Battery

Abstract

The invention provides a battery which comprises a roll core, the roll core comprises a positive plate, a diaphragm and a negative plate, the positive plate, the diaphragm and the negative plate are sequentially stacked and wound to form the roll core, the roll core is provided with a straight area and arc angle areas, and the arc angle areas are located at the two opposite ends of the straight area; the positive plate is provided with a first surface and a second surface which are opposite, the negative plate is provided with a third surface and a fourth surface which are opposite, the first surface and the third surface face the inner side of the roll core, and the second surface and the fourth surface face the outer side of the roll core; the negative plate comprises a negative current collector and negative active layers positioned on two opposite surfaces of the negative current collector, and the negative active layers comprise carbon-silicon composite materials; the positive plate is provided with a plurality of concave-convex structures, the concave-convex structures are positioned in at least one of the arc angle region and the straight region, each concave-convex structure comprises a concave part which is inwards concave from the first surface and a convex part which is outwards convex from the second surface, the concave parts and the convex parts are correspondingly arranged, and the concave parts and the fourth surface are correspondingly arranged. The battery disclosed by the invention is relatively high in safety.

Description

Technical Field

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

[0002] A lithium-ion battery may include a battery case and a battery cell. The battery cell includes electrodes and separators. The positive electrode, separator and negative electrode are stacked in sequence and wound to form a wound battery cell. In related technologies, the winding tension of the battery cell is increased to reduce the gap between the components of the core and increase the tightness of the core interface, thereby increasing the energy density of the lithium-ion battery.

[0003] However, increasing the winding tension will aggravate the lithium plating phenomenon of lithium-ion batteries. Summary of the invention

[0004] An embodiment of the present application provides a battery, which alleviates the lithium plating problem of the battery by providing a concave-convex structure on the positive electrode sheet.

[0005] The battery provided in the embodiment of the present application includes a winding core, which includes a positive electrode sheet, a separator and a negative electrode sheet. The positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and wound to form the winding core. The winding core has a straight area and an arc angle area, and the arc angle area is located at two opposite ends of the straight area.

[0006] The negative electrode sheet comprises 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;

[0007] The positive electrode sheet has a first surface and a second surface facing each other, and the negative electrode sheet has a third surface and a fourth surface facing each other, the first surface and the third surface face the inner side of the winding core, and the second surface and the fourth surface face the outer side of the winding core;

[0008] The positive electrode sheet is provided with a plurality of concave-convex structures, the concave-convex structures are located in at least one of the arc angle area and the straight area, the concave-convex structures include a concave portion sunken inward from the first surface and a convex portion protruding outward from the second surface, and the convex portion and the concave portion are arranged correspondingly;

[0009] The fourth surface of the negative electrode sheet is arranged opposite to the first surface having the concave portion.

[0010] In a possible implementation, the concavo-convex structure includes a first concavo-convex structure and a second concavo-convex structure, the first concavo-convex structure is located in the arc angle area, the first concavo-convex structure includes a first concave portion and a first convex portion, the second concavo-convex structure is located in the straight area, and the second concavo-convex structure includes a second concave portion and a second convex portion;

[0011] The depression depth h1 of the first depression and the depression depth h2 of the second depression satisfy:

[0012] h1<h2;

[0013] and / or, a protruding height h3 of the second protruding portion and a recessed depth h2 of the second recessed portion satisfy: h3<h2;

[0014] And / or, a protruding height h4 of the first protruding portion and a recessed depth h1 of the first recessed portion satisfy: h4

[0015] In a possible implementation, a protruding height h3 of the second protrusion and a recessed depth h2 of the second recess satisfy: 0.2≤h3 / h2<1.

[0016] In a possible implementation, the bending radius R1 of the arc angle area and the thickness T1 of the straight area satisfy: 0.45≤R1 / T1≤0.75.

[0017] In a possible implementation, the winding core has N folded winding layers from the inside to the outside, and the depth of the concave portion located in the innermost folded winding layer is h. n The depth h of the concave portion located at the outermost folded winding layer n+1 Satisfy: h n ≥h n+1 ;

[0018] Wherein, N is an integer greater than 1, and n is any value between 1 and N.

[0019] In a possible implementation, the gap H1 between two adjacent recesses and the diameter H2 of the recesses satisfy: 0.6≤H1 / H2≤2.

[0020] In a possible implementation, the outer contour circumference L1 of the concave portion is greater than the outer contour circumference L2 of the convex portion.

[0021] In a possible implementation, the outer contour circumference L1 of the concave portion and the outer contour circumference L2 of the convex portion satisfy: 1<L1 / L2≤2.

[0022] In a possible implementation, the outer contour perimeter L1 of the recess and the thickness T2 of the positive electrode sheet satisfy: 30≤L1 / T2≤160;

[0023] And / or, the outer contour circumference L1 of the recess satisfies: 4500 μm≤L1≤8000 μm.

[0024] In a possible implementation, the positive electrode sheet is provided with a concave-convex area and a void area, a plurality of concave-convex structures are located in the concave-convex area, the void area is staggered with the concave-convex area, and the void area is surrounded on at least one side of the concave-convex area.

[0025] In a possible implementation, the area S1 of the concave-convex region and the area S2 of the positive electrode sheet satisfy: 0.02≤S1 / S2≤0.85.

[0026] ​In a possible implementation, the positive electrode sheet includes a positive electrode current collector, a first coating layer and a second coating layer, wherein the first coating layer and the second coating layer are disposed on two opposite sides of the positive electrode current collector;

[0027] Along the unfolded length direction of the positive electrode sheet, the first end of the first coating layer is aligned with the first end of the second coating layer, the first end of the positive electrode current collector has a first empty foil area, the second end of the first coating layer exceeds the second end of the second coating layer, and the positive electrode sheet of the first coating layer exceeding the second coating layer constitutes a single-sided coating area;

[0028] Along the width direction of the positive electrode sheet, two sides of the positive electrode sheet have a first edge region and a second edge region;

[0029] The empty area includes at least one of a single-sided coating area, a first empty foil area, a first edge area, and a second edge area.

[0030] In one possible implementation, the winding core also includes a first pole ear, and the first edge area is provided with at least one pole ear connection groove, the pole ear connection groove exposes at least a portion of the positive electrode collector, the first pole ear is connected to the positive electrode collector in the pole ear connection groove, and the pole ear connection groove is staggered with the concave-convex area.

[0031] In a possible implementation, along the width direction of the positive electrode sheet, the spacing W1 between the tab connection groove and the concave-convex area satisfies: 0<W1≤10mm;

[0032] And / or, along the width direction of the positive electrode sheet, the extension dimension W2 of the second edge region satisfies: 2mm≤W2≤20mm;

[0033] And / or, along the unfolded length direction of the positive electrode sheet, the extension dimension A of the first empty foil area satisfies: 0<A≤20mm;

[0034] And / or, along the unfolded length direction of the positive electrode sheet, the extension dimension B of the single-sided coating area satisfies: 0<B≤C, wherein C is the difference between the length of the first coating and the length of the second coating.

[0035] In a possible implementation, the depth h of the concave portion is proportional to the tensile strength T of the positive electrode current collector. S Satisfy: 0.05≤h / T S ≤0.4.

[0036] The battery provided in the embodiment of the present application includes a winding core, which includes a positive electrode sheet, a separator and a negative electrode sheet. The winding core has a straight area and an arc angle area. The positive electrode sheet includes a concave-convex structure, which includes a concave portion and a convex portion. The concave-convex structure is located in at least one of the arc angle area and the straight area, so that the surface of the positive electrode sheet is uneven. When the battery cell expands, the convex portion can effectively support the separator, thereby preventing the separator from being deformed by the expansion stress of the negative electrode sheet. At the same time, a space for accommodating electrolyte is formed between the convex portion of the positive electrode sheet and the separator, thereby increasing the storage space for the electrolyte, improving the wetting ability of the electrolyte in this area, and avoiding abnormal situations such as insufficient electrolyte and poor wetting between the positive electrode and the separator.

[0037] Since the negative active coating of the negative electrode sheet contains a silicon-carbon composite material and / or a silicon-oxygen composite material, the volume of silicon will expand and contract violently during charge and discharge, thereby causing the negative electrode sheet to expand and contract, and the third surface of the negative electrode sheet is subjected to a greater extrusion pressure than the fourth surface of the negative electrode sheet. When the negative electrode sheet as a whole expands, the expansion degree of the fourth surface is greater than that of the third surface. The recess is arranged on the first surface and is recessed inward from the first surface, so that the recess can be opposite to the fourth surface that expands more severely. Therefore, when the negative electrode sheet expands, a larger expansion stress release space is provided for the fourth surface of the negative electrode sheet, thereby avoiding the collapse and deformation of the concave-convex structure caused by the expansion of the fourth surface, thereby avoiding the convex portion from losing its supporting function.

[0038] Furthermore, the first surface provided with the recess is opposite to the fourth surface, so that the migration path of the lithium ions of the positive electrode active material in the recess can be longer, and the migration path of the lithium ions of the positive electrode active material in other parts of the first surface can be shorter, thereby reducing the positive electrode active material participating in the charge and discharge reaction in the recess, so that the negative electrode active layer on the fourth surface has sufficient sites for lithium ion embedding. In this way, the recess can reduce the positive electrode active material participating in the charge and discharge reaction on the first surface, thereby improving the CB value (negative electrode surface capacity / positive electrode surface capacity) of the battery, so that the fourth surface has sufficient sites to accommodate the lithium ions deintercalated from the first surface, thereby reducing the probability of lithium plating on the fourth surface, thereby improving the lithium plating phenomenon on the positive and negative surfaces of the negative electrode sheet.

[0039] The convex portion is arranged on the second surface and protrudes outward from the second surface, so that the convex portion and the concave portion are arranged in pairs on the opposite sides of the positive electrode sheet, and the convex portion is opposite to the third surface of the negative electrode sheet. Since the expansion degree of the third surface is lighter than that of the fourth surface, the expansion of the third surface has less influence on the concave-convex structure, and the expansion of the third surface is not likely to cause the concave-convex structure to deform and fail, thereby effectively ensuring the supporting effect of the convex portion, and the convex portion can offset part of the expansion stress of the negative electrode sheet on the positive electrode sheet, thereby preventing the positive electrode sheet from being subjected to greater stress and breaking.

[0040] When a concave-convex structure is provided on the positive electrode sheet located in the arc corner area, the convex part can increase the gap between the positive electrode sheet and the negative electrode sheet, thereby increasing the bending radius of the arc corner area, thereby reducing the extrusion stress between the positive electrode sheet and the negative electrode sheet. Increasing the gap between the positive electrode sheet and the negative electrode sheet can also increase the storage space of the electrolyte, thereby improving the wetting effect of the electrolyte on the positive electrode sheet and the negative electrode sheet, thereby improving the lithium deposition problem of the negative electrode sheet, and the concave part can provide a release space for the expansion of the negative electrode sheet, so as to reduce the expansion stress of the negative electrode sheet on the positive electrode sheet due to the expansion of silicon, which leads to stress concentration in the arc corner area, and then causes the positive electrode sheet to break. In this way, the concave-convex structure in the arc corner area can improve the breakage problem of the positive electrode sheet, thereby avoiding lithium deposition or short circuit problems caused by the breakage of the positive electrode sheet.

[0041] Therefore, the battery provided by the embodiment of the present application has higher safety.

[0042] In addition to the technical problems solved by the embodiments of the present application described above, the technical features that constitute the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions, other technical problems that can be solved by the battery provided by the present application, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0044] Figure 1 A schematic diagram of the structure of a battery provided in an embodiment of the present application;

[0045] Figure 2 A schematic diagram of the structure of the positive electrode sheet and the negative electrode sheet in the battery provided in the embodiment of the present application;

[0046] Figure 3 Schematic diagram of the structure of the positive electrode sheet in the battery provided in the embodiment of the present application Figure 1 ;

[0047] Figure 4 Schematic diagram of the structure of the positive electrode sheet in the battery provided in the embodiment of the present application Figure 2 ;

[0048] Figure 5 Schematic diagram of the structure of the positive electrode sheet in the battery provided in the embodiment of the present application Figure 3 ;

[0049] Figure 6 Schematic diagram of the structure of the positive electrode sheet in the battery provided in the embodiment of the present application Figure 4 .

[0050] Reference numerals:

[0051] 10-winding core; 10a-straight area; 10b-arc angle area; 100-positive electrode sheet; 100a-first surface; 100b-second surface; 110-concave-convex structure; 111-concave portion; 112-convex portion; 110a-first concave-convex structure; 111a-first concave portion; 112a-first convex portion; 110b-second concave-convex structure; 111b-second concave portion; 112b-second convex portion; 120-concave-convex area; 130-avoidance area; 131-first empty foil area; 132-single-sided coating area; 133-first edge area; 1331-ear connection groove; 134-second edge area; 200-negative electrode sheet; 200a-third surface; 200b-fourth surface.

[0052] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiment of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. The embodiments of the present application are described in detail below in conjunction with the drawings.

[0054] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0055] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are orientations or positional relationships based on the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0056] The terms "first", "second", "third" (if any) in the specification and claims of this application and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the application described herein can be implemented in an order other than those illustrated or described herein, for example.

[0057] In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or display comprising a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such process, method, product, or display.

[0058] Lithium-ion batteries can include a battery case and a battery cell. The battery cell includes a pole piece and a separator. The positive pole piece, separator and negative pole piece are stacked and wound in sequence to form a wound battery cell. In the related art, the gap between the components of the winding core is reduced by increasing the winding tension of the battery cell to increase the tightness of the winding core interface, thereby increasing the energy density of the lithium-ion battery. However, increasing the winding tension will aggravate the lithium precipitation phenomenon of lithium-ion batteries.

[0059] This is because straight sections and arc sections are formed after the electrode sheet is wound. After the winding tension increases, the stress on the arc section is greater than that on the straight section. Moreover, for the negative electrode sheet, during the charge and discharge cycle, the volume change of the silicon-doped negative electrode active material will cause the negative electrode sheet to expand and contract, which will also increase the stress of the negative electrode arc section and intensify the extrusion of the arc section of the negative electrode sheet on the corresponding position of the positive electrode sheet, thereby causing the arc section of the positive electrode sheet to break.

[0060] Moreover, if the interlayer extrusion of the arc segment is too large, it is easy to squeeze out the electrolyte at that position, resulting in insufficient electrolyte retention in this area, and lithium deposition is prone to occur in the negative electrode sheet.

[0061] At the same time, when the negative electrode sheet expands, the inner side of the negative electrode sheet is squeezed to a greater extent, and the thickness of the negative electrode coating on the inner side of the expanded negative electrode sheet is smaller than that on the outer side of the expanded negative electrode sheet, which makes the transmission path of lithium ions on the negative electrode coating side of the expanded negative electrode sheet longer, thereby increasing the difficulty of lithium ions embedding into the negative electrode coating on the outer side of the negative electrode sheet, and thus making the outer side of the negative electrode sheet available for lithium ion embedding less than the inner side of the negative electrode sheet, resulting in lithium deposition on the outer side of the negative electrode sheet and no lithium deposition on the inner side of the negative electrode sheet, that is, the negative electrode sheet is prone to lithium deposition on the positive and negative sides.

[0062] The specific implementation of the battery provided in the embodiments of the present application is described in detail below with reference to the accompanying drawings.

[0063] Reference Figures 1 to 5 As shown, the battery provided in the embodiment of the present application includes a winding core 10, which includes a positive electrode sheet 100, a separator and a negative electrode sheet 200. The positive electrode sheet 100, the separator and the negative electrode sheet 200 are stacked and wound in sequence to form the winding core 10. The winding core 10 has a straight area 10a and an arc angle area 10b, and the arc angle area 10b is located at two opposite ends of the straight area 10a.

[0064] The negative electrode sheet 200 includes a negative electrode current collector and a negative electrode active layer located on the negative electrode current collector, and the negative electrode active layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material.

[0065] In one embodiment, the mass proportion of the silicon-carbon composite material and / or the silicon-oxygen composite material in the negative electrode active material is less than or equal to 50 wt %, for example, 1.5-40 wt %.

[0066] The silicon-carbon composite material includes a porous carbon matrix, silicon grains in the pores of the porous carbon matrix, and a carbon layer on the surface of the porous carbon matrix. The present invention can arrange silicon grains in the pores of the porous carbon matrix by deposition, by arranging silicon grains in the pores, and by forming a carbon layer on the surface of the porous carbon matrix, and the carbon layer can be shaped carbon or amorphous carbon. When the silicon grains expand, the interior of the porous carbon matrix can provide sufficient expansion space to prevent the overall structure of the silicon-carbon composite material from deforming, and the carbon layer can constrain the outward expansion force of the porous carbon matrix during the silicon expansion process, ensure the structural strength of the silicon-carbon material, thereby avoiding the problems of cracking, pulverization, and shedding of the negative electrode active layer, and improving the cycle performance and rate performance of the battery.

[0067] In a specific embodiment, the carbon layer includes openings arranged corresponding to the pores of the porous carbon matrix. When the carbon layer is provided with openings, the wettability of the electrolyte to the negative electrode sheet 200 can be improved, and the expansion performance of the silicon-based material can be reduced, thereby reducing the impedance of the battery and improving the cycle performance and rate performance of the battery.

[0068] In a specific embodiment, the specific surface area of ​​the silicon-carbon composite material and / or the silicon-oxygen composite material is 0.5-10 m 2 / g, for example 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g or 10m 2 When the specific surface area of ​​the silicon-carbon composite material is within the above range, the SEI film formed on the surface of the negative electrode active layer during the charge and discharge process is appropriate, which can reduce the impedance of the battery and improve the cycle performance and rate performance of the battery.

[0069] In a specific embodiment, the particle size Dv50 of the silicon-carbon composite material and / or silicon-oxygen composite material is 6-15μm, for example, any one of 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm is within any two numerical ranges.

[0070] When the particle size Dv50 of the silicon-carbon composite material and / or silicon-oxygen composite material is within the above range, the particle size Dv50 of the silicon-carbon composite material is appropriate, which can avoid the situation where the particle size is too small, resulting in an increase in the specific surface area of ​​the silicon particles and an increase in side reactions. At the same time, it can avoid the situation where the particle size is too large, resulting in excessive expansion of the silicon particles, which leads to blockage of the pores of the porous carbon matrix and affects the infiltration of the electrolyte, thereby improving the cycle performance and rate performance of the battery.

[0071] In a specific embodiment, the powder resistivity of the silicon-carbon composite material and / or silicon-oxygen composite material is 0.1-1000 Ω·cm, for example, 0.1Ω·cm, 0.5Ω·cm, 1Ω·cm, 5Ω·cm, 10Ω·cm, 50Ω·cm, 100Ω·cm, 200Ω·cm, 300Ω·cm, 400Ω·cm, 500Ω·cm, 600Ω·cm, 700Ω·cm, 800Ω·cm, 900Ω·cm or 1000Ω·cm.

[0072] When the powder resistivity of the silicon-carbon composite material is within the above range, the electrical conductivity of the silicon-carbon composite material is high, and the electrical conductivity of the negative electrode active layer can be increased, thereby improving the cycle performance and rate performance of the battery.

[0073] In a specific embodiment, the silicon content in the silicon-carbon composite material and / or silicon-oxygen composite material is 30-75%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%.

[0074] When the silicon content in the silicon-carbon composite material and / or silicon-oxygen composite material is within the above range, it is possible to avoid excessive silicon content in the silicon-carbon composite material and / or silicon-oxygen composite material, which may lead to excessive expansion of the silicon-carbon composite material and / or silicon-oxygen composite material, and deformation of the overall structure of the silicon-carbon composite material and / or silicon-oxygen composite material, thereby avoiding cracking and pulverization of the negative electrode active layer, ensuring the energy release of the silicon-carbon composite material and / or silicon-oxygen composite material, and improving the cycle performance and rate performance of the battery.

[0075] The positive electrode sheet 100 has a first surface 100 a and a second surface 100 b facing each other. The first surface 100 a faces the inside of the winding core 10 , and the second surface 100 b faces the outside of the winding core 10 .

[0076] The positive electrode sheet 100 is provided with a plurality of concave-convex structures 110, which are located in at least one of the arc angle area 10b and the straight area 10a. The concave-convex structure 110 includes a concave portion 111 recessed inward from the first surface 100a and a convex portion 112 protruding outward from the second surface 100b, and the concave portion 111 and the convex portion 112 are arranged correspondingly.

[0077] It should be noted that the corresponding arrangement of the recess 111 and the protrusion 112 can be understood as that the vertical projection of the protrusion 112 in the thickness direction of the positive electrode sheet 100 is completely located within the projection of the recess 111 in the thickness direction of the positive electrode sheet 100, or that the projection of the protrusion 112 in the thickness direction of the positive electrode sheet 100 partially overlaps with the vertical projection of the recess 111 in the thickness direction of the positive electrode sheet 100.

[0078] It can be understood that the positive electrode sheet 100, the separator and the negative electrode sheet 200 are stacked and wound in sequence to form a winding core 10, which has a straight area 10a and an arc angle area 10b. A portion of the positive electrode sheet 100, a portion of the separator and a portion of the negative electrode sheet 200 are located in the straight area 10a, and another portion of the positive electrode sheet 100, another portion of the separator and another portion of the negative electrode sheet 200 are located in the arc angle area 10b. The positive electrode sheet 100, the separator and the negative electrode sheet 200 located in the straight area 10a are in the shape of straight sheets, and the positive electrode sheet 100, the separator and the negative electrode sheet 200 located in the arc angle area 10b are in the shape of curved sheets.

[0079] The positive electrode sheet 100 has a first surface 100a and a second surface 100b opposite to each other, and the negative electrode sheet 200 has a third surface 200a and a fourth surface 200b opposite to each other, wherein the first surface 100a and the third surface 200a face the inner side of the winding core 10, and the second surface 100b and the fourth surface 200b face the outer side of the winding core 10. The first surface 100a and the second surface 100b are both coated with positive electrode active materials, and the third surface 200a and the fourth surface 200b are both coated with negative electrode active materials. The positive electrode active materials may include one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate, and the negative electrode active materials may include a silicon-carbon composite material or a mixture of a graphite-doped silicon-carbon composite material. The silicon in the silicon-carbon composite material expands and contracts by 100-300% during the charge and discharge process, thereby causing the negative electrode sheet 200 to expand and contract.

[0080] When the positive electrode sheet 100, the separator and the negative electrode sheet 200 are stacked and wound, a multi-fold winding layer can be formed. In the same fold winding layer, the second surface 100b of the positive electrode sheet 100 and the third surface 200a of the negative electrode sheet 200 are opposite. In two adjacent fold winding layers, the first surface 100a of the positive electrode sheet 100 and the fourth surface 200b of the negative electrode sheet 200 are opposite.

[0081] Since the concavo-convex structure 110 protrudes from the first surface 100a toward the second surface 100b, the concavo-convex structure 110 may include a concave portion 111 and a convex portion 112 that appear in pairs. The concave portion 111 is arranged on the first surface 100a and is recessed inward from the first surface 100a, so that the concave portion 111 of the first surface 100a is arranged corresponding to the fourth surface 200b, and the convex portion 112 is arranged on the second surface 100b and protrudes outward from the second surface 100b, so that the convex portion 112 of the second surface 100b is arranged corresponding to the third surface 200a. The concavo-convex structure 110 can make the surface of the positive electrode sheet 100 uneven.

[0082] In this way, since the fourth surface 200b faces the outside of the winding core 10 and the third surface 200a faces the inside of the winding core 10, the third surface 200a is squeezed. When the negative electrode sheet 200 expands, the expansion degree of the fourth surface 200b is higher than that of the third surface 200a, so that the thickness of the negative electrode active layer of the fourth surface 200b after expansion is greater than that of the negative electrode active layer of the third surface 200a after expansion, thereby reducing the lithium ion embedding sites of the negative electrode active layer of the fourth surface 200b. The first surface 100a with the recess 111 is opposite to the fourth surface 200b, so that the migration path of the positive electrode active material of the recess 111 can be longer, and the migration path of the positive electrode active material of other parts of the first surface 100a can be shorter, thereby making the positive electrode active material of the recess 111 The lithium ions of the positive electrode active material are difficult to embed into the negative electrode active layer of the fourth surface 200b, thereby reducing the positive electrode active material participating in the charge and discharge reaction in the recess 111, so that the negative electrode active layer of the fourth surface 200b has sufficient sites for the lithium ions of the positive electrode active material in other parts of the first surface 100a except the recess 111 to be embedded. In this way, the recess 111 can reduce the positive electrode active material participating in the charge and discharge reaction of the first surface 100a, thereby improving the CB value (negative electrode surface capacity / positive electrode surface capacity) of the battery, so that the fourth surface 200b has more sites for accommodating the lithium ions deintercalated from the first surface 100a, thereby reducing the probability of lithium deposition on the fourth surface 200b, thereby improving the lithium deposition phenomenon on the positive and negative surfaces of the negative electrode sheet 200.

[0083] Since the fourth surface 200b faces the outside of the winding core 10 and the third surface 200a faces the inside of the winding core 10, the third surface 200a is squeezed. When the negative electrode sheet 200 expands, the fourth surface 200b expands more than the third surface 200a. The fourth surface 200b needs a larger expansion space to avoid the positive electrode sheet 100 or the negative electrode sheet 200 from breaking due to greater stress during expansion. The presence of the recess 111 can better solve this problem. The recess 111 is opposite to the fourth surface 200b. The recess 111 can reserve a larger space for the expansion of the fourth surface 200b. That is, when the fourth surface 200b expands more seriously, the fourth surface 200b is Part of the negative electrode active layer of the surface 200b can enter the space of the concave portion 111, which is conducive to releasing the expansion stress of the fourth surface 200b, so as to avoid the expansion of the fourth surface 200b causing the concave-convex structure 110 to be squeezed and deformed, thereby ensuring the supporting effect of the convex portion 112 on the negative electrode sheet 200 or the diaphragm, thereby ensuring that there is enough gap between the positive electrode sheet 100 and the negative electrode sheet 200 for storing electrolyte and releasing stress, and the convex portion 112 opposite to the third surface 200a can offset part of the stress generated by the expansion of the negative electrode sheet 200, thereby effectively preventing the positive electrode sheet 100 or the negative electrode sheet 200 from breaking due to excessive stress.

[0084] Among them, the positive electrode sheet 100 located in the straight area 10a can be provided with a concave-convex structure 110, or the positive electrode sheet 100 located in the arc corner area 10b can be provided with a concave-convex structure 110, or both the positive electrode sheet 100 located in the straight area 10a and the positive electrode sheet 100 located in the arc corner area 10b can be provided with a concave-convex structure 110.

[0085] Since the interface of the arc angle area 10b is more compact, the extrusion stress on the arc angle area 10b is greater than that on the straight area 10a, and the smaller the bending radius of the arc angle area 10b, the greater the extrusion stress on the arc angle area 10b, and the easier it is to break. Therefore, when the positive electrode sheet 100 of the arc angle area 10b is provided with a concave-convex structure 110, the concave-convex structure 110 can increase the bending radius of the arc angle area 10b, and the convex portion 112 can increase the gap between the adjacent positive electrode sheet 100 and the negative electrode sheet 200, and the gap can be the positive electrode sheet 10 0 and the negative electrode sheet 200 provide a compression stress release space, thereby avoiding the adjacent positive electrode sheet 100 and negative electrode sheet 200 from squeezing each other, thereby avoiding the positive electrode sheet 100 and the negative electrode sheet 200 in the arc angle area 10b from being subjected to greater stress and causing powder shedding and breakage problems. Moreover, after the gap between the positive electrode sheet 100 and the negative electrode sheet 200 is increased, more storage space can be provided for the electrolyte, so as to improve the infiltration effect of the electrolyte on the positive electrode sheet 100 and the negative electrode sheet 200, thereby effectively improving the lithium precipitation phenomenon of the negative electrode sheet 200.

[0086] The battery provided in the embodiment of the present application includes a winding core 10, which includes a positive electrode sheet 100, a separator and a negative electrode sheet 200. The winding core 10 has a straight area 10a and an arc angle area 10b. The negative electrode sheet 200 includes a negative electrode collector and a negative electrode active layer. The negative electrode active layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material. The positive electrode sheet 100 includes a concave-convex structure 110. The concave-convex structure 110 includes a concave portion 111 and a convex portion 112, so that the surface of the positive electrode sheet 100 is uneven, and the convex portion 112 has a supporting effect on the negative electrode sheet 200, thereby increasing the gap between the positive electrode sheet 100 and the negative electrode sheet 200, thereby increasing the storage space of the electrolyte.

[0087] Since the negative electrode active coating of the negative electrode sheet 200 contains a silicon-carbon composite material and / or a silicon-oxygen composite material, the volume of silicon will expand and shrink during charge and discharge, thereby causing the volume of the negative electrode sheet 200 to expand and shrink, and the third surface 200a of the negative electrode sheet 200 is subjected to a greater extrusion force than the fourth surface 200b of the negative electrode sheet 200. When the negative electrode sheet 200 expands as a whole, the expansion degree of the fourth surface 200b is greater than the expansion degree of the third surface 200a. The concave portion 111 is arranged on the first surface 100a and is recessed inward from the first surface 100a, so that the concave portion 111 is opposite to the fourth surface 200b that expands more seriously, thereby providing a larger expansion stress release space for the fourth surface 200b of the negative electrode sheet 200, thereby preventing the concave-convex structure 110 from collapsing and deforming due to the expansion of the fourth surface 200b, thereby preventing the convex portion 112 from losing its supporting function;

[0088] Moreover, the recess 111 is opposite to the fourth surface 200b, so that the migration path of the positive electrode active material in the recess 111 can be longer, and the migration path of the positive electrode active material in other parts of the first surface 100a can be shorter, thereby reducing the positive electrode active material participating in the charge and discharge reaction in the recess 111, so that the negative electrode active layer of the fourth surface 200b has sufficient sites for lithium ion embedding. In this way, the recess 111 can reduce the positive electrode active material participating in the charge and discharge reaction on the first surface 100a, thereby improving the CB value (negative electrode surface capacity / positive electrode surface capacity) of the battery, so that the fourth surface 200b has more sites for accommodating the lithium ions deintercalated from the first surface 100a, thereby reducing the probability of lithium deposition on the fourth surface 200b, thereby improving the lithium deposition phenomenon on the positive and negative surfaces of the negative electrode sheet 200.

[0089] The convex portion 112 is arranged on the second surface 100b and protrudes outward from the second surface 100b, so that the convex portion 112 and the concave portion 111 are arranged in pairs on two opposite sides of the positive electrode sheet 100, and the convex portion 112 is opposite to the third surface 200a of the negative electrode sheet 200. Since the expansion degree of the third surface 200a is lighter than that of the fourth surface 200b, the expansion of the third surface 200a is not likely to cause deformation and failure of the concave-convex structure 110, and the supporting effect of the convex portion 112 on the negative electrode sheet 200 can be effectively guaranteed, and the convex portion 112 can offset part of the expansion stress of the negative electrode sheet 200 on the positive electrode sheet 100, thereby preventing the positive electrode sheet 100 from being subjected to greater stress and breaking.

[0090] When the positive electrode sheet 100 located in the arc angle area 10b is provided with a concave-convex structure 110, the convex portion 112 can increase the gap between the positive electrode sheet 100 and the negative electrode sheet 200, thereby increasing the bending radius of the arc angle area 10b, thereby reducing the extrusion stress between the positive electrode sheet 100 and the negative electrode sheet 200. Increasing the gap between the positive electrode sheet 100 and the negative electrode sheet 200 can also increase the storage space of the electrolyte, thereby improving the infiltration effect of the electrolyte on the positive electrode sheet 100 and the negative electrode sheet 200, thereby improving the lithium deposition problem of the negative electrode sheet 200, and the concave portion 111 can provide a release space for the expansion of the negative electrode sheet 200, so as to reduce the expansion stress of the negative electrode sheet 200 on the positive electrode sheet 100 due to the expansion of silicon, thereby causing stress concentration in the arc angle area 10b, and then causing the positive electrode sheet 100 to break. In this way, the concave-convex structure 110 in the arc angle area 10b can improve the breakage problem of the positive electrode sheet 100 and improve the lithium deposition phenomenon of the negative electrode sheet 200. Therefore, the battery provided by the embodiment of the present application has higher safety.

[0091] Reference Figure 4 As shown, in a possible implementation, the concave-convex structure 110 includes a first concave-convex structure 110a and a second concave-convex structure 110b, the first concave-convex structure 110a is located in the arc angle area 10b, the first concave-convex structure 110a includes a first concave portion 111a and a first convex portion 112a, the second concave-convex structure 110b is located in the straight area 10a, and the second concave-convex structure 110b includes a second concave portion 111b and a second convex portion 112b.

[0092] The depression depth h1 of the first concave portion 111a and the depression depth h2 of the second concave portion 111b satisfy: h1<h2. And / or, the protrusion height h3 of the second convex portion 112b and the depression depth h2 of the second concave portion 111b satisfy: h3<h2. And / or, the protrusion height h4 of the first convex portion 112a and the depression depth h1 of the first concave portion 111a satisfy: h4

[0093] That is to say, when the positive electrode sheet 100 in the straight area 10a and the arc angle area 10b are both provided with a concave-convex structure 110, the concave-convex structure 110 located in the arc angle area 10b is recorded as a first concave-convex structure 110a, and the concave-convex structure 110 located in the straight area 10a is recorded as a second concave-convex structure 110b. Correspondingly, the concave portion 111 located in the arc angle area 10b is recorded as a first concave portion 111a, and the convex portion 112 located in the arc angle area 10b is recorded as a first convex portion 112a, the concave portion 111 located in the straight area 10a is recorded as a second concave portion 111b, and the convex portion 112 located in the straight area 10a is recorded as a second convex portion 112b.

[0094] ​It should be noted that the depression depth h1 of the first concave portion 111a may be less than the depression depth h2 of the second concave portion 111b, that is, the depression depth of the arc angle region 10b is less than the depression depth of the straight region 10a, in order to prevent the arc angle region 10b from having too much rolling pressure when forming the concave-convex structure 110 (for example, when rolling the positive electrode sheet 100 by embossing), thereby causing the stress of the arc angle region 10b to be too large and causing the positive electrode sheet 100 to break. In addition, the convex portion 112 of the straight region 10a will increase the overall thickness of the winding core 10, and the convex portion 112 of the arc angle region 10b will increase the width of the winding core 10.

[0095] Therefore, the protruding height h3 of the second protrusion 112b can be smaller than the recessed depth h2 of the second recess 111b, thereby reducing the thickness of the winding core 10, thereby improving the energy density of the battery. The protruding height h4 of the first protrusion 112a can be smaller than the recessed depth h1 of the first recess 111a, thereby reducing the width of the winding core 10, thereby improving the energy density of the battery. In this way, the energy density and safety of the battery can be improved at the same time.

[0096] In some embodiments, the protrusion height h3 of the second protrusion 112b and the depression depth h2 of the second depression 111b satisfy: 0.2≤h3 / h2<1. Preferably, the protrusion height h3 of the second protrusion 112b and the depression depth h2 of the second depression 111b satisfy: 0.3≤h3 / h2≤0.7.

[0097] With such configuration, the protruding height h3 of the second protrusion 112b can be smaller than the recessed depth h2 of the second recess 111b, thereby reducing the thickness of the winding core 10 and improving the energy density of the battery.

[0098] Exemplarily, the ratio h3 / h2 of the protruding height h3 of the second protrusion 112b to the recessed depth h2 of the second recess 111b may be any one of 0.2, 0.3, 0.5, 0.7, 0.8, and 0.9 or be within any two value ranges.

[0099] In a possible implementation, the bending radius R1 of the arc-angle area 10b and the thickness T1 of the straight area 10a satisfy: 0.45≤R1 / T1≤0.75.

[0100] It should be noted that the bending radius R1 of the arc angle area 10b should be understood as the bending radius of the arc angle area 10b of the outermost circle of the unfinished side of the winding core 10, that is, the thickness of all the arc angle areas 10b. The thickness T1 of the straight area 10a is the thickness of the winding core 10, and the ratio R1 / T1 of the bending radius R1 of the arc angle area 10b to the thickness T1 of the straight area 10a can be between 0.45 and 0.75.

[0101] In this way, compared with the related art, after winding, the positive electrode sheet 100 provided with the concave-convex structure 110 can increase the bending radius R1 of the arc corner area 10b, thereby providing a compression stress release space for the positive electrode sheet 100 and the negative electrode sheet 200 in the arc corner area 10b, thereby reducing the compression stress of the arc corner area 10b, and during the charging and discharging process of the battery, the stress of the arc corner area 10b will not increase due to the expansion and contraction of the active material, thereby effectively alleviating the fracture phenomenon of the arc corner area 10b and the lithium plating problem caused by insufficient electrolyte due to excessive extrusion pressure.

[0102] Exemplarily, the ratio R1 / T1 of the bending radius R1 of the arc angle area 10b to the thickness T1 of the straight area 10a may be any one of 0.45, 0.55, 0.6, 0.64, 0.7, and 0.75, or may be within any two value ranges.

[0103] Since the electrolyte in the battery is stored in the gap between the core 10 and the shell, and in the gap between the positive electrode sheet 100 and the negative electrode sheet 200, the interlayer storage between the positive electrode sheet 100 and the negative electrode sheet 200 mainly relies on the infiltration of pores and capillary effects. The infiltration takes a long time and is difficult. Therefore, the liquid storage in the inner layer of the core 10 is less than that in the outer layer of the core 10.

[0104] Therefore, in a possible implementation, the winding core 10 has N folded winding layers from the inside to the outside, and the depression depth h of the concave portion 111 located in the innermost folded winding layer is n The depth h of the concave portion 111 located at the outermost folded winding layer is n+1 Satisfy: h n ≥h n+1 . Wherein, N is an integer greater than 1, and n is any value between 1 and N.

[0105] Exemplarily, N is 5, n is any integer from 1 to 5, and the core 10 may include the first fold winding layer, the second fold winding layer, the third fold winding layer, the fourth fold winding layer, and the fifth fold winding layer from the inside to the outside. For the first fold winding layer and the second fold winding layer, the depression depth of the recess 111 of the first fold winding layer may be greater than or equal to the depression depth of the recess 111 of the second fold winding layer. For the second fold winding layer and the third fold winding layer, the depression depth of the recess 111 of the second fold winding layer may be greater than or equal to the depression depth of the recess 111 of the third fold winding layer. For the first fold winding layer and the fifth fold winding layer, the depression depth of the recess 111 of the first fold winding layer may be greater than the depression depth of the recess 111 of the fifth fold winding layer.

[0106] In this way, the depth of the recess 111 of the inner layer of the core 10 is greater than or equal to the depth of the recess 111 of the outer layer of the core 10, which is beneficial for the recess 111 of the inner layer of the core 10 to store electrolyte, thereby reducing the probability of lithium plating in the inner layer of the core 10, thereby improving the cycle life of the battery.

[0107] In a possible implementation, the projection shape of the concave-convex structure 110 in the thickness direction of the positive electrode sheet 100 may include at least one of a circle, an ellipse, a line, a wave, a polygon, and a capsule, thereby facilitating selection of different shapes according to process conditions.

[0108] In a specific implementation, the positive electrode sheet 100 includes a positive electrode current collector, a first coating layer and a second coating layer. The first coating layer and the second coating layer are arranged on two opposite sides of the positive electrode current collector. The first coating layer and the second coating layer can use positive electrode active materials of the same component. The positive electrode current collector can be aluminum foil.

[0109] In some embodiments, the gap H1 between two adjacent recesses 111 and the diameter H2 of the recess 111 satisfy: 0.6≤H1 / H2≤2.

[0110] Since the positive electrode sheet 100 is provided with a plurality of concave-convex structures 110, the ratio H1 / H2 of the gap H1 between two adjacent recesses 111 to the diameter H2 of the recess 111 represents the density of the concave-convex structures 110. When the ratio H1 / H2 of the gap H1 between two adjacent recesses 111 to the diameter H2 of the recess 111 is between 0.6 and 2, the concave-convex structures 110 on the positive electrode sheet 100 can be ensured to be relatively evenly distributed, thereby avoiding the breakage of the positive electrode current collector due to excessive concentration of pressure during rolling due to the concave-convex structures 110 being too dense, and avoiding the failure to achieve the functions of liquid storage and stress relief due to the concave-convex structures 110 being too sparse.

[0111] It should be understood that when the recess 111 is circular, the caliber H2 of the recess 111 is the diameter of the circle, when the recess 111 is elliptical, the caliber H2 of the recess 111 is the length of the major axis of the ellipse, and when the recess 111 is linear, the caliber H2 of the recess 111 is the extended length of the line. When the recess 111 is capsule-shaped, the caliber H2 of the recess 111 is the length between the two ends of the capsule. When the recess 111 is irregularly formed, the caliber can be the size of the recess 111 in the width direction of the pole piece.

[0112] In a possible implementation, the outer perimeter L1 of the concave portion 111 is greater than the outer perimeter L2 of the convex portion 112 .

[0113] It can be understood that the recess 111 is recessed inward from the first surface 100a, and the protrusion 112 is protruded outward from the second surface 100b. The larger the recess 111 is, the larger the space for storing electrolyte and the space for releasing stress. Therefore, the outer contour circumference L1 of the recess 111 can be made larger than the outer contour circumference L2 of the protrusion 112.

[0114] In some embodiments, the outer perimeter L1 of the concave portion 111 and the outer perimeter L2 of the convex portion 112 satisfy: 1<L1 / L2≤2.

[0115] In this way, the concave space formed by the concave portion 111 is larger, thereby being able to store more electrolyte and provide a larger expansion stress release space for the negative electrode sheet 200. In addition, the convex portion 112 can be raised to a certain height, thereby enabling the convex portion 112 to expand the bending radius of the arc corner area 10b and offset part of the stress.

[0116] Exemplarily, the ratio L1 / L2 of the outer contour circumference L1 of the concave portion 111 to the outer contour circumference L2 of the convex portion 112 may be any one of 1.1, 1.2, 1.5, 1.7, 1.8, and 2, or may be within any two value ranges.

[0117] In a possible implementation, the outer perimeter L1 of the recess 111 and the thickness T2 of the positive electrode sheet 100 satisfy: 30≤L1 / T2≤160. And / or the outer perimeter L1 of the recess 111 satisfies: 4500 μm≤L1≤8000 μm.

[0118] It should be noted that the thickness T2 of the positive electrode sheet 100 described here can be understood as the thickness of other parts of the positive electrode sheet 100 that are not provided with the concave-convex structure 110, or the average value of the thickness of the positive electrode sheet 100 that is provided with the concave-convex structure 110 and the thickness of other parts that are not provided with the concave-convex structure 110.

[0119] The outer contour circumference L1 of the recess 111 can be matched and set according to the thickness T2 of the positive electrode sheet 100. When the ratio L1 / T2 of the outer contour circumference L1 of the recess 111 to the thickness T2 of the positive electrode sheet 100 is between 30 and 160, the recess 111 of the positive electrode sheet 100 of different thicknesses can have better liquid storage effect and stress release effect, thereby effectively alleviating the expansion and contraction phenomenon of the negative electrode sheet 200 and preventing the positive electrode sheet 100 or the negative electrode sheet 200 from breaking.

[0120] For example, the ratio L1 / T2 of the outer perimeter L1 of the recess 111 to the thickness T2 of the positive electrode sheet 100 may be any one of 30, 40, 50, 80, 100, and 160, or may be within any two numerical ranges. For another example, the outer perimeter L1 of the recess 111 may be any one of 4500 μm, 5000 μm, 6000 μm, 7000 μm, and 8000 μm, or may be within any two numerical ranges.

[0121] Reference Figure 6 As shown, in a possible implementation, the positive electrode sheet 100 is provided with a concave-convex area 120 and a void area 130 , a plurality of concave-convex structures 110 are located in the concave-convex area 120 , the void area 130 is staggered with the concave-convex area 120 , and the void area 130 is surrounded on at least one side of the concave-convex area 120 .

[0122] That is to say, the concave-convex area 120 is provided with the concave-convex structure 110 , and the concave-convex area 120 is an area surrounded by a plurality of concave-convex structures 110 , while the void area 130 is not provided with the concave-convex structure 110 , thereby avoiding the void area 130 from powdering and breaking.

[0123] In some embodiments, the area S1 of the concave-convex region 120 and the area S2 of the positive electrode sheet 100 satisfy: 0.02≤S1 / S2≤0.85.

[0124] It can be understood that the positive electrode sheet 100 has an avoidance area 130 where the concave-convex structure 110 is not set. Therefore, the ratio S1 / S2 of the area S1 of the concave-convex area 120 to the area S2 of the positive electrode sheet 100 is less than or equal to 0.85, which prevents the area of ​​the concave-convex structure 110 from occupying too large a proportion, thereby preventing the concave-convex structure 110 from causing the positive electrode sheet 100 to fall off or break, and the ratio S1 / S2 of the area S1 of the concave-convex area 120 to the area S2 of the positive electrode sheet 100 is greater than or equal to 0.02 to ensure the effective liquid storage and stress buffering function of the concave-convex structure 110. At least one of the arc angle area 10b and the straight area 10a is provided with the concave-convex structure 110, thereby reducing the stress in the arc angle area 10b or the straight area 10a.

[0125] Along the unfolded length direction of the positive electrode sheet 100, the first end of the first coating is aligned with the first end of the second coating, the first end of the positive electrode current collector has a first empty foil area 131, the second end of the first coating exceeds the second end of the second coating, the positive electrode sheet 100 where the first coating and the second coating overlap constitutes a double-sided coating area, and the positive electrode sheet 100 where the first coating exceeds the second coating constitutes a single-sided coating area 132. Along the width direction of the positive electrode sheet 100, both sides of the positive electrode sheet 100 have a first edge area 133 and a second edge area 134. The air avoidance area 130 includes at least one of the single-sided coating area 132, the first empty foil area 131, the first edge area 133, and the second edge area 134.

[0126] It should be understood that the single-sided coating area 132 has the first coating on only one side, and the second coating is not on the other side, and the positive electrode current collector is exposed on the other side. Therefore, the single-sided coating area 132 is not provided with the concave-convex structure 110, thereby avoiding uneven force on the two relative sides of the positive electrode current collector, thereby avoiding the first coating of the single-sided coating area 132 from falling off, and avoiding fractures at the junction of the single-sided coating area 132 and the double-sided coating area.

[0127] The first edge area 133 and the second edge area 134 are located on both sides of the width direction of the positive electrode sheet 100. The concave-convex structure 110 avoids the first edge area 133 and the second edge area 134, thereby preventing the first edge area 133 and the second edge area 134 from falling off. The first empty foil area 131 can be understood as a positive electrode current collector on which the first coating and the second coating are not provided on both sides. The concave-convex structure 110 is not provided therein to prevent the positive electrode current collector therefrom from being broken due to a large force.

[0128] Reference Figure 6 As shown, in a possible implementation, the battery also includes a first pole ear, the first edge area 133 is provided with at least one pole ear connection groove 1331, the pole ear connection groove 1331 exposes at least part of the positive electrode collector, the first pole ear is connected to the positive electrode collector in the pole ear connection groove 1331, and the pole ear connection groove 1331 is staggered with the concave-convex area 120.

[0129] Since the thickness of the first pole ear is relatively large, the force applied during processing to form the concave-convex structure 110 can easily cause the first pole ear to fracture the positive electrode current collector in the pole ear connecting groove 1331, thereby reducing the connection strength between the first pole ear and the positive electrode sheet 100. Therefore, when processing to form the concave-convex structure 110, the pole ear connecting groove 1331 can be avoided, thereby improving the connection strength between the first pole ear and the positive electrode sheet 100.

[0130] In a possible implementation, along the width direction of the positive electrode sheet 100, the spacing W1 between the tab connection groove 1331 and the concave-convex area 120 satisfies: 0<W1≤10mm. And / or, along the width direction of the positive electrode sheet 100, the extension dimension W2 of the second edge area 134 satisfies: 2mm≤W2≤20mm. And / or, along the unfolded length direction of the positive electrode sheet 100, the extension dimension A of the first empty foil area 131 satisfies: 0<A≤20mm. And / or, along the unfolded length direction of the positive electrode sheet 100, the extension dimension B of the single-sided coating area 132 satisfies: 0<B≤C, where C is the difference between the length of the first coating and the length of the second coating, which can be selected according to actual conditions.

[0131] Exemplarily, the spacing W1 between the tab connection groove 1331 and the concave-convex area 120 can be any one of 1mm, 2mm, 4mm, 5mm, 10mm or within any two numerical ranges. And / or, the extension dimension W2 of the second edge area 134 can be any one of 1mm, 6mm, 12mm, 15mm, 20mm or within any two numerical ranges. And / or, the extension dimension A of the first empty foil area 131 can be any one of 1mm, 2mm, 5mm, 10mm, 20mm or within any two numerical ranges.

[0132] In a possible implementation, the depth h of the concave portion 111 is proportional to the tensile strength T of the positive electrode current collector. S Satisfy: 0.05≤h / T S ≤0.4. Where, h / T S The unit is μm / Mpa.

[0133] It should be understood that the greater the depression depth h of the concave portion 111, the greater the compressive stress of the concave-convex structure 110 on the positive electrode current collector, and the more likely the positive electrode current collector is to break. Therefore, the depression depth h of the concave portion 111 is related to the tensile strength T of the positive electrode current collector. S The ratio h / T S can be between 0.05 and 0.4, thereby making the tensile strength T S The depth h of the concave portion 111 is matched to prevent the positive electrode current collector from being broken due to excessive extension while ensuring that the concave-convex structure 110 can function normally.

[0134] For example, the depth h of the concave portion 111 is related to the tensile strength T of the positive electrode current collector. S The ratio h / T S It can be any value among: 0.05, 0.1, 0.2, 0.3, 0.4 or within any range of two values.

[0135] Among them, the depression depth h of the recess 111 can be the depression depth h1 of the first recess 111a, or the depression depth h of the recess 111 can be the depression depth h2 of the second recess 111b, or the depression depth h of the recess 111 can be the average value of the depression depth h1 of the first recess 111a and the depression depth h2 of the second recess 111b.

[0136] The preparation process and related tests of the battery provided in this application are described below.

[0137] 1. Prepare the positive electrode sheet 100, mix (lithium cobalt oxide + Li2NiO2), SP (conductive carbon black), and PVDF in a mass ratio of 97.6 (the weight of Li2NiO2 accounts for 1% of the weight of LCO): 1.4: 1, add NMP, stir evenly, and prepare a positive electrode slurry. Apply the positive electrode slurry on the front and back surfaces of the aluminum foil, bake and roll to obtain the positive electrode sheet 100. The positive electrode sheet 100 is embossed from the first surface 100a to the second surface 100b by a roller, and then a concave-convex structure 110 is formed on the positive electrode sheet 100.

[0138] 2. The silicon-carbon-doped negative electrode active material is mixed with SP (conductive carbon black), CMC-Li, and PAA at a mass ratio of 97 (silicon-carbon weight accounts for 5% of graphite weight): 0.4: 0.1: 2.5, and deionized water is added to prepare a negative electrode slurry. The negative electrode slurry is coated on the front and back surfaces of the carbon-coated copper foil, and after baking and rolling, a negative electrode sheet 200 with a thickness of 110μm is obtained.

[0139] 3. The positive electrode sheet 100 and the negative electrode sheet 200 are cut, sheeted, and wound with a separator to obtain a winding core 10.

[0140] Fourth, the battery is obtained through packaging, baking, liquid injection, formation, secondary sealing, sorting and OCV.

[0141] Among them, the electrolyte is a conventional electrolyte and the lithium salt is LiFP6.

[0142] The following tests were performed on groups 1 to 16 of batteries.

[0143] 1. Pole fracture ratio test

[0144] In a 45℃ constant temperature room, 1C constant current and constant voltage were applied to the upper limit voltage, 0.05C was used as the cutoff, and the battery was allowed to stand for 10 minutes. The battery was then discharged at 0.5C to 3.0V. After 600T cycles, 100 pieces were disassembled and the number of batteries with broken electrodes was counted, where the electrodes included 100 positive electrodes and 200 negative electrodes.

[0145] 2. Volume energy density test

[0146] The volume energy density of the battery is ED=E / V, where E is the discharge energy of the battery. The test method is to charge the lithium-ion battery to the upper voltage limit at a current of 0.2C, then charge it at a constant voltage until the current drops to 0.02C, and then discharge it at a current of 0.2C to 3.0V. The discharged energy is E. V is the volume of the battery. The thickness, width and length of the battery are measured and the product of the three is calculated to obtain the volume of the battery. E / V is the volume energy density obtained by the test.

[0147] 3. 25℃ Cyclic 1000T Expansion Rate Test

[0148] Keep it in a constant temperature room or incubator at 25℃ for 2 hours, 1C constant current and constant voltage to the upper limit voltage, 0.05C is recorded at this time, the thickness of the core 10 is t1, stand for 10 minutes, then discharge at 0.5C to 3.0V, cycle 1000T, then 1C constant current and constant voltage to the upper limit voltage, 0.05C is recorded at this time, the thickness of the core 10 is t2, t2 / t1 is the expansion rate of 25℃ cycle 1000T;

[0149] 4. Voltage drop test

[0150] After being stored in a 45℃ high temperature room for 48-60 hours, take out the battery and place it in a 25℃ constant temperature room for 24 hours, test the battery voltage V1, and then place it in a 25℃ constant temperature room for 72-96 hours, test the voltage V2, where the voltage drop K value = (V1-V2) / interval between two tests.

[0151] 5. Tensile strength test

[0152] After the battery is discharged to 0% SOC, the positive electrode sheet 100 is disassembled and taken out, and then soaked in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsed with DMC to remove the lithium salt attached to the positive electrode sheet 100. The positive electrode sheet 100 (with paste) is cut into test samples with a width of 15 mm and a length of more than 50 mm using a cutter. A WD-D3 electronic universal testing machine (with a precision of 0.5 level and an accuracy of ±1% of the indicated value) is used to set the gauge length to 50 mm and the speed to 10 mm / min. A tensile test is performed on the test sample to measure the maximum tensile stress of the positive electrode sheet 100, and the tensile strength = maximum tensile stress / thickness of the positive electrode current collector.

[0153] Table 1 Battery structure parameters

[0154]

[0155] Table 2 Battery structure parameters

[0156]

[0157] Table 3 Test results

[0158]

[0159] According to Table 1 and Table 2, the structural parameters of the batteries of Group 1 and Group 7 are within the range required by this embodiment, and S1 of Group 7 is smaller than that of Group 1. The test results of Group 1 and Group 7 show that the battery arranged according to this embodiment can achieve no breakage of the electrode sheet, ensure that the battery has a high volume energy density, and have a low expansion rate and pressure drop.

[0160] Compared with the structural parameters and test results of Group 1, R1 / T1 of Group 2 is smaller, indicating that the winding core 10 is too tight during winding, and the stress of the arc angle area 10b is large. The stress of the arc angle area 10b cannot be released during the charge and discharge expansion process, which causes damage to the positive electrode sheet 100 and the negative electrode sheet 200, making it easy for the electrode sheet to break. Therefore, the electrode sheet breakage ratio of Group 2 is higher. R1 / T1 of Group 3 is larger, indicating that the winding core 10 is too loose, and the arc angle area 10b is larger, which increases the width of the winding core 10, thereby causing a loss of battery energy density. Therefore, the volume energy density of Group 3 is lower.

[0161] Compared with Group 1, L1 / T2 of Group 4 is smaller, and the contour perimeter of the concave portion 111 of the concave-convex structure 110 is smaller, which also affects the insufficient depth of the depression, and the limited storage space for the electrolyte, which limits the degree of improvement of the positive electrode side dynamics, resulting in lithium precipitation problems in the later stages of the battery cycle. L1 / T2 of Group 6 is larger, and the contour perimeter of the concave portion 111 of the concave-convex structure 110 is larger, which in turn causes the protrusion depth of the protrusion 112 to be too large, which damages the strength of the positive electrode current collector, making it less able to withstand stress changes, and the pole piece is prone to breakage.

[0162] Compared with Group 1, T2 of Group 5 is smaller, and T2 of Group 13 is larger. When the thickness of the positive electrode sheet 100 becomes smaller, under the condition of a certain volume, the proportion of the paste on the overall winding core 10 decreases (the proportion of components that do not contribute to capacity, such as the positive electrode current collector and diaphragm, increases), which in turn causes ED loss. Conversely, when the thickness of the electrode sheet increases, ED increases.

[0163] Compared with group 1, the S1 / S2 of group 8 is too small, the area ratio of the concavo-convex structure 110 is too small, the concavo-convex structure 110 is arranged relatively sparsely, the electrolyte storage space is limited, and the effect of improving the kinetics of the positive electrode side is limited, which makes the battery have lithium precipitation problems in the later stage of the cycle. The S1 / S2 of group 9 is too small, the area ratio of the concavo-convex structure 110 is too large, and the concavo-convex structure 110 is arranged relatively densely, which easily causes the pole piece to fall off, thereby increasing the battery voltage drop.

[0164] Compared with group 1, group 10 has smaller H1 / H2, sparsely arranged concavoconvex structures 110, limited electrolyte storage space, and limited effect on improving the kinetics of the positive electrode, which results in lithium deposition problems in the late cycle of the battery. Group 11 has larger H1 / H2, and sparsely arranged concavoconvex structures 110, which easily causes the pole piece to lose powder, thereby increasing the battery voltage drop.

[0165] It can be understood that the arc corner area 10b is subjected to much greater winding stress than the straight area 10a, so the strength of the positive electrode collector in the arc corner area 10b should be greater than that in the straight area 10a, so that it will have a significant effect on improving the fracture of the electrode piece. In the 12th group, h1 is greater than h2, that is, the depression depth of the second recess 111b is greater than the depression depth of the first recess 111a, so that the positive electrode collector in the arc corner area 10b has been subjected to greater stress during the formation of the concave-convex structure 110, which weakens the tensile strength of the positive electrode collector in the arc corner area 10b, thereby increasing the probability of electrode fracture.

[0166] Compared with the first group, the h3 / h2 of the 13th group is too small, and the depth of the depression of the concave portion 111 does not match the height of the protrusion of the convex portion 112. That is, when the depth of the depression of the concave portion 111 has reached the limit, the protrusion height of the convex portion 112 on the other side is still small because the positive electrode sheet 100 is thick. At this time, the positive electrode side dynamic improvement effect brought by the concave-convex structure 110 cannot be manifested because the positive electrode sheet 100 itself is thick. At the same time, because the concave portion 111 squeezes the positive electrode collector, the positive electrode collector faces a critical damage value, and there is a small proportion of electrode sheet fracture. However, because the positive electrode sheet 100 is thick, the overall space utilization can be improved, so the volume energy density is improved. The h3 / h2 of the 14th group is too small. At this time, the depth of the depression of the concave portion 111 is consistent with the height of the protrusion of the convex portion 112, the positive electrode collector is easy to be crushed, and the positive electrode sheet 100 is easy to break.

[0167] Compared with group 1, h / T in group 15 was S If the depth of the concave portion 111 is too large, the tensile strength of the positive electrode current collector cannot match the depth of the concave portion 111, that is, the positive electrode current collector cannot withstand the stress of forming the concave portion 111, and the positive electrode current collector is easily damaged, thereby causing the positive electrode sheet 100 to break. h / T of Group 16 S If the size is too small, the depth of the recess 111 is small, the electrolyte storage space is limited, and the effect of improving the kinetics on the positive electrode side is limited, resulting in lithium deposition problems in the later stages of the battery cycle.

[0168] Finally, it should be noted that those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include common knowledge or customary technical means in the art not disclosed by the present invention, are not limited to the precise structure described above and shown in the drawings, and may be modified and changed in various ways without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A battery, characterized in that: The winding core comprises a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and wound to form the winding core, and the winding core has a straight area and an arc angle area, wherein the arc angle area is located at two opposite ends of the straight area; The negative electrode sheet comprises 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; The positive electrode sheet has a first surface and a second surface facing each other, and the negative electrode sheet has a third surface and a fourth surface facing each other, wherein the first surface and the third surface face the inner side of the winding core, and the second surface and the fourth surface face the outer side of the winding core; The positive electrode sheet is provided with a plurality of concave-convex structures, the concave-convex structures are located in at least one of the arc angle area and the straight area, the concave-convex structures include a concave portion sunken inward from the first surface and a convex portion protruding outward from the second surface, and the convex portion and the concave portion are arranged correspondingly; The fourth surface of the negative electrode sheet and the first surface having the concave portion are arranged opposite to each other.

2. The battery according to claim 1, characterized in that The concavo-convex structure includes a first concavo-convex structure and a second concavo-convex structure, the first concavo-convex structure is located in the arc angle area, the first concavo-convex structure includes a first concave portion and a first convex portion, the second concavo-convex structure is located in the straight area, and the second concavo-convex structure includes a second concave portion and a second convex portion; The depression depth h1 of the first depression and the depression depth h2 of the second depression satisfy: h1<h2; and / or, a protruding height h3 of the second protruding portion and a recessed depth h2 of the second recessed portion satisfy: h3<h2; And / or, a protruding height h4 of the first protrusion and a recessed depth h1 of the first recess satisfy: h4<h1.

3. The battery according to claim 2, characterized in that A protruding height h3 of the second protruding portion and a recessed depth h2 of the second recessed portion satisfy: 0.2≤h3 / h2<1.

4. The battery according to any one of claims 1 to 3, characterized in that: The bending radius R1 of the arc angle area and the thickness T1 of the straight area satisfy: 0.45≤R1 / T1≤0.

75.

5. The battery according to any one of claims 1 to 3, characterized in that: The winding core has N folded winding layers from the inside to the outside, and the depth of the concave portion located at the innermost folded winding layer is h n The depth h of the concave portion located at the outermost fold of the winding layer n+1 Satisfy: h n ≥h n+1 ; Wherein, N is an integer greater than 1, and n is any value between 1 and N.

6. The battery according to any one of claims 1 to 3, characterized in that: The gap H1 between two adjacent recesses and the diameter H2 of the recesses satisfy: 0.6≤H1 / H2≤2.

7. The battery according to any one of claims 1 to 3, characterized in that: The outer perimeter L1 of the concave portion is greater than the outer perimeter L2 of the convex portion.

8. The battery according to claim 7, characterized in that The outer contour circumference L1 of the concave portion and the outer contour circumference L2 of the convex portion satisfy: 1<L1 / L2≤2.

9. The battery according to claim 8, characterized in that The outer contour circumference L1 of the concave portion and the thickness T2 of the positive electrode sheet satisfy: 30≤L1 / T2≤160; And / or, the outer contour circumference L1 of the recess satisfies: 4500 μm≤L1≤8000 μm.

10. The battery according to any one of claims 1 to 3, characterized in that: The positive electrode sheet is provided with a concave-convex area and a void area, a plurality of the concave-convex structures are located in the concave-convex area, the void area is staggered with the concave-convex area, and the void area is surrounded on at least one side of the concave-convex area.

11. The battery according to claim 10, characterized in that The area S1 of the concave-convex region and the area S2 of the positive electrode sheet satisfy: 0.02≤S1 / S2≤0.

85.

12. The battery according to claim 10, characterized in that The positive electrode sheet comprises a positive electrode current collector, a first coating layer and a second coating layer, wherein the first coating layer and the second coating layer are disposed on two opposite sides of the positive electrode current collector; Along the unfolded length direction of the positive electrode sheet, the first end of the first coating layer is aligned with the first end of the second coating layer, the first end of the positive electrode current collector has a first empty foil area, the second end of the first coating layer exceeds the second end of the second coating layer, and the positive electrode sheet of the first coating layer exceeding the second coating layer constitutes a single-sided coating area; Along the width direction of the positive electrode sheet, two sides of the positive electrode sheet have a first edge area and a second edge area; The empty area includes at least one of the single-sided coating area, the first empty foil area, the first edge area, and the second edge area.

13. The battery according to claim 12, characterized in that It also includes a first pole tab, the first edge area is provided with at least one pole tab connection groove, the pole tab connection groove exposes at least a portion of the positive electrode collector, the first pole tab is connected to the positive electrode collector in the pole tab connection groove, and the pole tab connection groove is staggered with the concave-convex area.

14. The battery according to claim 13, characterized in that Along the width direction of the positive electrode sheet, the spacing W1 between the tab connection groove and the concave-convex area satisfies: 0<W1≤10mm; And / or, along the width direction of the positive electrode sheet, the extension dimension W2 of the second edge region satisfies: 2mm≤W2≤20mm; And / or, along the unfolded length direction of the positive electrode sheet, the extension dimension A of the first empty foil area satisfies: 0<A≤20mm; And / or, along the unfolded length direction of the positive electrode sheet, the extension dimension B of the single-sided coating area satisfies: 0<B≤C, wherein C is the difference between the length of the first coating and the length of the second coating.

15. The battery according to claim 12, characterized in that The depth h of the concave portion and the tensile strength T of the positive electrode collector S Satisfy: 0.05≤h / T S ≤0.4.

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