Positive plate, battery and electric equipment

Abstract

The embodiment of the invention provides a positive plate, a battery and electric equipment. The positive plate comprises a positive current collector (1) and a first positive layer (2) located on at least one side surface of the positive current collector (1), the first positive layer (2) comprises a positive active material, and the positive active material comprises a ternary material; the ternary material comprises a solid secondary particles with the particle size of 6-20 [mu] m and b hollow secondary particles with the particle size of 3-6 [mu] m; wherein a and b satisfy 0.1 < = a / b < = 6. The positive electrode active material provided by the invention is relatively high in stability, and the cycle life and the energy density of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, to a positive electrode sheet, a battery, and an electrical device. Background Art

[0002] 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 the lithium-ion battery directly affects the performance of the lithium-ion battery, such as energy density and rate performance.

[0003] In the prior art, the positive electrode active material in the positive electrode sheet is prone to cracking and has low stability, thus affecting the cycle life of the battery. Summary of the Invention

[0004] Embodiments of the present application provide 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, inhibit 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 enables the positive electrode active material in the positive electrode sheet to be more closely packed during the compaction process, which helps to improve the energy density of the battery.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode sheet, which includes a positive electrode current collector (1) and a first positive electrode layer (2) located on at least one surface of the positive electrode current collector (1). The first positive electrode layer (2) includes a positive electrode active material, and the positive electrode active material includes a ternary material; the ternary material includes a solid secondary particles with a particle size of 6 μm to 20 μm and b hollow secondary particles with a particle size of 3 μm to 6 μm;

[0006] Wherein, a and b satisfy 0.1 ≤ a / b ≤ 6.

[0007] In a possible implementation manner, 0.2 ≤ a / b ≤ 1.2.

[0008] In a possible implementation manner, the morphology of the solid secondary particles is spherical-like.

[0009] In a possible implementation manner, the first average particle size of the b hollow secondary particles with a particle size of 3 μm to 6 μm is 3.5 μm to 5.5 μm;

[0010] The second average particle size of the a solid secondary particles with a particle size of 6 μm to 20 μm is 8 μm to 18 μm.

[0011] In a possible implementation manner, the cavity diameter inside the hollow secondary particles is 0.2 μm to 2.3 μm.

[0012] In a possible implementation manner, the molecular formula of the ternary material is LiNi x Mn y Co z M i O 2 ; 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.

[0013] In a possible implementation manner, the mass content of the hollow secondary particles in the first positive electrode layer (2) is 3% - 20%.

[0014] In a possible implementation manner, the positive electrode sheet further includes a second positive electrode layer (3), and the second positive electrode layer (3) is disposed on the surface of the first positive electrode layer (2) on the side facing away from the positive electrode current collector (1); the second positive electrode layer (3) includes solid particles having a single crystal structure.

[0015] In a possible implementation manner, a conductive coating (4) is disposed between the first positive electrode layer (2) and the positive electrode current collector (1)

[0016] In a second aspect, an embodiment of the present application provides a battery, including the positive electrode sheet described in the first aspect.

[0017] In a third aspect, an embodiment of the present application provides an electrical device, including the battery described in the second aspect.

[0018] The positive electrode sheet, battery, and electrical device provided by the embodiments of the present application. The positive electrode sheet includes a positive electrode current collector (1) and a first positive electrode layer (2) located on at least one surface of the positive electrode current collector (1). The first positive electrode layer (2) includes a positive electrode active material. The positive electrode active material includes a ternary material with 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, and the number a of the solid secondary particles and the number b of the hollow secondary particles satisfy 0.1 ≤ a / b ≤ 6. In this way, the ternary material is composed of a plurality of hollow secondary particles and solid secondary particles with appropriate particle sizes and having a secondary structure. The hollow secondary particles are not easily broken when heated, thereby reducing the risk of thermal runaway, buffering volume expansion during charge and discharge, reducing 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, the present application can improve the stability of the positive electrode active material, reduce material degradation in the positive electrode sheet, inhibit 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 enables the positive electrode active material in the positive electrode sheet to be more closely packed during the compaction process, which helps to improve the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a positive electrode sheet provided by an embodiment of the present application;

[0020] Figure 2 It is a schematic structural diagram of another positive electrode sheet provided by an embodiment of the present application;

[0021] Figure 3 It is a schematic structural diagram of another positive electrode sheet provided by an embodiment of the present application;

[0022] Figure 4 It is a particle morphology diagram of a positive electrode active material provided by an embodiment of the present application.

[0023] Description of the reference numerals: 1: Positive electrode current collector; 2: First positive electrode layer; 3: Second positive electrode layer; 4: Conductive coating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] The positive electrode active material includes solid particles and hollow particles for preparing a positive electrode sheet and a battery. Since the positive electrode active material expands in volume during the charge and discharge process of the battery, stress is generated between the particles in the positive electrode active material. The stress generated between the particles can cause individual particles to easily break. If an individual hollow particle breaks, it will cause the entire particle to fail, thereby reducing the stability of the positive electrode active material, resulting in easy structural changes or degradation of the material during the charge and discharge cycle, leading to rapid attenuation of the battery capacity and affecting the cycle life of the battery.

[0026] Based on this, an embodiment of the present application provides a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector (1) and a first positive electrode layer (2) located on at least one surface of the positive electrode current collector (1). The first positive electrode layer (2) includes a positive electrode active material, and the positive electrode active material includes a ternary material; the ternary material includes a solid secondary particles with a particle size of 6 μm to 20 μm and b hollow secondary particles with a particle size of 3 μm to 6 μm.

[0027] Wherein, a and b satisfy 0.1 ≤ a / b ≤ 6.

[0028] Exemplarily, the positive electrode sheet is composed of a positive electrode current collector (1) and a first positive electrode layer (2). The first positive electrode layer (2) is located on at least one surface of the positive electrode current collector (1). For example, the first positive electrode layer (2) can be provided on one surface of the positive electrode current collector (1), or the first positive electrode layer (2) is respectively provided on both surfaces of the positive electrode current collector (1). The first positive electrode layer (2) includes a positive electrode active material.

[0029] In the embodiment of the present invention, a conventional positive electrode current collector (1) in the art can be used. For example, the positive electrode current collector (1) includes aluminum foil.

[0030] The positive electrode active material uses a ternary material. The particles in the ternary material include solid secondary particles and hollow secondary particles. Among them, the solid secondary particles are particles composed of many small ternary material particles, and its interior is solid without a hollow structure. Its morphology can be spherical, sheet-shaped, or polyhedral; the hollow secondary particles are also particles composed of many small ternary material particles, and there is a cavity structure inside.

[0031] The number of solid secondary particles with a particle size of 6 μm to 20 μm in the ternary material is a, and the number of hollow secondary particles with a particle size of 3 μm to 6 μm in the ternary material is b. Among them, the number a and the number b satisfy 0.1 ≤ a / b ≤ 6. For example, a / b can be 0.1, 1, 2, 3, 4, 5, 6, or a range composed of any two of them.

[0032] In the process of preparing the positive electrode sheet of this embodiment of the present invention, by adjusting the particle size of the particles in the ternary material, a solid secondary particles with a particle size of 3 μm to 6 μm are selected, and b hollow secondary particles with a particle size of 6 μm to 20 μm are selected, the regulation of a / b can be achieved.

[0033] Therefore, the positive electrode sheet is composed of a positive electrode 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, and the number ratio between the solid secondary particles with a suitable particle size and the hollow secondary particles with a suitable particle size is appropriately selected. On the one hand, the hollow secondary particles are not easily broken when heated, thereby reducing the risk of thermal runaway, buffering the volume expansion during charge and discharge, reducing the 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, due to the uniformity and mechanical strength of the solid secondary particles, the structural stability of the positive electrode active material is improved; furthermore, improving the stability of the positive electrode active material can reduce the material degradation in the positive electrode sheet, inhibit 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 enables the positive electrode active material in the positive electrode sheet to be more closely packed during the compaction process, which helps to improve the energy density of the battery.

[0034] In a possible implementation manner, 0.2 ≤ a / b ≤ 1.2.

[0035] Exemplarily, when selecting the number ratio a / b between the solid secondary particles with a particle size of 6 μm to 20 μm and the hollow secondary particles with a particle size of 3 μm to 6 μm, the a / b can further satisfy the condition of 0.2 ≤ a / b ≤ 1.2. For example, a / b can be 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or the range composed of any two of them.

[0036] Furthermore, when the number ratio between the solid secondary particles with a suitable particle size and the hollow secondary particles with a suitable particle size is appropriately selected, the battery can have good cell dynamics performance, reduce the internal resistance of the cell, and at the same time improve the compaction density of the positive electrode sheet and the energy density of the battery.

[0037] In a possible implementation manner, the morphology of the solid secondary particles is quasi-spherical.

[0038] Exemplarily, the morphology of the solid secondary particles is quasi-spherical, which is close to a spherical shape as a whole but not strictly a perfect sphere structure. The solid secondary particles are quasi-spherical particles composed of many small primary particles, and their morphology is an ellipsoid, such as a long-axis ellipsoid or a short-axis ellipsoid; alternatively, the morphology of the solid secondary particles is a structure formed by the aggregation of primary particles with a spherical morphology, presenting a quasi-spherical shape as a whole. Quasi-spherical particles can often be packed more closely, thereby increasing the packing density of the positive electrode active material in the positive electrode sheet. This can increase the energy density of the applied battery because more positive electrode active material can be accommodated in the positive electrode sheet under the same volume.

[0039] Exemplarily, the morphology of the hollow secondary particles is irregular, that is, the hollow secondary particles are particles without a definite geometric shape or symmetry. For example, the morphology of the hollow secondary particles is an aggregate or an irregular mass. Irregular hollow secondary particles usually have a larger specific surface area. When applied to the positive electrode active material to prepare a battery, the contact area with the electrolyte can be increased, thereby increasing the rate of the electrochemical reaction, which helps to improve the rate performance of the battery.

[0040] In a possible implementation, the first average particle size of b hollow secondary particles with a particle size of 3 μm to 6 μm is 3.5 μm to 5.5 μm.

[0041] The second average particle size of a solid secondary particles with a particle size of 6 μm to 20 μm is 8 μm to 18 μm.

[0042] Exemplarily, the particle distribution in the ternary material also affects the stability of the ternary material. Therefore, the first average particle size of b hollow secondary particles with a particle size of 3 μm to 6 μm can be set to 3.5 μm to 5.5 μm. For example, it can be 3.5 μm, 4 μm, 5 μm, 5.5 μm or the range composed of any two of them; the second average particle size of a solid secondary particles with a particle size of 6 μm to 20 μm can be set to 8 μm to 18 μm. For example, it can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or the range composed of any two of them.

[0043] Selecting hollow secondary particles and solid secondary particles with a suitable particle size distribution in the ternary material can improve the mechanical stability of the positive electrode active material, reduce the structural damage caused by volume changes during charge and discharge cycles. At the same time, a suitable particle size distribution can ensure good contact between particles, thereby enabling the positive electrode active material in the positive electrode sheet to have good electrical conductivity, specific surface area and reaction activity, improving the rate performance of the battery, and enabling it to charge and discharge quickly at a high current density.

[0044] In a possible implementation, the cavity diameter inside the hollow secondary particles is 0.2 μm to 2.3 μm.

[0045] Exemplarily, for each of all the hollow secondary particles with a particle size of 3 μm to 6 μm, the hollow secondary particle has a cavity structure inside, and the cavity diameter of the cavity structure can be set to 0.2 μm to 2.3 μm. For example, the cavity diameter can be any one of 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.3 μm or a range composed of any two of them. The cavity structure can reduce the overall density of the particles, so that the positive electrode sheet can accommodate more positive electrode active materials under the same mass, thereby improving the energy density of the battery. At the same time, the hollow secondary particles contribute to improving the thermal management performance of the positive electrode active materials because they can provide a better heat diffusion path and reduce the risk of local overheating of the positive electrode sheet.

[0046] In a possible implementation, the molecular formula of the ternary material is LiNi x Mn y Co z M i O 2 ; 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.

[0047] Exemplarily, for the ternary material of the positive electrode active material in the positive electrode sheet, the molecular formula of the ternary material is LiNi x Mn y Co z M i O 2 ; 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. For example, the ternary material can be specifically NCM622, the doping element can be specifically selected as Zr, and i is preferably 0.0085. The chemical stability 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 attenuation during charge and discharge cycles can be reduced.

[0048] In a possible implementation, the mass content of the hollow secondary particles in the first positive electrode layer (2) is 3% to 20%.

[0049] Exemplarily, the first positive electrode layer (2) includes solid secondary particles and hollow secondary particles in the positive electrode active material, and the mass content of the hollow secondary particles in the first positive electrode layer (2) is 3% to 20% based on the mass of the first positive electrode layer (2). For example, the mass content of the hollow secondary particles in the first positive electrode layer (2) is in the range of 3%, 6%, 9%, 12%, 15%, 18%, 20%, or any combination of two thereof. Hollow secondary particles usually have a large specific surface area. Selecting a suitable mass content of the 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.

[0050] In a possible implementation, the first positive electrode layer (2) further includes a positive electrode conductor and a positive electrode binder.

[0051] Exemplarily, the first positive electrode layer (2) includes a positive electrode active material, a positive electrode conductor, and a positive electrode binder. For example, the positive electrode conductor includes at least one of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers. 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, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane.

[0052] 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 effectively transmitted, 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 the charge and discharge cycle.

[0053] In a possible implementation, the positive electrode conductive agent is one or more of carbon black, carbon nanotubes, and graphite microsheets.

[0054] Exemplarily, the positive electrode conductive agent is one or more of carbon black, carbon nanotubes, and graphite microsheets. 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.

[0055] In a possible implementation, the positive electrode sheet further comprises a second positive electrode layer (3); the second positive electrode layer (3) is arranged on a surface of the first positive electrode layer (2) that is away from the positive electrode current collector (1); and the second positive electrode layer (3) comprises solid particles having a single crystal structure.

[0056] Exemplarily, a second positive electrode layer (3) may be provided on the surface of the first positive electrode layer (2), and the second positive electrode layer (3) is disposed on the surface of the first positive electrode layer (2) on the side facing away from the positive electrode current collector (1). Figure 1 The following is a schematic structural diagram of a positive electrode sheet provided by an embodiment of the present application, as Figure 1 shown, the positive electrode sheet includes a positive electrode current collector (1), a first positive electrode layer (2) and a second positive electrode layer (3). The second positive electrode layer (3) may include common positive electrode active materials, such as lithium iron phosphate, lithium cobaltate, lithium manganate, ternary materials, etc. The positive electrode sheet with a multi-layer structure can improve the overall energy density of the battery where the positive electrode sheet is located. For example, different positive electrode active materials can be used in different layers to maximize the energy storage capacity. Or, the multi-layer 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 a high current density.

[0057] In a possible implementation manner, the second positive electrode layer (3) includes solid particles having a single crystal structure.

[0058] Exemplarily, a second positive electrode layer (3) may be provided on the surface of the first positive electrode layer (2), and the positive electrode active material in the second positive electrode layer (3) includes solid particles having 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 system, monoclinic system, orthorhombic system, hexagonal system, triclinic system, and rhombohedral system, so as to improve the structural stability of the positive electrode sheet.

[0059] In a possible implementation manner, a conductive coating (4) is provided between the first positive electrode layer (2) and the positive electrode current collector (1).

[0060] Exemplarily, Figure 2 The following is another schematic structural diagram of a positive electrode sheet provided by an embodiment of the present application, as Figure 2 shown, the positive electrode sheet further includes a conductive coating (4), and the conductive coating (4) may be provided between the first positive electrode layer (2) and the positive electrode current collector (1). For example, the conductive coating (4) is a combination of one or more of carbon black, carbon nanotubes, and graphite microflakes.

[0061] Or, Figure 3 The following is another schematic structural diagram of a positive electrode sheet provided by an embodiment of the present application, as Figure 3 shown, on the basis that the positive electrode sheet includes a positive electrode current collector (1), a first positive electrode layer (2) and a second positive electrode layer (3), a conductive coating (4) may be provided between the first positive electrode layer (2) and the positive electrode current collector (1) to improve the conductivity of the positive electrode sheet.

[0062] In the process of preparing the positive electrode sheet, the regulation of a / b can also be achieved by controlling the true density, particle size, and mass of the hollow secondary particles and solid secondary particles selected in the ternary material. Specifically, when calculating with the particles being spherical, the calculation method for the number is (mass / true density) / volume, where the calculation method for volume is 4 / 3*πr 3 , the radius r 空 of the hollow secondary particle = (the first average particle size of the hollow secondary particle - the cavity diameter inside the hollow secondary particle) / 2, and the radius r 实 of the solid secondary particle = the second average particle size of the solid secondary particle / 2. Therefore, a / b = (((the mass of the solid secondary particles in the first positive electrode layer) / (ρ 实 * 4 / 3*πr 实 3 ))) / (((the mass of the hollow secondary particles in the first positive electrode layer) / (ρ 空 * 4 / 3*πr 空 3 ))); where ρ 实 is the true density of the solid secondary particle, and ρ 空 is the true density of the hollow secondary particle; since the mass content of the solid secondary particles in the first positive electrode layer = the mass of the solid secondary particles in the first positive electrode layer / the total mass of the first positive electrode layer, and the mass content of the hollow secondary particles in the first positive electrode layer = the mass of the hollow secondary particles in the first positive electrode layer / the total mass of the first positive electrode layer, that is, a / b = (((the mass content of the solid secondary particles in the first positive electrode layer) / (ρ 实 * 4 / 3*πr 实 3 ))) / (((the mass content of the 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.

[0063] After obtaining the positive electrode sheet of the present invention, the number a of solid secondary particles with a particle size of 6 μm to 20 μm and the number b of hollow secondary particles with a particle size of 3 μm to 6 μm in the ternary material of the positive electrode sheet can be determined by scanning electron microscopy (SEM).

[0064] Specifically, for the positive electrode sheet prepared based on the positive electrode active material, a part of the positive electrode sheet with a size of 0.5 cm * 0.5 cm is intercepted, magnified 2000 times under a scanning electron microscope, and 50 SEM images are taken. Among them, the cross-sections of the solid secondary particles and hollow secondary particles in each SEM image should be smooth and flat. For each solid secondary particle with a particle diameter of 6 μm to 20 μm in each SEM image, if the particle cross-section appears completely or nearly completely in the image, it is counted as one solid secondary particle. For each hollow secondary particle with a particle diameter of 3 μm to 6 μm in each SEM image, if the particle cross-section appears completely or nearly completely in the image, it is counted as one hollow secondary particle. The number of solid secondary particles with a particle diameter of 6 μm to 20 μm and the number of hollow secondary particles with a particle diameter of 3 μm to 6 μm in each SEM image are obtained respectively. In this way, the total number A of solid secondary particles with a particle diameter of 6 μm to 20 μm and the total number B of hollow secondary particles with a particle diameter of 3 μm to 6 μm in 50 SEM images are statistically counted respectively, and the averages a = A / 50 and b = B / 50 are calculated respectively, obtaining the number a of solid secondary particles with a particle diameter of 6 μm to 20 μm, the number b of hollow secondary particles with a particle diameter of 3 μm to 6 μm, and the number ratio a / b.

[0065] For example, Figure 4 Figure showing the particle morphology of a positive electrode active material provided in an embodiment of the present application. As shown in the SEM image Figure 4 shown, it can be tested that the number a of solid secondary particles with a particle diameter of 6 μm to 20 μm is 36 and the number b of hollow secondary particles with a particle diameter of 3 μm to 6 μm is 22, then a / b is 1.63; among them, for individual particles with significantly too small particle sizes (such as the particle diameter of hollow secondary particles not within the single particle size range of 3 μm to 6 μm, and the particle diameter of solid secondary particles not within the single particle size range of 6 μm to 20 μm) or observed to be significantly crushed (such as the cross-section being not smooth and flat), they can be not counted in the particle number. In this way, by statistically counting the particle numbers in 50 SEM images and calculating the average value, it can be tested that the corresponding numbers a and b of the positive electrode sheet satisfy 0.1 ≤ a / b ≤ 6.

[0066] After obtaining the positive electrode sheet of the present invention, a CP-SEM (Cross Section Polisher-Scanning Electron Microscope) image can be obtained by magnifying 5000 times under CP-SEM. According to the aforementioned methods for testing the number of solid secondary particles and hollow secondary particles, the long side dimensions of 100 solid secondary particles and the long side dimensions of 100 hollow secondary particles are respectively counted. Then, by performing data statistical distribution respectively, the first average particle size of b hollow secondary particles with a particle size of 3 μm to 6 μm and the second average particle size of a solid secondary particles with a particle size of 6 μm to 20 μm can be obtained.

[0067] During specific implementation, the positive electrode sheet can be disassembled from the battery, and various parameters can be obtained by testing in the above manner.

[0068] It is worth supplementing that during the preparation process of the positive electrode sheet provided by the present invention, there may be deviations between the particle number ratio, addition amount, average particle size of each substance added, and the cavity diameter inside the particles, and the corresponding particle number ratio, corresponding addition amount, corresponding average particle size, and the cavity diameter inside the hollow secondary particles tested in the positive electrode sheet disassembled from the battery. However, within the error range, therefore, the particle number ratio, addition amount, average particle size of each substance during the preparation process of the positive electrode sheet, and the cavity diameter inside the particles are basically the same as those of each substance in the first positive electrode layer of the positive electrode sheet.

[0069] The embodiment of the present invention also provides a battery, including the above electrode sheet. This battery has the corresponding advantages as the above electrode sheet, which will not be elaborated here.

[0070] The battery of the embodiment of the present invention can be a lithium-ion battery (such as a lithium-ion power battery), a solar battery, or other new energy storage batteries.

[0071] Generally, a battery includes an electrolyte, an electrode core, and a package for packaging the electrode core. The electrolyte is injected into the electrode core within the package. The electrode core includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. Among them, the electrode core can be a stacked electrode core, that is, the electrode core is formed by laminating a positive electrode sheet, a separator, and a negative electrode sheet.

[0072] In the embodiment of the present invention, the positive electrode sheet is a positive electrode sheet with a ternary material including the aforementioned solid secondary particles and hollow secondary particles.

[0073] The electrolyte in the embodiments of the present invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which specifically may include an organic solvent and an electrolyte salt. The organic solvent may include, for example, one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The lithium salt may include, for example, lithium hexafluorophosphate (LiPF 6 ) etc., but is not limited thereto.

[0074] In the embodiments of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from contacting and short-circuiting. The negative electrode sheet is a mixture of artificial graphite and natural graphite. The particle size of the negative electrode active material is 7 μm - 20 μm. 3) The negative electrode current collector is a copper foil, and the surface of the copper foil has a continuous and dense conductive coating with a thickness of 300 nm - 500 nm. The negative electrode conductive agent is carbon black. The embodiments of the present invention can adopt a conventional separator in the art. For example, the separator includes a ceramic coating + a PE-based membrane ceramic coating, or a polypropylene membrane, but is not limited thereto.

[0075] In the embodiments of the present invention, a conventional encapsulation body (housing) material in the art can be used to encapsulate the battery cell. The battery can be a conventional battery type and structure in the art. For example, the battery can be a soft-packaged lithium-ion battery, and the encapsulation body may include an aluminum-plastic film.

[0076] In the embodiments of the present invention, components such as the positive electrode sheet, the separator, and the negative electrode sheet can be assembled into a battery by a conventional method in the art. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked to obtain a stacked battery cell; then the battery cell is placed in a housing (outer package), and after processes such as liquid injection (i.e., injecting the electrolyte) and encapsulation, the battery is obtained.

[0077] The present invention provides an electrical device including the battery or the battery pack as described above. The electrical device has the corresponding advantages corresponding to the negative electrode sheet as described above, which will not be elaborated herein.

[0078] The present invention is further introduced below through specific embodiments.

[0079] Embodiment 1

[0080] Preparation of Lithium-Ion Battery

[0081] The conductive agent graphite flakes are stirred evenly under the action of a vacuum mixer to obtain a conductive agent slurry, and the conductive agent slurry is evenly coated on one surface of the positive current collector aluminum foil to form a conductive coating. The positive active material, binder polyvinylidene fluoride, and conductive agent graphite flakes used for preparing the first positive electrode layer are mixed according to a mass ratio of 98:1:1, and then N-methylpyrrolidone (NMP) is added and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry. Then, the positive electrode slurry is evenly coated on the surface of the conductive coating to form a first positive electrode layer. After drying in an oven at 100 °C to 130 °C, the same coating process is applied to the other surface of the aluminum foil. Then, through cold pressing and slitting, a positive electrode sheet is obtained. Among them, the positive active material used for preparing the first positive electrode layer includes a ternary material, and the molecular formula of this ternary material is LiNi 0.6 Mn 0.2 C 0.2 O 2 ; in this ternary material, there are a solid secondary particles with a particle size of 6 μm to 20 μm and b hollow secondary particles with a particle size of 3 μm to 6 μm, and a / b is 1.09; the mass content of the solid secondary particles in the first positive electrode layer is 75%, the mass content of the hollow secondary particles in the first positive electrode layer is 20%, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm is 5.5 μm, the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm is 8 μm, and the cavity diameter inside the hollow secondary particles in the first positive electrode layer is 0.2 μm; the morphology of the solid secondary particles is spherical-like.

[0082] The negative active material graphite, thickening agent sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent carbon black are mixed according to a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on a copper foil with a thickness of 8 μm; after the copper foil is air-dried at room temperature, it is transferred to an oven at 120 °C for drying for 1 h, and then through cold pressing and slitting, a negative electrode sheet is obtained.

[0083] The organic solvent is a mixed solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Among them, the mass ratio of EC, EMC, and DEC is 30:30:40. In an argon atmosphere glove box with a water content < 10 ppm, fully dried LiPF 6 is dissolved in the organic solvent, and after mixing evenly, an electrolyte solution is obtained. Among them, the concentration of LiPF 6 is 1 mol / L.

[0084] A 12-μm-thick polypropylene film is selected as the separator.

[0085] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive and negative electrode sheets to play an insulating role. After winding into a square bare battery cell, it is placed into an aluminum-plastic film, then baked at 80°C to remove water, injected with the corresponding electrolyte and sealed. After processes such as standing, hot and cold pressing, formation, jigging, and grading, a lithium-ion battery is obtained.

[0086] Example 2

[0087] The preparation method of the lithium-ion battery in Example 2 is basically the same as that in Example 1. The difference lies in that a positive electrode sheet with a / b 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 for preparation.

[0088] Example 3

[0089] The preparation method of the lithium-ion battery in Example 3 is basically the same as that in Example 1. The difference lies in that a positive electrode sheet with a / b 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 for preparation.

[0090] Example 4

[0091] The preparation method of the lithium-ion battery in Example 4 is basically the same as that in Example 1. The difference lies in that a positive electrode sheet with a / b 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 an inner cavity diameter of 2.3 μm for the hollow secondary particles is used for preparation.

[0092] Example 5

[0093] The preparation method of the lithium-ion battery in Example 5 is basically the same as that in Example 1. The difference lies in that a positive electrode sheet with a / b 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 an inner cavity diameter of 0.46 μm for the hollow secondary particles is used for preparation.

[0094] Example 6

[0095] The preparation method of the lithium-ion battery in Example 6 is basically the same as that in Example 1, except that a cathode sheet with a / b being 1.18, the mass content of solid secondary particles in the first cathode layer being 92%, the mass content of hollow secondary particles in the first cathode layer being 3%, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm being 4.5 μm, the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm being 12 μm, and the cavity diameter inside the hollow secondary particle being 0.45 μm is used for preparation.

[0096] Example 7

[0097] The preparation method of the lithium-ion battery in Example 7 is basically the same as that in Example 1, except that a cathode sheet with a / b being 0.38, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm being 5 μm, the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm being 7 μm, and the cavity diameter inside the hollow secondary particle being 1.73 μm is used for preparation.

[0098] Example 8

[0099] The preparation method of the lithium-ion battery in Example 8 is basically the same as that in Example 1, except that a cathode sheet with a / b being 0.38, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm being 5 μm, the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm being 10 μm, and the cavity diameter inside the hollow secondary particle being 0.33 μm is used for preparation.

[0100] Example 9

[0101] The preparation method of the lithium-ion battery in Example 9 is basically the same as that in Example 1, except that a cathode sheet with a / b being 0.21, the mass content of solid secondary particles in the first cathode layer being 92%, the mass content of hollow secondary particles in the first cathode layer being 3%, the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm being 18 μm, and the cavity diameter inside the hollow secondary particle being 2.1 μm is used for preparation.

[0102] Example 10

[0103] The preparation method of the lithium-ion battery in Example 10 is basically the same as that in Example 1, except that a cathode sheet with a / b being 0.94, the mass content of solid secondary particles in the first cathode layer being 92%, the mass content of hollow secondary particles in the first cathode layer being 3%, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm being 3 μm, and the cavity diameter inside the hollow secondary particle being 0.5 μm is used for preparation.

[0104] Example 11

[0105] 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 a / b being 3.78, the mass content of solid secondary particles in the first positive electrode layer being 93%, the mass content of hollow secondary particles in the first positive electrode layer being 2%, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm being 5.4 μm, and the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm being 12 μm is used for preparation.

[0106] Example 12

[0107] 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 a / b being 0.12, the mass content of solid secondary particles in the first positive electrode layer being 72%, the mass content of hollow secondary particles in the first positive electrode layer being 23%, the first average particle size of each hollow secondary particle with a particle size of 3 μm to 6 μm being 5.4 μm, the second average particle size of each solid secondary particle with a particle size of 6 μm to 20 μm being 9 μm, and the cavity diameter inside the hollow secondary particles being 2.4 μm is used for preparation.

[0108] Example 13

[0109] The preparation method of the lithium-ion battery in Example 13 is basically the same as that in Example 1. The difference is that during the preparation of the positive electrode sheet in Example 13, after forming the first positive electrode layer, the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent graphite flakes for preparing the second positive electrode layer are mixed in a mass ratio of 98:1:1, and then N-methylpyrrolidone (NMP) is added and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on the surface of the first positive electrode layer to form the second positive electrode layer, and then the subsequent battery preparation process is carried out with reference to the preparation process in Example 1; among them, the positive electrode active material for preparing the second positive electrode layer includes a ternary material with the molecular formula LiNi 0.6 Mn 0.2 C 0.2 O 2 and the ternary material in this second positive electrode layer has solid particles with a single crystal structure.

[0110] Comparative Example 1

[0111] 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 the mass content of solid secondary particles in the first positive electrode layer being 0% and the mass content of hollow secondary particles in the first positive electrode layer being 95% is used for preparation.

[0112] Comparative Example 2

[0113] The preparation method of the lithium-ion battery of Comparative Example 2 is basically the same as that of Example 1, except that a positive electrode sheet with a mass content of 95% of solid secondary particles and a mass content of 0% of hollow secondary particles in the first positive electrode layer is used for preparation.

[0114] Comparative Example 3

[0115] The preparation method of the lithium-ion battery of Comparative Example 3 is basically the same as that of Example 1, except that a positive electrode sheet with a / b of 7.2, a mass content of 92% of solid secondary particles in the first positive electrode layer, a mass content of 3% of hollow secondary particles in the first positive electrode layer, 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 particle is used for preparation.

[0116] Comparative Example 4

[0117] The preparation method of the lithium-ion battery of Comparative Example 4 is basically the same as that of Example 1, except that a positive electrode sheet with a / b of 0.03, a mass content of 75% of solid secondary particles in the first positive electrode layer, a mass content of 20% of hollow secondary particles in the first positive electrode layer, 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 particle is used for preparation.

[0118] The performance tests of the positive electrode sheets of each example and comparative example are respectively carried out through the following processes, and the results are shown in Table 1.

[0119] Test Example

[0120] 1. DC internal resistance test of the battery

[0121] The battery is discharged at a constant current of 0.33C (0.6A) to 2.0V at room temperature, charged at a constant current of 0.33C to 50% SOC (charging power 0.9A), and discharged at a constant current of 1.5C (2.7A) for 30s. Record the voltage before and after discharge, and calculate the discharge DCIR (mΩ) = (voltage before discharge - voltage after discharge) / discharge current * 1000, and list this value in Table 1.

[0122] 2. Cycle performance test of the lithium-ion battery

[0123] At 25°C, the lithium-ion battery is charged at a 1C rate and discharged at a 1C rate for a full charge and full discharge cycle test until the capacity of the lithium-ion battery decays to 80% of the initial capacity. Record the number of cycles and list this value in Table 1.

[0124] 3. Compaction density of the positive electrode sheet

[0125] The positive electrode sheet prepared from the positive electrode active material can be cut into small round pieces of a certain size in a certain direction, the weight of the positive electrode active material in the small round pieces per unit area can be measured, the surface density can be calculated, and the thickness of the electrode sheet and the thickness of the current collector of the small round piece can be measured. The compaction density of the positive electrode sheet can be obtained by calculating surface density / (electrode sheet thickness - current collector thickness), and this value is listed in Table 1.

[0126] Table 1

[0127]

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

[0129] 1) Compared with Comparative Examples 1 to 4, in the positive electrode sheets of Examples 1 to 13, ternary materials with solid secondary particles and hollow secondary particles are used in the positive electrode active material, and the number a of solid secondary particles with a particle size of 6 μm to 20 μm and the number b of hollow secondary particles with a particle size of 3 μm to 6 μm in the ternary material satisfy 0.1 ≤ a / b ≤ 6, which can reduce the DC internal resistance of the battery, increase the number of battery cycles, and increase the compaction density of the positive electrode sheet, thereby improving the rate performance of the battery, increasing the cycle life, and increasing the 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 a / b of the number of solid secondary particles with a particle size of 6 μm to 20 μm to the number of hollow secondary particles with a particle size of 3 μm to 6 μm in the positive electrode active material is within a more preferable range of 0.2 to 1.2, which is beneficial to further increasing the number of cycles and further increasing the cycle life of the battery.

[0131] 3) Compared with Examples 11 and 12, in the positive electrode sheets of Examples 1 to 10 and Example 13, batteries are prepared by selecting positive electrode sheets with the mass content of hollow secondary particles in the first positive electrode layer being 3% to 20%, which can further reduce the DC internal resistance of the battery and increase the number of battery cycles, and contribute to improving the rate performance and cycle life of the battery.

[0132] The above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode sheet, characterized in that: 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), the first positive electrode layer (2) comprises a positive electrode active material, the positive electrode active material comprises a ternary material; the ternary material comprises a solid secondary particles with a particle size of 6 μm to 20 μm and b hollow secondary particles with a particle size of 3 μm to 6 μm; Among them, a and b satisfy 0.1≤a / b≤6.

2. The positive electrode sheet according to claim 1, characterized in that: 0.2≤a / b≤1.

2.

3. The positive electrode sheet according to claim 1, characterized in that: The solid secondary particles are spherical in shape.

4. The positive electrode sheet according to claim 1, characterized in that: The first average particle size of the b hollow secondary particles with a particle size of 3 μm to 6 μm is 3.5 μm to 5.5 μm; The second average particle size of the a solid secondary particles having a particle size of 6 μm to 20 μm is 8 μm to 18 μm.

5. The positive electrode sheet according to claim 1, characterized in that: The diameter of the cavity inside the hollow secondary particles is 0.2 μm to 2.3 μm.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: 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 to 5, characterized in that: The mass content of the 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 to 5, characterized in that: The positive electrode sheet further comprises a second positive electrode layer (3), the second positive electrode layer (3) being arranged on a surface of the first positive electrode layer (2) which is away from the positive electrode current collector (1); the second positive electrode layer (3) comprises solid particles having a single crystal structure.

9. The positive electrode sheet according to claim 8, characterized in that: A conductive coating (4) is provided between the first positive electrode layer (2) and the positive electrode current collector (1).

10. A battery, characterized in that: A positive electrode sheet comprising any one of claims 1 to 9.

11. An electrical device, characterized in that: Comprising the battery as claimed in claim 10.

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