Secondary battery, manufacturing method thereof, and electric device

Abstract

The present application relates to the technical field of secondary batteries, and provides a secondary battery, a manufacturing method thereof, and an electrical device, which are at least beneficial for improving the performance of the secondary battery. The secondary battery includes: a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a first conductive layer and a second conductive layer sequentially stacked on the surface of the positive electrode current collector; wherein the material of the first conductive layer includes a first nanometal wire, a first graphene, and a first carbon-coated copper powder, and the material of the second conductive layer includes a second nanometal wire, a second graphene, and a second carbon-coated copper powder; the diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and / or the diameter of the sheet of the first graphene is smaller than the diameter of the sheet of the second graphene.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a manufacturing method thereof, and an electrical device. Background Art

[0002] With the rapid development of new energy vehicles, electronic products and other fields, lithium batteries have been widely used due to their relatively high energy density, long cycle life and green environmental protection.

[0003] In secondary batteries, the conductivity of the positive electrode current collector directly impacts the battery's internal resistance, energy density, and cycle life. Conductive materials are typically applied to the positive electrode current collector to improve its conductivity. Carbon-based materials (such as conductive carbon black and graphite) are often used. However, these materials suffer from insufficient conductivity, poor interfacial adhesion, low corrosion resistance, and complex manufacturing processes, limiting the application of secondary batteries.

[0004] Therefore, improving the positive electrode current collector to make it have high conductivity, strong adhesion, corrosion resistance and excellent stability is an important means to improve the performance of secondary batteries. Summary of the Invention

[0005] The embodiments of the present application provide a secondary battery, a manufacturing method thereof, and an electrical device, which are at least beneficial to improving the performance of the secondary battery.

[0006] According to some embodiments of the present application, on the one hand, the embodiments of the present application provide a secondary battery, comprising: a positive electrode sheet, a negative electrode sheet and a separator, the separator being located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprising: a positive electrode collector; a first conductive layer, the first conductive layer being located on the surface of the positive electrode collector; a second conductive layer, the second conductive layer being located on the surface of the first conductive layer away from the positive electrode collector; wherein the material of the first conductive layer comprises a first nanometal wire, a first graphene and a first carbon-coated copper powder, and the material of the second conductive layer comprises a second nanometal wire, a second graphene and a second carbon-coated copper powder; the diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of flakes of the first graphene is smaller than the number of flakes of the second graphene, and / or the diameter of the flakes of the first graphene is smaller than the diameter of the flakes of the second graphene.

[0007] In some embodiments, a diameter of the first nanometal wire is greater than or equal to 10 nm and less than or equal to 20 nm; and a diameter of the second nanometal wire is greater than 20 nm and less than or equal to 50 nm.

[0008] In some embodiments, the aspect ratio of the first nanometal wire is greater than or equal to 1000 and less than or equal to 1500; and the aspect ratio of the second nanometal wire is greater than 1500 and less than or equal to 2000.

[0009] In some embodiments, the number of the first graphene sheets is 3 to 5 layers; the number of the second graphene sheets is 4 to 8 layers.

[0010] In some embodiments, the diameter of the first graphene sheet is 5 μm to 15 μm; the diameter of the second graphene sheet is 10 μm to 20 μm.

[0011] In some embodiments, the average particle size of the first carbon-coated copper powder is smaller than the average particle size of the second carbon-coated copper powder.

[0012] In some embodiments, in the first conductive layer, the mass ratio of the total mass of the first graphene and the first nanometal wire to the mass of the first conductive layer is greater than the mass ratio of the first carbon-coated copper powder to the mass of the first conductive layer; in the second conductive layer, the mass ratio of the total mass of the second graphene and the second nanometal wire to the mass of the second conductive layer is greater than the mass ratio of the second carbon-coated copper powder to the mass of the second conductive layer.

[0013] In some embodiments, in the first conductive layer, the mass ratio of the first graphene to the total mass of the first graphene and the first nanometal wire is a first ratio; in the second conductive layer, the mass ratio of the second graphene to the total mass of the second graphene and the second nanometal wire is a second ratio, and the first ratio is greater than the second ratio.

[0014] In some embodiments, the positive electrode sheet further includes: a third conductive layer, the third conductive layer is located on the surface of the second conductive layer away from the first conductive layer, the material of the third conductive layer includes a third nanometal wire, a third graphene, a third carbon-coated copper powder and silicon dioxide, the diameter of the third nanometal wire is smaller than the diameter of the first nanometal wire, and / or the aspect ratio of the third nanometal wire is smaller than the aspect ratio of the first nanometal wire.

[0015] In some embodiments, the number of flakes of the third graphene is smaller than the number of flakes of the second graphene and larger than the number of flakes of the first graphene; and / or, the diameter of a flake of the third graphene is smaller than the diameter of a flake of the second graphene and larger than the diameter of a flake of the first graphene.

[0016] In some embodiments, the average particle size of the third carbon-coated copper powder is smaller than the average particle size of the second carbon-coated copper powder and larger than the average particle size of the first carbon-coated copper powder.

[0017] According to some embodiments of the present application, the embodiments of the present application further provide a method for manufacturing a secondary battery, comprising: preparing a positive electrode sheet, the preparation steps comprising: providing a positive electrode current collector; preparing a first slurry, dispersing a first nanometal wire, a first graphene and a first carbon-coated copper powder in a solvent, adding an adhesive and stirring evenly; applying the first slurry to the surface of the positive electrode current collector by a doctor blade coating method, and drying by a thermal curing method to form a first conductive layer; preparing a second slurry, dispersing a second nanometal wire, a second graphene and a second carbon-coated copper powder in a solvent, adding an adhesive and stirring evenly; wherein, the first The diameter of the nanometal wire is smaller than the diameter of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of the first graphene sheets is smaller than the number of the second graphene sheets, and / or the sheet diameter of the first graphene is smaller than the sheet diameter of the second graphene; the second slurry is applied to the surface of the first conductive layer away from the positive electrode current collector by a doctor blade coating method, and is dried by a thermal curing method to form a second conductive layer; a negative electrode sheet and a separator are provided, and the positive electrode sheet, the separator and the negative electrode sheet are placed in a shell after winding or laminating, and an electrolyte is injected to form a secondary battery.

[0018] In some embodiments, the first slurry comprises the following components by weight: 10% to 30% of the first nanometal wires, 5% to 15% of the first graphene, 5% to 10% of the first carbon-coated copper powder, 20% to 40% of a binder, and the balance deionized water; and the second slurry comprises the following components by weight: 10% to 30% of the second nanometal wires, 5% to 15% of the second graphene, 5% to 10% of the second carbon-coated copper powder, 20% to 40% of a binder, and the balance deionized water. The proportions of the above components are the mass percentages of each component relative to the mass of the first slurry.

[0019] In some embodiments, the process parameters of the blade coating method include: a blade gap of 50μm~200μm, and a moving speed of 1m / min~10m / min; the process parameters of the thermal curing method include: a temperature of 120℃~250℃, and a time of 10min~60min.

[0020] According to some embodiments of the present application, on the other hand, the embodiments of the present application further provide an electrical device, which includes a secondary battery as in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments; or, the electrical device includes an energy storage system, which includes a secondary battery as in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments.

[0021] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0022] In the secondary battery provided by the embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a first conductive layer and a second conductive layer sequentially stacked on the positive electrode current collector. The materials of the first conductive layer and the second conductive layer both include graphene, nanometal wires and carbon-coated copper powder. The nanometal wires and the graphene sheets are intertwined to form an interwoven conductive network, so that the carbon-coated copper powder can be better connected to the nanometal wires and graphene, and the loose carbon-coated copper powder particles can also maintain good electrical contact. The carbon-coated copper powder can also reduce the porosity. The three-dimensional conductive network composed of "point-line-surface" is conducive to rapid electron conduction, reducing battery polarization, reducing the internal resistance of the secondary battery, and thus helping to improve the charge and discharge efficiency and cycle stability of the secondary lithium battery. In addition, the first conductive layer close to the positive electrode current collector serves as the inner layer, and the second conductive layer away from the positive electrode current collector serves as the outer layer. The inner layer uses a first nanowire with a finer diameter (and / or lower aspect ratio) than the outer layer, forming a high-density conductive network. This reduces the interfacial resistance between the positive electrode current collector and the active material, ensuring rapid electron transport. The outer layer uses a second nanowire with a thicker diameter (and / or higher aspect ratio) than the inner layer, forming a long-range continuous conductive network. This enhances the overall electron conductivity of the positive electrode sheet and reduces distortion during charge and discharge. The gradient conductive network improves the overall conductivity of the positive electrode sheet. The inner layer uses a first graphene with fewer layers (and / or a smaller diameter) than the outer layer, which helps expose more active edge sites, shorten the lithium ion diffusion path, and improve reaction kinetics. The outer layer uses a second graphene with more layers (and / or a larger diameter) than the inner layer, forming a porous structure that promotes electrolyte penetration into the interior of the positive electrode sheet while avoiding the problem of lithium ion transport being hindered by excessive densification, thereby optimizing lithium ion diffusion and electrolyte infiltration. The second nanometal wire with a larger diameter and / or aspect ratio in the outer layer and the second graphene with a larger number of layers and / or layer diameter can also provide mechanical support, alleviate the volume expansion of the active material during charging and discharging, reduce the pulverization and cracking problems of the positive electrode sheet, enhance the mechanical stability of the positive electrode sheet, and thus help improve the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1A schematic structural diagram of a positive electrode sheet provided in one embodiment of the present application;

[0025] Figure 2 A schematic diagram of a structure in which graphene and nanometal wires are entangled, provided in one embodiment of the present application.

[0026] Description of reference numerals:

[0027] 101. Positive electrode current collector; 102. First conductive layer; 103. Second conductive layer; 201. Graphene; 202. Nanometal wire. DETAILED DESCRIPTION

[0028] As can be seen from the background art, improving the positive electrode current collector to make it have high conductivity, strong adhesion, corrosion resistance and excellent stability is an important means to improve the performance of secondary batteries.

[0029] The embodiments of the present application provide a secondary battery, a manufacturing method thereof, and an electrical device. On the positive electrode current collector of the secondary battery, a gradient structural design of the conductive layer is used to precisely control the conductive network, ion channels, and mechanical properties at a microscopic scale, thereby achieving a synergistic improvement in the high conductivity and long cycle performance of the secondary battery.

[0030] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0031] In the description of the embodiments of the present application, “multiple” means more than two, unless otherwise clearly and specifically defined.

[0032] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0034] In the description of the embodiments of the present application, when a component “includes” another component, unless otherwise stated, other components are not excluded, and other components may be further included.

[0035] The terms used in the description of the various embodiments described herein are for describing specific embodiments only and are not intended to be limiting. As used in the description of the various embodiments described and the appended claims, "components" are also intended to include plural forms unless the context clearly indicates otherwise.

[0036] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0037] Figure 1 A schematic structural diagram of a positive electrode sheet provided in one embodiment of the present application; Figure 2 A schematic diagram of a structure in which graphene and nanometal wires are entangled, provided in one embodiment of the present application.

[0038] The secondary battery provided in the embodiment of the present application includes: a positive electrode sheet, a negative electrode sheet and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet.

[0039] refer to Figure 1 The positive electrode sheet includes: a positive electrode current collector 101, a first conductive layer 102 and a second conductive layer 103.

[0040] The first conductive layer 102 is located on the surface of the positive electrode current collector 101 . The material of the first conductive layer 102 includes a first nanometal wire, a first graphene, and a first carbon-coated copper powder.

[0041] The second conductive layer 103 is located on the surface of the first conductive layer 102 away from the positive electrode current collector 101 . The material of the second conductive layer 103 includes a second nanometal wire, a second graphene, and a second carbon-coated copper powder.

[0042] The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of the first graphene sheets is smaller than the number of the second graphene sheets, and / or the diameter of the first graphene sheets is smaller than the diameter of the second graphene sheets.

[0043] For example, the following situations:

[0044] (1) The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and the diameter of the sheets of the first graphene is smaller than the diameter of the sheets of the second graphene.

[0045] (2) The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is greater than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is smaller than the diameter of the sheet of the second graphene.

[0046] (3) The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is larger than the diameter of the sheet of the second graphene.

[0047] (4) The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is greater than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is smaller than the diameter of the sheet of the second graphene.

[0048] (5) The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is greater than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is greater than the diameter of the sheet of the second graphene.

[0049] (6) The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is greater than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is greater than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is smaller than the diameter of the sheet of the second graphene.

[0050] (7) The diameter of the first nanometal wire is greater than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and the diameter of the sheets of the first graphene is smaller than the diameter of the sheets of the second graphene.

[0051] (8) The diameter of the first nanometal wire is greater than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is greater than the diameter of the sheet of the second graphene.

[0052] (9) The diameter of the first nanometal wire is greater than the diameter of the second nanometal wire, and the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is greater than the number of sheets of the second graphene, and the diameter of the sheet of the first graphene is smaller than the diameter of the sheet of the second graphene.

[0053] In the secondary battery provided in the embodiment of the present application, the positive electrode sheet includes a positive electrode current collector 101 and a first conductive layer 102 and a second conductive layer 103 sequentially stacked on the positive electrode current collector 101. The materials of the first conductive layer 102 and the second conductive layer 103 both include graphene, nanometal wires, and carbon-coated copper powder. The first conductive layer 102 and the second conductive layer 103 are used to improve the conductivity of the positive electrode current collector 101. Figure 2 The nanowires 202 and graphene 201 sheets are intertwined, forming an interwoven conductive network. This allows the carbon-coated copper powder to better connect with the nanowires and graphene, while also maintaining good electrical contact between the loose carbon-coated copper powder particles. Furthermore, the carbon-coated copper powder can reduce porosity. The three-dimensional conductive network formed by the "point-line-surface" structure facilitates rapid electron conduction, reduces battery polarization, and lowers the internal resistance of the secondary battery, thereby improving the charge and discharge efficiency and cycle stability of the secondary lithium battery. Furthermore, the first conductive layer 102, located near the positive electrode current collector 101, serves as the inner layer, while the second conductive layer 103, located away from the positive electrode current collector 101, serves as the outer layer. The inner layer uses a first nanowire with a finer diameter (and / or lower aspect ratio) than the outer layer, forming a high-density conductive network. This reduces the interfacial resistance between the positive electrode current collector and the active material, ensuring rapid electron transport. The outer layer uses a second nanowire with a thicker diameter (and / or higher aspect ratio) than the inner layer, forming a long-range continuous conductive network. This enhances the overall electron conductivity of the positive electrode sheet and reduces distortion during charge and discharge. The gradient conductive network improves the overall conductivity of the positive electrode sheet. The inner layer uses a first graphene with fewer layers (and / or a smaller diameter) than the outer layer, which helps expose more active edge sites, shorten the lithium ion diffusion path, and improve reaction kinetics. The outer layer uses a second graphene with more layers (and / or a larger diameter) than the inner layer, forming a porous structure that promotes electrolyte penetration into the interior of the positive electrode sheet while avoiding the problem of lithium ion transport being hindered by excessive densification, thereby optimizing lithium ion diffusion and electrolyte infiltration. The second nanometal wire with a larger diameter and / or aspect ratio in the outer layer and the second graphene with a larger number of layers and / or layer diameter can also provide mechanical support, alleviate the volume expansion of the active material during charging and discharging, reduce the pulverization and cracking problems of the positive electrode sheet, enhance the mechanical stability of the positive electrode sheet, and thus help improve the cycle performance of the secondary battery.

[0054] The positive electrode sheet also includes a positive electrode coating (not shown). The positive electrode coating is located on the surface of the second conductive layer 103 away from the first conductive layer 102. The positive electrode coating includes a positive electrode active material, a conductive agent, and a binder. In other words, the positive electrode current collector 101, the first conductive layer 102, and the second conductive layer 103 form the base layer of the positive electrode coating. The first conductive layer 102 and the second conductive layer 103 are used to improve the conductivity of the positive electrode current collector 101, thereby enhancing the electron conduction between the positive electrode coating and the positive electrode current collector 101, thereby improving the cycle performance of the secondary battery.

[0055] The positive electrode active material includes a layered structure of LiM x The positive electrode active material may be an O2 (M = Co, Ni, Mn) material, a spinel LiMn2O4 material, or an olivine LiFePO4 material. The conductive agent may include at least one of Super P, acetylene black, Super S, KS-6, KS-15, SFG-6, SFG-15, or Ketjen Black. The binder may include at least one of polyvinylidene fluoride (PVDF), polyimide (PI), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC).

[0056] When the diameter or aspect ratio of the nanometal wire is too large, it is easy to cause excessive winding, resulting in excessive porosity and affecting the mechanical strength of the conductive layer; when the diameter or aspect ratio of the nanometal wire is too small, it is easy to cause insufficient density of network nodes.

[0057] In the first conductive layer 102 , the diameter of the first nanometal wire is greater than or equal to 10 nm and less than or equal to 20 nm, for example, it can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm.

[0058] In the second conductive layer 103 , the diameter of the second nanometal wire is greater than 20 nm and less than or equal to 50 nm, for example, it can be 21 nm, 23 nm, 28 nm, 30 nm, 33 nm, 36 nm, 39 nm, 40 nm, 42 nm, 45 nm, 48 nm or 50 nm.

[0059] In the first conductive layer 102 , the aspect ratio of the first nanometal wires is greater than or equal to 1000 and less than or equal to 1500, for example, it may be 1000, 1111, 1234, 1350, 1480 or 1500.

[0060] In the second conductive layer 103 , the aspect ratio of the second nanometal wires is greater than 1500 and less than or equal to 2000, for example, it may be 1540, 1630, 1745, 1852, 1933 or 2000.

[0061] It should be noted that in the first conductive layer 102, different individual first nanowires may have different diameters or aspect ratios. The diameter of a first nanowire refers to the average diameter of the first nanowire per unit mass, and the aspect ratio of a first nanowire refers to the average aspect ratio of the first nanowire per unit volume. Similarly, in the second conductive layer 103, the diameter of a second nanowire refers to the average diameter of the second nanowire per unit mass, and the aspect ratio of a second nanowire refers to the average aspect ratio of the second nanowire per unit volume.

[0062] When the number of graphene sheets is small, the conductivity is high, but the mechanical strength is poor, which can easily cause problems such as wrinkling and cracking in the conductive layer; when the number of graphene sheets is too large, it can easily cause interlayer contact resistance, which in turn increases the resistivity of the positive electrode sheet.

[0063] In the first conductive layer 102 , the number of first graphene layers is 3 to 5 layers, for example, 3 layers, 4 layers or 5 layers.

[0064] In the second conductive layer 103 , the number of second graphene layers is 4 to 8 layers, for example, 4, 5, 6, 7 or 8 layers.

[0065] When the diameter of the graphene sheet is too large, it is easy to form a continuous conductive surface, but the interface stress is concentrated; when the diameter of the graphene sheet is too small, the number of interfaces can be increased, but the loss of electron transition is aggravated.

[0066] In the first conductive layer 102 , the diameter of the first graphene sheet is 5 μm to 15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0067] In the second conductive layer 103 , the diameter of the second graphene sheet is 10 μm to 20 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0068] It should be noted that in the first conductive layer, the number of lamellae and lamellae diameter corresponding to different first graphene sheets may be different. The number of lamellae of the first graphene sheet refers to the average number of lamellae of the first graphene sheet per unit mass, and the lamellae diameter of the first graphene sheet refers to the average lamellae diameter of the first graphene sheet per unit mass. Similarly, in the second conductive layer 103, the number of lamellae of the second graphene sheet refers to the average number of lamellae of the second graphene sheet per unit mass, and the lamellae diameter of the second graphene sheet refers to the average lamellae diameter of the second graphene sheet per unit mass.

[0069] In some embodiments, the ratio of the graphene sheet diameter to the length of the nanometal wire is 0.4 to 0.6, for example, 0.4, 0.45, 0.5, 0.55, or 0.6. That is, in the first conductive layer 102, the ratio of the first graphene sheet diameter to the first nanometal wire length is 0.4 to 0.6; and in the second conductive layer 103, the ratio of the second graphene sheet diameter to the second nanometal wire length is 0.4 to 0.6. A ratio of the graphene sheet diameter to the nanometal wire length within the aforementioned range facilitates maintaining an appropriate degree of entanglement between the graphene and the nanometal wire, avoiding problems such as excessive entanglement leading to excessive porosity or insufficient entanglement leading to insufficient network node density.

[0070] In some embodiments, the average particle size of the first carbon-coated copper powder is smaller than the average particle size of the second carbon-coated copper powder. On the one hand, the smaller average particle size of the carbon-coated copper powder in the inner layer relative to the outer layer can facilitate matching the nanowires with finer diameters (and / or lower aspect ratios) and graphene with fewer layers (and / or smaller diameters) in the inner layer relative to the outer layer, thereby forming a continuous three-dimensional conductive network structure. On the other hand, the smaller particle size of the carbon-coated copper powder in the inner layer can reduce the proportion of ineffective mass, improve the utilization of active materials, allow for higher active material loading, and indirectly increase energy density.

[0071] The average particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%.

[0072] In the first conductive layer 102, the average particle size of the first carbon-coated copper powder is greater than or equal to 1 μm and less than or equal to 2 μm, and can be, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm. The average particle size refers to the average particle size per unit mass of the first carbon-coated copper powder.

[0073] In the second conductive layer 103 , the average particle size of the second carbon-coated copper powder is greater than or equal to 1.5 μm and less than or equal to 2.5 μm, for example, it can be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm or 2.5 μm.

[0074] In some embodiments, in the first conductive layer 102, the combined mass ratio of the first graphene and the first nanometal wire to the mass ratio of the first conductive layer 102 is greater than the mass ratio of the first carbon-coated copper powder to the mass ratio of the first conductive layer 102; and in the second conductive layer 103, the combined mass ratio of the second graphene and the second nanometal wire to the mass ratio of the second conductive layer 103 is greater than the mass ratio of the second carbon-coated copper powder to the mass ratio of the second conductive layer 103. In other words, in the conductive layer, the nanometal wires and graphene serve as the primary conductive materials, while the carbon-coated copper powder serves as the auxiliary conductive material. This facilitates the formation of a more continuous three-dimensional conductive skeleton, reducing electron transport resistance within the positive electrode sheet. Furthermore, reducing the mass ratio of the carbon-coated copper powder can reduce the risk of aggregation during cycling and avoid localized conductivity deficiencies.

[0075] In some embodiments, in the first conductive layer 102, the mass ratio of the first graphene to the total mass of the first graphene and the first nanometal wire is a first percentage; in the second conductive layer 103, the mass ratio of the second graphene to the total mass of the second graphene and the second nanometal wire is a second percentage, and the first percentage is greater than the second percentage. In other words, in the first conductive layer 102, the first graphene accounts for a higher proportion of the primary conductive material; in the second conductive layer 103, the second nanometal wire accounts for a higher proportion of the primary conductive material. Graphene has extremely high intrinsic conductivity and ultra-large specific surface area. A higher proportion of graphene in the first conductive layer 102 can quickly establish high-density, short-range electron transmission channels, reduce the interface resistance between the positive electrode current collector and the active material, and ensure that electrons are efficiently injected from the positive electrode current collector into the positive electrode sheet; the one-dimensional structure of nanometal wires is easier to form a long-range continuous conductive network. The proportion of nanometal wires in the second conductive layer 103 is higher, and the conductive path can be extended to the surface of the positive electrode sheet mainly with nanometal wires, reducing the electron transmission impedance of the overall positive electrode sheet. At the same time, its rigid structure provides mechanical support for the second conductive layer 103, inhibiting electrode deformation.

[0076] In some embodiments, the thickness of the first conductive layer 102 is 2 μm to 5 μm, for example, 2 μm, 3 μm, 4 μm or 5 μm. The thickness of the second conductive layer 103 is 2 μm to 5 μm, for example, 2 μm, 3 μm, 4 μm or 5 μm.

[0077] In some embodiments, the thickness of the first conductive layer 102 is equal to the thickness of the second conductive layer 103 .

[0078] In some embodiments, the positive electrode sheet may further include a third conductive layer (not shown), located on the surface of the second conductive layer away from the first conductive layer. The third conductive layer comprises a third nanometal wire, a third graphene layer, a third carbon-coated copper powder, and silicon dioxide. The diameter of the third nanometal wire is smaller than that of the first nanometal wire, and / or the aspect ratio of the third nanometal wire is smaller than that of the first nanometal wire. When the third conductive layer serves as the outermost layer of the positive electrode sheet, the diameter and / or aspect ratio of the third nanometal wire are small, forming chopped fibers. This maintains local conductivity while reducing surface roughness of the positive electrode sheet. Silicon dioxide is added to fill surface pores, improving the corrosion and wear resistance of the positive electrode sheet.

[0079] In some embodiments, the length of the third nanometal wire is less than 5 μm.

[0080] Furthermore, the number of the third graphene sheets is smaller than that of the second graphene sheets, but larger than that of the first graphene sheets; and / or the diameter of the third graphene sheets is smaller than that of the second graphene sheets, but larger than that of the first graphene sheets. In other words, the number and / or diameter of the graphene sheets are tailored to match the size of the third nanowire, thereby facilitating the construction of a local conductive network.

[0081] Furthermore, the average particle size of the third carbon-coated copper powder is smaller than that of the second carbon-coated copper powder and larger than that of the first carbon-coated copper powder. The size of the carbon-coated copper powder must be compatible with the size of the third nanowires and the third graphene to form a good three-dimensional conductive network structure.

[0082] In some embodiments, the thickness of the third conductive layer is 2 μm to 5 μm, for example, 2 μm, 3 μm, 4 μm or 5 μm.

[0083] Accordingly, another embodiment of the present application further provides a method for manufacturing a secondary battery, which can be used to manufacture the secondary battery provided in the above embodiment. For the same or corresponding parts as the previous embodiment, please refer to the corresponding description of the previous embodiment, and will not be described in detail below.

[0084] Another aspect of the present invention provides a method for manufacturing a secondary battery, comprising: preparing a positive electrode sheet, wherein the preparation steps include: providing a positive electrode current collector; preparing a first slurry, dispersing a first metal nanowire, a first graphene, and a first carbon-coated copper powder in a solvent, adding a binder, and stirring evenly; applying the first slurry to the surface of the positive electrode current collector by a doctor blade coating method, and drying by a thermal curing method to form a first conductive layer; preparing a second slurry, dispersing a second metal nanowire, a second graphene, and a second carbon-coated copper powder in a solvent, adding a binder, and stirring evenly; wherein the diameter of the first metal nanowire is greater than the diameter of the first graphene; and the first carbon-coated copper powder is greater than the diameter of the first graphene; wherein the diameter of the first metal nanowire is greater than the diameter of the first graphene; and wherein the first carbon-coated copper powder is greater than the diameter of the first graphene; wherein the first carbon-coated copper powder is greater than the diameter of the first nanowire. The diameter of the first nanometal wire is smaller than that of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than that of the second nanometal wire; and the number of the first graphene sheets is smaller than the number of the second graphene sheets, and / or the sheet diameter of the first graphene is smaller than the sheet diameter of the second graphene; the second slurry is applied to the surface of the first conductive layer away from the positive electrode current collector by a doctor blade coating method, and is dried by a thermal curing method to form a second conductive layer; a negative electrode sheet and a separator are provided, and the positive electrode sheet, the separator and the negative electrode sheet are placed in a shell after winding or laminating, and an electrolyte is injected to form a secondary battery.

[0085] Before preparing the first slurry or the second slurry, the first graphene or the second graphene may be surface-modified, for example, by using an aminosilane coupling agent for surface treatment, so as to improve the dispersibility and interfacial bonding strength of the first graphene or the second graphene.

[0086] When preparing the first slurry or the second slurry, the viscosity of the first slurry or the second slurry can be adjusted to 1000cp~1400cp to facilitate the coating of the slurry and avoid the inability to form a film due to too low viscosity or the difficulty in coating due to too high viscosity.

[0087] In some embodiments, the first slurry includes the following components by mass: 10% to 30% of the first nanometal wire, 5% to 15% of the first graphene, 5% to 10% of the first carbon-coated copper powder, 20% to 40% of the binder, and the balance deionized water; the second slurry includes the following components by mass: 10% to 30% of the second nanometal wire, 5% to 15% of the second graphene, 5% to 10% of the second carbon-coated copper powder, 20% to 40% of the binder, and the balance deionized water.

[0088] In some embodiments, the first slurry or the second slurry may further include functional additives, such as boron nitride nanosheets (1%~3%), which are used to improve thermal conductivity and mechanical strength; phosphoric acid high corrosion inhibitor (0.5%~2%), which is used to react with the positive electrode current collector to form a passivation film protective layer; polyether modified defoaming agent (0.1%~0.5%), which is used to remove bubbles in the slurry; leveling agent (0.2%~1%), which is used to improve the fluidity of the slurry.

[0089] It should be noted that the “%” in the above components represents the mass percentage of the substance in the first slurry or the second slurry.

[0090] In some embodiments, blade coating process parameters include a blade gap of 50 μm to 200 μm and a travel speed of 1 m / min to 10 m / min. Thermal curing process parameters include a temperature of 120°C to 250°C and a curing time of 10 to 60 minutes. This combined blade coating and thermal curing process offers a balanced approach to performance and cost-effectiveness.

[0091] In the preparation method of the secondary battery provided in the embodiment of the present application, when preparing the positive electrode sheet, a first conductive layer and a second conductive layer are sequentially formed on the positive electrode current collector, and the materials of the first conductive layer and the second conductive layer both include graphene, nanometal wires and carbon-coated copper powder. The nanometal wires and the graphene sheets are intertwined to form an interwoven conductive network, so that the carbon-coated copper powder can be better connected with the nanometal wires and graphene, and the loose carbon-coated copper powder particles can also maintain good electrical contact. The carbon-coated copper powder can also reduce the porosity. The three-dimensional conductive network composed of "point-line-surface" is conducive to rapid electron conduction, reducing battery polarization, reducing the internal resistance of the secondary battery, and thus helping to improve the charge and discharge efficiency and cycle stability of the secondary lithium battery. In addition, the first conductive layer close to the positive electrode current collector serves as the inner layer, and the second conductive layer away from the positive electrode current collector serves as the outer layer. The inner layer uses a first nanowire with a finer diameter (and / or lower aspect ratio) than the outer layer, forming a high-density conductive network. This reduces the interfacial resistance between the positive electrode current collector and the active material, ensuring rapid electron transport. The outer layer uses a second nanowire with a thicker diameter (and / or higher aspect ratio) than the inner layer, forming a long-range continuous conductive network. This enhances the overall electron conductivity of the positive electrode sheet and reduces distortion during charge and discharge. The gradient conductive network improves the overall conductivity of the positive electrode sheet. The inner layer uses a first graphene with fewer layers (and / or a smaller diameter) than the outer layer, which helps expose more active edge sites, shorten the lithium ion diffusion path, and improve reaction kinetics. The outer layer uses a second graphene with more layers (and / or a larger diameter) than the inner layer, forming a porous structure that promotes electrolyte penetration into the interior of the positive electrode sheet while avoiding the problem of lithium ion transport being hindered by excessive densification, thereby optimizing lithium ion diffusion and electrolyte infiltration. The second nanometal wire with a larger diameter and / or aspect ratio in the outer layer and the second graphene with a larger number of layers and / or layer diameter can also provide mechanical support, alleviate the volume expansion of the active material during charging and discharging, reduce the pulverization and cracking problems of the positive electrode sheet, enhance the mechanical stability of the positive electrode sheet, and thus help improve the cycle performance of the secondary battery.

[0092] According to some embodiments of the present application, on the other hand, the embodiments of the present application further provide an electrical device, which includes a secondary battery as in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments; or, the electrical device includes an energy storage system, which includes a secondary battery as in the above embodiments, or a secondary battery prepared by the manufacturing method of the secondary battery in the above embodiments.

[0093] The following are specific examples of this application.

[0094] Secondary batteries corresponding to Examples 1 to 10 were prepared using the following method. Examples 1 to 10 differ in the parameters corresponding to the first metal nanowire, the first graphene, the second metal nanowire, the second graphene, the first carbon-coated copper powder, and the second carbon-coated copper powder. Table 1 shows the parameters corresponding to the first metal nanowire, the first graphene, the second metal nanowire, the second graphene, the first carbon-coated copper powder, and the second carbon-coated copper powder in various embodiments provided in the present application. For details, see Table 1.

[0095] (1) Provide aluminum foil (positive electrode current collector).

[0096] (2) Prepare a first slurry, disperse 20% of the first nanometal wire, 10% of the first graphene, and 8% of the first carbon-coated copper powder in deionized water, add 30% of an aqueous polyurethane-acrylic copolymer (adhesive) and stir evenly; apply the first slurry to the surface of the positive electrode current collector by a doctor blade coating method, and dry it by a thermal curing method to form a first conductive layer.

[0097] (3) Prepare a second slurry, disperse 20% of the second nanometal wire, 10% of the second graphene and 8% of the second carbon-coated copper powder in deionized water, add 30% of the aqueous polyurethane-acrylic copolymer (adhesive) and stir evenly; apply the second slurry to the surface of the first conductive layer away from the positive electrode current collector by a doctor blade coating method, and dry it by thermal curing to form a second conductive layer.

[0098] (4) Prepare a positive electrode slurry by mixing 57% LiFePO4, 1.8% Super P, 1.2% PVDF and deionized water into a positive electrode slurry with a solid content of 60%. Apply the positive electrode slurry to the surface of the second conductive layer away from the first conductive layer and then dry it to form a positive electrode coating. The positive electrode current collector, the first conductive layer, the second conductive layer and the positive electrode coating constitute a positive electrode sheet.

[0099] (5) Providing a negative electrode sheet and a separator, winding or stacking the positive electrode sheet, separator, and negative electrode sheet into a housing, and injecting electrolyte to form a secondary battery.

[0100] Comparative Examples 1 to 3

[0101] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, only the first conductive layer is formed on the positive current collector, and the second conductive layer is not formed.

[0102] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the second conductive layer is directly formed on the positive electrode current collector, and the first conductive layer is not formed.

[0103] The difference between Comparative Example 3 and Example 1 is that the positions of the first conductive layer and the second conductive layer on the positive electrode current collector in Comparative Example 3 are swapped.

[0104] Table 1

[0105]

[0106] Table 1

[0107]

[0108] The internal resistance, charge and discharge efficiency, and capacity retention rate of the secondary batteries corresponding to Examples 1 to 10 and Comparative Examples 1 to 3 were tested, as well as the resistivity and contact angle of the positive electrodes corresponding to Examples 1 to 10 and Comparative Examples 1 to 3 were tested.

[0109] Charge and discharge test process: Place the secondary battery under test in a 25°C environment, charge it to 3.65V at a current of 0.5C, then charge it at a constant voltage until the current drops to 0.05C, and then discharge it to 2.5V at a current of 0.5C. Repeat these steps 100 times to test the capacity retention rate and charge and discharge efficiency of the secondary battery.

[0110] The test results are shown in Table 2.

[0111] Table 2

[0112]

[0113] By comparing the results of Examples 1 to 10 and Comparative Examples 1 to 3, it can be found that the secondary battery provided in the embodiments of the present application adopts a gradient structure design for the conductive layer on the positive electrode sheet, which is beneficial to reducing the resistivity of the positive electrode sheet, improving the wettability of the positive electrode sheet, improving the charge and discharge efficiency and cycle performance of the secondary battery, and reducing the internal resistance of the secondary battery.

[0114] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A secondary battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet includes: positive electrode current collector; a first conductive layer, the first conductive layer being located on the surface of the positive electrode current collector; a second conductive layer, the second conductive layer being located on a surface of the first conductive layer away from the positive electrode current collector; The material of the first conductive layer includes a first metal nanowire, a first graphene, and a first carbon-coated copper powder; the material of the second conductive layer includes a second metal nanowire, a second graphene, and a second carbon-coated copper powder; the average particle size of the first carbon-coated copper powder is smaller than the average particle size of the second carbon-coated copper powder; The diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and The number of the first graphene sheets is smaller than the number of the second graphene sheets, and / or the diameter of the first graphene sheets is smaller than the diameter of the second graphene sheets.

2. The secondary battery according to claim 1, wherein The diameter of the first nanometal wire is greater than or equal to 10 nm and less than or equal to 20 nm; the diameter of the second nanometal wire is greater than 20 nm and less than or equal to 50 nm.

3. The secondary battery according to claim 1, wherein The aspect ratio of the first nanometal wire is greater than or equal to 1000 and less than or equal to 1500; the aspect ratio of the second nanometal wire is greater than 1500 and less than or equal to 2000.

4. The secondary battery according to claim 1, wherein The number of the first graphene sheets is 3 to 5 layers; the number of the second graphene sheets is 4 to 8 layers.

5. The secondary battery according to claim 1, wherein The diameter of the first graphene sheet is 5 μm to 15 μm; the diameter of the second graphene sheet is 10 μm to 20 μm.

6. The secondary battery according to claim 1, wherein In the first conductive layer, the mass ratio of the total mass of the first graphene and the first nanometal wire to the mass of the first conductive layer is greater than the mass ratio of the first carbon-coated copper powder to the mass of the first conductive layer; in the second conductive layer, the mass ratio of the total mass of the second graphene and the second nanometal wire to the mass of the second conductive layer is greater than the mass ratio of the second carbon-coated copper powder to the mass of the second conductive layer.

7. The secondary battery according to claim 1, wherein In the first conductive layer, the mass ratio of the first graphene to the total mass of the first graphene and the first nanometal wire is a first proportion; in the second conductive layer, the mass ratio of the second graphene to the total mass of the second graphene and the second nanometal wire is a second proportion, and the first proportion is greater than the second proportion.

8. The secondary battery according to claim 1, wherein The positive electrode sheet also includes: a third conductive layer, which is located on a surface of the second conductive layer away from the first conductive layer, and the material of the third conductive layer includes a third nanometal wire, a third graphene, a third carbon-coated copper powder and silicon dioxide. The diameter of the third nanometal wire is smaller than the diameter of the first nanometal wire, and / or the aspect ratio of the third nanometal wire is smaller than the aspect ratio of the first nanometal wire.

9. The secondary battery according to claim 8, characterized in that The number of lamellae of the third graphene is smaller than the number of lamellae of the second graphene and larger than the number of lamellae of the first graphene; and / or the diameter of the lamellae of the third graphene is smaller than the diameter of the lamellae of the second graphene and larger than the diameter of the lamellae of the first graphene.

10. The secondary battery according to claim 8 or 9, characterized in that The average particle size of the third carbon-coated copper powder is smaller than the average particle size of the second carbon-coated copper powder, and larger than the average particle size of the first carbon-coated copper powder.

11. A method for manufacturing a secondary battery, characterized in that: include: Prepare the positive electrode sheet, the preparation steps include: providing a positive electrode current collector; Prepare a first slurry, disperse the first metal nanowire, the first graphene and the first carbon-coated copper powder in a solvent, add a binder and stir evenly; Applying the first slurry to the surface of the positive electrode current collector by a doctor blade coating method, and drying it by a thermal curing method to form a first conductive layer; A second slurry is prepared, wherein a second nanometal wire, a second graphene, and a second carbon-coated copper powder are dispersed in a solvent, and a binder is added and stirred uniformly; wherein the average particle size of the first carbon-coated copper powder is smaller than the average particle size of the second carbon-coated copper powder; the diameter of the first nanometal wire is smaller than the diameter of the second nanometal wire, and / or the aspect ratio of the first nanometal wire is smaller than the aspect ratio of the second nanometal wire; and the number of sheets of the first graphene is smaller than the number of sheets of the second graphene, and / or the sheet diameter of the first graphene is smaller than the sheet diameter of the second graphene; Applying the second slurry to the surface of the first conductive layer away from the positive electrode current collector by a doctor blade coating method, and drying it by a thermal curing method to form a second conductive layer; A negative electrode sheet and a separator are provided, and the positive electrode sheet, the separator and the negative electrode sheet are placed in a shell after being wound or stacked, and an electrolyte is injected to form a secondary battery.

12. The method for manufacturing a secondary battery according to claim 11, wherein: The first slurry includes the following components by mass: 10% to 30% of the first nanometal wire, 5% to 15% of the first graphene, 5% to 10% of the first carbon-coated copper powder, 20% to 40% of the adhesive, and the balance deionized water; the second slurry includes the following components by mass: 10% to 30% of the second nanometal wire, 5% to 15% of the second graphene, 5% to 10% of the second carbon-coated copper powder, 20% to 40% of the adhesive, and the balance deionized water.

13. The method for manufacturing a secondary battery according to claim 11, wherein: The process parameters of the blade coating method include: a blade gap of 50μm~200μm, and a moving speed of 1m / min~10m / min; the process parameters of the thermal curing method include: a temperature of 120℃~250℃, and a time of 10min~60min.

14. An electrical device, characterized in that: The electrical equipment includes the secondary battery according to any one of claims 1 to 10, or the secondary battery prepared by the method for manufacturing a secondary battery according to any one of claims 11 to 13; or, the electrical equipment includes an energy storage system, and the energy storage system includes the secondary battery according to any one of claims 1 to 10, or the secondary battery prepared by the method for manufacturing a secondary battery according to any one of claims 11 to 13.

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