Winding core and battery

Abstract

The application provides a winding core and a battery, relates to the technical field of batteries, and the winding core comprises a positive electrode sheet, a negative electrode sheet and a diaphragm between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet comprises a current collector, a first active layer on a first surface of the current collector and a second active layer on a second surface of the current collector, the second direction is perpendicular to the first direction, the first end of the first active layer exceeds the first end of the second active layer, the part of the first end of the first active layer exceeding the first end of the second active layer is a single-face area of the negative electrode sheet, the single-face area is provided with a recessed area, the recessed area comprises a recessed structure recessed in the direction from the second surface of the current collector to the first surface, and the recessed structure comprises a recess on the second surface. The winding core can avoid the first active layer of the single-face area from falling off the current collector, improve the liquid retention amount between layers of the winding core, and improve the cycle performance of the winding core.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a winding core and a battery. Background Technology

[0002] Because of its simple technology and low manufacturing cost, the wound lithium-ion battery is the mainstream structure for lithium-ion batteries.

[0003] The core of a wound lithium-ion battery generally includes a positive electrode sheet, a negative electrode sheet, and a separator. The negative electrode sheet includes an active layer and a current collector. The active layer in the negative electrode sheet has a single-sided region and a double-sided region. The current collector in the single-sided region is only provided on one surface in the thickness direction.

[0004] However, in the aforementioned related technologies, the active layer on one side of the negative electrode sheet is prone to powder shedding and falling off from the current collector, affecting the performance of the core. Summary of the Invention

[0005] This application provides a core and a battery to solve the technical problem in the above-mentioned related technologies where the active layer on a single side of the negative electrode sheet is prone to powder shedding and falling off from the current collector, affecting the performance of the core.

[0006] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0007] A first aspect of this application provides a wound core, which includes: a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet;

[0008] The negative electrode includes:

[0009] The current collector includes a first surface and a second surface disposed opposite to each other along a first direction;

[0010] The first active layer located on the first side of the current collector and the second active layer located on the second side of the current collector, wherein, along the second direction, the first end of the first active layer extends beyond the first end of the second active layer, and the second direction is perpendicular to the first direction; the portion of the first active layer extending beyond the first end of the second active layer constitutes a single-sided region of the negative electrode sheet.

[0011] The single-sided area has a recessed region, and the recessed region includes a recessed structure formed by recessing from the second surface of the current collector toward the first surface;

[0012] The recessed structure includes a recess located on the second surface.

[0013] This application provides a winding core. By extending the first active layer on the first surface of the current collector beyond the first active layer on the second surface of the current collector, a single-sided region is formed on the negative electrode sheet. A recessed region is formed on the current collector corresponding to the single-sided region, and the recessed structure within the recessed region is formed from the second surface of the current collector toward the first surface, thereby forming a recess on the second surface of the current collector. This improves the adhesion strength and connection stability between the first active layer in the single-sided region and the current collector, and reduces the amount of powder falling off the first active layer in the single-sided region from the current collector during the winding process. This reduces the probability of particles falling from the negative electrode's single-sided area moving to the positive electrode and causing self-discharge, thus preventing the risk of excessively high K values ​​and ensuring a lower K value level for the battery cell. Furthermore, in the later stages of cycling, the graphite, silicon-carbon composite material, or silicon-oxygen composite material in the negative electrode undergoes multiple expansions and contractions. By forming a recessed area in the corresponding current collector of the single-sided area, it can be ensured that the first active layer of the single-sided area of ​​the negative electrode will not develop cracks or deformations in the active material, ensuring uniform insertion and extraction of lithium ions in the negative electrode, reducing the growth of polarization in the core's negative electrode, and lowering the risk of lithium plating.

[0014] Furthermore, the single-sided area exhibits internal stress oriented towards the current collector. During rolling or winding, the single-sided area of ​​the negative electrode sheet tends to shrink and curl. If the recess is located on the first active layer, meaning the first active layer is under stress, this shrinkage problem will be exacerbated, potentially leading to short circuits due to shrinkage and folding. By creating a recessed area on the current collector corresponding to the single-sided area, and ensuring that the recessed structure within the recessed area forms from the second side of the current collector towards the first side, the shrinkage and folding problem of the single-sided area can be mitigated to some extent.

[0015] Furthermore, if a recessed structure is formed from the first active layer towards the current collector, creating pits on the first active layer, uneven stress on one side can easily lead to powder shedding during pit formation. Moreover, it can lengthen the lithium-ion transport path between the bottom wall of the recessed structure within the first active layer and the positive electrode active layer on the positive electrode sheet, thus increasing the risk of new lithium plating. By creating a recessed area on the current collector corresponding to the one-sided area, powder shedding can be avoided, and the risk of new lithium plating can be prevented.

[0016] In one possible implementation, the recess includes an inner recess located at the center of the recess and a protrusion located on the outer edge of the inner recess.

[0017] In one possible implementation, the distance from the bottom wall of the concave portion to the second surface of the current collector is L1, wherein L1 satisfies 1μm≤L1≤30μm;

[0018] And / or, the distance from the vertex of the protrusion to the second surface is L2, wherein L2 satisfies 1μm≤L2≤30μm.

[0019] In one possible implementation, the recessed structure further includes a protrusion located on the first surface of the current collector, the protrusion and the recess being correspondingly provided.

[0020] In one possible implementation, the surface of the first active layer of the single-sided region facing away from the current collector has a flat portion and a protrusion corresponding to the protrusion.

[0021] In one possible implementation, from the winding direction of the core, the single-sided area of ​​the negative electrode sheet includes a first bent section, a first straight section, a second bent section, and a second straight section, wherein the recessed areas of the first straight section and the recessed areas of the second straight section are arranged opposite to each other.

[0022] In one possible implementation, the first bent segment does not have the recessed area.

[0023] In one possible implementation, the single-sided area of ​​the negative electrode sheet further includes an extension portion located near the center of the core in the first bent section, a portion of which overlaps with a portion of the first straight section.

[0024] In one possible implementation, the negative electrode further includes a carbon coating layer located between the current collector and the first active layer, wherein the sum of the thicknesses of the current collector and the carbon coating layer is less than the depth of the recess in the current collector.

[0025] In one possible implementation, at least the first active layer of the single-sided region has a plurality of dot-shaped or line-shaped grooves;

[0026] And / or, the second active layer has a plurality of dot-shaped or line-shaped grooves.

[0027] In one possible implementation, the projection of the dotted or linear grooves in the first direction does not overlap with the orthographic projection of the recess of the current collector.

[0028] In one possible implementation, the depth of the groove is L3, where L3 satisfies 3μm≤L3≤30μm;

[0029] And / or, the width of the groove is L4, wherein L4 satisfies 40μm≤L4≤200μm;

[0030] And / or, the distance between two adjacent grooves is L5, wherein L5 satisfies 0.5mm≤L5≤10mm.

[0031] In one possible implementation, the diaphragm includes a base membrane, an adhesive layer on one side of the base membrane, and a ceramic layer on the other side of the base membrane.

[0032] The adhesive layer and the negative electrode are disposed opposite to each other, and the ceramic layer and the positive electrode are disposed opposite to each other.

[0033] In one possible implementation, the adhesive layer comprises at least one of aqueous polyvinylidene fluoride and aqueous polymethyl methacrylate, polyacrylic acid, polytetrafluoroethylene, epoxy resin, chloroprene rubber, and methyl methacrylate.

[0034] In one possible implementation, along the first direction, the area of ​​the recessed region is Sy, and the surface area of ​​the first active layer of the single-sided region is Sd, wherein Sy and Sd satisfy: 0.5≤Sy / Sd≤0.98;

[0035] And / or, along the first direction, the area of ​​the orthographic projection of the recess onto the plane containing the second surface is Sa, wherein Sa satisfies 0.2 mm. 2 ≤Sa≤10mm 2 ;

[0036] And / or, the sum of the areas of the orthographic projections of each of the said recesses onto the plane containing the second surface is Sta, and Sta and Sy satisfy that Sta / Sy≤20%;

[0037] And / or, the density of the recesses within the recessed region is ρ, wherein ρ satisfies 10 / cm². 2 ≤ρ≤100 pieces / cm 2 .

[0038] In one possible implementation, along the first direction, the vertical distance from the vertex of the protrusion to the first active layer is Hd, and the thickness of the straight portion of the first active layer is Hj. Hd and Hj satisfy 2%≤Hd / Hj≤50%.

[0039] In one possible implementation, Hj satisfies 30um≤Hj≤200um;

[0040] And / or, the Hd satisfies 2um≤Hd≤100um;

[0041] And / or, along the first direction, the distance from the vertex of the protrusion to the vertex of the protrusion is Hy, and Hy and Hj satisfy 80%≤Hy / Hj≤98%.

[0042] In one possible implementation, along the second direction, the distance between the recessed region and the first end of the second active layer is Ly, wherein Ly satisfies Ly≥1mm;

[0043] And / or, along the second direction, the distance between the recessed region and the first end of the first active layer is Lt, wherein Lt satisfies Lt≥0.5mm.

[0044] And / or, the negative electrode includes a first side and a second side opposite each other along a third direction, the third direction being perpendicular to the second direction;

[0045] Along the third direction, the distance from the concave region to the first side is La, and the distance from the concave region to the second side is Lb. La satisfies that La≥1.0mm; Lb satisfies that Lb≥1.0mm.

[0046] And / or, along the first direction, the thickness of the non-recessed region on the current collector is H, wherein H satisfies 3.5um≤H≤15um.

[0047] In one possible implementation, along the first direction, the shape of the orthographic projection of the protrusion onto the surface of the first active layer includes at least one of triangle, quadrilateral, pentagon, hexagon, heptagon, circle, ellipse, capsule, linear, and petal shapes.

[0048] A second aspect of this application provides a battery comprising a winding core as described above. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A schematic diagram of the structure of a winding core provided in this application embodiment;

[0051] Figure 2 A schematic diagram of the current collector side of a single-sided region on a negative electrode sheet, provided for an embodiment of this application;

[0052] Figure 3 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of this application;

[0053] Figure 4 This application provides a schematic diagram of the structure of a single-sided region on a negative electrode sheet according to an embodiment of the present application.

[0054] Figure 5 for Figure 3 A top view of the negative electrode plate in the process;

[0055] Figure 6 This application provides another schematic diagram of the structure of a single-sided region on a negative electrode sheet according to an embodiment of the present application.

[0056] Figure 7 for Figure 3 A bottom-view diagram of the negative electrode plate;

[0057] Figure 8 A table showing the relevant performance parameters of the core obtained as the parameters of the concave and convex portions change, provided in the embodiments of this application.

[0058] Explanation of reference numerals in the attached figures:

[0059] 10 - Core; 20 - Negative electrode sheet; 30 - Positive electrode sheet; 40 - Separator;

[0060] 31 - First side; 32 - Second side;

[0061] 100-current collector;

[0062] 110 - First side; 120 - Second side;

[0063] 200 - First active layer;

[0064] 210 - Protrusion; 220 - Straight section; 230 - Groove;

[0065] 300 - Second active layer;

[0066] 400 - Single-sided area;

[0067] 410 - Depressed area; 420 - First bend; 430 - First straight section;

[0068] 440 - Second bend; 450 - Second straight section; 460 - Extension;

[0069] 500-Concave structure;

[0070] 510-concave part; 520-convex part;

[0071] 511 - Concave portion; 512 - Protrusion;

[0072] 600 - Carbon coating layer. Detailed Implementation

[0073] As described in the background section, in related technologies, the active layer in the negative electrode sheet of the winding core is prone to detach from the current collector, affecting the performance of the winding core.

[0074] The reason for this problem is that in conventional wound lithium-ion batteries, the negative electrode sheet has a single-sided and double-sided active layer. In the single-sided area, the active layer is only set on one surface of the current collector, while in the double-sided area, it is set on both surfaces in the thickness direction of the current collector. This results in a certain difference in the thickness direction of the negative electrode sheet, that is, the thickness of the negative electrode sheet in the double-sided area is greater than that in the single-sided area. Due to the thickness difference of the negative electrode sheet, during the conventional rolling stage, the width of the roll gap is adapted according to the thickness of the double-sided area, which causes the problem of compaction difference between the single-sided and double-sided areas. That is, the single-sided area is not compacted enough compared to the double-sided area, and the adhesion between the active material layer and the current collector in the single-sided area is lower. During the transportation or winding of the negative electrode sheet into a core, problems such as demolding and powder shedding may occur in the single-sided area due to the lower compaction. The active layer in the single-sided area falls off the current collector, affecting the performance of the core.

[0075] Furthermore, due to the low bonding strength between the single-sided area and the current collector, the adhesion between the negative electrode active material layer and the current collector decreases during the repeated charging and discharging of the negative electrode sheet in the later stages of battery cycling. Cracks easily appear in the negative electrode active material layer, and the contact area between the negative electrode active material layer and the current collector gradually decreases. This leads to an increase in electronic impedance between the negative electrode active material layer and the negative electrode current collector, reducing the dynamics on the negative electrode side. Consequently, the lithium intercalation capability of the negative electrode sheet is further reduced, and lithium dendrites are easily deposited on the surface of the negative electrode active material layer, which in turn causes the problem of lithium plating on the negative electrode, thus reducing the performance of the battery core and the battery.

[0076] To address the aforementioned technical problems, this application provides a core and a battery. By extending the first active layer on the first surface of the current collector beyond the first active layer on the second surface of the current collector, a single-sided region is formed on the negative electrode. A recessed region is formed on the current collector corresponding to the single-sided region, and the recessed structure within the recessed region is formed from the second surface of the current collector towards the first surface, thus forming a recess on the second surface of the current collector. Firstly, this improves the electrolyte retention in the area where the single-sided region of the negative electrode is located, i.e., the inner layer region of the core, meaning the recessed structure can store electrolyte, thereby avoiding lithium plating problems caused by insufficient electrolyte. Secondly, it increases the electrolyte retention between the first active layer of the single-sided region and the current collector. The bonding strength and connection stability between the particles are improved, reducing the probability of the first active layer in the single-sided area falling off the current collector during the winding process. This prevents particles falling off the single-sided area of ​​the negative electrode from moving to the positive electrode and causing self-discharge, which could lead to an excessively high K value. This ensures that the K value level of the cell is reduced. Furthermore, in the later stages of cycling, the graphite, silicon-carbon composite material, or silicon-oxygen composite material in the negative electrode undergoes multiple expansions and contractions. By forming a recessed area in the corresponding current collector of the single-sided area, it can be ensured that the first active layer of the single-sided area of ​​the negative electrode will not develop cracks or deformations. This ensures the uniform insertion and extraction of lithium ions in the negative electrode, reduces the growth of polarization in the wound core, and reduces the risk of lithium plating.

[0077] Furthermore, the single-sided area exhibits internal stress oriented towards the current collector. During rolling or winding, the single-sided area of ​​the negative electrode sheet tends to shrink and curl. If the recess is located on the first active layer, meaning the first active layer is under stress, this shrinkage problem will be exacerbated, potentially leading to short circuits due to shrinkage and folding. By creating a recessed area on the current collector corresponding to the single-sided area, and ensuring that the recessed structure within the recessed area forms from the second side of the current collector towards the first side, the shrinkage and folding problem of the single-sided area can be mitigated to some extent.

[0078] Furthermore, if a recessed structure is formed from the first active layer towards the current collector, creating pits on the first active layer, uneven stress on one side can easily lead to powder shedding during pit formation. Moreover, it can lengthen the lithium-ion transport path between the bottom wall of the recessed structure within the first active layer and the positive electrode active layer on the positive electrode sheet, thus increasing the risk of new lithium plating. By creating a recessed area on the current collector corresponding to the one-sided area, powder shedding can be avoided, and the risk of new lithium plating can be prevented.

[0079] To make the above-mentioned objectives, features, and advantages of the embodiments of this application more apparent and understandable, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0080] refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 The first aspect of this application provides a core 10, which may include a positive electrode 30, a negative electrode 20, and a separator 40 located between the positive electrode 30 and the negative electrode 20.

[0081] The negative electrode 20 may include a current collector 100, a first active layer 200, and a second active layer 300. The current collector 100 may include components along a first direction (e.g., ...). Figure 4 The first active layer 200 is located on the first surface 110 of the current collector 100 (in the Y direction) and the second active layer 300 is located on the second surface 120 of the current collector 100.

[0082] Along the second direction (e.g.) Figure 3 In the X direction), the first end of the first active layer 200 extends beyond the first end of the second active layer 300. The portion of the first active layer 200 that extends beyond the first end of the second active layer 300 is the single-sided region 400 of the negative electrode 20. The first active layer 200 is only provided on the current collector 100 in the single-sided region 400, and the second active layer 300 is not provided.

[0083] It is understandable that the beginning ends of the first active layer 200 and the second active layer 300 are positioned close to the winding beginning end of the core 10. The area where the orthographic projections of the first active layer 200 and the second active layer 300 overlap in the first direction is a double-sided area.

[0084] The single-sided area 400 has a recessed area 410. The recessed area 410 may include a recessed structure 500 formed by the recess of the second surface 120 of the current collector 100 toward the first surface 110. The recessed structure 500 may include a recess 510 located on the second surface 120.

[0085] In some embodiments, the recessed structure 500 can be formed by roll forming. When the recessed structure 500 is formed on the current collector 100 by roll forming, the negative electrode 20 can form a protrusion 512 on the first surface 110 of the current collector 100 under the action of the roll pressure. Alternatively, a protrusion 210 can be formed on the surface of the first active layer 200 facing away from the current collector 100. Alternatively, when the roll pressure is small, the protrusion 210 may not be formed on the surface of the first active layer 200 facing away from the current collector 100. In embodiments where the protrusion 210 is not formed on the surface of the first active layer 200 facing away from the current collector 100, the first active layer 200 of the negative electrode is located in the inner ring, the contact area between the first active layer 200 of the negative electrode and the separator is larger, the bonding interface is flatter, the interface performance is better, ensuring the adhesion between the negative electrode and the separator, and ensuring that the negative electrode in the inner ring is not prone to lithium deposition.

[0086] This application provides a core 10, which forms a single-sided region 400 on a negative electrode 20 by extending the first end of the first active layer 200 on the first surface 110 of the current collector 100 beyond the first end of the second active layer 300 on the second surface 120 of the current collector 100. A recessed region 410 is provided on the current collector 100 corresponding to the single-sided region 400, and a recessed structure 500 in the recessed region 410 is formed from the second surface 120 of the current collector 100 toward the first surface 110 to form a recess 510 on the second surface 120 of the current collector 100. First, it can improve the electrolyte retention in the area where the single-sided region of the negative electrode is located, i.e., the inner layer region of the core, i.e., the recessed structure can be used to store electrolyte, thereby avoiding the lithium plating problem caused by insufficient electrolyte; in addition, This improves the adhesion strength and connection stability between the first active layer 200 of the single-sided region 400 and the current collector 100, reducing the probability of the first active layer 200 in the single-sided region 400 falling off the current collector 100. This prevents particles falling from the negative electrode single-sided region from moving to the positive electrode and causing self-discharge, resulting in an excessively high K value, thus ensuring that the K value level of the cell is reduced. Furthermore, in the later stages of cycling, the graphite, silicon-carbon composite material, or silicon-oxygen composite material in the negative electrode undergoes multiple expansions and contractions. By forming a recessed area in the corresponding current collector of the single-sided region, it can be ensured that the first active layer of the single-sided region of the negative electrode will not have cracks or deformations in the active material, ensuring the uniform insertion and extraction of lithium ions in the negative electrode, reducing the growth of polarization in the core negative electrode, and reducing the risk of lithium plating.

[0087] Furthermore, the single-sided area exhibits internal stress oriented towards the current collector. During rolling or winding, the single-sided area of ​​the negative electrode sheet tends to shrink and curl. If the recess is located on the first active layer, meaning the first active layer is under stress, this shrinkage problem will be exacerbated, potentially leading to short circuits due to shrinkage and folding. By creating a recessed area on the current collector corresponding to the single-sided area, and ensuring that the recessed structure within the recessed area forms from the second side of the current collector towards the first side, the shrinkage and folding problem of the single-sided area can be mitigated to some extent.

[0088] Furthermore, if a recessed structure is formed from the first active layer towards the current collector, creating pits on the first active layer, uneven stress on one side can easily lead to powder shedding during pit formation. Moreover, it can lengthen the lithium-ion transport path between the bottom wall of the recessed structure within the first active layer and the positive electrode active layer on the positive electrode sheet, thus increasing the risk of new lithium plating. By creating a recessed area on the current collector corresponding to the one-sided area, powder shedding can be avoided, and the risk of new lithium plating can be prevented.

[0089] refer to Figure 4 In some embodiments, the recess 510 may include an inner recess 511 located at the center of the recess 510 and a protrusion 512 located on the outer edge of the inner recess 511. The inner recess 511 is recessed from the second surface 120 of the current collector 100 toward the first surface 110, and the protrusion 512 protrudes from the second surface 120 of the current collector 100 toward the first surface 110.

[0090] In this way, in the single-sided area 400 of the core 10, the single-sided area 400 is in a wound state. Not only can the concave part 511 increase the interlayer gap of the inner ring of the core 10, but the protrusion 512 can also increase the interlayer gap while playing a supporting role between the layers, so that the electrolyte can flow into the interlayer gap, thereby improving the liquid storage capacity between the layers.

[0091] refer to Figure 4 In some embodiments, the distance from the bottom wall of the recess 511 to the second surface 120 of the current collector 100 is L1 (e.g., Figure 4 In the given L1, L1 satisfies 1μm ≤ L1 ≤ 30μm. For example, L1 can be one of 1μm, 3μm, 5μm, 6μm, 10μm, 12μm, 18μm, 23μm, 25μm, and 29μm. Alternatively, L1 can be any value within the range of 5μm or greater and 30μm or less.

[0092] This improves the bonding strength and connection stability between the first active layer 200 and the current collector 100 in the single-sided region 400, reducing the likelihood of the first active layer 200 in the single-sided region 400 detaching from the current collector 100. It avoids the problem of insufficient bonding strength between the first active layer 200 and the current collector 100 due to an excessively small L1, and also avoids the current collector 100 breaking due to excessive deformation during the formation of the recessed structure 500 or during winding due to an excessively large L1. Thus, while preventing the first active layer 200 in the single-sided region 400 from detaching from the current collector 100, it ensures the integrity of the negative electrode 20 and prevents it from breaking.

[0093] refer to Figure 4 In some embodiments, the distance from the vertex of protrusion 512 to the second surface 120 is L2 (e.g., Figure 4 In the given L2, L2 satisfies 1μm ≤ L2 ≤ 30μm. For example, L2 can be one of 1μm, 3μm, 5μm, 6μm, 10μm, 12μm, 18μm, 23μm, 25μm, and 29μm. Alternatively, L2 can be any value within the range of 5μm or greater and 30μm or less.

[0094] In this way, the protrusion 512 can ensure the interlayer support function and increase the interlayer gap, thereby improving the liquid storage capacity of the interlayer. This avoids the failure of L2 to provide support and increase the interlayer gap due to its small size, and also avoids the current collector 100 from cracking due to excessive deformation caused by L2 due to its large size during the formation of the protrusion 512 or during the winding process. Thus, it can both provide support and increase the liquid storage capacity, and prevent the current collector 100 from cracking.

[0095] refer to Figure 4 In some embodiments, the recessed structure 500 may further include a protrusion 520 located on the first surface 110 of the current collector 100, with the protrusion 520 and the recess 510 being correspondingly provided.

[0096] In some embodiments, when the recessed structure 500 is formed by rolling, the first surface 110 of the current collector 100 will also be deformed accordingly to form a protrusion 520 on the first surface 110 of the current collector 100. In this way, the protrusion 520 can be embedded into the surface of the first active layer 200 of the single-sided region 400 facing the current collector 100, thereby improving the peel force level between the negative electrode sheet 20 and the separator 40, and increasing the bonding strength and connection stability between the current collector 100 and the first active layer 200, avoiding the problem of the first active layer 200 of the single-sided region 400 falling off the current collector 100, and improving the quality of the core 10.

[0097] refer to Figure 1In some embodiments, from the winding direction of the core 10, the single-sided area 400 of the negative electrode sheet 20 may include a first bent section 420, a first straight section 430, a second bent section 440 and a second straight section 450, and the recessed area 410 of the first straight section 430 and the recessed area 410 of the second straight section 450 are arranged opposite to each other.

[0098] It is understandable that the recesses 510 in the recessed region 410 of the first straight section 430 and the recesses 510 in the recessed region 410 of the second straight section 450 can be correspondingly provided. Furthermore, if the recessed structure 500 has a protrusion 512, then the protrusions 520 in the recessed region 410 of the first straight section 430 and the protrusions 520 in the recessed region 410 of the second straight section 450 can also be correspondingly provided.

[0099] In this way, by arranging the recessed areas 410 of the first straight section 430 and the second straight section 450 opposite to each other, the gap between the inner layers of the core 10 can be increased, which facilitates the storage of electrolyte in the gap, improves the electrolyte storage capacity of the core 10, prevents lithium plating from occurring on the inner negative electrode sheet 20, and improves the performance of the core 10.

[0100] refer to Figure 1 In some embodiments, the first bending section 420 does not have a recessed region 410. Along the winding direction of the negative electrode 20, the first bending section 420 of the single-sided region 400 can be spaced apart from the recessed region 410 on the single-sided region 400. Since the electrode sheet in the inner layer of the core 10 is subjected to the greatest stress, especially the bending section, by not providing a recessed region 410 in the first bending section 420, the first bending section 420 can be free of a recessed structure 500. This prevents the negative electrode 20 with a recessed structure 500 from detaching from the current collector 100 due to excessive compressive force during winding.

[0101] refer to Figure 1 In some embodiments, the single-sided region 400 of the negative electrode 20 may also include an extension portion 460 located near the center of the core 10 in the first bending section 420, and a portion of the extension portion 460 overlaps with a portion of the first straight section 430.

[0102] In this way, by overlapping a portion of the epitaxial portion 460 of the negative electrode 20 with a portion of the first straight section 430, and by partially overlapping the first active material layer of the epitaxial portion 460 and the first straight section 430, a paste is formed, which can compensate for the thickness difference caused by the positive electrode 30 not being completely close to the arc area of ​​the core 10 (i.e., the projection of the positive electrode head and the epitaxial portion 460 does not overlap) at the position corresponding to the epitaxial portion 460, the flatness of the battery in the thickness direction can be improved and the energy density of the battery can be increased.

[0103] refer to Figure 4 In some embodiments, the negative electrode 20 may further include a carbon coating layer 600 located between the current collector 100 and the first active layer 200, wherein the sum of the thicknesses of the current collector 100 and the carbon coating layer 600 is less than the depth of the recess 510 of the current collector 100. It is understood that the carbon coating layer 600 is used to improve the conductivity between the first active layer 200 and the current collector 100.

[0104] In this way, by making the sum of the thicknesses of the current collector 100 and the carbon coating layer 600 less than the depth of the recess 510 of the current collector 100, the thickness of the carbon coating layer 600 in the recessed region 410 is less than the thickness of the carbon coating layer 600 in other regions. This allows the particles in the carbon coating layer 600 to be embedded in the first active layer 200, increasing the contact area between the carbon coating layer 600 and the first active layer 200, and further improving the adhesion between the first active layer 200 and the current collector 100.

[0105] refer to Figure 4 and Figure 5 In some embodiments, at least one side region 400 of the first active layer 200 has a plurality of dot-shaped or line-shaped grooves 230. The plurality of dot-shaped or line-shaped grooves 230 can be disposed on the surface of the first active layer 200 facing away from the current collector 100. The plurality of dot-shaped grooves 230 can be arranged at intervals, or the plurality of line-shaped grooves 230 can be arranged at intervals.

[0106] In some embodiments, the dot-shaped or line-shaped grooves 230 can be disposed not only on the first active layer 200 of the single-sided region 400, but also at positions on the first active layer 200 that are not in the single-sided region 400, or the dot-shaped or line-shaped grooves 230 can be disposed on both the first active layer 200 of the single-sided region 400 and the first active layer 200 of the non-single-sided region 400.

[0107] In this way, by providing dotted or linear grooves 230 on the first active layer 200 with at least one side area 400, electrolyte can flow into the dotted or linear grooves 230, thereby increasing the liquid storage capacity of the dotted or linear grooves 230 on the first active layer 200, and thus increasing the liquid storage capacity of the core 10.

[0108] refer to Figure 7In some embodiments, the second active layer 300 may also have multiple dot-shaped or line-shaped grooves 230. These dot-shaped or line-shaped grooves 230 can be disposed not only on the first active layer 200 but also on the second active layer 300. The dot-shaped or line-shaped grooves 230 can be disposed on the surface of the second active layer 300 facing away from the current collector 100, allowing electrolyte to flow into the dot-shaped or line-shaped grooves 230 on the second active layer 300. This increases the electrolyte storage capacity at the locations corresponding to the dot-shaped or line-shaped grooves 230 on the second active layer 300, thereby further increasing the electrolyte storage capacity of the core 10.

[0109] In some embodiments, the dotted or linear grooves 230 on the second active layer 300 are distributed in the same way as the dotted or linear grooves 230 on the first active layer 200.

[0110] refer to Figure 4 In some embodiments, the dotted or linear grooves 230 are in the first direction (e.g., Figure 4 The projection of the current collector 100 in the Y direction does not overlap with the orthographic projection of the concave portion 510 in the Y direction.

[0111] In this way, in the first direction, by ensuring that the orthogonal projections of the dotted or linear grooves 230 and the recesses 510 on the current collector 100 do not overlap, it is possible to avoid the dotted or linear grooves 230 and the recesses 510 on the current collector 100 from acting repeatedly. For example, during the rolling process of the single-sided area 400 of the negative electrode sheet 20 on which the dotted or linear grooves 230 are formed on the first active layer 200, if a recessed structure 500 is formed in the area corresponding to the dotted or linear grooves 230, it will cause the first active layer 200 at the dotted or linear grooves 230 to fall off the current collector 100 and lose powder.

[0112] refer to Figure 4 In some embodiments, the depth of the groove 230 is L3 (e.g., Figure 4 In the groove 230, the depth L3 satisfies 3μm ≤ L3 ≤ 30μm. For example, the depth L3 of the groove 230 can be one of 3μm, 6μm, 11μm, 15μm, 17μm, 21μm, 24μm, 26μm, and 29μm. Alternatively, the depth L3 of the groove 230 can be any value within the range of greater than or equal to 3μm and less than or equal to 30μm.

[0113] Thus, if the depth of the groove 230 is too small, it cannot effectively improve the liquid retention capacity; if the depth of the groove 230 is too large, it will affect the current collector 100 during the formation of the groove 230, causing the current collector 100 to be damaged. By keeping L3 within the range of 3μm≤L3≤30μm, it is possible to ensure the liquid storage capacity of the groove 230 while avoiding damage to the current collector 100 caused by the excessive depth of the groove 230, and further avoid problems such as strip breakage or pinholes in the negative electrode 20 caused by damage to the current collector 100.

[0114] In some embodiments, the width of the groove 230 is L4 (e.g., Figure 4 In the groove 230, the width L4 satisfies 40μm≤L4≤200μm. For example, the width L4 of the groove 230 can be one of 40μm, 50μm, 60μm, 80μm, 100μm, 120μm, 140μm, 150μm, 170μm and 190μm, or the width L4 of the groove 230 can be any value within the range of 40μm≤L4≤200μm.

[0115] This avoids the inability to effectively improve the liquid retention capacity due to an excessively small groove width 230, and also avoids lithium plating caused by insufficient lithium intercalation capacity of the first active layer 200 due to an excessively large groove width. Therefore, by keeping L4 within the range of 40μm≤L4≤200μm, it is possible to ensure the liquid retention capacity of the negative electrode 20, as well as its lithium intercalation capacity and reduce lithium plating problems.

[0116] In some embodiments, the distance between two adjacent grooves 230 is L5 (e.g., Figure 4 L5 satisfies the condition 0.5mm ≤ L5 ≤ 10mm. For example, the distance L5 between two adjacent grooves 230 can be one of 0.5mm, 1mm, 2mm, 4mm, 6mm, 8mm, and 9mm. Alternatively, the distance L5 between two adjacent grooves 230 can be any value within the range of 0.5mm ≤ L5 ≤ 10mm.

[0117] In this way, by keeping the distance L5 between two adjacent grooves 230 within the range of 0.5mm≤L5≤10mm, the liquid retention capacity of the entire area where the groove 230 is located, as well as the position adjacent to the groove 230, can be increased. However, if the distance is too large, the liquid absorption capacity of the groove 230 and the position near the groove 230 will be increased, but the position far away from the groove 230 will not be able to obtain the liquid retention improvement, which may cause lithium plating problems due to lack of liquid in the position far away from the groove 230.

[0118] refer to Figure 3 In some embodiments, along the second direction (e.g.) Figure 3In the X direction), the distance between the recessed region 410 and the beginning of the second active layer 300 is Ly (e.g., in the X direction). Figure 3 In the given condition, Ly satisfies the condition that Ly ≥ 1 mm. For example, Ly can be one of 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, and 5 mm, or any point value greater than or equal to 1 mm.

[0119] If the recessed area 410 is located at the boundary between the single-sided area 400 and the double-sided area, the core 10 will be subjected to compressive force during the hot pressing process after winding because the boundary between the single-sided area 400 and the double-sided area is in a bending section. If the recessed structure 500 is set at this position, it will increase the risk of powder shedding and breakage of the negative electrode sheet 20 in the boundary between the single-sided area 400 and the double-sided area. By making the distance Ly between the recessed area 410 and the first end of the second active layer 300 ≥ 1mm, the probability of the recessed structure 500 being in the bending section can be reduced, and the risk of powder shedding and breakage in the boundary between the single-sided area 400 and the double-sided area due to the recessed structure 500 being in the bending section can be avoided.

[0120] refer to Figure 3 In some embodiments, along the second direction (e.g.) Figure 3 In the X direction), the distance between the recessed region 410 and the beginning of the first active layer 200 is Lt (e.g., in the X direction). Figure 3 The distance Lt between the recessed region 410 and the first end of the first active layer 200 can be one of 0.5mm, 1mm, 1.2mm, 1.6mm, 2.3mm, 2.8mm, 3.7mm, 4.5mm and 5mm.

[0121] In this way, by ensuring that the distance Lt between the recessed region 410 and the first end of the first active layer 200 is ≥0.5mm, the risk of breakage of the current collector 100 due to the distance between the recessed region 410 and the first end of the first active layer 200 being too close can be avoided.

[0122] refer to Figure 4 In some embodiments, along the first direction (e.g.) Figure 4 In the Y direction, the thickness of the non-recessed region 410 on the current collector 100 is H, where H satisfies 3.5um ≤ H ≤ 15um. For example, H can be one of 4um, 5um, 6um, 7um, 8um, 10um, 12um, 13um, and 14um. Alternatively, H can be any value within the range of 3.5um ≤ H ≤ 15um.

[0123] In this way, by limiting the thickness H of the non-recessed region 410 on the current collector 100 to the range of 3.5um≤H≤15um, the risk of the current collector 100 easily breaking when a deep recessed structure 500 is formed on the current collector 100 due to an excessively small H value can be avoided. Furthermore, the problem of material waste and increased manufacturing cost of the core 10 due to an excessively large H value can be avoided.

[0124] refer to Figure 1 In some embodiments, the separator 40 may include a base membrane, an adhesive layer on one side of the base membrane, and a ceramic layer on the other side of the base membrane. The adhesive layer and the negative electrode 20 are disposed opposite to each other, and the ceramic layer and the positive electrode 30 are disposed opposite to each other.

[0125] In this way, by setting a ceramic layer on the base membrane and setting the ceramic layer and the positive electrode 30 in a corresponding manner, the ceramic layer is used to reduce the thermal shrinkage of the separator 40 and improve the thermal stability of the separator 40.

[0126] In some embodiments, the adhesive layer may include at least one of aqueous polyvinylidene fluoride and aqueous polymethyl methacrylate, polyacrylic acid, polytetrafluoroethylene, epoxy resin, chloroprene rubber, and methyl methacrylate.

[0127] In this way, compared with oil-based materials, the aqueous diaphragm 40 is formed by using an adhesive layer of aqueous material. Aqueous materials are more hydrophobic, making the aqueous diaphragm 40 drier. Moreover, the coating of the oil-based diaphragm 40 is fully coated, resulting in a larger contact area between the oil-based diaphragm 40 and the roller. The adhesive layer of aqueous material reduces the coefficient of friction of the diaphragm 40. Furthermore, the aqueous material is arranged in an array, resulting in a smaller contact area with the electrode, thereby reducing electrostatic effects.

[0128] refer to Figure 7 In some embodiments, along the first direction, the area of ​​the recessed region 410 is Sy, and the surface area of ​​the first active layer 200 of the single-sided region 400 is Sd, where Sy and Sd satisfy: 0.5 ≤ Sy / Sd ≤ 0.98. For example, the value of Sy / Sd can be one of 0.5, 0.57, 0.61, 0.68, 0.73, 0.85, 0.91, and 0.96. Alternatively, the value of Sy / Sd can be any value within the range of 0.5 ≤ Sy / Sd ≤ 0.98.

[0129] It is understandable that the length of the recessed region 410 can be the distance between the recessed structure 500 closest to the winding head end of the single-sided region 400 and the recessed structure 500 closest to the winding tail end of the current collector 100, and the width of the recessed region 410 is the distance between the two recessed structures 500 that are furthest apart in the width direction of the current collector 100.

[0130] By ensuring the Sy / Sd value is within the range of 0.5 ≤ Sy / Sd ≤ 0.98, the adhesion between the current collector 100 and the first active layer 200 within the single-sided region 400 can be improved due to an excessively small Sy / Sd ratio. Furthermore, the risk of breakage due to excessive rolling deformation at the edge of the first active layer 200 in the single-sided region 400 can be avoided if the Sy / Sd ratio is too large. Thus, while maintaining the connection stability and adhesion strength between the current collector 100 and the first active layer 200 in the single-sided region 400, breakage of the negative electrode 20 can be prevented.

[0131] refer to Figure 7 In some embodiments, along the first direction, the area of ​​the orthographic projection of the recess 510 onto the plane containing the second surface 120 is Sa, where Sa satisfies 0.2 mm. 2 ≤Sa≤10mm 2 For example, the area Sa of the orthographic projection of the recess 510 onto the plane containing the second surface 120 can be 0.3 mm. 2 0.9mm 2 1.3mm 2 1.8mm 2 2.5mm 2 3.7mm 2 4mm 2 6mm 2 7mm 2 8.3mm 2 and 9.5mm 2 One of them. Alternatively, the area Sa of the orthographic projection of the recess 510 onto the plane containing the second surface 120 can be 0.2 mm. 2 ≤Sa≤10mm 2 The value at any point within the range.

[0132] Thus, by making the area Sa of the orthographic projection of the recess 510 onto the plane containing the second surface 120 0.2 mm 2 ≤Sa≤10mm 2 Within the range, it can avoid the problem that the current collector 100 cannot improve the adhesion between the current collector 100 and the first active layer 200 due to the recess 510 being too small, and it can also avoid the problem that the current collector 100 in the single-sided area 400 has poor flatness due to the recess 510 being too large.

[0133] refer to Figure 7 In some embodiments, the sum of the areas of the orthographic projections of each recess 510 onto the plane containing the second surface 120 is Sta, and Sta and Sy satisfy 0 ≤ Sta / Sy ≤ 20%. For example, the ratio of Sta / Sy can be one of 5%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, 17%, and 18%.

[0134] In this way, by controlling the ratio of the sum of the areas Sta of the orthographic projections of each recess 510 onto the plane containing the second surface 120 to the area Sy of the recessed region 410 within the range of 0≤Sta / Sy≤20%, it is possible to avoid poor surface flatness of the current collector 100 due to the excessively large area of ​​the recess 510, and to avoid the problem of the current collector 100 breaking due to the excessively large area of ​​the recess 510.

[0135] refer to Figure 7 In some embodiments, the density of the recesses 510 within the recessed region 410 is ρ, where ρ satisfies 10 recesses / cm². 2 ≤ρ≤100 pieces / cm 2 For example, the density ρ of the recesses 510 within the recessed region 410 can be 10 recesses / cm³. 2 20 pieces / cm 2 30 pieces / cm 2 40 pieces / cm 2 60 pieces / cm 2 70 pieces / cm 2 and 90 / cm 2 One of them.

[0136] Thus, by setting the density ρ of the recesses 510 within the recessed region 410 to 10 per cm³, 2 ≤ρ≤100 pieces / cm 2 Within this range, it avoids the situation where the density of the recess 510 is too low, which would prevent it from failing to improve the adhesion and connection stability between the current collector 100 and the first active layer 200. It also avoids the situation where the density of the recess 510 is too high, which would result in poor surface flatness of the current collector 100 and increase the risk of breakage. Thus, while ensuring the adhesion and connection stability between the current collector 100 and the first active layer 200, it is possible to prevent the negative electrode 20 from breaking.

[0137] refer to Figure 6 In some embodiments, the first active layer 200 of the single-sided region 400 has a flat portion 220 and a protrusion 210 corresponding to the protrusion 520 on the side surface opposite to the current collector 100.

[0138] When the recessed structure 500 is formed by roller pressing, the deformation of the current collector 100 can be increased by increasing the roller pressure, so that the surface of the first active layer 200 facing away from the current collector 100 can form a protrusion 210 corresponding to the protrusion 520. The protrusion 210 and the protrusion 512 have the same protrusion direction.

[0139] In this way, by forming a protrusion 210 on the side surface of the first active layer 200 facing away from the current collector 100, the depth of the protrusion 520 on the current collector 100 embedded in the first active layer 200 can be increased, which can further improve the connection strength and connection stability between the current collector 100 and the first active layer 200, and prevent the first active layer 200 of the single-sided area 400 from falling off the current collector 100 and shedding powder.

[0140] The protrusion 210 can also increase the interlayer gap between the first active layer 200 on the negative electrode 20 and the separator 40, thereby improving the liquid storage capacity of the core 10.

[0141] refer to Figure 6 In some embodiments, along the first direction, the vertical distance from the apex of the protrusion 210 to the first active layer 200 is Hd (e.g., Figure 6 (Hd), the thickness Hj of the straight portion 220 of the first active layer 200 (e.g., Hd), Figure 6 In the equation (Hj), Hd and Hj satisfy 2% ≤ Hd / Hj ≤ 50%. For example, Hd / Hj can be one of 2%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, and 45%. Alternatively, Hd / Hj can be any value within the range of 2% ≤ Hd / Hj ≤ 50%.

[0142] If the Hd / Hj ratio is too small, the height of the protrusion 210 will be too small. The protrusion 210 will then gradually recover during the hot-pressing stage of the core 10 and the cell cycling stage, reducing its effectiveness in improving the adhesion between the first active layer 200 and the current collector 100 and the separator 40, as well as its effect on improving the electrolyte storage capacity. If the Hd / Hj ratio is too large, the height of the protrusion 210 will be too large, leading to a decrease in the surface flatness of the first active layer 200, and further reducing the flatness of the negative electrode 20. This will create gaps between the negative electrode 20 and the separator 40 that cannot be pressed together, exacerbating the lithium plating problem.

[0143] Therefore, by controlling the Hd / Hj ratio within the range of 2%≤Hd / Hj≤50%, it is possible to ensure improved adhesion between the first active layer 200 and the current collector 100 and the separator 40, as well as improved liquid storage capacity. At the same time, it is also possible to avoid the problem of lithium plating being aggravated by the reduced surface flatness of the negative electrode 20, which would result in an unpressable gap area between the negative electrode 20 and the separator 40 in the area where the protrusion 210 is located.

[0144] refer to Figure 6In some embodiments, the thickness Hj of the flat portion 220 of the first active layer 200 satisfies 30µm ≤ Hj ≤ 200µm. For example, Hj can be one of 30µm, 50µm, 70µm, 90µm, 100µm, 130µm, 150µm, 160µm, 170µm, and 190µm. Alternatively, Hj can be any value within the range of 30µm ≤ Hj ≤ 200µm.

[0145] In this way, by limiting the thickness Hj of the flat portion 220 of the first active layer 200 to the range of 30um≤Hj≤200um, it is possible to ensure the capacitance of the core 10 while preventing the first active layer 200 from falling off the current collector 100 when the thickness of the first active layer 200 is too large.

[0146] refer to Figure 6 In some embodiments, the vertical distance Hd from the apex of the protrusion 210 to the first active layer 200 satisfies 2µm ≤ Hd ≤ 100µm. For example, the value of Hd can be one of 10µm, 13µm, 20µm, 30µm, 50µm, 70µm, 90µm, and 100µm. Alternatively, Hd can be any value within the range of 2µm ≤ Hd ≤ 100µm.

[0147] In this way, by limiting the vertical distance Hd from the apex of the protrusion 210 to the first active layer 200 to within the range of 2µm ≤ Hd ≤ 100µm, it is possible to avoid the protrusion 210 failing to improve the adhesion and connection stability between the first active layer 200 and the current collector 100, as well as the effect of improving the liquid storage capacity, due to an excessively small Hd height. It also avoids the surface flatness of the first active layer 200 being poor due to an excessively large Hd height, which would further reduce the surface flatness of the negative electrode 20, resulting in an uncompressible gap area between the negative electrode 20 and the separator 40 in the area where the protrusion 210 is located, thus worsening the lithium plating problem.

[0148] refer to Figure 6 In some embodiments, along the first direction (e.g.) Figure 6 In the Y direction), the distance from the vertex of protrusion 210 to the vertex of protrusion 520 is Hy (e.g., in the Y direction). Figure 6 The thickness Hj of Hy and the straight portion 220 of the first active layer 200 satisfies 80% ≤ Hy / Hj ≤ 98%. For example, the ratio of Hy / Hj can be one of 80%, 82%, 84%, 87%, 89%, 91%, 93%, 95%, 97%, and 98%. Alternatively, the ratio of Hy / Hj can be any value within the range of 80% ≤ Hy / Hj ≤ 98%.

[0149] In this way, by making the ratio of Hy / Hj less than 1, the thickness of the first active layer 200 at the protrusion 210 can be compressed relative to the thickness at the flat portion 220, thereby improving the adhesion between the first active layer 200 at the protrusion 210 and the current collector 100.

[0150] Furthermore, by limiting the Hy / Hj ratio to within the range of 80% ≤ Hy / Hj ≤ 98%, it is possible to avoid the problem that an excessively large Hy / Hj ratio would result in insufficient compression of the first active layer 200 at the protrusion 210, leading to lower adhesion between the first active layer 200 and the current collector 100. Conversely, it is also possible to avoid the problem that an excessively small Hy / Hj ratio would result in excessive compression of the first active layer 200 at the protrusion 210, leading to reduced porosity, decreased liquid retention in the single-sided area 400, or even crushing of the particles in the first active layer 200.

[0151] refer to Figure 7 In some embodiments, the negative electrode 20 may include a third direction (e.g., Figure 7 The first side 31 and the second side 32 (in the Z direction) are opposite each other, and the third direction is perpendicular to the second direction. The third direction can be the width direction of the negative electrode 20.

[0152] Along the third direction, the distance from the concave region 410 to the first side 31 is La (e.g., Figure 7 (La), the distance from the concave region 410 to the second side 32 is Lb (e.g., ... Figure 7 In the given condition, La satisfies the condition that La ≥ 1.0 mm, and Lb satisfies the condition that Lb ≥ 1.0 mm. The values ​​of La and Lb can be the same; for example, both La and Lb can be one of the following: 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, and 5 mm.

[0153] In this way, by making La≥1.0mm and Lb≥1.0mm, it is possible to avoid the recessed area 410 being too close to the opposite first side 31 and second side 32 in the width direction of the negative electrode 20, thereby avoiding the risk of the first side 31 and second side 32 being broken due to tension during the winding stage.

[0154] refer to Figure 7 In some embodiments, the shape of the orthographic projection of the protrusion 210 onto the surface of the first active layer 200 along the first direction may include at least one of the following: triangle, quadrilateral, pentagon, hexagon, heptagon, circle, ellipse, capsule, line, and petal.

[0155] In some embodiments, the materials of the first active layer 200 and the second active layer 300 may be selected from at least one of lithium metal, artificial graphite, natural graphite, hard carbon, silicon-based materials, tin alloys, etc. The binder used in the negative electrode 20 may include at least one of styrene-butadiene rubber, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, and polyacrylate. The conductive agent used in the negative electrode 20 may include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon black, graphene, and acetylene black.

[0156] In some embodiments, the material of the positive electrode active layer in the positive electrode 30 may include at least one of lithium cobalt oxide, lithium iron phosphate, lithium nickel oxide, and lithium nickel cobalt manganese oxide. The binder used in the positive electrode 30 may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyamide. The conductive agent used in the positive electrode 30 may include at least one of conductive carbon black, acetylene black, single-arm carbon nanotubes, and multi-walled carbon nanotubes.

[0157] A second aspect of this application provides a battery that may include the winding core 10 as described above. By using the winding core 10, the adhesion between the first active layer 200 of the single-sided region 400 on the winding core 10 and the current collector 100 is improved, thereby avoiding the problem of powder shedding from the single-sided region 400 of the negative electrode sheet 20. This also avoids the increase in negative electrode impedance caused by powder shedding, reducing negative electrode kinetics and subsequently preventing lithium plating at the negative electrode, thus improving the overall performance of the battery.

[0158] refer to Figures 1 to 8 Based on the parameter characteristics of the negative electrode 20, the positive electrode 30, the negative electrode 20, and the core 10 are prepared, and the relevant performance parameters of the core 10 are detected. The specific preparation process is as follows.

[0159] Example 1

[0160] Preparation of negative electrode 20:

[0161] The active material graphite, the binder styrene-butadiene rubber, the dispersant lithium carboxymethyl cellulose, and the conductive agent multi-walled carbon nanotubes were added to deionized water in a mass ratio of 98.5:1.5:0.5:0.5. After high-speed stirring, a negative electrode slurry was formed. The negative electrode slurry was coated onto the surface of a 6µm thick copper foil using an extrusion coating machine. A 1µm thick carbon coating layer 600 was applied to both surfaces of the copper foil. After coating, the negative electrode sheet 20 was obtained by baking, rolling and slitting.

[0162] Negative electrode 20 single-sided region 400 recessed structure 500:

[0163] The negative electrode sheet 20 after roll pressing and slitting is placed on a special pressure plate. The pressure roller is made of stainless steel and has a pattern with a specific area, height and density. After the rolled negative electrode sheet 20 passes through the pressure plate and is positioned, the pressure plate presses down. After the pressure plate applies a certain pressure and time, a recessed area corresponding to the pattern on the pressure roller is formed on the single-sided area 400 of the current collector 100 of the negative electrode sheet 20. The parameters of the recessed part 510 of the recessed structure 500 in the recessed area 410 and the relevant parameters of the protrusion 210 on the first active layer 200 are shown in the table of Example 1.

[0164] A negative electrode 20, a separator 40, and a positive electrode 30 with a recessed structure 500 on one side 400 are wound in sequence to form a core 10. The core 10 is then subjected to processes such as hot pressing, encapsulation, drying, liquid injection, formation, air bag cutting, and sorting to obtain a lithium-ion battery.

[0165] In the negative electrode 20 of Example 1, the area Sa of the orthogonal projection of the single recess 510 of the single-sided region 400 to the plane containing the second surface 120 of the current collector 100 is 0.2 mm. 2 The ratio of the area Sy of the recessed region 410 to the surface area Sd of the first active layer 200 of the single-sided region 400, Sy / Sd, is 90%, and the density of the recesses 511 in the single-sided region 400 is 30 per cm³. 2 The ratio of the height of the protrusion 210 to the thickness of the first active layer 200 at the flat portion 220, Hd / Hj, is 0.2. The thickness Hy of the first active layer 200 at the protrusion 210 is 47 μm, and the thickness Hj at the flat portion 220 is 50 μm.

[0166] The following are some specific detection methods and steps for the relevant parameters.

[0167] 1. Loop testing method

[0168] The lithium-ion battery was charged using a 1C constant current and constant voltage charging method. The cutoff current during the constant voltage stage was 0.05C, and the discharge current was 0.5C. The test was conducted at room temperature of 25℃. The discharge capacity at the 1000th cycle and the discharge capacity at the 1st cycle, Q1000 / Q1, represent the capacity retention rate after 1000T cycles.

[0169] 2. Characterization of lithium plating in a 200T cycle

[0170] After fully charging the 200T cycle cell, remove it from the cabinet and disassemble it. Take the negative electrode single-sided area 400, gently peel off the separator 40, and observe the lithium plating on the negative electrode surface.

[0171] 3. Area measurement of the recess 510 of a single recessed structure 500

[0172] Using a 3D contour optical microscope with measurement function, the projected size of the concave portion 510 in the horizontal direction was measured at 100X magnification. Ten measurements were taken and the average value was taken as the area Sa of the concave portion 510.

[0173] 4. Density measurement of recess 510

[0174] Randomly select a 1cm×1cm area from the single-sided area 400 where there is a concave structure 500, calculate the number of concave parts 510 in the area, randomly select 5 times, and take the average value as the distribution density ρ of the concave parts 510.

[0175] 5. Height measurement of protrusion 210

[0176] Using a 3D contour optical microscope with measurement function, with the non-recessed area 410 as the horizontal plane, the height measurement function of the microscope is used to adjust the focus to the highest point of the protrusion 210 by adjusting the focus, and the average height of the 5 points is taken as the height Hd of the protrusion 210.

[0177] 6. Measurement of the thickness of the first active layer 200 at the protruding portion 210 and the thickness of the first active layer 200 at the non-protruding portion 210.

[0178] The recessed region 410 and the non-recessed region 410 of the single-sided region 400 of the negative electrode are selected and cut using an argon ion cutting device to expose the cross-sectional area of ​​the electrode sheet. The cut electrode sheet is observed using a SEM microscope and the thickest point of the corresponding area is measured, which is regarded as the thickness Hy of the first active layer 200 at the protrusion 210 and the thickness Hj of the first active layer 200 at the non-protrusion 210.

[0179] 7. The percentage of the concave area 410 to the single-sided area 400

[0180] The evenly distributed positions of the recessed structure 500 are regarded as recessed regions 410. The area of ​​the outer edge of the recessed region 410 is measured and regarded as the proportion Sy of the recessed region 410. The area Sd of the single-sided region 400 is measured. The ratio of Sy to Sd is regarded as the proportion of the recessed region 410 to the single-sided region 400.

[0181] 8. Single-sided area 400 diaphragm 40 peel strength

[0182] After the formed core 10 is discharged to the lower limit voltage, the battery is dissected. The single-sided area 400 of the negative electrode 20 with separator 40 is cut into strips with a size of 15mm×50mm using a ceramic knife. The tensile force between separator 40 and negative electrode is measured using a universal testing machine. The average value of the relatively stable area of ​​the curve is taken as the peel force of separator 40.

[0183] In Example 2, compared to Example 1, the area Sa of the orthographic projection of the single recess 510 of the single-sided area 400 to the plane containing the second surface 120 of the current collector 100 is 1 mm. 2 .

[0184] In Example 3, compared to Example 1, the area Sa of the orthographic projection of the single recess 510 of the single-sided area 400 onto the plane containing the second surface 120 of the current collector 100 is 10 mm. 2 .

[0185] In Example 4, compared to Example 1, the density of the recessed portion 511 in the single-sided area 400 is 10 particles / cm². 2 .

[0186] In Example 5, compared to Example 1, the density of the recessed portion 511 in the single-sided region 400 is 100 per cm². 2 .

[0187] In Example 6, compared with Example 1, the ratio of the height of the protrusion 210 to the thickness of the first active layer 200 at the flat portion 220, Hd / Hj, is 0.02.

[0188] In Example 7, compared with Example 1, the ratio of the height of the protrusion 210 to the thickness of the first active layer 200 at the flat portion 220, Hd / Hj, is 0.5.

[0189] In Example 8, compared with Example 1, the thickness Hy of the first active layer 200 at the protrusion 210 is 40 μm.

[0190] In Example 9, compared with Example 1, the thickness Hy of the first active layer 200 at the protrusion 210 is 49 μm.

[0191] In Example 10, compared with Example 1, the ratio of the area Sy of the recessed region 410 to the surface area Sd of the first active layer 200 of the single-sided region 400, Sy / Sd, is 50%.

[0192] In Example 11, compared with Example 1, the ratio of the area Sy of the recessed region 410 to the surface area Sd of the first active layer 200 of the single-sided region 400, Sy / Sd, is 98%.

[0193] Comparative Example 1, compared to Example 1, has an area Sa of 0.05 mm², which is the area of ​​the orthographic projection of the single recess 510 of the single-sided region 400 onto the plane containing the second surface 120 of the current collector 100. 2 .

[0194] Comparative Example 2, compared with Example 1, shows that the density of the recessed portion 511 in the single-sided region 400 is 200 per cm². 2 .

[0195] In Comparative Example 3, compared with Example 1, the ratio of the height of the protrusion 210 to the thickness of the first active layer 200 at the flat portion 220, Hd / Hj, is 0.8.

[0196] Comparative Example 4, compared with Example 1, has a thickness Hy of 35 μm in the first active layer 200 at the protrusion 210, and the ratio of the area Sy of the recessed region 410 to the surface area Sd of the first active layer 200 in the single-sided region 400, Sy / Sd, is 30%.

[0197] Comparative Example 5, compared with Example 1, has a ratio of the area Sy of the recessed region 410 to the surface area Sd of the first active layer 200 of the single-sided region 400, Sy / Sd is 30%.

[0198] Comparative Example 6, compared with Example 1, does not have a recessed area 410 and a recessed structure 500 provided in the single-sided area 400.

[0199] By testing the above 11 embodiments and 6 comparative examples, the peel force of the diaphragm 40 on one side of the core 10, the cycle retention rate (1000T), and the lithium plating were obtained. Figure 8 The following conclusions can be drawn from the information in the table.

[0200] As can be seen from Examples 1, 2, 3 and Comparative Example 1, increasing the area of ​​a single recess 510 increases the peeling force of the diaphragm 40 and improves the cycle performance. If the area of ​​the recess 510 is too small, it cannot increase the adhesion and connection stability between the first active layer 200 and the current collector 100, which can easily cause the first active layer 200 in the single-sided area 400 on the negative electrode 20 to fall off the current collector 100 and shed powder.

[0201] As can be seen from Examples 1, 4, 5 and Comparative Example 2, increasing the density of the recess 510 improves the peeling force of the separator 40 and the cycle performance. However, if the density of the recess 510 is too high, the surface flatness of the current collector 100 will be poor. The density of the recess 510 will also increase the risk of breakage of the current collector 100. The first active layer 200 of the single-sided region 400 is also more likely to fall off from the current collector 100, which will lead to a deterioration of lithium plating.

[0202] As can be seen from Examples 1, 6, 7 and Comparative Example 3, increasing the height of the protrusion 210 has little impact on the peeling force and cycle performance. However, if the height of the protrusion 210 is too large, it will seriously affect the appearance of the electrode, resulting in poor surface flatness of the first active layer 200, causing the negative electrode 20 to crack, and the lithium plating will be more serious.

[0203] As can be seen from Examples 1, 8, 9 and Comparative Example 4, when the first active layer 200 at the protrusion 210 is thinned twice, the position transmission path at the protrusion 210 in the single-sided area 400 is reduced, which improves the cycle retention rate to a certain extent. However, excessive compression will cause the current collector 100 and the first active layer 200 to break, affecting the cycle performance.

[0204] As can be seen from Examples 1, 10, 11 and Comparative Example 5, increasing the area of ​​the recessed region 410 in the single-sided region 400 can improve the peeling force between the negative electrode 20 and the separator 40 and improve cycle performance. However, an excessively low proportion of the recessed region 410 has no significant effect on improving lithium plating.

[0205] As can be seen from Example 1 and Comparative Example 6, adding a recessed region 410 and a recessed structure 500 to the single-sided region 400 can significantly improve the peeling force of the separator 40, and improve lithium plating and cycle performance.

[0206] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0207] It should be noted that phrases such as "in specific implementations," "in some embodiments," "in this embodiment," and "exemplarily" in the specification indicate that the described embodiments may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0208] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "a" or "the" can also be understood to convey either singular or plural usage.

[0209] It should be readily understood that “on,” “above,” and “on top of” in this disclosure should be interpreted in the broadest manner, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on something” but also “on something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0210] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90 degrees or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0211] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A type of winding core, characterized in that, include: A positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode; The negative electrode includes: The current collector includes a first surface and a second surface disposed opposite to each other along a first direction; The first active layer located on the first side of the current collector and the second active layer located on the second side of the current collector, with the first end of the first active layer extending beyond the first end of the second active layer along a second direction, the second direction being perpendicular to the first direction; the portion of the first active layer extending beyond the first end of the second active layer constitutes a single-sided region of the negative electrode sheet; The single-sided area has a recessed region, and the recessed region includes a recessed structure formed by recessing from the second surface of the current collector toward the first surface; The recessed structure includes a recess located on the second surface; The recess includes an inner recess located at the center of the recess and a protrusion located on the outer edge of the inner recess. The distance from the bottom wall of the concave portion to the second surface of the current collector is L1, and L1 satisfies 1μm≤L1≤30μm; And / or, the distance from the vertex of the protrusion to the second surface is L2, wherein L2 satisfies 1μm≤L2≤30μm.

2. The winding core according to claim 1, characterized in that, The recessed structure also includes a protrusion located on the first surface of the current collector, and the protrusion and the recess are correspondingly provided.

3. The winding core according to claim 2, characterized in that, The surface of the first active layer of the single-sided region facing away from the current collector has a flat portion and a protrusion corresponding to the protrusion.

4. The winding core according to claim 1, characterized in that, From the winding direction of the core, the single-sided area of ​​the negative electrode sheet includes a first bent section, a first straight section, a second bent section, and a second straight section, wherein the recessed areas of the first straight section and the recessed areas of the second straight section are arranged opposite to each other.

5. The winding core according to claim 4, characterized in that, The first bending segment does not have the aforementioned recessed area.

6. The winding core according to claim 4, characterized in that, The single-sided area of ​​the negative electrode sheet also includes an extension portion located near the center of the core in the first bent section, and a portion of the extension portion overlaps with a portion of the first straight section.

7. The winding core according to claim 1, characterized in that, At least the first active layer of the single-sided region has a plurality of dot-shaped or line-shaped grooves; And / or, the second active layer has a plurality of dot-shaped or line-shaped grooves.

8. The winding core according to claim 7, characterized in that, The projection of the dotted or linear grooves in the first direction does not overlap with the orthographic projection of the concave portion of the current collector.

9. The winding core according to claim 8, characterized in that, The depth of the groove is L3, and L3 satisfies 3μm≤L3≤30μm; And / or, the width of the groove is L4, wherein L4 satisfies 40μm≤L4≤200μm; And / or, the distance between two adjacent grooves is L5, wherein L5 satisfies 0.5mm≤L5≤10mm.

10. The winding core according to claim 1, characterized in that, The diaphragm includes a base membrane, an adhesive layer on one side of the base membrane, and a ceramic layer on the other side of the base membrane; The adhesive layer and the negative electrode are disposed opposite to each other, and the ceramic layer and the positive electrode are disposed opposite to each other.

11. The winding core according to claim 10, characterized in that, The adhesive layer includes at least one of aqueous polyvinylidene fluoride, aqueous polymethyl methacrylate, polyacrylic acid, polytetrafluoroethylene, epoxy resin, chloroprene rubber, and methyl methacrylate.

12. The winding core according to claim 1, characterized in that, Along the first direction, the area of ​​the recessed region is Sy, and the surface area of ​​the first active layer of the single-sided region is Sd. Sy and Sd satisfy: 0.5≤Sy / Sd≤0.98; And / or, along the first direction, the area of ​​the orthographic projection of the recess onto the plane containing the second surface is Sa, wherein Sa satisfies 0.2 mm. 2 ≤Sa≤10mm 2 ; And / or, the sum of the areas of the orthographic projections of each of the said recesses onto the plane containing the second surface is Sta, and Sta and Sy satisfy that Sta / Sy≤20%; And / or, the density of the recesses within the recessed region is ρ, wherein ρ satisfies 10 / cm². 2 ≤ρ≤100 pieces / cm 2 .

13. The winding core according to claim 3, characterized in that, Along the first direction, the vertical distance from the vertex of the protrusion to the first active layer is Hd, and the thickness of the straight portion of the first active layer is Hj. Hd and Hj satisfy 2%≤Hd / Hj≤50%.

14. The winding core according to claim 13, characterized in that, The Hj satisfies that 30μm≤Hj≤200μm; And / or, the Hd satisfies 2μm≤Hd≤100μm; And / or, along the first direction, the distance from the vertex of the protrusion to the vertex of the protrusion is Hy, and Hy and Hj satisfy 80%≤Hy / Hj≤98%.

15. The winding core according to claim 1, characterized in that, Along the second direction, the distance between the recessed region and the first end of the second active layer is Ly, wherein Ly satisfies Ly≥1mm; And / or, along the second direction, the distance between the recessed region and the first end of the first active layer is Lt, wherein Lt satisfies Lt≥0.5mm; And / or, the negative electrode includes a first side and a second side opposite each other along a third direction, the third direction being perpendicular to the second direction; Along the third direction, the distance from the recessed area to the first side is La, and the distance from the recessed area to the second side is Lb. La satisfies La≥1.0mm; Lb satisfies Lb≥1.0mm. And / or, along the first direction, the thickness of the non-recessed region on the current collector is H, wherein H satisfies 3.5μm≤H≤15μm.

16. The winding core according to claim 3, characterized in that, Along the first direction, the shape of the orthographic projection of the protrusion onto the surface of the first active layer includes at least one of the following: triangle, quadrilateral, pentagon, hexagon, heptagon, circle, ellipse, capsule, line, and petal.

17. A battery, characterized in that, Includes the core as described in any one of claims 1 to 16.

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