a whole sheet, and continuously on the surface of the negative electrode;
[0133] • Color: Bright silver-white, strong metallic luster, even white and shiny;
[0134] • Significantly increased thickness: raised, bulging, and feels granular / moss-like to the touch;
[0135] • Dendritic, needle-like, and whisker-like lithium crystals appear;
[0136] • The lithium plating layer is prone to peeling off, powdering, and friction against the diaphragm;
[0137] • Lithium buildup occurs at the edges / head of the negative electrode.
[0138] The test results are shown in Table 4.
[0139] Table 4
[0140]
[0141] As can be seen from the data in Tables 1 to 3, in Examples 1 to 3, the first N / P is greater than the second N / P (1.13), and the first N / P shows a decreasing trend from the side of the bending area closer to the straight area to the side farther away from the straight area (i.e. from n=1 to n=36).
[0142] As can be seen from the results in Table 4, 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, while the battery in Comparative Example 1 showed severe lithium plating at the negative electrode interface in the bending area of the electrode assembly after fast-charge cycle testing. This indicates that in the electrode assembly provided by this application, the ratio of the areal capacity of the negative electrode bending section to the nearest positive electrode bending section on the side of the negative electrode bending section away from the straight area, the first N / P, is greater than the ratio of the areal capacity of the negative electrode straight section to the positive electrode straight section, which is the second N / P. Furthermore, the first N / P decreases from the side of the bending area closer to the straight area to the side farther from the straight area. This effectively solves the problem of lithium plating caused by insufficient first N / P at the bending area of the electrode assembly at the end of the battery cycle, thereby improving the overall dynamic performance of the battery at the end of the cycle, and thus improving the cycle performance and safety performance of the battery.
[0143] 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.
[0144] 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, The device 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 portions of the positive electrode sheet located in the straight region and the bent region are respectively a positive electrode straight section and a positive electrode bent section; the portions of the negative electrode sheet located in the straight region and the bent region are respectively a negative electrode straight section and a negative electrode bent section. The ratio of the surface area of the negative electrode bending section to that of the nearest positive electrode bending section on the side of the negative electrode bending section away from the straight region is a first N / P, and the ratio of the surface area of the negative electrode straight section to that of the positive electrode straight section is a second N / P. The first N / P is greater than the second N / P, and the first N / P tends to decrease from the side of the bending section closer to the straight region to the side farther away from the straight region.
2. The electrode assembly according to claim 1, characterized in that, The surface density of the bent section of the positive electrode is less than the surface density of the straight section of the positive electrode.
3. The electrode assembly according to claim 2, characterized in that, In the positive electrode active layer of both the straight section and the bent section, the type and mass percentage of the positive electrode active material are the same; the areal density C1 of the straight section and the areal density C2 of the bent section satisfy the following relationship: ； Where k is a correction coefficient, with a value of 2 to 3; d1 is the thickness of the positive electrode bending section; and r is the radius of each positive electrode bending section.
4. The electrode assembly according to claim 2, characterized in that, The straight section of the positive electrode has the same thickness as the bent section of the positive electrode.
5. A method for preparing an electrode assembly, characterized in that, The method includes: A positive electrode, a negative electrode, and a separator are provided; the positive electrode includes a straight positive electrode section and a bent positive electrode section arranged alternately along a first direction; the negative electrode includes a straight negative electrode section and a bent negative electrode section arranged alternately along the first direction. The positive electrode, the separator, and the negative electrode are stacked in sequence and then wound along the first direction to form the electrode assembly. The electrode assembly includes a flat region and a bent region. The positive electrode flat section and the negative electrode flat section are located in the flat region, and the positive electrode bent section and the negative electrode bent section are located in the bent region. The ratio of the areal capacity of the negative electrode bent section to the nearest positive electrode bent section on the side of the negative electrode bent section away from the flat region is a first N / P, and the ratio of the areal capacity of the negative electrode flat section to the positive electrode flat section is a second N / P. The first N / P is greater than the second N / P, and the first N / P decreases from the side of the bent region closer to the flat region to the side away from the flat region. The first direction is the winding direction of the positive electrode sheet.
6. The method for preparing the electrode assembly according to claim 5, characterized in that, The positive electrode plates provided include: 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 current collector includes a first section and a second section arranged alternately along the first direction. The positive electrode slurry is coated on the surface of the first section and the second section respectively. After drying and rolling, a positive electrode sheet is obtained. The first section corresponds to the straight section of the positive electrode, and the second section corresponds to the bent section of the positive electrode. The coating surface density of the positive electrode slurry on the second section is less than the coating surface density on the first section.
7. The method for preparing the electrode assembly according to claim 6, characterized in that, The areal density C1 of the straight section of the positive electrode and the areal density C2 of the bent section of the positive electrode satisfy the following relationship: ； Where, k is a correction coefficient, taking a value of 2~3; d1 is the thickness of the straight section of the positive electrode; r is the radius of any of the bent sections of the positive electrode; and / or, The straight section of the positive electrode has the same thickness as the bent section of the positive electrode.
8. The method for preparing the electrode assembly according to claim 6, characterized in that, The areal densities of the straight section and the bent section of the positive electrode are C1 and C2, respectively, and the feed flow rates of the positive electrode slurry coated on the first section and the second section are V1 and V2, respectively; V2 and V1 satisfy: ； Optionally, C1 is 300g / m 2 ~450g / m 2 V1 is 10 mL / min to 60 mL / min.
9. The method for preparing the electrode assembly according to claim 6, characterized in that, If the dimension of the positive electrode bending section in the first direction is smaller than the minimum coating gap in the coating process, then the length of the second section is set to the minimum coating gap.
10. A battery, characterized in that, The electrode assembly includes the electrode assembly according to any one of claims 1 to 4, or the electrode assembly prepared by the method of the electrode assembly according to any one of claims 5 to 9.