Negative electrode sheet and lithium ion battery

Abstract

The application relates to a negative electrode sheet and a lithium ion battery. The negative electrode sheet comprises a negative electrode current collector and a double-layer coating arranged on at least one side surface of the negative electrode current collector, the double-layer coating comprises a first coating layer and a second coating layer arranged in a stack, and the first coating layer and the second coating layer each have at least one first active material coating block and at least one second active material coating block; wherein the first active material coating block comprises a silicon-carbon material, the second active material coating block comprises a carbon material, and the periphery of any first active material coating block is distributed with at least one second active material coating block. The scheme provided by the application can effectively inhibit the expansion rate of the negative electrode sheet, prevent the negative electrode sheet from being broken and invalid, ensure the fast-charging performance and thermal stability of the battery while ensuring the ultra-high capacity of the battery.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a negative electrode and a lithium-ion battery. Background Technology

[0002] With the continuous development of lithium-ion battery technology, electronic products are demanding increasingly higher energy density from lithium-ion batteries. Currently, adding silicon materials to the active material of the negative electrode has become the mainstream technical approach to improve battery energy density.

[0003] However, while silicon-carbon materials in the anode offer the advantage of ultra-high capacity, the silicon material undergoes significant volume expansion, leading to problems such as accelerated expansion of the lithium-ion battery and anode sheet breakage. Furthermore, the low conductivity and poor thermal stability of silicon-carbon anodes also degrade the overall performance of lithium-ion batteries.

[0004] Therefore, how to provide a battery that combines high energy density, effective suppression of volume expansion, high conductivity, and good thermal stability is a problem that needs to be solved. Summary of the Invention

[0005] To address or partially address the problems existing in related technologies, this application provides a negative electrode sheet and a lithium-ion battery that can effectively suppress the expansion rate of the negative electrode sheet and prevent it from breaking and failing; while ensuring the battery's ultra-high capacity, it also ensures the battery's fast-charging performance and thermal stability.

[0006] A first aspect of this application provides a negative electrode sheet, comprising a negative electrode current collector and a double-layer coating disposed on at least one surface of the negative electrode current collector. The double-layer coating comprises a first coating and a second coating stacked thereon, wherein both the first coating and the second coating have at least one first active material patch and at least one second active material patch; wherein: The first active material coating block comprises silicon-carbon material, and the second active material coating block comprises carbon material; at least one second active material coating block is distributed around the periphery of any first active material coating block.

[0007] In some embodiments, the edges of every two adjacent first and second active material coatings located on the same layer are aligned with each other.

[0008] In some embodiments, the projected area of ​​a single first active material patch on the negative electrode current collector is less than or equal to the projected area of ​​a single second active material patch.

[0009] In some embodiments, the thickness of the first coating is 10 μm to 50 μm, and the thickness of the second coating is 10 μm to 50 μm.

[0010] In some embodiments, the width of the first active material coating block is 1mm to 50mm, and the width of the second active material coating block is 1mm to 50mm; preferably, the widths of the first active material coating block and the second active material coating block are equal.

[0011] In some embodiments, the areal density of the first active material coating is 10 g / m³. 2 ~100g / m 2 The areal density of the second active material coating is 10 g / m³. 2 ~100g / m 2 .

[0012] In some embodiments, the silicon carbide material accounts for 10% to 100% of the mass percentage of the active material in the first active material coating.

[0013] In some embodiments, the carbon material accounts for 10% to 100% of the mass percentage of the active material in the second active material coating.

[0014] In some embodiments, the active material in the first active material coating also includes a carbon-containing material, wherein the mass percentage of the carbon-containing material in the active material of the first active material coating is 0-90%.

[0015] In some embodiments, the active material in the first active material coating accounts for 80% to 99.8% of the total mass of the coating. The active material in the second active material coating accounts for 80% to 99.8% of the total mass of the coating.

[0016] In some embodiments, the first active material coating further includes a conductive agent and a binder, wherein the conductive agent has a mass percentage of 0.1% to 10% in the first active material coating, and the binder has a mass percentage of 0.1% to 10% in the first active material coating.

[0017] In some embodiments, the active material in the second active material coating also includes a silicon-containing material, wherein the mass percentage of the silicon-containing material in the active material of the second active material coating is 0 to 10%.

[0018] In some embodiments, the second active material coating further includes a conductive agent and a binder, wherein the conductive agent has a mass percentage of 0.1% to 10% in the second active material coating, and the binder has a mass percentage of 0.1% to 10% in the second active material coating.

[0019] In some embodiments, the conductive agent is selected from at least one of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive graphite, vapor-deposited carbon fibers, graphene, etc.

[0020] In some embodiments, the adhesive is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyacrylonitrile, polyurethane, etc.

[0021] In some embodiments, the double-layer coating is provided on both sides of the negative electrode current collector and is symmetrically arranged along the negative electrode current collector.

[0022] In some embodiments, the double-layer coating is obtained by a combination of a double-layer coating process and an intermittent coating process.

[0023] A second aspect of this application provides a lithium-ion battery comprising the negative electrode sheet described in the first aspect above.

[0024] The technical solution provided in this application may include the following beneficial results: In the negative electrode of this application, the active material in the first active material coating is mainly silicon-carbon material with carbon-containing material (excluding silicon) as a supplement, while the active material in the second active material coating is mainly carbon material (excluding silicon) with silicon-containing material as a supplement. The two types of coatings are arranged alternately and continuously along the horizontal and thickness directions on the negative electrode current collector. The main active materials in the two types of coatings complement each other, resulting in complementary effects. Simultaneously, internal adjustments are made to the auxiliary active materials within each coating to ensure a balanced distribution of active material throughout the negative electrode. This achieves the ultra-high capacity provided by silicon while smoothly bridging the resistance differences between adjacent coatings. Furthermore, carbon elements improve the overall conductivity and thermal stability of the negative electrode.

[0025] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0026] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments thereof.

[0027] Figure 1 This is a side view of one side surface of a negative electrode sheet as shown in this application; Figure 2 yes Figure 1 A top view of the negative electrode structure is shown. Reference numerals: negative electrode current collector 10; first coating 20; second coating 30; first active material block 1; second active material block 2. Detailed Implementation

[0028] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0029] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0030] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0031] In related technologies, silicon-carbon anode materials possess the advantage of ultra-high capacity but also come with significant volume expansion, leading to problems such as accelerated expansion of lithium-ion batteries and anode sheet breakage. Simultaneously, the low conductivity and poor thermal stability of silicon-carbon anodes also reduce the overall performance of lithium-ion batteries. Since the silicon-carbon anode material is in direct contact with the anode current collector, continuous expansion stress causes deformation of the current collector along the width of the electrode sheet. The enormous stress during the expansion process of the silicon-carbon material easily leads to anode sheet breakage and failure.

[0032] To address the aforementioned issues, this application provides a negative electrode sheet and a lithium-ion battery. By using a carbon-containing coating to surround and / or cover a coating containing silicon-carbon material, the expansion rate of the silicon-carbon material is structurally suppressed, and the materials complement each other. The two work synergistically in structural and material design to avoid the breakage and failure of the negative electrode sheet, and to ensure the fast charging performance and ultra-high capacity of the battery.

[0033] One embodiment of this application provides a negative electrode sheet, including a negative electrode current collector and a double-layer coating disposed on at least one side surface of the negative electrode current collector. The double-layer coating includes a first coating and a second coating stacked together. Both the first coating and the second coating have at least one first active material patch and at least one second active material patch. The first active material patch includes silicon-carbon material, and the second active material patch includes carbon material. At least one second active material patch is distributed around the periphery of any first active material patch.

[0034] Specifically, the double-layer coating comprises two layers stacked from top to bottom: a first layer and a second layer. The positions of the first and second layers can be interchanged; that is, the first layer can be directly disposed on one side surface of the negative electrode current collector, or the second layer can be directly disposed on one side surface of the negative electrode current collector. The number of first active material blocks in the first and second layers can be the same or different, and the number of second active material blocks in the first and second layers can be the same or different. In the same layer, the first and second active material blocks are staggered and continuously disposed, such that any first active material block is adjacent to at least one second active material block along its horizontal periphery. The adjacent second active material blocks suppress the expansion of the first active material blocks along the horizontal direction (width and / or length direction) of the negative electrode sheet. In different layers, when any first active material block is located in the upper layer, a second active material block is disposed below it; when any first active material block is located in the lower layer, a second active material block is disposed above it. This design ensures that at least one second active material coating is adjacent to any first active material coating on its periphery along the thickness direction, thereby suppressing the expansion of the first active material coating along the thickness direction of the negative electrode sheet through the adjacent second active material coatings.

[0035] Furthermore, the active material in the first active material coating is mainly silicon-carbon, while the active material in the second active material coating is mainly carbon. This combination fully utilizes the ultra-high capacity of silicon-carbon materials and leverages the high conductivity and thermal stability of carbon materials to improve the overall fast-charging performance and thermal stability of the battery. By combining the advantages of both silicon-carbon and carbon materials and considering the positional design of the first and second active material coatings, the two types of coatings are arranged adjacently and continuously in both the horizontal and thickness directions of the negative electrode current collector. By encasing or forming a sandwich structure with the second active material coating in both the thickness and horizontal directions of each first active material coating, buffering and suppressing the expansion of the silicon-carbon negative electrode material in various directions is provided. This effectively releases and alleviates the expansion stress of the silicon-carbon negative electrode material in the length and width directions of the negative electrode current collector, eliminating the problem of negative electrode sheet breakage failure.

[0036] To better suppress the expansion of an active material coating, in some embodiments, the edges of every two adjacent first and second active material coatings located in the same layer are aligned with each other. That is, the adjacent edges of the first and second active material coatings have the same size and are perfectly aligned, thereby ensuring that the first active material coating is completely suppressed by the second active material coating in the horizontal direction.

[0037] To better suppress the expansion of the first active material coating, in some embodiments, the projected area of ​​a single first active material coating on the negative electrode current collector is less than or equal to the projected area of ​​a single second active material coating. That is, for example, in the thickness direction of the negative electrode sheet, the lower layer of the first active material coating is at least partially covered by the upper layer of the second active material coating. Preferably, the first active material coating is completely covered by the upper layer of the second active material coating, forming a sandwich structure along the thickness direction between the negative electrode current collector, the first active material coating, and the second active material coating, thereby completely suppressing the expansion of the first active material coating in the thickness direction.

[0038] Optionally, the first active material coating can be any regular or irregular geometric shape, such as rectangle, rhombus, or circle; the shapes of the first active material coatings in the same layer can be the same or different. The shapes of the first active material coatings in different layers can be the same or different. Correspondingly, the second active material coating can be adapted to the shape of the first active material coating, as long as the second active material coating can at least partially or completely surround and cover the adjacent first active material coating in the horizontal direction and / or thickness direction. This design can form a sandwich structure in both the horizontal and thickness directions, suppressing the expansion of the first active material coating in all directions.

[0039] In one embodiment, the total thickness of the double coating can be 20 μm to 100 μm. In some embodiments, the thickness of the first coating can be 10 μm to 50 μm, and the thickness of the second coating can be 10 μm to 50 μm. The thicknesses of the first and second coatings can be the same or different. For example, the thicknesses of the first and second coatings can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, etc., or any value within the above-defined range, and this application does not limit this. In the double coating structure, by controlling the thickness of each coating layer, the overall thickness of the negative electrode sheet is controlled, the transport dynamics of ions and electrons are optimized, and the rate performance and cycle life are improved.

[0040] In some embodiments, the areal density of the first active material coating is 10 g / m³. 2 ~100g / m 2 The areal density of the second active material coating block is 10 g / m³.2 ~100g / m 2 The areal densities of the first active material coating and the second active material coating can be the same or different. Preferably, the areal densities of the first active material coating and the second active material coating are the same, so that the negative electrode sheet has a uniform thickness after winding or stacking, thereby reducing internal resistance and improving interface stability.

[0041] In some embodiments, the width of the first active material coating is 1mm to 50mm, and the width of the second active material coating is 1mm to 50mm. For example, the widths of the first and second active material coatings can be 1mm, 2mm, 5mm, 10mm, 15mm, 20mm, 30mm, 40mm, 50mm, etc., or any value within the aforementioned range; this application does not limit this. Furthermore, to facilitate production and ensure maximum suppression of the expansion of the first active material coating, in some embodiments, the widths of the first and second active material coatings are equal. This design allows adjacent first and second active material coatings to be completely aligned and overlapped in both the horizontal and thickness directions, thereby suppressing the expansion of the first active material coating.

[0042] In this application, the active material in the first active material coating has a mass percentage of 80% to 99.8% in the coating. The active material in the first active material coating includes silicon-carbon material, which can refer to a compound or composite containing both silicon and carbon elements. In some embodiments, the mass percentage of silicon-carbon material in the active material of the first active material coating is 10% to 100%. For example, the mass percentage of silicon-carbon material in the active material can be 10%, 20%, 30%, 50%, 60%, 80%, 100%, or any value within the above-defined range, and this application does not limit this. Optionally, the silicon-carbon material can be, for example, SiO2. x -Carbon composite materials, SiO x - Commercially available or self-developed materials such as graphite composites, nano-silicon-carbon composites, and vapor-deposited silicon-carbon materials are not limited herein. Furthermore, in some embodiments, the mass percentage of silicon in the silicon-carbon material is 30% to 90%. For example, the mass percentage of silicon in the silicon-carbon material can be 30%, 50%, 60%, 80%, 90%, or any value within the above-mentioned range; this application does not limit this to any particular value.

[0043] In some embodiments, the active material in the first active material coating also includes a carbon-containing material. The carbon-containing material in the first active material coating can be graphite, hard carbon, soft carbon, mesophase carbon microspheres, or other carbon materials. The mass percentage of the carbon-containing material in the active material of the first active material coating is 0-90%. For example, after determining the mass percentage of silicon-carbon material in the active material, the remaining amount of active material is the carbon-containing material. In the first active material coating of this application, by using silicon-carbon material and carbon-containing material as active substances, and by appropriately adjusting the content of silicon-carbon material, the overall expansion rate of the negative electrode sheet is effectively controlled, and the conductivity and thermal stability of the first active material coating are adjusted by the carbon-containing material.

[0044] In some embodiments, the first active material coating further includes a conductive agent and a binder, wherein the conductive agent comprises 0.1% to 10% by mass in the first active material coating, and the binder comprises 0.1% to 10% by mass in the first active material coating. In some embodiments, the conductive agent is selected from at least one of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive graphite, vapor-deposited carbon fibers, graphene, etc. In some embodiments, the binder is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyacrylonitrile, polyurethane, etc.

[0045] In this application, the active material in the second active material coating comprises 80% to 99.8% of the total active material in the coating. The active material in the second active material coating includes carbon materials. In some embodiments, the carbon material comprises 10% to 100% of the total active material in the second active material coating. Exemplarily, the mass percentage of carbon material in the second active material coating can be 10%, 20%, 30%, 40%, 60%, 70%, 80%, 90%, 100%, or any value within the aforementioned range; this application does not limit this. The carbon material in the second active material coating can be graphite, hard carbon, soft carbon, mesophase carbon microspheres, or other carbon materials. The type of carbon material in the second active material coating may be the same as or different from the type of carbon-containing material in the first active material coating.

[0046] The active material of the second active material coating may further include a small amount of silicon-containing material. This silicon-containing material may be the aforementioned silicon-carbon material. The type of silicon-containing material in the second active material coating may be the same as or different from the type of silicon-carbon material in the first active material coating. In some embodiments, the mass percentage of silicon-containing material in the second active material coating is 0-10%. For example, after determining the mass percentage of carbon material in the active material of the second active material coating, the remainder of the active material is the silicon-containing material. In the second active material coating, by using carbon material as the main active material, it acts as a buffer layer to suppress the expansion of the first active material coating and improve the conductivity and thermal stability of the negative electrode. Optionally, a small amount of silicon-containing material can be added to help increase battery capacity without causing excessive expansion.

[0047] Furthermore, the second active material coating may further include a conductive agent and a binder, wherein the conductive agent comprises 0.1% to 10% by mass in the second active material coating, and the binder comprises 0.1% to 10% by mass in the second active material coating. In some embodiments, the conductive agent is selected from at least one of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive graphite, vapor-deposited carbon fibers, graphene, etc. In some embodiments, the binder is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyacrylonitrile, polyurethane, etc. Optionally, the second active material coating may use the same type of conductive agent and / or binder as the first active material coating, which is not limited thereto.

[0048] As can be seen from the above, the active material in the first active material coating of this application is mainly silicon-carbon material, supplemented by carbon-containing material (without silicon), while the active material in the second active material coating is mainly carbon material (without silicon), supplemented by silicon-containing material. The two types of coatings are arranged alternately and continuously along the horizontal and thickness directions on the negative electrode current collector. The main active materials in the two types of coatings complement each other, resulting in complementary effects. Simultaneously, through internal adjustment of the auxiliary active materials within each coating, the active material in the negative electrode sheet is distributed as evenly as possible. This achieves the ultra-high capacity provided by silicon-carbon material while smoothly transitioning the resistance differences between adjacent coatings, and also improves the overall conductivity and thermal stability of the negative electrode sheet through carbon elements.

[0049] Furthermore, the negative electrode current collector of this application has two side surfaces. In some embodiments, both side surfaces of the negative electrode current collector are provided with a double coating layer and are symmetrically arranged along the negative electrode current collector. For example, with the negative electrode current collector as the axis of symmetry, the structure of the negative electrode sheet can be "first coating layer - second coating layer - negative electrode current collector - second coating layer - first coating layer", or "second coating layer - first coating layer - negative electrode current collector - first coating layer - second coating layer".

[0050] In some embodiments, the double-layer coating is obtained by combining a double-layer coating process and an intermittent coating process. The intermittent coating process can be called the "zebra stripe coating process" because its coating effect resembles the alternating stripes of a zebra. To improve production efficiency, by combining the double-layer coating process with the intermittent coating process in related technologies, only two coats are needed to complete the slurry coating of the double-layer coating on the negative electrode current collector side.

[0051] Optionally, the double-layer coating is prepared using an intermittent coating process. It can be understood that if only an intermittent coating process is used, the first layer of the coating on the negative electrode current collector is applied in two coats, applying the first active material block and the second active material block respectively; then the second layer is applied, that is, the first layer is applied in two coats on the surface of the first layer, applying the first active material block and the second active material block respectively. A total of four coats are required to complete the slurry coating of the double-layer coating on the negative electrode current collector side.

[0052] For example, see Figure 1 and Figure 2 This embodiment illustrates a negative electrode sheet, comprising a negative electrode current collector 10 and a double-layer coating disposed on both sides of the negative electrode current collector 10. The double-layer coating comprises a first coating 20 and a second coating 30 stacked together. Both the first coating 20 and the second coating 30 have at least one first active material patch 1 and at least one second active material patch 2. The first active material patch 1 and the second active material patch 2 are alternately arranged adjacent to each other along the width direction of the negative electrode current collector 10 and along the thickness direction of the negative electrode current collector 10, such that at least one second active material patch 2 is distributed around the periphery of each first active material patch 1.

[0053] To facilitate processing and improve production efficiency, the first active material coating 1 and the second active material coating 2 have the same width, ensuring precise alignment of their edges in the horizontal direction and complete coverage in the thickness direction. This allows the second active material coating 2 to completely surround the first active material coating 1, suppressing its expansion. To maintain the flatness of the negative electrode surface, the first active material coating 1 and the second active material coating 2 have the same thickness within the same coating layer. The thicknesses of the first coating layer 20 and the second coating layer 30 can be the same or different; that is, the first active material coating 1 and the second active material coating 2 in different layers can have the same or different thicknesses.

[0054] In other embodiments, see also: Figure 1Along the thickness direction, the first active material coating 1 located on different vertical lines can have different widths; correspondingly, the width of the second active material coating 2 located on the same vertical line only needs to cover the first active material coating 1.

[0055] For example, in other embodiments not shown in the figures, the distribution direction of the first active material coating 1 can form an angle with the length direction of the negative electrode current collector, that is, the first active material coating 1 is not parallel to the length direction. Accordingly, the edge of the second active material coating 2 can be kept adjacent to and aligned with the edge of the first active material coating 1.

[0056] The shape and size of the first active material coating block 1 and the second active material coating block 2 can be customized, as long as they conform to the inventive concept of this application, and will not be elaborated further here.

[0057] Corresponding to the foregoing embodiments, this application provides a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode as described in any of the above embodiments, and an electrolyte.

[0058] The positive electrode sheet of this application includes a positive current collector and a positive active material layer coated on at least one side of the positive current collector. This application does not limit the selection of the positive current collector; it can be any known material suitable for use as a positive current collector, and can be selected according to actual needs, such as metal materials like aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials like carbon cloth and carbon paper. In some embodiments, the positive active material layer further includes a positive conductive agent, a positive binder, and a solvent. The type of positive conductive agent mentioned in the embodiments of this application is not limited; any known conductive agent can be used. The positive conductive agent can be, for example, at least one of the following carbon materials: natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The type of positive binder mentioned in the embodiments of this application is not limited; any known positive binder can be used. The positive binder can be, for example, at least one of the following: polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0059] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0060] It should be noted that this application does not impose any particular limitations on the electrolyte and its preparation method. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing the raw materials evenly according to the specified ratio.

[0061] In the lithium-ion batteries mentioned in this application, a separator is typically provided between the positive and negative electrodes to prevent short circuits. There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. In some embodiments, the separator includes a porous sheet-like or non-woven fabric-like material with excellent liquid retention properties, and the separator includes resin or glass fiber separator materials. Resin or glass fiber separator materials include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0062] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode components and electrolyte. In some embodiments, the outer packaging of the lithium-ion battery may be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion battery may also be a pouch, such as a soft pouch. The material of the pouch may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0063] This application does not impose any particular restrictions on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape.

[0064] The specific type of lithium-ion battery in this application is not particularly limited, and it can be a secondary battery, a power battery, an energy storage battery, etc. This application does not particularly limit the application fields of lithium-ion batteries; they can be used in consumer electronics, new energy vehicles, and energy storage, among other fields.

[0065] This application also provides an electrical device, including the aforementioned lithium-ion battery.

[0066] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0067] To further understand the present invention, the following embodiments are provided to illustrate the present application. These embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0068] Example 1 I. Preparation of Lithium-ion Batteries 1. Preparation of the negative electrode sheet: (1) Preparation of the slurry for the first active material coating. The active material "silicon-carbon material (such as vapor-deposited silicon-carbon material) and carbon-containing material (such as graphite)", conductive agent carbon black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are mixed thoroughly in an appropriate amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform first negative electrode slurry. Among them, the mass percentage of silicon-carbon material in the active material is 50%, and the balance of the active material is graphite.

[0069] (2) Preparation of the slurry for the second active material coating. The active material graphite, conductive agent carbon black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are mixed thoroughly in an appropriate amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform second negative electrode slurry. The graphite constitutes 100% of the active material by mass.

[0070] (3) Slurry Coating. Using a combination of double-layer coating and intermittent coating processes, the first and second negative electrode slurries are coated onto the Cu foil of the negative electrode current collector, dried, and cold-pressed to obtain the negative electrode sheet. Both sides of the negative electrode current collector are coated with a double layer, each layer consisting of a first active material block (referred to as block 1 in Table 1) and a second active material block (referred to as block 2 in Table 1). The coating width of each first and second active material block is 5 mm, and the coating surface density is 30 g / m³. 2 .

[0071] 2. Preparation of the positive electrode: The positive electrode active material lithium cobalt oxide, conductive agent carbon black, multi-walled carbon nanotubes, and binder polyvinylidene fluoride are mixed evenly in a mass ratio of 95:1:1:3, and then evenly dispersed with N-methylpyrrolidone solvent to form a uniform positive electrode slurry. The mixed slurry is coated on both sides of an aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0072] 3. Preparation of electrolyte: Ethylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed and stirred in a mass ratio of 1:1:1 to form a mixed solvent. Water was removed using a molecular sieve and the mixture was set aside. 1M LiPF6 was added and mixed thoroughly to obtain the electrolyte.

[0073] 4. Preparation of lithium-ion batteries: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. After winding and welding the tabs, a bare cell is obtained. The bare cell is placed in an aluminum-plastic film for electrolyte injection and encapsulation to obtain a lithium-ion battery. The preparation of lithium-ion batteries in each embodiment and comparative example is completed.

[0074] The basic content of Examples 2-13 and Comparative Examples 1-3 is the same as that of Example 1. The differences are shown in Table 1 for the changes in relevant parameters, which will not be repeated here.

[0075] Table 1

[0076] Note: "-" in Table 1 indicates that the parameter does not exist. Comparative Example 1 is a double-layer coating, with the total thickness of the double-layer coating being the same as the total thickness of the double-layer protrusion in this application. The upper coating (the coating away from the negative electrode current collector) of Comparative Example 1 uses the first negative electrode slurry, and the lower coating (the coating closer to the negative electrode current collector) uses the second negative electrode slurry. Comparative Example 2 is a double-layer coating, with the upper coating using the second negative electrode slurry and the lower coating using the first negative electrode slurry. Comparative Example 3 is a single-layer coating, applied using the first negative electrode slurry.

[0077] II. Performance Testing The lithium-ion batteries prepared according to the above embodiments and comparative examples were subjected to cycle charge-discharge tests. The test methods were as follows: Each lithium-ion battery was charged at a constant current and constant voltage of 4C to 4.5V, cut off at 0.05C, and then discharged at a constant current of 0.5C. This constitutes one charge-discharge cycle. The cycle expansion rate and cycle capacity retention rate of each lithium-ion battery were tested after 500 charge-discharge cycles to verify whether the battery capacity retention rate could be >80% and the expansion rate <10% after 500 cycles. The negative electrode of the battery was also tested for breakage, and a thermal shock test was conducted at 130℃ to test the thermal stability.

[0078] The battery-related test data results for each embodiment and comparative example are shown in Table 2 below.

[0079] Table 2

[0080] The test results of Examples 1, 2, and 4 show that, with the alternating arrangement of coating blocks 1 and 2 in the double-layer coating, as the proportion of silicon-carbon material in the active material of coating block 1 increases, the battery expansion rate remains within a reasonable level, ensuring that the negative electrode sheet will not break, and maintaining a high capacity retention rate after 500 charge-discharge cycles at high rates. The test results of Examples 1, 5, and 6 show that, although the expansion rate of the battery increases with the proportion of active material in coating block 1, the expansion rate is still maintained at a reasonable level under the suppression of coating block 2, ensuring that the negative electrode sheet will not break.

[0081] As can be seen from the test results of Examples 1, 3, 7 and 8, even if a small amount of silicon-containing material is added to the coating 2, it will not significantly increase the expansion rate of the battery. On the contrary, it is beneficial to improve the capacity retention rate of the battery and give full play to the ultra-high capacity advantage of silicon.

[0082] The test results from Examples 1, 9, 10, 11, and 14 show that the smaller the width of coating patch 1 and coating patch 2, the more frequently coating patch 2 surrounds coating patch 1, thus better suppressing the battery's expansion rate. Within a reasonable width range, the battery's expansion rate can be kept within a reasonable level, while maintaining a relatively good capacity retention rate. When the width of the coating patch is too large, suppression failure occurs, leading to the breakage of the negative electrode sheet.

[0083] The test results of Examples 1, 12, 13 and 15 show that when the areal density of coating 1 and coating 2 is within a reasonable range, the expansion rate of the battery can be suppressed. When the areal density of the coating is too high, the relative content of silicon element is higher, which leads to suppression failure and the breakage of the negative electrode sheet.

[0084] As can be seen from the comparison between Comparative Examples 1 to 3 and Example 1, a single double-layer coating structure cannot suppress battery expansion, and the battery capacity retention rate is poor.

[0085] As can be seen from the above, the specific double-layer coating structure of the negative electrode sheet of this application can fully integrate and give full play to the respective advantages of silicon-carbon materials and carbon materials, and their performance is complementary. Combined with reasonable coating width and areal density, they work synergistically to control the expansion rate of the battery and maintain the battery's excellent cycle performance and thermal stability under high rate and high temperature environments.

[0086] Although this application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for the elements, as long as they do not depart from the scope of this application. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of this application, as long as they do not depart from the essential scope of this application. Therefore, this application is not intended to be limited to the specific embodiments disclosed as the best mode of carrying out this application as conceived, but rather this application will include all embodiments falling within the scope of the appended claims.

[0087] All scopes disclosed in this application include endpoints, and endpoints can be combined with each other.

[0088] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a double-layer coating disposed on at least one surface of the negative electrode current collector. The double-layer coating comprises a first coating and a second coating stacked together. Both the first coating and the second coating have at least one first active material patch and at least one second active material patch. Wherein: The first active material coating block comprises silicon-carbon material, wherein the mass percentage of silicon-carbon material in the active material of the first active material coating block is 20% to 100%; the second active material coating block comprises carbon material and silicon-containing material, wherein the mass percentage of silicon-containing material in the active material of the second active material coating block is 0% to 10%; at least one second active material coating block is adjacent to the periphery of each first active material coating block along both the horizontal and thickness directions. The projected area of ​​a single first active material coating block in the thickness direction of the negative electrode current collector is less than or equal to the projected area of ​​a single second active material coating block.

2. The negative electrode sheet according to claim 1, characterized in that: The edges of every two adjacent first and second active material coating blocks located on the same layer are aligned with each other.

3. The negative electrode sheet according to claim 1, characterized in that: The thickness of the first coating is 10 μm to 50 μm, and the thickness of the second coating is 10 μm to 50 μm; and / or The width of the first active material coating block is 1mm to 50mm, and the width of the second active material coating block is 1mm to 50mm; and / or The areal density of the first active material coating block is 10 g / m³. 2 ~100g / m 2 The areal density of the second active material coating is 10 g / m³. 2 ~100g / m 2 .

4. The negative electrode sheet according to claim 1, characterized in that: The widths of the first active material coating block and the second active material coating block are equal.

5. The negative electrode sheet according to claim 1, characterized in that: The carbon material accounts for 10% to 100% of the mass percentage of the active material in the second active material coating.

6. The negative electrode sheet according to claim 5, characterized in that: The active material in the first active material coating also includes a carbon-containing material, wherein the mass percentage of the carbon-containing material in the active material of the first active material coating is 0-90%; and / or The first active material coating also includes a conductive agent and a binder, wherein the conductive agent has a mass percentage of 0.1% to 10% in the first active material coating, and the binder has a mass percentage of 0.1% to 10% in the first active material coating.

7. The negative electrode sheet according to claim 5, characterized in that: The second active material coating also includes a conductive agent and a binder, wherein the conductive agent has a mass percentage of 0.1% to 10% in the second active material coating, and the binder has a mass percentage of 0.1% to 10% in the second active material coating.

8. The negative electrode sheet according to claim 6 or 7, characterized in that: The conductive agent is selected from at least one of carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive graphite, vapor-deposited carbon fibers, and graphene; and / or The adhesive is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyacrylonitrile, and polyurethane.

9. The negative electrode sheet according to claim 1, characterized in that: The double-layer coating is provided on both sides of the negative electrode current collector and is symmetrically arranged along the negative electrode current collector.

10. The negative electrode sheet according to any one of claims 1 to 7 and 9, characterized in that: The double-layer coating is obtained by combining a double-layer coating process and an intermittent coating process.

11. A lithium-ion battery, characterized in that, The negative electrode sheet includes any one of claims 1 to 10.

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