WO2021223655A1 - 一种正极片、制备方法及包含其的锂离子电池 - Google Patents

一种正极片、制备方法及包含其的锂离子电池 Download PDF

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WO2021223655A1
WO2021223655A1 PCT/CN2021/091034 CN2021091034W WO2021223655A1 WO 2021223655 A1 WO2021223655 A1 WO 2021223655A1 CN 2021091034 W CN2021091034 W CN 2021091034W WO 2021223655 A1 WO2021223655 A1 WO 2021223655A1
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positive electrode
active material
electrode active
material layer
layer
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PCT/CN2021/091034
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English (en)
French (fr)
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张保海
彭冲
贺伟
施超
李俊义
徐延铭
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珠海冠宇电池股份有限公司
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Priority to EP21800204.6A priority Critical patent/EP4148819A4/en
Publication of WO2021223655A1 publication Critical patent/WO2021223655A1/zh
Priority to US18/053,278 priority patent/US20230118023A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/531—Electrode connections inside a battery casing
    • H01M50/538—Connection of several leads or tabs of wound or folded electrode stacks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • This application belongs to the technical field of lithium ion batteries, and specifically relates to a positive electrode sheet, a preparation method and a lithium ion battery containing the positive electrode sheet.
  • Lithium-ion batteries are widely used in portable mobile electronic equipment terminals because of their longer cycle life and higher power density.
  • people life rhythm becomes faster, people propose higher battery life and charging speeds.
  • fast-charging lithium-ion batteries have become the main development trend of consumer lithium-ion batteries.
  • the development of fast-charging lithium-ion battery technology brings convenience to people and also brings safety problems.
  • When lithium-ion batteries are cycled under high-rate fast charging conditions it is very easy to cause lithium-ion battery negative electrodes, especially on one side of the negative electrode.
  • the coating area is more serious, which brings about problems such as cyclic diving, swelling, and air swelling of the lithium-ion battery, which greatly reduces the service life of the lithium-ion battery.
  • the present application provides a positive electrode sheet, a preparation method and a lithium ion battery containing the positive electrode sheet.
  • the positive electrode sheet is mainly used to solve the problem of lithium precipitation in the single-sided coating area of the battery negative electrode of the winding structure during a long cycle under a high-rate fast charging system.
  • the inventor of the present application discovered that the basic cause of lithium precipitation in the single-sided coating area of the existing winding structure of the battery cell’s negative electrode is that the single-sided coating area is close to the tabs, resulting in high current density, low potential, and negative electrode dynamics. Insufficient performance.
  • the key to solving the problem of lithium precipitation in the single-sided coating area of the negative electrode under the premise of the same charging system is to improve the kinetics of the negative electrode and/or reduce the kinetic performance of the positive electrode.
  • the positive electrode sheet reduces the dynamic performance of the positive active material layer of the wound lithium-ion battery, so as to reduce the single-sided coating of the negative electrode without reducing the overall fast charging performance of the lithium-ion battery and the energy density of the lithium-ion battery.
  • the polarization of the coating area and the entire negative electrode surface can effectively improve the lithium-ion problem in the single-sided coating area of the conventional wound structure of the lithium-ion battery, and increase the lithium without reducing the overall fast charging performance of the lithium-ion battery and the energy density of the lithium-ion battery. Ion battery cycle life, improve cycle expansion.
  • the positive electrode sheet can solve the problem of lithium evolution in the single-sided coating area of the wound structure of the battery cell negative electrode during the long cycle process under the high-rate charging system without reducing the overall fast charging performance of the lithium ion battery and the energy density of the lithium ion battery.
  • a coiled positive electrode sheet specifically a coiled positive electrode sheet for a lithium ion battery, the positive electrode sheet includes a positive electrode current collector, and the positive electrode current collector includes a single-sided coating area and a double-sided coating area;
  • a second coating layer and a third coating layer are provided on one side of the positive electrode current collector, and the first coating layer, the second coating layer and the third coating layer are connected in sequence ;
  • a fourth coating layer is provided on the other side of the positive electrode current collector;
  • the second coating layer includes a first positive electrode active material layer and a second positive electrode active material layer, the second positive electrode active material layer is disposed on the surface of the positive electrode current collector, and the first positive electrode active material layer is disposed on the second positive electrode.
  • the third coating layer includes a first positive electrode active material layer, and the first positive electrode active material layer is disposed on the surface of the positive electrode current collector;
  • the fourth coating layer includes a first positive electrode active material layer and a second positive electrode active material layer, the second positive electrode active material layer is disposed on the surface of the positive electrode current collector, and the first positive electrode active material layer is disposed on the second positive electrode.
  • the first positive electrode active material layer includes a first positive electrode active material
  • the second positive electrode active material layer includes a second positive electrode active material
  • the particle size of the first positive electrode active material is larger than that of the second positive electrode active material. path.
  • the lithium ion extraction rate of the second positive electrode active material is greater than the lithium ion extraction rate of the first positive electrode active material.
  • the dynamic performance of the second positive electrode active material layer is better than that of the first positive electrode active material layer.
  • the dynamic performance refers to the deintercalation speed of lithium ions, and the faster the deintercalation speed, the better the dynamic performance.
  • the factors that affect the de-intercalation speed of lithium ions include at least the following two: (1) The size of the charge current that can be supported by the active material. The larger the charge current that can be supported, the better the dynamic performance; (2) The release per unit time The amount of lithium ions, that is, the rate of lithium ion extraction, the faster the rate of lithium ion extraction, the better the kinetic performance.
  • the deintercalation rate of lithium ions from the second positive electrode active material layer is greater than the deintercalation rate of lithium ions from the first positive electrode active material layer.
  • the lithium ion extraction speed of the second positive electrode active material layer is greater than the lithium ion extraction speed of the first positive electrode active material layer.
  • the deintercalation rate of lithium ions is slowed due to the deterioration of the dynamic performance, that is, the negative electrode
  • the number of lithium ions collected or accepted by the surface per unit time is reduced, so the lithium evolution problem on the surface of the negative electrode, especially in the single-sided coating area, can be greatly reduced.
  • the particle size distribution of the first positive electrode active material forming the first positive electrode active material layer is: 5 ⁇ m ⁇ D 10 ⁇ 8 ⁇ m, 16 ⁇ m ⁇ D 50 ⁇ 19 ⁇ m, 35 ⁇ m ⁇ D 90 ⁇ 45 ⁇ m;
  • the particle size distribution of the second positive electrode active material of the two positive electrode active material layer is: 4 ⁇ m ⁇ D 10 ⁇ 6 ⁇ m, 13 ⁇ m ⁇ D 50 ⁇ 16 ⁇ m, and 22 ⁇ m ⁇ D 90 ⁇ 33 ⁇ m.
  • the positive electrode current collector also includes a tab region, that is, the positive electrode current collector includes a single-sided coating region, a double-sided coating region, and a tab region that are sequentially arranged; in the tab region, the positive electrode collector No coating layer is provided on both sides of the fluid.
  • the first coating layer in the single-sided coating area, the second coating layer and the third coating layer in the double-sided coating area are successively arranged, that is, the single-sided coating There is no blank area in the first coating layer in the area, the second coating layer and the third coating layer in the double-sided coating area.
  • the single-sided coating area refers to coating the positive electrode active material layer on one surface of the two sides of the current collector.
  • the double-sided coating area refers to coating the positive electrode active material layer on both sides of the current collector.
  • the length of the tab area, the length of the single-sided coating area, and the length of the double-sided coating area are not specifically defined, and can be set according to different requirements, for example, the double-sided
  • the length of the coated area is greater than the length of the single-sided coated area
  • the length of the double-sided coated area is greater than the length of the tab area.
  • the length of the single-sided coating area is 123 ⁇ 2 mm.
  • the length of the first coating layer and the length of the third coating layer are not specifically defined.
  • the length of the first coating layer is longer than the length of the third coating layer. -10mm.
  • the length of the third coating layer is the same as the length of the single-sided coating area in the negative electrode sheet or is shorter by 1-2 mm.
  • the positive electrode tab is provided in the tab region, so there is no need to provide a coating layer in this region.
  • the distance between the positive electrode tab provided in the tab area and the double-sided coating area is not particularly limited, for example, 10-100mm; for example, for a battery of 386283 model, the distance between the tab area
  • the set distance between the positive electrode tab and the double-sided coating area is 35.5 ⁇ 0.5 mm.
  • the thickness of the first positive electrode active material layer in the first coating layer is 5-15 ⁇ m, for example, 5 ⁇ m, 10 ⁇ m, or 15 ⁇ m;
  • the thickness of the positive electrode active material layer is 55-75 ⁇ m, for example, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, or 75 ⁇ m; and the sum of the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 60- 80 ⁇ m.
  • the thickness of the first positive electrode active material layer in the second coating layer is 5-15 ⁇ m, for example, 5 ⁇ m, 10 ⁇ m, or 15 ⁇ m;
  • the thickness of the positive electrode active material layer is 55-75 ⁇ m, for example, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, or 75 ⁇ m; and the sum of the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 60- 80 ⁇ m.
  • the thickness of the first positive electrode active material layer in the third coating layer is 60-80 ⁇ m, for example, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, or 80 ⁇ m.
  • the thickness of the first positive electrode active material layer in the fourth coating layer is 5-15 ⁇ m, for example, 5 ⁇ m, 10 ⁇ m, or 15 ⁇ m;
  • the thickness of the positive electrode active material layer is 55-75 ⁇ m, for example, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, or 75 ⁇ m; and the sum of the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 60- 80 ⁇ m.
  • the thickness of the second coating layer, the thickness of the third coating layer, and the thickness of the fourth coating layer are the same.
  • the thickness of the first coating layer, the thickness of the second coating layer, the thickness of the third coating layer and the thickness of the fourth coating layer are the same.
  • the positive electrode current collector also includes a blank area, the blank area is arranged on the other side of the single-sided coating area connected to the double-sided coating area, and the blank area is, for example, in the production process of the positive electrode sheet. It is produced by medium cutting and is used to wrap the surface of the wound cell.
  • the length of the blank area may be, for example, 35 ⁇ 2 mm.
  • the positive electrode current collector from one end of the positive electrode current collector and along the length direction of the positive electrode current collector includes a blank area, a single-sided coating area, a double-sided coating area, and a tab area sequentially arranged;
  • a fourth coating layer including a first positive electrode active material layer and a second positive electrode active material layer is coated on the surface (N side) of the positive electrode current collector, and the second positive electrode active material layer is coated on the surface of the positive electrode current collector ,
  • the first positive electrode active material layer is coated on the surface of the second positive electrode active material layer; and the length of the fourth coating layer is equal to the sum of the lengths of the second coating layer and the third coating layer , To ensure that the single-sided coating area (the area formed by the first coating layer) and the double-sided coating area (the second coating layer, the third coating layer and the fourth coating layer are formed in the positive electrode sheet) Area).
  • the preparation of the N side can be, for example, that the slurry for forming the first positive electrode active material layer and the slurry for forming the second positive electrode active material layer are coated together from point E of the positive electrode current collector, and The slurry for forming the second positive electrode active material layer is close to the positive electrode current collector, and the slurry for forming the first positive electrode active material layer is far from the positive electrode current collector; the slurry for forming the second positive electrode active material layer is applied to point D, or, forming The slurry for the first positive electrode active material layer and the slurry for forming the second positive electrode active material layer are applied together from point D of the positive electrode current collector, and the slurry for forming the second positive electrode active material layer is close to the positive electrode current collector to form the first positive electrode The slurry of the active material layer is far away from the positive electrode current collector; the slurry forming the second positive electrode active material layer is coated to the end of point E; and the line connecting
  • the single-sided coating area and the double-sided coating area are successively arranged, that is, there is no blank area in the single-sided coating area and the double-sided coating area.
  • the thickness of the first coating layer and the thickness of the second coating layer are the same, both being 95-120 ⁇ m.
  • the negative electrode current collector also includes a blank area, the blank area is arranged on the other side of the double-sided coating area connected to the single-sided coating area, and the blank area is for example used in the production process of the negative electrode sheet.
  • the length of the blank area may be 0.5-2 mm, such as 1 mm, for example.
  • the third step using a two-layer coater to coat the slurry for forming the first positive electrode active material layer and the slurry for forming the second positive electrode active material layer on the surface of the positive electrode current collector, specifically:
  • the slurry for forming the first positive electrode active material layer and the slurry for forming the second positive electrode active material layer are applied together from point A of the positive electrode current collector, and the first The slurry of the second positive electrode active material layer is close to the positive electrode current collector, and the slurry that forms the first positive electrode active material layer is far away from the positive electrode current collector;
  • the slurry path of a positive electrode active material layer is applied to point E and point B to point C, wherein the area between AE is a single-sided coating area, and the area between EC is a double-sided coating area, and the single-sided coating area is guaranteed
  • the thickness of the first coating layer (between AE), the second coating layer (between EB) and the third coating layer (between BC) in the double-sided coating area are the same;
  • the negative electrode current collector from one end of the negative electrode current collector and along the length of the negative electrode current collector includes a tab area, a single-sided coating area and a double-sided coating in sequence. Covered area
  • no coating layer is provided on both sides of the negative electrode current collector; in the single-sided coating region, a first coating layer is provided on one side of the negative electrode current collector, and the first coating layer includes the above-mentioned negative electrode slurry
  • the negative active material layer formed by the material, the negative active material layer is disposed on the surface of the negative current collector; in the double-sided coating area, the second coating layer is respectively disposed on both sides of the negative current collector, and the second coating
  • the layer includes a negative electrode active material layer formed from the above-mentioned negative electrode slurry, and the negative electrode active material layer is disposed on the surface of the negative electrode current collector;
  • Step 5 Assemble the battery cell: The positive electrode sheet prepared in the first to third steps above, the negative electrode sheet prepared in the fourth step and the separator are wound together to form a core, packaged with aluminum plastic film, baked to remove moisture, and then injected The electrolytic solution can be formed into the electric core by the hot-pressing forming process.
  • Example 1 The other operation steps are the same as in Example 1, the difference is only that the thickness of the first positive electrode active material layer and the second positive electrode active material layer in the single-sided coating area and the double-sided coating area are different, as shown in Table 1.
  • the thickness before “/” represents the thickness of the first positive electrode active material layer
  • the thickness after “/” represents the thickness of the second positive electrode active material layer; taking 5 ⁇ m/75 ⁇ m as an example, the thickness of the second coating layer
  • the thickness of the first positive electrode active material layer was 5 ⁇ m
  • the thickness of the second positive electrode active material layer in the second coating layer was 75 ⁇ m.
  • the positive electrode plates prepared in each embodiment were compacted the same, and assembled into a soft-packed battery cell of model 386283.
  • the energy density was tested by 0.2C/0.2C charging and discharging at 25°C.
  • Each soft-packed battery was made The core is charged at 2.5C/0.7C at 25°C, and the battery is disassembled under different cycles to confirm the single-sided coating area of the negative electrode of the battery and the lithium deposit on the negative electrode surface.
  • the dismantling results, energy density, and charging speed are as follows 2 shown.
  • the battery cell prepared by the method in this application can effectively improve the lithium-ion battery's conventional winding structure negative electrode single-chromatographic lithium problem without reducing the energy density of the battery, and improve the cycle life of the lithium-ion battery. Improve the cycle expansion, and at the same time improve the fast charging performance of the battery.
  • the simple use of negative electrode active materials with better kinetic performance and smaller particle size can effectively improve the problem of lithium precipitation in the single-sided coating area of the negative electrode during long cycles, it greatly reduces its energy density.

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Abstract

一种正极片、制备方法及包含其的锂离子电池，该正极片包括正极集流体，正极集流体包括单面涂覆区域、双面涂覆区域；单面涂覆区域中，正极集流体一侧表面设置第一涂覆层，第一涂覆层包括第一正极活性物质层（1）和第二正极活性物质层（2），第二正极活性物质层（2）设置在正极集流体表面，第一正极活性物质层（1）设置在第二正极活性物质层（2）表面，第一正极活性物质的粒径大于第二正极活性物质的粒径。包含正极片的锂离子电池具有如下效果：可以有效改善常规卷绕结构的锂离子电池负极单面涂覆区域的析锂问题，提高锂离子电池的循环寿命，降低锂离子电池的循环膨胀。不降低电池的快充性能的前提下，提高正极压实密度，增加电芯的能量密度。

Description

一种正极片、制备方法及包含其的锂离子电池
本申请要求于2020年5月8日提交中国专利局、申请号为202010383203.9、申请名称为“一种正极片、制备方法及包含其的锂离子电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请属于锂离子电池技术领域，具体涉及一种正极片、制备方法及包含其的锂离子电池。
背景技术
随着现代化社会的快速发展，便携式电子设备(手机、电脑等)的应用日益广泛。锂离子电池因其具有较长的循环寿命和较高的功率密度被广泛的应用在便携式移动电子设备终端，但随着人们生活节奏的变快，人们对其续航能力和充电速度提出更高的要求，目前看来快充锂离子电池成为消费类锂离子电池主要发展的趋势。快充锂离子电池技术的发展给人们带来便捷的同时也带来了安全问题，锂离子电池在大倍率快速充电条件下长循环时非常容易造成锂离子电池负极析锂，尤其是负极单面涂覆区域更为严重，由此带来锂离子电池循环跳水，膨胀，鼓气等问题，大大降低了锂离子电池的使用寿命。
发明内容
为了改善现有技术的不足，本申请提供了一种正极片、制备方法及包含其的锂离子电池。所述正极片主要用于解决大倍率快速充电制度下长循环过程中卷绕结构的电芯负极单面涂覆区域析锂问题。
本申请的发明人研究发现，现有的卷绕结构的电芯负极单面涂覆区域析锂的根本原因是单面涂覆区域靠近极耳，导致电流密度大，电势较低，负极动力学性能不足，在充电制度不变的前提下解决负极单面涂覆区域析锂的关键在于提高负极的动力学和/或降低正极的动力学性能。然而整个负极动力学 性能的提升必然会导致锂离子电池能量密度的降低，整个正极动力学性能的降低也必然导致锂离子电池快充能力的降低，而本申请通过提供一种具有特定结构的正极片，所述正极片是通过降低卷绕式锂离子电池正极活性物质层的动力学性能，实现在不降低锂离子电池整体快充性能和锂离子电池能量密度的条件下，降低负极单面涂覆区域及整个负极表面的极化，有效改善锂离子电池常规卷绕结构负极单面涂覆区域析锂问题，在不降低锂离子电池整体快充性能和锂离子电池能量密度的前提下提高锂离子电池循环寿命，改善循环膨胀。所述正极片可以在不降低锂离子电池整体快充性能和锂离子电池能量密度的情况下解决大倍率充电制度下长循环过程中卷绕结构的电芯负极单面涂覆区域析锂问题。
本申请目的是通过如下技术方案实现的：
一种卷绕式正极片，具体的为锂离子电池用卷绕式正极片，所述正极片包括正极集流体，正极集流体包括单面涂覆区域和双面涂覆区域；
所述单面涂覆区域中，正极集流体一侧表面设置第一涂覆层，所述第一涂覆层包括第一正极活性物质层和第二正极活性物质层，所述第二正极活性物质层设置在正极集流体表面，所述第一正极活性物质层设置在第二正极活性物质层表面；
所述双面涂覆区域中，正极集流体一侧表面设置第二涂覆层和第三涂覆层，且所述第一涂覆层、第二涂覆层和第三涂覆层依次连接；正极集流体另一侧表面设置第四涂覆层；
所述第二涂覆层包括第一正极活性物质层和第二正极活性物质层，所述第二正极活性物质层设置在正极集流体表面，所述第一正极活性物质层设置在第二正极活性物质层表面；
所述第三涂覆层包括第一正极活性物质层，所述第一正极活性物质层设置在正极集流体表面；
所述第四涂覆层包括第一正极活性物质层和第二正极活性物质层，所述第二正极活性物质层设置在正极集流体表面，所述第一正极活性物质层设置在第二正极活性物质层表面；
所述第一正极活性物质层包括第一正极活性物质，所述第二正极活性物质层包括第二正极活性物质，所述第一正极活性物质的粒径大于所述第二正 极活性物质的粒径。
根据本申请，所述第一正极活性物质的粒径大于形成所述第二正极活性物质的粒径。锂离子在正极活性物质内的扩散路径越短，动力学性能越好，因此这样选择，可以保证所述第二正极活性物质层的动力学性能优于第一正极活性物质层的动力学性能。
根据本申请，所述第二正极活性物质的脱出锂离子速度大于第一正极活性物质的脱出锂离子速度。
本申请中，所述第二正极活性物质层的动力学性能优于第一正极活性物质层的动力学性能。
根据本申请，所述动力学性能是指锂离子的脱嵌速度，脱嵌速度越快，动力学性能越好。影响锂离子的脱嵌速度的因素至少包括下述两种：(1)活性物质的可支持的充电电流大小，可支持的充电电流越大，动力学性能越好；(2)单位时间内脱出的锂离子的量、即脱出锂离子速度，脱出锂离子速度越快，动力学性能越好。
示例性地，所述第二正极活性物质层的锂离子的脱嵌速度大于第一正极活性物质层的锂离子的脱嵌速度。
示例性地，所述第二正极活性物质层的可支持的充电电流大于第一正极活性物质层的可支持的充电电流。
示例性地，所述第二正极活性物质层的脱出锂离子速度大于第一正极活性物质层的脱出锂离子速度。
本申请中，当在动力学性能好的正极片中，引入动力学性能相对差的第一正极活性物质层时，由于其动力学性能变差，导致锂离子的脱嵌速度变慢，即负极表面单位时间内聚集或接受的锂离子的数量变少，因此可以大幅减少负极表面、特别是单面涂覆区域部分的析锂问题。
根据本申请，形成所述第一正极活性物质层的第一正极活性物质的粒径分布为：5μm<D 10<8μm，16μm<D 50<19μm，35μm<D 90<45μm；形成所述第二正极活性物质层的第二正极活性物质的粒径分布为：4μm<D 10<6μm，13μm<D 50<16μm，22μm<D 90<33μm。
根据本申请，所述正极集流体还包括极耳区域，即所述正极集流体包括依次设置的单面涂覆区域、双面涂覆区域和极耳区域；所述极耳区域中，正 极集流体两侧不设置涂覆层。
根据本申请，所述单面涂覆区域、双面涂覆区域和极耳区域依次相连设置，即所述单面涂覆区域、双面涂覆区域和极耳区域中没有空白区域。
根据本申请，所述单面涂覆区域中的第一涂覆层、所述双面涂覆区域中的第二涂覆层和第三涂覆层依次相连设置，即所述单面涂覆区域中的第一涂覆层、所述双面涂覆区域中的第二涂覆层和第三涂覆层中没有空白区域。
本申请中，所述的单面涂覆区域是指的在集流体的两侧中的一侧表面涂覆正极活性物质层。所述的双面涂覆区域是指的在集流体的两侧表面涂覆正极活性物质层。
根据本申请，所述集流体的长度和宽度没有特别的定义，根据需要的电芯的不同选取不同长度、不同宽度的集流体。示例性地，针对386283型号的电池，所述集流体的长度为500-1000mm，例如为885±2mm，所述集流体的宽度为400-900mm，例如为773±2mm。
根据本申请，所述极耳区域的长度、所述单面涂覆区域的长度、所述双面涂覆区域的长度均没有特别的定义，可以根据不同的要求进行设置，例如所述双面涂覆区域的长度大于所述单面涂覆区域的长度，所述双面涂覆区域的长度大于所述极耳区域的长度。还例如，针对386283型号的电池，所述单面涂覆区域的长度为123±2mm。
根据本申请，所述第一涂覆层的长度和所述第三涂覆层的长度没有特别的定义，例如所述第一涂覆层的长度比所述第三涂覆层的长度长8-10mm。还例如所述第三涂覆层的长度与负极片中单面涂覆区域的长度相同或者短1-2mm。
根据本申请，所述极耳区域设置正极极耳，故在该区域内无需设置涂覆层。
根据本申请，所述极耳区域中设置的正极极耳与双面涂覆区域的距离也没有特别的限定，例如为10-100mm；还例如，针对386283型号的电池，所述极耳区域中设置的正极极耳与双面涂覆区域的距离为35.5±0.5mm。
根据本申请，所述单面涂覆区域中，第一涂覆层中的第一正极活性物质层的厚度为5-15μm，例如为5μm、10μm或15μm；第一涂覆层中的第二正极活性物质层的厚度为55-75μm，例如为55μm、60μm、65μm、70μm或 75μm；且所述第一正极活性物质层的厚度和所述第二正极活性物质层的厚度之和为60-80μm。
根据本申请，所述双面涂覆区域中，第二涂覆层中的第一正极活性物质层的厚度为5-15μm，例如为5μm、10μm或15μm；第一涂覆层中的第二正极活性物质层的厚度为55-75μm，例如为55μm、60μm、65μm、70μm或75μm；且所述第一正极活性物质层的厚度和所述第二正极活性物质层的厚度之和为60-80μm。
根据本申请，所述双面涂覆区域中，第三涂覆层中的第一正极活性物质层的厚度为60-80μm，例如为60μm、65μm、70μm、75μm或80μm。
根据本申请，所述双面涂覆区域中，第四涂覆层中的第一正极活性物质层的厚度为5-15μm，例如为5μm、10μm或15μm；第一涂覆层中的第二正极活性物质层的厚度为55-75μm，例如为55μm、60μm、65μm、70μm或75μm；且所述第一正极活性物质层的厚度和所述第二正极活性物质层的厚度之和为60-80μm。
根据本申请，所述双面涂覆区域中，第二涂覆层的厚度、第三涂覆层的厚度和第四涂覆层的厚度相同。
根据本申请，所述正极片中，第一涂覆层的厚度、第二涂覆层的厚度、第三涂覆层的厚度和第四涂覆层的厚度相同。
根据本申请，所述正极集流体还包括空白区域，所述空白区域设置在与双面涂覆区域相连的单面涂覆区域的另一侧，所述空白区域例如是在正极片的生产过程中剪裁而产生的，其用于包住卷绕式电芯的表面，所述空白区域的长度例如可以是35±2mm。
根据本申请，如图1所示，自正极集流体一端且沿正极集流体长度方向所述正极集流体包括依次设置的空白区域、单面涂覆区域、双面涂覆区域和极耳区域；
在正极集流体一侧表面(M面)依次涂覆包括第一正极活性物质层和第二正极活性物质层的第一涂覆层、包括第一正极活性物质层和第二正极活性物质层的第二涂覆层和包括第一正极活性物质层的第三涂覆层；其中，所述第一涂覆层和所述第二涂覆层中，所述第二正极活性物质层涂覆在正极集流体表面，所述第一正极活性物质层涂覆在第二正极活性物质层表面；所述第 三涂覆层中，所述第一正极活性物质层涂覆在正极集流体表面；
在正极集流体一侧表面(N面)涂覆包括第一正极活性物质层和第二正极活性物质层的第四涂覆层，且所述第二正极活性物质层涂覆在正极集流体表面，所述第一正极活性物质层涂覆在第二正极活性物质层表面；且所述第四涂覆层的长度等于所述第二涂覆层和所述第三涂覆层的长度之和，以保证在所述正极片中形成单面涂覆区域(第一涂覆层形成的区域)和双面涂覆区域(第二涂覆层、第三涂覆层和第四涂覆层形成的区域)。
具有上述结构的正极片在制备过程中，M面的制备例如可以是形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体A点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到B点结束，形成第一正极活性物质层的浆料继续涂覆到C点，且确保单面涂覆区域中的第一涂覆层(AE之间)、双面涂覆区域中的第二涂覆层(EB之间)和第三涂覆层(BC之间)的厚度相同。
具有上述结构的正极片在制备过程中，N面的制备例如可以是形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体E点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到D点结束，或者，形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体D点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到E点结束；且C点和D点的连线垂直于正极集流体，在实际制备过程中，C点和D点之间存在0-1mm左右的错位，AC之间的距离大于DE之间的距离，以确保可以在正极片中形成单面涂覆区域和双面涂覆区域。
上述结构的正极片制备完成后，对正极集流体进行剪裁，在与双面涂覆区域相连的单面涂覆区域的另一侧留有空白区域。
根据本申请，所述第一正极活性物质层中包括第一正极活性物质、第一导电剂和第一粘结剂，所述第二正极活性物质层中包括第二正极活性物质、第二导电剂和第二粘结剂。其中，形成所述第一正极活性物质层和第二正极 活性物质层的第一正极活性物质和第二正极活性物质相同或不同、第一导电剂和第二导电剂相同或不同、第一粘结剂和第二粘结剂相同或不同。
根据本申请，所述第一正极活性物质层中各组分的质量百分含量为：
70-99wt％的第一正极活性物质、0.5-15wt％的第一导电剂、0.5-15wt％的第一粘结剂；其中，所述第一正极活性物质的粒径分布为：5μm<D 10<8μm，16μm<D 50<19μm，35μm<D 90<45μm。
优选地，所述第一正极活性物质层中各组分的质量百分含量为：
80-98wt％的第一正极活性物质、1-10wt％的第一导电剂、1-10wt％的第一粘结剂。
根据本申请，所述第二正极活性物质层中各组分的质量百分含量为：
70-99wt％的第二正极活性物质、0.5-15wt％的第二导电剂、0.5-15wt％的第二粘结剂；其中，所述第二正极活性物质的粒径分布为：4μm<D 10<6μm，13μm<D 50<16μm，22μm<D 90<33μm。
优选地，所述第二正极活性物质层中各组分的质量百分含量为：
80-98wt％的第二正极活性物质、1-10wt％的第二导电剂、1-10wt％的第二粘结剂。
其中，所述第一导电剂和第二导电剂相同或不同，彼此独立地选自导电炭黑、乙炔黑、科琴黑、导电石墨、导电碳纤维、碳纳米管、金属粉、碳纤维中的至少一种。
其中，所述第一粘结剂和第二粘结剂相同或不同，彼此独立地选自聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚丙烯酸锂(PAALi)中的至少一种。
其中，所述第一正极活性物质和第二正极活性物质相同或不同，彼此独立地选自钴酸锂、镍钴锰酸锂、锰酸锂、镍锰酸锂、镍钴铝酸锂、磷酸铁锂或富锂锰中的至少一种；优选地，所述第一正极活性物质的粒径分布为：5μm<D 10<8μm，16μm<D 50<19μm，35μm<D 90<45μm；所述第二正极活性物质的粒径分布为：4μm<D 10<6μm，13μm<D 50<16μm，22μm<D 90<33μm；且第一正极活性物质的粒径分布大于第二正极活性物质的粒径分布。
本申请还提供上述正极片的制备方法，所述方法包括如下步骤：
1)分别配制形成第一正极活性物质层的浆料和形成第二正极活性物质层 的浆料；
2)使用双层涂布机，将形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料涂覆在正极集流体的两侧表面，制备得到所述正极片。
根据本申请，步骤1)中，所述形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料的固含量为70wt％～75wt％。
根据本申请，步骤2)中，在正极集流体一侧表面，形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体A点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到B点结束，形成第一正极活性物质层的浆料继续涂覆到C点，且确保单面涂覆区域中的第一涂覆层(AE之间)、双面涂覆区域中的第二涂覆层(EB之间)和第三涂覆层(BC之间)的厚度相同。
根据本申请，步骤2)中，在正极集流体另一侧表面，将形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体E点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到D点结束，或者，形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体D点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到E点结束；且C点和D点的连线垂直于正极集流体，在实际制备过程中，C点和D点之间存在0-1mm左右的错位，AC之间的距离大于DE之间的距离，以确保可以在正极片中形成单面涂覆区域和双面涂覆区域。
本申请还提供一种锂离子电池，所述电池包括上述的正极片。
根据本申请，所述电池还包括负极片和隔膜。
本申请的有益效果：
本申请提供了一种正极片、制备方法及包含其的锂离子电池。包含所述正极片的锂离子电池具有如下效果：
(1)可以有效改善常规卷绕结构的锂离子电池负极单面涂覆区域的析锂 问题，提高锂离子电池的循环寿命，降低锂离子电池的循环膨胀。
(2)不降低电池的快充性能的前提下，提高正极压实密度，增加电芯的能量密度。
附图说明
图1为本申请一个优选方案所述的正极片结构，其中1为第一正极活性物质层，2为第二正极活性物质层。
图2为常规正极片结构。
图3为本申请的一种负极片结构。
具体实施方式
如前所述，使用本申请的正极片的锂离子电池中还包括负极片，所述负极片为卷绕式负极片，具体的是锂离子电池用卷绕式负极片，所述负极片包括负极集流体，负极集流体包括单面涂覆区域和双面涂覆区域；
所述单面涂覆区域中，负极集流体一侧表面设置第一涂覆层，所述第一涂覆层包括负极活性物质层，所述负极活性物质层设置在负极集流体表面；
所述双面涂覆区域中，负极集流体两侧表面分别设置第二涂覆层，且所述第二涂覆层包括负极活性物质层，所述负极活性物质层设置在负极集流体表面。
具体的，负极片的结构如图3所示。
其中，所述单面涂覆区域和双面涂覆区域依次相连设置，即所述单面涂覆区域和双面涂覆区域中没有空白区域。
其中，所述第一涂覆层的厚度和第二涂覆层的厚度相同，均为95-120μm。
其中，所述负极集流体还包括空白区域，所述空白区域设置在与单面涂覆区域相连的双面涂覆区域的另一侧，所述空白区域例如是在负极片的生产过程中为了避免剪裁到负极集流体表面的活性物质层而产生的，所述空白区域的长度例如可以是0.5-2mm，如1mm。
其中，所述负极活性物质层中各组分的质量百分含量为：
70-99wt％的负极活性物质、0.5-15wt％的导电剂、0.5-15wt％的粘结剂。
优选地，所述负极活性物质层中各组分的质量百分含量为：
80-98wt％的负极活性物质、1-10wt％的导电剂、1-10wt％的粘结剂。
其中，所述导电剂选自导电炭黑、乙炔黑、科琴黑、导电石墨、导电碳纤维、碳纳米管、金属粉、碳纤维中的至少一种。
其中，所述粘结剂选自羧甲基纤维素钠、丁苯胶乳、聚四氟乙烯、聚氧化乙烯中的至少一种。
其中，所述负极活性物质选自人造石墨、天然石墨、中间相碳微球、钛酸锂中的至少一种。
上述负极片的制备方法，所述方法包括如下步骤：
1)分别配制形成负极活性物质层的浆料；
2)使用涂布机，将形成负极活性物质层的浆料涂覆在负极集流体的两侧表面，制备得到所述负极片。
其中，步骤1)中，所述形成负极活性物质层的浆料的固含量为40wt％～45wt％。
下文将结合具体实施例对本申请做更进一步的详细说明。应当理解，下列实施例仅为示例性地说明和解释本申请，而不应被解释为对本申请保护范围的限制。凡基于本申请上述内容所实现的技术均涵盖在本申请旨在保护的范围内。
下述实施例中所使用的实验方法如无特殊说明，均为常规方法；下述实施例中所用的试剂、材料等，如无特殊说明，均可从商业途径得到。
在本申请的描述中，需要说明的是，术语“第一”、“第二”、“第三”、“第四”等仅用于描述目的，而并非指示或暗示相对重要性。
下述实施例中制备的正极片是用于386283型号的电池的，其中，极耳区域中设置的正极极耳与单面涂覆区域的距离为35.5±0.5mm，单面涂覆区域的长度为113±2mm，所述集流体的长度为885±2mm，所述集流体的宽度为773±2mm。
实施例1
第一步：制备形成第一正极活性物质层的浆料：将第一正极活性物质(钴酸锂)、第一导电剂(导电炭黑)和第一粘结剂(PVDF)按照97.2：1.5：1.3 的质量比加入到搅拌罐中，加入NMP配制成形成第一正极活性物质层的浆料，正极浆料固含量为70wt％～75wt％；其中，所述第一正极活性物质的粒径分布为：5μm<D 10<8μm，16μm<D 50<19μm，35μm<D 90<45μm；
第二步：制备形成第二正极活性物质层的浆料：将第二正极活性物质(钴酸锂)、第二导电剂(导电炭黑)和第二粘结剂(PVDF)按照97.2：1.5：1.3的质量比加入到搅拌罐中，加入NMP配制成形成第二正极活性物质层的浆料，正极浆料固含量为70wt％～75wt％；其中，所述第二正极活性物质的粒径分布为：4μm<D 10<6μm，13μm<D 50<16μm，22μm<D 90<33μm；
第三步：使用双层涂布机，将形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料涂覆在正极集流体表面，具体地：
如图1所示，在正极集流体一侧表面M，将形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体A点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料途径E点涂覆到B点结束，形成第一正极活性物质层的浆料途径E点和B点涂覆到C点，其中，AE之间为单面涂覆区域，EC之间为双面涂覆区域，且确保单面涂覆区域中的第一涂覆层(AE之间)、双面涂覆区域中的第二涂覆层(EB之间)和第三涂覆层(BC之间)的厚度相同；
在正极集流体另一侧表面N，将形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体E点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到D点结束，或者，形成第一正极活性物质层的浆料和形成第二正极活性物质层的浆料从正极集流体D点一起涂覆，且形成第二正极活性物质层的浆料靠近正极集流体，形成第一正极活性物质层的浆料远离正极集流体；形成第二正极活性物质层的浆料涂覆到E点结束；且C点和D点的连线垂直于正极集流体，在实际制备过程中，C点和D点之间存在0-1mm左右的错位，BC之间的距离等于AE之间的距离，以确保可以在正极片中形成极耳区域、单面涂覆区域和双面涂覆区域；
将制备得到的正极片在120℃温度下烘干；
第四步：制备负极片：以人造石墨为负极活性材料，然后和导电剂(乙 炔黑)和粘结剂(羧甲基纤维素钠)按照97:1.5:1.5的质量比加入到搅拌罐中，加入去离子水进行充分搅拌，过200目的筛网，配成负极浆料，负极浆料固含量为40wt％～45wt％，再利用涂布机将负极浆料涂覆到铝箔上，在100℃温度下烘干，即得到负极片，所得负极片中，自负极集流体一端且沿负极集流体长度方向所述负极集流体包括依次设置的极耳区域、单面涂覆区域和双面涂覆区域；
所述极耳区域中，负极集流体两侧不设置涂覆层；所述单面涂覆区域中，负极集流体一侧设置第一涂覆层，所述第一涂覆层包括上述负极浆料形成的负极活性物质层，所述负极活性物质层设置在负极集流体表面；所述双面涂覆区域中，负极集流体两侧分别设置第二涂覆层，且所述第二涂覆层包括上述负极浆料形成的负极活性物质层，所述负极活性物质层设置在负极集流体表面；
第五步：组装电芯：将上述第一步至第三步制备的正极片与第四步制备的负极片及隔膜一起卷绕形成卷芯，用铝塑膜包装，烘烤去除水分后注入电解液，采用热压化成工艺化成即可得到电芯。
实施例2-3和对比例1-2
其他操作步骤同实施例1，区别仅在于在单面涂覆区域和双面涂覆区域中的第一正极活性物质层和第二正极活性物质层的厚度不同，具体如表1所示。
表1实施例1-3和对比例1-2的正极片的结构参数
Figure PCTCN2021091034-appb-000001
表1中，“/”前面的厚度代表第一正极活性物质层的厚度，“/”后面的 厚度代表第二正极活性物质层的厚度；以5μm/75μm为例，第二涂覆层中的第一正极活性物质层的厚度为5μm，第二涂覆层中的第二正极活性物质层的厚度为75μm。
各实施例制备的正极片压实相同，并将组装成型号为386283的软包电芯，在25℃下进行0.2C/0.2C充放电测试其能量密度，对制成每种的软包电芯在25℃条件下进行2.5C充电/0.7C放电，并在不同循环次数下拆解电池确认电池负极单面涂覆区域及负极表面析锂情况，拆解结果和能量密度、充电速度如下表2所示。
表2各实施例的电池的能量密度及循环过程中负极表面析锂情况、容量保持率和膨胀数据
Figure PCTCN2021091034-appb-000002
表2中，单面涂覆区域轻微析锂:单面涂覆区域的析锂面积小于单面涂覆区域总面积的10％；单面涂覆区域析锂：单面涂覆区域的析锂面积占单面涂覆区域总面积的10％～30％；单面涂覆区域严重析锂：单面涂覆区域的析锂面积大于单面涂覆区域总面积的50％；
负极表面轻微析锂:析锂面积占整个负极表面积的10％以内；负极表面析锂：析锂面积占整个负极表面积的10％～30％；负极表面严重析锂：析锂面积占整个负极表面积的50％以上。
从表2中可以看出，采用本申请中的方法制备的电芯在不降低电池能量密度的条件下有效改善锂离子电池常规卷绕结构负极单层析锂问题，提高锂离子电池循环寿命，改善循环膨胀，同时提高电池的快充性能。单纯使用动力学性能更优粒径小的负极活性物质虽然可以有效改善长循环过程中负极单面涂覆区域析锂的问题，但却大大降低了其能量密度。
以上，对本申请的实施方式进行了说明。但是，本申请不限定于上述实施方式。凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (13)

  1. 一种卷绕式正极片，其中，所述正极片包括正极集流体，正极集流体包括单面涂覆区域和双面涂覆区域；
    所述单面涂覆区域中，正极集流体一侧表面设置第一涂覆层，所述第一涂覆层包括第一正极活性物质层和第二正极活性物质层，所述第二正极活性物质层设置在正极集流体表面，所述第一正极活性物质层设置在第二正极活性物质层表面；
    所述双面涂覆区域中，正极集流体一侧表面设置第二涂覆层和第三涂覆层，且所述第一涂覆层、第二涂覆层和第三涂覆层依次连接；正极集流体另一侧表面设置第四涂覆层；
    所述第二涂覆层包括第一正极活性物质层和第二正极活性物质层，所述第二正极活性物质层设置在正极集流体表面，所述第一正极活性物质层设置在第二正极活性物质层表面；
    所述第三涂覆层包括第一正极活性物质层，所述第一正极活性物质层设置在正极集流体表面；
    所述第四涂覆层包括第一正极活性物质层和第二正极活性物质层，所述第二正极活性物质层设置在正极集流体表面，所述第一正极活性物质层设置在第二正极活性物质层表面；
    所述第一正极活性物质层包括第一正极活性物质，所述第二正极活性物质层包括第二正极活性物质，所述第一正极活性物质的粒径大于所述第二正极活性物质的粒径。
  2. 根据权利要求1所述的正极片，其中，所述第二正极活性物质的脱出锂离子速度大于第一正极活性物质的脱出锂离子速度。
  3. 根据权利要求1或2所述的正极片，其中，形成所述第一正极活性物质层的第一正极活性物质的粒径分布为：5μm<D 10<8μm，16μm<D 50<19μm，35μm<D 90<45μm；形成所述第二正极活性物质层的第二正极活性物质的粒径分布为：4μm<D 10<6μm，13μm<D 50<16μm，22μm<D 90<33μm。
  4. 根据权利要求1-3任一项所述的正极片，其中，所述正极集流体还包括空白区域，所述空白区域设置在与双面涂覆区域相连的单面涂覆区域的另一侧，所述空白区域的长度是35±2mm。
  5. 根据权利要求1-4任一项所述的正极片，其中，所述单面涂覆区域中，第一涂覆层中的第一正极活性物质层的厚度为5-15μm，第一涂覆层中的第二正极活性物质层的厚度为55-75μm，且所述第一正极活性物质层的厚度和所述第二正极活性物质层的厚度之和为60-80μm。
  6. 根据权利要求1-5任一项所述的正极片，其中，所述双面涂覆区域中，第二涂覆层中的第一正极活性物质层的厚度为5-15μm，第一涂覆层中的第二正极活性物质层的厚度为55-75μm，且所述第一正极活性物质层的厚度和所述第二正极活性物质层的厚度之和为60-80μm。
  7. 根据权利要求1-6任一项所述的正极片，其中，所述双面涂覆区域中，第三涂覆层中的第一正极活性物质层的厚度为60-80μm。
  8. 根据权利要求1-7任一项所述的正极片，其中，所述双面涂覆区域中，第四涂覆层中的第一正极活性物质层的厚度为5-15μm，第一涂覆层中的第二正极活性物质层的厚度为55-75μm，且所述第一正极活性物质层的厚度和所述第二正极活性物质层的厚度之和为60-80μm。
  9. 根据权利要求1-8任一项所述的正极片，其中，所述第一正极活性物质层中还包括第一导电剂和第一粘结剂，
    所述第一正极活性物质层中各组分的质量百分含量为：
    70-99wt％的第一正极活性物质、0.5-15wt％的第一导电剂、0.5-15wt％的第一粘结剂；其中，所述第一正极活性物质的粒径分布为：5μm<D 10<8μm，16μm<D 50<19μm，35μm<D 90<45μm。
  10. 根据权利要求9所述的正极片，其中，所述第一正极活性物质层中各组分的质量百分含量为：
    80-98wt％的第一正极活性物质、1-10wt％的第一导电剂、1-10wt％的第一粘结剂。
  11. 根据权利要求1-10任一项所述的正极片，其中，所述第二正极活性物质层中还包括第二导电剂和第二粘结剂；
    所述第二正极活性物质层中各组分的质量百分含量为：
    70-99wt％的第二正极活性物质、0.5-15wt％的第二导电剂、0.5-15wt％的第二粘结剂；其中，所述第二正极活性物质的粒径分布为：4μm<D 10<6μm，13μm<D 50<16μm，22μm<D 90<33μm。
  12. 根据权利要求11所述的正极片，其中，所述第二正极活性物质层中各组分的质量百分含量为：
    80-98wt％的第二正极活性物质、1-10wt％的第二导电剂、1-10wt％的第二粘结剂。
  13. 一种锂离子电池，所述电池包括权利要求1-12任一项所述的正极片。
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