Negative electrode sheet and battery

Abstract

The application provides a negative electrode sheet and a battery, comprising a negative electrode current collector and negative electrode active material layers coated on both sides of the negative electrode current collector, the negative electrode current collector comprises a flat area and a circular arc area, a first negative electrode active material layer is coated on one side of the negative electrode current collector located at the inside of winding, a second negative electrode active material layer is coated on one side of the negative electrode current collector located at the outside of winding, a third negative electrode active material layer is coated on the surface of the second negative electrode active material layer away from the flat area, and a fourth negative electrode active material layer is coated on the surface of the second negative electrode active material layer away from the circular arc area; the lithium intercalation capacity of the fourth negative electrode active material layer is stronger than that of the first negative electrode active material layer, the second negative electrode active material layer and the third negative electrode active material layer; the fourth negative electrode active material layer is coated on the surface of the circular arc area, and the lithium intercalation capacity of the fourth negative electrode active material layer is strong, so that the lithium intercalation capacity of the negative electrode sheet located at the circular arc area at the outside of winding is improved, and the problem of lithium precipitation in the circular arc area of the negative electrode sheet is solved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a negative electrode and a battery. Background Technology

[0002] At the curved edges of the battery cell, i.e., the corners where the electrode sheets are wound, the electrolyte storage capacity is poor, and the CB value on the positive-to-negative electrode side (cathode-to-anode) is low, making it more prone to lithium plating. Current main solutions include: ① increasing the overall CB value of the system to ensure lithium intercalation capability at the curved edges; ② processing the negative electrode sheets, such as laser etching, to create more lithium intercalation channels; ③ reducing the surface density or compacting the negative electrode sheets to increase porosity and improve lithium intercalation capability. However, these methods suffer from a significant reduction in energy density. Therefore, overcoming these technical problems and defects is a key issue that needs to be addressed. Summary of the Invention

[0003] To address the problem of low CB value on the negative electrode side of the positive electrode in existing batteries, which easily leads to lithium plating, this invention provides a negative electrode sheet and a battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0005] This invention provides a negative electrode sheet, comprising a negative electrode current collector and negative electrode active material layers coated on both sides of the negative electrode current collector. The negative electrode current collector includes a flat region and an arc region. The negative electrode active material layers include a first negative electrode active material layer, a second negative electrode active material layer, a third negative electrode active material layer, and a fourth negative electrode active material layer. The first negative electrode active material layer is coated on the side of the negative electrode current collector located on the inner side of the winding, and the second negative electrode active material layer is coated on the side of the negative electrode current collector located on the outer side of the winding. The second negative electrode active material layer is located away from the flat region. The surface of the first negative electrode active material layer is coated with the third negative electrode active material layer, and the surface of the second negative electrode active material layer facing away from the arc region is coated with the fourth negative electrode active material layer; the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer all include the first negative electrode active material, and the fourth negative electrode active material layer includes the second negative electrode active material; the OI value of the first negative electrode active material is OI1, and the OI value of the second negative electrode active material is OI2; the relationship between OI1 and OI2 is: 1.1≤OI1 / OI2≤2.0;

[0006] The thickness of the second negative electrode active material layer is h2, in μm; the thickness of the fourth negative electrode active material layer is h4, in μm.

[0007] h2 and h4 satisfy the relationship: 1≤h2 / h4≤4;

[0008] The width of the arc area is 2~10mm;

[0009] The D50 of the second negative electrode active material is 10μm-16μm, and the D50 of the first negative electrode active material is 12μm-20μm; the D50 of the second negative electrode active material is smaller than the D50 of the first negative electrode active material.

[0010] Optionally, the thickness of the third negative electrode active material layer is h3, in μm;

[0011] The h2 and h3 satisfy the relationship: 1≤h2 / h3≤4.

[0012] Optionally, the thickness of the first negative electrode active material layer is h1, in μm; h3 and h4 satisfy the relationship: h3=h4;

[0013] The h1, h2, and h3 satisfy the relationship: h1 = h2 + h3.

[0014] Optionally, the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer each comprise a first negative electrode active material, a first conductive agent, and a first binder; in the first negative electrode active material layer, based on the total mass of the first negative electrode active material layer, the first negative electrode active material accounts for 90-98.4% of the mass of the first negative electrode active material layer; the first conductive agent accounts for 0.8-5% of the mass of the first negative electrode active material layer; the first binder accounts for 0.8-5% of the mass of the first negative electrode active material layer; and / or, in the second negative electrode active material layer, based on the total mass of the second negative electrode active material layer, the first negative electrode active material layer comprises a first negative electrode active material, a first conductive agent, and a first binder. A negative electrode active material accounts for 90-98.4% of the mass of the second negative electrode active material layer; a first conductive agent accounts for 0.8-5% of the mass of the second negative electrode active material layer; a first binder accounts for 0.8-5% of the mass of the second negative electrode active material layer; and / or, in the third negative electrode active material layer, based on the total mass of the first negative electrode active material layer, the first negative electrode active material accounts for 90-98.4% of the mass of the third negative electrode active material layer; the first conductive agent accounts for 0.8-5% of the mass of the third negative electrode active material layer; the first binder accounts for 0.8-5% of the mass of the third negative electrode active material layer; and / or,

[0015] The fourth negative electrode active material layer includes a second negative electrode active material, a second conductive agent, and a second binder; based on the total mass of the fourth negative electrode active material layer, the second negative electrode active material accounts for 90-98.4% of the mass of the fourth negative electrode active material layer; the second conductive agent accounts for 0.8-5% of the mass of the fourth negative electrode active material layer; and the second binder accounts for 0.8-5% of the mass of the fourth negative electrode active material layer.

[0016] Optionally, the content of the first conductive agent is w1; the content of the second conductive agent is w2; and w1 and w2 satisfy the relationship: w1≤w2.

[0017] Optionally, the D10 of the second negative electrode active material is 5μm-8μm, and the D10 of the first negative electrode active material is 5μm-8μm.

[0018] Optionally, the D90 of the second negative electrode active material is 18μm-28μm, and the D90 of the first negative electrode active material is 20μm-30μm.

[0019] Optionally, the first negative electrode active material and the second negative electrode active material are each independently selected from one or more of the following: artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, organic polymer compound carbon, lithium titanate, and silicon-carbon composites.

[0020] Optionally, the first conductive agent and the second conductive agent are each independently selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive carbon fiber, carbon nanotubes, graphene, and carbon fiber.

[0021] Optionally, the first adhesive and the second adhesive are each independently selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber, or polyacrylate.

[0022] Another aspect of the present invention provides a battery comprising a positive electrode, a separator, and the aforementioned negative electrode.

[0023] According to the present invention, a negative electrode sheet and battery are provided, wherein a second negative electrode active material layer is coated on the side of the negative electrode sheet located on the outer side of the winding, a third negative electrode active material layer is coated on the surface of the second negative electrode active material layer facing away from the flat region, and a fourth negative electrode active material layer is coated on the surface of the second negative electrode active material layer facing away from the arc region; the present application has a double-layer coating of negative electrode active material layers on the side of the negative electrode sheet located on the outer side of the winding, which has stronger lithium intercalation capability and liquid retention than the negative electrode active material layer in the flat region, resulting in stronger charging capability and significantly reduced risk of lithium plating in the arc region; simultaneously, a third negative electrode active material layer is coated on the surface of the second negative electrode active material layer facing away from the flat region, and a fourth negative electrode active material layer is coated on the surface of the second negative electrode active material layer facing away from the arc region, the first The OI1 value of the first negative electrode active material in the negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer is greater than the OI2 value of the second negative electrode active material in the fourth negative electrode active material layer. The electronic conductivity of the second negative electrode active material is lower than that of the first negative electrode active material, which helps to reduce the electron aggregation degree on the surface of the fourth negative electrode active material layer away from the negative electrode current collector 1, and helps to reduce the overpotential of the negative electrode surface in the arc region. The lithium intercalation capability of the fourth negative electrode active material layer is stronger than that of the first, second, and third negative electrode active material layers, which improves the lithium intercalation capability of the arc region of the negative electrode sheet located on the outer side of the winding, and improves the problem of lithium plating in the arc region of the negative electrode sheet; at the same time, it does not reduce the energy density of the battery. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of the negative electrode sheet located on the outer side of the winding according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the structure of the negative electrode sheet located on the inner side of the winding according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the structure of a battery provided in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 1 of the present invention;

[0030] Figure 6 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 2 of the present invention;

[0031] Figure 7 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 3 of the present invention;

[0032] Figure 8 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 4 of the present invention;

[0033] Figure 9 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 5 of the present invention;

[0034] Figure 10 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 6 of the present invention;

[0035] Figure 11 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 7 of the present invention;

[0036] Figure 12 This is a schematic diagram of the negative electrode sheet provided in Comparative Example 8 of the present invention;

[0037] The reference numerals in the accompanying drawings are as follows:

[0038] 101-Negative electrode sheet; 1-Negative electrode current collector; 2-Negative electrode active material layer; 21-First negative electrode active material layer; 22-Second negative electrode active material layer; 23-Third negative electrode active material layer; 24-Fourth negative electrode active material layer; 100-Battery; 102-Positive electrode sheet; 103-Separator; 104-Straight region; 105-Circular region. Detailed Implementation

[0039] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0040] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0044] like Figures 1-3 As shown, in one embodiment, the present invention provides a negative electrode sheet 101, including a negative electrode current collector 1 and negative electrode active material layers 2 coated on both sides of the negative electrode current collector 1. The negative electrode current collector 1 includes a flat region 104 and an arc region 105. The negative electrode active material layers 2 include a first negative electrode active material layer 21, a second negative electrode active material layer 22, a third negative electrode active material layer 23, and a fourth negative electrode active material layer 24. The side of the negative electrode current collector 1 located on the inner side of the winding is coated with the first negative electrode active material layer 21, and the side of the negative electrode current collector 1 located on the outer side of the winding is coated with the second negative electrode active material layer 22. The surface of the active material layer 22 facing away from the flat region 104 is coated with a third negative electrode active material layer 23, and the surface of the second negative electrode active material layer 22 facing away from the arc region 105 is coated with a fourth negative electrode active material layer 24; the first negative electrode active material layer 21, the second negative electrode active material layer 22 and the third negative electrode active material layer 23 all include the first negative electrode active material, and the fourth negative electrode active material layer 24 includes the second negative electrode active material. The OI value of the first negative electrode active material is OI1, and the OI value of the second negative electrode active material is OI2. OI1 and OI2 satisfy the relationship: 1.1≤OI1 / OI2≤2.0;

[0045] The thickness of the second negative electrode active material layer 22 is h2, in μm;

[0046] The thickness of the fourth negative electrode active material layer 24 is h4, in μm;

[0047] h2 and h4 satisfy the relation: 1≤h2 / h4≤4;

[0048] The width of the arc area 105 is 2~10mm;

[0049] The D50 of the second negative electrode active material is 10μm-16μm, and the D50 of the first negative electrode active material is 12μm-20μm; the D50 of the second negative electrode active material is smaller than that of the first negative electrode active material.

[0050] At the arc of the cell, that is, at the corner when the electrode is wound, the electrolyte storage capacity is poor, and the CB value of the negative electrode 101 located on the outer side of the winding is small, which makes it more prone to lithium plating.

[0051] This invention involves coating a second negative electrode active material layer 22 on the outer side of the negative electrode sheet 101, coating a third negative electrode active material layer 23 on the surface of the second negative electrode active material layer 22 away from the flat region 104, and coating a fourth negative electrode active material layer 24 on the surface of the second negative electrode active material layer 22 away from the arc region 105. This application employs a double-layer coating of negative electrode active material layer 2 on the outer side of the negative electrode sheet 101, which provides stronger lithium intercalation capability and liquid retention compared to the negative electrode active material layer 23 in the flat region 104, resulting in stronger charging capability and significantly reduced lithium plating risk in the arc region 105. Simultaneously, the third negative electrode active material layer 23 is coated on the surface of the second negative electrode active material layer 22 away from the flat region 104, and the fourth negative electrode active material layer 24 is coated on the surface of the second negative electrode active material layer 22 away from the arc region 105. The OI1 value of the first negative electrode active material in the first negative electrode active material layer 21, the second negative electrode active material layer 22, and the third negative electrode active material layer 23 is greater than the OI2 value of the second negative electrode active material in the fourth negative electrode active material layer 24. The electronic conductivity of the second negative electrode active material is lower than that of the first negative electrode active material, which helps to reduce the electron aggregation degree on the surface of the fourth negative electrode active material layer 24 away from the negative electrode current collector 1, and helps to reduce the overpotential of the negative electrode surface in the arc region 105. The lithium intercalation capability of the fourth negative electrode active material layer 24 is stronger than that of the first negative electrode active material layer 21, the second negative electrode active material layer 22, and the third negative electrode active material layer 23, thereby improving the lithium intercalation capability of the arc region 105 located on the outer side of the negative electrode sheet 101 and improving the problem of lithium deposition in the arc region 105 of the negative electrode sheet 101; at the same time, it does not reduce the energy density of the battery 100.

[0052] Specifically, the ratio of OI1 to OI2 is any one of the following values ​​or a range of any two values: 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2. In a preferred embodiment, OI1 and OI2 satisfy the relationship: 1.3 ≤ OI1 / OI2 ≤ 1.8.

[0053] When the ratio of OI1 to OI2 is 1.1-2.0, it helps to reduce the electron accumulation on the surface of the fourth negative electrode active material layer 24 away from the negative electrode current collector 1, which in turn helps to reduce the overpotential on the negative electrode surface of the arc region 105 and reduces the risk of lithium plating in the arc region 105. When the ratio of OI1 to OI2 is less than 1.1, it cannot effectively reduce the electron accumulation on the surface of the fourth negative electrode active material layer 24 away from the negative electrode current collector 1, nor can it effectively reduce the overpotential on the negative electrode surface of the arc region 105, and it cannot reduce the risk of lithium plating. When the ratio of OI1 to OI2 is greater than 2.0, if the value of OI1 is large, the risk of lithium plating in the flat region 104 increases; if the value of OI2 is small, the expansion of the fourth negative electrode active material layer 24 in the arc region 105 is small, the expansion of the negative electrode sheet 101 is uneven, and the battery 100 is prone to deformation, which can lead to performance failure.

[0054] In a specific embodiment, the ratio of h2 to h4 is any one of the following values: 1, 1.5, 2, 2.5, 3, 3.5, or 4, or a range of any two values. In a preferred embodiment, h2 and h4 satisfy the relationship: 1.5 ≤ h2 / h4 ≤ 3.5.

[0055] When the ratio of h2 to h4 is between 1 and 4, the process efficiency and yield of the negative electrode 101 are good, the expansion of the negative electrode 101 is uniform, and the lithium intercalation capability of the arc region 105 is improved, reducing the risk of lithium plating in the arc region 105. When the ratio of h2 to h4 is less than 1, the upper layer of the double coating is thicker, the compaction density of the negative electrode 101 is reduced, and the energy density of the battery 100 is reduced; when the ratio of h2 to h4 is greater than 4, the upper layer of the double coating is thinner, and the improvement effect on lithium plating in the arc region 105 is smaller.

[0056] In a specific embodiment, the width of the arc region 105 is any one value or a range of any two values ​​from 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm; in a preferred embodiment, the width of the arc region 105 is 4~8mm.

[0057] When the width of the arc region 105 is 2~10mm, the manufacturing efficiency and yield of the negative electrode 101 are good, which can reduce the risk of lithium plating in the arc region 105. When the width of the arc region 105 is less than 2mm, the manufacturing difficulty of the negative electrode 101 increases, and the coating amount of the fourth negative electrode active material layer 24 is less, so the improvement effect of lithium plating in the arc region 105 is not obvious. When the width of the arc region 105 is greater than 10mm, the arc region 105 is too wide and extends to the flat region 104, which can easily lead to uneven expansion of the negative electrode active material layer 2, resulting in deformation or powder shedding of the negative electrode 101, thereby reducing the capacity of the battery 100 and causing performance failure.

[0058] In a specific embodiment, the D50 of the second negative electrode active material is any one value or a range of any two values ​​among 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or 16μm; in a preferred embodiment, the D50 of the second negative electrode active material is 10μm-14μm.

[0059] When the D50 of the second negative electrode active material is 10μm-16μm, the use of a smaller particle size of the second negative electrode active material in the arc region 105 is beneficial to improving the rate performance of the arc region 105. When the D50 of the second negative electrode active material is less than 10μm, it is prone to agglomeration during the slurry preparation process, making it unable to assist in the transport of lithium ions in the negative electrode. When the D50 of the second negative electrode active material is greater than 16μm, the particle size of the second negative electrode active material is larger, the lithium intercalation ability of the negative electrode sheet 101 is reduced, and the rate performance is reduced.

[0060] In a specific embodiment, the D50 of the first negative electrode active material is any one value or a range of any two values ​​among 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm; in a preferred embodiment, the D50 of the first negative electrode active material is 15μm-20μm.

[0061] When the D50 of the first negative electrode active material is 12μm-20μm, the process efficiency and yield of the negative electrode 101 are good, and the lithium intercalation capability is moderate, meeting the performance requirements. When the D50 of the first negative electrode active material is less than 12μm, the process difficulty of the negative electrode 101 increases, and the particles are prone to agglomeration; when the D50 of the first negative electrode active material is greater than 20μm, the particle size of the first negative electrode active material is larger, the lithium intercalation capability of the negative electrode 101 decreases, and the rate performance decreases.

[0062] When the D50 of the second negative electrode active material is less than that of the first negative electrode active material, the lithium intercalation capability of the fourth negative electrode active material layer 24 is stronger than that of the first negative electrode active material layer 21, the second negative electrode active material layer 22, and the third negative electrode active material layer 23; this is beneficial to improving the rate performance of the arc region 105. When the D50 of the second negative electrode active material is greater than that of the first negative electrode active material, the rate performance of the negative electrode 101 decreases, the lithium intercalation capability of the negative electrode 101 decreases, and the risk of lithium plating in the arc region 105 increases.

[0063] When the D50 of the second negative electrode active material is less than that of the first negative electrode active material, lithium plating at the arc of the wound cell can be effectively alleviated.

[0064] like Figures 1-3 As shown, in one embodiment, the thickness of the third negative electrode active material layer 23 is h3, in μm;

[0065] h2 and h3 satisfy the relation: 1≤h2 / h3≤4.

[0066] Specifically, the ratio of h2 to h3 is any one of the following values: 1, 1.5, 2, 2.5, 3, 3.5, or 4, or a range of any two values. In a preferred embodiment, h2 and h3 satisfy the relationship: 1.5 ≤ h2 / h3 ≤ 3.5.

[0067] When the ratio of h2 to h3 is 1-4, the process efficiency and yield of the negative electrode 101 are good, the expansion of the negative electrode 101 is uniform, and the lithium intercalation capability of the arc region 105 is improved, reducing the risk of lithium plating in the arc region 105. When the ratio of h2 to h3 is less than 1, the upper layer of the double coating is thicker, the compaction density of the negative electrode 101 is reduced, and the energy density of the battery 100 is reduced; when the ratio of h2 to h3 is greater than 4, the upper layer of the double coating is thinner, and the improvement effect on lithium plating in the arc region 105 is smaller.

[0068] like Figures 1-3 As shown, in one embodiment, the thickness of the first negative electrode active material layer 21 is h1, in μm; h3 and h4 satisfy the relationship: h3=h4;

[0069] h1, h2, and h3 satisfy the relation: h1 = h2 + h3.

[0070] Specifically, the negative electrode current collector 1 is coated with a first negative electrode active material layer 21 by a double coating method on the inner side of the winding. The thickness of the first coating of the negative electrode active material layer on the negative electrode current collector 1 is h1 / 2, and the thickness of the second coating of the negative electrode active material layer on the negative electrode current collector 1 is h1 / 2.

[0071] The negative electrode current collector 1 is coated with a second negative electrode active material layer 22, a third negative electrode active material layer 23, and a fourth negative electrode active material layer 24 on the outer side of the winding using a double-layer coating method. The thickness of the second negative electrode active material layer 22 coated on the negative electrode current collector 1 in the first coating is h2. In the second coating on the negative electrode current collector 1, the third negative electrode active material layer 23 is coated on the flat area 104 of the negative electrode current collector 1 using a dual-die coating method, and the fourth negative electrode active material layer 24 is coated on the arc area 105 of the negative electrode current collector 1. The thicknesses of the third negative electrode active material layer 23 and the fourth negative electrode active material layer 24 are h3 and h4, respectively, so that the thickness of the negative electrode active material layer 2 on both sides of the negative electrode current collector 1 is the same. The process efficiency and yield of the negative electrode sheet 101 are good, and the expansion rate of the negative electrode active material layer 2 on both sides is similar, so there will be no deformation of the negative electrode sheet 101 due to uneven expansion.

[0072] like Figures 1-3As shown, in one embodiment, the first negative electrode active material layer 21, the second negative electrode active material layer 22, and the third negative electrode active material layer 23 include a first negative electrode active material, a first conductive agent, and a first binder; in the first negative electrode active material layer 21, the first negative electrode active material accounts for 90-98.4% of the total mass of the first negative electrode active material layer 21; the first conductive agent accounts for 0.8-5% of the mass of the first negative electrode active material layer 21; the first binder accounts for 0.8-5% of the mass of the first negative electrode active material layer 21; and / or,

[0073] In the second negative electrode active material layer 22, based on the total mass of the second negative electrode active material layer 22, the first negative electrode active material accounts for 90-98.4% of the mass of the second negative electrode active material layer 22; the first conductive agent accounts for 0.8-5% of the mass of the second negative electrode active material layer 22; the first binder accounts for 0.8-5% of the mass of the second negative electrode active material layer 22; and / or

[0074] In the third negative electrode active material layer 23, based on the total mass of the third negative electrode active material layer 23, the first negative electrode active material accounts for 90-98.4% of the mass of the third negative electrode active material layer 23; the first conductive agent accounts for 0.8-5% of the mass of the third negative electrode active material layer 23; the first binder accounts for 0.8-5% of the mass of the third negative electrode active material layer 23; and / or

[0075] The fourth negative electrode active material layer 24 includes a second negative electrode active material, a second conductive agent, and a second binder. Based on the total mass of the fourth negative electrode active material layer 24, the second negative electrode active material accounts for 90-98.4% of the mass of the fourth negative electrode active material layer 24; the second conductive agent accounts for 0.8-5% of the mass of the fourth negative electrode active material layer 24; and the second binder accounts for 0.8-5% of the mass of the fourth negative electrode active material layer 24.

[0076] Specifically, the mass of the first negative electrode active material in the first negative electrode active material layer 21, the second negative electrode active material layer 22, or the third negative electrode active material layer 23 is any one value or a range of any two values ​​from 90%, 90.7%, 91.4%, 92.1%, 92.8%, 93.5%, 94.2%, 94.9%, 95.6%, 96.3%, 97%, 97.7%, or 98.4%; in a preferred embodiment, the mass of the first negative electrode active material in the first negative electrode active material layer 21, the second negative electrode active material layer 22, or the third negative electrode active material layer 23 is 92.1-97.7%.

[0077] Specifically, the mass of the first conductive agent in the first negative electrode active material layer 21, the second negative electrode active material layer 22, or the third negative electrode active material layer 23 is any one value or a range of any two values ​​from 0.8%, 1.5%, 2.2%, 2.9%, 3.6%, 4.3%, or 5%; in a preferred embodiment, the mass of the first conductive agent in the first negative electrode active material layer 21, the second negative electrode active material layer 22, or the third negative electrode active material layer 23 is 1.5%-2.9%.

[0078] Specifically, the mass of the first binder in the first negative electrode active material layer 21, the second negative electrode active material layer 22, or the third negative electrode active material layer 23 is any one value or a range of any two values ​​from 0.8%, 1.5%, 2.2%, 2.9%, 3.6%, 4.3%, or 5%; in a preferred embodiment, the mass of the first binder in the first negative electrode active material layer 21, the second negative electrode active material layer 22, or the third negative electrode active material layer 23 is 1.5%-2.9%.

[0079] Preferably, the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer comprise the same substances and have the same proportions.

[0080] Specifically, the second negative electrode active material accounts for any one of the following mass values ​​of the fourth negative electrode active material layer 24: 90%, 90.7%, 91.4%, 92.1%, 92.8%, 93.5%, 94.2%, 94.9%, 95.6%, 96.3%, 97%, 97.7%, or 98.4%, or a range of any two of these values; in a preferred embodiment, the second negative electrode active material accounts for 92.1-97.7% of the mass of the fourth negative electrode active material layer 24.

[0081] Specifically, the second conductive agent accounts for any one of the following mass values ​​of the fourth negative electrode active material layer 24: 0.8%, 1.5%, 2.2%, 2.9%, 3.6%, 4.3%, or 5%, or any two of these values; in a preferred embodiment, the second conductive agent accounts for 1.5%-2.9% of the mass of the fourth negative electrode active material layer 24.

[0082] Specifically, the second binder accounts for any one or any two values ​​of 0.8%, 1.5%, 2.2%, 2.9%, 3.6%, 4.3%, or 5% of the mass of the fourth negative electrode active material layer 24; in a preferred embodiment, the second binder accounts for 1.5%-2.9% of the mass of the fourth negative electrode active material layer 24.

[0083] When the mass ratio of various materials in the first negative electrode active material layer 21, the second negative electrode active material layer 22, the third negative electrode active material layer 23 and the fourth negative electrode active material layer 24 is within the above range, the battery 100 can have excellent long cycle performance under both normal temperature and high temperature environments.

[0084] The negative electrode 101 can be prepared according to conventional methods in the art. For example, the negative electrode active material layer 2 is typically formed by coating a negative electrode slurry, consisting of a negative electrode active material, a second conductive agent, a second binder, and any other components, onto the negative electrode current collector 1, followed by drying and cold pressing. The solvent can be an aqueous solvent, but is not limited to it.

[0085] like Figures 1-3 As shown, in one embodiment, the content of the first conductive agent is w1, and the mass percentage content of the first conductive agent in the first negative electrode active material layer 21, the second negative electrode active material layer 22, and the third negative electrode active material layer 23 is all w1; the content of the second conductive agent is w2, that is, the mass percentage content of the second conductive agent in the fourth negative electrode active material layer 24 is all w2; w1 and w2 satisfy the relationship: w1≤w2.

[0086] When w1≤w2, the lithium intercalation capability of the fourth negative electrode active material layer 24 is stronger than that of the first negative electrode active material layer 21, the second negative electrode active material layer 22, and the third negative electrode active material layer 23; the conductivity of the arc region 105 is improved, the lithium intercalation capability of the negative electrode sheet 101 is enhanced, and the risk of lithium plating in the arc region 105 is reduced. When w1>w2, the conductivity of the arc region 105 deteriorates, the lithium intercalation capability of the negative electrode sheet 101 is reduced, and the risk of lithium plating in the arc region 105 is increased.

[0087] like Figures 1-3 As shown, in one embodiment, the D10 of the second negative electrode active material is 5μm-8μm, and the D10 of the first negative electrode active material is 5μm-8μm.

[0088] Specifically, the D10 of the second negative electrode active material is any one value or a range of any two values ​​among 5μm, 6μm, 7μm or 8μm; in a preferred embodiment, the D10 of the second negative electrode active material is 6μm-7μm.

[0089] Specifically, the D10 of the first negative electrode active material is any one value or a range of any two values ​​among 5μm, 6μm, 7μm or 8μm; in a preferred embodiment, the D10 of the first negative electrode active material is 6μm-7μm.

[0090] like Figures 1-3 As shown, in one embodiment, the D90 of the second negative electrode active material is 18μm-28μm, and the D90 of the first negative electrode active material is 20μm-30μm.

[0091] Specifically, the D90 of the second negative electrode active material is any one value or a range of any two values ​​selected from 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm or 28μm; in a preferred embodiment, the D90 of the second negative electrode active material is 20μm-26μm.

[0092] Specifically, the D90 of the first negative electrode active material is any one value or a range of any two values ​​selected from 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm or 30μm; in a preferred embodiment, the D90 of the first negative electrode active material is 23μm-27μm.

[0093] like Figures 1-3 As shown, in one embodiment, the first negative electrode active material and the second negative electrode active material are each independently selected from one or more of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, organic polymer compound carbon, lithium titanate, and silicon-carbon composites.

[0094] like Figures 1-3 As shown, in one embodiment, the first conductive agent and the second conductive agent are each independently selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive carbon fiber, carbon nanotubes, graphene, and carbon fiber.

[0095] like Figures 1-3 As shown, in one embodiment, the first adhesive and the second adhesive are each independently selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber, or polyacrylate.

[0096] In one embodiment, the negative electrode current collector 1 is selected from a metallic material that can conduct electrons. Preferably, the negative electrode current collector 1 includes metals such as stainless steel, Al, Ni, tin, copper, nickel, titanium, and iron, or their alloys. In a more preferred embodiment, the negative electrode current collector 1 is selected from aluminum foil.

[0097] like Figure 4 As shown, in one embodiment, the present invention provides a battery 100, including a positive electrode 102, a separator 103 and the aforementioned negative electrode 101.

[0098] In the electrode sheet of the present invention, for the positive electrode sheet, a positive electrode active material layer is used; the positive electrode active material layer can be selected from various positive electrode active materials known in the art suitable for use in lithium battery 100, and its composition and preparation method are known in the art. The positive electrode active material layer contains a positive electrode active substance, and various positive electrode active substances known to those skilled in the art for preparing the positive electrode of lithium-ion secondary battery 100 can be used. For example, the positive electrode active substance is a lithium-containing composite metal oxide, and specific materials are, for example, one or more of LiCoO2, LiNiO2, LiMn2O4, LiFePO4, and lithium nickel cobalt manganese oxides (such as LiNi). 0.5 Co 0.2 Mn 0.3 One or more of O2 and lithium nickel manganese oxide.

[0099] In some embodiments, the positive electrode further includes a positive current collector, and the positive electrode material layer covers the surface of the positive current collector. It should be noted that, in this application, the portion of the positive electrode other than the positive current collector is referred to as the positive electrode material layer.

[0100] The positive current collector is selected from a metallic material that can conduct electrons. Preferably, the positive current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0101] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent.

[0102] In some embodiments, the positive electrode binder includes one or more of the following: polyvinylidene fluoride, copolymers of polyvinylidene fluoride, polytetrafluoroethylene, copolymers of polyvinylidene fluoride and hexafluoropropylene, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ethers, copolymers of ethylene and tetrafluoroethylene, copolymers of polyvinylidene fluoride and tetrafluoroethylene, copolymers of polyvinylidene fluoride and trifluoroethylene, copolymers of polyvinylidene fluoride and trichloroethylene, copolymers of polyvinylidene fluoride and fluorinated vinylides, copolymers of polyvinylidene fluoride, hexafluoropropylene and tetrafluoroethylene, thermoplastic polyimide, polyethylene and polypropylene, etc.; acrylic resins; and styrene-butadiene rubber.

[0103] In some embodiments, the positive electrode conductive agent includes one or more of the following: metallic conductive agent, carbon-based material, metal oxide-based conductive agent, and composite conductive agent. Specifically, the metallic conductive agent can be metals such as copper powder, nickel powder, and silver powder; the carbon-based material can be carbon-based materials such as conductive graphite, conductive carbon black, conductive carbon fiber, or graphene; the metal oxide-based conductive agent can be tin oxide, iron oxide, zinc oxide, etc.; and the composite conductive agent can be composite powder, composite fiber, etc. More specifically, the conductive carbon black can be one or more of the following: acetylene black, 350G, Ketjen black, carbon fiber (VGCF), and carbon nanotubes (CNTs).

[0104] In some embodiments, the diaphragm 103 is located between the positive and negative electrodes.

[0105] The diaphragm 103 can be any existing conventional diaphragm 103, such as a polymer diaphragm 103, non-woven fabric, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and triple-layer PP / PE / PP diaphragms 103.

[0106] The positive electrode 102, separator 103, and negative electrode 101 of this application are stacked and wound to form a wound battery cell, which is then injected with electrolyte and packaged to obtain the battery 100 of this application. Due to the use of the negative electrode 101 of this invention, the battery 100 can have improved lithium intercalation capability at the arc position and improved lithium deposition characteristics in the arc region 105.

[0107] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0108] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0109] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combination steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combination connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combination of devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0110] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0111] Table 1. Design of the negative electrode active material layer in Examples 1-10 and Comparative Examples 1-17;

[0112]

[0113]

[0114] Note: C1 is the first negative electrode active material layer; C2 is the second negative electrode active material layer; C3 is the third negative electrode active material layer; C4 is the fourth negative electrode active material layer; the C1 / C2 / C3 ratio refers to the mass ratio of artificial graphite, conductive carbon black, and PVDF in the first / second / third negative electrode active material layers; the C4 ratio refers to the mass ratio of artificial graphite, conductive carbon black, and PVDF in the fourth negative electrode active material layer.

[0115] F1 represents the first negative electrode active material; F2 represents the second negative electrode active material;

[0116] A1 represents the first layer of the negative electrode coil wound on the inner side; A2 represents the second layer of the negative electrode coil wound on the inner side; B1 represents the first layer of the negative electrode coil wound on the outer side; B2 represents the second layer of the negative electrode coil wound on the outer side; a represents the straight area; b represents the arc area.

[0117] Example 1

[0118] Preparation of negative electrode:

[0119] Preparation of the first negative electrode active material slurry: Artificial graphite, conductive carbon black, and PVDF were mixed in a mass ratio of 98:1:1. The mixture was thoroughly stirred in a deionized aqueous solvent to form a uniform first negative electrode active material slurry; wherein the first negative electrode active material had a D50 of 15 μm.

[0120] Preparation of the second negative electrode active material slurry: Artificial graphite, conductive carbon black, and PVDF are mixed in a mass ratio of 97:2:1. The mixture is thoroughly stirred in a deionized aqueous solvent to form a uniform first negative electrode active material slurry; wherein, the second negative electrode active material has a D50 of 12 μm.

[0121] The first negative electrode active material slurry is coated on the side of the negative electrode current collector located on the inner side of the winding, and two layers are coated (i.e., layers A1 and A2 in Table 1). The first negative electrode active material slurry is coated on the side of the negative electrode current collector located on the outer side of the winding, and one coating is applied to form the first negative electrode active material layer (i.e., layer B1 in Table 1). After drying, based on the first coating, the first negative electrode active material slurry is coated on the straight area of ​​the first negative electrode active material layer (to obtain layer B2a in Table 1), and the second negative electrode active material layer is coated on the arc area (to obtain layer B2b in Table 1). The width of the arc area is 5 mm, and the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 7:3.

[0122] Preparation of positive electrode:

[0123] Lithium cobalt oxide (CCO) as the positive electrode active material, SP (SP) as the conductive agent, and PVDF (PVDF) as the binder are mixed in a mass ratio of 97:1.8:1.2. The mixture is thoroughly stirred in NMP solvent to form a uniform positive electrode slurry. This slurry is then coated onto at least one side of the positive and negative electrode current collector aluminum foil. After drying, rolling, and die-cutting, a satisfactory positive electrode sheet is obtained.

[0124] Preparation of the diaphragm:

[0125] A porous PE polymer film is used as the separator;

[0126] Electrolyte preparation:

[0127] Lithium salt LiPF6 was dissolved in organic solvent EC-DMC (1:1 volume ratio) at a concentration of 1M to obtain a liquid electrolyte.

[0128] Battery manufacturing:

[0129] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, one end of each of the positive electrode, separator, and negative electrode is wound around the electrolyte separator to form a core. The wound core is then placed in a pre-formed aluminum-plastic film bag. The electrolyte prepared above is injected into the baked and dried cell. After vacuum sealing, settling, and formation processes, a 1Ah battery is obtained.

[0130] Example 2-10

[0131] Examples 2-10 illustrate the negative electrode and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0132] The various parameters of the negative electrode shown in Table 1 are used.

[0133] Comparative Examples 1-17

[0134] Comparative Examples 1-17 are used to illustrate the negative electrode sheet and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being:

[0135] The various parameters of the negative electrode shown in Table 1 are used.

[0136] Test method:

[0137] The batteries obtained in Examples 1-10 and Comparative Examples 1-17 were subjected to charge-discharge tests and cycle tests. Unless otherwise specified, the techniques or conditions described in the literature or the product instructions were followed. Reagents or instruments whose manufacturers are not specified were all commercially available conventional products.

[0138] Energy density test

[0139] Energy density = Cell capacity * Nominal voltage / Cell height / Cell width / Cell thickness.

[0140] 2. Cyclic performance test method: Charge the cell at 3C constant current and constant voltage to 4.5V, cut off at 0.05C, and discharge at 0.5C. Test the battery discharge capacity after every 100 cycles. Record the cycle number when the battery discharge capacity decays to less than 80% of the initial capacity. Disassemble the battery to check the lithium plating in the arc area of ​​the electrode. Classify it as no lithium plating, slight lithium plating, moderate lithium plating, and severe lithium plating.

[0141] Test results: See Table 2.

[0142] Table 2

[0143]

[0144] As shown in Table 2, compared with Comparative Examples 1-10, Comparative Examples 1-17, such as Figure 1 As shown, when a first negative electrode active material layer is coated on the side of the negative electrode current collector located on the inner side of the winding, a second negative electrode active material layer is coated on the side of the negative electrode current collector located on the outer side of the winding, a third negative electrode active material layer is coated on the surface of the second negative electrode active material layer away from the flat area, and a fourth negative electrode active material layer is coated on the surface of the second negative electrode active material layer away from the arc area, the battery has a high energy density and good cycle performance, and no lithium plating phenomenon occurs in the arc area of ​​the negative electrode sheet.

[0145] like Figure 5 As shown in Comparative Example 1, when the first negative electrode active material layer is coated on both sides of the negative electrode current collector, the battery has a high energy density but poor cycle performance, and severe lithium plating occurs in the arc area of ​​the negative electrode sheet.

[0146] like Figure 6 As shown in Comparative Example 2, when the fourth negative electrode active material layer is coated on both sides of the negative electrode current collector, the cycle performance is better, and no lithium plating occurs in the arc area of ​​the negative electrode sheet, but the energy density of the battery is reduced.

[0147] like Figure 7 As shown in Comparative Example 3, when the first negative electrode active material layer is coated on the inner side of the negative electrode current collector and the fourth negative electrode active material layer is coated on the outer side of the negative electrode current collector, the cycle performance is better and no lithium plating occurs in the arc area of ​​the negative electrode sheet, but the energy density of the battery is reduced.

[0148] like Figure 8As shown in Comparative Example 4, when a first negative electrode active material layer is coated on the inner side of the negative electrode current collector, a second negative electrode active material layer is coated on the first layer on the outer side of the negative electrode current collector, and a fourth negative electrode active material layer is coated on the second layer on the outer side of the negative electrode current collector, the battery has a high energy density but poor cycle performance, and moderate lithium plating occurs in the arc area of ​​the negative electrode sheet.

[0149] like Figure 9 As shown in Comparative Example 5, when a first negative electrode active material layer is coated on the first layer inside the winding of the negative electrode current collector, and a fourth negative electrode active material layer is coated on the second layer inside the winding of the negative electrode current collector; and a second negative electrode active material layer is coated on the first layer outside the winding of the negative electrode current collector, and a fourth negative electrode active material layer is coated on the second layer outside the winding of the negative electrode current collector, the battery has a high energy density but poor cycle performance, and moderate lithium plating occurs in the arc region of the negative electrode sheet.

[0150] like Figure 10 As shown in Comparative Example 6, when only one layer of negative active material is coated on both sides of the negative electrode current collector, and the first negative active material layer is coated on the straight areas on the inner and outer sides of the negative electrode current collector, and the fourth negative active material layer is coated on the arc areas on the inner and outer sides of the negative electrode current collector, the cycle performance is better, and no lithium plating occurs in the arc area of ​​the negative electrode sheet, but the energy density of the battery is reduced.

[0151] like Figure 11 As shown in Comparative Example 7, when a first negative electrode active material layer is coated on the flat areas of the first and second layers inside the winding of the negative electrode current collector, a second negative electrode active material layer is coated on the first layer outside the winding of the negative electrode current collector, a third negative electrode active material layer is coated on the flat areas of the second layer outside the winding of the negative electrode current collector, and a fourth negative electrode active material layer is coated on the arc areas of the second layer inside the winding of the negative electrode current collector and the arc areas of the second layer outside the winding of the negative electrode current collector, the cycle performance is good, and no lithium plating phenomenon occurs in the arc areas of the negative electrode sheet, but the energy density of the battery is reduced.

[0152] like Figure 12 As shown in Comparative Example 8, when the first negative electrode active material layer is coated in the straight area inside the winding of the negative electrode current collector, and the second and third negative electrode active material layers are laminated in the straight area outside the winding of the negative electrode current collector, and the first negative electrode active material layer is coated in the arc area inside the winding of the negative electrode current collector and the arc area outside the winding of the negative electrode current collector, the cycle performance is good, and no lithium plating phenomenon occurs in the arc area of ​​the negative electrode sheet, but the energy density of the battery is reduced.

[0153] In Comparative Examples 9-10, the OI1 / OI2 ratio exceeded the range of 1.1-2.0, resulting in moderate and severe lithium plating, respectively. In Comparative Examples 11-13, the h2 / h4 ratio or the width of the arc region did not match, leading to lithium plating or a decrease in cycle performance. In Comparative Examples 14-17, the particle size of the negative electrode active material did not meet the requirement that the D50 of F2 is smaller than the D50 of F1, resulting in lithium plating problems as well.

[0154] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The device includes a negative electrode current collector and negative electrode active material layers coated on both sides of the negative electrode current collector. The negative electrode current collector includes a flat region and an arc region. The negative electrode active material layers include a first negative electrode active material layer, a second negative electrode active material layer, a third negative electrode active material layer, and a fourth negative electrode active material layer. The side of the negative electrode current collector located on the inner side of the winding is coated with the first negative electrode active material layer, and the side of the negative electrode current collector located on the outer side of the winding is coated with the second negative electrode active material layer. The surface of the second negative electrode active material layer facing away from the flat region is coated with a certain amount of... The third negative electrode active material layer is described above, and the surface of the second negative electrode active material layer facing away from the arc region is coated with the fourth negative electrode active material layer; the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer all include a first negative electrode active material, and the fourth negative electrode active material layer includes a second negative electrode active material. The OI value of the first negative electrode active material is OI1, and the OI value of the second negative electrode active material is OI2. The relationship between OI1 and OI2 is: 1.1≤OI1 / OI2≤2.0; The thickness of the second negative electrode active material layer is h2, in μm; the thickness of the fourth negative electrode active material layer is h4, in μm. h2 and h4 satisfy the relationship: 1≤h2 / h4≤4; The width of the arc area is 2~10mm; The D50 of the second negative electrode active material is 10μm-16μm, and the D50 of the first negative electrode active material is 12μm-20μm; the D50 of the second negative electrode active material is smaller than the D50 of the first negative electrode active material.

2. The negative electrode sheet according to claim 1, characterized in that: The thickness of the third negative electrode active material layer is h3, in μm; The h2 and h3 satisfy the relationship: 1≤h2 / h3≤4.

3. The negative electrode sheet according to claim 2, characterized in that: The thickness of the first negative electrode active material layer is h1, in μm; h3 and h4 satisfy the relationship: h3=h4; The h1, h2, and h3 satisfy the relationship: h1 = h2 + h3.

4. The negative electrode sheet according to claim 1, characterized in that: The first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer each comprise a first negative electrode active material, a first conductive agent, and a first binder. In the first negative electrode active material layer, based on the total mass of the first negative electrode active material layer, the first negative electrode active material accounts for 90-98.4% of the mass of the first negative electrode active material layer; the first conductive agent accounts for 0.8-5% of the mass of the first negative electrode active material layer; the first binder accounts for 0.8-5% of the mass of the first negative electrode active material layer; and / or, in the second negative electrode active material layer, based on the total mass of the second negative electrode active material layer, the first negative electrode active material comprises a first negative electrode active material, a first conductive agent, and a first binder. The active material accounts for 90-98.4% of the mass of the second negative electrode active material layer; the first conductive agent accounts for 0.8-5% of the mass of the second negative electrode active material layer; the first binder accounts for 0.8-5% of the mass of the second negative electrode active material layer; and / or, in the third negative electrode active material layer, based on the total mass of the first negative electrode active material layer, the first negative electrode active material accounts for 90-98.4% of the mass of the third negative electrode active material layer; the first conductive agent accounts for 0.8-5% of the mass of the third negative electrode active material layer; the first binder accounts for 0.8-5% of the mass of the third negative electrode active material layer; and / or, The fourth negative electrode active material layer includes a second negative electrode active material, a second conductive agent, and a second binder; based on the total mass of the fourth negative electrode active material layer, the second negative electrode active material accounts for 90-98.4% of the mass of the fourth negative electrode active material layer; the second conductive agent accounts for 0.8-5% of the mass of the fourth negative electrode active material layer; and the second binder accounts for 0.8-5% of the mass of the fourth negative electrode active material layer.

5. The negative electrode sheet according to claim 4, characterized in that: The content of the first conductive agent is w1; the content of the second conductive agent is w2; w1 and w2 satisfy the relationship: w1≤w2.

6. The negative electrode sheet according to claim 1, characterized in that: The D10 of the second negative electrode active material is 5μm-8μm, and the D10 of the first negative electrode active material is 5μm-8μm.

7. The negative electrode sheet according to claim 1, characterized in that: The D90 of the second negative electrode active material is 18μm-28μm, and the D90 of the first negative electrode active material is 20μm-30μm.

8. The negative electrode sheet according to claim 1, characterized in that: The first negative electrode active material and the second negative electrode active material are each independently selected from one or more of the following: artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, organic polymer compound carbon, lithium titanate, and silicon-carbon composites.

9. The negative electrode sheet according to claim 4, characterized in that: The first conductive agent and the second conductive agent are each independently selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive carbon fiber, carbon nanotube, graphene, and carbon fiber.

10. The negative electrode sheet according to claim 4, characterized in that: The first adhesive and the second adhesive are each independently selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber or polyacrylate.

11. A battery, characterized in that: It includes a positive electrode, a separator, and a negative electrode as described in any one of claims 1-10.

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