Foil for a positive electrode and battery with the same

Abstract

A positive electrode film comprising a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material layer comprises a concave-convex region, and the concave-convex region comprises a plurality of concave portions and convex portions respectively arranged corresponding to the concave portions; the active material layer for the positive electrode has a weight loss rate p in a nitrogen environment in a temperature range of 35 °C to 450 °C and p satisfies the following condition: 1.1% ≤ ρ ≤ 6%

Description

TECHNICAL FIELDThe present application relates to the technical field of batteries, more particularly to a positive electrode foil and a battery including the same.BACKGROUNDIn general, batteries are constructed as a layered structure with a plurality of electrode foils, wherein a certain squeezing (squeeze) occurs between different layers of the batteries or between different parts of the same layer. When batteries are subjected to a charge and discharge cycle, the electrode foils expand, thereby enhancing the aforementioned crush. This pinch may impair the stability of the layered structure of the battery, which may lead to local electrolyte deficiency and poor wetting and may easily lead to interface degradation and even to safety issues such as rapid battery capacity degradation or precipitation of lithium.SUMMARYThe present application relates to a positive electrode foil and a battery, in which, based on ensuring the structural stability of the positive electrode foil, the technical problems of electrolyte deficiency between the layers and poor wetting, which can lead to rapid deterioration of the battery capacity or precipitation of lithium according to the prior art, can be solved or at least alleviated.According to a first aspect, the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material; the positive electrode active material layer includes a concave-convex region, and the concave-convex region includes a plurality of concave portions and convex portions disposed corresponding to the respective concave portions; the positive electrode active material layer has a weight loss rate p in a temperature range of 35° C. to 450° C. in a nitrogen environment; and p satisfies the following condition: 1.1%≤p≤6%.Such a positive electrode film according to the first aspect of the present application, because the positive electrode active material layer is provided with the concave-convex portion, a local micro gap can be formed between the positive electrode film and the negative electrode film, thereby providing a spatial condition for storing more electrolyte, providing more electrolyte for long cycles of the battery, improving wettability of the electrolyte in this portion, and avoiding occurrence of abnormal situations such as electrolyte shortage and poor wetting between the positive electrode and a separator. Accordingly, the cycle life of the battery is improved. By forming the concave-convex portion, the surface of the positive electrode foil is rough, so that when the battery cell expands, the convex portions can effectively support the separator, thereby preventing the separator from being deformed by the stress of the negative electrode foil due to the expansion.The positive electrode foil is provided with the convex portions to improve the deformation capability of the positive electrode foil. When the positive electrode sheet contacts the expanded negative electrode sheet, the stress due to expansion of the negative electrode sheet can be effectively absorbed by the convex portions of the positive electrode sheet, and the expansion of the negative electrode sheet can be buffered during the cycle process of the battery, thereby preventing cracks due to excessive stress due to expansion of the negative electrode sheet. Moreover, a part of the stress caused by expansion of the negative electrode foil may be absorbed by the convex portions provided in the positive electrode foil, so that the negative electrode foil does not fully rely on the resistance of its own material during expansion. This retards the fatigue of the negative electrode material and thereby increases the life of the negative electrode foil.Since the weight loss rate of the positive electrode film is defined in the above range and used to represent the structural stability of the positive electrode film, these problems prevent such as an elongation of the binder in the positive electrode active material layer due to excessive pressure for forming the concave-convex portion during the formation of the concave-convex portion in the positive electrode film, thereby reducing the effect of the binder in bonding the positive electrode active particles, or an excessive packing density during the rolling process, or a power drop due to an excessive force acting on the positive electrode active material layer caused by the content of the binder in the positive electrode active material layer being too low. Moreover, too high a binder content may not only impair the energy density of the positive electrode foil, but also result in the overall structure of the positive electrode foil becoming brittle and hard and having poor overall toughness, which results in the positive electrode foil as a whole being not ductile and therefore being easily crushed due to an excessive stress concentration during the formation of the concavo-convex portion. That is, by balancing the density of compaction of the positive electrode sheet, the binder content, and the height of the convex portions to control the weight loss rate of the positive electrode sheet within this range, the positive electrode sheet can be prevented from being damaged during the formation of the concave-convex portion, while the energy density is maintained.In one possible embodiment, the height of a top surface of the convex portions from the surface of the positive electrode active material layer is h, and h and p satisfy the following relationship: 50<h / p<3600; and / or 3 μm≤h<40 μm.In one possible embodiment, the concave portions have a diameter R, and a distance between two adjacent convex portions is L, and R, L, and p satisfy the following relationship: 10<L / R / p<1000 and / or 1000 μm≤R≤ 5000 μm and / or 1500 μm≤L≤ 5000 μm.In one possible embodiment, the positive electrode foil has a density of densification D, and D, h and R satisfy the following relationship: 0.004<D*h / R<0.12, and / or 3 g / cm 3 ≤ D ≤ 4.5 g / cm 3.In a possible embodiment, the number N of convex portions or concave portions per unit area of the concave-convex region, measured in cm, is 2, and N holds: 2≤N≤25, preferably 4≤N≤15.In one possible embodiment, the positive electrode active material layer comprises an electrically conductive material, and the electrically conductive material comprises single wall carbon nanotubes extending into the positive electrode active material layer at the top of the convex portions.In a possible embodiment, two adjacent convex portions each form a first protrusion and a second protrusion, wherein the first protrusion has a first circumscribing circle and a first circumscribing circle is associated with the first protrusion, and the second protrusion has a second circumscribing circle and a second circumscribing circle is associated with the second protrusion, respectively; a distance between a center point of the first circumscribing circle and a center point of the second circumscribing circle is L1, a distance between the first protrusion and the second protrusion is L2, and L1 and L2 satisfy the following relationship: 1.05≤L1 / L2≤3, preferably 1.1≤L1 / L2≤2.In one possible embodiment, L1: 3 mm≤10 mm, preferably 2 mm≤L1≤8 mm; and / or L2: 0.5 mm≤L2≤8 mm, preferably 1 mm≤L2≤4 mm.In a possible embodiment, the convex portions have or are associated with a circumscribing sphere, and the circumscribing sphere comprises an outer surface; wherein a flat region is formed between two adjacent convex portions, the outer surface has a sphere radius R 1, the distance between the top side of the convex portions and the flat region is R 3, and R 1 and R 3 satisfy the following relationship: R 3<R 1, PREFERABLY R 3<1 / 5R 1.In one possible embodiment, the outer surface has a surface Q 1, and a projection of the outer surface formed on the positive electrode current collector along a thickness direction of the electrode foil has a surface S 1; wherein the circumscribing sphere further comprises an inner surface, the inner surface has a surface Q 2, and a projection of the inner surface formed on the positive electrode current collector along the thickness of the electrode foil has a surface S 2; wherein Q 1and Q 2contain the following relationship: 1.02≤Q 1 / Q 2≤1.21, and / or S 1and S 2contain the following relationship: 1.02≤S 1 / S 2≤1.21.In one possible embodiment, the sum of the areas of a protrusion of each of the convex portions on the positive electrode current collector is S 11 and the area of the positive electrode foil is S, and S 11 and S satisfy the following relationship: 0.02≤S 11 / S≤0.85.In a possible embodiment, the single-wall carbon nanotubes are interwoven to form a mesh structure and the positive electrode active material at the top of the convex portions is enveloped within the mesh structure.In a possible embodiment, the single-wall carbon nanotubes have a diameter of 1 nm to 1000 nm and a length of 1 μm to 100 μm; and / or based on a total mass of the positive electrode active material layer, the single-wall carbon nanotubes have a mass fraction of 0.5% to 5%; and / or the single-wall carbon nanotubes in the positive electrode active material layer have a thickness of 10 nm to 500 nm.In one possible embodiment, the positive electrode active material comprises a binder, and based on the total mass of the positive electrode active material layer, the binder has a mass fraction of 1 to 5 wt %; and / or the binder contains at least one of the following compounds: polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinyl acetate, polyethylenepyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.According to a second aspect, the present application provides a battery including a separator, a negative electrode foil, and the positive electrode foil as set forth above, wherein the separator is disposed between the positive electrode foil and the negative electrode foil, and the separator, the positive electrode foil, and the negative electrode foil are wound in the longitudinal direction of the positive electrode foil to form a wound core structure.In one possible embodiment, the negative electrode foil comprises a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material.In one possible embodiment, the convex portions along a thickness direction of the positive electrode foil have a size h3and the concave portions have a size h4, where h3and h4contain the following relationship: 0.2≤h3 / h4≤1.BRIEF DESCRIPTION OF THE DRAWINGSIn order to more clearly illustrate the technical solutions in the embodiments of the present application or according to the prior art, the accompanying drawings required for describing the embodiments or the prior art will be briefly presented below. It is obvious that the accompanying drawings illustrate some embodiments of the present application in the following description. Further drawings or embodiments can also be created for a person skilled in the art on the basis of these drawings without inventive intervention. FIG. 1 is a schematic structural diagram of a battery according to an embodiment of the present application. FIG. 2 is a schematic structural diagram of a positive electrode foil according to an embodiment of the present application. FIG. 3 is a schematic structural diagram of a convex portion according to an embodiment of the present application. FIG. 4 is a schematic structural diagram of two adjacent convex portions of a positive electrode foil according to an embodiment of the present application. FIG. 5 is a side view of a positive electrode foil according to an embodiment of the present application.DESCRIPTION OF THE EMBODIMENTSIn order to clarify the purposes, technical solutions, and advantages of the embodiments of the present application, the technical solutions according to the embodiments of the present application will be clearly and fully described in the embodiments of the present application with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application and do not represent all possible embodiments according to the present application. Based on the embodiments of the present application, all other embodiments that can be obtained by those skilled in the art without inventive intervention fall within the scope of protection of the present application.With the rapid development of lithium ion batteries, the demands of the market on the various performance characteristics of such batteries have also increased. For example, when a lithium ion battery is used in a new power source automobile, it is required to have a better charging speed, life and safety, etc. If a lithium ion battery is used, for example, in household appliances, for example a desk lamp and a shaving apparatus, or in electronic devices, for example in a mobile telephone and a tablet computer, it must have a higher energy density.In recent years, the technology of new energy storage devices has rapidly evolved, and the lithium ion battery also undergoes rapid development. The material selection, manufacturing methods, and structural design of lithium ion batteries are continually being optimized and developed. In the construction of lithium-ion batteries, challenges such as capacity, safety and service life are to be overcome in particular. The continuous research of materials, processes and structures has also continuously improved the performance of lithium-ion batteries, which is manifested above all in a high energy density, a long service life and a high level of safety and further advantages. Therefore, the lithium ion batteries are often used in the field of renewable energies, portable consumer electronics appliances, portable electronic appliances, and other fields.Battery life, energy density, safety and other performance characteristics are determined primarily by the choice of materials for the individual components, the manufacturing process of each component, the structure of each component, the connection construction between these components, etc., in the battery. The performance characteristics of the battery may be improved through optimization and improvement of materials, manufacturing processes, structure, interconnect construction, and the like. Material selection and manufacturing process are related to advances in some basic technologies and sciences, particularly in the fields of physics and chemistry. At the current stage of the development of batteries, it is difficult to optimize and improve materials and manufacturing processes. The structure and connection design of batteries are constantly being improved and altered. Therefore, in order to improve the performance of batteries, at the present stage where the development of materials and manufacturing methods are subject to restrictions, the structure and connection design of the battery can be optimized to achieve the objective of improving the performance of batteries.Unless otherwise stated, the battery described in the present application may be a lithium ion battery. The lithium ion battery may be formed as a stacked structure or a wound core structure. The stacked structure and the wound core structure are both layered structures in the more general sense. A stacked structure refers to a layered structure formed of a plurality of laminated electrode foils and separators. A wound structure refers to a layered structure formed by winding a plurality of electrode foils and separators in a plurality of turns in a clockwise or counter-clockwise direction. Here, the electrode foil may include a positive electrode foil and a negative electrode foil.During the manufacturing process of the battery, for example, when the battery is formed with the above-mentioned stacked structure or the wound core structure, the battery is generally formed as a layered structure having a plurality of electrode foils, and crushing may occur between different layers of the battery or between different parts of the same layer. When such a battery is subjected to a charge and discharge cycle, the electrode sheet expands, thereby enhancing the aforementioned squeezing. This pinch may impair the stability of the layer structure of the battery, which may lead to local electrolyte deficiency and poor wetting and thus may easily lead to degradation of the interface and even to safety risks such as rapid capacity loss or precipitation of lithium.Due to the foregoing situation and problems, an embodiment of the present application provides a positive electrode foil which, based on ensuring its structural stability, can solve or at least alleviate the technical problems of insufficient amount of electrolyte between the layers and poor wetting, which can lead to rapid decrease in battery capacity or precipitation of lithium in the foregoing prior art.The positive electrode foil according to the embodiment of the present application changes the conventional general design idea of a fit between the electrode foils. By appropriately providing support structures, for example, concave portions and convex portions, in the positive electrode foil and by combining the content of a binder in the positive electrode active material layer, a local micro gap can be formed between the positive electrode foil and the negative electrode foil based on ensuring the overall structure strength and the structural stability, thereby creating a spatial condition for storage of additional electrolyte and the additional provision of electrolyte for a long cycle of the battery and improving the cycle life of the battery as a whole. Moreover, according to the embodiment of the present application, by appropriately adjusting the material ratio of the positive electrode active material layer in the positive electrode foil, the energy density of the battery can be increased while at the same time preventing the positive electrode foil from being damaged during the formation of the concave-convex portion.FIG. 1 is a schematic structural diagram of a battery according to an embodiment of the present application.The embodiment of the present application provides a battery. As shown in FIG. 1, the battery includes a positive electrode foil 100, a negative electrode foil 200, and a separator 300; wherein the separator 300 is disposed between the positive electrode foil 100 and the negative electrode foil 200; and wherein the separator 300, the positive electrode foil 100, and the negative electrode foil 200 are wound in the longitudinal direction of the positive electrode foil 100 to form a wound core structure.The positive electrode sheet 100 in the battery may be selected from the aforementioned positive electrode sheet 100 provided with the concave portions 103 and the convex portions 102. At the same time, the content of the binder in the positive electrode film 100 is further optimized. Due to the arrangement of the positive electrode foil 100, the battery has excellent power stability, while also the energy density and cycle life of the battery can be improved.The positive electrode foil 100 may include a positive electrode current collector 110 and a positive electrode active material. The positive electrode current collector 110 may be an aluminum foil or other commonly used positive electrode current collector 110. The thickness of the positive electrode current collector 110 may be set according to actual requirements. In some embodiments, the thickness of the positive electrode current collector 110 may be designed in conjunction with the thickness of the positive electrode active material to ensure the toughness of the positive electrode foil 100. The positive electrode active material may be applied to one or both surfaces of the positive electrode current collector 110.The positive electrode active material typically uses lithium-containing compounds. For example, the positive electrode active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt oxide, lithium nickel cobalt aluminate, ternary material, or lithium nickel manganese oxide. The positive electrode active material further includes a binder and an electrically conductive material. The binder in the positive electrode active material may include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinyl acetate, polyethylenepyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The electrically conductive material may include at least one of conductive carbon black, acetylene black, boiling carbon black (boiling black), flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder has a mass ratio of 1 to 5 wt % based on the total mass of the positive electrode active material layer.The negative electrode sheet 200 may include a negative electrode current collector 210 and a negative electrode active material. The negative electrode current collector 210 may use a copper foil or other commonly used negative electrode current collector 210. The thickness of the negative electrode current collector 210 may be provided according to actual requirements. In some embodiments, the thickness of the negative electrode current collector 210 may be designed in conjunction with the thickness of the negative electrode active material to ensure the toughness of the negative electrode foil 200. The negative electrode active material may be deposited on one or both surfaces of the negative electrode current collector 210.The negative electrode active material may include graphite or a silicon-based material. The silicon-based material may provide a higher energy density and include at least one of silicon, silicon oxide compound, silicon carbon compound, or silicon alloy. An electrically conductive material and / or a binder may be further included. For example, the electrically conductive material in the negative electrode active material may include at least one of carbon black, acetylene black, boiling black (boiling black), flake graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. The binder in the negative electrode active material may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylic acid ester, polyvinyl pyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.In the aforementioned positive electrode sheet 100, the positive electrode active material and the electrically conductive material and the binder thereof may form an integrated structure and be coated on at least one surface of the positive electrode current collector 110; and for convenience of description, the integrated structure may be a positive electrode active material layer 120. In the aforementioned negative electrode film 200, the negative electrode active material and the electrically conductive material and binder thereof may form an integrated structure and be coated on at least one surface of the negative electrode current collector 210; and for convenience of description, the integrated structure may be a negative electrode active material layer 220.In some embodiments, the negative electrode foil 200 includes a negative electrode current collector 210 and a negative electrode active material layer 220, and the negative electrode active material layer 220 may include a silicon-carbon composite material and / or a silicon-oxygen composite material.The content of silicon elements is relatively high in the silicon-carbon composite material and / or the silicon-oxygen composite material. The energy density of the battery may be increased by incorporating the silicon-carbon composite material and / or the silicon-oxygen composite material into the negative electrode active material layer 220.The silicon-carbon composite material may comprise a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon layer located on the surface of the porous carbon matrix. The material of the carbon layer may be crystalline carbon or amorphous carbon. In some embodiments, the carbon layer may include openings provided corresponding to the pores of the porous carbon matrix.In this way, by providing the openings associated with the pores of the porous carbon matrix in the carbon layer, the wetting performance of the electrolyte on the negative electrode active material can be improved while reducing the expansion capability of the silicon, whereby the cycle life of the battery cell can be improved and the life of the battery can be extended.In some embodiments, the material of the negative electrode active layer may further include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, graphene, soft carbon, hard carbon, soft carbon coated graphite, and hard carbon coated graphite.In some embodiments, the silicon-carbon composite material has a specific surface area of 0.5 m 2 / g to 10 m 2 / g. For example, the specific surface area of the silicon-carbon composite material may be 0.5 m 2 / g, 0.9 m 2 / g, 1.3 m 2 / g, 1.5 m 2 / g, 1 85 m 2 / g, 2.0 m 2 / g, 2.3 m 2 / g, 2.7 m 2 / g, 3.2 m2 / g, 3.6 m2 / g, 3.8 m 2 / g, 4.6 m 2 / g, 4.8 m 2 / g, 5.1 m 2 / g, 5.4 m 2 / g, 5.8 m 2 / g, 6.1 m 2 / g, 6.5 m 2 / g, 6.8 m 2 / g, 7.2 m 2 / g, 7.5 m2 / g, 7.8 m2 / g, 8.3 m2 / g, 8.9 m2 / g, 9.4 m 2 / g or 9.9 m 2 / g. Alternatively, the specific surface area of the silicon-carbon composite material may have any value in a range of greater than or equal to 0.5 m 2 / g and less than or equal to 10 m 2 / g. The specific surface area of the silicon-carbon composite particles can be determined by conventional means in this field, for example by means of a TRI STAR II surface analyzer.In this way, by controlling the specific surface area of the silicon-carbon composite material, the SEI (Solid Electrolyte Interface) during the charging process can be reduced, whereby cycle performance and durability can be improved. Thus, the SEI layer can be prevented from becoming too thin due to a too low specific surface area of the silicon-carbon composite material, thereby avoiding the situation that the electrolyte and the negative active layer cannot be effectively insulated from each other. Moreover, the SEI layer can be prevented from becoming too thick due to too large a specific surface area, and the influence of too thick an SEI layer on the capacity and efficiency of the battery can be reduced.In some embodiments, the silicon-carbon composite material has a particle size Dv 50 of 6 μm to 15 μm, for example, a particle size Dv 50 of 6 μm, 7 μm, 8 μm, 9 μm, 11 μm, 13 μm, or 14 μm. Or, the silicon-carbon composite material has a particle size Dv 50 having an arbitrary value in a range of greater than or equal to 6 μm and less than or equal to 15 μm. The particle size Dv50of the silicon-carbon composite particles can be determined by conventional means in this range, such as a laser particle analyzer.In this way, by controlling the particle size of the silicon-carbon composite material within the above range, it is possible to prevent the specific surface area of the silicon particles from increasing at too small a particle size, thereby enhancing side reactions. In addition, the problem that the silicon particles tend to expand excessively at too large a particle size can be avoided, thereby plugging the pores of the porous carbon matrix and impairing the wetting of the electrolyte.The silicon-carbon composite material has an average spheroidicity of 0.5 to 1. Compared to non-spherical particles, the particle shape more closely resembles a sphere with higher spheroidity, which leads to less influence on the structure of the film for the negative electrode during its volume expansion. The balancing capability of the overall structure of the negative electrode foil can be maintained during particle expansion. The average spheroidicity of the silicon-carbon composite particles can be determined in this range by conventional means. For example, using image processing software (such as IMAGE PRO PLUS), at least ten of silicon-carbon composite particles in an SEM image (scanning electron microscope) having a certain magnification (for example, 2500×) are selected, and the circumference and the area of each particle are measured to calculate a circumference equivalent radius r 1 and an area equivalent radius r 2 of each particle, and further obtain a spheroidity r 2 / r 1 of each particle. The average spheroidicity of the silicon-carbon composite particles is obtained by averaging the spheroidicity results.Moreover, the spherical particles may improve the mechanical strength and stability of the material, reduce the stress concentration between the particles caused by expansion, and thus reduce the risk of mechanical wear and damage to the material during the cycle.In some embodiments, the silicon-carbon composite material has a powder resistivity of 0.1 Ω • cm - 1000 Ω • cm. For example, the powder resistance coefficient of the silicon-carbon composite material may be 0.1 Ω •cm, 0.9 Ω •cm, 1.2 Ω •cm, 1.3 Ω •cm, 1.8 Ω •cm, 2.7 Ω •cm, 4.6 Ω •cm, 7.8 Ω •cm, 11 Ω •cm, 25 Ω •cm, 38 Ω •cm, 60 Ω •cm, 100 Ω •cm, 200 Ω •cm, 300 Ω •cm, 400 Ω •cm, 500 Ω •cm, 600 Ω •cm, 700 Ω •cm, 800 Ω •cm, 900 Ω •cm, or 1000 Ω •cm. Alternatively, the resistivity of the silicon-carbon composite material may have any value in a range of greater than or equal to 0.1 Ω •cm and less than or equal to 1000 Ω •cm.In some embodiments, the silicon-carbon composite material may have a silicon content of 30% to 75%. For example, the silicon content of the silicon-carbon composite material may be 30%, 35%, 41%, 45%, 49%, 51%, 55%, 59%, 61%, 64%, 71%, or 84%. Alternatively, the silicon content of the silicon-carbon composite material may have any value in a range of greater than or equal to 30% and less than or equal to 75%.In this way, excessive expansion of the negative electrode foil due to too high a silicon content of the negative electrode active layer can be avoided, which would result in deformation of the overall structure of the silicon-carbon particles. In addition, a reduction in the energy density of the battery due to too low a silicon content can be avoided.In some embodiments, the convex portions 102 of the positive electrode foil 100 along a thickness direction of the positive electrode foil 100 have a size h3, and the concave portions 103 of the positive electrode foil 100 have a size h4, where h3and h4appear the following relationship: 0.2≤h3 / h4≤1.Referring to FIG. 1, in the thickness direction of the positive electrode foil 100, the convex portion 102 and the concave portion 103 are formed on different sides of the positive electrode foil 100. The convex portion 102 is disposed corresponding to the concave portion 103. At a certain position of the positive electrode foil 100, the convex portion 102 is located on one side of the positive electrode foil 100, and the concave portion 103 is located on the other side of the positive electrode foil 100. In the aforementioned embodiment, the size h 3 of the convex portions 102 is equal to or smaller than the size h 4 of the concave portions 103. Due to the presence of the concave portions 103, sufficient local micro gaps can be formed between the positive electrode foil 100 and the negative electrode foil 200. The smaller size of the convex portions 102 may also avoid increasing the thickness of the battery and provide more storage space for the electrolyte based on ensuring the energy density of the battery, thereby achieving a balance between the energy density and the life of the battery. In addition, the smaller size of the convex portions 102 can prevent the positive electrode foil from breaking forcibly due to excessive stress when the positive electrode foil 100 forms the convex portions. In a specific embodiment, h3 / h4may be one of 0.2, 0.4, 0.6, 0.8, or 1, or may be in a range consisting of any two of these values.FIG. 2 is a schematic structural diagram of a positive electrode foil according to an embodiment of the present application.As shown in FIGS. 1 and 2, the positive electrode sheet 100 includes the above-mentioned positive electrode current collector 110 and the positive electrode active material layer 120 disposed on the surface of the positive electrode current collector 110. The positive electrode active material layer 120 includes the positive electrode active material; the positive electrode active material layer 120 includes a concave-convex portion 101 including a plurality of concave portions 103 and convex portions 102 provided corresponding to the concave portions 103. In a nitrogen environment, the positive electrode active material layer 120 has a weight loss rate p in a temperature range of 35° C. to 450° C. that satisfies the following condition: 1.1%≤p≤6%.In some specific embodiments, the concave-convex portion is formed by punching the active material layer of the electrode foil. By punching the positive electrode active material layer 120 of the positive electrode foil, the electrode foil is deformed, thereby improving the overall deformability of the positive electrode foil.It should be noted that the above weight loss rate can be determined by a TGA (Thermoplastically Gravimetric Analysis) test. When TGA testing is performed, some materials are subject to thermal carbonization and decomposition, resulting in mass loss of the positive electrode foil 100, thus causing the aforementioned weight loss phenomenon. The weight loss rate indicates the mass reduction ratio of the positive electrode foil 100 during the high test.In the aforementioned embodiment, the weight loss rate of the positive electrode film is in the aforementioned range, and the weight loss rate is used to indicate the structural stability of the positive electrode film. The weight loss rate is influenced by factors such as the density of compaction of the positive electrode sheet, the height of the convex portions, and the content of the binder. By controlling the weight loss rate, problems such as an extension of the binder in the positive electrode active material layer due to excessive pressure for forming the concave-convex portion during the formation of the concave-convex portion in the positive electrode sheet are solved, thereby reducing the effect of the binder in the joining of the positive electrode active particles, or an excessive compaction density during the rolling process or a power drop due to an excessive force acting on the positive electrode active material layer caused by too small a content of the binder in the positive electrode active material layer are avoided. Moreover, too high a binder content may not only impair the energy density of the positive electrode foil, but also cause the overall structure of the positive electrode foil to become brittle and hard with a greater weight loss rate and have a poor overall toughness, which would result in the positive electrode foil being not ductile as a whole and thus being easily crushed due to an excessive stress concentration during the formation of the concavo-convex portion. That is, by balancing the density of compaction of the positive electrode sheet, the binder content, and the height of the convex portions to adjust the weight loss rate of the positive electrode sheet within this range, the positive electrode sheet can be prevented from being damaged during the formation of the concave-convex portion, thereby ensuring the energy density.In a specific embodiment, the weight loss rate p may be 1.1%, 1%, 2%, 3%, 4%, 5%, or 6%, or may be within a range consisting of any two of these values.In the embodiment of the present application, because the positive electrode active material layer 120 is provided with the concave-convex portion 101, a local micro gap can be formed between the positive electrode foil 100 and the negative electrode foil 200, thereby providing a spatial condition for storing more electrolyte, providing more electrolyte for long cycles of the battery, improving wettability of the electrolyte in this portion, and avoiding occurrence of abnormal situations such as lack of electrolyte or poor wetting between the positive electrode and the separator. Accordingly, the cycle life of the battery is improved. Moreover, the surface of the positive electrode foil is rough by the formation of the concave-convex portion, so that when the battery cell expands, the convex portions can effectively support the separator, thereby preventing the separator from being deformed by the stress of the negative electrode foil due to the expansion.In addition, the positive electrode foil is provided with the convex portions to improve the deformation capability of the positive electrode foil. When the positive electrode sheet contacts the expanded negative electrode sheet, the stress due to expansion of the negative electrode sheet can be effectively absorbed by the convex portions of the positive electrode sheet, and the expansion of the negative electrode sheet can be buffered during the cycle process of the battery, whereby cracks due to excessive stress due to expansion of the negative electrode sheet can be avoided. Moreover, a part of the stress caused by the expansion of the negative electrode foil can be absorbed by the convex portions provided in the positive electrode foil, so that the negative electrode foil does not fully rely on the resistance of its own material during expansion. This retards the fatigue of the negative electrode material and thereby increases the life of the negative electrode foil.FIG. 3 is a schematic structural diagram of a convex portion according to an embodiment of the present application. FIG. 4 is a schematic structural diagram of two adjacent convex portions of a positive electrode foil according to an embodiment of the present application.In some embodiments (see FIG. 3 ), the height of the top of the convex portions 102 above the surface of the positive electrode active material layer is 120 h, and h and p satisfy the following relationship: 50<h / p<3600 and / or 3 μm≤h≤40 μm.It can be seen that a larger value of h, i.e., a larger height of the top of the convex portions, means a larger load of the positive electrode foil during the formation of the convex portions 102, i.e., a higher probability that the positive electrode active material forcibly suffers powder loss in the positive electrode foil. In addition, when the height of the top of the convex portions is greater, the positive electrode material on the top of the convex portions tends to be cracked or dropped, whereby the positive electrode material can more easily contact the negative electrode foil through the separator, which would lead to self-discharge. At this moment, by cooperation with the weight loss rate (i.e., the content of binder), a good combination relationship or effect can be obtained. That is, the structural stability of the convex portions 102 can be secured, thereby preventing problems such as powder loss from the positive electrode active material layer or breakage of the positive electrode piece, preventing detachment of the positive electrode active material at the top, and also preventing poor toughness of the positive electrode foil due to an excessive content of binder that easily breaks under pressure. In addition, a large expansion of the silicon-doped negative electrode foil during the charge-discharge process, which would otherwise result in squeezing of the convex portions of the positive electrode foil, can be prevented, so that the convex portions collapse and deform, and deterioration of the energy density is prevented. In a specific embodiment, h / ρ may be 50, 200, 400, 600, 800, 1200, 1400, 1600, 1800, 2400, 3000, 3200, 3400, 3600, or within a range of any two of these values; and h may be 3 μm, 10 μm, 20 μm, 30 μm, or 40 μm, or within a range of any two of these values.In some embodiments (see FIG. 4 ), the convex portions 102 have a diameter R, the distance between the two adjacent convex portions 102 is L, and R, L, and p satisfy the following relationship: 10<L / R / p<1000 and / or 1000 μm≤R≤ 5000 μm and / or 1500 μm≤L≤ 5000 μm.It is understood that L / R may reflect the density degree of the convex portions 102 of the positive electrode current collector 110. This degree of density is related to the value of the weight loss rate. A higher degree of density means more convex portions 102, which promotes wetting of the electrolyte and improvement of the durability. However, if the ratio L / R is too large, i.e., if the convex portions are too dense, this may easily result in an excessive stress concentration during the formation of the convex portions 102, thereby making it difficult to effectively relieve the stress, and the positive electrode film active material layer 100 becomes more prone to powder loss or even breakage of the positive electrode film, which makes higher demands on the toughness of the positive electrode film. Here, it is advantageous to provide L / R / p within the above range in order to achieve a balance between the degree of compaction and the weight loss rate. The ratio of the degree of compaction of the embossed concave portions to the weight loss rate is controlled, i.e., the degree of compaction of the embossed convex portions is controlled to ensure the energy density. When the concave portions or the convex portions of the positive electrode are subjected to a force, the convex portions within this ratio range can effectively distribute the stress applied to the convex portions, thus preventing the occurrence of cracks or powder loss. In a specific embodiment, L / R / p may be 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000, or may be within a range of any two of these values; R may be 1000 μm, 2000 μm, 3000 μm, 4000 μm, or 5000 μm, or may be within a range of any two of these values; and L may be 1500 μm, 2000 μm, 3000 μm, 4000 μm, or 5000 μm, or may be within a range of any two of these values.In some embodiments, the positive electrode foil 100 has a density of densification D; and D, h and R satisfy a relationship: 0.004<D*h / R<0.12 and / or 3 g / cm 3≤D≤4.5 g / cm 3.Note that the density of densification D of the positive electrode foil is 100=(mass of the positive electrode foil - mass of the positive electrode current collector) / [surface of the positive electrode foil (one-side coated surface)*(thickness of the positive electrode foil - thickness of the positive electrode current collector)].The density of the positive electrode foil 100 indicates the degree of compaction of the particles in the positive electrode active material layer 120, and the ratio h / R may reflect the size of the aforementioned particles. The greater the density of the positive electrode foil, the narrower the bonding of the active material. With the same embossing shape, the height of the convex portions decreases with increasing density. Further increase in height of the convex portions leads to a risk of breakage of the positive electrode foil. By aiming at a balance between the density of compaction and the size of the particles, the structural stability of the positive electrode foil 100 can be improved, which facilitates the formation of the aforementioned concave-convex portion 101 in the positive electrode foil 100 and can prevent breakage of the positive electrode foil 100. In a specific embodiment, the ratio D*h / R may be 0.004, 0.008, 0.012, 0.016, 0.036, 0.056, 0.076, 0.1 or 0.12 or within a range of any two of these values, and D may be 3 g / cm 3, 3, 5 g / cm 3, 4 g / cm 3 or 4.5 g / cm 3 or within a range of any two of these values.In some embodiments, the number of the convex portions 102 or the concave portions 103 of the concave-convex region 101 per unit area in cm is 2 N, and N is 2≤N≤25, preferably 4≤N≤15.The value of N may reflect the degree of compaction of the convex portions 102. By setting the value of N in the above range, the cycle life and the energy density of the battery can be appropriately balanced while at the same time ensuring the structural stability of the positive electrode foil 100, which can prevent the convex portions from being too close to each other and prevent the positive electrode foil 100 from breaking due to an excessive force during the formation of the convex portions.In some embodiments, the positive electrode active material layer comprises an electrically conductive material, wherein the electrically conductive material comprises single wall carbon nanotubes that extend into the positive electrode active material at the top of the convex portions 102.It can be seen that after the formation of the convex portions 102, the distance between the particles at the top of the convex portions 102 is larger than the distance between the particles at other positions of the convex portions 102. By providing the conductive material including the single-wall carbon nanotubes, the single-wall carbon nanotubes are linearly connected to adjacent positive electrode active materials. In addition, the single-wall carbon nanotubes can adapt to stresses during the embossing process by tensile deformation and always maintain their connection to the adjacent positive electrode active material. Thereby, the conductivity of the particles on the upper surface of the convex portions 102 can be secured.In some specific embodiments, the single wall carbon nanotubes are interwoven into a mesh structure and the positive electrode active material at the top of the convex portions 102 is encapsulated within the mesh structure.By incorporating the single-wall carbon nanotubes into the mesh structure, better contact between the particles and the single-wall carbon nanotubes is achieved, and also the contact area between the particles and the single-wall carbon nanotubes can be increased, thereby improving the conductivity between the particles at the top of the convex portions 102.In some specific embodiments, the single-wall carbon nanotubes have a diameter of 1 nm to 1000 nm and a length of 1 μm to 100 μm; and / or based on a total mass of the positive electrode active material layer 120, the single-wall carbon nanotubes have a mass fraction (in wt %) of 0.5% to 5%; and / or the single-wall carbon nanotubes in the positive electrode active material layer 120 have a thickness of 10 nm to 500 nm.In the aforementioned embodiment, the content and the size of the single-wall carbon nanotubes in the positive electrode active material layer 120 may be defined in terms of diameter, length, mass fraction, and thickness. By providing the diameter, length, mass fraction, and thickness of the single-wall carbon nanotubes in the above range, the positive electrode foil 100 in the above embodiment can be more adjusted, so that the basic characteristics of the positive electrode foil 100 can be ensured under the condition that the conductivity between the particles on the upper surface of the convex portions 102 is improved. The basic properties here include the above-mentioned structural stability, lifetime, energy density, etc.In a specific embodiment, the diameter of the single-wall carbon nanotubes may be 1 nm, 100 nm, 500 nm or 1000 nm or may be within a range formed from any two of these values; the length of the single-wall carbon nanotubes may be 1 μm, 10 μm, 30 μm, 50 μm, 70 μm, 90 μm or 100 μm or may be within a range formed from any two of these values; the mass fraction of the single-wall carbon nanotubes may be 0.5%, 1%, 1, 5%, 2%, 2.5%, 3%, 4% or 5%; the thickness of the single-wall carbon nanotubes may be 10 nm, 200 nm, 300 nm, 400 nm or 500 nm or may be within a range formed from any two of these values.In some embodiments, two adjacent convex portions 102 each form a first protrusion and a second protrusion, the first protrusion having a first circumscribing circle and the second protrusion having a second circumscribing circle; wherein a distance between a center of the first circumscribing circle and a center of the second circumscribing circle is L 1, a distance between the first protrusion and the second protrusion is L 2; and L 1 and L 2 satisfy the following relationship: 1.05≤L 1 / L 2≤3, preferably 1.1≤L 1 / L 2≤2.The value L 1 / L 2 may reflect the degree of compaction of the convex portions 102. By setting the value L 1 / L 2 to a value in the above range, an appropriate distance between the convex portions 102 can be obtained, thereby ensuring the wetting effect of the electrolyte, ensuring the life of the battery, and also preventing the positive electrode foil 100 from breaking. In a specific embodiment, L1 / L2 may be 1.05, 1.1, 1.3, 1.5, 1.7, 2, 2.5 or 3, or may be within a range formed from any two of these values.In some specific embodiments, 3 mm ≤ L1 ≤ 10 mm, preferably 2 mm ≤ L1 ≤ 8 mm; and / or 0.5 mm ≤ L2 ≤ 8 mm, preferably 1 mm ≤ L2 ≤ 4 mm.When the distance between the convex portion 102 and the convex portion 102 is less than 2 mm, the protrusions of a processing roll used for manufacturing are disposed too close. In this case, the extension of the positive electrode foil 100 cannot satisfy the high density degree of the convex portions 102 and the height of the convex portions 102; and the positive electrode foil 100 has less space for deformation, and the positive electrode foil 100 is likely to crack. When the distance between the convex portion 102 and the convex portion 102 is larger than 8 mm, the protrusions of a processing roller used for manufacturing are too sparsely arranged. In this case, the convex portions 102 are excessively dispersed and the supporting area for the convex portions 102 is insufficient, whereby the wetting effect of the electrolyte cannot be obtained. In the embodiment according to the present application, by setting the ratio of L 1 and L 2, the degree of compaction of the convex points can be ensured, thereby providing sufficient support for the electrode foil such that the positive electrode foil 100 has sufficient space for deformation to reduce the expansion of the negative electrode foil 200.In some embodiments, the convex portions 102 include or are each associated with a circumscribing sphere, the circumscribing sphere having an outer surface and a flat region being formed between two adjacent convex portions 102; the outer surface having a sphere radius R 1, the distance between the top of the convex portions 102 and the flat region being R 3, and R 1 and R 3 satisfy the following relationship: R 3<R 1, PREFERABLY R 3<1 / 5R 1.The circumscribing sphere is an idealized shape of the convex portions 102. It will be appreciated that when the positive electrode foil 100 is processed into the concave-convex region 101, the convex portions 102 generally do not have an absolutely regular shape similar to the aforementioned circumscribing sphere due to factors such as the processing method used, the manufacturing process used, and other defects. For example, during the formation of the convex portions 102, the convex portions 102 are compressed by rolling during the rolling process, resulting in deformation or expansion of the electrode foil, so that the convex portions 102 are partially relatively flattened, thereby causing the relationship of R3<R1 to be satisfied. In the aforementioned embodiment, the manufacturing process can be simplified by setting the values of R1 and R3 so as to satisfy the relationship of R3<1 / 5R1, and at the same time, the basic characteristics of the positive electrode foil 100 after the concave-convex portion 101 is formed can be ensured.In some embodiments, the outer surface has a surface Q 1, and a projection of the outer surface formed on the positive electrode current collector 110 along a thickness direction of the electrode sheet has an area S 1; wherein the circumscribing sphere further comprises an inner surface, the inner surface has a surface Q 2, and a projection of the inner surface formed on the positive electrode current collector 110 along the thickness direction of the electrode sheet has an area S 2; and wherein Q 1 and Q 2 satisfy the following relationship: 1.02≤Q 1 / Q 2≤1.21, and / or wherein S 1 and S 2 satisfy the following relationship: 1.02≤S 1 / S 2≤1.21.The volume of the convex portions 102 can be controlled appropriately by the above relationship, thereby achieving a balance between the cycle performance and the energy density and the structural stability of the positive electrode foil 100, creating space for the expansion of the negative electrode foil 200, and preventing adverse effects such as breakage of the negative electrode foil 200. In a specific embodiment, the ratio Q1 / Q2 may be 1.02, 1.05, 1.07, 1.12, 1.15, 1.19 or 1.21, or the value of this ratio may be within a range formed by any two of these values, and the ratio S1 / S2 may be 1.02, 1.05, 1.07, 1.12, 1.15, 1.19 or 1.21, or may be within a range formed by any two of these values.In some embodiments, a sum of the areas of projection of each of the convex portions 102 onto the positive electrode current collector 110 is S 11, and the area of the positive electrode foil 100 is S, where S 11 and S satisfy the following relationship: 0.02≤S 11 / S≤0.85.The value S 11 / S may reflect the degree of compaction of the convex portions 102 of the positive electrode current collector 110. When the value S11 / S is small, the number of the convex portions 102 is small, making it difficult to achieve the purpose of improving the cycle life and the energy density. When the value S11 / S is large, the number of the convex portions 102 is large, which may easily result in wrinkling, deformation, and even breakage of the positive electrode foil 100. In the aforementioned embodiment, by setting the value of S11 / S in the aforementioned range, damage to the positive electrode foil 100 can be prevented, whereby improvement in cycle life and energy density can be achieved. In a specific embodiment, the value S11 / S may be 0.02, 0.04, 0.1, 0.2, 0.32, 0.4, 0.5, 0.6, 0.7 or 0.85, or may be within a range formed by any two of these values.In some embodiments, as shown in FIG. 2, the positive electrode active material layer 120 further includes a tab region 104 and an end avoidance region 105. The tab portion 104 is located on at least one side of the concave-convex portion 101 in a width direction of the positive electrode foil 100, and a positive electrode tab 130 is disposed on the tab portion 104. The end avoidance region 105 is located on a side of the concave-convex region 101 in the longitudinal direction of the positive electrode foil 100.In conjunction with the above description, the concave-convex portion 101 is a portion provided with the convex portions 102 and the concave portions 103. Thereby, by disposing the tab portion 104 on one side of the concave-convex portion 101, stable environmental conditions for mounting the positive electrode tab 130 can be provided, which contributes to reducing the installation difficulty and process of the positive electrode tab 130, improving the installation stability of the positive electrode tab 130, and avoiding the deterioration of the interface of the portion around the positive electrode tab 130 due to the interaction between the positive electrode tab 130 and the positive electrode foil 100, thereby facilitating the installation of the tab by avoiding problems such as poor wetting, deterioration of the interface, cycle failure, and precipitation of lithium.In some embodiments, the tab portion 104 has a width W 2, and W 2 satisfies the following relationship: 1 mm≤W 2≤30 mm.The tab portion 104 is located at the edge of the positive electrode foil 100 as viewed in the width direction, and the value W 2 may indicate the ratio of the tab portion 104 in the width direction of the positive electrode foil 100. In a specific embodiment, W2may be 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, or 30 mm, or may be within a range formed by any two of these values. It can be seen that the tab region 104 is a region where no convex portions 102 or concave portions 103 are provided. Accordingly, in the case where W2 exceeds 30 mm, the width of the tab portion 104 is large enough; although the tab portion 104 is conducive to the attachment of the positive electrode tab 130, the convex portions 102 make a smaller proportion to the positive electrode foil 100, resulting in insufficient electrolyte storage in the tab portion 104, whereby problems such as poor wetting and even precipitation of lithium may easily occur. When W 2 is less than 1 mm, abnormal structures such as bends, rough and wavy edges may occur at the edges of the positive electrode foil 100 viewed in the width direction, which is not conducive to correction of the positive electrode foil 100 by laser during the manufacturing process and may lead to the problem of poor coverage of the positive electrode foil 100 by the negative electrode foil 200. Therefore, by setting the value of W2 within the above-mentioned size range according to the embodiment of the present application, the abnormal structures formed at the edges of the positive electrode foil 100 can be controlled and the wetting of the electrolyte can be ensured.The tab portion 104 is provided with a tab, and a distance between the tab and the concave-concave portion 101 in the width direction is W1, where W1 satisfies the following condition: 1 mm≤W1≤5 mm.In a specific embodiment, W1may be 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm, or may be within a range formed by any two of these values. It is understood that in the case where the value of W 1 exceeds 5 mm, the space between the convex portions 102 and the tab is relatively large, which can facilitate the installation of the positive electrode tab 130, but affects the number of the convex portions 102, thereby impairing the aforementioned basic characteristics of the positive electrode foil 100. This is not conducive to wetting of the electrolyte and, in addition, is not conducive to avoiding precipitation of lithium. When W 1 is less than 1 mm, the distance between the convex portions 102 and the positive electrode tab 130 is smaller, which makes it difficult to install the positive electrode tab 130 and also increases the number of the convex portions 102, which facilitates wetting of the electrolyte and prevents precipitation of lithium. Therefore, by setting the value of W 1 within the aforementioned size range according to the embodiment of the present application, the basic characteristics of the positive electrode foil 100 can be ensured, enabling simplification of the installation of the positive electrode tab 130.The end avoidance region 105 is a structure corresponding to the single-side coated region 107 on the positive electrode foil 100. Here, the single-side coated region 107 refers to the position where the positive electrode active material layer 120 is provided only on one side of the positive electrode current collector 110, while the positive electrode active material layer 120 is not provided on the other side, i.e., on the opposite side.FIG. 5 is a side view of a positive electrode foil 100 according to an embodiment of the present application.As shown in FIGS. 2 and 5, the positive electrode foil 100 has a double-coated region 106 and a single-coated region 107 along the longitudinal direction. The double-coated region 106 denotes a region where the positive electrode active material layer 120 is provided on both sides of the positive electrode current collector 110 of the positive electrode foil 100, and the single-coated region 107 denotes a region where the positive electrode active material layer 120 is provided on only one side of the positive electrode current collector 110. Here, the concave-convex portion 101 is formed in the double-side coated portion 106.In some embodiments, a top end 108 and a bottom end 109 are formed along the longitudinal direction of the positive electrode foil 100. The end avoidance region 105 includes a first avoidance region 1051 located at the head end 108 and a second avoidance region 1052 located at the bottom end 109. The size or length of the first avoidance region 1051 along the longitudinal direction is A, and the size or length of the second avoidance region 1052 along the longitudinal direction is B; wherein A satisfies the following condition: 1 mm≤A≤5 mm, and wherein B satisfies the following condition: 100 mm≤B≤800 mm.In a specific embodiment, the size of A may be 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm, or may be within a range formed by any two of these values. It is seen that if A exceeds 5 mm in size, structural stability of the inner portion of the core structure can be improved, but this is not conducive to wetting. However, in the case where the size of A is smaller than 1 mm, the structural stability of the inner portion of the wound core structure may be reduced, but the wetting may be increased. Therefore, in the embodiments according to the present application, by setting the size of A within the above range, balance can be achieved between the structural stability of the inner portion of the wound core structure and the wetting properties.In a specific embodiment, the size of B may be 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, 700 mm, or 800 mm, or may be within a range bounded by any two of these values. When the size B of the second avoidance region 1052 is in the range of 100 mm to 800 mm, the second avoidance region 1052 has a suitable length for finishing, thereby improving the connection stability of the outer side of the wound core structure. Thus, the battery as a whole has good winding stability, and the convex portions 102 in the vicinity of the outer winding rings have an appropriate distribution, whereby the winding units can be supported in the outer winding rings and the crush problem of the outer winding rings of the wound core structure can be alleviated. When the size of B is smaller than the lower limit value of 100 mm, the second avoidance area 1052 becomes too small and the distance between the convex portions 102 and the edge of the entire electrode sheet in the longitudinal direction of the entire electrode sheet becomes too small, which makes it difficult to improve the stability of encapsulation after completion of the wound core structure. When the size of B is larger than the upper limit value of 500 mm, the second avoidance area 1052 is too large and takes too large an area, resulting in insufficient distribution of the convex portions 102. This results in poor support of the convex portions 102, making it difficult to improve wetting properties of the electrolyte or achieve the required wetting at all.The batteries provided by this application and the applications thereof will be described in detail below with reference to specific exemplary embodiments.Without particular description, the materials, materials and means used in the following examples are and are generally commercially available from conventional materials, materials and means in this field; the materials used may also be synthetically prepared by conventional methods in this field.The present application is explained in more detail below with reference to the electrode arrangement of a lithium ion battery as an example and in combination with specific exemplary embodiments. It will be apparent to those skilled in the art that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.In each of the embodiment and the comparative example of the present application, the method described below is used for manufacturing a lithium ion battery and testing the performance of such a lithium ion battery.I. Method of Manufacturing a Lithium-Ion Battery1. Production of Positive Electrode Sheet 100(Lithium cobalt oxide+Li 2 NiO 2), conductive carbon black (SP), and polyvinylidene difluoride (PVDF) are mixed in a mass ratio of 97 (the weight fraction of the Li being 2 NiO being 21 wt % of the weight fraction of the lithium cobalt oxide): 1:2, N-methylpyrrolidone (NMP) is added, followed by uniform stirring to prepare a positive electrode suspension. The positive electrode suspension is applied to the front and back surfaces of an aluminum foil, and after baking in an oven and rolling, a foil for the positive electrode 100 having a thickness of 100 μm is obtained. The positive electrode foil 100 is embossed by a roller from an A side to a C side to obtain circular convex portions 102, the convex portions 102 having a diameter R of 2000 μm, the distance L between a convex portion 102 and a convex portion 102 being 2000 μm, and the height h of the top surface of the convex portions 102 from the surface of the positive electrode active material layer 120 being 20 μm.2. Production of Negative Electrode Sheet 200A silicon carbon doped negative electrode active material is mixed with conductive carbon black (SP), carboxymethylcellulose lithium (CMC-Li), and polyacrylic acid (PAA) in a mass ratio of 97 (wherein the weight proportion of the silicon carbon is 5 wt % of the weight proportion of the graphite): 0.4: 0.1: 2.5, and deionized water is added to prepare a negative electrode suspension. The negative electrode suspension is applied to the front and back surfaces of a carbon-coated copper foil, and after baking in an oven and rolling, a negative electrode foil 200 having a thickness of 110 μm is obtained. The negative electrode foil 200 is provided with a slit of fixed size at a predetermined position, and a nickel plated copper tab is welded into this slit by laser or ultrasonic welding.3. Preparation of a Wound Core StructureThe positive electrode foil 100 and the negative electrode foil 200 are cut, formed into a single foil, or treated as such, and then wound with a separator 300 to form a wound core structure.4. Battery Mount AssemblyThe wound core structure is encapsulated, baked, and appropriately heated in an oven, an electrolyte is filled, appropriately shaped, further encapsulated in a second encapsulation step, and the structure is then subjected to sorting and open circuit voltage (OCV) testing to finally obtain a battery. The electrolyte used for electrolyte filling may be a conventional electrolyte, and the lithium salt is LiFP6.Performance Testing of a Lithium-Ion Battery1. K valueAfter the battery is stored in a room having a temperature of 45° C. for 48 to 60 hours, it is taken out and allowed to stand in a room having a constant temperature of 25° C. for 24 hours, and the battery voltage V 1 is measured. The battery is allowed to stand in a room at a constant temperature of 25° C. for 72 to 96 hours, and the battery voltage V 2 is measured. The voltage drop over the time interval between the two tests is (V1-V2) / time interval.2. Cycle life at 25°CIn an environment at a temperature of 25° C., the electrode assembly is charged with a direct current at a charging current of 2 C / 5 C (the battery is designed for a maximum voltage of 4.5 V) to the full charge voltage and then charged with a direct current at the maximum voltage until the current is 0.02, and then discharged with a discharge current of 0.5 C to a final voltage of 3.0 V with a direct current, wherein the discharge capacity for the first cycle is recorded. Subsequently, the above steps are repeated for the charge and discharge cycles, and the number of cycles N at which the cycle capacity maintenance rate starts to become equal to or less than 80% is recorded.Here, a charging current of 2C means that the battery is charged at twice its rated capacity per hour, while 5C means that it is charged at five times its capacity per hour. For example, a 1000 mAh battery charged with 2C would have a charging current of 2000 mA (2A) and at 5C a charging current of 5000 mA (5A).3. Expansion Rate for 1000T Cycles at 25° CThe battery is stored in a constant temperature room or a constant temperature box at 25° C. for 2 hours, charged with a constant current to the upper limit voltage at 1 C. until the upper limit voltage is reached with an accuracy of 0.05 C.; then, a cell thickness h 1 is detected. The battery is then allowed to stand for 10 minutes and then discharged at 0.5C to a voltage of 3.0 V. The above steps of charging and discharging are repeated for 1000 T cycles. Subsequently, the battery is charged with a constant current to the upper limit voltage at 1C until the upper limit voltage is reached with an accuracy of 0.05C; then, the cell thickness h2at this time is detected. The ratio h2 / h1is the expansion rate for 1000 T cycles at 25° C.4. Probability of breaking of the electrode foilIn a space having a constant temperature of 45°C, the battery is charged with constant current and constant voltage to the upper limit voltage at 1C until the upper limit voltage is reached with an accuracy of 0.05C, then allowed to stand for 10 minutes and discharged at 0.5C to a voltage of 3.0V. After 600 T cycles, 10 batteries are decomposed to determine the number of broken electrode foils.Table 1 below shows various parameters of Examples 1 to 5 and Comparative Examples 1 to 3. Table 1 Table 1Example 1202%10002000200015040,04Comparative Example 1201%200020002000110040,04Comparative Example 22010%2002000200011040,04Example 236%5020002000116,6666740,006Comparative Example 3401,1%3636,364300020000,66666760,6060640,053333Example 351,1%454,5455100030003272,727340,02Example 4402%200010002000210030,12Example 532%150300020000,66666733,333334,50,0045Table 2Table 2Example 1No loss of powder, good toughness and good electrolyte friction0,0050%1500TComparative Example 1Loss of Powder0,010%1200TComparative Example 2High binder content, poor toughness and fracture of the embossed electrode sheet0,01100%1000TExample 2Low Embossing Depth and Poor Retention of Electrolyte0,00880%1250TComparative Example 3Large Embossing Depth and Breakage of the Aluminum Layer0,01100%1300TExample 3Impressions are rare and retention of electrolyte poorer than in Example 10,00520%1200TExample 4Low Densification and Good Toughness0,0110%1200TExample 5High Densification and Poor Toughness0,00850%1200TThe following conclusions can be drawn from the analysis of Tables 1 and 2.1) By comparing Example 1, Comparative Example 1 and Comparative Example 2, it is apparent that the structural stability of the positive electrode film can be changed by changing the weight loss rate. At a low weight loss rate, the positive electrode sheet has poor structural stability and is liable to be lost in powder. At a high weight loss rate, the positive electrode film has high brittleness and tends to crack. By maintaining the weight loss rate between 1.1% and 6%, structural stability of the positive electrode film can be ensured, powder loss and other problems of the positive electrode film can be prevented, and damage to the positive electrode film during the formation of the concavo-convex portion can be prevented while ensuring the desired energy density.Comparing Example 2 and Comparative Example 3, it can be seen that when the ratio h / ρ is too small, the height of the convex portions is small, the storage space for the electrolyte is small, and the electrolyte content is small, which affects the life of the battery.2) If the ratio h / ρ is too large, the content of binder in the positive electrode material at this time is low, and the positive electrode paste tends to fall, which deteriorates the life of the battery cell. At the same time, the height of the convex portions is too large, the nip stress on the positive electrode foil is high, and the positive electrode foil is more likely to crack.By comparing Examples 1 to 5 and Comparative Examples 1 to 3, it can be seen that the ratio L / R / p is selected so as to satisfy the condition 10<L / R / p<1000. If the ratio L / R / p is too small and the binder content is high, the positive electrode foil becomes brittle and the flexibility of the electrode foil is reduced. In such cases, breakage of the positive electrode foil is likely to occur upon stamping of the foil. If the ratio L / R / p is too large, there are too few embossed regions, resulting in reduced electrolyte storage capacity and a decrease in electrolyte content, thereby significantly shortening the life of the battery cell. When the condition 10<L / R / p<1000 is satisfied, the battery has a long life without breakage of the electrode sheet, thereby ensuring safety and desired characteristics of the battery.By comparing Examples 1 to 5 and Comparative Examples 1 to 3, it can be seen that the ratio D*h / R is selected so as to satisfy the condition of 0.004<D*h / R<0.12. If the ratio D*h / R is too large, the densification of the positive electrode film becomes greater, resulting in poor flexibility of the electrode film. The greater height of the convex portions promotes breaking of the electrode foil. If the ratio D*h / R is too small, the densification of the positive electrode foil is low, which adversely affects the improvement of the overall energy density of the battery cell. Moreover, the reduced height of the convex portions makes electrolyte less likely to be filled, which deteriorates the life of the battery. When the condition 0.004<D*h / R<0.12 is satisfied, the entire battery has a high energy density and at the same time, a long life is secured.It should be noted that in the above description of the present application, the terms "including", "with", and all variants thereof used to describe the embodiments of the present application are not to be understood exclusively. For example, methods, methods, systems, products, or devices that include a series of steps or units are not limited to the steps or units specifically disclosed herein, but may also include other steps or units that are not specifically listed or inherent to these methods, methods, products, or devices.Unless otherwise indicated and defined, terms such as "installed", "mounted", "connected", "connecting", "fixed" are to be understood broadly. These terms can stand for example for "fixedly connected to one another", "detachably connected to one another" or "integrated" or "formed integrally with one another"; the relevant elements can be connected to one another directly or indirectly via an intermediate medium; it can be a connection within two elements or an interaction between the two elements. Those skilled in the art will appreciate the specific meaning of the foregoing terms in the present application from the specific circumstances. Moreover, terms such as "first", "second" are used merely for description and should not be understood as indicating or interpreting a relative meaning or the number of technical features specified.Finally, it should be noted that the embodiments disclosed above are intended to be illustrative only and not to limit the technical solutions according to the present application. Although the present application has been described in detail with reference to the above-disclosed embodiments, it will be apparent to those skilled in the art that the technical solutions described in the above-disclosed embodiments can be well changed or that some or all of the technical features thereof can be replaced with equivalent technical features. Such alterations or substitutions are also intended to be included within the general spirit and scope of the appended claims.Reference numerals denote reference numerals100 Positive electrode foil 110 Positive electrode current collector 120 Positive electrode active material layer 130 Positive electrode tab 101 Concave-convex region 102 Convex portion 103 Concave portion 104 Tab region 105 End avoidance region 106 Double-coated region 107 Single-coated region 108 Tip end 109 Bottom end 1051 First avoidance region 1052 Second avoidance region; 200 Negative electrode foil 210 Negative electrode current collector 220 Negative electrode active material 300 Separator

Claims

A positive electrode foil comprising a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material layer comprises a concave-convex region, and the concave-convex region comprises a plurality of concave portions and convex portions respectively disposed corresponding to the concave portions; the positive electrode active material layer has a weight loss rate p in a temperature range of 35°C to 450°C under a nitrogen environment, and p satisfies the following condition: 1.1% ≤ ρ ≤ 6% The positive electrode foil according to claim 1, wherein a height of a top surface of the convex portions above a surface of the positive electrode active material layer is h, and wherein h and p satisfy the following relationship: 50 < h / ρ < 3600 ; and / or 3 μm ≤ h ≤ 40 μm The positive electrode foil according to claim 2, wherein the concave portions have a diameter R and a distance between two adjacent concave portions is L, and wherein R, L and p satisfy the following relationship(s): 10 < L / R / ρ < 1000, and / or 1000 μm ≤ R ≤ 5000 μm, and / or 1500 μm ≤ L ≤ 5000 μm. The positive electrode film according to claim 3, wherein the positive electrode film has a density of compaction D, and wherein D, h and R satisfy the following relationship(s): 0.004 < D*h / R < 0.12, and / or 3 g / cm 3 ≤ D ≤ 4.5 g / cm 3. The positive electrode foil according to any one of the preceding claims, wherein the number of the convex portions or the concave portions in the concave-convex region per unit area in cm is 2 N, and N is 2 ≤ N ≤ 25, preferably 4 ≤ N ≤ 15. The positive electrode foil of any preceding claim, wherein the positive electrode active material layer comprises an electrically conductive material and the electrically conductive material comprises single wall carbon nanotubes extending into the positive electrode active material layer at the top of the convex portions.The positive electrode foil according to claim 3, wherein two adjacent convex portions each form a first protrusion and a second protrusion, a first circumscribing circle is associated with the first protrusion, and a second circumscribing circle is associated with the second protrusion, a distance between a center of the first circumscribing circle and a center of the second circumscribing circle is L1, a distance between the first protrusion and the second protrusion is L2, and L1 and L2 satisfy the following relationship: 1.05 ≤ L1 / L2 ≤ 3, preferably 1.1 ≤ L1 / L2 ≤ 2. The positive electrode foil according to claim 7, wherein for L1 and L2: 3 mm ≤ L1 ≤ 10 mm, preferably 2 mm ≤ L1 ≤ 8 mm; and / or 0.5 mm ≤ L2 ≤ 8 mm, preferably 1 mm ≤ L2 ≤ 4 mm.The positive electrode foil according to claim 3, wherein a circumscribing ball is associated with the convex portions, and the circumscribing ball has an outer surface, a flat region is formed between two adjacent convex portions, the outer surface has a ball radius R1, a distance between the top surface of the convex portions and the flat region is R3, and R1 and R3 satisfy the following relationship: R3 < R1, preferably R3 < 1 / 5 R1, The positive electrode sheet according to claim 9, wherein the outer surface has a surface Q1, and a projection of the outer surface formed on the positive electrode current collector along a thickness direction of the electrode sheet has an area S1, the circumscribing sphere further has an inner surface, the inner surface has a surface Q2, and a projection of the inner surface formed on the positive electrode current collector along the thickness direction of the electrode sheet has an area S2, and Q1 and Q2 satisfy the relationship 1.02 ≤ Q1 / Q2 ≤ 1.21, and / or S1 and S2 satisfy the relationship 1.02 ≤ S1 / S2 ≤ 1.21.The positive electrode foil according to any one of the preceding claims, wherein the sum of the areas of a protrusion of each of the convex portions on the positive electrode current collector is S11, the area of the positive electrode foil is S, and S11 and S satisfy the following relationship: 0.02 ≤ S11 / S ≤ 0.

85. The positive electrode sheet according to any one of claims 6 to 11, wherein the single-wall carbon nanotubes are woven into a mesh structure, and the positive electrode active material is coated on the top of the convex portions inside the mesh structure.The positive electrode sheet according to claim 12, wherein the single-wall carbon nanotubes have a diameter of 1 nm to 1000 nm and a length of 1 μm to 100 μm; and / or the single-wall carbon nanotubes have a mass proportion of 0.05 wt% to 5 wt% based on the total mass of the positive electrode active material layer; and / or the single-wall carbon nanotubes in the positive electrode active material layer have a thickness of 10 nm to 500 nmThe positive electrode film according to any one of the preceding claims, wherein the positive electrode active material comprises a binder, and the binder has a mass proportion of 1 to 5 wt% with respect to the total mass of the positive electrode active material layer; and / or the binder comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinyl acetate, polyethylene pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.A battery comprising a separator, a negative electrode foil, and the positive electrode foil according to any one of claims 1 to 14, wherein the separator is disposed between the positive electrode foil and the negative electrode foil, and the separator, the positive electrode foil, and the negative electrode foil are wound in a longitudinal direction of the positive electrode foil to form a wound core structure.The battery of claim 15, wherein the negative electrode foil comprises a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material.The battery according to claim 15 or 16, wherein along a thickness direction of the positive electrode foil, the convex portions have a height h3 and the concave portions have a size h4, and h3 and h4 satisfy the following relationship: 0.2 ≤ h3 / h4 ≤ 1.

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