Positive electrode sheet for lithium ion battery, method of manufacturing the same, and lithium ion battery comprising the same

Abstract

This invention relates to a positive electrode sheet for lithium-ion batteries, a method for preparing the same, and a lithium-ion battery comprising the same. The positive electrode sheet includes a current collector and at least four active material layers attached to one side of the current collector, each containing a positive electrode active material, conductive carbon, and a binder. The at least four active material layers are characterized by having different particle sizes of the active material, conductive carbon content, and binder content, and from the side closer to the current collector to the side farther away, the particle size gradient decreases, the conductive carbon content gradient increases, and the binder content gradient decreases.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries. More specifically, this invention relates to a positive electrode sheet for lithium-ion batteries, a method for preparing the same, and a lithium-ion battery comprising the same. Background Technology

[0002] In recent years, with the rapid development of the new energy industry, lithium-ion batteries have received increasing attention due to their advantages such as high energy density, long cycle life, low self-discharge, and no memory effect, especially in the field of new energy vehicles where they have significant application potential. However, currently, besides driving range, consumers are primarily concerned about the fast-charging performance of batteries in new energy vehicles. Since the charging time for electric vehicles is still significantly shorter than the refueling time for gasoline vehicles, improving the fast-charging performance of lithium-ion batteries is crucial for expanding the new energy electric vehicle market.

[0003] Furthermore, in the electrolyte environment, the positive electrode continuously undergoes lithium-ion insertion and extraction during charging and discharging. The continuous expansion and contraction of the crystalline lattice makes it prone to breakage, leading to the separation of the active material from the current collector and reducing the battery's safety and reliability. However, a high content of binder coated on the electrode surface reduces the electrode's kinetic performance, failing to meet the requirements of fast charging. Therefore, it is necessary to optimize the proportions of various materials and the structure of the electrode to maximize its fast-charging performance while ensuring product reliability, thereby improving end-customer satisfaction with new energy electric vehicles.

[0004] Therefore, there is still a need for lithium-ion batteries with improved kinetic performance, improved adhesion between active materials and current collectors, and / or improved lifespan and reliability. Summary of the Invention

[0005] The purpose of this invention is to provide a positive electrode sheet for lithium-ion batteries, which can greatly improve the dynamic performance of lithium-ion batteries, improve the adhesion between active materials and current collectors, and / or improve the lifespan and reliability of lithium-ion batteries.

[0006] In one aspect, the present invention relates to a positive electrode sheet for a lithium-ion battery, the positive electrode sheet comprising a current collector and at least four active material layers comprising positive electrode active material, conductive carbon and binder attached to one side surface of the current collector, characterized in that: the at least four active material layers have different particle sizes of active materials, conductive carbon content and binder content, and from the side closer to the current collector to the side farther away from the current collector, the particle size gradient of the active material decreases, the conductive carbon content gradient increases, and the binder content gradient decreases.

[0007] In some embodiments, the positive electrode includes a current collector, a first active material layer, a second active material layer, a third active material layer, and a fourth active material layer stacked sequentially, wherein in the first active material layer, the active material particles D 50 The particle size is 15μm-20μm, the conductive carbon content is 1.2%-1.6% by weight, and the binder content is 1.5%-2% by weight; in the second active material layer, the active material particles D 50 The particle size is 10μm-15μm, the conductive carbon content is 1.7%-2.2% by weight, and the binder content is 1.3%-1.5% by weight; in the third active material layer, the active material particles D 50 The thickness is 5μm-10μm, the conductive carbon content is 2.3%-2.6% by weight, and the binder content is 1.1%-1.3% by weight; and in the fourth active material layer, the active material D 50 The thickness ranges from 2μm to 5μm, the conductive carbon content is 2.7% to 3% by weight, and the adhesive content is 0.9% to 1.1% by weight.

[0008] In some embodiments, the thickness of the first active material layer is greater than 0 to 50 μm, for example 40 μm; the thickness of the second active material layer is greater than 0 to 63 μm, for example 50 μm; the thickness of the third active material layer is greater than 0 to 62 μm, for example 50 μm; and the thickness of the fourth active material layer is greater than 0 to 75 μm, for example 60 μm.

[0009] In some embodiments, the active material includes an active material selected from lithium iron phosphate, ternary materials, lithium cobalt oxide, lithium titanate, or lithium manganese iron phosphate, preferably ternary materials, and more preferably LiNi. x Co y Mn z M a O2, where x+y+z+a=1, and M is one or more of Al, Zr, Mg, Nd, Zn, Ti and Nb.

[0010] In some embodiments, the conductive carbon is selected from one or more of carbon fiber, acetylene black, Super P, carbon nanotubes, and graphene. In some embodiments, the adhesive is selected from one or more of polyacrylic acid, polyvinylidene fluoride, or polytetrafluoroethylene, preferably polyvinylidene fluoride. In some embodiments, the particle size gradient is achieved by airflow impingement. In some embodiments, the current collector is aluminum foil, such as carbon-coated aluminum foil.

[0011] In another aspect, the present invention relates to a method for preparing a positive electrode sheet for a lithium-ion battery, comprising the following steps:

[0012] (1) Spray the adhesive of the first content onto the surface of the current collector;

[0013] (2) The active material with the first particle size is premixed with the conductive carbon of the first content and then sprayed onto the adhesive adhering to the surface of the current collector.

[0014] (3) Repeat steps (1) and (2) until a first active material layer with a desired coating thickness, such as 20% of the total thickness, is formed.

[0015] (4) Spray the adhesive of the second content onto the first active material layer;

[0016] (5) The active material with the second particle size is premixed with the conductive carbon with the second content, and then sprayed onto the adhesive adhering to the surface of the first active material layer.

[0017] (6) Repeat steps (4) and (5) until a second active material layer with a desired coating thickness, such as 25% of the total thickness, is formed.

[0018] (7) Spray the adhesive of the third content onto the second active material layer;

[0019] (8) The active material with a third particle size is premixed with the conductive carbon with a third content, and then sprayed onto the adhesive adhering to the surface of the second active material layer.

[0020] (9) Repeat steps (7) and (8) until a third active material layer with a desired coating thickness, such as 25% of the total thickness, is formed.

[0021] (10) Spray the adhesive of the fourth content onto the third active material layer;

[0022] (11) The active material with the fourth particle size is premixed with the conductive carbon with the fourth content, and then sprayed onto the adhesive that adheres to the surface of the third active material layer.

[0023] (12) Repeat steps (10) and (11) until a fourth active material layer with a desired coating thickness, such as 30% of the total thickness, is formed; and

[0024] (13) Optionally, the above actions may be repeated as needed until at least four active material layers are formed, the at least four active material layers having different particle sizes, conductive carbon contents and binder contents of the active materials, and the particle size gradient decreases, the conductive carbon content gradient increases and the binder content gradient decreases from the side closer to the current collector to the side farther away from the current collector.

[0025] In another aspect, the present invention relates to a lithium-ion battery, characterized in that the lithium-ion battery comprises the positive electrode sheet of the present invention. Attached Figure Description

[0026] Figure 1 This is a positive electrode sheet for a lithium-ion battery according to one embodiment of the present invention, wherein the black dots correspond to conductive carbon and the gray dots correspond to active material particles.

[0027] Figure 2 This is a schematic diagram showing the capacity retention rate of lithium-ion batteries of Comparative Example 1, Comparative Example 2 and Example 1 at different discharge rates at room temperature. Detailed Implementation

[0028] Several aspects of the invention are described below with reference to illustrative examples. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. However, those skilled in the art will readily recognize that the invention may be practiced without one or more of these specific details or may be practiced in other ways.

[0029] Unless otherwise defined herein, scientific and technical terms used in connection with this application shall have the meanings commonly understood by one of ordinary skill in the art. Furthermore, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” used herein are intended to include the plural forms as well. Additionally, the open-ended expressions “comprising” and “including” are interpreted as potentially containing structural components or method steps not mentioned, but it should be noted that these open-ended expressions also cover situations where the application consists solely of the stated components and method steps (i.e., they cover the closed-ended expression “consisting of…”).

[0030] It should be understood that this disclosure is not limited to the specific methodologies, schemes, and materials described herein, and therefore they may vary. The terminology used herein is intended only to describe specific embodiments and is not intended to limit the scope of this disclosure.

[0031] As used throughout, a range is used as a shorthand to describe each and all values ​​within that range. Any value within the range, such as an integer or a value incremented by one-tenth (when the range ends in one decimal place), can be chosen as the end of the range. For example, the range 15μm-20μm is used to describe all values ​​within that range, such as 15, 16, 17, 18, 19, and 20 (all integer values) μm, and includes all subranges, such as 15-18 μm, 18-20 μm, 16-19 μm, 17-20 μm, etc. As another example, the range 1.2%-1.6% is used to describe all values ​​within that range, such as 1.2%, 1.3%, 1.4%, 1.5%, and 1.6% (in increments of one-tenth), and includes all subranges, such as 1.2%-1.5%, 1.3%-1.6%, 1.4%-1.6%, 1.5%-1.6%, etc.

[0032] Unless otherwise stated herein, all percentages used herein are weight percentages.

[0033] This invention discloses a positive electrode sheet with gradients in active material particle size, conductive carbon content, and binder content, as well as its preparation method. A single-layer coating of the electrode material is achieved through electrostatic spraying combined with ultrasonic spraying, resulting in a gradient positive electrode sheet with large active material particles, high binder content, and low conductive carbon content near the substrate, gradually decreasing in particle size, binder content, and conductive carbon content towards the substrate. This positive electrode sheet not only significantly improves kinetic performance but also enhances the adhesion between the active material and the current collector, thereby improving the lifespan and reliability of lithium-ion batteries.

[0034] The active material layer of the positive electrode sheet of the present invention has a gradient of active material particle size, a gradient of conductive carbon content, and a gradient of binder content, the number of which n ≥ 4, and can be adjusted as needed. When the number of gradients is infinitely large, a linear decrease in active material particle size, a linear decrease in binder content, and a linear increase in conductive carbon content are achieved from the substrate side to the side away from the substrate side. The following description uses a gradient number n = 4 as an example to illustrate various embodiments of the present invention; however, it should be understood that, under the guidance of the present invention, each embodiment can be adjusted accordingly based on the number of gradients.

[0035] In some implementations, the electrode thickness at the current collector is set to 0 μm, with 0 μm-50 μm (excluding 0 μm, including 50 μm) being the closest to the current collector side (corresponding to the first active material layer), 50 μm-113 μm (excluding 50 μm, including 113 μm) being the next closest to the current collector side (corresponding to the second active material layer), 113 μm-175 μm (excluding 113 μm, including 175 μm) being the next furthest from the current collector side (corresponding to the third active material layer), and 175 μm-250 μm (excluding 175 μm, including 250 μm) being the furthest from the current collector side (corresponding to the fourth active material layer). It should be noted that the cross-sectional area and shape of each active material layer can be independently the same or different, and can independently be the same or different from the cross-sectional area and shape of the current collector. In addition, the positive electrode active material, conductive carbon and binder contained in each active material layer may be the same or different, preferably the same, and each is independently selected from the positive electrode active material, conductive carbon and binder described in the first aspect under the title "Summary of the Invention", and / or have the same properties as them.

[0036] In some embodiments, the first active material layer may be formed as follows: (1) spraying, for example, microwave spraying, an adhesive of a first content onto the surface of the current collector; (2) premixing, for example, an active material having a first particle size with a first content of conductive carbon, and then spraying, for example, electrostatically spraying, onto the adhesive adhered to the surface of the current collector; and (3) repeating steps (1) and (2) until a coating thickness of 20% of the desired total thickness is formed. The first content of adhesive, the active material having a first particle size, and the first content of conductive carbon correspond to the required adhesive content, active material particle size, and conductive carbon content of the first active material layer, respectively, and are screened and added accordingly. In some embodiments, in the first active material layer, the active material particles D 50 The thickness is 15μm-20μm, for example 16μm-20μm, 18μm-20μm, or 15μm-18μm; the conductive carbon content is 1.2%-1.6% by weight, for example 1.3%-1.6% by weight, 1.4%-1.6% by weight, or 1.2%-1.5% by weight; and the adhesive content is 1.5%-2% by weight, for example 1.6%-2% by weight, 1.7%-2% by weight, or 1.6%-1.9% by weight. In some embodiments, the adhesive is heated to a molten state by a built-in heating device of the coating equipment before spraying. In some embodiments, the heating temperature is 170°C-180°C, for example 175°C-180°C. In some embodiments, the coating thickness in step (1) is calculated based on the adhesive content closest to the current collector side. In some embodiments, the premixing time is 10 min-20 min, for example 15 min.

[0037] In some embodiments, the second active material layer may be formed as follows: (4) spraying a second amount of adhesive onto the first active material layer; (5) premixing an active material having a second particle size with a second amount of conductive carbon, for example by airflow premixing, and then spraying, for example by electrostatic spraying, onto the adhesive adhering to the surface of the first active material layer; and (6) repeating steps (4) and (5) until a second active material layer having a desired coating thickness, for example, 25% of the total thickness, is formed. The second amount of adhesive, the active material having a second particle size, and the second amount of conductive carbon correspond to the required adhesive content, active material particle size, and conductive carbon content for the second active material layer, respectively, and are screened and added accordingly. In some embodiments, in the second active material layer, the active material particles D 50The thickness is 10μm-15μm, for example, 10μm-14μm, 10μm-13μm, or 11μm-12μm; the conductive carbon content is 1.7%-2.2% by weight, for example, 1.7%-2.1% by weight, 1.8%-2.0% by weight, or 1.9%-2.2% by weight; and the adhesive content is 1.3%-1.5% by weight, for example, 1.35%-1.45% by weight, or 1.3%-1.4% by weight. In some embodiments, the adhesive is heated to a molten state by a built-in heating device of the coating equipment before spraying. In some embodiments, the heating temperature is 170°C-180°C, for example, 175°C-180°C. In some embodiments, the coating thickness in step (4) is calculated based on the adhesive content closest to the current collector side. In some embodiments, the premixing time is 10 min-20 min, for example, 15 min.

[0038] In some embodiments, the third active material layer may be formed as follows: (7) spraying a third amount of adhesive onto the second active material layer; (8) premixing an active material having a third particle size with a third amount of conductive carbon, for example by airflow premixing, and then spraying, for example by electrostatic spraying, onto the adhesive adhering to the surface of the second active material layer; and (9) repeating steps (7) and (8) until a third active material layer having a desired coating thickness, for example, 25% of the total thickness, is formed. The third amount of adhesive, the active material having a third particle size, and the third amount of conductive carbon correspond to the required adhesive content, active material particle size, and conductive carbon content for the third active material layer, respectively, and are screened and added accordingly. In some embodiments, in the third active material layer, the active material particles D 50 The conductive carbon content is 2.3%-2.6% by weight, for example, 2.35%-2.55% by weight, 2.4%-2.5% by weight, or 2.45%-2.55% by weight, and the adhesive content is 1.1%-1.3% by weight, for example, 1.15%-1.25% by weight, 1.2%-1.3% by weight, or 1.25%-1.3% by weight. In some embodiments, the adhesive is heated to a molten state by a built-in heating device of the coating equipment before spraying. In some embodiments, the heating temperature is 170°C-180°C, for example, 175°C-180°C. In some embodiments, the coating thickness in step (7) is calculated based on the adhesive content on the side furthest from the current collector. In some embodiments, the premixing time is 10 min-20 min, for example, 15 min.

[0039] In some embodiments, the fourth active material layer may be formed as follows: (10) spraying an adhesive of a fourth content onto the third active material layer; (11) premixing an active material having a fourth particle size with a conductive carbon of a fourth content, for example by airflow premixing, and then spraying, for example by electrostatic spraying, onto the adhesive adhering to the surface of the third active material layer; and (12) repeating steps (10) and (11) until a fourth active material layer having a desired coating thickness, for example, 30% of the total thickness, is formed. The fourth content of adhesive, the active material having a fourth particle size, and the fourth content of conductive carbon correspond to the required adhesive content, active material particle size, and conductive carbon content of the fourth active material layer, respectively, and are screened and added accordingly. In some embodiments, in the fourth active material layer, the active material D 50 The conductive carbon content is 2.7%-3% by weight, for example, 2.75%-2.95% by weight, 2.8%-2.9% by weight, or 2.85%-2.95% by weight, and the adhesive content is 0.9%-1.1% by weight, for example, 0.95%-1.05% by weight or 0.95%-1.1% by weight. In some embodiments, the adhesive is heated to a molten state by a built-in heating device of the coating equipment before spraying. In some embodiments, the heating temperature is 170°C-180°C, for example, 175°C-180°C. In some embodiments, the coating thickness in step (10) is calculated based on the adhesive content furthest from the current collector side. In some embodiments, the premixing time is 10 min-20 min, for example, 15 min.

[0040] In some implementations, the content of active material in the active material layer is 95%-98% by weight.

[0041] While various embodiments of the invention have been described above, it should be understood that they are provided by way of example only and not as limitations. Many changes to the disclosed embodiments may be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Therefore, the breadth and scope of the invention should not be limited by any of the embodiments described above. Example

[0042] Unless otherwise stated, all materials used in the embodiments herein are commercially available, and all specific experimental methods used to conduct the experiments are conventional experimental methods in the art or are performed according to the steps and conditions recommended by the manufacturer, and can be conventionally determined by those skilled in the art as needed.

[0043] Comparative Example 1:

[0044] Weigh the prepared ternary material (LiNi) 0.5 Co 0.2 Mn0.3 40 kg of O2, 0.923 kg of conductive Super P material, and 0.57 kg of PVDF binder were placed in a 100 L planetary mixer. The mixture was premixed for 30 min at 25 rpm and 800 rpm. Then, 13.8 kg of NMP solvent was added, and the mixer was stirred for another 170 min at 25 rpm and 1800 rpm. The resulting slurry was coated onto a 13 μm aluminum foil surface using an extrusion coating machine to form a 200 μm thick positive electrode. The prepared positive electrode was then rolled, slit, and die-cut into soft-pack batteries. Artificial graphite was used as the negative electrode, and the electrolyte system consisted of 1 mol / L LiFP6 as the lithium salt and EC / DEC / EMC as the solvent, thus preparing a lithium-ion battery as shown in Comparative Example 1.

[0045] Comparative Example 2:

[0046] The prepared initial ternary material (LiNi) 0.5 Co 0.2 Mn 0.3 O2) is broken into particles of size D by airflow impact. 50 The electrodes are 18μm, 14μm, and 8μm in diameter, and are labeled as Substance 1, Substance 2, and Substance 3, respectively. 13kg of Substance 1, 0.216kg of Super P material, and 0.269kg of PVDF material are weighed. The PVDF material is placed in an ultrasonic heating device and heated to 175℃ until it melts. It is then ultrasonically sprayed onto the surface of a 13μm aluminum foil, with a spray thickness of approximately 2μm. At the same time, Substance 1 and Super P are mixed by airflow for 15 minutes, and then electrostatically sprayed onto the molten PVDF until many particles cannot adhere and fall off. This process is repeated sequentially, ultrasonically spraying PVDF, electrostatically spraying the mixture of Substance 1 and Super P, until the electrode thickness reaches 67μm.

[0047] Weigh 13 kg of Substance No. 2, 0.283 kg of Super P material, and 0.203 kg of PVDF material. Place the PVDF material in an ultrasonic heating device and heat it to a molten state at 175°C. Then, spray it onto the electrode formed by Substance No. 1 using an ultrasonic device to a thickness of about 2 μm. At the same time, mix Substance No. 2 and Super P with an airflow for 15 min, and then electrostatically spray it onto the molten PVDF until many particles cannot be adhered and fall off. Continue to ultrasonically spray PVDF, electrostatically spray Substance No. 2 and Super P mixture in sequence until the electrode formed by Substance No. 2 has a thickness of 66 μm.

[0048] Weigh 14 kg of substance No. 3, 0.363 kg of Super P material, and 0.160 kg of PVDF material. Place the PVDF material in an ultrasonic heating device and heat it to a molten state at 175°C. Then, spray it onto the electrode formed by substance No. 2 using an ultrasonic device to a thickness of about 2 μm. At the same time, mix substance No. 3 and Super P with airflow for 15 min, and then electrostatically spray it onto the molten PVDF until many particles cannot be adhered and fall off. Continue to ultrasonically spray PVDF, electrostatically spray the mixture of substance No. 3 and Super P in sequence until the electrode formed by substance No. 3 has a thickness of 66 μm.

[0049] After the prepared positive electrode sheet is rolled, slit and die-cut, it is assembled into a soft-pack battery. The negative electrode is made of artificial graphite, and the electrolyte is an electrolyte system containing 1 mol / L LiFP6 as lithium salt and EC / DEC / EMC as solvent. Comparative Example 2 lithium-ion battery was prepared.

[0050] Example 1:

[0051] A positive electrode sheet and its lithium-ion battery that combine active material particle gradient, conductive carbon content gradient, and binder content gradient are synthesized by the following main method:

[0052] The prepared initial ternary material (LiNi) was then passed through... 0.5 Co 0.2 Mn 0.3 O2) The airflow impact crushes the particles to a particle size D. 50 The electrode materials are 18μm, 12μm, 7μm, and 3μm, respectively, and are labeled as Substance 1, Substance 2, Substance 3, and Substance 4. Weigh 10kg of Substance 1, 0.166kg of Super P material, and 0.207kg of PVDF material. Place the PVDF material in an ultrasonic heating device and heat it to a molten state at 175℃. Then, spray it onto the surface of a 13μm aluminum foil using an ultrasonic device to achieve a coating thickness of approximately 2μm. Simultaneously, mix Substance 1 and Super P with an airflow for 15 minutes, and then electrostatically spray it onto the molten PVDF until many particles cannot adhere and fall off. Continue to ultrasonically spray PVDF, then electrostatically spray the mixture of Substance 1 and Super P until the electrode thickness reaches 40μm.

[0053] Weigh 10 kg of Substance No. 2, 0.218 kg of Super P material, and 0.156 kg of PVDF material. Place the PVDF material in an ultrasonic heating device and heat it to a molten state at 175°C. Then, spray it onto the electrode formed by Substance No. 1 using an ultrasonic device to a thickness of about 2 μm. At the same time, mix Substance No. 2 and Super P with an airflow for 15 min, and then electrostatically spray it onto the molten PVDF until many particles cannot be adhered and fall off. Continue to ultrasonically spray PVDF, electrostatically spray Substance No. 2 and Super P mixture in sequence until the electrode formed by Substance No. 2 has a thickness of 50 μm.

[0054] Weigh 10 kg of substance No. 3, 0.259 kg of Super P material, and 0.114 kg of PVDF material. Place the PVDF material in an ultrasonic heating device and heat it to a molten state at 175°C. Then, spray it onto the electrode formed by substance No. 2 using an ultrasonic device to a thickness of about 2 μm. At the same time, mix substance No. 3 and Super P with airflow for 15 min, and then electrostatically spray it onto the molten PVDF until many particles cannot be adhered and fall off. Continue to ultrasonically spray PVDF, electrostatically spray the mixture of substance No. 3 and Super P in sequence until the electrode formed by substance No. 3 has a thickness of 50 μm.

[0055] Weigh 10 kg of substance No. 4, 0.280 kg of Super P material, and 0.093 kg of PVDF material. Place the PVDF material in an ultrasonic heating device and heat it to a molten state at 175°C. Then, spray it onto the electrode formed by substance No. 3 using an ultrasonic device to a thickness of about 2 μm. At the same time, mix substance No. 4 and Super P with airflow for 15 min, and then electrostatically spray it onto the molten PVDF until many particles cannot be adhered and fall off. Continue to ultrasonically spray PVDF, electrostatically spray the mixture of substance No. 4 and Super P in sequence until the electrode formed by substance No. 4 has a thickness of 60 μm.

[0056] After the prepared positive electrode sheet is rolled, slit and die-cut, it is assembled into a soft-pack battery. The negative electrode is made of artificial graphite, and the electrolyte is an electrolyte system containing 1 mol / L LiFP6 as lithium salt and EC / DEC / EMC as solvent, thus preparing the lithium-ion battery of Example 1.

[0057] The lithium-ion batteries of Comparative Example 1, Comparative Example 2, and Example 1 were tested at room temperature for capacity retention at different discharge rates, and the results were compared. Figure 2 As shown in Table 1. Additionally, the positive electrode sheets prepared in Comparative Example 1, Comparative Example 2, and Example 1 were subjected to adhesion strength tests using a high-speed rail tensile testing machine. The test results are shown in Table 1 below.

[0058] Table 1 shows the test data on the adhesion strength of the positive electrode sheets of Comparative Example 1, Comparative Example 2, and Example 1.

[0059] Electrode adhesion Comparative Example 1 Comparative Example 2 Example 1 Parallel sample 1# 10N×m 11 N × m 11 N × m Parallel sample 2# 18 N × m 20N×m 21N×m

[0060] It should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A positive electrode sheet for a lithium-ion battery, the positive electrode sheet comprising a current collector and at least four active material layers comprising a positive electrode active material, conductive carbon, and a binder attached to one side surface of the current collector, characterized in that: The at least four active material layers have different particle sizes, conductive carbon contents, and binder contents of the active materials, and from the side closer to the current collector to the side farther away from the current collector, the particle size gradient decreases, the conductive carbon content gradient increases, and the binder content gradient decreases. The positive electrode sheet comprises a current collector, a first active material layer, a second active material layer, a third active material layer, and a fourth active material layer stacked sequentially, wherein in the first active material layer, active material particles D... 50 The particle size is 15μm-20μm, the conductive carbon content is 1.2%-1.6% by weight, and the binder content is 1.5%-2% by weight; in the second active material layer, the active material particles D 50 The particle size is 10μm-15μm, the conductive carbon content is 1.7%-2.2% by weight, and the binder content is 1.3%-1.5% by weight; in the third active material layer, the active material particles D 50 The thickness is 5μm-10μm, the conductive carbon content is 2.3%-2.6% by weight, and the binder content is 1.1%-1.3% by weight; and in the fourth active material layer, the active material D 50 The thickness ranges from 2μm to 5μm, the conductive carbon content is 2.7% to 3% by weight, and the adhesive content is 0.9% to 1.1% by weight.

2. The positive electrode sheet for a lithium-ion battery according to claim 1, wherein the thickness of the first active material layer is greater than 0 to 50 μm, the thickness of the second active material layer is greater than 0 to 63 μm, the thickness of the third active material layer is greater than 0 to 62 μm, and the thickness of the fourth active material layer is greater than 0 to 75 μm.

3. The positive electrode sheet for a lithium-ion battery according to claim 1 or 2, wherein the active material comprises an active material selected from lithium iron phosphate, ternary materials, lithium cobalt oxide, lithium titanate, or lithium manganese iron phosphate.

4. The positive electrode sheet for a lithium-ion battery according to claim 1 or 2, wherein the active material is a ternary material.

5. The positive electrode sheet for a lithium-ion battery according to claim 4, wherein the active material is LiNi. x Co y Mn z M a O2, where x+y+z+a=1, and M is one or more of Al, Zr, Mg, Nd, Zn, Ti and Nb.

6. The positive electrode sheet for a lithium-ion battery according to any one of claims 1-2, wherein the conductive carbon is selected from one or more of carbon fiber, acetylene black, Super P, carbon nanotubes and graphene.

7. The positive electrode sheet for a lithium-ion battery according to any one of claims 1-2, wherein the adhesive is selected from one or more of polyacrylic acid, polyvinylidene fluoride or polytetrafluoroethylene.

8. The positive electrode sheet for a lithium-ion battery according to claim 7, wherein the adhesive is polyvinylidene fluoride.

9. The positive electrode sheet for a lithium-ion battery according to any one of claims 1-2, wherein the particle size gradient is achieved by airflow impact.

10. A method for preparing a positive electrode sheet for a lithium-ion battery according to any one of claims 1-9, comprising the following steps: (1) Spray the adhesive of the first content onto the surface of the current collector; (2) The active material with the first particle size is premixed with the conductive carbon of the first content and then sprayed onto the adhesive adhering to the surface of the current collector. (3) Repeat steps (1) and (2) until a first active material layer with the desired coating thickness is formed; (4) Spray the adhesive of the second content onto the first active material layer; (5) The active material with the second particle size is premixed with the conductive carbon with the second content, and then sprayed onto the adhesive adhering to the surface of the first active material layer. (6) Repeat steps (4) and (5) until a second active material layer with the desired coating thickness is formed; (7) Spray the adhesive of the third content onto the second active material layer; (8) The active material with a third particle size is premixed with the conductive carbon with a third content, and then sprayed onto the adhesive adhering to the surface of the second active material layer. (9) Repeat steps (7) and (8) until a third active material layer with the desired coating thickness is formed. (10) Spray the adhesive of the fourth content onto the third active material layer; (11) The active material with the fourth particle size is premixed with the conductive carbon with the fourth content, and then sprayed onto the adhesive that adheres to the surface of the third active material layer. (12) Repeat steps (10) and (11) until a fourth active material layer with the desired coating thickness is formed; and (13) Optionally, the above actions may be repeated as needed until at least four active material layers are formed, the at least four active material layers having different particle sizes, conductive carbon contents and binder contents of the active materials, and the particle size gradient decreases, the conductive carbon content gradient increases and the binder content gradient decreases from the side closer to the current collector to the side farther away from the current collector.

11. The method according to claim 10, wherein the thickness of the first active material layer is 20% of the total thickness.

12. The method of claim 10, wherein the thickness of the second active material layer is 25% of the total thickness.

13. The method according to claim 10, wherein the thickness of the third active material layer is 25% of the total thickness.

14. The method according to claim 10, wherein the thickness of the fourth active material layer is 30% of the total thickness.

15. A lithium-ion battery, characterized in that... The lithium-ion battery comprises a positive electrode sheet for a lithium-ion battery as described in any one of claims 1-9.

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