Winding type battery cell and battery pack

Abstract

The embodiment of the utility model provides a winding type battery cell and a battery pack, the battery cell comprises a shell, an electrolyte positioned in the shell, and a positive plate, a negative plate and a diaphragm which are positioned in the shell and are laminated, the diaphragm is positioned between the positive plate and the negative plate, and the positive plate, the negative plate and the diaphragm are wound to form a battery cell main body; the negative plate comprises a corner which is provided with a hole. According to the invention, the corner tension is released by performing laser drilling or laser scribing treatment on the corner of the negative pole piece, and the macromolecular coating layer is assisted to release stress and lock liquid, so that the decarburization of the corner is relieved, the wettability of the electrolyte is improved, and the sodium precipitation of the corner in the circulating process is relieved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular to a wound battery cell and a battery pack. Background Art

[0002] The problem of lithium or sodium deposition at the corners of the pole piece is a difficulty and pain point in the industry. In the related technology, the N / P ratio at the corner is adjusted to increase the excess degree of the negative electrode capacity at the corner. However, 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 still occur due to kinetic differences. Therefore, the problem of lithium or sodium deposition at the corners of the pole piece is a problem that needs to be solved urgently. Utility Model Content

[0003] The embodiments of the present application provide a wound battery cell and a battery pack, which can effectively solve the problem of lithium or sodium deposition on the negative electrode sheet and increase the service life of the battery cell.

[0004] 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 that are 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 a battery cell body; the negative electrode sheet includes a corner, and the corner is provided with a hole.

[0005] In this embodiment, since a hole is provided at the corner, the tension of the corner can be released by the hole provided at the corner. After the tension of the corner is effectively reduced, the problem of active material shedding and sodium and lithium precipitation at the corner of the negative electrode sheet can be effectively reduced. Since the corner of the negative electrode sheet in the related art is the most serious position for sodium and lithium precipitation, the problem of sodium and lithium precipitation at the corner of the negative electrode sheet is solved in this embodiment, and the problem of sodium and lithium precipitation of the battery cell can be solved to effectively improve the service life of the battery cell. Moreover, since a hole is provided at the corner, the electrolyte can be accommodated in the hole, thereby improving the wettability of the electrolyte at the corner. After the wettability of the electrolyte at the corner is improved, the problem of active material shedding and sodium and lithium precipitation at the corner can also be effectively reduced, and the problem of decarbonization at the corner can also be effectively alleviated, thereby effectively improving the service life of the battery cell.

[0006] 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 hole is opened on the slurry layer and does not penetrate the foil layer. In this embodiment, since the hole is opened on the slurry layer and does not penetrate the foil layer, the structural strength brought by the foil layer can be ensured, and even if the hole is opened disorderly, it will not cause the structural collapse of the corner of the negative electrode sheet.

[0007] In some embodiments, the depth of the hole in the thickness direction of the negative electrode sheet is 10um-100μm. 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.

[0008] In some embodiments, the width of the hole in the winding direction of the battery body is less than 100 μm. Here, the width of the hole in the winding direction of the battery 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 body to a range of less than 100 μm, the tension of the corner can be effectively released, which can effectively solve the problem of sodium or lithium precipitation at the corner of the negative electrode sheet.

[0009] In some embodiments, the number of holes is multiple, and the multiple holes are arranged at intervals 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. And 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.

[0010] 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, the width of the combined hole in the winding direction of the battery cell body is less than 100μm. In this embodiment, 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.

[0011] 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.

[0012] 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 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 body gradually decreases, so that for the hole of the slurry layer located near the winding center of the battery body, the closer to the winding center of the battery body, the larger the size, thereby effectively solving the problem that the closer the slurry layer near the winding center of the battery body is to the winding center of the battery body, the greater the extrusion tension it is subjected to, and it can also reduce the material peeling off the slurry layer due to the opening of the hole, so as to effectively reduce the loss of active substances.

[0013] 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.

[0014] In some embodiments, the polymer coating layer is disposed on the inner wall of the hole. In this embodiment, since the polymer coating layer is disposed on the inner wall of the hole, the electrolyte is also more easily accumulated in the hole, so that 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, so as to reduce the energy density of the battery cell as little as possible.

[0015] In some embodiments, the thickness of the polymer coating layer is 10nm-20μm. In this embodiment, the polymer coating layer is set to 10nm-20μm, which will not occupy too much space, will not have a significant impact on the energy density of the battery cell, and can effectively alleviate the problem of corner stress concentration and effectively improve the wettability of the electrolyte.

[0016] In some embodiments, the slurry layers on both sides of the foil layer are provided with holes, and the depths of the holes in the slurry layers on both sides of the foil layer are different. In this embodiment, the problem of different tensions on the slurry layers on both sides of the foil layer can be effectively solved.

[0017] 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 body, and the depth of the hole opened on the corner closer to the winding center of the battery 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 corner closer to the winding center of the battery body receives greater tension, and thus by opening deeper holes on the corners closer to the winding center of the battery body, the problem of different tensions on the corners at different distances from the winding center of the battery body can be effectively solved. Thereby, while releasing the tension, each corner can reduce the loss of active materials as little as possible.

[0018] 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, so that the corner can be wound to a curvature less than 1. The curvature of the corner less than 1 can make the battery body be wound more tightly, so as to improve the energy density of the battery body.

[0019] 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

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0021] Figure 1 A schematic diagram of the structure of a battery pack provided in an embodiment of the present application;

[0022] Figure 2 A schematic diagram of the structure of a battery cell provided in an embodiment of the present application;

[0023] Figure 3 for Figure 2 A top view of the battery cell body in FIG.

[0024] Figure 4 for Figure 2 A top view of a negative electrode sheet of a battery cell after winding;

[0025] Figure 5 for Figure 4 An enlarged structural schematic diagram of one corner of the negative electrode sheet;

[0026] Figure 6 for Figure 4 A schematic diagram of the front view of the negative electrode sheet when it is unfolded;

[0027] Figure 7 for Figure 4 Schematic diagram of a top view of the negative electrode sheet when it is unfolded;

[0028] Figure 8 for Figure 4 A schematic diagram of the front view of the negative electrode sheet when it is unfolded;

[0029] Fig. 9 for Figure 4 Schematic diagram of a top view of the negative electrode sheet when it is unfolded;

[0030] Fig.10 A partially enlarged schematic diagram of a corner of another negative electrode sheet provided in an embodiment of the present application. Description of the drawings:

[0032] R, winding direction of the battery body; Z, height direction of the battery body; L, winding center of the battery body; m1, width of the hole in the height direction of the battery body; m2, width of the hole in the winding direction of the battery body; m3, depth of the hole; m4, spacing between two adjacent holes; m5, thickness of the polymer coating layer;

[0033] 1. Battery pack; 2. Shell; 3. Battery cell; 4. Battery cell body; 5. Shell; 6. Electrolyte;

[0034] 10. Positive electrode;

[0035] 20, negative electrode sheet; 21, corner; 211, hole; 212, hole opening; 213, hole bottom; 22, foil layer; 23, slurry layer; x, extension direction of negative electrode sheet; y, width direction of negative electrode sheet; z, thickness direction of negative electrode sheet;

[0036] 30. Diaphragm;

[0037] 40. Polymer coating. DETAILED DESCRIPTION

[0038] The following first explains some terms involved in the embodiments of the present application.

[0039] The terms "first", "second", "third", "fourth", etc. in the specification 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 sequence. 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 of their variations 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.

[0040] In this specification, the terms "perpendicular", "parallel", etc. are explained.

[0041] Vertical: The verticality 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 influence of structural flatness. It also 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.

[0042] Parallelism: The parallelism defined in this application is not limited to absolute parallelism. This definition of parallelism can be understood as basic parallelism, which allows for situations where the absolute parallelism is not caused by factors such as assembly tolerance, design tolerance, and 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 parallelism.

[0043] In the related technology, winding is an important internal forming process of the battery cell, which has the advantages of mature technology, low cost and high yield, and can be applied to soft-pack, square and cylindrical batteries. However, due to the characteristics of the winding structure, the curvature of the pole piece is large at the corner of the winding, the stress is large, and the active material is prone to fall off and the electrolyte wettability is poor; for example, for lithium-ion and sodium-ion batteries, the corner of the negative electrode winding is prone to interface problems such as lithium and sodium deposition, causing safety problems and cycle life reduction.

[0044] In order to solve the problem of sodium or lithium precipitation at the corner. A more common method is to adjust the corner N / P ratio. 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. Thereby increasing the excess of the negative electrode capacity at the corner to reduce sodium or lithium precipitation. However, this method can only slightly slow down the sodium or lithium precipitation. 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 precipitation will occur due to poor kinetics. In addition, by increasing the gap at the corner to improve the wettability of the pole piece at the corner, in an attempt to improve the problem of sodium or lithium precipitation, but this method will still cause stress concentration at the corner, resulting in the shedding of active materials, resulting in insufficient negative active materials and sodium or lithium precipitation. Therefore, solving the problems of active material shedding at the corner, poor electrolyte wettability, sodium precipitation and lithium precipitation is a problem that needs to be solved urgently.

[0045] Figure 1 A schematic diagram of the structure of a battery pack 1 provided in an embodiment of the present application. Figure 1 The battery pack 1 in the embodiment can be applied not only to energy storage devices, but also to the vehicle field or other fields that require the use of the battery pack 1.

[0046] Reference Figure 1 The battery pack 1 includes a shell 2 and a plurality of battery cells 3 in the shell 2, and the plurality of battery cells 3 are stacked and arranged in the shell 2. It is understandable that the plurality of battery cells 3 can be arranged in one row or in multiple rows. The battery cells 3 in this embodiment can well solve the problems of active material shedding at the corner 21, poor wettability of the electrolyte, sodium precipitation and lithium precipitation.

[0047] In some embodiments, the battery core 3 is roughly in the shape of a rectangular parallelepiped. Of course, in other embodiments, the battery core 3 may also be in other flat structures or cylindrical structures.

[0048] Figure 2 A schematic diagram of the structure of a battery cell 3 provided in an embodiment of the present application; Figure 3 for Figure 2 A top view of the battery cell body 4 in FIG. Figure 2 The battery cell 3 in the embodiment can be used not only Figure 1 The battery pack 1 in the embodiment can also be applied 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 three, four, one or other numbers of battery cell bodies 4.

[0049] 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 other types of battery cells 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.

[0050] Reference Figure 2 and Figure 3 The battery cell 3 includes a housing 5, an electrolyte 6 in the housing 5, and a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30 stacked in 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 the winding center L of the battery cell body 4 to form the battery cell body 4.

[0051] 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 .

[0052] Figure 4 for Figure 2 FIG. 2 is a top view of the negative electrode sheet 20 of the battery cell 3 after winding.

[0053] Reference Figure 3 and Figure 4In some embodiments, the negative electrode sheet 20 includes a corner 21 formed by winding along the winding direction R of the battery body 4, and the corner 21 is provided with a hole 211. It can be understood that the corner 21 in this embodiment refers to the corner 21 formed when the negative electrode sheet 20 is wound as understood by those skilled in the art, that is, the area where the curvature of the negative electrode sheet 20 suddenly changes greatly during the winding along the winding direction R of the battery body 4. In this embodiment, since the hole 211 is provided at the corner 21, the tension of the corner 21 can be released by the hole 211 opened at the corner 21. After the tension of the corner 21 is effectively reduced, the problem of active material shedding and sodium and lithium precipitation 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 most serious position for sodium and lithium precipitation, the problem of sodium and lithium precipitation at the corner 21 of the negative electrode sheet 20 is solved in this embodiment, and the problem of sodium and lithium precipitation of the battery cell 3 can be solved, so as to effectively improve the service life of the battery cell 3. Moreover, since the corner 21 is provided with a hole 211, the electrolyte 6 can be accommodated in the hole 211, 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, the problem of active material shedding and sodium and lithium precipitation at the corner 21 can also be effectively reduced, and the problem of decarbonization at the corner 21 can also be effectively alleviated, thereby effectively improving the service life of the battery cell 3.

[0054] In this embodiment, the negative electrode sheet 20 forms a plurality of corners 21 during the winding process, and the curvature radii of the plurality of corners 21 may be different, and the curvature radii at different positions of each corner 21 may also be different. For example, the curvature radius of the corner 21 that is farther from the winding center L of the battery body 4 is often larger, and the curvature radius of the corner 21 that is closer to the winding center L of the battery body 4 is often smaller.

[0055] 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 the radius of curvature of the corner 21 in this embodiment is less than 1, which means that the radius of curvature of each position of the corner 21 is less than 1. In this embodiment, since a hole 211 is provided at the corner 21, the tension at the corner 21 can be effectively released, so that the corner 21 can 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 body 4 be wound more tightly, so as to improve the energy density of the battery body 4.

[0056] In some embodiments, after the negative electrode sheet 20 is wound around the winding center L of the battery body 4, the areas on the negative electrode sheet 20 with a curvature 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, so that the tension of the areas on the negative electrode sheet 20 with a curvature radius less than 1 can be reasonably and effectively released, so as to effectively reduce the problems of active material shedding at the corners 21 and sodium and lithium precipitation.

[0057] 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 there is basically no problem of sodium precipitation and lithium precipitation at the corners of the positive electrode sheet 10, the corners of the positive electrode sheet 10 may not be provided with holes.

[0058] Figure 5 for Figure 4 FIG. 2 is an enlarged structural diagram of one corner 21 of the negative electrode sheet 20. It should be noted that: Figure 5 The color layer on the negative electrode sheet 20 in the figure is to clearly show the layer structure of the negative electrode sheet 20 and does not represent the current Figure 5 It is a cross-sectional view.

[0059] Reference Figure 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, the structure of the corner 21 of the negative electrode sheet 20 will not collapse. In addition, since the corner 21 of the negative electrode sheet 20 is opened 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, so as to reduce the decarbonization of the corner 21 of the negative electrode sheet 20.

[0060] 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 from the winding center L of the battery body 4. Among them, the slurry layer 23 farther from the winding center is mainly stretched, while the slurry layer 23 closer to the winding center is mainly squeezed. The hole 211 opened in the slurry layer 23 farther from the winding center is used to release the tension caused by the stretching, thereby effectively reducing the lithium or sodium precipitation of the slurry layer 23 farther from the winding center. The hole 211 opened in the slurry layer 23 closer to the winding center is used to release the tension caused by the extrusion, thereby effectively reducing the lithium or sodium precipitation of the slurry layer 23 closer to the winding center.

[0061] In some embodiments, the depths m3 of the holes 211 of the slurry layers 23 on both sides of the foil layer 22 are different. The depth m3 of the holes 211 of the slurry layer 23 closer to the winding center is greater than the depth m3 of the holes 211 of the slurry layer 23 farther from the winding center. This can effectively solve the problem of the slurry layers 23 on both sides of the foil layer 22 being subjected to different tensions.

[0062] In some embodiments, the foil layer 22 may be a metal material such as aluminum foil or copper foil, and the proportion of 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, etc. The conductive agent in the negative electrode slurry may be a nano-carbon fiber conductive agent and a carbon nanotube conductive agent, etc. The binder in the negative electrode slurry may be SBR styrene butadiene rubber, etc. The thickener may be CMC sodium carboxymethyl cellulose, etc.

[0063] Figure 6 for Figure 4 A front view schematic diagram of the negative electrode sheet 20 when it is unfolded; Figure 7 for Figure 4 Schematic diagram of the top view of the unfolded negative electrode sheet 20 in FIG. The unfolded 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 is also equivalent to the length direction of the unfolded negative electrode sheet 20, wherein the extension direction x of the negative electrode sheet 20 is perpendicular to 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 body 4, and the thickness direction z of the negative electrode sheet 20 is the same as the depth direction of the hole 211.

[0064] Reference Figure 6 and Figure 7In some embodiments, the number of holes 211 opened on the corner 21 is multiple, specifically multiple blind holes opened on the two slurry layers 23, for example, in some embodiments, in the width direction y of the negative electrode sheet 20, multiple holes 211 are arranged at intervals. For another example, in some embodiments, in the extension direction x of the negative electrode sheet 20, multiple holes 211 are arranged at intervals. In some embodiments, for example, in the width direction y of the negative electrode sheet 20, multiple holes 211 are arranged in rows at intervals, and multiple rows of holes 211 are opened on the corner 21 along the extension direction x of the negative electrode sheet 20.

[0065] 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 located within this interval, 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, and in some other embodiments, the depth direction of the hole 211 can also be at a certain angle to 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 change to a certain extent before and after winding because the negative electrode sheet 20 is appropriately squeezed or stretched during the winding process.

[0066] In some embodiments, the width m2 of the hole 211 in the winding direction R of the battery cell body 4 (eg Figure 5 ) 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, 100 um. 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 100 μm. It should be noted that the width m2 of the hole 211 in the winding direction R of the battery body 4 in this embodiment is less than 100 μm, which means that the maximum width of the hole 211 is less than 100 μm. It should be noted that due to Figure 5 is a top view of the negative electrode sheet 20 after winding. Figure 5 The width m2 of the hole 211 shown in FIG. 1 is the width m2 of the hole 211 in the winding direction R of the battery cell body 4 .

[0067] By setting the width m2 of the hole 211 in the winding direction R of the battery cell body 4 to be within a range of less than 100 μm, the tension of the corner 21 can be effectively released, and the problem of sodium or lithium precipitation at the corner 21 of the negative electrode sheet 20 can be effectively solved. 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.

[0068] 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 understandable that the width m2 of the hole 211 in the extension direction x of the negative electrode sheet 20 will change to a certain extent compared with the width m2 of the hole 211 in the winding direction R of the battery body 4 due to moderate compression or stretching during the winding process.

[0069] In some embodiments, the width m1 of the hole 211 in the height direction B of the battery cell body 4 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, 100 um. That is, the width of the hole 211 in the width direction y of the negative electrode sheet 20 is less than 100 μm. 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 100 μm, which means that the maximum width is less than 100 μm. Combined with the width m2 of the hole 211 in the winding direction R of the battery cell body 4 being less than 100 μm, in this embodiment, a plurality of holes 211 can be spaced apart in the width direction y of the negative electrode sheet 20 so that the tension can be evenly released 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 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 size of the width m1 of the hole 211 in the height direction of the battery cell body 4 will change to a certain extent before and after the negative electrode sheet 20 is wound because it is appropriately squeezed or stretched during the winding process.

[0070] 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 may be 10 um, 20 um, 30 um, 40 um, 50 um, 60 um, 70 um, 80 um, 90 um, or 100 um.

[0071] In some embodiments, the number of holes 211 is multiple, and the multiple holes 211 are arranged at intervals along the winding direction R of the battery body 4, and in the winding direction R of the battery body 4, the spacing m4 between any two adjacent holes 211 is 50μm-2mm, for example, it can be 10um, 20um, 30um, 40um, 50um, 60um, 70um, 80um, 90um, 100um. Since in the winding direction R of the battery body 4, the spacing m4 between any two adjacent holes 211 is set in the range of 50μm-2mm, it can be ensured that the tension at the corner 21 of the negative electrode sheet 20 can be effectively released to solve the problem of sodium or lithium precipitation 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, it can also be ensured that the wetting ability of the electrolyte 6 at each position of the corner 21 along the winding direction R of the battery cell body 4 is uniformly and effectively improved. It can be understood that the size of the spacing m4 between any two adjacent holes 211 will change to a certain extent before and after the negative electrode sheet 20 is wound because it is appropriately squeezed or stretched during the winding process.

[0072] 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 away from the winding center L of the battery cell body 4, the greater the tensile tension it is subjected to. In the present 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 away from the winding center L of the battery cell body 4, the larger the size of the hole 211. 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 away from the winding center L of the battery cell body 4, the greater the tensile tension it is subjected to. In addition, the material peeling off the slurry layer 23 due to the opening of the hole 211 can be reduced, 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 the present 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 is. This can effectively solve the problem that the slurry layer 23 near the winding center L of the battery cell body 4 is closer to the winding center L of the battery cell body 4, the greater the extrusion tension it is subjected to. In addition, the material peeling off the slurry layer 23 due to the opening of the hole 211 can be reduced, thereby effectively reducing the loss of active substances.

[0073] In some embodiments, the negative electrode sheet 20 includes a plurality of corners 21 formed by winding, and the plurality of 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 on the corner 21 closer to the winding center L of the battery cell body 4 is deeper. In this embodiment, since the corner 21 closer to the winding center L of the battery cell body 4 receives greater tension among the plurality of corners 21, the deeper hole 211 is opened on the corner 21 closer to the winding center L of the battery cell body 4, which can effectively solve the problem of different tensions received by the corners 21 at different distances from the winding center L of the battery cell body 4. Thereby, each corner 21 can reduce the loss of active materials as little as possible while releasing the tension.

[0074] It can be understood 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.

[0075] Figure 8 for Figure 4 A front view schematic diagram of the negative electrode sheet 20 when it is unfolded; Fig. 9 for Figure 4 A schematic top view of the negative electrode sheet 20 when it is unfolded. Figure 8 and Fig. 9 The embodiment of Figure 6 and Figure 7 The main difference between the embodiments is that the shape of the hole 211 is different.

[0076] Reference Figure 8 and Fig. 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 laid flat. 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 breaking or tearing due to insufficient strength 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. Thereby, the problem of sodium or lithium precipitation at the corner 21 of the negative electrode sheet 20 can be well solved.

[0077] It is understandable 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-80 μm.

[0078] 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.

[0079] The technical features disclosed in this embodiment: hole 211, corner 21, slurry layer 23, foil layer 22, negative electrode sheet 20, height direction B of battery body 4, width direction y of negative electrode sheet 20, etc. can all refer to the previous embodiments and will not be repeated here. In addition, other implementations of the above technical features are also applicable to this embodiment.

[0080] Fig.10 A partially enlarged schematic diagram of a corner 21 of another negative electrode sheet 20 provided in an embodiment of the present application. Fig.10The negative electrode sheet 20 in the embodiment is compared with the negative electrode sheet 20 in the previous embodiment. The polymer coating layer 40 is used to release the stress at the hole opening 212, and the polymer coating layer 40 can also adsorb the electrolyte 6 to alleviate the decarbonization of the corner 21 and improve the wettability of the electrolyte 6.

[0081] Reference Fig.10 In some embodiments, the corner 21 is provided with a polymer coating layer 40, and the polymer coating layer 40 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 (Al g), carboxymethyl cellulose (CMC), gum arabic (GA), styrene-butadiene rubber (SBR), polyamide (PAI), polyvinyl alcohol (PVA), polyethyleneimine (PE I), and polyimide (PI). The polymer coating layer 40 in this embodiment has a liquid locking function, and the electrolyte 6 can be adsorbed 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.

[0082] In this embodiment, the polymer coating layer 40 is formed by coating the polymer coating on the corner 21 of the negative electrode sheet 20 and then drying it.

[0083] In some implementations, the polymer coating has a solubility of 0.5%-50%. Setting the polymer coating solubility in the range of 0.5%-50% can effectively alleviate the stress concentration problem at the corner 21 and can also effectively improve the wettability of the electrolyte 6 .

[0084] In some embodiments, the thickness m5 of the polymer coating layer 40 is 10nm-20μm. In this embodiment, the polymer coating layer 40 is set to 10nm-20μm, which will not occupy too much space, will not have a significant impact on the energy density of the battery cell 3, and can effectively alleviate the problem of stress concentration at the corner 21, and can also effectively improve the wettability of the electrolyte 6.

[0085] In some embodiments, the polymer coating layer 40 is disposed on the inner wall of the hole 211. In this embodiment, since the polymer coating layer 40 is disposed on the inner wall of the hole 211, the electrolyte 6 is also relatively easy to gather in the hole 211, so that 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. In addition, 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, so as to reduce the energy density of the battery cell 3 as small as possible.

[0086] The technical features disclosed in this embodiment: hole 211, corner 21, negative electrode sheet 20, etc. can all refer to the previous embodiments, and will not be repeated here. In addition, other implementation methods of the above technical features are also applicable to this embodiment.

[0087] Referring to Table 1 below, the following are some specific embodiments provided by the present application, and the following implementation methods are specific embodiments after combining the above embodiments. It should be noted that the "line" in the following table refers to the hole 211 that passes through the negative electrode sheet 20 in the height direction B of the battery body 4, and the "punch" in the following table refers to the hole 211 that is circular in shape.

[0088]

[0089]

[0090] Table 1

[0091] Referring to Table 1, in Example 1, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width of the hole 211 in the winding direction R of the battery 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 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0092] Referring to Table 1, in Example 2, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width m2 of the hole 211 in the winding direction R of the battery body 4 is 100 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 body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0093] Referring to Table 1, in Example 3, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width m2 of the hole 211 in the winding direction R of the battery body 4 is 50 μm, 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 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0094] Referring to Table 1, in Example 4, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width m2 of the hole 211 in the winding direction R of the battery body 4 is 50 μm, the depth m3 of the hole 211 is 80 μm, the spacing m4 between two adjacent holes 211 in the winding direction R of the battery body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0095] Referring to Table 1, in Example 5, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width m2 of the hole 211 in the winding direction R of the battery body 4 is 50 μm, the depth m3 of the hole 211 is 30 μm, the spacing m4 between two adjacent holes 211 in the winding direction R of the battery body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0096] Referring to Table 1, in Example 6, the hole 211 is a circular hole 211, the diameter of the hole 211 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 body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0097] Referring to Table 1, in Example 7, the hole 211 is a circular hole 211, the diameter of the hole 211 is 50 μm, the depth m3 of the hole 211 is 50 μm, the spacing m4 between two adjacent holes 211 in the winding direction R of the battery body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0098] Referring to Table 1, in Example 8, the hole 211 is a circular hole 211, the diameter of the hole 211 is 20 μm, the depth m3 of the hole 211 is 100 μm, the spacing m4 between two adjacent holes 211 in the winding direction R of the battery body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0099] Referring to Table 1, in Example 9, the hole 211 is a circular hole 211, the diameter of the hole 211 is 20 μm, the depth m3 of the hole 211 is 30 μm, the spacing m4 between two adjacent holes 211 in the winding direction R of the battery body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0100] Referring to Table 1, in Example 10, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width m2 of the hole 211 in the winding direction R of the battery 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 body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0101] Referring to Table 1, in Example 11, the hole 211 penetrates the negative electrode sheet 20 in the height direction B of the battery body 4, the width m2 of the hole 211 in the winding direction R of the battery body 4 is 50 μm, 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 body 4 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 kept from falling off, and the problem of sodium or lithium precipitation of the negative electrode sheet 20 can be effectively improved and solved.

[0102] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A wound battery cell, characterized in that: The battery cell comprises a shell, an electrolyte in the shell, and a positive electrode sheet, a negative electrode sheet and a separator in a stacked arrangement 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 comprises a foil layer and slurry layers stacked on both sides of the foil layer, and 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 um-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: The number of the holes is multiple, 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 spacing 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, 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 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 10nm-20μm.

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 inside to 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 radius of curvature 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 as claimed in any one of claims 1 to 14, wherein the plurality of wound battery cells are arranged in the shell.

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