A negative electrode sheet, a wound-type battery cell, and a battery

Abstract

This invention relates to the field of battery technology, specifically to a negative electrode sheet, a wound battery cell, and a battery. The negative electrode sheet of this invention includes a corner region and a straight region. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on one or both surfaces of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode film layer includes a corner region negative electrode film layer and a straight region negative electrode film layer. The average particle size of the negative electrode active material in the corner region negative electrode film layer is larger than the average particle size of the negative electrode active material in the straight region negative electrode film layer. In this invention, the negative electrode sheet has a larger average particle size of negative electrode active material in the corner region negative electrode film layer than in the straight region negative electrode film layer. During charging and discharging, the larger average particle size of the negative electrode active material in the corner region provides a buffer space for the volume expansion of the negative electrode sheet, effectively reducing mechanical stress and improving the cycle stability of the battery.

Description

[0001] Cross-references to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202510339158X, filed on March 20, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of battery technology, specifically to a negative electrode, a wound cell, and a battery. Background Technology

[0004] A rechargeable battery, also known as a secondary battery, is an energy storage device that stores electrical energy in the form of chemical energy and can be charged and discharged multiple times through a reversible electrochemical reaction. Its working principle is based on an electrochemical redox reaction; during charging, electrical energy is converted into chemical energy for storage, and during discharging, the stored chemical energy is converted back into electrical energy for output. A rechargeable battery mainly consists of a positive electrode, a negative electrode, an electrolyte, and a separator. Based on the different electrode materials, it is mainly divided into lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and lithium-ion batteries. Among them, lithium-ion batteries have become the mainstream technology due to their high energy density, long cycle life, and low self-discharge rate. However, in applications, it has been found that as the number of charge-discharge cycles of lithium-ion batteries increases, the probability of lithium plating at the negative electrode also increases. This lithium plating problem leads to a sharp reduction in the cycle performance of lithium-ion batteries and causes problems such as battery swelling and gas buildup, ultimately shortening the battery's lifespan.

[0005] Therefore, existing negative electrode plates still need improvement. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a negative electrode sheet, a wound cell, and a battery. The negative electrode sheet provided by this invention can effectively alleviate lithium plating in the battery and improve the battery's cycle performance.

[0007] Therefore, in a first aspect, the present invention provides a negative electrode sheet, including a corner region and a straight region, wherein the straight region and the corner region are connected; the longitudinal section of the corner region is arc-shaped;

[0008] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on one or both surfaces of the negative electrode current collector;

[0009] The negative electrode film layer includes a negative electrode active material;

[0010] The negative electrode film layer includes a corner region negative electrode film layer and a straight region negative electrode film layer;

[0011] The average particle size of the negative electrode active material in the corner region negative electrode film layer is greater than the average particle size of the negative electrode active material in the straight region negative electrode film layer.

[0012] The average particle size of the negative electrode active material in the flat region negative electrode film layer is ≥1μm.

[0013] The negative electrode sheet of this invention has a larger average particle size of the negative electrode active material in the corner region of the negative electrode film layer than that in the straight region. This differentiated design has the following advantages: During charging and discharging, the larger average particle size of the negative electrode active material in the corner region provides a buffer space for the volume expansion of the negative electrode sheet, effectively reducing mechanical stress and thus reducing the risk of breakage and detachment of the negative electrode active material, improving the cycle stability of the battery. Secondly, in the later stages of battery cycling, the larger average particle size of the negative electrode active material can improve the electrolyte wettability in this area, effectively alleviating the lithium plating problem caused by insufficient electrolyte, further improving the safety and cycle life of the battery. In addition, this structural design can also reduce the risk of internal short circuits caused by volume changes, thereby reducing the probability of cell thermal runaway.

[0014] In some embodiments of the present invention, the negative electrode active material includes one or more of silicon, carbon, tin, and lithium titanate.

[0015] In some embodiments of the present invention, the silicon material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0016] In some embodiments of the present invention, the carbon material includes one or more of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0017] In some embodiments of the present invention, the tin material includes one or more of elemental tin, tin oxide, and tin alloy.

[0018] In some embodiments of the present invention, the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the flat region negative electrode film layer is 0.5-20 μm. In these embodiments, when the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the flat region negative electrode film layer is within the above range, the wetting of the electrode by the electrolyte can be improved, lithium plating can be suppressed, thereby improving the battery to achieve excellent cycle performance.

[0019] In some preferred embodiments of the present invention, the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the straight region negative electrode film layer is 5-15 μm. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0020] In some embodiments of the present invention, the average particle size of the negative electrode active material in the corner region negative electrode film layer is 10.5-30 μm; the average particle size of the negative electrode active material in the flat region negative electrode film layer is 0.5-10 μm. In these embodiments, when the average particle size of the negative electrode active material in the corner region negative electrode film layer is within the above range, and the porosity of the flat region negative electrode film layer is within the above range, the wetting of the electrode by the electrolyte can be improved, lithium plating can be suppressed, thereby improving the battery to achieve excellent cycle performance.

[0021] In some preferred embodiments of the present invention, the average particle size of the negative electrode active material in the corner region negative electrode film layer is 15-25 μm; and the average particle size of the negative electrode active material in the straight region negative electrode film layer is 5-10 μm. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0022] In some embodiments of the present invention, the porosity of the corner region negative electrode film is greater than that of the straight region negative electrode film; the porosity of the straight region negative electrode film is ≥0.1.

[0023] In some embodiments of the present invention, the porosity difference between the corner region negative electrode film layer and the flat region negative electrode film layer is 0.01-0.4. In these embodiments, when the porosity difference between the corner region negative electrode film layer and the flat region negative electrode film layer is within the above range, the bonding between the negative electrode active material and the negative electrode current collector can be improved, and the lithium plating suppression effect can be further enhanced, thereby improving the battery to achieve excellent cycle performance.

[0024] In some preferred embodiments of the present invention, the porosity difference between the corner region negative electrode film layer and the straight region negative electrode film layer is 0.03-0.1. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0025] In some embodiments of the present invention, the porosity of the negative electrode film layer in the flat region is 0.1-0.3; and the porosity of the negative electrode film layer in the corner region is 0.31-0.5. In these embodiments, when the porosity difference of the negative electrode film layer in the corner region is within the above-mentioned range, and the porosity of the negative electrode film layer in the flat region is within the above-mentioned range, the wetting of the electrode by the electrolyte can be improved, lithium plating can be suppressed, thereby improving the battery to achieve excellent cycle performance.

[0026] In some embodiments of the present invention, the thickness of the negative electrode film layer in the flat region is greater than the thickness of the negative electrode film layer in the corner region; the thickness of the negative electrode film layer in the corner region is ≥45μm. In these embodiments, controlling the thickness of the negative electrode film layer in the flat region to be greater than the thickness of the negative electrode film layer in the corner region allows for a negative electrode sheet with a higher porosity in the corner region than in the flat region, thereby improving the cycle performance of the battery.

[0027] In some embodiments of the present invention, the thickness difference between the flat region negative electrode film and the corner region negative electrode film is 1-55 μm. In these embodiments, when the thickness difference between the flat region negative electrode film and the corner region negative electrode film is within the above range, the bonding between the negative electrode active material and the negative electrode current collector can be improved, and the lithium plating suppression effect can be further enhanced, thereby improving the battery to achieve excellent cycle performance.

[0028] In some embodiments of the present invention, the thickness of the negative electrode film in the flat region is 50-100 μm; the thickness of the negative electrode film in the corner region is 45-85 μm. When the thickness of the negative electrode film is within the above range, the battery can have sufficient energy density, while also improving the wettability of the electrolyte on the negative electrode sheet.

[0029] In some embodiments of the present invention, the negative electrode film layer further includes a conductive agent and / or a binder. The conductive agent increases the conductive contact between the active negative electrode materials and improves electronic conductivity. The binder enhances the contact between the active negative electrode materials, the conductive agent, and the negative electrode current collector, and stabilizes the negative electrode structure.

[0030] In some embodiments of the present invention, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (70-99):(0.5-6):(0.5-20). This is beneficial for ensuring the dispersion stability of each component in the negative electrode film.

[0031] A second aspect of the present invention provides a wound battery cell, comprising a battery cell body; the battery cell body includes a negative electrode plate, a positive electrode plate, and a separator disposed between the negative electrode plate and the positive electrode plate; the battery cell body is formed by winding the negative electrode plate, the positive electrode plate, and the separator.

[0032] A third aspect of the present invention provides a battery comprising the aforementioned negative electrode and / or the aforementioned wound cell.

[0033] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0034] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0035] Figure 1 A longitudinal sectional view of a negative electrode sheet according to an embodiment of the present invention is shown;

[0036] Figure 2 A longitudinal sectional view of a wound battery cell according to an embodiment of the present invention is shown.

[0037] Explanation of reference numerals in the attached figures:

[0038] 100 is the negative electrode sheet; 110 is the negative electrode current collector; 121 is the negative electrode film layer in the corner region; 122 is the negative electrode film layer in the straight region; 200 is the wound cell; 210 is the cell in the corner region; 220 is the cell in the straight region. Detailed Implementation

[0039] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0040] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] During the later stages of battery cycling, wound cells expand, but due to the rigidity of the steel casing, the expansion at the cell corners is subject to the greatest constraint. This uneven distribution of mechanical stress leads to two main problems: First, the corner areas are prone to lithium plating due to stress concentration, directly affecting the battery's cycle life; second, as the number of cycles increases, the expansion force caused by lithium plating continues to accumulate, and the confined space cannot effectively release these stresses, potentially leading to electrode breakage. This mechanical failure can further cause internal short circuits within the cell, increasing the risk of thermal runaway.

[0042] The first aspect of the present invention provides a negative electrode sheet, including a corner region and a straight region, wherein the straight region and the corner region are connected; the longitudinal section of the corner region is arc-shaped;

[0043] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on one or both surfaces of the negative electrode current collector;

[0044] The negative electrode film layer includes a negative electrode active material;

[0045] The negative electrode film layer includes a corner region negative electrode film layer and a straight region negative electrode film layer;

[0046] The average particle size of the negative electrode active material in the corner region negative electrode film layer is greater than the average particle size of the negative electrode active material in the straight region negative electrode film layer.

[0047] The average particle size of the negative electrode active material in the flat region negative electrode film layer is ≥1μm.

[0048] The negative electrode sheet of this invention has a larger average particle size of the negative electrode active material in the corner region of the negative electrode film layer than that in the straight region. This differentiated design has the following advantages: During charging and discharging, the larger average particle size of the negative electrode active material in the corner region provides a buffer space for the volume expansion of the negative electrode sheet, effectively reducing mechanical stress and thus reducing the risk of breakage and detachment of the negative electrode active material, improving the cycle stability of the battery. Secondly, in the later stages of battery cycling, the larger average particle size of the negative electrode active material can improve the electrolyte wettability in this area, effectively alleviating the lithium plating problem caused by insufficient electrolyte, further improving the safety and cycle life of the battery. In addition, this structural design can also reduce the risk of internal short circuits caused by volume changes, thereby reducing the probability of cell thermal runaway.

[0049] In some embodiments of the present invention, such as Figure 1 As shown, the negative electrode 100 of the present invention includes a negative electrode current collector 110, and a corner region negative electrode film layer 121 and a straight region negative electrode film layer 122 located on one side of the negative electrode current collector. The negative electrode of the present invention can form a wound battery cell. A wound battery cell is a cylindrical or flat battery cell formed by winding a positive electrode, a negative electrode, and a separator material in a certain order.

[0050] In some embodiments of the present invention, the negative electrode active material of the present invention may be a negative electrode active material known in the art for use in batteries, for example, the negative electrode active material includes one or more of silicon material, carbon material, tin material, and lithium titanate; the silicon material includes one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy; the carbon material includes one or more of artificial graphite, natural graphite, hard carbon, and soft carbon; the tin material includes one or more of elemental tin, tin oxide compound, and tin alloy.

[0051] In some embodiments of the present invention, the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the flat region negative electrode film layer is 0.5-20 μm. As an example, the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the flat region negative electrode film layer can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 μm. In these embodiments, when the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the flat region negative electrode film layer is within the above range, the wetting of the electrode by the electrolyte can be improved, lithium plating can be suppressed, thereby improving the battery's excellent cycle performance.

[0052] In some preferred embodiments of the present invention, the difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the straight region negative electrode film layer is 5-15 μm. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0053] In some embodiments of the present invention, the average particle size of the negative electrode active material in the corner region negative electrode film layer is 10.5-30 μm; the average particle size of the negative electrode active material in the flat region negative electrode film layer is 0.5-10 μm. As an example, the average particle size of the negative electrode active material in the corner region negative electrode film layer can be 10.5, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 μm. As an example, the average particle size of the negative electrode active material in the flat region negative electrode film layer can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 μm. In these embodiments, when the average particle size of the negative electrode active material in the corner region negative electrode film layer is within the above range, and the porosity of the straight region negative electrode film layer is within the above range, the wetting of the electrode by the electrolyte can be improved, lithium plating can be suppressed, thereby improving the battery to achieve excellent cycle performance.

[0054] In some preferred embodiments of the present invention, the average particle size of the negative electrode active material in the corner region negative electrode film layer is 15-25 μm; and the average particle size of the negative electrode active material in the straight region negative electrode film layer is 5-10 μm. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0055] In some embodiments of the present invention, the porosity of the corner region negative electrode film is greater than that of the straight region negative electrode film; the porosity of the straight region negative electrode film is ≥0.1.

[0056] In some embodiments of the present invention, the porosity difference between the corner region negative electrode film layer and the straight region negative electrode film layer is 0.01-0.4. As an example, the porosity difference between the corner region negative electrode film layer and the straight region negative electrode film layer can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.32, 0.35, 0.38, or 0.4. In these embodiments, when the porosity difference between the corner region negative electrode film layer and the straight region negative electrode film layer is within the above-mentioned range, the bonding between the negative electrode active material and the negative electrode current collector can be improved, and the lithium plating suppression effect can be further enhanced, thereby improving the battery to achieve excellent cycle performance.

[0057] In some preferred embodiments of the present invention, the porosity difference between the corner region negative electrode film layer and the straight region negative electrode film layer is 0.03-0.1. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0058] In some embodiments of the present invention, the porosity of the flat region negative electrode film layer is 0.1-0.3; the porosity of the corner region negative electrode film layer is 0.31-0.5. As an example, the porosity of the flat region negative electrode film layer can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or 0.3. As an example, the porosity of the negative electrode film layer in the corner region can be 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, or 0.5. In these embodiments, when the porosity difference of the negative electrode film layer in the corner region is within the above-mentioned range, and the porosity of the negative electrode film layer in the straight region is within the above-mentioned range, the wetting of the electrode by the electrolyte can be improved, lithium plating can be suppressed, thereby improving the battery to achieve excellent cycle performance.

[0059] In some embodiments of the present invention, the thickness of the negative electrode film layer in the flat region is greater than the thickness of the negative electrode film layer in the corner region; the thickness of the negative electrode film layer in the corner region is ≥45μm. In these embodiments, controlling the thickness of the negative electrode film layer in the flat region to be greater than the thickness of the negative electrode film layer in the corner region allows for a negative electrode sheet with a higher porosity in the corner region than in the flat region, thereby improving the cycle performance of the battery.

[0060] In some embodiments of the present invention, the thickness difference between the flat region negative electrode film layer and the corner region negative electrode film layer is 1-55 μm. As an example, the thickness difference between the flat region negative electrode film layer and the corner region negative electrode film layer can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, or 55 μm. In these embodiments, when the thickness difference between the negative electrode film layer in the flat region and the negative electrode film layer in the corner region is within the above range, the bonding between the negative electrode active material and the negative electrode current collector can be improved, and the lithium plating suppression effect can be further enhanced, thereby improving the battery to achieve excellent cycle performance.

[0061] In some embodiments of the present invention, the thickness of the negative electrode film layer in the flat region is 50-100 μm; the thickness of the negative electrode film layer in the corner region is 45-85 μm. As an example, the thickness of the negative electrode film layer in the flat region can be 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 μm. As an example, the thickness of the negative electrode film in the corner region can be 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, or 85 μm. When the thickness of the negative electrode film is within the above range, the battery can have sufficient energy density, while also improving the wettability of the electrolyte on the negative electrode sheet.

[0062] In some embodiments of the present invention, such as Figure 1As shown, the thickness of the negative electrode film in the corner region is the same as the thickness of the negative electrode film 121 in the corner region; the thickness of the negative electrode film in the straight region is the same as the thickness of the negative electrode film 122 in the straight region.

[0063] In some embodiments of the present invention, the negative electrode film layer further includes a negative electrode conductive agent and / or a negative electrode binder. Further, the negative electrode conductive agent may include one or more of acetylene black, Ketjen black, conductive carbon black material Super P, conductive carbon black material SuperS, graphene, carbon nanotubes, carbon fibers, and activated carbon; the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0064] In some embodiments of the present invention, the negative electrode film layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0065] In some embodiments of the present invention, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (70-99):(0.5-6):(0.5-20). This is beneficial for ensuring the dispersion stability of each component in the negative electrode film.

[0066] In some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0067] In some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent to form a negative electrode slurry; coating the negative electrode slurry on one or both surfaces of the negative electrode current collector, drying and pressing to obtain the negative electrode sheet.

[0068] In some embodiments of the present invention, the coating may be performed using any one of extrusion coating, transfer coating, or roller coating.

[0069] In some embodiments of the present invention, the first coating specifically includes: performing a first coating on the surface of the negative electrode current collector used to form the straight region or the corner region; the second coating specifically includes: performing a second coating on the surface of the negative electrode current collector used to form the other of the straight region or the corner region; controlling the average particle size of the negative electrode active material in the slurry used to form the corner region to be greater than the average particle size of the negative electrode active material in the slurry used to form the straight region; further, the average particle size of the negative electrode active material in the slurry used to form the straight region is 0.5-10 μm; the average particle size of the negative electrode active material in the slurry used to form the corner region is 10.5-30 μm.

[0070] A second aspect of the present invention provides a wound battery cell, comprising a battery cell body; the battery cell body includes a negative electrode plate, a positive electrode plate, and a separator disposed between the negative electrode plate and the positive electrode plate; the battery cell body is formed by winding the negative electrode plate, the positive electrode plate, and the separator.

[0071] In some embodiments of the present invention, such as Figure 2 As shown, the wound battery cell 200 of the present invention includes a corner area battery cell 210 and a straight area battery cell 220.

[0072] In some embodiments of the present invention, the positive electrode includes a flat region and a corner region; the corner region is arc-shaped.

[0073] In some embodiments of the present invention, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on one or both surfaces of the positive current collector.

[0074] In some embodiments of the present invention, the positive electrode film layer comprises a positive electrode active material.

[0075] In some embodiments of the present invention, when the battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. For example, the positive electrode active material may include one or more of the following: olivine-structured lithium-containing phosphates or their modified compounds, lithium transition metal oxides or their modified compounds; examples of olivine-structured lithium-containing phosphates include one or more of the following: lithium iron phosphate (such as LiFePO4), lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites.

[0076] In some embodiments of the present invention, the content of the positive electrode active material is 90%-99% based on the mass of the positive electrode film. This is beneficial for improving the conductivity of the positive electrode sheet while maintaining the stability of the positive electrode film.

[0077] In some embodiments of the present invention, the positive electrode film layer further includes a positive electrode conductive agent; the positive electrode conductive agent includes, but is not limited to, one or more of the following: conductive carbon black material Super P, conductive carbon black material Super S, graphene, acetylene black, carbon fiber, Ketjen black, C60, and carbon nanotubes. Further, the content of the positive electrode conductive agent in the positive electrode film layer can be 1wt%-5wt%.

[0078] In some embodiments of the present invention, the positive electrode film layer further includes a positive electrode binder; the positive electrode binder includes, but is not limited to, one or more of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, carboxymethyl chitosan, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polymethacrylic acid, polyacrylamide, polyurethane, polyvinyl alcohol, polyvinyl butyral, and sodium alginate. Further, the content of the positive electrode binder in the positive electrode film layer can be 2wt%-4wt%.

[0079] In some embodiments of the present invention, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (90-99):(0.5-5):(0.5-5). This is beneficial for ensuring the dispersion stability of each component in the positive electrode film.

[0080] In some embodiments of the present invention, the thickness of the positive electrode film is 100-150 μm and the porosity is 0.2-0.3.

[0081] In some embodiments of the present invention, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0082] In some embodiments of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0083] In some embodiments of the present invention, the present invention does not have any particular limitation on the type of diaphragm, and any known diaphragm with good chemical and mechanical stability can be selected.

[0084] In some embodiments of the present invention, the material of the separator can be common battery separators such as aqueous separators, macroporous oil separators, and gravure oil separators; specifically, it includes one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation.

[0085] In some embodiments of the present invention, when the diaphragm is a multilayer composite film, the materials of each layer can be the same or different, without particular limitation.

[0086] In some embodiments of the present invention, the diaphragm may include a diaphragm substrate, a ceramic coating disposed on at least one side of the diaphragm substrate, and a polymer adhesive coating disposed on at least one side of the ceramic coating away from the diaphragm substrate. The present invention does not limit the thickness of the diaphragm, as long as the purpose of the present invention can be achieved. For example, the thickness of the diaphragm may be 5μm-54μm. The present invention also does not limit the thickness of the diaphragm substrate, the ceramic coating, and the polymer adhesive coating, as long as the purpose of this application can be achieved. For example, the thickness of the diaphragm substrate may be 5μm-50μm, the thickness of the ceramic coating may be 3μm, and the thickness of the polymer adhesive coating may be 1μm.

[0087] A third aspect of the present invention provides a battery comprising the aforementioned negative electrode and / or the aforementioned wound cell.

[0088] The battery of the present invention may be in the form of a battery cell, a battery module, or a battery pack. In some embodiments, battery cells may be assembled into a battery module, and the number of battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, and the number of battery modules contained in a battery pack may be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0089] In some embodiments of the present invention, the battery further includes an electrolyte. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The present invention does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be liquid, gel, or all-solid.

[0090] In some embodiments of the present invention, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0091] In some embodiments of the present invention, the electrolyte salt may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0092] In some embodiments of the present invention, the solvent may include one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0093] In some embodiments of the present invention, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0094] The battery of the present invention may be in the form of a battery cell, a battery module, or a battery pack. In some embodiments, battery cells may be assembled into a battery module, and the number of battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, and the number of battery modules contained in a battery pack may be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0095] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0096] Example 1

[0097] The lithium-ion battery of this embodiment is prepared by the following steps:

[0098] (1) Preparation of negative electrode sheet

[0099] A. Preparation of the first slurry: 97 wt% graphite, 1.5 wt% binder, 0.5 wt% carbon nanotubes (CNTs) and 1.0 wt% conductive carbon black (Super P) are mixed in deionized water to obtain the first slurry; wherein the average particle size of the graphite is 15 μm, and the binder is a mixture of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) in a mass ratio of 3:2.

[0100] B. Preparation of the second slurry: 97 wt% graphite, 1.5 wt% binder, 0.5 wt% carbon nanotubes (CNTs) and 1.0 wt% conductive carbon black (Super P) are mixed in deionized water to obtain the second slurry; wherein the average particle size of the graphite is 10 μm, and the binder is a mixture of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) in a mass ratio of 3:2.

[0101] C. The first slurry is coated on both sides of the copper foil, with a thickness of 85μm on one side, forming the corner area of ​​the wound cell. According to the cell model, a blank foil is left in the middle for secondary coating. The blank foil is used to form the straight area of ​​the wound cell. The second slurry is coated on both sides of the copper foil for secondary coating, with a thickness of 85μm on one side. The electrode is baked at 80℃. After baking, the electrode is rolled at a pressure of 100t. After slitting, the negative electrode is obtained. The negative electrode includes an aluminum foil current collector and a negative electrode film layer on the aluminum foil current collector. The porosity of the negative electrode film layer in the corner area is 0.35 and the thickness is 70μm (single layer thickness). The porosity of the negative electrode film layer in the straight area is 0.28 and the thickness is 70μm (single layer thickness).

[0102] (2) Preparation of positive electrode sheet

[0103] 96.9 wt% lithium iron phosphate, 0.5 wt% carbon nanotubes (CNTs), 0.6 wt% conductive carbon black (SuperP), and 2.0 wt% polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) and stirred until homogeneous to obtain a positive electrode active slurry. The positive electrode active slurry was coated on both sides of an aluminum foil, dried, rolled, and slit to obtain a positive electrode sheet. In the positive electrode sheet, the thickness of the positive electrode film layer was 83 μm (single layer thickness), and the porosity was 0.25.

[0104] (3) Preparation of lithium-ion batteries

[0105] Electrolyte: A mixed solution of LiPF6 and solvent, with a lithium salt to solvent mass ratio of 13:87; the solvent is composed of ethylene carbonate, propylene carbonate, propyl propionate and ethyl propionate, with a mass ratio of ethylene carbonate, propylene carbonate, propyl propionate and ethyl propionate of 10:15:65:10.

[0106] Separator: Using 20μm thick ultra-high molecular weight polyethylene (PE) as a bare mold, a 3μm thick alumina ceramic coating is coated on both sides of the bare mold, and then a 1μm thick polymer adhesive coating is coated on the surface of the ceramic coating to obtain the separator. The polymer is polyvinylidene fluoride (PVDF).

[0107] The negative electrode, separator, and positive electrode are stacked in sequence and wound to obtain a wound cell. The stacked cell is placed in an aluminum shell outer packaging, electrolyte is injected into the aluminum shell outer packaging, and the lithium-ion battery is obtained through vacuum sealing, standing, formation and other processes.

[0108] Example 2

[0109] The lithium-ion battery in this embodiment differs from that in Example 1 only in that the average particle size of the graphite in the first slurry in this embodiment is 20 μm; the remaining steps are performed in accordance with the method in Example 1.

[0110] Example 3

[0111] The lithium-ion battery in this embodiment differs from that in Example 1 only in that the average particle size of the graphite in the first slurry in this embodiment is 25 μm; the remaining steps are performed in accordance with the method in Example 1.

[0112] Comparative Example 1

[0113] The lithium-ion battery in this comparative example differs from that in Example 1 only in that the average particle size of graphite in the first and second slurries of this comparative example is the same, which is 10 μm; the remaining steps are performed in accordance with the method in Example 1.

[0114] Comparative Example 2

[0115] The only difference between the lithium-ion battery in this comparative example and Example 1 is that the average particle size of graphite in the first slurry of this comparative example is 45 μm, and the average particle size of graphite in the second slurry is 15 μm; the remaining steps are performed in accordance with the method in Example 1.

[0116] Comparative Example 3

[0117] The only difference between this comparative example of lithium-ion battery and Example 1 is that the average particle size of graphite in the first slurry of this comparative example is 10 μm, and the average particle size of graphite in the second slurry is 9.8 μm; the remaining steps are performed in accordance with the method in Example 1.

[0118] Test case

[0119] The batteries of Examples 1-3 and Comparative Examples 1-3 were tested as follows: At room temperature (25°C), the batteries were charged at a constant power of 0.5P until the cutoff voltage reached 3.65V. The number of cycle times at 80% SOH was recorded. Simultaneously, the degree of lithium plating in the lithium-ion batteries was determined according to the following criteria:

[0120] No lithium deposition: No lithium is deposited on the surface of the negative electrode;

[0121] Slight lithium plating: The lithium deposition area on the surface of the negative electrode is less than 10%;

[0122] Moderate lithium deposition: The lithium deposition area on the surface of the negative electrode is 10% to 30%;

[0123] Severe lithium plating: The lithium deposition area on the surface of the negative electrode is greater than 30%.

[0124] The test results are shown in Table 1.

[0125] Table 1

[0126] Group Lithium plating degree Number of cycles (80% SOH) Example 1 Slight lithium plating 2980 Example 2 Non-lithium plating 4566 Example 3 Non-lithium plating 5020 Comparative Example 1 Severe lithium plating 2040 Comparative Example 2 Severe lithium plating 2100 Comparative Example 3 Severe lithium plating 1668

[0127] As shown in Table 1, compared with Comparative Examples 1-3, the lithium-ion batteries provided in Examples 1-3 of the present invention have a lower tendency for lithium plating and a higher number of cycles. This indicates that there is a certain difference in the average particle size of the negative electrode active material in the corner region negative electrode film layer and the straight region negative electrode film layer, which can effectively improve the lithium plating and electrochemical performance of the battery.

[0128] Furthermore, as can be seen from Examples 1-3, in the negative electrode sheet, as the average particle size of graphite in the corner region of the negative electrode film increases, the lithium plating problem is improved, and the battery cycle count increases accordingly. This indicates that, within a certain range, increasing the average particle size of graphite in the corner region of the negative electrode sheet can further improve the lithium plating and electrochemical performance of the battery.

[0129] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "some implementations," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0130] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a corner area and a straight area, wherein the straight area and the corner area are connected; the longitudinal section of the corner area is arc-shaped. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on one or both surfaces of the negative electrode current collector; The negative electrode film layer includes a negative electrode active material; The negative electrode film layer includes a corner region negative electrode film layer and a straight region negative electrode film layer; The average particle size of the negative electrode active material in the corner region negative electrode film layer is greater than the average particle size of the negative electrode active material in the straight region negative electrode film layer. The average particle size of the negative electrode active material in the flat region negative electrode film layer is ≥1μm.

2. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material includes one or more of silicon, carbon, tin, and lithium titanate. The silicon material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; The carbon material includes one or more of artificial graphite, natural graphite, hard carbon, and soft carbon; The tin material includes one or more of elemental tin, tin oxides, and tin alloys.

3. The negative electrode sheet according to claim 1, characterized in that, The difference between the average particle size of the negative electrode active material in the corner region negative electrode film layer and the average particle size of the negative electrode active material in the straight region negative electrode film layer is 0.5-20 μm.

4. The negative electrode sheet according to claim 1, characterized in that, The average particle size of the negative electrode active material in the negative electrode film layer in the corner region is 10.5-30 μm; and / or, The average particle size of the negative electrode active material in the flat region negative electrode film layer is 0.5-10 μm.

5. The negative electrode sheet according to claim 4, characterized in that, The average particle size of the negative electrode active material in the negative electrode film layer in the corner region is 15-25 μm; and / or, The average particle size of the negative electrode active material in the flat region negative electrode film layer is 5-10 μm.

6. The negative electrode sheet according to claim 1, characterized in that, The porosity of the negative electrode film in the corner region is greater than that in the negative electrode film in the straight region; the porosity of the negative electrode film in the straight region is ≥0.

1. The porosity difference between the negative electrode film layer in the corner region and the negative electrode film layer in the straight region is 0.01-0.

4. The porosity of the negative electrode film in the straight region is 0.1-0.3; the porosity of the negative electrode film in the corner region is 0.31-0.

5.

7. The negative electrode sheet according to claim 1, characterized in that, The thickness of the negative electrode film in the straight region is greater than the thickness of the negative electrode film in the corner region; the thickness of the negative electrode film in the corner region is ≥45μm; The thickness difference between the straight region negative electrode film layer and the corner region negative electrode film layer is 1-55 μm; The thickness of the negative electrode film in the straight region is 50-100 μm; the thickness of the negative electrode film in the corner region is 45-85 μm.

8. The negative electrode sheet according to claim 1, characterized in that, The negative electrode film layer also includes a conductive agent and / or a binder; The mass ratio of the negative electrode active material, the conductive agent, and the binder is (70-99):(0.5-6):(0.5-20).

9. A wound battery cell, characterized in that, The battery cell body includes a negative electrode sheet, a positive electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet as described in any one of claims 1-8; the battery cell body is formed by winding the negative electrode sheet, the positive electrode sheet, and the separator.

10. A battery, characterized in that, It includes the negative electrode sheet as described in any one of claims 1-8 and / or the wound cell as described in claim 9.

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