Winding Core and Battery

Abstract

The present application provides a core and a battery, relating to the technical field of batteries, and is used to solve the technical problem that insufficient electrolyte between layers is caused by extrusion between the electrode sheets of the core in the related art. The core includes: a negative electrode sheet and a positive electrode sheet with opposite polarities. The negative electrode sheet includes a negative current collector. The negative current collector has a first surface and a second surface along a first direction. A first paste layer is provided on the first surface, and a second paste layer is provided on the second surface; a plurality of grooves are provided on the first paste layer, and the center distance between adjacent two grooves is a first distance; a plurality of protrusions and recesses corresponding to the protrusions are provided on the positive electrode sheet, and the surface where the protrusions of the positive electrode sheet are located is opposite to the surface where the grooves of the negative electrode sheet are located; along the width direction of the groove, the projection size of the protrusion on the negative electrode sheet is greater than the first distance. By providing protrusions and recesses opposite to the protrusions on the positive electrode sheet, and at the same time providing grooves opposite to the protrusions on the negative electrode sheet, supports exist between the electrode sheets, the micro-spacing between the electrode sheets is increased, and it is ensured that the electrolyte is sufficiently infiltrated.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and particularly to a core and a battery. Background Art

[0002] With the rapid development of lithium-ion battery technology, people have higher requirements for the energy density, cycle life and safety performance of lithium-ion batteries.

[0003] During the charge and discharge process of a lithium-ion battery, the negative electrode sheet will expand, and there will be extrusion between the layers of the electrode sheet; especially for a wound lithium-ion battery formed by winding, the arc area of its winding structure has a large stress accumulation, and there is already extrusion between the electrode sheets in the arc area itself; in addition, during the charge and discharge process, the negative electrode sheet will expand, and the extrusion between the electrode sheets will be aggravated; at the same time, this extrusion will also be transmitted from the arc area to the flat area. This interlayer extrusion will ultimately lead to insufficient interlayer electrolyte and poor infiltration, resulting in interface deterioration, and even lithium deposition on the negative electrode sheet, affecting the safety of the battery cell. Summary of the Invention

[0004] In view of the above problems, the embodiments of the present application provide a core and a battery to solve the problems of insufficient electrolyte and poor electrolyte infiltration caused by the extrusion between the layers of the electrode sheet of the core in the related art.

[0005] In order to achieve the above object, the embodiments of the present application provide the following technical solutions:

[0006] The embodiments of the present application provide a core, which includes: a negative electrode sheet and a positive electrode sheet stacked; a plurality of convex portions and concave portions opposite to the convex portions are provided on the positive electrode sheet.

[0007] By providing convex portions and corresponding concave portions on the positive electrode sheet, the convex portions provide support for the contact of the separator, increasing the micro-spacing between the electrode sheet and the separator. These micro-spacings form spaces that can accommodate the electrolyte, enabling the electrolyte to have a sufficient infiltration amount for the electrode sheet, and avoiding abnormal situations such as insufficient electrolyte, poor infiltration, and even lithium deposition on the negative electrode sheet between the electrode sheet and the separator caused by the interlayer extrusion of the electrode sheet.

[0008] The negative electrode sheet includes a negative electrode current collector, the negative electrode current collector has opposite first and second surfaces along a first direction, a first paste layer is provided on the first surface, and a second paste layer is provided on the second surface; a plurality of grooves are provided on the first paste layer, and the surface where the convex portion of the positive electrode sheet is located and the surface where the groove of the negative electrode sheet is located are arranged opposite to each other.

[0009] A groove is provided on the negative electrode plate opposite to the convex portion. The groove provided on the negative electrode plate can effectively enhance the wetting of the negative electrode plate by the electrolyte. In addition, the surface where the convex portion of the positive electrode plate is located and the surface where the groove of the negative electrode plate is located are arranged opposite to each other, providing an expansion space for the expansion of the negative electrode plate, thereby slowing down the situation of the extrusion deformation of the positive electrode convex portion or the deformation of the negative electrode groove caused by the expansion of the negative electrode plate during hot pressing formation or battery charge and discharge processes, ensuring the structural strength of the protrusion and the groove and the interfacial adhesion strength between the electrode plate and the separator, enabling it to stably play a supporting role for the separator. At the same time, the sufficient expansion space can also prevent the negative electrode plate from squeezing the separator during the expansion process, causing the deformation of the separator.

[0010] The centers of two adjacent grooves are arranged at a first distance, and along the width direction of the groove, the size of the projection of the convex portion on the negative electrode plate is greater than the first distance.

[0011] While the positive electrode convex portion and the negative electrode groove are arranged opposite to each other, the size of the projection of the positive electrode convex portion on the negative electrode plate is greater than the center distance of the negative electrode groove, preventing the positive electrode convex portion from being embedded into the negative electrode groove, which is beneficial to the formation of the SEI film on the protruding portion of the positive electrode, thereby effectively protecting the protruding portion of the positive electrode and preventing problems such as the fragmentation of the active particles of the protruding portion of the positive electrode and even the precipitation of cobalt, resulting in a reduction in the structural stability of the positive electrode active material and an accelerated attenuation of the battery capacity.

[0012] In an embodiment of the present application, a plurality of such grooves are respectively provided on the first surface and the second surface of the negative electrode plate; the convex portion and the groove are arranged opposite to each other; the concave portion and the groove are arranged opposite to each other.

[0013] Grooves are provided on both sides of the negative electrode plate, such that while the positive electrode convex portion and the negative electrode groove are arranged opposite to each other, the positive electrode concave portion is also arranged opposite to the negative electrode groove; the arrangement of the positive electrode concave portion and the negative electrode groove opposite to each other can increase the space between the positive electrode plate and the negative electrode plate, providing a larger wetting space for the electrolyte, thereby increasing the amount of stored electrolyte.

[0014] In an embodiment of the present application, along the width direction of the groove, the size of the projection of the convex portion in the thickness direction of the negative electrode plate is R1, the first distance is S, and R1 / S = 1.02 - 8.

[0015] Within the above ratio range, it is possible to slow down the extrusion deformation of the positive electrode convex part or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing forming or the charge and discharge process of the battery. If it is lower than the above ratio range, it indicates that the groove width of the first distance is relatively large. When the negative electrode sheet expands and causes extrusion between the electrode layers, the positive electrode convex part is likely to be embedded into the negative electrode groove, easily causing damage to the SEI film of the positive electrode convex part and resulting in a lack of protection for the positive electrode convex part. If it is higher than the above ratio range, it indicates that the groove width of the first distance is relatively small, and the setting of the first distance will be meaningless. The groove cannot provide an expansion space for the expansion of the negative electrode sheet. At the same time, during hot pressing forming or the charge and discharge process of the battery, with the expansion of the negative electrode sheet, the extrusion deformation of the positive electrode convex part or the deformation of the negative electrode groove is likely to occur.

[0016] In an embodiment of the present application, along the width direction of the groove, the size of the projection of the convex part in the thickness direction of the negative electrode sheet is R1, the groove width of the groove is M, and R1 / M = 8 - 50.

[0017] Within the above ratio range, it is possible to slow down the extrusion deformation of the positive electrode convex part or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing forming or the charge and discharge process of the battery. If it is lower than the above ratio range, it indicates that the groove width of the groove is relatively large. When the negative electrode sheet expands and causes extrusion between the electrode layers, the positive electrode convex part is likely to be embedded into the negative electrode groove, easily causing damage to the SEI film of the positive electrode convex part and resulting in a lack of protection for the positive electrode convex part. If it is higher than the above ratio range, it indicates that the groove width of the groove is relatively small, and the setting of the groove will be meaningless. The groove is difficult to store enough electrolyte, cannot provide an expansion space for the expansion of the negative electrode sheet, and cannot slow down the extrusion deformation of the positive electrode convex part or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing forming or the charge and discharge process of the battery.

[0018] In an embodiment of the present application, the first coating layer and / or the second coating layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material, and the mass ratio of the silicon-carbon composite material and / or the silicon-oxygen composite material in the first coating layer and / or the second coating layer is less than or equal to 50 wt%.

[0019] In an embodiment of the present application, the positive electrode sheet includes a positive electrode current collector. The positive electrode current collector has opposite third and fourth surfaces along the first direction. A third coating layer is provided on the third surface, and a fourth coating layer is provided on the fourth surface; the negative electrode sheet and the positive electrode sheet are wound around a first central plane. The surface of the positive electrode current collector facing the first central plane is the third surface, and the surface of the positive electrode current collector facing away from the first central plane is the fourth surface; the third surface and the first surface are disposed opposite to each other, and the fourth surface and the second surface are disposed opposite to each other; the core includes a straight region and corner regions located at opposite ends of the straight region; the convex part protrudes from the third coating layer towards the fourth coating layer.

[0020] Due to the curvature of the corner area, the first surface of the silicon-doped negative electrode sheet is subjected to a greater extrusion force than the second surface of the silicon-doped negative electrode sheet. When the silicon-doped negative electrode sheet expands as a whole, the expansion degree of the second surface is greater than that of the first surface, which easily causes cracks to appear on the second surface of the negative electrode sheet; the first surface and the groove of the negative electrode are arranged opposite to the third surface of the positive electrode, that is, the depression of the second surface of the negative electrode is arranged opposite to the third surface of the positive electrode. When the second surface of the negative electrode expands severely, a part of the coating on the second surface can enter the concave part of the positive electrode, releasing the stress of the negative electrode expansion, so as not to affect the depth of the convex part of the positive electrode and ensure the normal supporting effect of the convex part of the positive electrode;

[0021] In addition, due to the curvature of the corner area, when the arc on the outer side of the positive electrode sheet wraps the negative electrode sheet, the arc circumference of the third coating layer on the inner side of the positive electrode sheet is greater than the circumference of the first surface of the negative electrode sheet in the corner area, resulting in a decrease in the ratio of the negative electrode surface capacity to the positive electrode surface capacity in this area, and there is a risk of lithium precipitation. In the embodiment of the present application, the convex part protrudes from the third coating layer to the fourth coating layer, and the depression on the first surface of the negative electrode is arranged opposite to the concave part of the third surface of the positive electrode. The migration path of the positive electrode active material in the concave part is longer, and the migration path of the positive electrode active material in other parts is shorter. Furthermore, the positive electrode active material participating in the charge and discharge reaction in the concave part is reduced, so that there are sufficient sites on the negative electrode coating layer on the third surface for the insertion and extraction of lithium ions, thereby increasing the CB value (negative electrode surface capacity / positive electrode surface capacity) in this area and reducing the probability of lithium precipitation in this area.

[0022] In an embodiment of the present application, the total projected area of the plurality of convex parts on the negative electrode sheet is 60% - 90% of the area of the fourth coating layer; the winding core further includes an electrolyte doped with 1,4-dicyano-2-butene additive, and the content of the 1,4-dicyano-2-butene additive in the electrolyte accounts for 0.05% - 3%.

[0023] Defining the proportion of the positive electrode convex part area on the coating layer can ensure the supporting effect of the positive electrode convex part; at the same time, the electrolyte infiltrating between the positive and negative electrode sheets is also doped with a certain content of 1,4-dicyano-2-butene additive. 1,4-dicyano-2-butene can protect the edge of the positive electrode convex part and strengthen the convex part edge; prevent the problem that the active particles at the edge of the positive electrode convex part are broken or even cobalt precipitates, resulting in a decrease in the structural stability of the positive electrode active material and an accelerated attenuation of the battery capacity.

[0024] In an embodiment of the present application, the shape of the projection of the convex part on the negative electrode sheet includes a circle, a semicircle, an ellipse, a plum blossom shape, a polygon, a rhombus, a capsule shape or an island shape, etc.

[0025] In an embodiment of the present application, the positive electrode sheet includes an upper surface and a lower surface disposed opposite to each other, and the convex portion protrudes outward from the upper surface of the positive electrode sheet; the convex portion includes a protruding portion and a root portion connecting the protruding portion and the upper surface; the protruding portion has an arc surface, and / or the protruding portion is connected to the upper surface through an arc-shaped edge surface, and the edge of the convex portion in the shape of a polygon, a rhombus or an island is an arc edge.

[0026] Avoid having sharp edges on the convex portion to prevent powder falling from the edges during the processing of the convex portion; at the same time, avoid the edges or the top of the convex portion piercing the positive electrode paste, preventing cracks in the paste and causing powder falling. The powder particles are likely to fall onto the negative electrode sheet, leading to short circuit and fire risks. Moreover, it can also prevent the top of the convex portion from piercing the separator and contacting the negative electrode sheet to cause a short circuit.

[0027] In an embodiment of the present application, the line connecting the root portion and the vertex of the protruding portion is the first line, and the angle between the first line and the upper surface is the first angle, and the first angle is 3° - 45°.

[0028] By defining the angle between the first line and the upper surface, it is ensured that the positive electrode convex portion has an appropriate slope, enabling the positive electrode convex portion to play a supporting role between the positive and negative electrode sheets, and at the same time preventing the positive electrode convex portion from being too sharp and piercing the separator. When the first angle is less than 3°, the convex portion is too small to play a supporting role between the positive and negative electrode sheets; when the first angle is greater than 45°, the convex portion has too high a slope, causing a problem of a protruding tip, which is likely to pierce the separator and cause safety problems.

[0029] In an embodiment of the present application, the corner region has a first thickness H1, the straight region has a second thickness H2, and the following relationship exists between the first thickness H1 and the second thickness H2: H1 / (H2 / 2) = 1.05 - 1.5.

[0030] Due to the structural characteristics and stress accumulation in the corner region, the outward expansion of the corner region is restricted, ultimately leading to the problem of lithium plating caused by interlayer extrusion of the electrode sheet. In the embodiment of the present application, by providing a convex portion and a concave portion opposite to the convex portion on the positive electrode sheet, and a groove opposite to the convex portion on the negative electrode sheet to achieve the above thickness relationship, the setting of the above thickness relationship can effectively improve the lithium plating problem in the corner region. At the same time, ensure that the convex portions and grooves in the corner region and the straight region match in thickness, so that the interaction force between the layers of the battery cell is appropriate, and ensure that the protrusions of the positive electrode sheet and the depressions of the negative electrode will not deform during charge and discharge.

[0031] In an embodiment of the present application, along the width direction of the groove, the size of the projection of the convex portion on the negative electrode sheet is R1 = 0.3 mm to 8 mm; and / or the center distance between the projections of two adjacent convex portions on the negative electrode sheet is D1, D1 = 1 mm to 6 mm; and / or in the first direction, there is a vertical distance between the root portion and the vertex of the convex portion, and the vertical distance is H3 = 3 um to 80 um.

[0032] Ensure that the size of the projection of the convex portion on the negative electrode sheet is within the above range, avoid the tip effect caused by too small a size of the convex portion, and prevent the diaphragm from being punctured; avoid the large span of the convex surface of the convex portion caused by too large a size of the convex portion, which affects the supporting effect of the convex portion. Ensure that the center distance of the convex portions is within the above range, avoid the overlap of the convex portions or too high a density of the convex portions caused by too small a center distance of the convex portions. When forming the convex portions, the rolling pressure is too large and the convex portions are too dense. During the charge and discharge process, the interlayer stress of the battery cell is difficult to release, which easily leads to powder falling off the electrode sheet; avoid the large span of the convex surfaces of two adjacent convex portions caused by too large a center distance of the convex portions, which affects the supporting effect of the convex portions. Ensure that the height of the convex portion is within the above range, avoid poor supporting effect caused by too small a convex portion and inability to provide sufficient infiltration space for the electrolyte; avoid the serious delamination between the positive and negative electrode sheets caused by too large a convex portion, resulting in new interface problems.

[0033] In an embodiment of the present application, in the corner area, the vertical distance from the vertex of the convex portion of the innermost circle of the core to the root of the convex portion is the first vertical distance, and the vertical distance from the vertex of the convex portion of the outermost circle of the core to the root of the convex portion is the second vertical distance, and the first vertical distance is greater than the second vertical distance.

[0034] The extrusion in the corner area mainly occurs in several layers close to the inner circle of the core. The closer to the outer circle, the smaller the extrusion pressure, the smaller the lack of electrolyte, and the lower the risk of lithium plating; the vertical distance of the convex portion of the innermost circle of the core being greater than the vertical distance of the convex portion of the outermost circle of the core can increase the retention amount of the electrolyte in the innermost circle of the core, ensuring that there is no lithium plating or other situations in the inner circle of the battery cell; moreover, reducing the convex portion in the corner area of the inner circle can reduce the width of the corner area, thereby improving the problem of the battery cell being too wide and increasing the energy density of the battery cell.

[0035] In an embodiment of the present application, the groove width is M = 30 um to 170 um; and / or in the first direction, the groove has a groove depth, and the groove depth is T = 10 um to 60 um; and / or the first distance is S = 0.5 mm to 3 mm.

[0036] Ensure that the groove width of the groove is within the above range, so as to avoid the situation that the groove cannot provide expansion space for the expansion of the negative electrode sheet due to too small groove width, and also cannot slow down the extrusion deformation of the positive electrode convex part or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing formation or battery charge and discharge; at the same time, avoid the problem that when the negative electrode sheet expands and causes interlayer extrusion of the electrode sheet, the positive electrode convex part is likely to be embedded in the negative electrode groove due to too large groove width. Ensure that the groove depth of the groove is within the above range, so as to avoid the situation that the effect of slowing down the convex part deformation caused by the expansion of the electrode sheet during charge and discharge cannot be achieved due to too small groove depth, and too small groove depth will also reduce the storage capacity of the electrolyte; at the same time, avoid the problem that the negative electrode sheet is prone to break in the groove area due to too large groove depth. Ensure that the center spacing of the grooves is within the above range, so that the grooves on the negative electrode sheet have an appropriate density.

[0037] In an embodiment of the present application, each of the convex parts has a center point in the projection on the negative electrode sheet, and some of the center points are distributed on the second connection line; the projection of the groove on the negative electrode current collector is a rectangular surface, and the second connection line is parallel or intersects with the rectangular surface; when the second connection line intersects with the rectangular surface, the included angle between the second connection line and the rectangular surface is 0° to 45°.

[0038] When the second connection line is parallel to the rectangular surface, it enables a plurality of convex parts located on the second connection line to be oppositely arranged with a groove, making the processing of the convex part and the groove more convenient; when the second connection line intersects with the rectangular surface, a plurality of convex parts located on the second connection line are respectively opposite to different grooves, and at the same time, the included angle between the second connection line and the rectangular surface is limited within the above range to ensure that each convex part on the second connection line can be oppositely arranged with the groove.

[0039] An embodiment of the present application further provides a battery, which includes the core described above. Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a schematic structural diagram of the core provided in the related art;

[0042] Figure 2 It is a schematic structural diagram of the negative electrode sheet and the positive electrode sheet of the core provided in the embodiment of the present application;

[0043] Figure 3 It is a schematic structural diagram of the negative electrode sheet of the core provided in the embodiment of the present applicationFigure 1 ;

[0044] Figure 4 Schematic structure of the negative electrode sheet of the core provided by the embodiment of the present application Figure 2 ;

[0045] Figure 5 Top view structure schematic diagram of the negative electrode sheet of the core provided by the embodiment of the present application;

[0046] Figure 6 Schematic structure diagram of the positive electrode sheet of the core provided by the embodiment of the present application;

[0047] Figure 7 Schematic structure diagram of the positive and negative electrode sheets stacked in the corner area of the core provided by the embodiment of the present application;

[0048] Figure 8 Schematic structure of the positive electrode sheet of the core provided by the embodiment of the present application Figure 1 ;

[0049] Figure 9 Schematic structure of the positive electrode sheet of the core provided by the embodiment of the present application Figure 2 ;

[0050] Figure 10 Schematic structure diagram of the convex part of the positive electrode sheet of the core provided by the embodiment of the present application;

[0051] Figure 11 Schematic diagram of the slope of the convex part provided by the embodiment of the present application;

[0052] Figure 12 Intersection schematic of the convex part and the groove provided by the embodiment of the present application Figure 1 ;

[0053] Figure 13 Intersection schematic of the convex part and the groove provided by the embodiment of the present application Figure 2 ;

[0054] Figure 14 Thickness data of the flat area and the corner area of 10 cores provided by the embodiment of the present application;

[0055] Figure 15 Specific values of the first width and the first distance of 10 cores provided by the embodiment of the present application;

[0056] Figure 16 Vertical distances of each layer in the core provided by the embodiment of the present application;

[0057] Figure 17 Specific values of the first width and the groove width of 10 cores provided by the embodiment of the present application.

[0058] Reference Signs:

[0059] 100: negative electrode sheet;

[0060] 101: negative electrode current collector; 102: first coating layer; 103: second coating layer; 110: groove;

[0061] 1011: first surface; 1012: second surface;

[0062] 200: positive electrode sheet;

[0063] 201: positive electrode current collector; 202: third coating layer; 203: fourth coating layer; 210: convex portion;

[0064] 2011: third surface; 2012: fourth surface;

[0065] 301: first connection line; 302: first horizontal plane;

[0066] 401: rectangular surface; 402: second connection line. Detailed Implementation Manner

[0067] The winding core structure of the wound lithium-ion battery in the related art is as Figure 1 shown. The electrode assembly is laminated and wound to form the winding structure of the battery core. The cross-section of the winding structure presents a flat oval structure. The two sides of the oval structure are arc areas, and the middle of the oval structure is a flat area. The area surrounded by the dotted line in the arc area in the figure is the stress concentration area, and the direction indicated by the arrow is the expansion direction when the positive and negative electrode sheets expand. During the charge and discharge process of the lithium-ion battery, the positive and negative electrode sheets will expand. The flat area can expand freely up and down, but due to its structural characteristics and stress accumulation in the arc area, its outward expansion is restricted.

[0068] At the same time, the extrusion in the arc area will also be transmitted to the flat area. Also, due to the extrusion of the flat area during the hot pressing process in the production process, the flat area will be squeezed very tightly, which further leads to poor electrolyte infiltration in the flat area.

[0069] Finally, the interlayer extrusion of the electrode sheet leads to poor electrolyte infiltration, resulting in too low liquid retention of the electrolyte between the electrode sheets, which means that this area loses the lithium-ion transmission channel, making it impossible for the lithium ions in the positive electrode sheet to escape, and the number of lithium ions embedded at the corresponding position of the negative electrode sheet is insufficient, thus resulting in purple spots. Finally, the lithium ions in the negative electrode sheet cannot return to the positive electrode sheet either and are finally deposited on the surface of the negative electrode sheet, that is, lithium plating. In addition, during the cycling process, due to the large expansion of the negative electrode sheet, it is easy to squeeze the two sides of the separator in contact with the negative electrode sheet, resulting in the deformation of the separator and the blockage of the micropores of the separator, further increasing the risk of lithium plating in this area.

[0070] The core provided by the embodiment of the present application, by providing protrusions and corresponding recesses on the positive electrode sheet, the protrusions provide support for the diaphragm contact, increasing the micro-spacing between the electrode sheet and the diaphragm, and these micro-spacings form spaces that can accommodate the electrolyte, enabling the electrolyte to have sufficient wetting amount for the electrode sheet, avoiding the abnormal situations such as insufficient electrolyte between the electrode sheet and the diaphragm, poor wetting and even lithium deposition on the negative electrode sheet caused by the interlayer extrusion of the electrode sheet.

[0071] Meanwhile, a groove is provided on the negative electrode sheet opposite to the protrusion. The groove provided on the negative electrode sheet can effectively enhance the wetting of the electrolyte on the negative electrode sheet. In addition, the surface where the protrusion of the positive electrode sheet is located and the surface where the groove of the negative electrode sheet is located are arranged opposite to each other, providing an expansion space for the expansion of the negative electrode sheet, thereby slowing down the situation of the extrusion deformation of the positive electrode protrusion or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing formation or the charge and discharge process of the battery, ensuring the structural strength of the protrusion and the groove and the interfacial adhesion strength between the electrode sheet and the diaphragm, and stably exerting its supporting effect on the diaphragm. At the same time, the sufficient expansion space can also prevent the negative electrode sheet from extruding the diaphragm during the expansion process, causing the diaphragm to deform.

[0072] Furthermore, it is defined that the size of the vertical projection of the protrusion in the thickness direction of the negative electrode sheet is greater than the center distance between two adjacent grooves, preventing the positive electrode protrusion from being embedded into the groove of the negative electrode, which is beneficial to the formation of the SEI film on the protruding part of the positive electrode, thereby effectively protecting the protruding part of the positive electrode and preventing problems such as the fragmentation of the active particles of the protruding part of the positive electrode and even cobalt precipitation, resulting in the reduction of the structural stability of the positive electrode active material and the acceleration of the battery capacity attenuation.

[0073] In order to make the above objects, features and advantages of the embodiments of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present application.

[0074] Refer to Figure 2 , the core provided by the embodiment of the present application includes: a negative electrode sheet 100 and a positive electrode sheet 200, the negative electrode sheet 100 and the positive electrode sheet 200 are stacked, and the polarities of the negative electrode sheet 100 and the positive electrode sheet 200 are opposite.

[0075] Refer to Figure 3 and Figure 5, the negative electrode sheet 100 includes a negative electrode current collector 101. The negative electrode current collector 101 has opposite first and second surfaces 1011 and 1012 along the first direction (the z-axis shown in the figure). A first coating layer 102 is provided on the first surface 1011, and a second coating layer 103 is provided on the second surface 1012. Similarly, the positive electrode sheet 200 includes a positive electrode current collector 201. The positive electrode current collector 201 has opposite third and fourth surfaces 2011 and 2012 along the first direction (the z-axis shown in the figure). A third coating layer 202 is provided on the third surface 2011, and a fourth coating layer 203 is provided on the fourth surface 2012.

[0076] A plurality of grooves 110 extending along the second direction (the y-axis shown in the figure) are provided on the first coating layer 102, and the plurality of grooves 110 are arranged at the same distance intervals along the third direction (the x-axis shown in the figure); that is to say, the grooves 110 extend along the width direction of the negative electrode sheet 100, and the plurality of grooves 110 are arranged at intervals along the length direction of the negative electrode sheet 100.

[0077] Reference Figures 8 - 10 , the positive electrode sheet 200 has a plurality of convex portions 210 arranged in an array, and a plurality of concave portions arranged in an array. The convex portions 210 and the concave portions are arranged opposite to each other; the convex portions 210 may be protrusions on the upper surface of the positive electrode sheet 200, and the concave portions may be depressions on the lower surface of the positive electrode sheet 200.

[0078] Among them, when the negative electrode sheet 100 and the positive electrode sheet 200 are stacked, in the first direction (the z-axis shown in the figure), the first coating layer 102 and the fourth coating layer 203 are opposite to each other; at the same time, the grooves 110 on the first coating layer 102 and the convex portions 210 on the fourth coating layer 203 are arranged opposite to each other along the first direction (the z-axis shown in the figure).

[0079] The fact that the surface where the convex portion of the positive electrode sheet and the surface where the groove of the negative electrode sheet are arranged opposite to each other means that: the projection of the convex portion 210 along the first direction and the projection of the groove 110 along the first direction (the z-axis shown in the figure) at least partially overlap, or the projection of the convex portion 210 along the first direction and the projection of the groove 110 along the first direction completely overlap.

[0080] The core provided by the embodiment of the present application increases the micro-spacing between the negative electrode sheet 100, the separator and the positive electrode sheet 200 by providing convex portions 210 and concave portions arranged opposite to the convex portions 210 on the positive electrode sheet 200. The convex portions provide support for the contact of the separator, so that there is a certain support between the negative electrode sheet 100 and the positive electrode sheet 200. These micro-spacings form a space for accommodating the electrolyte, so that the electrolyte has sufficient wetting amount for the electrode sheet, avoiding abnormal situations such as insufficient electrolyte between the electrode sheet and the separator, poor wetting and even lithium deposition on the negative electrode sheet caused by the interlayer extrusion of the electrode sheet, and ensuring that the electrolyte has sufficient wetting amount.

[0081] The core provided by the embodiment of the present application is provided with a groove 110 on the negative electrode sheet 100 opposite to the convex portion 210, providing an expansion space for the expansion of the negative electrode sheet, thereby slowing down the extrusion deformation of the positive electrode convex portion or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing forming or battery charging and discharging processes, ensuring the structural strength of the protrusion and the groove and the interfacial adhesion strength between the electrode sheet and the separator, and stably exerting the supporting effect on the separator. At the same time, the sufficient expansion space can also prevent the negative electrode sheet from extruding the separator during the expansion process, causing the separator to deform.

[0082] Continue to refer to Figure 3 , in the embodiment of the present application, the central distance between two adjacent grooves 110 is set as the first distance S; the size of the perpendicular projection of the convex portion 210 in the thickness direction of the electrode sheet is the first width R1, and the first width R1 is greater than the first distance S.

[0083] When the convex portion 210 is opposite to the groove 110, it prevents the convex portion 210 from being embedded into the groove 110 of the negative electrode, which is beneficial to the formation of the SEI film on the protruding portion of the positive electrode, thereby effectively protecting the convex portion 210 of the positive electrode and preventing problems such as the fragmentation of the active particles of the convex portion 210 of the positive electrode and even the precipitation of cobalt, resulting in a decrease in the structural stability of the positive electrode active material and an accelerated attenuation of the battery capacity.

[0084] In the embodiment of the present application, the ratio between the first width R1 and the first distance S is: R1 / S = 1.02 - 8.

[0085] Within the above ratio range, it is possible to slow down the extrusion deformation of the convex portion 210 of the positive electrode or the deformation of the groove 110 of the negative electrode caused by the expansion of the negative electrode sheet 100 during hot pressing forming or battery charging and discharging processes.

[0086] If the ratio between the first width R1 and the first distance S is less than 1.02, it indicates that the groove width of the first distance S is relatively large. When the negative electrode sheet 100 expands and causes interlayer extrusion of the electrode sheet, the convex portion 210 of the positive electrode is likely to be embedded into the groove 110 of the negative electrode, easily causing damage to the SEI film of the positive electrode convex portion and resulting in a lack of protection for the positive electrode convex portion; if the ratio between the first width R1 and the first distance S is greater than 8, it indicates that the groove width of the first distance S is relatively small, and the setting of the first distance S will be meaningless. The first distance S cannot provide an expansion space for the expansion of the negative electrode sheet, nor can it slow down the extrusion deformation of the positive electrode convex portion or the deformation of the negative electrode groove caused by the expansion of the negative electrode sheet during hot pressing forming or battery charging and discharging processes.

[0087] Refer to Figure 15 , 10 kinds of cores (core 1 - 10) are respectively provided, and the above ratio relationship is illustrated through 10 embodiments. Among them, the 10 kinds of cores respectively have different first widths R1 and first distances S, and the first width R1 and the first distance S of each core have the above ratio relationship.

[0088] Among the 10 kinds of cores with the above ratio relationship, when the positive and negative electrode plates of the core expand and cause extrusion between the electrode layers, especially when the extrusion between the layers in the corner area is intensified, it can prevent the convex part 210 from being embedded into the groove 110, and prevent the convex part 210 or the groove 110 from deforming.

[0089] Preferably, the ratio between the first width R1 and the first distance S is: R1 / S = 1.05 - 4.

[0090] In the embodiment of the present application, the first width R1 = 0.3 mm - 8 mm.

[0091] When the first width R1 is less than 0.3 mm, the tip effect is likely to occur. That is to say, the highest point of the convex part 210 forms a sharp protrusion, which will cause the diaphragm to be damaged; when the first width R1 is greater than 8 mm, the span of the convex surface of the convex part 210 is relatively large, which is not conducive to playing a supporting role between the positive and negative electrode plates.

[0092] Preferably, the first width R1 = 1 mm - 3 mm.

[0093] It should be noted that when the projection of the convex part 210 on the electrode plate is fitted into a circle, the first width R1 of the projection of the convex part 210 on the electrode plate can be the diameter of the circle.

[0094] In the embodiment of the present application, the center distance between the projections of two adjacent convex parts 210 on the negative electrode plate 100 is D1, and D1 = 1 mm - 6 mm.

[0095] When the center distance D1 is less than 1 mm, the convex parts 210 are likely to overlap or the density of the convex parts is too high. When forming the convex parts, the rolling pressure is too large and the convex parts are too dense. During the charge and discharge process, the interlayer stress of the battery cell is difficult to release, which is likely to cause the electrode plate to shed powder; when the center distance D1 is greater than 6 mm, the span of the convex surfaces of the two convex parts 210 is relatively large, and it cannot play a supporting role.

[0096] Preferably, the center distance is D1 = 1.5 mm - 4 mm.

[0097] In the embodiment of the present application, the groove 110 has a groove width M in the third direction (the x-axis shown in the figure). The first width R1 is greater than the groove width M, and the ratio between the first width R1 and the groove width M can be: R1 / M = 8 - 50.

[0098] Within the above ratio range, it can slow down the situation of the extrusion deformation of the convex part 210 of the positive electrode or the deformation of the groove 110 of the negative electrode caused by the expansion of the negative electrode during hot pressing formation or the charge and discharge process of the battery.

[0099] If the ratio between the first width R1 and the groove width M is less than 8, it indicates that the groove width of the groove 110 is relatively large. When the negative electrode sheet expands and causes inter-layer extrusion of the electrode sheet, especially when the inter-layer extrusion in the corner area intensifies, it is very easy for the convex portion 210 to be embedded in the groove 110, which easily causes damage to the SEI film of the positive electrode convex portion and makes the positive electrode convex portion lack protection. If the ratio between the first width R1 and the groove width M is greater than 50, it indicates that the groove width of the groove 110 is relatively small, and the setting of the groove 110 will be meaningless. It is difficult for the groove 110 to store enough electrolyte, and the groove 110 cannot provide an expansion space for the expansion of the negative electrode sheet, nor can it slow down the deformation of the convex portion 210 or the groove 110 caused by the expansion of the negative electrode sheet during hot pressing formation or charge and discharge processes.

[0100] Reference Figure 17 , ten kinds of cores (cores 1-10) are respectively provided, and the above ratio relationship is illustrated through ten embodiments. Among them, the ten kinds of cores respectively have different first widths R1 and groove widths M, and the first width R1 and the groove width M of each core have the above ratio relationship.

[0101] For the ten kinds of cores having the above ratio relationship, when the positive and negative electrode sheets of the core expand and cause inter-layer extrusion of the electrode sheet, especially when the inter-layer extrusion in the corner area intensifies, it can prevent the convex portion 210 from being embedded in the groove 110 and prevent the convex portion 210 or the groove 110 from deforming.

[0102] Preferably, the ratio between the first width R1 and the groove width M can be: R1 / M = 16~40.

[0103] In the embodiments of the present application, the groove 110 has a groove width M in the third direction (the x-axis shown in the figure), and the groove width M = 30um~170um; ensuring that the groove width M of the groove 110 is within the above range. When the groove width M is less than 30um, the groove width M is too small, and the setting of the groove 110 will be meaningless, resulting in the groove 110 being unable to provide an expansion space for the expansion of the negative electrode sheet, nor can it slow down the extrusion deformation of the convex portion 210 of the positive electrode or the deformation of the groove 110 of the negative electrode caused by the expansion of the negative electrode sheet during hot pressing formation or battery charge and discharge processes; when the groove width M is greater than 170um, when the negative electrode sheet 100 expands and causes inter-layer extrusion of the electrode sheet, the convex portion 210 of the positive electrode is easily embedded in the groove 110 of the negative electrode.

[0104] Preferably, the groove width M = 60um~120um.

[0105] The groove 110 has a groove depth T in the first direction (the z-axis shown in the figure), and the groove depth T = 10um to 60um; when the groove depth T is less than 10um, it will not be able to slow down the deformation of the convex part 210 caused by the expansion of the electrode plate during the charge and discharge process, and it will also affect the increase in the amount of stored electrolyte; when the groove depth T is greater than 60um, it will affect the thickness of the negative electrode plate, and the area where the groove 110 is set is prone to fracture.

[0106] Preferably, the groove depth T = 12um to 30um.

[0107] A plurality of grooves 110 are spaced at the same distance in the second direction (the y-axis shown in the figure), and the center of two adjacent grooves 110 is spaced at a first distance S, and the first distance S = 0.5mm to 3mm. When the first distance S is less than 0.5mm, the setting of the groove 110 will be meaningless, and it is easy to cause the deformation of the convex part 210 or the groove 110 during the charge and discharge process due to the expansion of the electrode plate; when the first distance S is greater than 3mm, it means that the first width R1 of the convex part 210 opposite thereto also needs to be increased. When the first width R1 is too large, the span of the convex surface of the convex part 210 is large, which is not conducive to playing a supporting role between the positive and negative electrode plates.

[0108] Continue to refer to Figure 3 , in the cross-section where the first direction (the z-axis shown in the figure) is located, the cross-sectional shape of the groove 110 can be V-shaped.

[0109] Continue to refer to Figure 4 , a plurality of grooves 110 are respectively provided on the first surface 1011 and the second surface 1012 of the negative electrode current collector 101; the convex part 210 and the groove 110 are arranged oppositely; the concave part and the groove 110 are arranged oppositely.

[0110] That is to say, grooves are provided on both sides of the negative electrode plate 100, so that while the convex part 210 of the positive electrode and the groove 110 of the negative electrode are arranged oppositely, the concave part of the positive electrode is also arranged oppositely to the groove 110 of the negative electrode; the arrangement of the concave part of the positive electrode and the groove 110 of the negative electrode oppositely can increase the space between the positive electrode plate 200 and the negative electrode plate 100, provide a larger wetting space for the electrolyte, and thus increase the amount of stored electrolyte.

[0111] In the embodiment of the present application, the winding core includes a flat area and corner areas located at opposite ends of the flat area. The corner area has a first thickness H1, and the flat area has a second thickness H2. The following relationship exists between the first thickness H1 and the second thickness H2: H1 / (H2 / 2)=1.05 to 1.5.

[0112] It should be noted that the second thickness H2 of the flat area refers to Figure 1The vertical thickness shown in [Figure] is such that the corner region is formed as an arc, and the first thickness H1 of the corner region is the radius of the arc. In one embodiment, the thickness of the flat region may also refer to the thickness of all the flat regions of the battery cell, i.e., the thickness of the battery cell. Correspondingly, the thickness of the corner region is the thickness of all the corner regions that connect the two ends of the innermost corner region in the width direction and pass through the center point.

[0113] Reference Figure 14 , ten kinds of wound cores (Wound Core 1 - 10) were provided respectively, and the above thickness relationship was illustrated through ten embodiments. Among them, the ten wound cores have different thicknesses of the flat region and the corner region respectively, and the thicknesses of the flat region and the corner region of each wound core have the above thickness relationship.

[0114] Due to the structural characteristics of the corner region and the accumulation of stress, the outward expansion of the corner region is restricted, and finally, the problem of lithium plating caused by the extrusion between the electrode layers appears. In the embodiments of the present application, for the ten wound cores provided, by providing convex portions 210 on the positive electrode sheet 200 of each wound core and concave portions opposite to the convex portions 210, and providing grooves 110 on the negative electrode sheet 100 opposite to the convex portions 210 to achieve the above thickness relationship, the setting of the above thickness relationship can effectively improve the problem of lithium plating in the corner region. At the same time, by ensuring the matching of the convex portions, the concave portions and the thickness between the corner region and the flat region, the interaction force between the layers of the battery cell is appropriate, and it is ensured that the protrusions of the positive electrode sheet and the depressions of the negative electrode will not be deformed during the charge and discharge process.

[0115] Preferably, the first thickness H1 and the second thickness H2 have the following relationship: H1 / (H2 / 2)=1.08~1.3.

[0116] Reference Figure 9 , in the embodiments of the present application, the positive electrode sheet 200 includes an upper surface and a lower surface which are oppositely arranged, and the convex portions protrude outward from the upper surface of the positive electrode sheet 200; the convex portion 210 includes a protruding portion and a root connecting the protruding portion and the upper surface.

[0117] In the first direction (the z-axis shown in the figure), the root of the convex portion 210 intersects with the surface of the positive electrode sheet 200, and the root of the convex portion 210 and the vertex of the convex portion 210 have a vertical distance, and the vertical distance is H3 = 3um~80um.

[0118] When the vertical distance H3 is less than 3um, it indicates that the convex portion 210 is too small to play a supporting role between the positive and negative electrode sheets. The convex portion 210 is an ineffective protrusion and cannot make the electrolyte have sufficient infiltration; when the vertical distance H3 is greater than 80um, it indicates that the convex portion 210 is too large, which will cause serious delamination between the positive and negative electrode sheets and cause new interface problems.

[0119] Among them, the extrusion in the corner area mainly occurs in several layers of the core near the inner circle. The closer to the outer circle, the smaller the extrusion force, the less the lack of electrolyte, and the lower the risk of lithium deposition. Therefore, increasing the vertical distance of the convex part of the innermost circle of the core compared to that of the outermost circle can increase the retention of electrolyte in the innermost circle of the core, ensuring that no lithium deposition occurs in the inner circle of the battery cell. Moreover, reducing the convex part in the corner area of the inner circle can reduce the width of the corner area, thereby improving the problem of the battery cell being too wide and enhancing the energy density of the battery cell.

[0120] Reference Figure 16 , the vertical distances H3 of all layers in a core are respectively provided to illustrate the above relationship.

[0121] The innermost circle of the core refers to the layer where the starting section of the winding of the electrode sheet is located, and the outermost circle of the core refers to the layer where the ending section of the winding of the electrode sheet is located. There are also multiple intermediate circles between the innermost circle and the outermost circle of the core.

[0122] The first intermediate circle is adjacent to the innermost circle of the core and surrounds the innermost circle of the core. The second intermediate circle is adjacent to the first intermediate circle and surrounds the first intermediate circle, and so on until the outermost circle of the core.

[0123] When the vertical distance H3 of the convex part 210 of the innermost circle of the core is 80 um, the vertical distance H3 of the convex part 210 of the first intermediate circle can be 75 um; the vertical distance H3 of the convex part 210 of the second intermediate circle can be 70 um; the vertical distance H3 of the convex part 210 of the third intermediate circle can be 65 um; the vertical distance H3 of the convex part 210 of the outermost circle of the core can be 3 um.

[0124] Continue to refer to Figure 11 , in the embodiment of the present application, the convex part 210 protrudes outward from the upper surface of the positive electrode sheet 200; the convex part 210 includes a protruding part and a root connecting the protruding part and the upper surface. The root of the convex part 210 intersects with the upper surface of the positive electrode sheet 200. The connection line between the root of the convex part 210 and the vertex of the convex part 210 is the first connection line 301, and the angle between the first connection line 301 and the first horizontal plane 302 is the first angle, and the first angle is 3° - 45°.

[0125] When the first angle is less than 3°, the convex part 210 is too small to play a supporting role between the positive and negative electrode sheets; when the first angle is greater than 45°, the convex part 210 has too high a slope, which will cause problems at the protruding tip and is likely to pierce the separator, leading to safety problems.

[0126] Preferably, the first angle can be 5° - 25°.

[0127] In the embodiment of the present application, the shape of the protrusion 210 may include a circle, a semicircle, an ellipse, a plum blossom, a polygon, a diamond, a capsule or an island.

[0128] In the embodiment of the present application, the positive electrode sheet 200 includes an upper surface and a lower surface that are arranged opposite to each other, and the protrusion is formed by protruding outward from the upper surface of the positive electrode sheet 200; the protrusion 210 includes a protrusion portion and a root portion connecting the protrusion portion and the upper surface.

[0129] The raised portion is an arc-shaped surface, and / or the raised portion is connected to the upper surface through the arc-shaped edge surface, and the edge of the polygonal, rhombus or island-shaped raised portion is an arc edge.

[0130] That is to say, when the shape of the protrusion 210 is a polygon or rhombus with corners, the corners of the protrusion 210 are all provided with arc corners; or when the shape of the protrusion 210 is a polygon or rhombus with obvious sharp edges, the edge of the protrusion 210 is an arc edge.

[0131] Avoid having sharp edges on the protrusions to prevent powder falling from the edges when processing the protrusions; at the same time, avoid the edges or tops of the protrusions from piercing the positive electrode paste to prevent cracks in the paste and cause powder falling. The powder particles can easily fall onto the negative electrode sheet, causing short circuits and fire risks. It can also prevent the tops of the protrusions from piercing the diaphragm and contacting the negative electrode sheet to cause a short circuit.

[0132] Preferably, the shape of the protrusion 210 may be circular without sharp corners.

[0133] It should be noted that when a 3D profilometer is used to test the state of the positive electrode sheet 200 , it can be clearly detected that the edge of the protrusion 210 is quasi-circular.

[0134] Continue to refer Figure 2 and Figure 7 In the embodiment of the present application, the negative electrode sheet 100 and the positive electrode sheet 200 are wound around the first center plane, the surface of the positive electrode collector 201 facing the first center plane is the third surface 2011, and the surface of the positive electrode collector 201 away from the first center plane is the fourth surface 2012. The third surface 2011 is provided with a third paste layer 202, and the fourth surface 2012 is provided with a fourth paste layer 203. The protrusion 210 protrudes from the third paste layer 202 to the fourth paste layer 203.

[0135] The first center plane refers to Figure 1 The center is the horizontal plane perpendicular to the paper surface at the innermost circle of the winding core.

[0136] Due to the curvature of the corner area, the first surface of the silicon-doped negative electrode sheet is subjected to a greater extrusion force than the second surface of the silicon-doped negative electrode sheet. When the silicon-doped negative electrode sheet expands as a whole, the degree of expansion of the second surface is greater than that of the first surface, which easily causes cracks to appear on the second surface of the negative electrode sheet; the first surface and the groove of the negative electrode are arranged opposite to the third surface of the positive electrode, that is, the depression on the second surface of the negative electrode is arranged opposite to the third surface of the positive electrode. When the second surface of the negative electrode expands severely, part of the coating on the second surface can enter the concave part of the positive electrode, releasing the stress of the negative electrode expansion, so as not to affect the depth of the convex part of the positive electrode and ensure the normal supporting effect of the convex part of the positive electrode.

[0137] Due to the curvature of the corner area, when the arc formed by the third paste layer 202 wraps the negative electrode sheet 100, the arc circumference of the third paste layer 202 will be greater than the circumference of the negative electrode sheet 100 in the corner area. This results in a greater amount of positive electrode active material in this area than the designed amount of positive electrode active material in this area. That is to say, the ratio of the negative electrode surface capacity to the positive electrode surface capacity in this area decreases, leading to the risk of lithium deposition.

[0138] Under the condition that the above facts cannot be changed, in the embodiment of the present application, by making the convex part protrude from the third paste layer to the fourth paste layer, and the depression on the first surface of the negative electrode is arranged opposite to the concave part of the third surface of the positive electrode, the migration path of the positive electrode active material in the concave part is longer, and the migration path of the positive electrode active material in other parts is shorter. Furthermore, the positive electrode active material participating in the charge and discharge reaction in the concave part is reduced, so that there are sufficient sites on the negative electrode paste layer of the third surface for the insertion and extraction of lithium ions, thereby improving the CB value (negative electrode surface capacity / positive electrode surface capacity) in this area and reducing the probability of lithium deposition in this area.

[0139] Continue to refer to Figure 6 and Figure 7 , in the embodiment of the present application, the total projected area of the plurality of convex parts 210 on the negative electrode sheet 100 is 60% - 90% of the area of the fourth paste layer 203, ensuring the supporting effect of the convex parts 210; if it is less than 60%, the supporting effect of the convex parts 210 will be affected; if it is higher than 90%, it will affect the normal operation of the paste.

[0140] At the same time, the winding core further includes an electrolyte doped with 1,4-dicyano-2-butene additive, and the content of the 1,4-dicyano-2-butene additive in the electrolyte accounts for 3% - 60%.

[0141] The electrolyte infiltrated between the positive and negative electrode sheets is also doped with a certain content of 1,4-dicyano-2-butene additive, so that the electrolyte can play a film-forming protection role for the convex part 210 of the positive electrode; preventing problems such as the crushing of the active particles of the convex part 210 of the positive electrode and even the cobalt precipitation, resulting in a reduction in the structural stability of the positive electrode active material and an accelerated attenuation of the battery capacity.

[0142] When the content of the 1,4-dicyano-2-butene additive is lower than this range, it cannot play a role in protecting the edge of the convex portion 210; when the content of the 1,4-dicyano-2-butene additive is higher than this range, it will affect the normal use of the electrolyte.

[0143] Reference Figure 10 , in the embodiment of the present application, each convex portion 210 has a center point in the projection on the first horizontal plane (the horizontal plane where the y-axis is located), and some center points are distributed on the second connection line 402. The second connection line 402 is parallel to the second direction (the y-axis shown in the figure); the projection of the groove 110 on the first horizontal plane is a rectangular surface 401, and the second connection line 402 is parallel to the rectangular surface 401.

[0144] When the second connection line is parallel to the rectangular surface, multiple convex portions located on the second connection line can be arranged opposite to a groove, making the processing of the convex portion and the groove more convenient.

[0145] Reference Figure 11 , in another embodiment of the present application, each convex portion 210 has a center point in the projection on the first horizontal plane (the horizontal plane where the y-axis is located), and some center points are distributed on the second connection line 402. The second connection line 402 is parallel to the second direction (the y-axis shown in the figure); the projection of the groove 110 on the first horizontal plane is a rectangular surface 401, and the second connection line 402 intersects the rectangular surface 401; when the second connection line 402 intersects the rectangular surface 401, the included angle between the second connection line 402 and the rectangular surface 401 is 0° to 45°.

[0146] When the second connection line intersects the rectangular surface, multiple convex portions located on the second connection line are respectively opposite to different grooves, and at the same time, the included angle between the second connection line and the rectangular surface is limited within the above range to ensure that each convex portion on the second connection line can be arranged opposite to the groove.

[0147] Reference Figure 7 , in the embodiment of the present application, the first paste layer 102 and / or the second paste layer 103 includes a silicon-carbon composite material and / or a silicon-oxygen composite material, and the mass ratio of the silicon-carbon composite material and / or the silicon-oxygen composite material in the first paste layer 102 and / or the second paste layer 103 is less than or equal to 50 wt%.

[0148] The silicon-carbon composite material includes a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon layer located on the surface of the porous carbon matrix. In the present invention, the silicon grains can be arranged in the pores of the porous carbon matrix by deposition. By arranging the silicon grains in the pores and forming a carbon layer on the surface of the porous carbon matrix, the carbon layer can be a shaped carbon or an amorphous carbon. When the silicon grains expand, sufficient expansion space can be provided inside the porous carbon matrix, thereby preventing the overall structure of the silicon-carbon composite material from deforming. Moreover, the carbon layer can restrain the outward expansion force of the porous carbon matrix during the silicon expansion process, ensuring the structural strength of the silicon-carbon material, thereby avoiding problems such as cracking, pulverization, and shedding of the negative electrode active layer, and improving the cycle performance and rate performance of the battery.

[0149] In a specific embodiment, the carbon layer includes openings corresponding to the pores of the porous carbon matrix. When openings are provided on the carbon layer, it can improve the wettability of the electrolyte to the negative electrode sheet and reduce the expansion performance of the silicon-based material, thereby reducing the impedance of the battery and improving the cycle performance and rate performance of the battery.

[0150] In a specific embodiment, the specific surface area of the silicon-carbon composite material and / or the silicon-oxygen composite material is 0.5 - 10 m 2 / g, for example, 0.5 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g or 10 m 2 / g, etc. When the specific surface area of the silicon-carbon composite material and / or the silicon-oxygen composite material is within the above range, the SEI film formed on the surface of the negative electrode active layer during the charge and discharge process is appropriate, which can reduce the impedance of the battery and improve the cycle performance and rate performance of the battery.

[0151] In a specific embodiment, the particle size Dv50 of the silicon-carbon composite material and / or the silicon-oxygen composite material is 6 - 15 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm. When the particle size Dv50 of the silicon-carbon composite material and / or the silicon-oxygen composite material is within the above range, the particle size Dv50 of the silicon-carbon composite material is appropriate. When the particle size is too small, it is easy to increase the specific surface area of the silicon particles, resulting in an increase in side reactions. At the same time, when the particle size is too large, it is easy for the silicon particles to expand too much, resulting in clogging of the pores of the porous carbon matrix and affecting the wettability of the electrolyte. Therefore, it can improve the cycle performance and rate performance of the battery.

[0152] In a specific embodiment, the powder resistivity of the silicon-carbon composite material and / or the silicon-oxygen composite material is 0.1-1000 Ω·cm, for example, 0.1Ω·cm, 0.5Ω·cm, 1Ω·cm, 5Ω·cm, 10Ω·cm, 50Ω·cm, 100Ω·cm, 200Ω·cm, 300Ω·cm, 400Ω·cm, 500Ω·cm, 600Ω·cm, 700Ω·cm, 800Ω·cm, 900Ω·cm or 1000Ω·cm. When the powder resistivity of the silicon-carbon composite material and / or the silicon-oxygen composite material is within the above range, the conductivity of the silicon-carbon composite material and / or the silicon-oxygen composite material is high, which can improve the conductivity of the negative electrode active layer, thereby improving the cycle performance and rate performance of the battery.

[0153] In a specific embodiment, the silicon content in the silicon-carbon composite material and / or the silicon-oxygen composite material is 30-75%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%, etc. When the silicon content in the silicon-carbon composite material is within the above range, it is possible to avoid excessive silicon content in the silicon-carbon composite material, which leads to excessive expansion of the silicon-carbon composite material and deformation of the overall structure of the silicon-carbon composite material, thereby avoiding cracking and pulverization of the negative electrode active layer, ensuring the energy of the silicon-carbon composite material, and improving the cycle performance and rate performance of the battery.

[0154] The third surface 2011 of the positive current collector 201 is the inner surface of the positive electrode, and the corresponding first surface 1011 of the negative current collector 101 is the outer surface of the negative electrode. Since the outer surface of the negative electrode in the arc area expands greatly, and the silicon-carbon composite material of the negative electrode itself expands greatly, on this basis, the groove 110 on the outer surface of the negative electrode corresponds to the concave portion of the inner surface of the positive electrode, which can provide space for the negative electrode silicon-doped active layer on the outer surface of the negative electrode to fully expand, and the concave portion on the inner surface of the positive electrode provides avoidance for the expansion of the outer surface of the negative electrode, thereby not affecting the depth of the convex portion 210 of the positive electrode, thereby ensuring the normal supporting function of the convex portion 210 of the positive electrode.

[0155] An embodiment of the present application also provides a battery, which includes the winding core described above.

[0156] In summary, the embodiment of the present application provides a core and a battery. The core includes a negative electrode sheet 100 and a positive electrode sheet 200 stacked on top of each other, and the polarities of the negative electrode sheet 100 and the positive electrode sheet 200 are opposite; the negative electrode sheet 100 includes a negative electrode current collector 101, the negative electrode current collector 101 has opposite first surface 1011 and second surface 1012 along the first direction (the z-axis shown in the figure), a first coating layer 102 is provided on the first surface 1011, and a second coating layer 103 is provided on the second surface 1012; a plurality of grooves 110 extending along the second direction (the y-axis shown in the figure) are provided on the first coating layer 102, and the centers of adjacent two grooves 110 are spaced apart by a first distance S along the third direction; the positive electrode sheet 200 has a plurality of convex portions 210 and concave portions oppositely arranged with the convex portions 210, and the grooves 110 are oppositely arranged with the convex portions 210; the size of the projection of the convex portion 210 on the electrode sheet is a first width R1, and the first width R1 is greater than the first distance S.

[0157] In the core provided by the embodiment of the present application, by providing the convex portions 210 and the concave portions oppositely arranged with the convex portions 210 on the positive electrode sheet 200, the micro-spacing between the negative electrode sheet 100, the separator and the positive electrode sheet 200 is increased. The convex portions provide support for the contact of the separator, so that there is a certain support between the negative electrode sheet 100 and the positive electrode sheet 200. These micro-spacings form a space for accommodating the electrolyte, so that the electrolyte has sufficient infiltration amount for the electrode sheet, avoiding the abnormal situation of insufficient electrolyte between the electrode sheet and the separator, poor infiltration or even lithium deposition on the negative electrode sheet caused by the interlayer extrusion of the electrode sheet, and ensuring that the electrolyte has sufficient infiltration amount.

[0158] At the same time, the core is provided with grooves 110 facing the convex portions 210 on the negative electrode sheet 100 to provide an expansion space for the expansion of the negative electrode sheet, thereby slowing down the situation of extrusion deformation of the positive electrode convex portions or deformation of the negative electrode grooves caused by the expansion of the negative electrode sheet during hot pressing formation or battery charge and discharge processes, ensuring the structural strength of the protrusions and grooves and the interfacial bonding strength between the electrode sheet and the separator, and enabling it to stably play a supporting role for the separator. At the same time, the sufficient expansion space can also prevent the negative electrode sheet from extruding the separator during the expansion process, causing the separator to deform.

[0159] Furthermore, when the convex portion 210 faces the groove 110, it prevents the convex portion 210 from being embedded into the groove 110 of the negative electrode, which is beneficial to the formation of the SEI film on the protruding portion of the positive electrode, thereby effectively protecting the convex portion 210 of the positive electrode and preventing problems such as the crushing of the active particles of the convex portion 210 of the positive electrode and even cobalt precipitation, resulting in a decrease in the structural stability of the positive electrode active material and an accelerated attenuation of the battery capacity.

[0160] In this specification, the embodiments or examples are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0161] It should be noted that phrases such as "an embodiment", "embodiments", "exemplary embodiments", "some embodiments", etc. mentioned in the specification indicate that the described embodiments may include specific features, structures, or characteristics, but not necessarily every embodiment includes such specific features, structures, or characteristics. In addition, such phrases do not necessarily refer to the same embodiment. Moreover, when combining specific features, structures, or characteristics with an embodiment, it is within the knowledge scope of those skilled in the art to implement such features, structures, or characteristics in combination with other embodiments, whether explicitly or implicitly described.

[0162] Generally speaking, terms should be understood at least partially by their usage in the context. For example, at least partially according to the context, the term "one or more" used in the text can be used to describe any feature, structure, or characteristic in a singular sense, or can be used to describe a combination of features, structures, or characteristics in a plural sense. Similarly, at least partially according to the context, terms such as "a" or "the" can also be understood to convey a singular usage or a plural usage.

[0163] It should be easily understood that the terms "on", "above", and "over" in this disclosure should be interpreted in the broadest manner, so that "on" not only means "directly on something", but also includes the meaning of "on something" with intermediate features or layers therebetween, and "above" or "over" not only includes the meaning of "above" or "over something", but may also include the meaning of "above" or "over something" with no intermediate features or layers therebetween (i.e., directly on something).

[0164] In addition, for the convenience of description, spatial relative terms such as "below", "beneath", "under", "above", "over", etc. may be used in the text to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatial relative terms are intended to include different orientations of the device in use or operation in addition to the orientation shown in the drawings. The device may have other orientations (rotated 90 degrees or in other orientations), and the spatial relative descriptive terms used in the text can be correspondingly interpreted as well.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A winding core, characterized in that: The winding core includes a straight area and corner areas located at opposite ends of the straight area, and further includes: A negative electrode sheet and a positive electrode sheet are stacked; The negative electrode sheet comprises a negative electrode current collector, wherein the negative electrode current collector has a first surface and a second surface opposite to each other along a first direction, wherein the first surface is provided with a first paste layer, and the second surface is provided with a second paste layer; The first paste layer is provided with a plurality of grooves, and the centers of two adjacent grooves are spaced a first distance apart; The positive electrode sheet is provided with a plurality of convex portions and concave portions corresponding to the convex portions, and the surface where the convex portions of the positive electrode sheet are located and the surface where the concave portions of the negative electrode sheet are located are arranged opposite to each other; Along the width direction of the groove, the vertical projection size of the protrusion in the thickness direction of the negative electrode sheet is greater than the first distance; The first surface and the second surface of the negative electrode sheet are respectively provided with a plurality of grooves; The convex part and the concave part are arranged opposite to each other; the concave part and the concave part are arranged opposite to each other; Along the width direction of the groove, the projection size of the protrusion in the thickness direction of the negative electrode sheet is R1, the first distance is S, and R1 / S=1.02~8; The groove width is M, R1 / M=8~50; R1 = 0.3 mm ~ 8 mm; The groove width is M=30um~170um; The first distance is S=0.5mm~3mm; The winding core also includes an electrolyte doped with 1,4-dicyano-2-butene, and the content of the 1,4-dicyano-2-butene additive in the electrolyte is 0.05% to 3%.

2. The winding core according to claim 1, characterized in that: The first paste layer and / or the second paste layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the mass proportion of the silicon-carbon composite material and / or the silicon-oxygen composite material in the first paste layer and / or the second paste layer is less than or equal to 50wt%.

3. The winding core according to claim 1, characterized in that: The positive electrode sheet comprises a positive electrode current collector, the positive electrode current collector has a third surface and a fourth surface opposite to each other along the first direction, the third surface is provided with a third paste layer, and the fourth surface is provided with a fourth paste layer; The negative electrode sheet and the positive electrode sheet are wound around a first central plane, the surface of the positive electrode current collector facing the first central plane is the third surface, and the surface of the positive electrode current collector away from the first central plane is the fourth surface; the third surface is arranged opposite to the first surface, and the fourth surface is arranged opposite to the second surface; The convex portion protrudes from the third paste layer toward the fourth paste layer.

4. The winding core according to claim 3, characterized in that: The total projection area of ​​the plurality of protrusions on the negative electrode sheet is 60% to 90% of the area of ​​the fourth paste layer.

5. The winding core according to claim 3, characterized in that: The projection of the protrusion on the negative electrode sheet may be in the shape of a circle, a semicircle, an ellipse, a plum blossom, a polygon, a rhombus, a capsule or an island.

6. The winding core according to claim 5, characterized in that: The positive electrode sheet comprises an upper surface and a lower surface which are arranged opposite to each other, and the convex portion is formed by protruding outward from the upper surface of the positive electrode sheet; The convex portion includes a protruding portion and a root portion connecting the protruding portion and the upper surface; The raised portion is an arc-shaped surface, and / or The protrusion is connected to the upper surface via an arc-shaped edge surface.

7. The winding core according to claim 6, characterized in that: A line connecting the root and the vertex of the raised portion is a first line, an angle between the first line and the upper surface is a first angle, and the first angle is 3° to 45°.

8. The winding core according to claim 3, characterized in that: The winding core has a first thickness H1 in the corner area, and the winding core has a second thickness H2 in the straight area. The first thickness H1 and the second thickness H2 have the following relationship: H1 / (H2 / 2)=1.05~1.

5.

9. The winding core according to claim 6, characterized in that: The center distance between the vertical projections of two adjacent protrusions in the thickness direction of the negative electrode sheet is D1=1 mm~6 mm; and / or In the first direction, the root portion and the vertex of the protrusion portion have a vertical distance, and the vertical distance is H3=3um~80um.

10. The winding core according to claim 9, characterized in that: In the corner area, the vertical distance from the apex of the convexity of the innermost circle of the winding core to the root of the convexity is a first vertical distance, and the vertical distance from the apex of the convexity of the outermost circle of the winding core to the root of the convexity is a second vertical distance, and the first vertical distance is greater than the second vertical distance.

11. The winding core according to claim 1, characterized in that: In the first direction, the groove has a groove depth, and the groove depth is T=10um~60um.

12. The winding core according to claim 7, characterized in that: The projection of each of the protrusions on the negative electrode sheet has a center point, and some of the center points are distributed on the second connecting line; The projection of the groove on the negative electrode current collector is a rectangular surface, and the second connecting line is parallel to or intersects with the rectangular surface; When the second connecting line intersects the rectangular surface, an angle between the second connecting line and the rectangular surface is 0° to 45°.

13. A battery, characterized in that: The winding core comprises the winding core according to any one of claims 1 to 12.

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