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

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode sheet, a wound cell and a battery. The negative electrode sheet comprises a corner area and a flat area, the flat area is connected with the corner area, the longitudinal section of the corner area is arc-shaped, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on one side or both sides of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode film layer comprises a corner area negative electrode film layer and a flat area negative electrode film layer, the porosity of the flat area negative electrode film layer is 0.1-0.3, and the porosity of the corner area negative electrode film layer is 0.33-0.5. The negative electrode sheet adopts the corner area negative electrode film layer and the flat area negative electrode film layer with specific porosities, the negative electrode sheet can be safely expanded in the charging and discharging process, the mechanical stress caused by volume change is reduced, the rupture or shedding of the negative electrode active material is improved, and the cycle performance of the battery is improved.

Description

[0001] Cross-references to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 2025103391683, 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 secondary battery (also known as a rechargeable battery) is a type of battery that can be repeatedly charged and discharged using an external current. Unlike primary batteries (i.e., non-rechargeable batteries), secondary batteries can recover their chemical energy during charging, thus allowing for repeated use in multiple cycles. In recent years, with the increasingly wide range of applications, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. During the charging process, lithium plating is prone to occur at the negative electrode of a secondary battery, which can lead to internal short circuits and thermal runaway, seriously affecting the battery's lifespan and safety performance.

[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, a wound cell, and a battery. The improved negative electrode of this invention can effectively alleviate lithium plating in the battery and improve its cycle performance.

[0007] Therefore, in a first aspect, the present invention provides a negative electrode sheet, comprising a corner region and a straight region; 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 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 0.33-0.5.

[0012] The negative electrode of this invention employs a corner region negative electrode film layer and a straight region negative electrode film layer with specific porosities. The porosity of the straight region negative electrode film layer is 0.1-0.3, and the porosity of the corner region negative electrode film layer is 0.33-0.5. This allows the negative electrode to expand safely during charging and discharging, reducing mechanical stress caused by volume changes, thereby improving the cracking or shedding of the negative electrode active material, thus enhancing the cycle performance of the battery and reducing the probability of cell thermal runaway caused by short circuits within the cell. Furthermore, in the later stages of battery cycling, the porosity of the corner region negative electrode film layer is greater than that of the straight region negative electrode film layer, which can improve the lithium plating problem caused by the lack of electrolyte in the corner region of the electrode, thereby improving the cycle performance of the battery.

[0013] In some embodiments of the present invention, the porosity of the negative electrode film layer in the flat region is 0.2-0.3; and the porosity of the negative electrode film layer in the corner region is 0.33-0.4. In these embodiments, when the porosity 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 further improved, lithium plating can be suppressed, thereby improving the battery to achieve excellent cycle performance.

[0014] In some embodiments of the present invention, the porosity of the negative electrode film layer in the flat region is 0.25-0.3; and the porosity of the negative electrode film layer in the corner region is 0.33-0.36. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0015] In some embodiments of the present invention, the compaction density of the negative electrode film layer in the flat region is greater than the compaction density of the negative electrode film layer in the corner region; the compaction density of the negative electrode film layer in the corner region is ≥0.01 g / cm³. 3 The compaction density and the porosity of the negative electrode are usually negatively correlated. When the compaction density of the negative electrode film in the straight region is greater than that in the corner region, the porosity of the negative electrode film in the corner region is greater than that in the straight region, thereby improving the cycle performance of the battery.

[0016] In some embodiments of the present invention, the compaction density difference between the flat region negative electrode film layer and the corner region negative electrode film layer is 0.01-0.7 g / cm³. 3 In these embodiments, when the difference in compaction density between the negative electrode film layer in the flat region and the negative electrode film layer in the corner region 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.

[0017] In some embodiments of the present invention, the compaction density of the flat region negative electrode film layer is 1.53-1.8 g / cm³. 3The compaction density of the negative electrode film layer in the corner region is 1.1-1.52 g / cm³. 3 In these embodiments, the compaction density of the negative electrode film in the flat region and the compaction density of the negative electrode film in the corner region are within the above-mentioned range, which can improve the liquid retention capacity of the negative electrode sheet and reduce the large degradation that occurs in the battery during cycling.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] A third aspect of the present invention provides a battery comprising the aforementioned negative electrode and / or the aforementioned wound cell.

[0025] 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

[0026] 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:

[0027] Figure 1 A longitudinal sectional view of a negative electrode sheet according to an embodiment of the present invention is shown;

[0028] Figure 2 A longitudinal sectional view of a wound battery cell according to an embodiment of the present invention is shown.

[0029] Explanation of reference numerals in the attached figures:

[0030] 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

[0031] 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.

[0032] 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.

[0033] This invention is based on the following problems and findings: During the later stages of battery cycling, wound cells expand. Due to the rigidity of the battery's steel casing, the corners of the expanded wound cells experience the greatest constraint, resulting in compression and lithium plating at these corners, thus affecting the battery's cycle life. Furthermore, in the later stages of cell cycling, lithium plating causes the cell's expansion force to continuously increase, and the lack of space to release this force leads to increasing stress on the electrodes, eventually causing electrode breakage, which in turn triggers an internal short circuit and thermal runaway.

[0034] In view of this, 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;

[0035] 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;

[0036] The negative electrode film layer includes a negative electrode active material;

[0037] The negative electrode film layer includes a corner region negative electrode film layer and a straight region negative electrode film layer;

[0038] 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 0.33-0.5.

[0039] The negative electrode of this invention employs a corner region negative electrode film layer and a straight region negative electrode film layer with specific porosities. The porosity of the straight region negative electrode film layer is 0.1-0.3, and the porosity of the corner region negative electrode film layer is 0.33-0.5. This allows the negative electrode to expand safely during charging and discharging, reducing mechanical stress caused by volume changes, thereby improving the cracking or shedding of the negative electrode active material, thus enhancing the cycle performance of the battery and reducing the probability of cell thermal runaway caused by short circuits within the cell. Furthermore, in the later stages of battery cycling, the porosity of the corner region negative electrode film layer is greater than that of the straight region negative electrode film layer, which can improve the lithium plating problem caused by the lack of electrolyte in the corner region of the electrode, thereby improving the cycle performance of the battery.

[0040] 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.

[0041] In some embodiments of the present invention, as an example, the porosity of the negative electrode film layer in the flat region 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 0.33, 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.

[0042] In some embodiments of the present invention, the porosity of the negative electrode film layer in the flat region is 0.2-0.3; and the porosity of the negative electrode film layer in the corner region is 0.33-0.4. In these embodiments, when the porosity 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.

[0043] In some embodiments of the present invention, the porosity of the negative electrode film layer in the flat region is 0.25-0.3; and the porosity of the negative electrode film layer in the corner region is 0.33-0.36. This further enhances the suppression of lithium plating and improves the battery's excellent cycle performance.

[0044] In some embodiments of the present invention, the compaction density of the negative electrode film layer in the flat region is greater than the compaction density of the negative electrode film layer in the corner region; the compaction density of the negative electrode film layer in the corner region is ≥0.01 g / cm³. 3 The compaction density and the porosity of the negative electrode are usually negatively correlated. When the compaction density of the negative electrode film in the straight region is greater than that in the corner region, it is equivalent to the porosity of the negative electrode film in the corner region being greater than that in the straight region, thereby improving the cycle performance of the battery.

[0045] In some embodiments of the present invention, the compaction density difference between the flat region negative electrode film layer and the corner region negative electrode film layer is 0.01-0.7 g / cm³. 3 As an example, the compaction density difference between the negative electrode film layer in the flat region and the negative electrode film layer in the corner region can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7 g / cm³. 3 In these embodiments, when the difference in compaction density between the negative electrode film layer in the flat region and the negative electrode film layer in the corner region 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.

[0046] In some embodiments of the present invention, the compaction density of the flat region negative electrode film layer is 1.53-1.8 g / cm³. 3 The compaction density of the negative electrode film layer in the corner region is 1.1-1.52 g / cm³. 3 As an example, the compaction density of the negative electrode film layer in the flat region can be 1.53, 1.54, 1.55, 1.6, 1.65, 1.7, 1.75, or 1.8 g / cm³. 3As an example, the compaction density of the negative electrode film layer in the corner region can be 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.49, 1.5, 1.51, or 1.52 g / cm³. 3 In these embodiments, the compaction density of the negative electrode film in the flat region and the compaction density of the negative electrode film in the corner region are within the above-mentioned range, which can improve the liquid retention capacity of the negative electrode sheet and reduce the large degradation that occurs in the battery during cycling.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] In some embodiments of the present invention, such as Figure 1 As 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.

[0051] 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 may include one or more of silicon materials, carbon materials, tin materials, and lithium titanate; silicon materials include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; carbon materials include one or more of artificial graphite, natural graphite, hard carbon, and soft carbon; and tin materials include one or more of elemental tin, tin oxide compounds, and tin alloys.

[0052] In some embodiments of the present invention, the negative electrode film layer further includes a conductive agent and / or a binder. Further, the conductive agent includes, but is not limited to, one or more of conductive graphite, conductive carbon black (such as acetylene black, Ketjen black, etc.), conductive carbon fiber (such as vapor-grown carbon fiber, carbon nanotubes), and graphene; the 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. The conductive agent increases the conductive contact between the negative electrode active materials and improves the electronic conductivity. The binder enhances the contact between the negative electrode active materials, the conductive agent, and the negative electrode current collector, and stabilizes the negative electrode structure.

[0053] 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.

[0054] In some embodiments of the present invention, the negative electrode current collector includes one or more of the following: metal foil (such as aluminum foil, silver foil, tin foil, iron foil, titanium foil, nickel foil, copper foil, or alloy foil of the above metals), metal mesh (such as aluminum mesh, silver mesh, tin mesh, iron mesh, titanium mesh, nickel mesh, copper mesh, or alloy mesh of the above metals), and composite current collector; the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on the surface of a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE)). The negative electrode current collector can serve as a supporting substrate for the negative electrode film layer, providing a current conduction path.

[0055] 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 (e.g., deionized water) 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.

[0056] In some embodiments of the present invention, the coating may be performed using any one of extrusion coating, transfer coating, or roller coating.

[0057] In some embodiments of the present invention, a negative electrode slurry is coated twice on the surface of the negative electrode current collector. Further, the first coating specifically includes: performing a first coating on the surface of the negative electrode current collector; the second coating specifically includes: performing a second coating on the surface of the negative electrode current collector used to form the flat region; the thickness of the first coating is 30-130 μm; the thickness of the second coating is 10-30 μm.

[0058] In some other 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 coating thickness used to form the straight region to be greater than the coating thickness used to form the corner region; further, the coating thickness used to form the straight region is 40-160 μm; the coating thickness used to form the corner region is 30-130 μm.

[0059] 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.

[0060] 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.

[0061] In some embodiments of the present invention, the positive electrode includes a flat region and a corner region; the corner region is arc-shaped.

[0062] 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.

[0063] In some embodiments of the present invention, the positive electrode film layer comprises a positive electrode active material.

[0064] 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 phosphates or their modified compounds, lithium transition metal oxides or their modified compounds; examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0065] 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.

[0066] In some embodiments of the present invention, the positive electrode film layer further includes a conductive agent; the conductive agent includes, but is not limited to, one or more of conductive graphite, conductive carbon black (such as acetylene black, Ketjen black, etc.), conductive carbon fiber (such as vapor-grown carbon fiber, carbon nanotubes) and graphene.

[0067] In some embodiments of the present invention, the positive electrode film layer further includes an adhesive; the adhesive 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.

[0068] In some embodiments of the present invention, the mass ratio of the positive electrode active material, the conductive agent, and the 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.

[0069] In some embodiments of the present invention, the thickness of the positive electrode film is 100-150 μm, the porosity is 0.2-0.3, and the compaction density is 2-3 g / cm³. 3 .

[0070] In some embodiments of the present invention, the positive electrode current collector includes one or more of the following: metal foil (such as aluminum foil, silver foil, tin foil, iron foil, titanium foil, nickel foil, copper foil, or alloy foil of the above metals), metal mesh (such as aluminum mesh, silver mesh, tin mesh, iron mesh, titanium mesh, nickel mesh, copper mesh, or alloy mesh of the above metals), and composite current collector; the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on the surface of a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE)). The positive electrode current collector can serve as a supporting substrate for the positive electrode film layer, providing a current conduction path.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] A third aspect of the present invention provides a battery comprising the aforementioned negative electrode and / or the aforementioned wound cell.

[0077] 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.

[0078] In some embodiments of the present invention, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Example 1

[0084] The lithium-ion battery of this embodiment is prepared by the following steps:

[0085] (1) Preparation of negative electrode sheet

[0086] A. 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 a negative electrode active slurry; wherein the average particle size of graphite is 11 μm, and the binder is a mixture of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) in a mass ratio of 3:2.

[0087] B. The negative electrode active slurry is coated on both sides of the copper foil, with a single-sided coating thickness of 85μm. A blank foil is left in the middle for secondary coating, depending on the cell model. This blank foil forms the flat area of ​​the wound cell, with a secondary single-sided coating thickness of 92μm. The electrode is then baked at 80℃. After baking, the electrode sheet undergoes a rolling process at a pressure of 100t. Following a slitting process, the negative electrode sheet is obtained. The negative electrode sheet comprises an aluminum foil current collector and a negative electrode film layer on top of the aluminum foil current collector. In the negative electrode sheet, the thickness of the negative electrode film layer in the corner area is 70μm (single-layer thickness), with a porosity of 0.33 and a compaction density of 1.48g / cm³. 3 The thickness of the negative electrode active material layer in the flat region of the negative electrode sheet is 70 μm (single layer thickness), the porosity is 0.3, and the compaction density is 1.53 g / cm³. 3 .

[0088] (2) Preparation of positive electrode sheet

[0089] 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. This slurry was then coated onto both sides of an aluminum foil, dried, rolled, and slit to obtain the positive electrode sheet. The positive electrode sheet had a film thickness of 83 μm (single-layer thickness), a porosity of 0.25, and a compaction density of 2.6 g / cm³. 3 .

[0090] (3) Preparation of lithium-ion batteries

[0091] 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.

[0092] 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).

[0093] 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.

[0094] Example 2

[0095] The lithium-ion battery in this embodiment differs from that in Embodiment 1 only in that the coating thickness of the negative electrode active material layer in the corner region of the negative electrode sheet prepared in this embodiment is 79 μm, the porosity of the negative electrode active material layer in the corner region of the prepared negative electrode sheet is 0.34, and the compaction density is 1.45 g / cm³. 3 The thickness is 70 μm (single layer thickness); the remaining steps are performed according to the method in Example 1.

[0096] Example 3

[0097] The lithium-ion battery in this embodiment differs from that in Embodiment 1 only in that the coating thickness of the negative electrode active material layer in the corner region of the negative electrode sheet prepared in this embodiment is 72 μm, the porosity of the negative electrode active material layer in the corner region of the prepared negative electrode sheet is 0.36, and the compaction density is 1.44 g / cm³. 3 The thickness is 70 μm (single layer thickness); the remaining steps are performed according to the method in Example 1.

[0098] Comparative Example 1

[0099] The lithium-ion battery in this comparative example differs from that in Example 1 only in that, in the preparation of the negative electrode sheet, the coating thickness of the negative electrode active slurry on both the corner and straight regions is 92 μm. The resulting negative electrode sheet has a porosity of 0.3 in both the corner and straight regions and a compaction density of 1.53 g / cm³. 3 The thickness is 70μm (single layer thickness).

[0100] The remaining steps are performed in accordance with the method in Example 1.

[0101] Comparative Example 2

[0102] The lithium-ion battery in this comparative example differs from that in Example 1 only in that, during the preparation of the negative electrode sheet, the coating thickness of the negative electrode active slurry on one side of the corner region is set to 100 μm, and the coating thickness on one side of the negative electrode active slurry on both sides of the straight region is 92 μm. The resulting negative electrode sheet has a porosity of 0.28 and a compaction density of 1.55 g / cm³ for the negative electrode active material layer in the corner region. 3 The thickness is 70 μm (single-layer thickness), the porosity of the negative electrode active material layer in the flat region of the negative electrode sheet is 0.3, and the compaction density is 1.53 g / cm³. 3 The thickness is 70μm (single layer thickness).

[0103] The remaining steps are performed in accordance with the method in Example 1.

[0104] Comparative Example 3

[0105] The lithium-ion battery in this comparative example differs from that in Example 1 only in that, during the preparation of the negative electrode sheet, the coating thickness of the negative electrode active slurry on one side of the corner region is set to 90 μm, and the coating thickness on one side of the negative electrode active slurry on both sides of the straight region is 95 μm. The resulting negative electrode sheet has a porosity of 0.32 and a compaction density of 1.51 g / cm³ for the negative electrode active material layer in the corner region. 3 The thickness is 70 μm (single-layer thickness), the porosity of the negative electrode active material layer in the flat region of the negative electrode sheet is 0.3, and the compaction density is 1.53 g / cm³. 3 The thickness is 70μm (single layer thickness).

[0106] The remaining steps are performed in accordance with the method in Example 1.

[0107] Test case

[0108] The batteries of Examples 1-3 and Comparative Examples 1-3 were tested as follows:

[0109] At room temperature (25℃), the battery was charged at a constant power of 0.5P to a cutoff voltage of 3.65V, and the number of cycle times was recorded when the cell reached 80% SOH. Simultaneously, the degree of lithium plating in the lithium-ion battery was determined according to the following criteria:

[0110] No lithium deposition: No lithium is deposited on the surface of the negative electrode;

[0111] Slight lithium plating: The lithium deposition area on the surface of the negative electrode is less than 10%;

[0112] Moderate lithium deposition: The lithium deposition area on the surface of the negative electrode is 10% to 30%;

[0113] Severe lithium plating: The lithium deposition area on the surface of the negative electrode is greater than 30%.

[0114] The test results are shown in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] Compared with Comparative Examples 1-3, the lithium-ion batteries provided in Examples 1-3 of the present invention exhibit less lithium plating and a higher number of cycles, indicating that the corner region negative electrode film layer and the straight region negative electrode film layer have a certain porosity difference, which can effectively improve the lithium plating and electrochemical performance of the battery.

[0119] Furthermore, as can be seen from Examples 1-3, in the negative electrode sheet, as the porosity of the negative electrode film layer in the corner region increases, the lithium plating problem is improved, and the battery cycle count increases accordingly. This indicates that, within a certain range, increasing the porosity of the negative electrode film layer in the corner region of the negative electrode sheet can further improve the lithium plating and electrochemical performance of the battery.

[0120] 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.

[0121] 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 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 0.33-0.

5.

2. The negative electrode sheet according to claim 1, characterized in that, The porosity of the negative electrode film in the straight region is 0.2-0.3; the porosity of the negative electrode film in the corner region is 0.33-0.

4.

3. The negative electrode sheet according to claim 2, characterized in that, The porosity of the negative electrode film in the straight region is 0.25-0.3; the porosity of the negative electrode film in the corner region is 0.33-0.

36.

4. The negative electrode sheet according to claim 1, characterized in that, The compaction density of the negative electrode film layer in the straight region is greater than that in the corner region; the compaction density of the negative electrode film layer in the corner region is ≥0.01 g / cm³. 3 ; The density difference between the flat region negative electrode film layer and the corner region negative electrode film layer is 0.01-0.7 g / cm³. 3 .

5. The negative electrode sheet according to claim 1, characterized in that, The compaction density of the negative electrode film layer in the flat region is 1.53-1.8 g / cm³. 3 The compaction density of the negative electrode film layer in the corner region is 1.1-1.52 g / cm³. 3 .

6. 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 negative electrode film layer in the straight region and the negative electrode film layer in the corner region is 1-55 μm.

7. The negative electrode sheet according to claim 6, characterized in that, 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, 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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