Roll core and battery

Abstract

The invention provides a roll core and a battery, and relates to the technical field of batteries, a positive plate, a diaphragm and a negative plate of the roll core are wound to form the roll core; the positive plate comprises a first surface and a second surface, the positive plate is provided with a plurality of convex parts and straight parts located between the adjacent convex parts, and the convex parts are formed by part of the positive plate protruding from the second surface to the first surface; the maximum distance between the vertex of the convex part and the plane where the first surface is located is h1; the thickness of the straight part on the positive plate is h; 5% < = h1 / h < = 30%; the negative plate comprises a negative current collector and a negative active layer located on the negative current collector, the negative active layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage content of silicon in the negative active layer is W1; 0.3 < = W1 / (h1 / h) < = 5. According to the roll core, the interlayer liquid storage space can be increased, the interlayer liquid retention capacity can be improved, and the attenuation of the battery capacity can be delayed.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a winding core and a battery. Background Art

[0002] Lithium-ion batteries (LIBs) are widely used in electronic devices due to their high specific energy density, wide temperature range and long cycle life. Among them, silicon-based negative electrode materials can be used as part of the negative electrode sheet in the core of some batteries. Silicon-based negative electrode materials are increasingly widely used in lithium-ion batteries due to their high lithium insertion capacity.

[0003] However, silicon-based materials have a volume expansion problem during the charging and discharging process. During the charging and discharging process, silicon and lithium will undergo an alloying reaction, and the volume of silicon will expand by 100% to 300%. This continuous shrinkage and expansion will intensify the extrusion between the battery core layers, resulting in insufficient electrolyte between the layers and poor infiltration, which will cause the battery capacity to decay rapidly. Summary of the invention

[0004] The embodiments of the present application provide a winding core and a battery, which are used to solve the technical problem in the above-mentioned related technologies that insufficient electrolyte between layers and poor wetting will cause rapid attenuation of battery capacity.

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

[0006] A first aspect of an embodiment of the present application provides a winding core, comprising: a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet, the separator, and the negative electrode sheet are wound to form the winding core;

[0007] A positive electrode sheet, comprising a first surface and a second surface opposite to each other along a first direction, the positive electrode sheet being provided with a plurality of convex portions and a straight portion located between adjacent convex portions, the convex portion being formed by a portion of the positive electrode sheet protruding from the second surface toward the first surface;

[0008] The maximum distance from the vertex of the convex portion to the plane where the first surface is located is h1;

[0009] Along the first direction, the thickness of the straight portion on the positive electrode sheet is h;

[0010] The h and h1 satisfy the following conditions: 5%≤h1 / h≤30%;

[0011] A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer located on the positive electrode current collector, wherein the negative electrode active layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage content of silicon in the negative electrode active layer is W1;

[0012] The W1, h1 and h satisfy the following: 0.3≤W1 / (h1 / h)≤5.

[0013] Based on the above technical solution, the present application can also be improved as follows.

[0014] In a possible implementation, W1 satisfies: 3%≤W1≤50%, and / or,

[0015] The h1 satisfies: 3μm≤h1≤50μm.

[0016] In a possible implementation, the positive electrode sheet includes a winding head end and a winding tail end opposite to each other along the length direction;

[0017] The protrusions are arranged at intervals along the direction from the winding head end to the winding tail end; the maximum distance from the vertex of the protrusion arranged near the winding head end to the plane where the first surface is located is greater than the maximum distance from the vertex of the protrusion arranged near the winding tail end to the plane where the first surface is located.

[0018] In a possible implementation, the positive electrode sheet includes a plurality of curved segments and a plurality of straight segments;

[0019] Along the direction from the winding head end to the winding tail end, the straight sections and the curved sections are arranged alternately;

[0020] The convex portion is provided on both the curved section and the straight section;

[0021] The maximum distance from the outer surface of the convex portion on the straight section to the first surface is h11;

[0022] The maximum distance from the outer surface of the convex portion on the curved segment to the first surface is h12;

[0023] The h11 and h12 satisfy: h11<h12.

[0024] In a possible implementation, the relationship between h11 and h12 satisfies: 0.1≤h11 / h12≤0.9;

[0025] And / or, h11 satisfies: 3μm≤h11≤30μm;

[0026] And / or, h12 satisfies: 5μm≤h12≤50μm.

[0027] In a possible implementation, the area on the second surface of the positive electrode sheet corresponding to the convex portion is a concave portion;

[0028] The outer surface of the convex portion is a first arc surface, and the inner surface of the concave portion is a second arc surface;

[0029] The curvature radius of the first curved surface is R1, and the curvature radius of the second curved surface is R2;

[0030] The R1 and the R2 satisfy: R1>R2.

[0031] In a possible implementation, along the radial direction of the first arc surface, the distance between the vertex of the convex portion and the vertex of the concave portion is less than or equal to the thickness of the straight portion on the positive electrode sheet.

[0032] In a possible implementation, the R1, the R2 and the thickness h of the positive electrode sheet satisfy: R1-R2≤h;

[0033] And / or, R1 satisfies: 0.5 mm ≤ R1 ≤ 8 mm;

[0034] And / or, R2 satisfies: 0.5mm≤R2≤8mm;

[0035] And / or, R1 and R2 satisfy the following relationship: 1.01≤R1 / R2≤1.1.

[0036] In a possible implementation, along the first direction, the circumscribed lines of the orthographic projections of three adjacent convex portions that are not on the same straight line together form a circumscribed triangle, and the area of ​​the circumscribed triangle is S3;

[0037] Along the first direction, the intangent lines of the orthographic projections of three adjacent convex portions that are not on the same straight line together form an inscribed triangle, and the area of ​​the inscribed triangle is S4;

[0038] The distance between the centers of the orthographic projections of two adjacent convex portions to the surface where the first surface is located is L1;

[0039] The S3, the S4, the R1 and the L1 satisfy the following: 3πR1²≤S3-S4≤1.3L1².

[0040] In a possible implementation manner, the relationship between h1 and the radius R1 of the first arc surface satisfies: 0.02≤h1 / 2R1≤0.1.

[0041] In a possible implementation manner, along the first direction, a projection of the inner concave portion onto the surface where the second surface is located is a circle, an ellipse, or a polygon;

[0042] Along the first direction, a projection of the convex portion onto the surface where the first surface is located is circular, elliptical or polygonal.

[0043] In a possible implementation, along the first direction, a distance between centers of orthographic projections of two adjacent convex portions onto the surface where the first surface is located is L1;

[0044] The shortest distance between two adjacent convex portions is L2;

[0045] The relationship between L1 and L2 satisfies: 1.05≤L1 / L2≤3.

[0046] In a possible implementation, L1 satisfies: 3 mm ≤ L1 ≤ 10 mm;

[0047] And / or, L2 satisfies: 0.5mm≤L2≤8mm.

[0048] In a possible implementation, the convex portion includes an abutment portion;

[0049] The surface of the abutting portion facing the diaphragm is a third curved surface.

[0050] In a possible implementation, the convex portion further includes a supporting portion located between the straight portion of the positive electrode sheet and the abutting portion;

[0051] The support portion is disposed around the outer periphery of the abutment portion;

[0052] The support portion is a fourth arc surface;

[0053] Along the first direction, the maximum distance from the outer surface of the abutting portion to the plane where the second surface is located is R3; the radius of curvature of the fourth arc surface is R4;

[0054] The R3 and the R4 satisfy: R3<R4.

[0055] In a possible implementation, R3 and R4 satisfy the following relationship: R3<1 / 5R4.

[0056] In a possible implementation, the surface area of ​​the outer surface of the convex portion is Q1, and the surface area of ​​the inner surface of the concave portion is Q2;

[0057] Q1 and Q2 satisfy the following: 1.02≤Q1 / Q2≤1.21; and / or along the first direction, the surface area of ​​the orthographic projection of the convex portion to the surface where the first surface is located is S1; the surface area of ​​the orthographic projection of the concave portion to the plane where the second surface is located is S2;

[0058] The S1 and S2 satisfy the following: 1.02≤S1 / S2≤1.21.

[0059] In a possible implementation, an angle between a tangent line on an outer surface of the convex portion connected to the first surface and the first surface is α1;

[0060] The α1 satisfies: 0°≤α1≤90°, and / or the angle between the tangent line on the inner surface of the inner concave portion and the second surface and the second surface is α2;

[0061] The α2 satisfies: 0°≤α2≤90°.

[0062] In a possible implementation manner, the α1 and the α2 satisfy: 0°≤α1-α2≤40°.

[0063] In a possible implementation, along the first direction, the total area of ​​the orthographic projections of the convex portions on the first surface is S5, and the surface area of ​​the first surface of the positive electrode sheet is S;

[0064] The S5 and the S satisfy: 0.2≤S5 / S≤0.95.

[0065] In a possible implementation, the positive electrode sheet includes a plurality of convex portion groups; each of the convex portion groups includes a plurality of convex portions;

[0066] Two adjacent convex portion groups are arranged at intervals along a second direction, and the second direction is a length extension direction of the positive electrode sheet; the positive electrode sheet includes a tab connection groove;

[0067] Along the second direction, the tab connection groove is located between two adjacent protrusion groups.

[0068] Along the second direction, the shortest distance from the slot wall of the tab connecting slot to the convex portion in one of the convex portion groups is J;

[0069] The J satisfies: 2mm≤J≤30mm.

[0070] And / or, the positive electrode sheet comprises a positive electrode current collector layer and a positive electrode active layer which are stacked;

[0071] The positive electrode active layer is arranged on the surface of the positive electrode current collector layer;

[0072] Along the width direction of the positive electrode sheet, the positive electrode active layer includes a first side and a second side opposite to each other, and the shortest distance from the protrusion to the first side or the second side is M;

[0073] The M satisfies: 0.5mm≤M≤30mm.

[0074] In a possible implementation, the positive electrode sheet includes a winding head end and a winding tail end opposite to each other along a second direction, and the second direction is a length extension direction of the positive electrode sheet;

[0075] Along the second direction, the minimum distance between the convex portion closest to the winding head end and the winding head end is K1;

[0076] The K1 satisfies: 10mm≤K1≤200mm; and / or

[0077] Along the second direction, the minimum distance between the protrusion closest to the winding tail end and the winding tail end is K2;

[0078] The K2 satisfies: 5mm≤K2≤200mm.

[0079] In a possible implementation, the silicon-carbon composite material includes a porous carbon matrix, silicon grains located in pores of the porous silicon matrix, and a carbon layer located on a surface of the porous carbon matrix.

[0080] In a possible implementation, the carbon layer includes openings arranged corresponding to the pores of the porous silicon substrate.

[0081] In a possible implementation, the specific surface area of ​​the silicon-carbon composite material is 0.5 m 2 / g-10m 2 / g; and / or

[0082] The particle size Dv50 of the silicon-carbon composite material is 6 μm-15 μm; and / or

[0083] The powder resistivity of the silicon-carbon composite material is in the range of 0.1 Ω·cm-1000 Ω·cm; and / or

[0084] The silicon content in the silicon-carbon composite material is 30%-75%.

[0085] In a possible implementation, the negative electrode sheet is provided with a plurality of grooves, the sum of the volumes of all the grooves on the negative electrode sheet is V1, and the volume of the negative electrode active layer is V2;

[0086] The V1 and V2 satisfy the following: 1%≤V1 / V2≤60%.

[0087] A second aspect of an embodiment of the present application provides a battery, which includes the winding core as described above.

[0088] An embodiment of the present application provides a winding core and a battery, wherein the winding core includes a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is provided with a plurality of protrusions and a straight portion located between adjacent protrusions, wherein the protrusions are formed by part of the positive electrode sheet protruding from the second surface toward the first surface. Firstly, the protrusions can effectively support the diaphragm, ensure that there is sufficient liquid storage space between the layers of the positive electrode sheet and the negative electrode sheet, and between the positive electrode sheet and the diaphragm, improve the electrolyte distribution, increase the liquid storage capacity of the area, and ensure a good wetting effect, thereby reducing the problem of insufficient electrolyte and poor wetting caused by squeezing between the positive electrode sheet and the negative electrode sheet layers inside the winding core due to repeated expansion and contraction of the silicon-doped negative electrode sheet, thereby improving the problems of deterioration of the electrode sheet interface, poor cycle stability of the negative electrode, and reduced battery capacity retention rate, reducing the attenuation rate of the battery capacity, and improving the cycle life of the battery cell.

[0089] A convex portion is provided on the positive electrode sheet to improve the deformation capacity of the positive electrode sheet. When the positive electrode sheet contacts the expanded negative electrode sheet, the convex portion on the positive electrode sheet can effectively absorb the expansion stress of the negative electrode sheet, which can buffer the expansion of the negative electrode sheet during the battery cycle and avoid the excessive expansion stress of the negative electrode sheet and cracks. In addition, the convex portion provided on the positive electrode sheet can absorb part of the expansion stress of the negative electrode sheet, so that the negative electrode sheet does not completely rely on the resistance of its own material when expanding, delaying the fatigue of the negative electrode material, thereby increasing the service life of the negative electrode sheet.

[0090] In addition, by satisfying the relationship between h and h1: 5%≤h1 / h≤30%, the height of the convex portion and the thickness of the positive electrode sheet can be adjusted within a reasonable range while ensuring the effect of the convex portion, so as to avoid the positive electrode sheet being cracked or fractured due to excessive pressure when the convex portion is formed on the positive electrode sheet due to the thin positive electrode sheet and the convex portion being too high. It can also avoid the situation where the thickness of the positive electrode sheet is too high and the height of the convex portion is too small, which may lead to the convex portion having an insignificant effect in relieving the negative electrode expansion stress and improving the electrolyte wettability, and still easily lead to poor interface between the electrode sheets or excessive stress between the layers.

[0091] Since the negative electrode active layer in the negative electrode sheet is a silicon-carbon composite material and / or a silicon-oxygen composite material, the silicon content will affect the expansion of the negative electrode sheet during the charge and discharge process. The higher the silicon content in the negative electrode active layer, the greater the expansion of the negative electrode sheet, and the more severe the extrusion between the positive electrode sheet and the negative electrode sheet. Therefore, the height of the convex portion needs to be higher. It is understandable that the higher the height of the convex portion, the larger the force-bearing surface of the convex portion, and the stronger its deformation ability, thereby more effectively alleviating the expansion of the negative electrode sheet and ensuring the liquid storage space between the positive electrode sheet and the negative electrode sheet. By making W1, h1 and h satisfy: 0.3≤W1 / (h1 / h)≤5, while being able to match the positive electrode sheet structure itself, it can further ensure that the height of the protrusion on the positive electrode sheet is adjusted with the change in the silicon content in the negative electrode active layer on the negative electrode sheet, so that the height setting of the protrusion can be further made more reasonable, so that the protrusion can ensure that there is sufficient liquid storage space between the electrode sheets and effectively absorb the expansion stress of the negative electrode sheet, while also avoiding the increase in the thickness of the core due to the height of the protrusion of the positive electrode sheet being too high to affect the energy density of the battery, and also avoiding the height of the protrusion being too low to be effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0093] Figure 1 A schematic diagram of the structure of a winding core provided in an embodiment of the present application;

[0094] Figure 2 A schematic diagram of the structure of a positive electrode sheet provided in an embodiment of the present application;

[0095] Figure 3 A schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present application;

[0096] Figure 4 for Figure 2 A schematic cross-sectional view of the positive electrode sheet at AA;

[0097] Figure 5 A schematic diagram of the arrangement of protrusions on a positive electrode sheet provided in an embodiment of the present application;

[0098] Figure 6 for Figure 2 Another cross-sectional schematic diagram of the positive electrode sheet at AA;

[0099] Figure 7 A schematic diagram of the structure of another positive electrode sheet provided in an embodiment of the present application;

[0100] Figure 8 This is a table showing the changes in relevant performance parameters of the winding core of the embodiment of the present application as the convex parameters change.

[0101] Description of reference numerals:

[0102] 10-winding core; 20-positive electrode sheet; 30-negative electrode sheet; 40-diaphragm;

[0103] 21- curved section; 22- straight section; 23- positive electrode current collector layer; 24- positive electrode active layer;

[0104] 31-negative electrode active layer; 32-negative electrode current collector layer;

[0105] 100- first side;

[0106] 110-winding head end; 120-winding tail end; 130-first side; 140-second side;

[0107] 200-side 2;

[0108] 300-convex part;

[0109] 310-abutment portion; 320-support portion;

[0110] 400 - inner concave portion;

[0111] 500-convex group;

[0112] 600-ear connection slot;

[0113] 700-straight part. DETAILED DESCRIPTION

[0114] As described in the background technology, the silicon-based materials in the related technology have a volume expansion problem during the charging and discharging process. During the charging and discharging process, silicon and lithium will undergo an alloying reaction, and the volume of silicon will expand by 100% to 300%. This continuous shrinkage and expansion will intensify the extrusion between the battery core layers, resulting in insufficient electrolyte between the layers and poor infiltration, which will cause the battery capacity to decay rapidly.

[0115] The reason for this problem is that the continuous shrinkage and expansion will intensify the extrusion between the battery layers, causing the interlayer gap to become smaller, resulting in insufficient electrolyte between the positive and negative electrode layers, poor wetting, and easy interface deterioration, which affects the cycle stability and capacity retention rate of the negative electrode, causing rapid decay of the battery capacity.

[0116] Furthermore, the expansion will generate a lot of stress inside the winding core, and the positive and negative electrodes and the separator of the winding core will be squeezed. With multiple cycles, the micro cracks in the negative electrode material are more likely to form and propagate in the areas where the expansion stress of the positive and negative electrodes is concentrated, and the negative electrode is at risk of breaking, affecting the safety of the battery. This stress may also reduce the internal porosity of the battery, reduce the migration channel of lithium ions, cause lithium metal precipitation, and also affect the safety of the battery.

[0117] In view of the above technical problems, the embodiments of the present application provide a winding core and a battery, wherein the winding core includes a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is provided with a plurality of convex portions and a straight portion located between adjacent convex portions, and the convex portion is formed by a portion of the positive electrode sheet protruding from the second surface to the first surface;

[0118] The maximum distance from the vertex of the convex portion to the plane where the first surface is located is h1, and the thickness of the straight portion on the positive electrode sheet along the first direction is h; h and h1 satisfy: 5%≤h1 / h≤30%;

[0119] A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector, wherein the negative electrode active layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage content of silicon element in the negative electrode active layer is W1;

[0120] W1, h1 and h satisfy the following: 0.3≤W1 / (h1 / h)≤5.

[0121] The convex portion can effectively support the diaphragm, ensure that there is sufficient liquid storage space between the layers of the positive electrode sheet and the negative electrode sheet, as well as between the positive electrode sheet and the diaphragm, improve the electrolyte distribution, increase the liquid storage capacity of the area, and ensure a good wetting effect, thereby reducing the problem of insufficient electrolyte and poor wetting caused by squeezing the positive and negative electrode sheets between the layers inside the winding core due to repeated expansion and contraction of the silicon-doped negative electrode sheet, thereby improving the problems of deterioration of the electrode interface, poor negative electrode cycle stability and reduced battery capacity retention rate, reducing the attenuation rate of the battery capacity and increasing the cycle life of the battery cell.

[0122] The convex portion is provided on the positive electrode sheet, so that the deformation capacity of the positive electrode sheet can be improved. When the positive electrode sheet contacts the expanded negative electrode sheet, the convex portion on the positive electrode sheet can effectively absorb the expansion stress of the negative electrode sheet, which can buffer the expansion of the negative electrode sheet during the battery cycle and avoid the excessive expansion stress of the negative electrode sheet and the occurrence of cracks. In addition, the convex portion provided on the positive electrode sheet can absorb part of the expansion stress of the negative electrode sheet, so that the negative electrode sheet does not completely rely on the resistance of its own material when expanding, delaying the fatigue of the negative electrode material, thereby increasing the service life of the negative electrode sheet.

[0123] In addition, by satisfying the relationship between h and h1: 5%≤h1 / h≤30%, the height of the convex portion and the thickness of the positive electrode sheet can be adjusted within a reasonable range while ensuring the effect of the convex portion, so as to avoid the positive electrode sheet being cracked or fractured due to excessive pressure when the convex portion is formed on the positive electrode sheet due to the thin positive electrode sheet and the convex portion being too high. It can also avoid the situation where the thickness of the positive electrode sheet is too high and the height of the convex portion is too small, which may lead to the convex portion having an insignificant effect in relieving the negative electrode expansion stress and improving the electrolyte wettability, and still easily lead to poor interface between the electrode sheets or excessive stress between the layers.

[0124] Since the negative electrode active layer in the negative electrode sheet is a silicon-carbon composite material and / or a silicon-oxygen composite material, the silicon content will affect the expansion of the negative electrode sheet during the charge and discharge process. The higher the silicon content in the negative electrode active layer, the greater the expansion of the negative electrode sheet, and the more severe the extrusion between the positive electrode sheet and the negative electrode sheet. Therefore, the height of the convex portion needs to be higher. It is understandable that the higher the height of the convex portion, the larger the force-bearing surface of the convex portion, and the stronger its deformation ability, thereby more effectively alleviating the expansion of the negative electrode sheet and ensuring the liquid storage space between the positive electrode sheet and the negative electrode sheet. By making W1, h1 and h satisfy: 0.3≤W1 / (h1 / h)≤5, while being able to match the positive electrode sheet structure itself, it can further ensure that the height of the protrusion on the positive electrode sheet is adjusted with the change in the silicon content in the negative electrode active layer on the negative electrode sheet, so that the height setting of the protrusion can be further made more reasonable, so that the protrusion can ensure that there is sufficient liquid storage space between the electrode sheets and effectively absorb the expansion stress of the negative electrode sheet, while also avoiding the increase in the thickness of the core due to the height of the protrusion of the positive electrode sheet being too high to affect the energy density of the battery, and also avoiding the height of the protrusion being too low to be effective.

[0125] In order to make the above-mentioned purposes, 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 part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of this application.

[0126] refer to Figures 1 to 4 An embodiment of the present application provides a winding core 10 , which may include a positive electrode sheet 20 and a negative electrode sheet 30 , and a separator 40 disposed between the positive electrode sheet 20 and the negative electrode sheet 30 . The positive electrode sheet 20 , the negative electrode sheet 30 , and the separator 40 are wound to form the winding core 10 .

[0127] The positive electrode sheet 20 may include a Figure 4The positive electrode sheet 20 has a first surface 100 and a second surface 200 that are opposite to each other (in the middle Z direction), and a plurality of convex portions 300 and a straight portion 700 located between adjacent convex portions 300 are provided on the positive electrode sheet 20, and the convex portions 300 are formed by a portion of the positive electrode sheet 20 protruding from the second surface 200 toward the first surface 100. The first direction may be the thickness direction of the positive electrode sheet 20, and the first surface 100 and the second surface 200 may be two opposite surfaces in the thickness direction of the positive electrode sheet 20.

[0128] The embodiment of the present application provides a winding core 10, which includes a positive electrode sheet 20 and a negative electrode sheet 30. The positive electrode sheet 20 is provided with a plurality of protrusions 300 and a straight portion 700 located between adjacent protrusions 300. The protrusions 300 are formed by part of the positive electrode sheet 20 protruding from the second surface 200 to the first surface 100. The protrusions 300 can effectively support the diaphragm 40, ensure that there is sufficient liquid storage space between the layers of the positive electrode sheet 20 and the negative electrode sheet 30, and between the positive electrode sheet 20 and the diaphragm 40, improve the electrolyte distribution, increase the liquid storage capacity of the area, and ensure a good infiltration effect, thereby reducing the problem of insufficient electrolyte and poor infiltration caused by the squeezing of the positive electrode sheet 20 and the negative electrode sheet 30 between the layers of the winding core 10 due to repeated expansion and contraction of the silicon-doped negative electrode sheet, thereby improving the problems of deterioration of the electrode interface, poor cycle stability of the negative electrode, and reduced battery capacity retention rate, reducing the attenuation rate of the battery capacity, and improving the cycle life of the battery cell.

[0129] The protrusion 300 is provided on the positive electrode sheet 20, so that the deformation capacity of the positive electrode sheet 20 can be improved. When the positive electrode sheet 20 contacts the expanded negative electrode sheet 30, the protrusion 300 on the positive electrode sheet 20 can effectively absorb the expansion stress of the negative electrode sheet 30, which can buffer the expansion of the negative electrode sheet 30 during the battery cycle, and avoid the negative electrode sheet 30 from cracking due to excessive expansion stress. In addition, the protrusion 300 provided on the positive electrode sheet 20 can absorb part of the expansion stress of the negative electrode sheet 30, so that the negative electrode sheet 30 does not completely rely on the resistance of its own material when expanding, delaying the fatigue of the negative electrode material, thereby increasing the service life of the negative electrode sheet 30.

[0130] Along the first direction, the maximum distance from the vertex of the convex portion 300 to the plane where the first surface 100 is located is h1 (eg Figure 4 h1), along the first direction, the area on the positive electrode sheet 20 where the convex portion 300 is not provided is a straight portion, and the thickness of the straight portion is h (such as Figure 4 Middle h).

[0131] The apex of the convex portion 300 is in contact with the diaphragm 40. It is understandable that the apex of the convex portion 300 may be a region on the convex portion 300, and the distance between the region and the plane where the first surface 100 is located is approximately equal.

[0132] In some embodiments, h and h1 can satisfy: 5%≤h1 / h≤30%. For example, the ratio of h1 / h can be one of 5%, 7%, 10%, 12%, 18%, 20%, 21%, 23%, 26%, 27% and 29%. Alternatively, h and h1 can satisfy any point value within the range of 5%≤h1 / h≤30%.

[0133] In this way, by satisfying the relationship between h and h1: 5%≤h1 / h≤30%, the height of the protrusion 300 and the thickness of the positive electrode sheet 20 can be adjusted within a reasonable range on the basis of ensuring the function of the protrusion 300, so as to avoid the positive electrode sheet 20 being cracked or broken due to excessive pressure when the protrusion 300 is formed on the positive electrode sheet 20 due to the thin positive electrode sheet 20 and the height of the protrusion 300 being too high. It can also avoid the situation that if the thickness of the positive electrode sheet 20 is too high and the height of the protrusion 300 is small, it is easy to cause the protrusion 300 to have an insignificant effect in relieving the negative electrode expansion stress and improving the electrolyte wettability, and it is still easy to cause a poor interface between the electrode sheets or excessive stress between the layers.

[0134] refer to Figure 3 The negative electrode sheet 30 may include a negative electrode active layer 31 and a negative electrode current collector layer 32. The negative electrode active layer 31 is located on the negative electrode current collector layer 32. The negative electrode active layer 31 includes a silicon-carbon composite material and / or a silicon-oxygen composite material. The percentage of silicon in the negative electrode active layer 31 is W1. The greater the amount of silicon doped in the negative electrode active layer 31, the greater the expansion of the negative electrode sheet 30 during the charge and discharge process of the battery. Therefore, there is a certain relationship between the height of the convex portion 300 on the positive electrode sheet 20 and the silicon content in the negative electrode active layer 31. For example, the greater the amount of silicon doped, the greater the height of the convex portion 300 on the corresponding positive electrode sheet 20 needs to be. The higher the height of the convex portion 300, the larger the force-bearing surface of the convex portion 300, and the stronger its deformation ability, so that the expansion of the negative electrode sheet can be more effectively alleviated.

[0135] refer to Figure 4 In some embodiments, W1, h1 and h satisfy: 0.3≤W1 / (h1 / h)≤5. For example, W1 / (h1 / h) can be one of 0.4, 0.7, 1.2, 1.5, 1.7, 2.4, 2.6, 2.9, 3.3, 3.5, 3.8, 4.1, 4.3, 4.6 and 4.9. Alternatively, W1 / (h1 / h) can be any point value within the range of greater than or equal to 0.3 and less than or equal to 5.

[0136] In this way, by making W1, h1 and h satisfy: 0.3≤W1 / (h1 / h)≤5, while being able to match the structure of the positive electrode sheet 20 itself, it can further ensure that the height of the protrusion 300 on the positive electrode sheet 20 is adjusted with the change in the silicon content in the negative electrode active layer 31 on the negative electrode sheet 30, so that the height setting of the protrusion 300 can be further made more reasonable, so that the protrusion 300 can ensure that there is sufficient liquid storage space between the electrodes and effectively absorb the expansion stress of the negative electrode sheet 30, while avoiding the increase in the thickness of the core 10 due to the excessive height of the protrusion 300 of the positive electrode sheet 20, affecting the energy density of the battery, and avoiding the height of the protrusion 300 being too low and difficult to achieve the effect.

[0137] refer to Figure 2 and Figure 3 In some embodiments, the percentage content of silicon in the negative electrode active layer 31 is W1, which satisfies: 3%≤W1≤50%. For example, W1 may be one of 3%, 5%, 10%, 12%, 16%, 19%, 21%, 24%, 29%, 33%, 36%, 41%, 46% and 49%. Alternatively, W1 may be any point value within the range of greater than or equal to 3% and less than or equal to 50%.

[0138] In this way, it is possible to avoid excessive expansion of the negative electrode sheet 30 due to excessive silicon content, thereby causing the negative electrode sheet 30 to shed or break, and it is possible to avoid affecting the lithium insertion capacity of the negative electrode material due to too low silicon content, thereby affecting the energy density of the battery.

[0139] refer to Figure 4 In some embodiments, h1 satisfies: 3μm≤h1≤50μm. For example, h1 can be one of 3μm, 3.7μm, 5μm, 9μm, 10μm, 12μm, 23μm, 34μm, 36μm, 40μm, 43μm and 47μm. Alternatively, h1 can be any point value within the range of greater than or equal to 3μm and less than or equal to 50μm.

[0140] In this way, it is possible to ensure that the convex portion 300 satisfies the requirements of providing liquid storage space and absorbing the expansion stress of the negative electrode sheet 30, while avoiding the problem that the positive electrode sheet 20 is easily broken due to excessive force during the formation of the convex portion 300 due to the convex portion 300 being too high. It is also possible to avoid the problem that the expansion stress of the negative electrode sheet 30 cannot be fully absorbed by deformation and sufficient liquid storage space cannot be provided due to the convex portion 300 being too low.

[0141] In some embodiments, the negative electrode active layer 31 may include a silicon-carbon composite material and / or a silicon-oxygen composite material, and the silicon-carbon composite material may include a porous carbon matrix, silicon grains in the pores of the porous silicon matrix, and a carbon layer on the surface of the porous carbon matrix. The material of the carbon layer may be shaped carbon or amorphous carbon.

[0142] In some embodiments, the carbon layer may include openings arranged corresponding to the pores of the porous silicon substrate.

[0143] In this way, by providing openings on the carbon layer corresponding to the pores of the porous silicon substrate, the wettability of the electrolyte to the negative electrode active material can be improved, while the expansion performance of silicon can be reduced, the cycle life of the battery cell can be improved, and the service life of the battery can be increased.

[0144] In some embodiments, the material of the negative electrode active layer 31 may also include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, graphene, soft carbon, hard carbon, soft carbon-coated graphite material, and hard carbon-coated graphite material.

[0145] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.5 m 2 / g-10m 2 / g, for example, the specific surface area of ​​the silicon-carbon composite material can be 0.5m 2 / g, 0.9m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.85m 2 / g, 2.0m 2 / g, 2.3m 2 / g, 2.7m 2 / g, 3.2m 2 / g, 3.6m 2 / g, 3.8m 2 / g, 4.6m 2 / g, 4.8m 2 / g, 5.1m 2 / g, 5.4m 2 / g, 5.8m 2 / g, 6.1m 2 / g, 6.5m 2 / g, 6.8m 2 / g, 7.2m 2 / g, 7.5m 2 / g, 7.8m 2 / g, 8.3m 2 / g, 8.9m 2 / g, 9.4m 2 / g and 9.9m 2Alternatively, the specific surface area of ​​the silicon-carbon composite material may be greater than or equal to 0.5 m 2 / g and less than or equal to 10m 2 Any value within the range of / g.

[0146] In this way, by controlling the specific surface area in the silicon-carbon composite material, the solid electrolyte interface (SEI) film can be reduced during the charging process, and the cycle performance and service life can be improved. It can avoid the situation where the thickness of the SEI film is too small due to the small specific surface area, thereby failing to effectively isolate the electrolyte and the negative electrode active layer 31. It can also avoid the SEI film being too large due to the large specific surface area, and can reduce the impact of the SEI film being too thick on the capacity and efficiency of the battery.

[0147] In some embodiments, the particle size Dv50 of the silicon-carbon composite material is 6 μm-15 μm, for example, it can be one of 6 μm, 7 μm, 8 μm, 9 μm, 11 μm, 13 μm and 14 μm, or it can be any point value within the range of 6 μm or more and 15 μm or less.

[0148] Thus, by controlling the particle size of the silicon-carbon composite material within the above range, it is possible to avoid the situation where the specific surface area of ​​the silicon particles is increased when the particle size is too small, thereby increasing the side reactions. It is also possible to avoid the problem where the silicon particles are easily expanded too much when the particle size is too large, thereby blocking the pores of the porous carbon matrix and affecting the infiltration of the electrolyte.

[0149] The average sphericity of the silicon-carbon material is in the range of 0.5-1, for example, the average sphericity can be one of 0.6, 0.7, 0.8 and 0.9. Compared with non-spherical particles, the higher the sphericity, the closer the shape is to a sphere, so that when its volume expands, the impact on the structure of the negative electrode sheet 30 is smaller, and the overall structural stability of the negative electrode sheet 30 can be maintained during expansion.

[0150] In addition, spherical particles can improve the mechanical strength and stability of the material and reduce the stress concentration between particles caused by expansion, thereby reducing the risk of mechanical wear and damage to the material during the cycle.

[0151] In some embodiments, the powder resistivity of the silicon-carbon composite material ranges from 0.1Ω·cm to 1000Ω·cm. For example, the powder resistivity of the silicon-carbon composite material may be one of 0.1Ω·cm, 0.9Ω·cm, 1.2Ω·cm, 1.3Ω·cm, 1.8Ω·cm, 2.7Ω·cm, 4.6Ω·cm, 7.8Ω·cm, 11Ω·cm, 25Ω·cm, 38Ω·cm, 60Ω·cm, 100Ω·cm, 200Ω·cm, 300Ω·cm, 400Ω·cm, 500Ω·cm, 600Ω·cm, 700Ω·cm, 800Ω·cm, 900Ω·cm and 1000Ω·cm. Alternatively, the powder resistivity of the silicon-carbon composite material may be any point value within the range of greater than or equal to 0.1Ω·cm and less than or equal to 1000Ω·cm.

[0152] In some embodiments, the silicon content in the silicon-carbon composite material may be 30%-75%, for example, the silicon content in the silicon-carbon composite material may be one of 30%, 35%, 41%, 45%, 49%, 51%, 55%, 59%, 61%, 64%, 71% and 84%. Alternatively, the silicon content in the silicon-carbon composite material may be any value within the range of greater than or equal to 30% and less than or equal to 75%.

[0153] In this way, it is possible to avoid excessive silicon content in the negative electrode active layer 31 causing excessive expansion of the negative electrode sheet, thereby deforming the overall structure of the silicon-carbon particles, and to avoid too little silicon content reducing the energy density of the battery.

[0154] refer to Figure 1 and Figure 2 In some embodiments, the positive electrode sheet 20 may include a winding head end 110 and a winding tail end 120 opposite to each other along the length direction, and a plurality of protrusions 300 are arranged at intervals along the direction from the winding head end 110 to the winding tail end 120 .

[0155] The maximum distance from the vertex of the convex portion 300 disposed near the winding head end 110 to the plane where the first surface 100 is located is greater than the maximum distance from the vertex of the convex portion 300 disposed near the winding tail end 120 to the plane where the first surface 100 is located.

[0156] The electrolyte storage positions inside the battery cell are distributed in the gap between the winding core 10 and the aluminum-plastic film, and in the gap between the electrode layers. The interlayer storage mainly relies on the electrode pores and capillary effect to slowly infiltrate. The time required and the difficulty of infiltration are relatively large between the winding core 10 and the aluminum-plastic film gap. Therefore, the liquid storage capacity of the inner electrode of the winding core 10 is significantly less than that of the outer electrode. More storage spaces can be provided by increasing the embossing depth of the inner electrode. The depth of the outer protrusion 300 is smaller than that of the inner protrusion 300, and the depth of the inner protrusion 300 is higher, thereby effectively supporting the diaphragm 40 and the negative electrode 30. The micro-spacing formed between the inner protrusion 300 and the diaphragm 40 is larger, which is more conducive to the electrolyte storage between the inner electrode sheets, reduces the probability of lithium plating of the inner negative electrode sheet 30, and improves the cycle life of the battery cell.

[0157] refer to Figure 1 In some embodiments, the positive electrode sheet 20 may include a plurality of curved segments 21 and a plurality of straight segments 22 from the center of the winding to the outermost portion of the winding. The straight segments 22 and the curved segments 21 are arranged alternately along the direction from the winding head end 110 to the winding tail end 120. The curved segments 21 and the straight segments 22 are both provided with convex portions 300.

[0158] The maximum distance from the outer surface of the convex portion 300 on the straight section 22 to the first surface 100 is h11 (eg Figure 1 h11), the maximum distance from the outer surface of the convex portion 300 on the curved segment 21 to the first surface 100 is h12 (such as Figure 1 h12), h11 and h12 satisfy: h11<h12.

[0159] Due to the different forces on the straight section 22 and the curved section 21 in the winding core 10, the curved section 21 has a greater bending stress and a more severe extrusion stress after expansion, which makes the negative electrode sheet 30 of the curved section 21 more likely to break; therefore, the curved section 21 needs a higher convex portion 300, which absorbs the stress of the expansion of the negative electrode sheet 30 to better buffer the stress of the curved section 21 and ensure a larger liquid storage space. Therefore, it is necessary to make the height of the convex portion 300 set on the curved section 21 greater than the height of the convex portion 300 on the straight section 22.

[0160] refer to Figure 1 In some embodiments, h11 and h12 satisfy: 0.1≤h11 / h12≤0.9, for example, h11 / h12 can be one of 0.2, 0.4, 0.5, 06, 0.7 and 0.8. Alternatively, it can be any point value within the range of greater than or equal to 0.1 and less than or equal to 0.9. Through the above arrangement, it can be ensured that the convex portion 300 effectively absorbs the expansion stress of the curved section 21 and provides a larger liquid storage space, and it can also avoid that the convex portion 300 of the curved section 21 is too high, resulting in the overall width of the battery cell being too wide, and the convex portion 300 is too small, which makes it difficult to effectively relieve the expansion stress of the curved section 21.

[0161] In some examples, h11 may satisfy 3 μm≤h11≤30 μm, for example, h11 may be one of 3.7 μm, 4.9 μm, 5.2 μm, 8 μm, 10 μm, 13 μm, 19 μm, 21 μm, 22 μm, 25 μm, and 29 μm.

[0162] In some examples, h12 may satisfy 5μm≤h12≤50μm, for example, h12 may be one of 5.2μm, 8μm, 10μm, 13μm, 19μm, 21μm, 22μm, 25μm, 29μm, 31μm, 33μm, 37μm, 41μm, 43μm, 46μm and 49μm.

[0163] refer to Figure 4 In some embodiments, the area on the second surface 200 of the positive electrode sheet 20 corresponding to the convex portion 300 is an inner concave portion 400. In this way, a liquid storage space can be formed between the concave portion side and the corresponding diaphragm 40 and the negative electrode sheet 30, which can further improve the electrolyte wettability, improve the electrolyte distribution, and increase the liquid storage capacity.

[0164] In some embodiments, the outer surface of the convex portion 300 is a first curved surface, and the inner surface of the concave portion 400 is a second curved surface. The curvature radius of the first curved surface is R1 (eg Figure 4 R1 in the figure), the radius of curvature of the second arc surface is R2 (such as Figure 4 In the embodiment of the present invention, R2 is greater than R1, and R1 and R2 satisfy the following: R1>R2. In this way, the orthographic projection of the first curved surface can be made larger than the orthographic projection of the second curved surface in the first direction, thereby increasing the surface area of ​​the outer surface of the protrusion 300, increasing the contact area between the protrusion 300 and the diaphragm 40, increasing the gap between the protrusion 300 side of the positive electrode sheet 20 and the diaphragm 40 and the negative electrode sheet 30, and increasing the liquid storage space and improving the electrolyte wettability.

[0165] refer to Figure 4 In some embodiments, the outer surface of the convex portion 300 may be a hemispherical surface, and the inner surface of the concave portion 400 may be a hemispherical surface. By setting the outer surface of the convex portion 300 and the inner surface of the concave portion 400 as hemispherical surfaces, the processing of the convex portion 300 and the concave portion 400 can be facilitated. For example, the positive electrode sheet 20 can be processed by stamping. After the stamping is completed, the protruding portion on the first surface 100 is the convex portion 300, and the concave portion 400 on the second surface 200 corresponding to the convex portion 300 is the concave portion 400.

[0166] refer to Figure 4In some embodiments, the cross section of the inner recess 400 is semicircular, the perimeter of the semicircle may be the perimeter of the inner surface of the inner recess 400, the perimeter of the inner surface may be C1, wherein C1 may be equal to πR2, and C1 may change with the change of R2, and C1 satisfies 0.5πmm<C1<8πmm. For example, C1 may be one of 0.6πmm, 1.6πmm, 2.5πmm, 2.8πmm, 3.1πmm, 3.7πmm, 4.6πmm, 5.8πmm, 6.3πmm, 6.7πmm and 7.8πmm.

[0167] In this way, by limiting the circumference of the inner surface, the projected area of ​​the protrusion 300 is appropriate, and it is also possible to prevent the protrusion 300 from being too large, causing a loss in volume energy density, or to prevent the protrusion 300 from being too small, resulting in less deformation space for the positive electrode sheet 20 and difficulty in playing a buffering effect on the expansion of the negative electrode sheet 30.

[0168] refer to Figure 4 In some embodiments, along the radial direction of the first arc surface, the distance between the vertex of the convex portion 300 and the vertex of the concave portion 400 is less than or equal to the thickness of the straight portion 700 on the positive electrode sheet 20 .

[0169] That is, the thickness of the positive electrode sheet 20 at the convex portion 300 is smaller, thereby improving the deformation capacity of the convex portion 300, making it easier for the convex portion 300 to effectively deform and absorb the expansion stress of the negative electrode sheet 30 when it contacts the expanded negative electrode sheet 30 during the battery charging and discharging process.

[0170] In some embodiments, R1 satisfies: 0.5 mm ≤ R1 ≤ 8 mm. For example, R1 may be one of 0.5 mm, 0.5 mm, 1.5 mm, 2.4 mm, 2.9 mm, 3.1 mm, 3.7 mm, 4.8 mm, 5.5 mm, 6.7 mm, 7.1 mm, and 7.5 mm. Alternatively, R1 may be any value within a range of greater than or equal to 0.5 mm and less than or equal to 8 mm.

[0171] In some embodiments, R2 satisfies: 0.5 mm ≤ R2 ≤ 8 mm; R2 can be one of 0.5 mm, 0.5 mm, 1.5 mm, 2.4 mm, 2.9 mm, 3.1 mm, 3.7 mm, 4.8 mm, 5.5 mm, 6.7 mm, 7.1 mm and 7.5 mm. Alternatively, R2 can be any point value within a range of greater than or equal to 0.5 mm and less than or equal to 8 mm.

[0172] In this way, by limiting the radius of the outer surface of the convex portion 300 and the inner surface of the concave portion 400, the projection area of ​​the convex portion 300 in the first direction can be adjusted. When R1 or R2 is less than 0.5 mm, the projection area of ​​the convex portion 300 is too small, and the convex portion 300 is too sharp. When it abuts against the diaphragm 40, it is easy to cause damage to the negative electrode sheet 30 and the diaphragm 40, and the positive electrode sheet 20 has little deformation space, and the effect of improving the expansion of the silicon-doped negative electrode is not good. When R1 or R2 is greater than 10 mm, the projection area of ​​the convex portion 300 is too large, so that the convex portion 300 is easily deformed excessively under the action of the extrusion force, the extension force and the cyclic expansion force during the formation process, so that the structure of the convex portion 300 collapses and the effect of improving the expansion of the negative electrode sheet 30 is not good.

[0173] In some embodiments, R1 and R2 satisfy: 1.01≤R1 / R2≤1.1. For example, R1 / R2 may be one of 1.02, 1.03, 1.04, 1.05, 1.06, and 1.09, or R1 / R2 may be any value within the range of greater than or equal to 1.01 and less than or equal to 1.1.

[0174] refer to Figure 4 and Figure 5 In some embodiments, along the first direction, the tangent lines of the orthographic projections of three adjacent convex portions 300 that are not on the same straight line together form an circumscribed triangle, and the area of ​​the circumscribed triangle is S3. Along the first direction, the intangent lines of the orthographic projections of three adjacent convex portions 300 that are not on the same straight line together form an inscribed triangle, and the area of ​​the inscribed triangle is S4. The distance between the center of the orthographic projection of two adjacent convex portions 300 to the surface where the first surface 100 is located is L1 (as shown in FIG. Figure 4 Among S3, S4, R1 and L1, 3πR1²≤S3-S4≤1.3L1² is satisfied.

[0175] In some embodiments, if the distances between the centers of the orthographic projections of every two adjacent protrusions 300 to the surface where the first surface 100 is located are equal, the circumscribed triangle and the inscribed triangle may both be equilateral triangles.

[0176] In this way, by ensuring that 3πR1²≤S3-S4≤1.3L1², the volume between the protrusions 300 and the volume of the protrusion 300 can be limited to remain within a reasonable range, thereby ensuring the supporting force of the protrusion 300 on the diaphragm 40 and the deformation force of the protrusion 300 itself.

[0177] refer to Figure 4In some embodiments, if the outer surface of the convex portion is a hemispherical surface, h1 and the radius R1 of the hemispherical surface satisfy: 0.02≤h1 / 2R1≤0.1. For example, h1 / 2R1 can be one of 0.03, 0.04, 0.05, 0.06, 0.07, 0.08 and 0.09.

[0178] In this way, by limiting the ratio of the height of the protrusion 300 to the diameter of the outer surface of the protrusion 300, the positive electrode sheet 20 has a suitable deformation space, which can ensure that the protrusion 300 has sufficient supporting force and deformation space while alleviating the expansion of the silicon negative electrode.

[0179] refer to Figure 2 In some embodiments, along the first direction, the projection of the inner concave portion 400 onto the surface where the second surface 200 is located is circular, elliptical or polygonal. Along the first direction, the projection of the convex portion 300 onto the surface where the first surface 100 is located is circular, elliptical or polygonal. The projection of the inner concave portion 400 onto the surface where the second surface 200 is located and the projection of the convex portion 300 onto the surface where the first surface 100 is located may be the same shape.

[0180] refer to Figure 4 In some embodiments, along the first direction, the distance between the centers of the orthographic projections of two adjacent convex portions 300 to the surface where the first surface 100 is located is L1 (eg Figure 4 The shortest distance between two adjacent protrusions 300 is L2. L1 and L2 satisfy: 1.05≤L1 / L2≤3. For example, L1 / L2 can be one of 1.05, 1.07, 1.11, 1.14, 1.18, 2.07, 2.11, 2.5, 2.63, 2.76 and 2.94. Or L1 / L2 can be any point value within the range of greater than or equal to 1.05 and less than or equal to 3.

[0181] In this way, by limiting the ratio of L1 / L2, the density of the protrusions 300 can be guaranteed, thereby providing sufficient support for the positive electrode sheet 20, so that the positive electrode sheet 20 has sufficient deformation space to alleviate the expansion of the silicon negative electrode. Each protrusion 300 can provide a support point for it, and multiple support points can disperse the expansion stress of the negative electrode sheet 30, and by making L1 / L2 greater than or equal to 1.05 and less than or equal to 3, the contact area between the protrusion 300 of the positive electrode sheet 20 and the negative electrode sheet 30 can be effectively guaranteed, thereby preventing the contact area from being too small and causing local overheating.

[0182] refer to Figure 4In some embodiments, L1 satisfies: 3mm≤L1≤10mm. For example, L1 can be one of 3mm, 3.5mm, 4mm, 4.7mm, 5mm, 5.2mm, 6mm, 6.7mm, 7mm, 7.7mm, 8mm, 8.6mm, 9.2mm and 9.7mm. Alternatively, L1 can be any point value within the range of greater than or equal to 3mm and less than or equal to 10mm.

[0183] In this way, by limiting the size of the distance L1 between the middle centers of two adjacent protrusions 300, it is possible to ensure that there is an appropriate distance between the protrusions 300, avoid the protrusions 300 being too dense or too sparse, and ensure the number of protrusions 300 to meet the requirements of regulating the appropriate volume of the protrusions 300, thereby achieving the benefits of alleviating the expansion of the negative electrode sheet 30 and improving the electrolyte infiltration effect.

[0184] When the distance between the convex portions 300 is less than 2 mm, the convex points of the processing roller are too dense, and in the process of forming the convex portions 300 on the positive electrode sheet 20, the extension of the electrode sheet cannot meet the density of the convex portions 300, which easily makes the height of the convex portions 300 also unable to meet the positive electrode sheet 20. The space is small, and the convex portions 300 are too dense, which also makes it easy for the electrode sheet to break during the formation of the convex portions 300. When the distance between the convex portions 300 and the convex portions 300 is greater than 10 mm, the convex points of the processing roller are too sparse, the convex portions 300 are too dispersed, and the support area of ​​the convex portions 300 is insufficient, thereby failing to improve the electrolyte infiltration effect.

[0185] In some embodiments, L2 satisfies: 0.5 mm ≤ L2 ≤ 8 mm. For example, L2 may be one of 0.7 mm, 0.9 mm, 1.2 mm, 1.7 mm, 2.5 mm, 2.8 mm, 3.1 mm, 3.5 mm, 4 mm, 4.7 mm, 5 mm, 5.2 mm, 6 mm, 6.7 mm, 7 mm, 7.7 mm, and 8 mm. Alternatively, L2 may be any value within a range of greater than or equal to 0.5 mm and less than or equal to 8 mm.

[0186] refer to Figure 6 In some embodiments, the convex portion 300 may include an abutting portion 310 , and a surface of the abutting portion 310 facing the diaphragm 40 is a third arc surface.

[0187] In this way, by limiting the surface of the protrusion 300 that contacts the diaphragm 40 to the third curved surface, the protrusion 300 can be prevented from being too sharp, thereby preventing the protrusion 300 from piercing the diaphragm 40 and causing a short circuit.

[0188] refer to Figure 6In some embodiments, the convex portion 300 may further include a supporting portion 320 located between the straight portion 700 of the positive electrode sheet 20 and the abutting portion 310, and the supporting portion 320 is disposed around the outer periphery of the abutting portion 310. The supporting portion 320 may be a fourth arc surface, and the curvature of the third arc surface is different from the curvature of the fourth arc surface.

[0189] refer to Figure 6 In some embodiments, when the outer surface of the supporting portion 320 is a fourth arc surface, the center of the fourth arc surface is located on the plane where the second surface 200 is located. Along the first direction, the maximum distance from the outer surface of the abutting portion 310 to the plane where the second surface 200 is located is R3 (e.g. Figure 6 R3 in the figure), the radius of curvature of the fourth arc surface is R4 (such as Figure 6 R4), R3 and R4 satisfy: R3<R4.

[0190] refer to Figure 6 In some embodiments, R3 and R4 satisfy: R3<1 / 5R4. For example, R3 / R4 may be less than 1 / 5, 1 / 6, 1 / 7, 1 / 8 or 1 / 9. In this way, by limiting the height of the protrusion 300 on the positive electrode sheet 20 after winding, a suitable gap can be provided between the positive electrode sheet 20 and the diaphragm 40, and on the basis of ensuring sufficient liquid storage space and absorbing the expansion stress of the negative electrode sheet 30, the thickness of the winding core 10 and the battery can be prevented from being too large.

[0191] refer to Figure 4 and Figure 7 In some embodiments, the surface area of ​​the outer surface of the convex portion 300 is Q1, and the surface area of ​​the inner surface of the concave portion 400 is Q2, Q2=2πR2². Q1 and Q2 satisfy: 1.02≤Q1 / Q2≤1.21. For example, Q1 / Q2 can be one of 1.06, 1.09, 1.11, 1.13, 1.15, 1.17 and 1.19. Alternatively, Q1 / Q2 can be any point value within the range of greater than or equal to 1.02 and less than or equal to 1.21.

[0192] In this way, by making Q1 / Q2 greater than or equal to 1.02 and less than or equal to 1.21, the volume of the protrusion 300 can be better controlled so that the protrusion 300 of the positive electrode sheet 20 has a suitable deformation space, thereby better improving the expansion problem of the negative electrode sheet 30 .

[0193] refer to Figure 7In some embodiments, along the first direction, the surface area of ​​the orthographic projection of the convex portion 300 to the surface where the first surface 100 is located is S1. The surface area of ​​the orthographic projection of the inner concave portion 400 to the plane where the second surface 200 is located is S2. S1 and S2 satisfy: 1.02≤S1 / S2≤1.21. For example, S1 / S2 can be one of 1.06, 1.09, 1.11, 1.13, 1.15, 1.17 and 1.19. Alternatively, S1 / S2 can be any point value within the range of greater than or equal to 1.02 and less than or equal to 1.21.

[0194] In this way, by making S1 / S2 greater than or equal to 1.02 and less than or equal to 1.21, the volume of the protrusion 300 can be better controlled so that the protrusion 300 of the positive electrode sheet 20 has a suitable deformation space, thereby better improving the expansion problem of the negative electrode sheet 30.

[0195] refer to Figure 4 In some embodiments, the outer surface of the convex portion 300 is a first curved surface, and the inner surface of the concave portion 400 is a second curved surface. The angle between the tangent direction of the outer surface of the convex portion 300 and the first surface 100 and the first surface 100 is α1 (e.g. Figure 4 α1 satisfies: 0°≤α1≤90°. For example, α1 can be one of 10°, 20°, 25°, 30°, 37°, 40°, 45°, 50°, 60°, 70°, 80° and 85°. Alternatively, α1 can be any point value within the range of greater than or equal to 0° and less than or equal to 90°.

[0196] The angle between the tangent line of the inner surface of the inner concave portion 400 and the second surface 200 and the second surface 200 is α2 (eg Figure 4 α2 in the figure). α2 satisfies: 0°≤α2≤90°. For example, α2 can be one of 10°, 20°, 25°, 30°, 37°, 40°, 45°, 50°, 60°, 70°, 80° and 85°. Alternatively, α2 can be any point value within the range of greater than or equal to 0° and less than or equal to 90°.

[0197] refer to Figure 4 In some embodiments, α1 and α2 satisfy: 0°≤α1-α2≤40°. For example, α1-α2 can be one of 10°, 15°, 18°, 21°, 25°, 27°, 31°, 37° and 40°. Alternatively, α1-α2 can be any point value within the range of greater than or equal to 0° and less than or equal to 40°.

[0198] Thus, by making α1 greater than or equal to 0° and less than or equal to 90°, it is possible to avoid the connection between the convex portion 300 and the first surface 100 of the positive electrode sheet 20 being easily broken due to the angle being too large during the process of forming the convex portion 300. When α1 is too small, the inclination angle of the convex portion 300 is too large, the height of the convex portion 300 is insufficient, the supporting force of the convex portion 300 is insufficient, and the effect of improving the expansion of the silicon negative electrode is not good.

[0199] By making α2 greater than or equal to 0° and less than or equal to 90°, it is possible to avoid the connection between the inner recess 400 and the second surface 200 of the positive electrode sheet 20 being easily broken during the process of forming the convex portion 300 due to too large an angle. When α2 is too small, the inclination angle of the inner recess 400 is too small, and the height of the inner recess 400 is insufficient, which also leads to insufficient support force of the convex portion 300, resulting in poor improvement effect on silicon negative electrode expansion.

[0200] refer to Figure 7 In some embodiments, along the first direction, the total area of ​​the orthographic projections of the convex portions 300 on the first surface 100 is S5, the surface area of ​​the first surface 100 of the positive electrode sheet 20 is S, and S5 and S satisfy: 0.2≤S5 / S≤0.95. For example, S5 / S can be one of 0.2, 0.3, 0.4, 0.5, 0.64, 0.7, 0.83, 0.87 and 0.93. Alternatively, S5 / S can be any point value within the range of greater than or equal to 0.2 and less than or equal to 0.95.

[0201] Thus, if the convex portion 300 occupies a small area of ​​the positive electrode sheet 20, for example, S5 / S is 0.1, the convex portion 300 occupies too little area, resulting in the convex portion 300 being unable to absorb the expansion stress of the negative electrode sheet 30 and being unable to provide sufficient liquid storage space. If the convex portion 300 occupies a large area of ​​the positive electrode sheet 20, for example, S5 / S is 1, the convex portion 300 occupies a large area, resulting in the edge of the positive electrode sheet 20 being easily damaged, affecting the quality of the positive electrode sheet 20 in the winding core 10; and if the area occupies too large an area, the convex portions 300 are relatively dense, and it is also easy for the pressure to be too concentrated during the formation of the convex portions 300, thereby causing the electrode sheet to break.

[0202] refer to Figure 7 In some embodiments, along the first direction, the surface area of ​​the first surface 100 of the positive electrode sheet 20 excluding the convex portion 300 is S6, and S5 and S6 satisfy: 0.8≤S5 / S6≤2. For example, S5 / S6 can be one of 0.9, 1.1, 1.3, 1.4, 1.6 and 1.9. Alternatively, S5 / S6 can be any point value within the range of greater than or equal to 0.8 and less than or equal to 2.

[0203] In this way, by limiting the density of the protrusions 300, the protrusions 300 can have better supporting stability, and by making S5 / S6 greater than or equal to 0.8 and less than or equal to 2, the liquid storage capacity, wettability and absorption of the expansion stress of the negative electrode sheet 30 can be more effectively improved.

[0204] refer to Figure 7 In some embodiments, the positive electrode sheet 20 may include a plurality of convex portion groups 500, and each convex portion group 500 may include a plurality of convex portions 300. Two adjacent convex portion groups 500 are arranged along the second direction (eg Figure 7 The second direction is the length extension direction of the positive electrode sheet 20. The positive electrode sheet 20 may include a tab connection groove 600. Along the second direction, the tab connection groove 600 is located between two adjacent convex portion groups 500. Along the second direction, the shortest distance from the groove wall of the tab connection groove 600 to the convex portion 300 in one of the convex portion groups 500 is J (e.g. Figure 7 In J), J satisfies: 2mm≤J≤30mm.

[0205] For example, J may be one of 3 mm, 4 mm, 6 mm, 9 mm, 12 mm, 15 mm, 19 mm, 21 mm, 35 mm, 37 mm, and 29 mm. Alternatively, J may be any value within a range of 2 mm or more and 30 mm or less.

[0206] The shortest distance from the protrusion 300 to the tab connection groove 600 is a straight region, and the protrusion 300 is not provided in this region, so that a clearance area is formed in this region.

[0207] Thus, by setting the clearance area to be greater than or equal to 2 mm and less than or equal to 30 mm, the current collector corresponding to the tab position on the positive electrode sheet 20 can be prevented from being damaged due to rolling stress, thereby avoiding affecting the stability of the tab welding and the interface uniformity there.

[0208] refer to Figure 7 In some embodiments, the positive electrode sheet 20 may include a positive electrode current collector layer 23 and a positive electrode active layer 24 that are stacked. The positive electrode active layer 24 is disposed on the surface of the positive electrode current collector layer 23 and extends along the width direction of the positive electrode sheet 20 (eg, Figure 7 In the Y direction, the positive electrode active layer 24 may include a first side 130 and a second side 140 opposite to each other, and the shortest distance from the protrusion 300 to the first side 130 or the second side 140 is M (eg Figure 7In M, M satisfies: 0.5 mm ≤ M ≤ 30 mm. For example, M can be one of 0.6 mm, 1.5 mm, 1.8 mm, 2.9 mm, 3 mm, 7 mm, 11 mm, 15 mm, 19 mm, 21 mm and 25 mm. Alternatively, M can be any point value within the range of greater than or equal to 0.5 mm and less than or equal to 30 mm.

[0209] Thus, by making M greater than or equal to 0.5 mm and less than or equal to 30 mm, edge curling and poor interface uniformity caused by rolling stress in the edge area of ​​the positive electrode sheet 20 can be prevented, thereby ensuring the cycle performance and service life of the battery cell.

[0210] refer to Figure 7 In some embodiments, the positive electrode sheet 20 may include a second direction (such as Figure 7 The second direction is the length extension direction of the positive electrode sheet 20. Along the second direction, the minimum distance from the protrusion 300 closest to the winding head end 110 to the winding head end 110 is K1 (e.g. Figure 7 K1 satisfies: 10mm≤K1≤200mm. For example, K1 can be one of 20mm, 30mm, 40mm, 60mm, 80mm, 100mm, 110mm, 120mm, 130mm, 150mm, 160mm and 190mm. Alternatively, K1 can be any point value within the range of 10mm or more and 200mm or less. In this way, a certain avoidance zone can be formed between the convex portion 300 of the winding head end 110 and the winding head end 110, and the convex portion 300 is not provided in the zone.

[0211] Thus, by making K1 greater than or equal to 10 mm and less than or equal to 200 mm, it is possible to avoid the problem of the positive electrode sheet 20 being folded when inserted and the problem of unstable structure caused by unstable insertion during winding.

[0212] Along the second direction, the minimum distance between the protrusion 300 closest to the winding tail end 120 and the winding tail end 120 is K2 (eg Figure 7 In K2, K2 satisfies: 5mm≤K2≤200mm. For example, K2 can be one of 5mm, 20mm, 10mm, 20mm, 30mm, 40mm, 60mm, 80mm, 100mm, 110mm, 120mm, 130mm, 150mm, 160mm and 190mm. Alternatively, K2 can be any point value within the range of greater than or equal to 5mm and less than or equal to 200mm. In this way, a certain avoidance zone can be formed between the convex portion 300 of the winding tail end 120 and the winding tail end 120, and the convex portion 300 is not provided in this area.

[0213] The winding tail end 120 has an empty foil area. By making K2 greater than or equal to 5 mm and less than or equal to 200 mm, it is possible to avoid the problem of the foil being subjected to large rolling stress and being damaged.

[0214] refer to Figures 1 to 3 In some embodiments, the negative electrode sheet 30 is provided with grooves, the sum of the volumes of all the grooves of the negative electrode sheet 30 is V1, the volume of the entire negative electrode active layer 31 is V2, V1 and V2 satisfy 1%≤V1 / V2≤60%, for example, V1 / V2 can be one of 2%, 7%, 10%, 20%, 31%, 38%, 40%, 50% and 58%. The sum of the areas of all the grooves on the negative electrode sheet 30 is S7, the area of ​​the entire negative electrode active layer 31 is S8, S7 and S8 satisfy 1%≤S7 / S8≤50%. For example, S7 / S8 can be one of 2%, 7%, 10%, 20%, 31%, 38%, 40% and 45%.

[0215] Thus, by providing a groove in the negative electrode sheet 30 , the lithium insertion dynamics of the negative electrode sheet 30 can be improved and the lithium insertion tortuosity of the negative electrode sheet 30 can be reduced. Meanwhile, by providing a protrusion 300 in the positive electrode sheet 20 , the battery can have better cycle performance.

[0216] In some embodiments, the recess on the negative electrode sheet 30 may be a hole, such as a cylindrical hole, a conical hole or an irregular hole. Alternatively, the recess on the negative electrode sheet 30 may also be a groove, such as a rectangular groove, a trapezoidal groove or an irregular groove.

[0217] refer to Figures 1 to 3 The embodiment of the present application also provides a battery, which may include the above winding core 10. The battery of the present application can increase the cycle life of the battery, reduce the decay rate, and improve the performance of the battery by using the above winding core 10.

[0218] refer to Figure 1 According to the parameter characteristics of the positive electrode sheet and the negative electrode sheet, the positive electrode sheet, the negative electrode sheet and the winding core are prepared, and the relevant performance parameters of the winding core are detected. The specific preparation process is as follows. The relevant performance of each winding core is as follows Figure 8 shown.

[0219] Example 1

[0220] 1. Preparation of positive electrode sheet 20

[0221] Lithium cobalt oxide, a conductive agent (a mixture of conductive carbon black and carbon nanotubes), and polyvinylidene fluoride (PVDF) were placed in N-methylpyrrolidone (NMP) at a mass ratio of 97.60:1.35:1.05, and stirred evenly to prepare a positive electrode slurry.

[0222] The positive electrode slurry was evenly coated on both sides of the aluminum foil, with a coating surface density of 0.01704 g / cm 2 .

[0223] After drying and rolling (rolling compaction is 4.2), a positive electrode sheet 20 with a double-sided thickness h of 110 μm was obtained.

[0224] The cut positive electrode sheet 20 is processed with a special roller having protrusions 300, and the height h1 of the protrusions 300 is 20 μm, the pitch L2 of the protrusions 300 is 3 mm, and the diameter R1 is 4 mm. The ratio S5 / S of the total area of ​​the orthographic projection of each protrusion on the first surface to the surface area of ​​the first surface of the positive electrode sheet is 0.4.

[0225] The obtained positive electrode parameters are shown in Table 1.

[0226] 2. Preparation process of negative electrode sheet 30

[0227] Silicon-containing artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are placed in deionized water in a mass ratio of 97.2:0.5:1.3:1, wherein the silicon content W in the silicon-containing artificial graphite is 10%.

[0228] The above slurry is stirred evenly to obtain negative electrode slurry.

[0229] The negative electrode slurry is uniformly coated on the negative electrode collector layer 32, and is sequentially dried, rolled and cut. The cut negative electrode sheet 30 is grooved by laser, and grooves are set on the entire surface of the negative electrode sheet 30. The grooves are matrix grooves, the spacing between adjacent grooves is set to 1.2 mm, and the groove depth is 18 μm.

[0230] The negative electrode sheet 30 after laser treatment is cleaned and sheeted to obtain the negative electrode sheet 30 .

[0231] 3. Battery preparation process

[0232] The separator 40 is composed of 9 μm thick substrate + ceramic + glue-coated separator 40. The electrolyte includes lithium salt LiPF6 and a solvent, wherein the solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), wherein the molar ratio of the three is DEC:EC:EMC=1:1:1.

[0233] The above-cut positive electrode sheet 20, separator 40, and negative electrode sheet 30 are stacked in sequence and wound into a wound-type structure battery cell. The battery cell is packaged, injected, formed, and sealed again to obtain a lithium-ion battery.

[0234] It is understandable that the arrangement of the convex portion on the positive electrode sheet is mainly related to the thickness of the positive electrode sheet, the height of the convex portion, the percentage of silicon in the negative electrode sheet, etc. By adjusting the percentage of silicon on the negative electrode sheet, the ratio between the height of the convex portion and the thickness of the positive electrode sheet, and the coverage area of ​​the convex portion on the positive electrode sheet, positive electrode sheets of multiple different embodiments are obtained and performance tests are performed.

[0235] In Example 2, compared with Example 1, the maximum distance h1 from the vertex of the protrusion 300 to the plane where the first surface is located is 6 μm.

[0236] In Example 3, compared with Example 1, the maximum distance h1 from the vertex of the protrusion 300 to the plane where the first surface is located is 30 μm.

[0237] In Example 4, compared with Example 1, the maximum distance h1 from the vertex of the protrusion 300 to the plane where the first surface is located is 7 μm, and the percentage content W1 of silicon in the negative electrode active layer 31 is 30%.

[0238] In Example 5, compared with Example 1, the percentage content W1 of silicon in the negative electrode active layer 31 is 20%.

[0239] Example 6, as comparative example 1, compared with Example 1, the shortest distance L2 between two adjacent protrusions 300 is 7 μm, and the radius R1 of the protrusion 300 is 7 μm.

[0240] In Example 7, as Comparative Example 2, the shortest distance L2 between two adjacent protrusions 300 is 0.5 μm, and the radius R1 of the protrusion 300 is 0.5 μm.

[0241] Example 8, as comparative example 3, compared with Example 1, the maximum distance h1 from the vertex of the protrusion 300 to the plane where the first surface is located is 2 μm.

[0242] Example 9, as comparative example 4, compared with Example 1, the maximum distance h1 from the vertex of the protrusion 300 to the plane where the first surface is located is 40 μm.

[0243] Example 10, as comparative example 5, is compared with Example 1, but the positive electrode sheet 20 in comparative example 5 is not adjusted.

[0244] The following are some specific detection methods and steps for relevant parameters.

[0245] 1. It is necessary to test the liquid retention volume (test method: each battery is filled with liquid according to a certain amount of liquid, for example, the liquid filling volume n1 of each battery is 8.5g±0.1g, and then aged. After aging, the battery is formed into a second seal after sorting. The second seal is to extract excess electrolyte, and the remaining electrolyte volume is the liquid retention volume n2. Then n2=(weight after second sealing m2-weight before liquid filling m1).

[0246] 2. It is necessary to test the appearance of the positive electrode sheet 20 after the protrusion 300 is manufactured. Test method: After the protrusion 300 is manufactured, the electrode sheet is observed using a 3D microscope to observe whether there is damage on the electrode sheet and the size of the damaged area.

[0247] 3. Test the cycle retention rate and expansion change rate. Cycle test: The lithium-ion battery is cycled in a blue electric test cabinet. The test conditions are 25℃±2℃, 3.2C charge to 4.37V, 2.8C charge to 4.37V, 2C charge to 4.53V, 1.5C charge to 4.58V, cut off at 0.05C; 0.7C discharge to 3V.

[0248] The specific method is: the specific charging system is: stand at 25℃±2℃ for 5 minutes, discharge at 0.2C to the lower limit voltage. Stand for 5 minutes, charge at 0.7C to the upper limit voltage, cut off at 0.025C, stand for 5 minutes, and discharge at 0.2C to the lower limit voltage.

[0249] Do an initial capacity test, let it stand for 5 minutes, charge at 3.2C to 4.37V, charge at 2.8C to 4.37V, charge at 2C to 4.53V, charge at 1.5C to 4.58V, measure at 0.05C and record the data of the fully charged state, voltage, and thickness.

[0250] Stand for 5min at 25℃±2℃, discharge 3V at 0.7C, stand for 5min, charge 4.37V at 3.2C, charge 4.37V at 2.8C, charge 4.53V at 2C, charge 4.58V at 1.5C, cut off at 0.05C, stand for 5min, discharge 3V at 0.7C, stand for 5min, 8~9 1200 times, repeat 3~4 steps at 25℃ for capacity test every 100 times, first 200T: measure the voltage and thickness of the fully charged cell every 50T, after 200T: measure the voltage and thickness of the fully charged cell every 100T. Then test the capacity retention rate and expansion change rate of the lithium-ion battery at 200T and 400T.

[0251] Battery expansion rate = (battery thickness at full charge after N cycles - battery sample thickness) / battery sample thickness × 100%).

[0252] By testing the winding cores 10 in the above 10 embodiments, the liquid retention, cycle retention rate 600T, expansion change rate 600T, battery K value, and lithium precipitation of the ten winding cores 10 were obtained. Figure 8 From the information in the table:

[0253] Compared with the fifth winding core in comparative example 5 in which no protrusion 300 is provided on the positive electrode sheet 20. In Example 1, the positive electrode sheet 20 is prepared according to the relevant parameters of the protrusion 300 in Example 1, and the negative electrode sheet 30 is prepared according to the percentage of silicon in the negative electrode active layer 31 in Example 1, and the prepared positive electrode sheet 20 and negative electrode sheet 30 are processed to obtain the first winding core. Compared with the tenth winding core, the first winding core has a significantly increased liquid retention amount, a significantly reduced expansion change rate, and no lithium deposition occurs in the first winding core. Therefore, by providing a protrusion 300 on the positive electrode sheet 20 of the winding core 10, the liquid storage performance and cycle life of the winding core 10 can be effectively improved, and the problem of lithium deposition in the winding core 10 can be avoided, thereby improving the safety of the battery.

[0254] By comparing Example 2 with Example 1, while keeping other parameters of the second winding core unchanged, lowering the height of the protrusion 300 will lead to a decrease in the liquid retention capacity of the winding core 10, affecting the liquid storage capacity of the winding core 10 and the battery, and will lead to an increase in the expansion rate of the winding core 10.

[0255] By comparing Example 3 with Example 1, when the height of the protrusion 300 is increased while keeping other parameters of the third winding core unchanged, the height of the protrusion 300 increases, so that the liquid storage space between the positive electrode sheet 20 and the negative electrode sheet 30 can be increased, thereby increasing the liquid retention capacity and expansion change rate of the winding core 10, reducing the cycle retention rate and the battery K value, and slightly damaging the appearance of the positive electrode sheet 20. It can be seen that when the protrusion 300 is increased and other parameters remain unchanged, although the liquid retention capacity is increased, there is a risk of rupture of the positive electrode sheet 20.

[0256] By comparing Example 4 with Example 1, when the height of the protrusion 300 of the fourth winding core is reduced and the percentage of silicon in the negative active layer 31 is increased, the liquid retention amount is reduced, the cycle retention rate is reduced, and the expansion change rate is increased. This is because the protrusion 300 with a lower height cannot provide sufficient liquid storage space between the positive electrode sheet 20 and the negative electrode sheet 30. The reduced liquid storage amount will affect the cycle retention rate, and the increase in the percentage of silicon will cause the expansion of the negative electrode sheet 30 to increase.

[0257] By comparing Example 5 with Example 1, while keeping other parameters of the fifth winding core unchanged, only increasing the percentage of silicon in the negative electrode active layer 31 has a relatively small impact on the relevant performances, and its relevant performance parameters remain basically unchanged from those of the first winding core in Example 1.

[0258] By comparing Example 6 with Example 1, while keeping other parameters of the fifth winding core unchanged, only the shortest distance between two adjacent protrusions 300 and the radius of the protrusion 300 are increased, so that the protrusion 300 on the positive electrode sheet 20 in the sixth winding core becomes sparse relative to the protrusion 300 on the positive electrode sheet 20 in the first winding core, which will increase the liquid retention, expansion change rate and K value of the sixth winding core, and lead to a decrease in the cycle retention rate and the occurrence of lithium precipitation. Therefore, if the protrusion 300 is too sparse, the performance of the winding core 10 and the battery will be reduced, and the safety of the battery will also be affected.

[0259] By comparing Example 7 with Example 1, while keeping other parameters of the seventh winding core unchanged, only the shortest distance between two adjacent protrusions 300 and the radius of the protrusion 300 are reduced, so that the protrusions 300 on the positive electrode sheet 20 in the seventh winding core become denser than the protrusions 300 on the positive electrode sheet 20 in the first winding core, which will reduce the liquid retention, expansion change rate and cycle retention rate of the seventh winding core, and lithium deposition will occur. Therefore, if the protrusions 300 are too dense, the performance of the winding core 10 and the battery will be reduced, and the safety of the battery will also be affected.

[0260] By comparing Example 8 with Example 1, while keeping other parameters of the eighth winding core unchanged, the maximum distance h1 from the vertex of the convex portion 300 to the plane where the first surface is located is significantly reduced to 2 μm. Since the height of the convex portion 300 is too low, the liquid retention and cycle retention rate of the eighth winding core will be reduced, the expansion change rate and the K value of the battery will increase, and lithium deposition will occur. Therefore, if the convex portion 300 is too low, the performance of the winding core 10 and the battery will be reduced, and the safety of the battery will also be affected.

[0261] By comparing Example 9 with Example 1, while keeping other parameters of the ninth winding core unchanged, the maximum distance h1 from the vertex of the convex portion 300 to the plane where the first surface is located is significantly increased to 40 μm, so that the liquid retention capacity, expansion change rate and K value of the ninth winding core are increased, while the cycle retention rate is significantly reduced, and the positive electrode sheet 20 is damaged, and lithium deposition occurs. Therefore, if the convex portion 300 is too high, the performance of the winding core 10 and the battery will be reduced, and the safety of the battery will also be affected.

[0262] The various embodiments or implementation methods in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referenced to each other.

[0263] It should be noted that the phrases "in specific implementation", "in some embodiments", "in this embodiment", "exemplarily" and the like mentioned in the specification indicate that the described embodiment may include specific features, structures or characteristics, but not every embodiment may include the specific features, structures or characteristics. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when describing specific features, structures or characteristics in conjunction with an embodiment, it is within the knowledge of those skilled in the art to implement such features, structures or characteristics in conjunction with other embodiments that are explicitly or not explicitly described.

[0264] In general, terms should be understood, at least in part, by the context in which they are used. For example, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in a singular sense, or may be used to describe a combination of features, structures, or characteristics in a plural sense, depending, at least in part, on the context. Similarly, terms such as "a," "an," or "the" may also be understood to convey singular usage or to convey plural usage, depending, at least in part, on the context.

[0265] It should be easily understood that “on,” “above,” and “over” in the present 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 intervening features or layers therebetween, and “above” or “over” not only includes the meaning of “above” or “over,” but also may include the meaning of “above” or “over something” with no intervening features or layers therebetween (i.e., directly on something).

[0266] In addition, spatially relative terms, such as "below," "below," "beneath," "above," "above," etc., may be used herein for ease of description 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 in addition to the orientation shown in the figures. The device may have other orientations (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0267] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, 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: include: A positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet, the separator, and the negative electrode sheet are wound to form the winding core; A positive electrode sheet, comprising a first surface and a second surface opposite to each other along a first direction, the positive electrode sheet being provided with a plurality of convex portions and a straight portion located between adjacent convex portions, the convex portion being formed by a portion of the positive electrode sheet protruding from the second surface toward the first surface; The maximum distance from the vertex of the convex portion to the plane where the first surface is located is h1; Along the first direction, the thickness of the straight portion on the positive electrode sheet is h; The h and h1 satisfy the following conditions: 5%≤h1 / h≤30%; A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector, wherein the negative electrode active layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material, and the percentage content of silicon element in the negative electrode active layer is W1; The W1, h1 and h satisfy the following: 0.3≤W1 / (h1 / h)≤5.

2. The winding core according to claim 1, characterized in that: The W1 satisfies: 3%≤W1≤50%, and / or The h1 satisfies: 3μm≤h1≤50μm.

3. The winding core according to claim 1, characterized in that: The positive electrode sheet comprises a winding head end and a winding tail end opposite to each other along the length direction; The convex parts are arranged at intervals along the direction from the winding head end to the winding tail end; The maximum distance from the vertex of the convex portion disposed near the winding head end to the plane where the first surface is located is greater than the maximum distance from the vertex of the convex portion disposed near the winding tail end to the plane where the first surface is located.

4. The winding core according to claim 3, characterized in that: The positive electrode sheet comprises a plurality of curved segments and a plurality of straight segments; Along the direction from the winding head end to the winding tail end, the straight sections and the curved sections are arranged alternately; The convex portion is provided on both the curved section and the straight section; The maximum distance from the outer surface of the convex portion on the straight section to the first surface is h11; The maximum distance from the outer surface of the convex portion on the curved segment to the first surface is h12; The h11 and h12 satisfy: h11<h12.

5. The winding core according to claim 4, characterized in that: The h11 and h12 satisfy: 0.1≤h11 / h12≤0.9; And / or, h11 satisfies: 3μm≤h11≤30μm; And / or, h12 satisfies: 5μm≤h12≤50μm.

6. The winding core according to claim 1, characterized in that: The area on the second surface of the positive electrode sheet corresponding to the convex portion is a concave portion; The outer surface of the convex portion is a first arc surface, and the inner surface of the concave portion is a second arc surface; The curvature radius of the first curved surface is R1, and the curvature radius of the second curved surface is R2; The R1 and the R2 satisfy: R1>R2.

7. The winding core according to claim 6, characterized in that: Along the radial direction of the first arc surface, the distance between the vertex of the convex portion and the vertex of the inner concave portion is less than or equal to the thickness of the straight portion on the positive electrode sheet.

8. The winding core according to claim 7, characterized in that: The R1 satisfies: 0.5mm≤R1≤8mm; And / or, R2 satisfies: 0.5mm≤R2≤8mm; And / or, R1 and R2 satisfy the following relationship: 1.01≤R1 / R2≤1.

1.

9. The winding core according to claim 6, characterized in that: Along the first direction, the circumscribed lines of the orthographic projections of three adjacent convex portions that are not on the same straight line together form a circumscribed triangle, and the area of ​​the circumscribed triangle is S3; Along the first direction, the intangent lines of the orthographic projections of three adjacent convex portions that are not on the same straight line together form an inscribed triangle, and the area of ​​the inscribed triangle is S4; The distance between the centers of the orthographic projections of two adjacent convex portions to the surface where the first surface is located is L1; The S3, the S4, the R1 and the L1 satisfy the following: 3πR1²≤S3-S4≤1.3L1².

10. The winding core according to claim 6, characterized in that: The relationship between h1 and the radius R1 of the first arc surface satisfies: 0.02≤h1 / 2R1≤0.1; and / or, along the first direction, the projection of the inner concave portion onto the surface where the second surface is located is circular, elliptical or polygonal; And / or, along the first direction, a projection of the convex portion onto the surface where the first surface is located is circular, elliptical or polygonal.

11. The winding core according to claim 6, characterized in that: Along the first direction, the distance between the centers of the orthographic projections of two adjacent convex portions to the surface where the first surface is located is L1; The shortest distance between two adjacent convex portions is L2; The relationship between L1 and L2 satisfies: 1.05≤L1 / L2≤3; And / or, L1 satisfies: 3mm≤L1≤10mm; And / or, L2 satisfies: 0.5mm≤L2≤8mm.

12. The winding core according to claim 1, characterized in that: The convex portion includes an abutment portion; The surface of the abutting portion facing the diaphragm is a third curved surface.

13. The winding core according to claim 12, characterized in that: The convex portion further includes a supporting portion located between the straight portion of the positive electrode sheet and the abutting portion; The support portion is disposed around the outer periphery of the abutment portion; The support portion is a fourth arc surface; Along the first direction, the maximum distance from the outer surface of the abutting portion to the plane where the second surface is located is R3; the radius of curvature of the fourth arc surface is R4; The R3 and the R4 satisfy: R3<R4.

14. The winding core according to claim 13, characterized in that: The relationship between R3 and R4 is as follows: R3<1 / 5R4.

15. The winding core according to claim 6, characterized in that: The surface area of ​​the outer surface of the convex portion is Q1, and the surface area of ​​the inner surface of the concave portion is Q2; Q1 and Q2 satisfy: 1.02≤Q1 / Q2≤1.21, and / or, along the first direction, the surface area of ​​the orthographic projection of the convex portion to the surface where the first surface is located is S1; the surface area of ​​the orthographic projection of the concave portion to the plane where the second surface is located is S2; The S1 and S2 satisfy the following: 1.02≤S1 / S2≤1.

21.

16. The winding core according to claim 6, characterized in that: The angle between the tangent line on the outer surface of the convex portion where the convex portion is connected to the first surface and the first surface is α1; The α1 satisfies: 0°≤α1≤90°, and / or The angle between the tangent line at the connection point between the inner surface of the inner concave portion and the second surface and the second surface is α2; The α2 satisfies: 0°≤α2≤90°.

17. The winding core according to claim 16, characterized in that: The α1 and the α2 satisfy: 0°≤α1-α2≤40°.

18. The winding core according to claim 1, characterized in that: Along the first direction, the total area of ​​the orthographic projections of the convex portions on the first surface is S5, and the surface area of ​​the first surface of the positive electrode sheet is S; The S5 and the S satisfy: 0.2≤S5 / S≤0.

95.

19. The winding core according to claim 1, characterized in that: The positive electrode sheet includes a plurality of convex portion groups; each of the convex portion groups includes a plurality of convex portions; Two adjacent protrusion groups are arranged at intervals along a second direction, and the second direction is the length extension direction of the positive electrode sheet; The positive electrode sheet includes a tab connection groove; Along the second direction, the tab connection groove is located between two adjacent convex portion groups; Along the second direction, the shortest distance from the slot wall of the tab connecting slot to the convex portion in one of the convex portion groups is J; The J satisfies: 2mm≤J≤30mm.

20. The winding core according to claim 1, characterized in that: The positive electrode sheet comprises a positive electrode current collector layer and a positive electrode active layer which are stacked; The positive electrode active layer is arranged on the surface of the positive electrode current collector layer; Along the width direction of the positive electrode sheet, the positive electrode active layer includes a first side and a second side opposite to each other, and the shortest distance from the protrusion to the first side or the second side is M; The M satisfies: 0.5 mm ≤ M ≤ 30 mm; And / or, the positive electrode sheet comprises a winding head end and a winding tail end opposite to each other along a second direction, and the second direction is a length extension direction of the positive electrode sheet; Along the second direction, the minimum distance between the convex portion closest to the winding head end and the winding head end is K1; The K1 satisfies: 10mm≤K1≤200mm; and / or, Along the second direction, the minimum distance between the protrusion closest to the winding tail end and the winding tail end is K2; The K2 satisfies: 5mm≤K2≤200mm.

21. The winding core according to claim 1, characterized in that: The silicon-carbon composite material comprises a porous carbon matrix, silicon grains located in the pores of the porous silicon matrix, and a carbon layer located on the surface of the porous carbon matrix.

22. The winding core according to claim 21, characterized in that The carbon layer includes openings arranged corresponding to the pores of the porous silicon substrate.

23. The winding core according to claim 21, characterized in that: The specific surface area of ​​the silicon-carbon composite material is 0.5 m 2 / g-10m 2 / g; and / or The particle size Dv50 of the silicon-carbon composite material is 6 μm-15 μm; and / or The powder resistivity of the silicon-carbon composite material is in the range of 0.1 Ω·cm-1000 Ω·cm; and / or The silicon content in the silicon-carbon composite material is 30%-75%.

24. The winding core according to claim 1, characterized in that: The negative electrode sheet is provided with a plurality of grooves, the sum of the volumes of all the grooves on the negative electrode sheet is V1, and the volume of the negative electrode active layer is V2; The V1 and V2 satisfy the following: 1%≤V1 / V2≤60%.

25. A battery, characterized in that: Comprising the winding core according to any one of claims 1 to 24.

Images