Wound-type battery cell and battery pack

Abstract

A wound-type battery cell and a battery pack. The battery cell (3) comprises a casing (5), an electrolyte (6) located in the casing (5), and a positive electrode sheet (10), a negative electrode sheet (20) and a separator (30) which are stacked in the casing (5). The separator (30) is located between the positive electrode sheet (10) and the negative electrode sheet (20), and the positive electrode sheet (10), the negative electrode sheet (20) and the separator (30) are wound to form a battery cell body (4). The negative electrode sheet (20) comprises corners (21), and holes (211) are provided at the corners (21). By providing the holes (211) at the corners (21) of the negative electrode sheet (20), tension at the corners (21) is released; in addition, a polymer coating layer (40) is used to release stress and retain electrolyte, thereby alleviating carbon loss at the corners (21), improving the wettability of the electrolyte (6), and alleviating sodium plating at the corners (21) during cycles.

Description

Wound cells and battery packs

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 29, 2024, with application number 202420647224.0 and application name “Wound-type battery cell and battery pack”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of batteries, and in particular to a wound battery cell and a battery pack. Background Art

[0003] The problem of lithium or sodium deposition at the corners of the electrode is a difficulty and pain point in the industry. In related technologies, the excess degree of negative electrode capacity at the corner is increased by adjusting the N / P ratio at the corner. However, during the charging process, this method will cause the battery to produce ohmic polarization, concentration polarization, and electrochemical polarization. Even if the negative electrode is far in excess, sodium or lithium deposition will still occur due to kinetic differences. Therefore, the problem of lithium or sodium deposition at the corners of the electrode is a problem that needs to be solved urgently.

[0004] Application Contents

[0005] The embodiments of the present application provide a wound battery cell and a battery pack to effectively solve the problem of lithium or sodium deposition on the negative electrode sheet and to increase the service life of the battery cell.

[0006] In a first aspect, an embodiment of the present application provides a wound battery cell, which includes a shell, an electrolyte located in the shell, and a positive electrode sheet, a negative electrode sheet and a separator stacked in the shell, the separator is located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the negative electrode sheet and the separator are wound to form the battery cell body; the negative electrode sheet includes a corner, and the corner is provided with a hole.

[0007] In this embodiment, since holes are provided at the corners, the tension at the corners can be released by opening the holes at the corners. After the tension at the corners is effectively reduced, the problems of active material shedding at the corners of the negative electrode sheet and sodium and lithium precipitation can be effectively reduced. Since the corners of the negative electrode sheet in the related art are the most serious locations for sodium and lithium precipitation, this embodiment solves the problems of sodium and lithium precipitation at the corners of the negative electrode sheet, which can solve the problems of sodium and lithium precipitation in the battery cell, thereby effectively improving the service life of the battery cell. Moreover, since holes are provided at the corners, electrolyte can be accommodated in the holes, thereby improving the wettability of the electrolyte at the corners. After the wettability of the electrolyte at the corners is improved, the problems of active material shedding at the corners and sodium and lithium precipitation can also be effectively reduced. The problem of decarbonization at the corners can also be effectively alleviated, thereby effectively improving the service life of the battery cell.

[0008] In some embodiments, the negative electrode sheet includes a foil layer and a slurry layer stacked on both sides of the foil layer, and the holes are formed in the slurry layer without penetrating the foil layer. In this embodiment, because the holes are formed in the slurry layer without penetrating the foil layer, the structural strength provided by the foil layer is maintained. Even if the holes are formed randomly, the corners of the negative electrode sheet will not collapse.

[0009] In some embodiments, the depth of the hole in the thickness direction of the negative electrode sheet is 10 μm-100 μm. In this embodiment, the depth of the hole is within this range, which can effectively release the tension of the corner and effectively solve the problem of sodium or lithium deposition at the corner of the negative electrode sheet.

[0010] In some embodiments, the width of the hole in the winding direction of the battery cell body is less than 100 μm. Here, the width of the hole in the winding direction of the battery cell body is less than 100 μm, which means that the maximum width is less than 100 μm. In this embodiment, by setting the width of the hole in the winding direction of the battery cell body to less than 100 μm, the tension in the corners can be effectively released, effectively solving the problem of sodium or lithium deposition in the corners of the negative electrode sheet.

[0011] In some embodiments, the number of holes is multiple, and the multiple holes are spaced apart along the winding direction of the battery body, and the spacing between any two adjacent holes in the winding direction of the battery body is 50μm-2mm. In this embodiment, since the spacing between any two adjacent holes in the winding direction of the battery body is set in the range of 50μm-2mm, it can be ensured that the tension at the corner of the negative electrode sheet can be effectively released to solve the problem of sodium or lithium precipitation at the corner of the negative electrode sheet. Moreover, since the spacing between any two adjacent holes in the winding direction of the battery body is set in the range of 50μm-2mm, it can also be ensured that the wetting ability of the electrolyte at each corner position along the winding direction of the battery body is uniformly and effectively improved.

[0012] In some embodiments, the height direction of the battery cell body is perpendicular to the winding direction of the battery cell body, and the width of the hole in the height direction of the battery cell body is less than 100μm. Here, the width of the hole in the height direction of the battery cell body is less than 100μm, which means that the maximum width is less than 100μm. In this embodiment, in conjunction with the width of the hole in the winding direction of the battery cell body being less than 100μm, multiple holes can be spaced apart in the width direction of the negative electrode sheet to evenly release tension in the width direction of the negative electrode sheet.

[0013] In some embodiments, the height direction of the battery cell body is perpendicular to the winding direction of the battery cell body, and the hole penetrates the negative electrode sheet in the height direction of the battery cell body. In this embodiment, since the hole is opened on the slurry layer and does not penetrate the foil layer, the overall strength of the negative electrode sheet can be ensured by the foil layer, and the problem of insufficient strength and breakage or tearing during winding will not be affected. Moreover, since the hole penetrates the negative electrode sheet in the height direction of the battery cell body, the tension can be effectively released in the height direction of the battery cell body, and the problem of stress concentration can be effectively reduced. Thereby, the problem of sodium or lithium precipitation at the corner of the negative electrode sheet can be well solved.

[0014] In some embodiments, in the depth direction of the hole, the hole includes a hole opening and a hole bottom, and along the depth direction of the hole, from the hole opening to the hole bottom, the size of the hole in the winding direction of the battery cell body gradually decreases. In this embodiment, along the depth direction of the hole, from the hole opening to the hole bottom, the size of the hole in the winding direction of the battery cell body gradually decreases. Therefore, for the holes in the slurry layer located near the winding center of the battery cell body, the closer they are to the winding center of the battery cell body, the larger their size. This can effectively solve the problem that the slurry layer near the winding center of the battery cell body is subjected to greater extrusion tension as it gets closer to the winding center of the battery cell body. It can also reduce the material peeling off the slurry layer due to the opening of the hole, thereby effectively reducing the loss of active material.

[0015] In some embodiments, a polymer coating layer is provided at the corner, and the polymer coating layer is used to adsorb the electrolyte. In this embodiment, the polymer coating layer has a liquid locking function, and the electrolyte can be adsorbed on the polymer coating layer to improve the wettability of the electrolyte. In addition, the polymer coating layer can also improve the stress concentration problem at the corner to reduce the problem of decarbonization at the corner. After the stress concentration problem at the corner is improved, the problem of sodium or lithium precipitation of the negative electrode sheet can also be effectively improved.

[0016] In some embodiments, the polymer coating layer is provided on the inner wall of the hole. In this embodiment, since the polymer coating layer is provided on the inner wall of the hole, the electrolyte is more likely to accumulate in the hole. Therefore, the combination of the polymer coating layer on the inner wall of the hole and the hole can greatly improve the wettability of the electrolyte. In addition, it can also effectively reduce the stress concentration problem of the hole at the corner. Moreover, by not providing the polymer coating layer on the surface of the corner, the space occupied by the polymer coating layer can be further reduced, thereby minimizing the energy density of the battery cell.

[0017] In some embodiments, the thickness of the polymer coating layer is 10 nm to 20 μm. In this embodiment, setting the polymer coating layer to 10 nm to 20 μm does not occupy too much space and does not significantly affect the energy density of the battery cell. It can also effectively alleviate the problem of stress concentration at corners and effectively improve the wettability of the electrolyte.

[0018] In some embodiments, the slurry layers on both sides of the foil layer are provided with holes, and the holes in the slurry layers on both sides of the foil layer have different depths. In this embodiment, the problem of the slurry layers on both sides of the foil layer being subjected to different tensions can be effectively solved.

[0019] In some embodiments, the negative electrode sheet includes multiple layers from the inside to the outside, each layer includes a corner, and the depth of the hole on the corner of the inner layer is greater than the depth of the hole on the corner of the outer layer. That is to say, the negative electrode sheet includes multiple corners formed by winding, and the multiple corners are at different distances from the winding center of the battery cell body, and the depth of the hole opened on the corner that is closer to the winding center of the battery cell body is deeper. In this embodiment, since the depth of the hole on the corner of the inner layer is greater than the depth of the hole on the corner of the outer layer among the multiple corners, that is to say, the greater the tension received by the corner closer to the winding center of the battery cell body, the problem of different tensions received by the corners at different distances from the winding center of the battery cell body can be effectively solved by opening deeper holes on the corners closer to the winding center of the battery cell body. As a result, each corner can reduce the loss of active material as much as possible while releasing the tension.

[0020] In some embodiments, the radius of curvature of the corner is less than 1. In this embodiment, since a hole is provided at the corner, the tension at the corner can be effectively released, thereby allowing the corner to be wound to a curvature less than 1. The corner curvature less than 1 can make the battery cell body more tightly wound, thereby improving the energy density of the battery cell body.

[0021] In a second aspect, an embodiment of the present application provides a battery pack comprising a housing and a plurality of wound battery cells as described in any one of the first aspects above, wherein the plurality of wound battery cells are disposed in the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art.

[0023] FIG1 is a schematic structural diagram of a battery pack provided in an embodiment of the present application;

[0024] FIG2 is a schematic structural diagram of a battery cell provided in an embodiment of the present application;

[0025] FIG3 is a top view of the battery cell body in FIG2 ;

[0026] FIG4 is a top view of the negative electrode sheet of the battery cell in FIG2 after winding;

[0027] FIG5 is an enlarged structural diagram of one corner of the negative electrode sheet in FIG4 ;

[0028] FIG6 is a front view of the negative electrode sheet in FIG4 when it is unfolded;

[0029] FIG7 is a schematic top view of the negative electrode sheet in FIG4 when it is unfolded;

[0030] FIG8 is a front view of the negative electrode sheet in FIG4 when it is unfolded;

[0031] FIG9 is a schematic top view of the negative electrode sheet in FIG4 when it is unfolded;

[0032] FIG10 is a partially enlarged schematic diagram of a corner of another negative electrode sheet provided in an embodiment of the present application.

[0033] Explanation of the accompanying symbols: R, winding direction of the battery cell body; Z, height direction of the battery cell body; L, winding center of the battery cell body; m1, width of the hole in the height direction of the battery cell body; m2, width of the hole in the winding direction of the battery cell body; m3, depth of the hole; m4, spacing between two adjacent holes; m5, thickness of the polymer coating layer; 1, battery pack; 2, shell; 3, battery cell; 4, battery cell body; 5, shell; 6, electrolyte; 10, positive electrode sheet; 20, negative electrode sheet; 21, corner; 211, hole; 212, hole opening; 213, hole bottom; 22, foil layer; 23, slurry layer; x, extension direction of the negative electrode sheet; y, width direction of the negative electrode sheet; z, thickness direction of the negative electrode sheet; 30, diaphragm; 40, polymer coating layer. DETAILED DESCRIPTION

[0034] The following first explains some of the terms involved in the embodiments of this application.

[0035] The terms "first", "second", "third", "fourth", etc. in the description and claims of the embodiments of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0036] In this specification, the terms "perpendicular" and "parallel" are explained.

[0037] Vertical: The vertical defined in this application is not limited to an absolute vertical intersection relationship (angle of 90 degrees). It allows for non-absolute vertical intersection relationships caused by factors such as assembly tolerance, design tolerance, and structural flatness. It allows for errors in a small angle range. For example, the assembly error range of 80 to 100 degrees can be understood as a vertical relationship.

[0038] Parallel: The parallel defined in this application is not limited to absolute parallelism. This definition of parallelism can be understood as basic parallelism, allowing for situations where the absolute parallelism is not caused by factors such as assembly tolerance, design tolerance, and the influence of structural flatness. These situations will lead to the sliding fitting part and the first door panel not being absolutely parallel, but this application also defines this situation as parallel.

[0039] Winding is a key internal forming process for battery cells, offering advantages such as maturity, low cost, and high yield, and can be applied to soft-pack, prismatic, and cylindrical batteries. However, due to the characteristics of the winding structure, the electrode curvature and stress at the winding corners are significant, making active material shedding and electrolyte wettability more likely. For example, in lithium-ion and sodium-ion batteries, the winding corners of the negative electrode are prone to interfacial issues such as lithium and sodium deposition, leading to safety issues and reduced cycle life.

[0040] In order to solve the problem of sodium or lithium deposition at the corners. A more common method is to adjust the N / P ratio at the corners. N / P (Negative / Positive) refers to the ratio of the actual capacity of the negative electrode material to the actual capacity of the positive electrode material per unit area. This increases the excess capacity of the negative electrode at the corners to reduce sodium or lithium deposition. However, this method can only slightly slow down the sodium or lithium deposition. During the charging process, the battery will produce ohmic polarization, concentration polarization, and electrochemical polarization. Even if the negative electrode is far in excess, sodium or lithium deposition will occur due to poor kinetics. In addition, by increasing the gap at the corners to improve the wettability of the electrode at the corners, an attempt is made to improve the problem of sodium or lithium deposition. However, this method still causes stress concentration at the corners, resulting in the shedding of active materials, which leads to insufficient negative electrode active materials and sodium or lithium deposition. Therefore, solving the problems of active material shedding at the corners, poor electrolyte wettability, sodium deposition, and lithium deposition is a problem that needs to be solved urgently.

[0041] Figure 1 is a schematic diagram of the structure of a battery pack 1 provided in an embodiment of the present application. The battery pack 1 in the embodiment of Figure 1 can be used not only in energy storage devices, but also in the automotive field or other fields requiring the use of the battery pack 1.

[0042] Referring to Figure 1 , a battery pack 1 includes a housing 2 and a plurality of battery cells 3 within the housing 2. The plurality of battery cells 3 are stacked and arranged within the housing 2. It is understood that the plurality of battery cells 3 can be arranged in a single row or in multiple rows. The battery cells 3 in this embodiment can effectively solve problems such as active material shedding at corners 21, poor electrolyte wettability, and sodium and lithium precipitation.

[0043] In some embodiments, the battery core 3 is substantially in the shape of a rectangular parallelepiped. Of course, in other embodiments, the battery core 3 may also be in other flat or cylindrical structures.

[0044] Figure 2 is a schematic structural diagram of a battery cell 3 provided in an embodiment of the present application; Figure 3 is a top view of the battery cell body 4 in Figure 2. The battery cell 3 in the embodiment of Figure 2 can be applied not only to the battery pack 1 in the embodiment of Figure 1, but also to other charging and discharging equipment, such as site energy, photovoltaic, household energy storage, industrial and commercial energy storage, and large-scale ground power station energy storage equipment. For the battery cell 3 of the present application, the number of battery cell bodies 4 of each battery cell 3 is not limited. For example, in some embodiments, the battery cell 3 includes two battery cell bodies 4 in a chain. In other embodiments, the battery cell 3 can also include other numbers of battery cell bodies 4, such as three, four, or one.

[0045] The battery cell 3 in the embodiment of the present application may be a lithium-ion battery cell 3, a sodium-ion battery cell 3, or another type of battery cell 3. For example, the negative electrode active material may be one or more of graphite, soft carbon, hard carbon, etc. For example, the positive electrode active material may be one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, NaxMO2 (M is a transition metal atom, 0<X≤1), Prussian blue and its homologues, polyanions (phosphates, fluorinated phosphates, pyrophosphates, and sulfates), etc.

[0046] 2 and 3 , the battery cell 3 includes a housing 5, an electrolyte 6 located within the housing 5, and a stacked positive electrode sheet 10, a negative electrode sheet 20, and a separator 30 located within the housing 5. The separator 30 is located between the positive electrode sheet 10 and the negative electrode sheet 20. The positive electrode sheet 10, the negative electrode sheet 20, and the separator 30 are wound to form a battery cell body 4. For example, the positive electrode sheet 10, the negative electrode sheet 20, and the separator 30 are wound around a winding center L of the battery cell body 4 to form the battery cell body 4.

[0047] The winding direction R of the battery cell body 4 and the height direction B of the battery cell body 4 are perpendicular to each other, and the winding direction R of the battery cell body 4 is a direction surrounding the winding center L of the battery cell body 4 .

[0048] FIG4 is a top view of the negative electrode sheet 20 of the battery cell 3 in FIG2 after winding.

[0049] 3 and 4 , in some embodiments, the negative electrode sheet 20 includes a corner 21 formed by winding along the winding direction R of the battery cell body 4, and the corner 21 is provided with a hole 211. It is understood that the corner 21 in this embodiment refers to the corner 21 formed when winding the negative electrode sheet 20 as understood by those skilled in the art, that is, the area where the curvature of the negative electrode sheet 20 suddenly changes significantly during winding along the winding direction R of the battery cell body 4. In this embodiment, since the hole 211 is provided at the corner 21, the tension at the corner 21 can be released by the hole 211 provided at the corner 21. After the tension at the corner 21 is effectively reduced, the problem of active material shedding and sodium and lithium deposition at the corner 21 of the negative electrode sheet 20 can be effectively reduced. Since the corner 21 of the negative electrode sheet 20 in the related art is the location where sodium and lithium deposition are most serious, this embodiment solves the problem of sodium and lithium deposition at the corner 21 of the negative electrode sheet 20, thereby solving the problem of sodium and lithium deposition in the battery cell 3, thereby effectively improving the service life of the battery cell 3. Moreover, since the corner 21 is provided with a hole 211, the hole 211 can accommodate the electrolyte 6, thereby improving the wettability of the electrolyte 6 at the corner 21. After the wettability of the electrolyte 6 at the corner 21 is improved, it can also effectively reduce the problem of active material shedding and sodium and lithium precipitation at the corner 21, and can also effectively alleviate the problem of decarbonization at the corner 21, thereby effectively improving the service life of the battery cell 3.

[0050] In this embodiment, the negative electrode sheet 20 forms multiple corners 21 during the winding process. The curvature radii of the multiple corners 21 may vary, and the curvature radii at different locations of each corner 21 may also vary. For example, the curvature radius of the corner 21 that is farther from the winding center L of the battery cell body 4 is generally larger, while the curvature radius of the corner 21 that is closer to the winding center L of the battery cell body 4 is generally smaller.

[0051] In some embodiments, the radius of curvature of the corner 21 is less than 1. It is understandable that the corner 21 in this embodiment is only one of the multiple corners 21 of the negative electrode sheet 20. It should be noted that in this embodiment, the radius of curvature of the corner 21 is less than 1, which means that the radius of curvature at each position of the corner 21 is less than 1. In this embodiment, since the hole 211 is provided at the corner 21, the tension at the corner 21 can be effectively released, thereby allowing the corner 21 to be wound to a radius of curvature less than 1. The radius of curvature of the corner 21 less than 1 can make the battery cell body 4 be wound more tightly, thereby improving the energy density of the battery cell body 4.

[0052] In some embodiments, after the negative electrode sheet 20 is wound around the winding center L of the battery cell body 4, the areas on the negative electrode sheet 20 with a curvature radius less than 1 are all corners 21 of the negative electrode sheet 20, and holes 211 are provided at the corners 21. In this embodiment, since the areas on the negative electrode sheet 20 with a curvature radius less than 1 are all corners 21 of the negative electrode sheet 20, the areas on the negative electrode sheet 20 with a curvature radius less than 1 are all provided with holes 211. This allows for reasonable and effective tension release in the areas on the negative electrode sheet 20 with a curvature radius less than 1, thereby effectively reducing the problems of active material shedding at the corners 21 and sodium and lithium precipitation.

[0053] It is understandable that the positive electrode sheet 10 and the separator 30 are also wound around the winding center L of the battery cell body 4 and along the winding direction R of the battery cell body 4. The positive electrode sheet 10 and the separator 30 also have corners. In some embodiments, holes are provided at the corners of the positive electrode sheet 10. When holes are provided at the corners of the positive electrode sheet 10, the wettability of the electrolyte 6 at the corners of the positive electrode sheet 10 can be effectively improved, and the tension at the corners of the positive electrode sheet 10 can also be relieved. In some other embodiments, since the problems of sodium precipitation and lithium precipitation basically do not occur at the corners of the positive electrode sheet 10, the corners of the positive electrode sheet 10 may not be provided with holes.

[0054] Figure 5 is an enlarged structural diagram of one corner 21 of the negative electrode sheet 20 in Figure 4. It should be noted that the color layer on the negative electrode sheet 20 in Figure 5 is for the purpose of clearly showing the layer structure of the negative electrode sheet 20 and does not mean that Figure 5 is a cross-sectional view.

[0055] 5 , the negative electrode sheet 20 includes a foil layer 22 and a slurry layer 23 stacked on both sides of the foil layer 22. The hole 211 opened on the corner 21 of the negative electrode sheet 20 is a blind hole. For example, in some embodiments, the hole 211 is opened on the slurry layer 23 and does not penetrate the foil layer 22. Since the hole 211 is opened on the slurry layer 23 and does not penetrate the foil layer 22, the structural strength brought by the foil layer 22 can be ensured, and even if the hole 211 is opened disorderly, it will not cause the structural collapse of the corner 21 of the negative electrode sheet 20. In addition, since the corner 21 of the negative electrode sheet 20 is provided with a blind hole, the electrolyte 6 on both sides of the negative electrode sheet 20 will not circulate, so that the electrolyte 6 on both sides of the negative electrode sheet 20 is more uniform, thereby reducing the decarbonization of the corner 21 of the negative electrode sheet 20.

[0056] In some embodiments, the slurry layers 23 on both sides of the foil layer 22 are provided with holes 211, and the holes 211 are all blind holes. After the negative electrode sheet 20 is wound along the winding direction R of the battery body 4, one of the two layers of slurry at the corner 21 of the negative electrode sheet 20 is closer to the winding center L of the battery body 4, and the other layer is farther away from the winding center L of the battery body 4. Among them, the slurry layer 23 farther from the winding center is mainly subjected to tension, while the slurry layer 23 closer to the winding center is mainly subjected to compression. The holes 211 opened in the slurry layer 23 farther from the winding center are used to release the tension caused by the tension, thereby effectively reducing the lithium or sodium precipitation of the slurry layer 23 farther from the winding center. The holes 211 opened in the slurry layer 23 closer to the winding center are used to release the tension caused by the compression, thereby effectively reducing the lithium or sodium precipitation of the slurry layer 23 closer to the winding center.

[0057] In some embodiments, the depths m3 of the holes 211 in the slurry layer 23 on either side of the foil layer 22 are different. The depth m3 of the holes 211 in the slurry layer 23 closer to the winding center is greater than the depth m3 of the holes 211 in the slurry layer 23 farther from the winding center. This effectively solves the problem of different tensions on the slurry layers 23 on either side of the foil layer 22.

[0058] In some embodiments, the foil layer 22 may be made of a metal material such as aluminum foil or copper foil. The slurry layer 23 may include a negative electrode active material, a conductive agent, a binder, a thickener, and a solvent. The negative electrode active material may be a hard carbon negative electrode, but is not limited to hard carbon or soft carbon amorphous carbon. The conductive agent in the negative electrode slurry may be a nano-carbon fiber conductive agent or a carbon nanotube conductive agent. The binder in the negative electrode slurry may be SBR styrene butadiene rubber, etc. The thickener may be CMC sodium carboxymethyl cellulose, etc.

[0059] Figure 6 is a front view of the unfolded negative electrode sheet 20 in Figure 4 ; Figure 7 is a top view of the unfolded negative electrode sheet 20 in Figure 4 . When unfolded, the negative electrode sheet 20 has an extension direction x, a width direction y, and a thickness direction z. The extension direction x of the negative electrode sheet 20 also corresponds to the length of the unfolded negative electrode sheet 20 . The extension direction x of the negative electrode sheet 20 is perpendicular to both the width direction y and the thickness direction z of the negative electrode sheet 20 . The width direction y of the negative electrode sheet 20 is the same as the height direction B of the battery cell body 4 , and the thickness direction z of the negative electrode sheet 20 is the same as the depth direction of the hole 211 .

[0060] 6 and 7 , in some embodiments, the number of holes 211 provided on the corner 21 is multiple, specifically, multiple blind holes provided on the two slurry layers 23. For example, in some embodiments, the multiple holes 211 are arranged at intervals in the width direction y of the negative electrode sheet 20. For another example, in some embodiments, the multiple holes 211 are arranged at intervals in the extension direction x of the negative electrode sheet 20. For example, in some embodiments, the multiple holes 211 are arranged in rows in the width direction y of the negative electrode sheet 20, and multiple rows of holes 211 are provided on the corner 21 along the extension direction x of the negative electrode sheet 20.

[0061] In some embodiments, the depth m3 of the hole 211 is 10um-100um, for example, it can be 10um, 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um. In this embodiment, the depth m3 of the hole 211 is within this range, which can effectively release the tension of the corner 21, and can effectively solve the problem of sodium or lithium precipitation at the corner 21 of the negative electrode sheet 20. It can be understood that in some embodiments, the depth direction of the hole 211 is the thickness direction z of the negative electrode sheet 20. In other embodiments, the depth direction of the hole 211 can also form a certain angle with the thickness direction z of the negative electrode sheet 20. It should be noted that the depth m3 of the hole 211 in this embodiment can refer to the depth after the negative electrode sheet 20 is wound, or it can refer to the depth when the negative electrode sheet 20 is flattened before winding. It is understandable that the depth m3 of the hole 211 may vary to a certain extent before and after winding because the negative electrode sheet 20 is appropriately squeezed or stretched during the winding process.

[0062] In some embodiments, the width m2 of the hole 211 in the winding direction R of the battery cell body 4 (as shown in Figure 5) is less than 100μm, for example, it can be 10um, 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um. It is understandable that the width m2 of the hole 211 in the extension direction x of the negative electrode sheet 20 is also roughly less than 100μm. It should be noted that the width m2 of the hole 211 in the winding direction R of the battery cell body 4 in this embodiment is less than 100μm, which means that the maximum width of the hole 211 is less than 100μm. It should be noted that since Figure 5 is a top view of the negative electrode sheet 20 after winding, the width m2 of the hole 211 shown in Figure 5 is the width m2 of the hole 211 in the winding direction R of the battery cell body 4.

[0063] By setting the width m2 of the hole 211 in the winding direction R of the battery cell body 4 to be less than 100 μm, the tension in the corner 21 can be effectively released, effectively solving the problem of sodium or lithium deposition at the corner 21 of the negative electrode sheet 20. It should also be noted that the width m2 of the hole 211 in the winding direction R of the battery cell body 4 in this embodiment refers to the size of the negative electrode sheet 20 after winding.

[0064] In some embodiments, the width m2 of the hole 211 in the extension direction x of the negative electrode sheet 20 is also less than 100 μm. It is understood that the width m2 of the hole 211 in the extension direction x of the negative electrode sheet 20 may vary to a certain extent compared to the width m2 of the hole 211 in the winding direction R of the battery cell body 4 due to appropriate compression or stretching during the winding process.

[0065] In some embodiments, the width m1 of the hole 211 in the height direction B of the battery cell body 4 is less than 100μm, for example, it can be 10um, 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, or 100um. That is, the width of the hole 211 in the width direction y of the negative electrode sheet 20 is less than 100μm. Similarly, it should be noted that the width m1 of the hole 211 in the height direction B of the battery cell body 4 in this embodiment is less than 100μm, which means that the maximum width is less than 100μm. In combination with the width m2 of the hole 211 in the winding direction R of the battery cell body 4 being less than 100μm, in this embodiment, a plurality of holes 211 can be spaced apart in the width direction y of the negative electrode sheet 20 to evenly release tension in the width direction y of the negative electrode sheet 20. It should also be noted that the width m1 of the hole 211 in the height direction B of the battery cell body 4 in this embodiment can refer to either the size of the negative electrode sheet 20 after winding or the size of the negative electrode sheet 20 when it is flattened before winding. It is understandable that the width m1 of the hole 211 in the height direction of the battery cell body 4 will vary to a certain extent before and after the negative electrode sheet 20 is wound due to appropriate compression or stretching during the winding process.

[0066] In some embodiments, the shape of the hole 211 is substantially a circular hole 211 , and the diameter of the hole 211 is less than 100 μm, for example, it can be 10 um, 20 um, 30 um, 40 um, 50 um, 60 um, 70 um, 80 um, 90 um, or 100 um.

[0067] In some embodiments, there are multiple holes 211, and the multiple holes 211 are spaced apart along the winding direction R of the battery cell body 4. In the winding direction R of the battery cell body 4, the spacing m4 between any two adjacent holes 211 is 50μm-2mm, for example, 10um, 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, or 100um. Because the spacing m4 between any two adjacent holes 211 in the winding direction R of the battery cell body 4 is set within the range of 50μm-2mm, the tension at the corner 21 of the negative electrode sheet 20 can be effectively released, thereby solving the problem of sodium or lithium deposition at the corner 21 of the negative electrode sheet 20. Furthermore, since the spacing m4 between any two adjacent holes 211 in the winding direction R of the battery cell body 4 is set within the range of 50 μm-2 mm, the electrolyte 6 wetting ability at each position of the corner 21 along the winding direction R of the battery cell body 4 can be uniformly and effectively improved. It is understood that the spacing m4 between any two adjacent holes 211 will vary to a certain extent before and after the negative electrode sheet 20 is wound due to appropriate compression or stretching during the winding process.

[0068] In some embodiments, since the hole 211 is a blind hole, in the depth direction of the hole 211, the hole 211 includes a hole opening 212 and a hole bottom 213. Along the depth direction of the hole 211, from the hole opening 212 to the hole bottom 213, the size of the hole 211 in the winding direction R of the battery body 4 (equivalent to the extension direction x of the hole 211 in the negative electrode sheet 20) gradually decreases. For the slurry layer 23 located away from the winding center L of the battery cell body 4, the farther it is from the winding center L of the battery cell body 4, the greater the tensile tension it is subjected to. In this embodiment, along the depth direction of the hole 211, from the opening of the hole 211 to the bottom wall of the hole 211, the size of the hole 211 in the winding direction R of the battery cell body 4 gradually decreases. Therefore, for the hole 211 located away from the winding center L of the battery cell body 4, the farther it is from the winding center L of the battery cell body 4, the larger the size. This can effectively solve the problem that the slurry layer 23 located away from the winding center L of the battery cell body 4 is farther from the winding center L of the battery cell body 4, the greater the tensile tension it is subjected to. It can also reduce the material peeling off the slurry layer 23 due to the opening of the hole 211, thereby effectively reducing the loss of active substances. Similarly, for the slurry layer 23 located near the winding center L of the battery cell body 4, the closer it is to the winding center L of the battery cell body 4, the greater the extrusion tension it is subjected to. In this embodiment, along the depth direction of the hole 211, from the hole opening 212 to the hole bottom 213, the size of the hole 211 in the winding direction R of the battery cell body 4 gradually decreases. Therefore, for the hole 211 located near the winding center L of the battery cell body 4, the closer it is to the winding center L of the battery cell body 4, the larger the size. This can effectively solve the problem that the closer the slurry layer 23 near the winding center L of the battery cell body 4 is to the winding center L of the battery cell body 4, the greater the extrusion tension it is subjected to. It can also reduce the material peeling off the slurry layer 23 due to the opening of the hole 211, thereby effectively reducing the loss of active substances.

[0069] In some embodiments, the negative electrode sheet 20 includes multiple corners 21 formed by winding, and the multiple corners 21 are at different distances from the winding center L of the battery cell body 4, and the depth m3 of the hole 211 opened in the corner 21 closer to the winding center L of the battery cell body 4 is deeper. In this embodiment, because the corners 21 closer to the winding center L of the battery cell body 4 are subjected to greater tension, the problem of different tensions on the corners 21 at different distances from the winding center L of the battery cell body 4 can be effectively solved by opening deeper holes 211 in the corners 21 closer to the winding center L of the battery cell body 4. This allows each corner 21 to release tension while minimizing the loss of active material.

[0070] It is understandable that, in some other embodiments, the hole 211 may also be a through hole 211 , that is, it penetrates the foil layer 22 and the two slurry layers 23 at the same time.

[0071] Figure 8 is a front view of the unfolded negative electrode sheet 20 in Figure 4 ; Figure 9 is a top view of the unfolded negative electrode sheet 20 in Figure 4 . The main difference between the embodiments of Figures 8 and 9 and those of Figures 6 and 7 is the shape of the hole 211 .

[0072] 8 and 9 , in some embodiments, the hole 211 is provided on the slurry layer 23 and does not penetrate the foil layer 22. The hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4, that is, the hole 211 penetrates the negative electrode sheet 20 in the width direction y of the negative electrode sheet 20 when flattened. Since the hole 211 is provided on the slurry layer 23 and does not penetrate the foil layer 22, the overall strength of the negative electrode sheet 20 can be ensured by the foil layer 22, and the problem of insufficient strength and breakage or tearing during winding will not be affected. Moreover, since the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4, the tension can be effectively released in the height direction B of the battery cell body 4, and the problem of stress concentration can be effectively reduced. This can effectively solve the problem of sodium or lithium precipitation at the corner 21 of the negative electrode sheet 20.

[0073] It is understood that both slurry layers 23 of the foil layer 22 in this embodiment can also be provided with the elongated holes 211. The width of the holes 211 in the winding direction in this embodiment is also less than 100 μm. The depth m3 of the holes 211 in this embodiment (in the thickness direction of the negative electrode sheet 20) is also 10 μm to 80 μm.

[0074] In some embodiments, the corner 21 is provided with a plurality of the elongated holes 211 , which are arranged at intervals along the winding direction R of the battery cell body 4 , and in the winding direction R of the battery cell body 4 , the spacing m4 between any two adjacent holes 211 is 50 μm-2 mm.

[0075] The technical features disclosed in this embodiment, such as the hole 211, corner 21, slurry layer 23, foil layer 22, negative electrode sheet 20, the height direction B of the battery cell body 4, and the width direction y of the negative electrode sheet 20, can all be referred to in the previous embodiments and will not be repeated here. In addition, other implementations of the above technical features are also applicable to this embodiment.

[0076] Figure 10 is a partially enlarged schematic diagram of a corner 21 of another negative electrode sheet 20 provided in an embodiment of the present application. Compared to the negative electrode sheet 20 in the previous embodiment, the negative electrode sheet 20 in the embodiment of Figure 10 has an additional polymer coating layer 40. The polymer coating layer 40 relieves stress at the pore opening 212 and also serves to adsorb the electrolyte 6, thereby alleviating decarbonization at the corner 21 and improving wettability with the electrolyte 6.

[0077] 10 , in some embodiments, the corner 21 is provided with a polymer coating layer 40, which is used to adsorb the electrolyte 6. The solvent of the polymer coating layer 40 in this embodiment can be one or more of N-methylpyrrolidone, deionized water, N-dimethylformamide, N-dimethylacetamide, and acetone. The solute of the polymer coating layer 40 in this embodiment can be one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polymethyl methacrylate (PMMA), sodium alginate (Alg), carboxymethyl cellulose (CMC), gum arabic (GA), styrene-butadiene rubber (SBR), polyamide (PAI), polyvinyl alcohol (PVA), polyethyleneimine (PEI), and polyimide (PI). The polymer coating layer 40 in this embodiment has a liquid locking function and can adsorb the electrolyte 6 on the polymer coating layer 40 to improve the wettability of the electrolyte 6. In addition, the polymer coating layer 40 can also improve the stress concentration problem on the corner 21 to reduce the problem of decarbonization of the corner 21. After the stress concentration problem on the corner 21 is improved, the problem of sodium or lithium deposition on the negative electrode sheet 20 can also be effectively improved.

[0078] In this embodiment, the polymer coating layer 40 is formed by coating the corner 21 of the negative electrode sheet 20 with a polymer coating and then drying it.

[0079] In some embodiments, the solubility of the polymer coating is 0.5%-50%. Setting the solubility of the polymer coating to 0.5%-50% can effectively alleviate the stress concentration problem at the corner 21 and effectively improve the wettability of the electrolyte 6.

[0080] In some embodiments, the thickness m5 of the polymer coating layer 40 is 10 nm to 20 μm. In this embodiment, setting the polymer coating layer 40 to 10 nm to 20 μm does not occupy too much space and does not significantly affect the energy density of the battery cell 3. It can also effectively alleviate the stress concentration problem at the corner 21 and effectively improve the wettability of the electrolyte 6.

[0081] In some embodiments, the polymer coating layer 40 is provided on the inner wall of the hole 211. In this embodiment, since the polymer coating layer 40 is provided on the inner wall of the hole 211, the electrolyte 6 is more likely to accumulate in the hole 211. Therefore, the combination of the polymer coating layer 40 on the inner wall of the hole 211 and the hole 211 can greatly improve the wettability of the electrolyte 6. In addition, it can also effectively reduce the stress concentration problem of the hole 211 at the corner 21. Moreover, by not providing the polymer coating layer 40 on the surface of the corner 21, the space occupied by the polymer coating layer 40 can be further reduced, thereby reducing the energy density of the battery cell 3 as much as possible.

[0082] The technical features disclosed in this embodiment: hole 211, corner 21, negative electrode sheet 20, etc. can all refer to the previous embodiment and will not be repeated here. In addition, other implementation methods of the above technical features are also applicable to this embodiment.

[0083] With reference to Table 1 below, some specific embodiments provided herein are provided. The following embodiments are specific embodiments obtained by combining the above embodiments. It should be noted that the "line" in the table below refers to the hole 211 that passes through the negative electrode sheet 20 in the height direction B of the battery cell body 4, and the "punch" in the table below refers to the circular hole 211.

[0084] Table 1

[0085] Referring to Table 1, in Example 1, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width of the hole 211 in the winding direction R of the battery cell body 4 is 50 μm, the depth m3 of the hole 211 is 20 μm, the spacing m4 between two adjacent holes 211 in the winding direction R of the battery cell body 4 is 50 μm, the thickness m5 of the polymer coating layer 40 is 100 nm, and the solute of the polymer coating layer 40 is polyvinylidene fluoride (PVDF). In Example 1, the active material can be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation on the negative electrode sheet 20.

[0086] Referring to Table 1, in Example 2, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width m2 of the hole 211 in the winding direction R of the battery cell body 4 is 100 μm, and the depth m3 of the hole 211 is 20 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 50 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is polyvinylidene fluoride (PVDF). In Example 2, the active material can also be effectively prevented from falling off, effectively improving and solving the problem of sodium or lithium precipitation on the negative electrode sheet 20.

[0087] Referring to Table 1, in Example 3, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width m2 of the hole 211 in the winding direction R of the battery cell body 4 is 50 μm, and the depth m3 of the hole 211 is 40 μm. The spacing m4 between two adjacent holes 211 in the winding direction R of the battery cell body 4 is 50 μm. The thickness m5 of the polymer coating layer 40 is 200 nm, and the solute of the polymer coating layer 40 is styrene-butadiene rubber (SBR). In Example 3, the active material can also be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation on the negative electrode sheet 20.

[0088] Referring to Table 1, in Example 4, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width m2 of the hole 211 in the winding direction R of the battery cell body 4 is 50 μm, and the depth m3 of the hole 211 is 80 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 50 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is styrene-butadiene rubber (SBR). In Example 4, the active material can also be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation on the negative electrode sheet 20.

[0089] Referring to Table 1, in Example 5, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width m2 of the hole 211 in the winding direction R of the battery cell body 4 is 50 μm, and the depth m3 of the hole 211 is 30 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 50 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is a combination of styrene-butadiene rubber (SBR) and polyamide (PAI). In Example 5, the active material can also be effectively prevented from falling off, effectively improving and solving the problem of sodium or lithium precipitation in the negative electrode sheet 20.

[0090] Referring to Table 1, in Example 6, the holes 211 are circular, with a diameter of 50 μm and a depth m3 of 20 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 100 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is polyvinylidene fluoride (PVDF). In Example 6, the active material can also be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation in the negative electrode sheet 20.

[0091] Referring to Table 1, in Example 7, the holes 211 are circular, with a diameter of 50 μm and a depth m3 of 50 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 100 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is polyacrylic acid (PAA). In Example 7, the active material can also be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation in the negative electrode sheet 20.

[0092] Referring to Table 1, in Example 8, the holes 211 are circular, with a diameter of 20 μm and a depth m3 of 100 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 100 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is polyacrylic acid (PAA). In Example 8, the active material can also be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation in the negative electrode sheet 20.

[0093] Referring to Table 1, in Example 9, the holes 211 are circular, with a diameter of 20 μm and a depth m3 of 30 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 50 μm. The thickness m5 of the polymer coating layer 40 is 500 nm, and the solute of the polymer coating layer 40 is a combination of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA). In Example 9, the active material can also be effectively prevented from falling off, effectively improving and resolving the problem of sodium or lithium precipitation in the negative electrode sheet 20.

[0094] Referring to Table 1, in Example 10, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width m2 of the hole 211 in the winding direction R of the battery cell body 4 is 50 μm, and the depth m3 of the hole 211 is 20 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 100 μm. The thickness m5 of the polymer coating layer 40 is 100 nm, and the solute of the polymer coating layer 40 is polyvinylidene fluoride (PVDF). In Example 10, the active material can also be effectively prevented from falling off, effectively improving and solving the problem of sodium or lithium precipitation on the negative electrode sheet 20.

[0095] Referring to Table 1, in Example 11, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery cell body 4. The width m2 of the hole 211 in the winding direction R of the battery cell body 4 is 50 μm, and the depth m3 of the hole 211 is 40 μm. In the winding direction R of the battery cell body 4, the spacing m4 between two adjacent holes 211 is 100 μm. The thickness m5 of the polymer coating layer 40 is 100 nm, and the solute of the polymer coating layer 40 is polyacrylic acid (PAA). In Example 11, the active material can also be effectively prevented from falling off, effectively improving and solving the problem of sodium or lithium precipitation on the negative electrode sheet 20.

[0096] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A wound battery cell, characterized in that: The battery cell comprises a shell, an electrolyte located in the shell, and a positive electrode sheet, a negative electrode sheet, and a separator stacked in the shell, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the negative electrode sheet, and the separator are wound to form the battery cell body; The negative electrode sheet includes a corner, and the corner is provided with a hole.

2. The wound battery cell according to claim 1, characterized in that The negative electrode sheet includes a foil layer and slurry layers stacked on both sides of the foil layer. The hole is opened on the slurry layer and does not penetrate the foil layer.

3. The wound battery cell according to claim 1 or 2, characterized in that: The depth of the hole in the thickness direction of the negative electrode sheet is 10 μm-100 μm.

4. The wound battery cell according to any one of claims 1 to 3, characterized in that: The width of the hole in the winding direction of the battery cell body is less than 100 μm.

5. The wound battery cell according to any one of claims 1 to 4, characterized in that: There are multiple holes, and the multiple holes are arranged at intervals along the winding direction of the battery body. In the winding direction of the battery body, the distance between any two adjacent holes is 50 μm-2 mm.

6. The wound battery cell according to any one of claims 1 to 5, characterized in that: The height direction of the battery cell body is perpendicular to the winding direction of the battery cell body, and the width of the hole in the height direction of the battery cell body is less than 100 μm.

7. The wound battery cell according to claim 2, characterized in that: The height direction of the battery cell body is perpendicular to the winding direction of the battery cell body, and the hole penetrates the negative electrode sheet in the height direction of the battery cell body.

8. The wound battery cell according to claim 6 or 7, characterized in that: In the depth direction of the hole, the hole includes a hole opening and a hole bottom. Along the depth direction of the hole, from the hole opening to the hole bottom, the size of the hole in the winding direction of the battery cell body gradually decreases.

9. The wound battery cell according to any one of claims 1 to 8, characterized in that: The corner is provided with a polymer coating layer, and the polymer coating layer is used for absorbing electrolyte.

10. The wound battery cell according to claim 9, characterized in that: The polymer coating layer is arranged on the inner wall of the hole.

11. The wound battery cell according to claim 9 or 10, characterized in that: The thickness of the polymer coating layer is 10 nm-20 μm.

12. The wound battery cell according to claim 2, characterized in that: The slurry layers on both sides of the foil layer are provided with the holes, and the depths of the holes in the slurry layers on both sides of the foil layer are different.

13. The wound battery cell according to any one of claims 1 to 12, characterized in that: The negative electrode sheet includes multiple layers from the inside to the outside, each layer includes the corner, and the depth of the hole on the corner of the inner layer is greater than the depth of the hole on the corner of the outer layer.

14. The wound battery cell according to any one of claims 1 to 13, characterized in that: The curvature radius of the corner is less than 1.

15. A battery pack, characterized in that: The invention comprises a shell and a plurality of wound battery cells according to any one of claims 1 to 14, wherein the plurality of wound battery cells are arranged in the shell.

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