Positive electrode sheet, battery, and electric device

Abstract

A positive electrode sheet, a battery, and an electric device. The positive electrode sheet comprises a positive electrode current collector (1), and a first positive electrode layer (2) located on at least one side surface of the positive electrode current collector (1), wherein the first positive electrode layer (2) comprises a positive electrode active material, and the positive electrode active material comprises a ternary material; the ternary material comprises a solid secondary particles having a particle size of 6 µm to 20 µm and b hollow secondary particles having a particle size of 3 µm to 6 µm, wherein a and b satisfy: 0.1≤a / b≤6. The positive electrode active material provided in the present application has high stability, and can improve the cycle life and energy density of batteries.

Description

Positive electrode plates, batteries and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202510121460.8, filed on January 24, 2025, entitled "Positive Electrode Sheet, Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular to a positive electrode, a battery, and an electrical device. Background Technology

[0003] Lithium-ion batteries have been widely used in power batteries, consumer electronics, energy storage and other fields due to their advantages such as high energy density and long cycle life. Among them, the positive electrode active material in the positive electrode sheet of lithium-ion batteries directly affects the energy density, rate capability and other performance of lithium-ion batteries.

[0004] In existing technologies, the positive electrode active material in the positive electrode sheet is prone to cracking and has low stability, which affects the cycle life of the battery. Summary of the Invention

[0005] This application provides a positive electrode sheet, a battery, and an electrical device, which can reduce the generation of particle cracks in the positive electrode active material, improve the stability of the positive electrode active material, reduce material degradation in the positive electrode sheet, suppress side reactions, and maintain the structural integrity of the positive electrode sheet, thereby improving the cycle life of the battery. At the same time, improving the stability of the positive electrode active material allows the positive electrode active material in the positive electrode sheet to be more tightly packed during the compaction process, which helps to improve the energy density of the battery.

[0006] In a first aspect, embodiments of this application provide a positive electrode sheet, the positive electrode sheet comprising a positive current collector (1) and a first positive electrode layer (2) located on at least one side surface of the positive current collector (1), the first positive electrode layer (2) comprising a positive active material, the positive active material comprising a ternary material; the ternary material comprising a solid secondary particles with a particle size of 6μm to 20μm and b hollow secondary particles with a particle size of 3μm to 6μm;

[0007] Among them, a and b satisfy 0.1≤a / b≤6.

[0008] In one possible implementation, 0.2 ≤ a / b ≤ 1.2.

[0009] In one possible implementation, the solid secondary particles have a spherical shape.

[0010] In one possible implementation, the first average particle size of the b hollow secondary particles, which have a particle size of 3 μm to 6 μm, is 3.5 μm to 5.5 μm.

[0011] The second average particle size of the a solid secondary particles with a particle size of 6μm to 20μm is 8μm to 18μm.

[0012] In one possible implementation, the cavity diameter inside the hollow secondary particle is 0.2 μm to 2.3 μm.

[0013] In one possible implementation, the molecular formula of the ternary material is LiNi. x Mn y Co z M i O2; M is selected from at least one of Al, Zr, Ti, B, Sr, W and V, 0.5≤x≤0.9, 0.05≤y≤0.35, 0.05≤z≤0.2, 0≤i≤0.01.

[0014] In one possible implementation, the mass content of hollow secondary particles in the first positive electrode layer (2) is 3% to 20%.

[0015] In one possible implementation, the positive electrode sheet further includes a second positive electrode layer (3), which is disposed on the surface of the first positive electrode layer (2) away from the positive current collector (1); the second positive electrode layer (3) includes solid particles with a single crystal structure.

[0016] In one possible implementation, a conductive coating (4) is provided between the first positive electrode layer (2) and the positive electrode current collector (1).

[0017] Secondly, embodiments of this application provide a battery including the positive electrode sheet described in the first aspect.

[0018] Thirdly, embodiments of this application provide an electrical device including the battery described in the second aspect.

[0019] The positive electrode sheet, battery, and electrical device provided in this application embodiment include a positive electrode current collector (1) and a first positive electrode layer (2) located on at least one side surface of the positive electrode current collector (1). The first positive electrode layer (2) includes a positive electrode active material, which is a ternary material with a particle size of 6μm to 20μm and b hollow secondary particles with a particle size of 3μm to 6μm. The number of solid secondary particles a and the number of hollow secondary particles b satisfy 0.1≤a / b≤6. In this way, the ternary material is composed of a combination of hollow and solid secondary particles with suitable particle size and secondary structure. The hollow secondary particles are not easy to break when heated, thereby reducing the risk of thermal runaway. During charging and discharging, they buffer the volume expansion, reduce the stress between particles, thereby reducing the generation of particle cracks and improving the thermal stability of the positive electrode active material. At the same time, due to the uniformity and mechanical strength of the solid secondary particles, the structural stability of the positive electrode active material can be improved. Therefore, this application can improve the stability of the positive electrode active material, reduce material degradation in the positive electrode sheet, suppress side reactions and maintain the structural integrity of the positive electrode sheet, thereby improving the cycle life of the battery; at the same time, improving the stability of the positive electrode active material in the positive electrode sheet allows the positive electrode active material in the positive electrode sheet to be more tightly packed during the compaction process, which helps to improve the energy density of the battery. Attached Figure Description

[0020] Figure 1 is a schematic diagram of a positive electrode sheet provided in an embodiment of this application;

[0021] Figure 2 is a schematic diagram of another positive electrode sheet provided in an embodiment of this application;

[0022] Figure 3 is a schematic diagram of another positive electrode sheet provided in an embodiment of this application;

[0023] Figure 4 is a particle morphology diagram of a positive electrode active material provided in an embodiment of this application.

[0024] Explanation of reference numerals in the attached figures: 1: Positive current collector; 2: First positive electrode layer; 3: Second positive electrode layer; 4: Conductive coating. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Positive electrode active materials include solid and hollow particles for use in the fabrication of positive electrode sheets and batteries. During battery charging and discharging, the volume of the positive electrode active material expands, creating stress between the particles. This stress can cause individual particles to easily break, and if a single hollow particle breaks, the entire particle fails, reducing the stability of the positive electrode active material. This leads to structural changes or degradation during charge-discharge cycles, resulting in rapid capacity decay and impacting the battery's cycle life.

[0027] Based on this, this application provides a positive electrode sheet, which includes a positive current collector (1) and a first positive electrode layer (2) located on at least one side surface of the positive current collector (1). The first positive electrode layer (2) includes a positive active material, which includes a ternary material. The ternary material includes a solid secondary particles with a particle size of 6μm to 20μm and b hollow secondary particles with a particle size of 3μm to 6μm.

[0028] Among them, a and b satisfy 0.1≤a / b≤6.

[0029] For example, the positive electrode sheet is composed of a positive current collector (1) and a first positive electrode layer (2). The first positive electrode layer (2) is located on at least one side surface of the positive current collector (1). For example, the first positive electrode layer (2) can be provided on one side surface of the positive current collector (1), or the first positive electrode layer (2) can be provided on both surfaces of the positive current collector (1). The first positive electrode layer (2) includes a positive active material.

[0030] The embodiments of this application may employ conventional positive current collectors (1) in the art, for example, the positive current collector (1) may include aluminum foil.

[0031] The positive electrode active material adopts ternary material, and the particle composition of the ternary material includes solid secondary particles and hollow secondary particles. The solid secondary particles are composed of many small ternary material particles, and their interior is solid without hollow structure. Their morphology can be spherical, plate-like, or polyhedral. The hollow secondary particles are also composed of many small ternary material particles, and their interior has a cavity structure.

[0032] The number of solid secondary particles with a particle size of 6μm to 20μm in the ternary material is 'a', and the number of hollow secondary particles with a particle size of 3μm to 6μm in the ternary material is 'b'. The number of particles a and b satisfy 0.1 ≤ a / b ≤ 6. For example, a / b can be a range of 0.1, 1, 2, 3, 4, 5, 6, or any combination of two of these.

[0033] In the process of preparing the positive electrode sheet of this embodiment, the a / b ratio can be controlled by adjusting the particle size of the particles in the ternary material, selecting a solid secondary particles with a particle size of 3μm to 6μm, and selecting b hollow secondary particles with a particle size of 6μm to 20μm.

[0034] Therefore, the positive electrode sheet is composed of a positive current collector (1) and a first positive electrode layer (2). The first positive electrode layer (2) includes a positive electrode active material. The ternary material in the positive electrode active material is a combination of solid secondary particles and hollow secondary particles. The ratio of solid secondary particles with appropriate particle size to hollow secondary particles with appropriate particle size is selected appropriately. On the one hand, hollow secondary particles are less likely to break when heated, thereby reducing the risk of thermal runaway. During charging and discharging, they buffer volume expansion, reduce stress between particles, thereby reducing the generation of particle cracks and improving the thermal stability of the positive electrode active material. On the other hand, the uniformity and mechanical strength of solid secondary particles improve the structural stability of the positive electrode active material. Furthermore, improving the stability of the positive electrode active material can reduce material degradation in the positive electrode sheet, suppress side reactions, and maintain the structural integrity of the positive electrode sheet, thereby improving the cycle life of the battery. At the same time, improving the stability of the positive electrode active material in the positive electrode sheet allows the positive electrode active material in the positive electrode sheet to be more tightly packed during the compaction process, which helps to improve the energy density of the battery.

[0035] In one possible implementation, 0.2 ≤ a / b ≤ 1.2.

[0036] For example, when selecting the ratio a / b between solid secondary particles with a particle size of 6μm to 20μm and hollow secondary particles with a particle size of 3μm to 6μm, the a / b can further satisfy the condition 0.2≤a / b≤1.2. For example, a / b can be a range of 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or any combination thereof.

[0037] Furthermore, by selecting an appropriate ratio between solid secondary particles of suitable size and hollow secondary particles of suitable size, the battery can have good cell dynamics performance, reduce cell internal resistance, and at the same time improve the positive electrode compaction density and increase the battery energy density.

[0038] In one possible implementation, the solid secondary particles have a spherical morphology.

[0039] For example, solid secondary particles have a spherical morphology, approaching a sphere overall but not strictly a perfect sphere. These solid secondary particles are spherical particles composed of many small primary particles, with an ellipsoidal morphology, such as a major-axis ellipsoid or a minor-axis ellipsoid. Alternatively, solid secondary particles can be structures formed by the aggregation of multiple primary particles with small spherical morphologies, exhibiting an overall spherical shape. Spherical particles tend to pack more tightly, thereby increasing the packing density of the positive electrode active material in the cathode sheet. This can increase the energy density of the applied battery because the cathode sheet can accommodate more positive electrode active material in the same volume.

[0040] For example, hollow secondary particles have an irregular morphology, meaning they are particles without a defined geometric shape or symmetry. For instance, they may appear as aggregates or irregular clumps. Irregularly shaped hollow secondary particles typically have a larger specific surface area. When used in cathode active materials to prepare batteries, they can increase the contact area with the electrolyte, thereby improving the rate of electrochemical reactions and contributing to enhanced battery rate performance.

[0041] In one possible implementation, the first average particle size of the b hollow secondary particles, which have a particle size of 3 μm to 6 μm, is 3.5 μm to 5.5 μm.

[0042] The second average particle size of a solid secondary particles with a particle size of 6μm to 20μm is 8μm to 18μm.

[0043] For example, the particle distribution in a ternary material also affects its stability. Therefore, the first average particle size of b hollow secondary particles with a particle size of 3μm to 6μm can be set to 3.5μm to 5.5μm, for example, it can be 3.5μm, 4μm, 5μm, 5.5μm or any combination thereof; the second average particle size of a solid secondary particles with a particle size of 6μm to 20μm can be set to 8μm to 18μm, for example, it can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or any combination thereof.

[0044] Selecting hollow and solid secondary particles with suitable particle size distribution in ternary materials can improve the mechanical stability of the positive electrode active material and reduce structural damage caused by volume changes during charge-discharge cycles. At the same time, a suitable particle size distribution can ensure good contact between particles, thereby giving the positive electrode active material in the positive electrode sheet good conductivity, specific surface area and reactivity, improving the rate performance of the battery and enabling it to charge and discharge rapidly at high current densities.

[0045] In one possible implementation, the cavity diameter inside the hollow secondary particle is 0.2 μm to 2.3 μm.

[0046] For example, for each hollow secondary particle among all hollow secondary particles with a particle size of 3μm to 6μm, the hollow secondary particle has an internal cavity structure. The cavity diameter can be set to 0.2μm to 2.3μm. For example, the cavity diameter can be any one or any combination of two of the following: 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1.0μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2.0μm, and 2.3μm. The cavity structure can reduce the overall particle density, allowing the cathode sheet to accommodate more positive electrode active material with the same mass, thereby increasing the energy density of the battery. At the same time, hollow secondary particles help improve the thermal management performance of the positive electrode active material because they can provide better heat diffusion paths and reduce the risk of local overheating of the cathode sheet.

[0047] In one possible implementation, the molecular formula of the ternary material is LiNi. x Mn y Co z M i O2; M is selected from at least one of Al, Zr, Ti, B, Sr, W and V, 0.5≤x≤0.9, 0.05≤y≤0.35, 0.05≤z≤0.2, 0≤i≤0.01.

[0048] For example, consider a ternary material as the positive electrode active material in a positive electrode sheet, where the molecular formula of the ternary material is LiNi. x Mn y Co z M i O2; M is selected from at least one of Al, Zr, Ti, B, Sr, W, and V, with 0.5≤x≤0.9, 0.05≤y≤0.35, 0.05≤z≤0.2, and 0≤i≤0.01. For example, the ternary material can specifically be NCM622, and the doping element can specifically be Zr, with i preferably being 0.0085. The chemical and structural stability of the ternary material can affect the cycle life of the battery. By optimizing the ratio of nickel, cobalt, manganese, or aluminum, the cycle stability of the positive electrode active material in the positive electrode sheet can be improved, and the capacity decay during charge-discharge cycles can be reduced.

[0049] In one possible implementation, the mass content of hollow secondary particles in the first positive electrode layer (2) is 3% to 20%.

[0050] For example, the first positive electrode layer (2) includes solid secondary particles and hollow secondary particles from the positive electrode active material. Based on the mass of the first positive electrode layer (2), the mass content of the hollow secondary particles in the first positive electrode layer (2) is 3% to 20%. For example, the mass content of the hollow secondary particles in the first positive electrode layer (2) is 3%, 6%, 9%, 12%, 15%, 18%, 3%, 20%, or any combination of two of these. Hollow secondary particles typically have a large specific surface area. Selecting an appropriate mass content of hollow secondary particles can increase the contact area between the prepared positive electrode sheet and the electrolyte, thereby improving the reaction activity and initial capacity.

[0051] In one possible implementation, the first positive electrode layer (2) further includes a positive electrode conductive agent and a positive electrode binder.

[0052] For example, the first positive electrode layer (2) includes a positive electrode active material, and also includes a positive electrode conductive agent and a positive electrode binder. For example, the positive electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber. The positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0053] The main function of the positive electrode conductive agent is to improve the conductivity of the positive electrode sheet. By forming a conductive network between the positive electrode active material particles, the conductive agent ensures that electrons can be transported effectively, thereby improving the rate performance of the battery. The main function of the positive electrode binder is to bond the positive electrode active material particles and the positive electrode conductive agent together and fix them on the positive electrode current collector (1). Good bonding performance can improve the mechanical stability of the positive electrode sheet and reduce particle shedding or electrode structure damage caused by volume changes during charge and discharge cycles.

[0054] In one possible implementation, the positive electrode conductive agent is one or more of carbon black, carbon nanotubes, and graphite flakes.

[0055] For example, the positive electrode conductive agent is one or more of carbon black, carbon nanotubes, and graphite flakes. By selecting suitable conductive agents and binders, and optimizing their dosage and distribution, the overall performance of lithium-ion batteries, including energy density, power density, cycle life, and safety, can be significantly improved.

[0056] In one possible implementation, the positive electrode sheet further includes a second positive electrode layer (3); the second positive electrode layer (3) is disposed on the surface of the first positive electrode layer (2) away from the positive current collector (1); the second positive electrode layer (3) includes solid particles with a single crystal structure.

[0057] For example, a second positive electrode layer (3) may be disposed on the surface of the first positive electrode layer (2). The second positive electrode layer (3) is disposed on the surface of the first positive electrode layer (2) facing away from the positive current collector (1). Figure 1 is a schematic diagram of the structure of a positive electrode sheet provided in an embodiment of this application. As shown in Figure 1, the positive electrode sheet includes a positive current collector (1), a first positive electrode layer (2), and a second positive electrode layer (3). The second positive electrode layer (3) may include commonly used positive electrode active materials, such as lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, ternary materials, etc. A multi-layered positive electrode sheet can improve the overall energy density of the battery in which the positive electrode sheet is located. For example, different positive electrode active materials can be used in different layers to maximize energy storage capacity. Alternatively, the multi-layered structure can be designed to use materials with different conductivity and ion conductivity in different layers, thereby optimizing the charge and discharge performance of the battery at high current density.

[0058] In one possible implementation, the second positive electrode layer (3) comprises solid particles having a single crystal structure.

[0059] For example, a second positive electrode layer (3) may be disposed on the surface of the first positive electrode layer (2). The positive electrode active material in the second positive electrode layer (3) includes solid particles with a single crystal structure. For example, the crystal structure of the solid particles in the second positive electrode layer (3) is at least one of cubic, monoclinic, orthorhombic, hexagonal, triclinic, and rhombohedral crystal systems to improve the structural stability of the positive electrode sheet.

[0060] In one possible implementation, a conductive coating (4) is provided between the first positive electrode layer (2) and the positive electrode current collector (1).

[0061] For example, Figure 2 is a schematic diagram of another positive electrode sheet provided in the embodiment of this application. As shown in Figure 2, the positive electrode sheet also includes a conductive coating (4), which can be disposed between the first positive electrode layer (2) and the positive electrode current collector (1). For example, the conductive coating (4) is one or a combination of carbon black, carbon nanotubes, and graphite microplates.

[0062] Alternatively, Figure 3 is a schematic diagram of another positive electrode structure provided in the embodiment of this application. As shown in Figure 3, a conductive coating (4) can be provided between the first positive electrode layer (2) and the positive electrode current collector (1) to improve the conductivity of the positive electrode.

[0063] In the process of preparing the positive electrode sheet, this application can also control the a / b ratio by controlling the true density, particle size, and mass of the hollow and solid secondary particles selected in the ternary material. Specifically, taking the particles as spherical, the number of particles is calculated as (mass / true density) / volume, where the volume is calculated as 4 / 3*πr. 3 The radius r of the hollow secondary particle 空 = (First average particle size of hollow secondary particles - Diameter of the internal cavity of hollow secondary particles) / 2, where r is the radius of solid secondary particles. 实 = the second average particle size of the solid secondary particles / 2, therefore, a / b = ((mass of the solid secondary particles in the first positive electrode layer) / (ρ 实 *4 / 3*πr 实 3 )) / ((mass of hollow secondary particles in the first positive electrode layer) / (ρ 空 *4 / 3*πr 空 3 )); where ρ 实 ρ is the true density of solid secondary particles. 空 Let a be the true density of the hollow secondary particles; since the mass content of solid secondary particles in the first positive electrode layer = mass of solid secondary particles in the first positive electrode layer / total mass of the first positive electrode layer, and the mass content of hollow secondary particles in the first positive electrode layer = mass of hollow secondary particles in the first positive electrode layer / total mass of the first positive electrode layer, that is, a / b = ((mass content of solid secondary particles in the first positive electrode layer) / (ρ 实 *4 / 3*πr 实 3 )) / ((mass content of hollow secondary particles in the first positive electrode layer / (ρ 空 *4 / 3*πr 空 3 Therefore, a / b can be adjusted by controlling the true density, particle size, and mass of each particle in the first positive electrode layer.

[0064] After obtaining the positive electrode sheet, the number of solid secondary particles with a particle size of 6μm to 20μm and the number of hollow secondary particles with a particle size of 3μm to 6μm in the ternary material of the positive electrode sheet can be determined by scanning electron microscopy (SEM).

[0065] Specifically, based on the positive electrode sheet prepared from the positive electrode active material, a 0.5cm*0.5cm portion of the positive electrode sheet was cut and magnified 2000 times under a scanning electron microscope to obtain 50 SEM images. In each SEM image, the cross-sections of solid and hollow secondary particles should be smooth and flat. For each solid secondary particle with a particle size of 6μm to 20μm, the cross-section of the particle should appear completely or nearly completely in the image, and it should be counted as one solid secondary particle. Similarly, for each hollow secondary particle with a particle size of 3μm to 6μm, the cross-section of the particle should appear completely or nearly completely in the image, and it should be counted as one hollow secondary particle. The number of solid secondary particles with a particle size of 6μm to 20μm and the number of hollow secondary particles with a particle size of 3μm to 6μm in each SEM image were then determined. In this way, the total number A of solid secondary particles with a particle size of 6μm to 20μm and the total number B of hollow secondary particles with a particle size of 3μm to 6μm were counted in 50 SEM images, and the average values ​​a = A / 50 and b = B / 50 were calculated respectively to obtain the number a of solid secondary particles with a particle size of 6μm to 20μm, the number b of hollow secondary particles with a particle size of 3μm to 6μm, and the ratio a / b.

[0066] For example, Figure 4 shows the particle morphology of a positive electrode active material provided in an embodiment of this application. As shown in the SEM image in Figure 4, the number of solid secondary particles with a particle size of 6μm to 20μm (a) is 36, and the number of hollow secondary particles with a particle size of 3μm to 6μm (b) is 22, resulting in a / b = 1.63. Specifically, particles that are significantly too small (e.g., hollow secondary particles whose particle size is not within the range of 3μm to 6μm, or solid secondary particles whose particle size is not within the range of 6μm to 20μm) or that appear to be clearly crushed (e.g., with uneven or rough cut surfaces) can be excluded from the particle count. By counting the number of particles in 50 SEM images in this way and calculating the average, the number of particles (a) and (b) corresponding to the positive electrode sheet can be found to satisfy 0.1 ≤ a / b ≤ 6.

[0067] After obtaining the positive electrode sheet, this application can obtain CP-SEM images by magnifying them 5000 times under a cross-section polisher-scanning electron microscope (CP-SEM). Based on the aforementioned method for testing the number of solid and hollow secondary particles, the long side dimensions of 100 solid secondary particles and 100 hollow secondary particles are counted respectively. Then, the data distribution is statistically analyzed to obtain the first average particle size of b hollow secondary particles with a particle size of 3μm to 6μm and the second average particle size of a solid secondary particles with a particle size of 6μm to 20μm.

[0068] In practice, the positive electrode can be obtained by disassembling the battery and testing it in the manner described above to obtain the parameters.

[0069] It is worth noting that, in the preparation process of the positive electrode sheet provided in this application, the particle number ratio, addition amount, average particle size, and cavity diameter of each added substance may deviate from the corresponding particle number ratio, addition amount, average particle size, and cavity diameter of the hollow secondary particles obtained from the positive electrode sheet obtained after disassembling the battery. However, these deviations are within the error range. Therefore, the particle number ratio, addition amount, average particle size, and cavity diameter of each substance in the preparation process of the positive electrode sheet are basically consistent with the particle number ratio, addition amount, average particle size, and cavity diameter of each substance in the first positive electrode layer of the positive electrode sheet.

[0070] This application also provides a battery including the above-described electrode sheet, which has advantages corresponding to the above-described electrode sheet, and will not be described in detail here.

[0071] The battery in this application embodiment can be a lithium-ion battery (such as a lithium-ion power battery), a solar cell, or other novel energy storage battery.

[0072] Generally, a battery includes an electrolyte, a battery cell, and a package containing the battery cell. The electrolyte is injected into the battery cell within the package. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of a positive electrode, a separator, and a negative electrode stacked together.

[0073] In this embodiment, the positive electrode is a positive electrode having the aforementioned ternary material including solid secondary particles and hollow secondary particles.

[0074] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and lithium salts include lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0075] In this embodiment, the separator is used to separate the positive electrode and the negative electrode to prevent short circuit between them. The negative electrode is a mixture of artificial graphite and natural graphite. The particle size of the negative electrode active material is 7μm-20μm. 3) The negative electrode current collector is copper foil with a continuous and dense conductive coating on its surface, with a thickness of 300nm-500nm. The negative electrode conductive agent is carbon black. In this embodiment, conventional separators in the art can be used. For example, the separator includes a ceramic coating + PE base film ceramic coating or a polypropylene film, but it is not limited to these.

[0076] In this embodiment, the battery cell can be packaged using conventional encapsulation (shell) materials in the art. The battery can be a conventional battery type and structure in the art. For example, the battery can be a soft-pack lithium-ion battery, and the encapsulation can include an aluminum-plastic film.

[0077] The embodiments of this application can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked to obtain a stacked cell; then the cell is placed in a casing (outer packaging), and after liquid injection (i.e., injection of electrolyte) and encapsulation processes, a battery is obtained.

[0078] This application provides an electrical device including a battery or a battery pack as described above. This electrical device has advantages corresponding to the negative electrode plate described above, which will not be elaborated further.

[0079] The present application will be further described below through specific embodiments.

[0080] Example 1

[0081] Preparation of lithium-ion batteries

[0082] Conductive agent graphite sheets are stirred uniformly under vacuum to obtain a conductive agent slurry. This slurry is then uniformly coated onto one surface of the positive electrode current collector aluminum foil to form a conductive coating. The positive electrode active material for preparing the first positive electrode layer, polyvinylidene fluoride (PVDF) binder, and conductive agent graphite sheets are mixed at a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) is then added, and the mixture is stirred uniformly under vacuum to obtain a positive electrode slurry. This slurry is then uniformly coated onto the surface of the conductive coating to form the first positive electrode layer. After drying in an oven at 100℃~130℃, the same coating process is applied to the other surface of the aluminum foil. The positive electrode is then cold-pressed and slit to obtain the positive electrode sheet. The positive electrode active material used to prepare the first positive electrode layer includes a ternary material with the molecular formula LiNi. 0.6 Mn 0.2 C 0.2 O2; The ternary material includes a solid secondary particles with a particle size of 6μm to 20μm and b hollow secondary particles with a particle size of 3μm to 6μm, with an a / b ratio of 1.09; The mass content of solid secondary particles in the first cathode layer is 75%, and the mass content of hollow secondary particles in the first cathode layer is 20%. The first average particle size of each hollow secondary particle with a particle size of 3μm to 6μm is 5.5μm, and the second average particle size of each solid secondary particle with a particle size of 6μm to 20μm is 8μm. The cavity diameter inside the hollow secondary particles in the first cathode layer is 0.2μm. The solid secondary particles have a spherical morphology.

[0083] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent carbon black were mixed in a mass ratio of 97:1:1:1. Deionized water was added, and the negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated on a copper foil with a thickness of 8 μm. After the copper foil was dried at room temperature, it was transferred to a 120℃ oven to dry for 1 hour. Then, it was cold-pressed and slit to obtain the negative electrode sheet.

[0084] The organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the mass ratio of EC, EMC, and DEC is 30:30:40. Thoroughly dried LiPF6 is dissolved in the organic solvent in an argon-atmosphere glove box with a water content of <10 ppm. After thorough mixing, the electrolyte is obtained, wherein the concentration of LiPF6 is 1 mol / L.

[0085] A 12μm thick polypropylene membrane was selected as the separator.

[0086] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, injected with the appropriate electrolyte, and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a lithium-ion battery is obtained.

[0087] Example 2

[0088] The preparation method of the lithium-ion battery in Example 2 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 5.91, a mass content of solid secondary particles in the first positive electrode layer of 92%, a mass content of hollow secondary particles in the first positive electrode layer of 3%, a first average particle size of 5.4 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, and a second average particle size of 9 μm for each solid secondary particle with a particle size of 6 μm to 20 μm is used.

[0089] Example 3

[0090] The preparation method of the lithium-ion battery in Example 3 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.5, a mass content of solid secondary particles in the first positive electrode layer of 90%, a mass content of hollow secondary particles in the first positive electrode layer of 5%, and a second average particle size of 18 μm for each solid secondary particle with a particle size of 6 μm to 20 μm is used.

[0091] Example 4

[0092] The preparation method of the lithium-ion battery in Example 4 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.13, a mass content of solid secondary particles in the first positive electrode layer of 85%, a mass content of hollow secondary particles in the first positive electrode layer of 10%, a second average particle size of 13 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 2.3 μm inside the hollow secondary particles is used.

[0093] Example 5

[0094] The preparation method of the lithium-ion battery in Example 5 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.18, a mass content of solid secondary particles in the first positive electrode layer of 82%, a mass content of hollow secondary particles in the first positive electrode layer of 13%, a first average particle size of 3.5 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, a second average particle size of 10 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 0.46 μm inside the hollow secondary particles is used for preparation.

[0095] Example 6

[0096] The preparation method of the lithium-ion battery in Example 6 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 1.18, a mass content of solid secondary particles in the first positive electrode layer of 92%, a mass content of hollow secondary particles in the first positive electrode layer of 3%, a first average particle size of 4.5 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, a second average particle size of 12 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 0.45 μm inside the hollow secondary particles is used.

[0097] Example 7

[0098] The preparation method of the lithium-ion battery in Example 7 is basically the same as that in Example 1, except that a positive electrode sheet is prepared using hollow secondary particles with an a / b ratio of 0.38 and a particle size of 3μm to 6μm, a first average particle size of 5μm, solid secondary particles with a particle size of 6μm to 20μm and a second average particle size of 7μm, and a cavity diameter of 1.73μm inside the hollow secondary particles.

[0099] Example 8

[0100] The preparation method of the lithium-ion battery in Example 8 is basically the same as that in Example 1, except that a positive electrode sheet is prepared using hollow secondary particles with an a / b ratio of 0.38 and a particle size of 3μm to 6μm, a first average particle size of 5μm, solid secondary particles with a particle size of 6μm to 20μm and a second average particle size of 10μm, and a cavity diameter of 0.33μm inside the hollow secondary particles.

[0101] Example 9

[0102] The preparation method of the lithium-ion battery in Example 9 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.21, a mass content of solid secondary particles in the first positive electrode layer of 92%, a mass content of hollow secondary particles in the first positive electrode layer of 3%, a second average particle size of 18 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 2.1 μm inside the hollow secondary particles is used.

[0103] Example 10

[0104] The preparation method of the lithium-ion battery in Example 10 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.94, a mass content of solid secondary particles in the first positive electrode layer of 92%, a mass content of hollow secondary particles in the first positive electrode layer of 3%, a first average particle size of 3 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, and a cavity diameter of 0.5 μm inside the hollow secondary particles is used.

[0105] Example 11

[0106] The preparation method of the lithium-ion battery in Example 11 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 3.78, a mass content of solid secondary particles in the first positive electrode layer of 93%, a mass content of hollow secondary particles in the first positive electrode layer of 2%, a first average particle size of 5.4 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, and a second average particle size of 12 μm for each solid secondary particle with a particle size of 6 μm to 20 μm is used.

[0107] Example 12

[0108] The preparation method of the lithium-ion battery in Example 12 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.12, a mass content of solid secondary particles in the first positive electrode layer of 72%, a mass content of hollow secondary particles in the first positive electrode layer of 23%, a first average particle size of 5.4 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, a second average particle size of 9 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 2.4 μm inside the hollow secondary particles is used for preparation.

[0109] Example 13

[0110] The preparation method of the lithium-ion battery in Example 13 is basically the same as that in Example 1, except that in the preparation process of the positive electrode sheet in Example 13, after the formation of the first positive electrode layer, the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent graphite sheet used to prepare the second positive electrode layer are mixed at a mass ratio of 98:1:1. Then, N-methylpyrrolidone (NMP) is added and stirred evenly under the action of a vacuum stirrer to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of the first positive electrode layer to form the second positive electrode layer. The subsequent battery preparation process is then carried out in accordance with the preparation process in Example 1. The positive electrode active material used to prepare the second positive electrode layer includes LiNi 0.6 Mn 0.2 C 0.2 The ternary material of O2, wherein the ternary material in the second cathode layer has solid particles with a single crystal structure.

[0111] Comparative Example 1

[0112] The preparation method of the lithium-ion battery in Comparative Example 1 is basically the same as that in Example 1, except that a positive electrode sheet with a solid secondary particle content of 0% and a hollow secondary particle content of 95% in the first positive electrode layer is used.

[0113] Comparative Example 2

[0114] The preparation method of the lithium-ion battery in Comparative Example 2 is basically the same as that in Example 1, except that a positive electrode sheet with a mass content of 95% solid secondary particles and a mass content of 0% hollow secondary particles in the first positive electrode layer is used.

[0115] Comparative Example 3

[0116] The preparation method of the lithium-ion battery in Comparative Example 3 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 7.2, a mass content of solid secondary particles in the first positive electrode layer of 92%, a mass content of hollow secondary particles in the first positive electrode layer of 3%, a first average particle size of 4 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, a second average particle size of 6 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 0.3 μm inside the hollow secondary particles is used.

[0117] Comparative Example 4

[0118] The preparation method of the lithium-ion battery in Comparative Example 4 is basically the same as that in Example 1, except that a positive electrode sheet with an a / b ratio of 0.03, a mass content of solid secondary particles in the first positive electrode layer of 75%, a mass content of hollow secondary particles in the first positive electrode layer of 20%, a first average particle size of 3 μm for each hollow secondary particle with a particle size of 3 μm to 6 μm, a second average particle size of 12 μm for each solid secondary particle with a particle size of 6 μm to 20 μm, and a cavity diameter of 0.5 μm inside the hollow secondary particles is used.

[0119] The performance of the positive electrode sheets of each embodiment and comparative example was tested through the following process, and the results are shown in Table 1.

[0120] Test case

[0121] 1. Battery DC internal resistance test

[0122] The battery was discharged to 2.0V at a constant current of 0.33C (0.6A) at room temperature, and then charged to 50% SOC at a constant current of 0.33C (charging capacity 0.9A). It was then discharged at a constant current of 1.5C (2.7A) for 30 seconds. The voltage before and after discharge was recorded. The discharge DCIR (mΩ) was calculated as (voltage before discharge - voltage after discharge) / discharge current * 1000, and this value is listed in Table 1.

[0123] 2. Cycle performance testing of lithium-ion batteries

[0124] At 25°C, the lithium-ion battery was charged and discharged at a 1C rate for a full charge-discharge cycle test until the capacity of the lithium-ion battery decayed to 80% of the initial capacity. The number of cycles was recorded and the value is listed in Table 1.

[0125] 3. Compacted density of the positive electrode sheet

[0126] The positive electrode sheet prepared from the positive electrode active material can be cut into small circular pieces of a certain size in a certain direction. The weight of the positive electrode active material in the small circular piece per unit area is measured, the areal density is calculated, and the electrode thickness and current collector thickness of the small circular piece are measured. The compaction density of the positive electrode sheet is calculated by the areal density / (electrode thickness - current collector thickness), and the value is listed in Table 1.

[0127] Table 1

[0128] The following conclusions can be drawn from Table 1:

[0129] 1) Compared with Comparative Examples 1 to 4, in the positive electrode sheets of Examples 1 to 13, a ternary material of solid secondary particles and hollow secondary particles is used in the positive electrode active material, and the number a of solid secondary particles with a particle size of 6μm to 20μm and the number b of hollow secondary particles with a particle size of 3μm to 6μm in the ternary material satisfy 0.1≤a / b≤6. This can reduce the DC internal resistance of the battery, increase the cycle number of the battery, and increase the compaction density of the positive electrode sheet, thereby improving the rate performance, cycle life and energy density of the battery.

[0130] 2) Compared with Examples 2, 4, 5, 11, and 12, in the positive electrode sheets of Examples 1, 3, 6, 7, 8, 9, 10, and 13, the ratio of the number of solid secondary particles with a particle size of 6μm to 20μm to the number of hollow secondary particles with a particle size of 3μm to 6μm, a / b, is more preferably in the range of 0.2 to 1.2, which is beneficial to further increase the number of cycles and thus further improve the cycle life of the battery.

[0131] 3) Compared with Examples 11 and 12, in Examples 1 to 10 and Example 13, the positive electrode sheet with a mass content of 3% to 20% of hollow secondary particles in the first positive electrode layer is selected to prepare the battery. This can further reduce the DC internal resistance of the battery and increase the number of cycles, which helps to improve the rate performance and cycle life of the battery.

[0132] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode sheet, wherein, The positive electrode sheet includes a positive current collector (1) and a first positive electrode layer (2) located on at least one side surface of the positive current collector (1). The first positive electrode layer (2) includes a positive active material, which includes a ternary material. The ternary material includes a solid secondary particles with a particle size of 6μm to 20μm and b hollow secondary particles with a particle size of 3μm to 6μm. Among them, a and b satisfy 0.1≤a / b≤6.

2. The positive electrode sheet according to claim 1, wherein 0.2≤a / b≤1.

2.

3. The positive electrode sheet according to claim 1 or 2, wherein The solid secondary particles have a spherical shape.

4. The positive electrode sheet according to any one of claims 1 to 3, wherein The first average particle size of the b hollow secondary particles, which have a particle size of 3μm to 6μm, is 3.5μm to 5.5μm. The second average particle size of the a solid secondary particles with a particle size of 6μm to 20μm is 8μm to 18μm.

5. The positive electrode sheet according to any one of claims 1-4, wherein The cavity diameter inside the hollow secondary particle is 0.2μm to 2.3μm.

6. The positive electrode sheet according to any one of claims 1-5, wherein, The molecular formula of the ternary material is LiNi. x Mn y Co z M i O2; M is selected from at least one of Al, Zr, Ti, B, Sr, W and V, 0.5≤x≤0.9, 0.05≤y≤0.35, 0.05≤z≤0.2, 0≤i≤0.

01.

7. The positive electrode sheet according to any one of claims 1-6, wherein, The mass content of hollow secondary particles in the first positive electrode layer (2) is 3% to 20%.

8. The positive electrode sheet according to any one of claims 1-7, wherein, The positive electrode sheet further includes a second positive electrode layer (3), which is disposed on the surface of the first positive electrode layer (2) away from the positive current collector (1); the second positive electrode layer (3) includes solid particles with a single crystal structure.

9. The positive electrode sheet according to any one of claims 1-8, wherein, A conductive coating (4) is provided between the first positive electrode layer (2) and the positive electrode current collector (1).

10. A battery, wherein, The positive electrode includes any one of claims 1-9.

11. An electrical appliance, wherein, Includes the battery as described in claim 10.

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