Positive plate, preparation method thereof and battery

Abstract

The invention relates to a positive plate, a preparation method thereof and a battery. The positive plate comprises a positive current collector and a positive active layer coating at least one side of the positive current collector, the positive active layer comprises a positive active material, and the positive active material comprises single-crystal particles and / or single-crystal-like secondary particles. The included angle between the (003) crystal face of a plurality of primary crystal grains of the single-crystal particles and / or the single-crystal-like secondary particles and the plane of the positive electrode current collector is 15-75 degrees, and the positive electrode active material meets at least one of the following conditions: the ratio of the intensity of diffraction peaks of the (003) crystal face to the intensity of diffraction peaks of the (104) crystal face in an X-ray diffraction pattern of the positive electrode active material is greater than or equal to 1.5; the half-peak width of a (003) crystal face diffraction peak is smaller than or equal to 0.15 degrees; (003) the texture coefficient gt of the crystal face; and 1.5. According to the scheme provided by the invention, the positive electrode can effectively resist mechanical stress transmitted by volume change of the negative electrode, and particle breakage and pole piece breakage are inhibited, so that the cycle life of the battery is remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a preparation method thereof and a battery. BACKGROUND

[0002] Lithium-ion batteries have become the core energy storage devices for consumer electronics, electric vehicles and large-scale energy storage systems due to their high energy density and long cycle life. To meet the increasing demand for energy density, silicon-based materials (especially silicon-carbon composite materials) are considered as an important development direction for the next generation of anodes due to their extremely high theoretical specific capacity. However, silicon materials will undergo about 300% volume expansion and contraction during lithium intercalation and deintercalation. This inherent property not only challenges the stability of the anode structure, but also has a profound impact on the long-term cycle reliability of the entire battery system.

[0003] In related technologies, to address the volume change problem of silicon-based anodes, the main technical means include nanosizing silicon materials to reduce absolute strain, designing porous or hollow structures to reserve expansion space, developing new elastic binders to buffer volume changes, and building a stable carbon composite framework to limit the expansion of silicon particles. These strategies aim to alleviate the pulverization of the anode material, maintain electrical contact integrity and stabilize the solid electrolyte interface film, thereby improving the cycle performance of silicon-based anodes to some extent.

[0004] However, most of these studies focus on the modification and strengthening of the anode itself, but relatively ignore the indirect mechanical impact of the dramatic volume change of silicon-carbon anodes on other components of the battery, especially the positive electrode. During the cycle process, the periodic and large expansion and contraction of the anode will be transmitted to the positive electrode through the electrolyte and separator, causing a continuous "pull-saw effect" on the positive electrode. This results in a sharp rise in battery internal resistance, rapid capacity decay, and ultimately leads to premature termination of the battery cycle life.

[0005] Therefore, focusing only on the improvement of the anode itself is not enough to solve the failure problem of the entire battery system caused by mechanical interaction, and new solutions need to be sought from a system perspective. SUMMARY

[0006] To solve or partially solve the problems in the related art, the present application provides a positive electrode sheet, a preparation method thereof and a battery. The positive electrode can effectively resist the mechanical stress transmitted by the volume change of the anode, inhibit particle breakage and sheet fracture, and thus significantly improve the cycle life of the battery.

[0007] The first aspect of the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer coated on at least one side of the positive electrode current collector, wherein the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises single crystal particles and / or quasi-single crystal secondary particles, the angle between the (003) crystal plane of the plurality of primary crystal grains of the single crystal particles and / or the quasi-single crystal secondary particles and the plane of the positive electrode current collector is 15°-75°, and the positive electrode active material satisfies at least one of the following conditions: The ratio of the intensity of the diffraction peak of the (003) crystal plane to the intensity of the diffraction peak of the (104) crystal plane in the X-ray diffraction pattern of the positive electrode active material is A, and A≥1.5; The half-peak width of the diffraction peak of the (003) crystal plane in the X-ray diffraction pattern of the positive electrode active material is B, and B≤0.15°; The texture coefficient of the (003) crystal plane of the positive electrode active material is C, and C>1.5.

[0008] As an optional embodiment, the general formula of the single crystal particles and / or quasi-single crystal secondary particles is LiM （1-x） A x O2, wherein M contains one or more of Ni, Co, and Mn; A is at least one magnetic doping element selected from Fe, Cr, Al, Mg, Zr, Ti, Y, W, Mo, Nb, Ta, and rare earth elements; and 0≤x≤0.08.

[0009] As an optional embodiment, the percentage of the atoms of the magnetic doping element to all transition metal sites is 0.1mol%-2mol%.

[0010] As an optional embodiment, the particle size of the single crystal particles and / or quasi-single crystal secondary particles is 8μm-20μm.

[0011] As an optional embodiment, the positive electrode active layer further comprises a conductive agent and a binder.

[0012] As an optional embodiment, the conductive agent comprises a first conductive agent and a second conductive agent, the first conductive agent comprises carbon nanotubes, and the second conductive agent comprises Super P and / or acetylene black; and / or, the binder comprises a first binder and a second binder, the first binder comprises polyvinylidene fluoride, and the second binder comprises a polyacrylate-based elastic binder and / or styrene-butadiene rubber.

[0013] As an optional embodiment, the first conductive agent accounts for 0.5% to 2% of the mass percentage of the positive electrode active layer, and / or, the second conductive agent accounts for 1% to 3% of the mass percentage of the positive electrode active layer, and / or, the first adhesive agent accounts for 1% to 3% of the mass percentage of the positive electrode active layer, and / or, the second adhesive agent accounts for 0.5% to 2.5% of the mass percentage of the positive electrode active layer.

[0014] The second aspect of the present application further provides a preparation method of a positive electrode sheet, comprising: Preparation of a positive electrode slurry; the positive electrode slurry comprises a positive electrode active material, the positive electrode active material comprises single crystal particles and / or single-crystal-like secondary particles, and the positive electrode active material satisfies at least one of the following conditions: The ratio of the intensity of the diffraction peak of the (003) crystal face to the intensity of the diffraction peak of the (104) crystal face in the X-ray diffraction pattern of the positive electrode active material is A, and A≥1.5; The half-peak width of the (003) crystal face diffraction peak in the X-ray diffraction pattern of the positive electrode active material is B, and B≤0.15°; The texture coefficient of the (003) crystal face of the positive electrode active material is C, and C>1.5; Coating the positive electrode slurry on a positive electrode current collector; Before the positive electrode slurry is dried and solidified, an external magnetic field with a preset angle with the plane of the positive electrode current collector is applied, so that the angle between the (003) crystal face of the single crystal particles and / or the plurality of primary crystal grains of the single-crystal-like secondary particles and the plane of the positive electrode current collector is 15° to 75°; Drying and rolling the oriented positive electrode slurry to obtain a positive electrode sheet.

[0015] As an optional embodiment, the preparation method of the positive electrode active material further comprises: A mixed salt solution of nickel, cobalt and manganese is reacted with a precipitating agent and ammonia water to obtain a spherical transition metal hydroxide precursor; The precursor is mixed with a lithium source; The mixed material is subjected to first-stage sintering; The product after the first-stage sintering is subjected to second-stage heat treatment to obtain the positive electrode active material.

[0016] The third aspect of the present application further provides a battery comprising the positive electrode sheet or the positive electrode sheet prepared by the preparation method.

[0017] The technical solution provided by the present application can include the following beneficial results: The application selects single crystal particles and / or quasi-single crystal secondary particles with a (003) crystal face as the dominant one as the positive active material, so that the control of the crystal face orientation by controlling the magnetic field becomes very direct and efficient. The angle between the (003) crystal face of multiple primary grains of the single crystal particles and / or quasi-single crystal secondary particles and the plane of the positive current collector is controlled within 15°-75°. When the stress from the silicon-carbon negative electrode expansion (mainly represented as the tensile / compressive stress in the electrode sheet plane) acts on the particles, the orientation is conducive to converting the harmful stress that causes particle cracking into relatively harmless slip along the (003) crystal face direction, thereby safely dissipating mechanical energy in a controllable micro-deformation and preventing the particle internal grain boundary from cracking (for polycrystalline particles) or the whole from breaking, fundamentally solving the mechanical failure problem of the positive active material in the silicon-carbon system, thereby significantly improving the cycle life of the battery. Not less than 15° ensures that the stress has enough component to drive the crystal face slip, avoiding insufficient slip driving force caused by too small angle; not more than 75° prevents the particle from directly losing stability or peeling under stress caused by too large angle.

[0018] It should be understood that the general description above and the following detailed description are only exemplary and explanatory, and cannot limit the application. DETAILED DESCRIPTION

[0019] The embodiments of the application will be described in more detail below. It should be understood that the application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the application more thorough and complete, and to fully convey the scope of the application to those skilled in the art.

[0020] The terms used in the present application are only for the purpose of describing specific embodiments, and are not intended to limit the application. The singular forms "a", "an" and "the" used in the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein means and includes any or all possible combinations of one or more associated listed items.

[0021] It should be understood that although the terms "first", "second", "third" and the like can be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information without departing from the scope of the present application. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0022] In the related art, in order to cope with the volume change problem of the silicon-based negative electrode, the main technical means include nanometerizing the silicon material to reduce the absolute strain, designing a porous or hollow structure to reserve the expansion space, developing a new type of elastic binder to buffer the volume change, and constructing a stable carbon composite framework to limit the expansion of the silicon particles. These strategies aim to alleviate the pulverization of the negative electrode material, maintain the integrity of the electrical contact and stabilize the solid electrolyte interface film, thereby improving the cycle performance of the silicon-based negative electrode to a certain extent. However, these studies mainly focus on the modification and strengthening of the negative electrode itself, but relatively ignore the indirect mechanical influence of the severe volume change of the silicon-carbon negative electrode on other components of the battery, especially the positive electrode. During the cycle process, the periodic large expansion and contraction of the negative electrode will be transmitted to the positive electrode through the electrolyte and the separator, causing a continuous "pull-saw effect" on the positive electrode. This results in a rapid rise in the internal resistance of the battery, a rapid decay in the capacity, and ultimately leads to the premature termination of the cycle life of the battery. Therefore, only focusing on the improvement of the negative electrode itself is not enough to solve the failure problem of the entire battery system caused by mechanical interaction, and new solutions need to be sought from a system perspective.

[0023] To solve the above problems, the embodiments of the present application provide a positive electrode sheet and a preparation method thereof. The positive electrode can effectively resist the mechanical stress transmitted by the volume change of the negative electrode, inhibit particle breakage and sheet fracture, and thus significantly improve the cycle life of the battery.

[0024] The embodiments of the present application provide a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active layer coated on at least one side of the positive electrode current collector. The positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises single crystal particles and / or single-crystal-like secondary particles, the angle between the (003) crystal face of the plurality of primary crystal grains of the single crystal particles and / or single-crystal-like secondary particles and the plane of the positive electrode current collector is 15°-75°, and the positive electrode active material satisfies at least one of the following conditions: The ratio of the intensity of the diffraction peak of the (003) crystal face to the intensity of the diffraction peak of the (104) crystal face in the X-ray diffraction pattern of the positive electrode active material is A, and A≥1.5; The half-peak width of the (003) crystal face diffraction peak in the X-ray diffraction pattern of the positive electrode active material is B, and B≤0.15°; The texture coefficient of the (003) crystal face of the positive electrode active material is C, and C>1.5.

[0025] In the embodiments of the present application, the single-crystal-like secondary particle can refer to a large particle formed by a large number of primary crystal grains (i.e. single crystal particles) tightly packed along a specific direction (for example, the c-axis direction), which has a common dominant crystallographic orientation inside, so that it exhibits physical properties similar to single crystals on a macroscopic scale. This design is the basis for realizing the overall controllable orientation of the particles.

[0026] The (003) crystal plane of multiple primary grains of single crystal particles and / or quasi-single crystal secondary particles refers to the channel plane of lithium ion layered intercalation and deintercalation.

[0027] In the embodiments of this application, the positive electrode active material satisfies at least one of conditions ①②③: ① The ratio of the intensity of the diffraction peaks of the (003) crystal plane to that of the (104) crystal plane in the X-ray diffraction pattern of the positive electrode active material is A, where A ≥ 1.5. For example, under the test conditions of using a Cu-Kα ray source and a scanning speed of 2° / min, the ratio of the intensity of the diffraction peak of the (003) crystal plane to that of the diffraction peak of the (104) crystal plane in the XRD pattern of the positive electrode active material powder or the electrode sheet composed thereof is A, where A ≥ 1.5. For layered oxides, I(003) / I(104) is a classic indicator for measuring cation mixing and preferred orientation of crystal planes. Usually, this ratio is about 1.0~1.3 for randomly oriented NCM materials. A value significantly greater than 1.5 indicates that there is a significant preferred orientation in the normal direction of the (003) plane.

[0028] ② The full width at half maximum (FWHM) of the (003) crystal plane diffraction peak in the X-ray diffraction pattern of the positive electrode active material is B, where B ≤ 0.15°. For example, under test conditions using a Cu-Kα ray source and a scanning speed of 2° / min, the FWHM of the (003) crystal plane diffraction peak in the X-ray diffraction pattern of the positive electrode active material powder or its constituent electrode sheet is B, where B ≤ 0.15°. The FWHM reflects grain size and crystal integrity. For "quasi-single-crystal" particles with a clearly preferred orientation, the diffraction peaks of their dominant crystal plane are very sharp. This parameter distinguishes them from ordinary polycrystalline materials composed of many randomly oriented small grains.

[0029] ③ The texture coefficient of the (003) crystal plane of the positive electrode active material is C, where C>1.5. For example, by analyzing or calculating the texture coefficient (TC) using a pole figure, the texture coefficient of the (003) crystal plane of the positive electrode active material is C, where C>1.5. This indicates that the positive electrode active material exhibits a clear preferred orientation in the direction of the (003) crystal plane normal, while the texture coefficient is 1 in random orientation.

[0030] When the positive electrode active material satisfies at least one of conditions ①②③, it indicates that the (003) crystal plane of the positive electrode active material is dominant, that is, the large surface area of ​​the plate-like particles is the (003) plane. When the particles are aligned in the slurry under the action of a magnetic field, their macroscopic plane directly represents their microscopic (003) crystal plane. This makes it very direct and efficient to control the crystal plane orientation by controlling the magnetic field. The magnetic field forces the (003) crystal plane to be parallel to the direction of the magnetic field, realizing the basic unity of macroscopic morphology and microscopic crystal orientation.

[0031] The flaky and (003) plane orientation consistent particles can more cooperatively undergo crystal plane slip when subjected to in-plane stress, thereby more effectively releasing stress. If the particle morphology is irregular, even if the crystal orientation is regulated, the complex geometry of the outer surface can cause local stress concentration.

[0032] In the embodiments of the present application, the positive active material can be selected from single-crystal high-nickel ternary materials (such as LiNi 0.8 Co 0.1 Mn 0.1 O2, NCM811) or high-voltage lithium cobaltate (LiCoO2) without or with magnetic doping. The particles can be subjected to an external magnetic field, so that the angle between the (003) crystal plane and the pole piece plane is mainly distributed between about 15° and 75°.

[0033] Exemplarily, the preparation method comprises: after slurry coating, a static magnetic field with a strength of 1.0T and an angle of 15° to 75° with the pole piece plane is applied in the initial drying stage. Due to the magnetic anisotropy of the material (the easy magnetization axis is located in the (003) plane), the particles will rotate under the action of the magnetic field, so that the easy magnetization axis is parallel to the direction of the magnetic field, which inevitably leads to the c-axis (i.e. the normal line of the (003) crystal plane) perpendicular to the direction of the magnetic field. By controlling the angle between the magnetic field and the pole piece, the angle of the c-axis and the (003) crystal plane of the particles relative to the pole piece can be accurately regulated. After the magnetic field is stopped, the particle orientation is locked by drying and solidification, and finally the angle between the (003) crystal plane of most particles and the pole piece plane is precisely controlled in the range of, for example, 15° to 75°.

[0034] The embodiments of the present application realize efficient, accurate and repeatable macroscopic regulation of the particle crystal plane orientation by controlling the angle between the (003) crystal plane of the single-crystal particles and / or the plurality of primary crystal grains of the single-crystal-like secondary particles and the positive electrode current collector plane to be 15° to 75°, and the oriented electrode has optimal stress release resistance.

[0035] Therefore, the embodiments of the present application select single crystal particles and / or quasi-single crystal secondary particles with a (003) crystal plane as the positive active material, so that the control of the crystal plane orientation by controlling the magnetic field becomes very direct and efficient. By controlling the angle between the (003) crystal plane of the plurality of primary grains of the single crystal particles and / or quasi-single crystal secondary particles and the plane of the positive current collector to be within 15°-75°, when the stress (mainly represented as tensile / compressive stress in the surface of the electrode sheet) from the expansion of the silicon-carbon negative electrode acts on the particles, the orientation is beneficial to convert the harmful stress causing the particle to break into a relatively harmless slip along the (003) crystal plane direction, thereby safely dissipating mechanical energy with controllable micro-deformation, preventing the particle internal grain boundary from cracking (for polycrystalline particles) or breaking as a whole, fundamentally solving the mechanical failure problem of the positive active material in the silicon-carbon system, thereby significantly improving the cycle life of the battery. The angle is not less than 15° to ensure that the stress has enough component to drive the crystal plane slip, and the angle is not greater than 75° to prevent the particle from directly losing stability or peeling under stress due to the angle being too large.

[0036] As an optional embodiment, the general formula of the single crystal particles and / or quasi-single crystal secondary particles is LiM （1-x） A x O2, wherein M contains one or more of Ni, Co, and Mn; A is at least one magnetic doping element selected from Fe, Cr, Al, Mg, Zr, Ti, Y, W, Mo, Nb, Ta, and rare earth elements; 0≤x≤0.08 When X=0, the magnetic doping element is not doped, and when X>0, the magnetic doping element is doped.

[0037] When X=0, the general formula of the single crystal particles and / or quasi-single crystal secondary particles is LiMO2, wherein M contains one or more of Ni, Co, and Mn. The single crystal particles and / or quasi-single crystal secondary particles can be selected from at least one of high-nickel layered oxide materials, high-voltage lithium cobaltate, high-voltage / high-capacity manganese-based lithium-rich manganese-based materials, and lithium nickel manganese oxide spinel materials.

[0038] When X>0, the general formula of the single crystal particles and / or quasi-single crystal secondary particles is LiM （1-x） A xO2, wherein M comprises one or more of Ni, Co, Mn; A is at least one magnetic doping element selected from Fe, Cr, Al, Mg, Zr, Ti, Y, W, Mo, Nb, Ta, and rare earth elements, 0 < x < 0.08; the rare earth elements can include rare earth elements other than La (such as Nd, Ce, Pr, Sm, etc.). The embodiments of the present application further magnetically design the positive electrode active material particles. Since conventional layered oxide materials (NCM, NCA, LCO) are mostly diamagnetic or weak paramagnetic, the torque generated in the magnetic field is very small, and it is difficult to achieve effective and batch-oriented arrangement in viscous slurry. By doping magnetic elements, the response ability of the particles to the external magnetic field can be significantly enhanced, providing a material basis for realizing high-precision and high-efficiency magnetic field directional arrangement.

[0039] The embodiments of the present application specifically set the crystal structure general formula of the magnetic doping material. Among them, A is a doping element itself with unpaired electrons, thereby introducing ferromagnetism or strong paramagnetism. For example, when A is Fe 3+ (high spin, 5 unpaired d electrons), Co 2+ or some rare earth ions (such as Nd 3+ ), the local magnetic moment can be effectively introduced. The doping amount x < 0.02 ensures that the doping is trace amount, which can give the main material sufficient magnetism without significantly changing the electrochemical performance (such as specific capacity, working voltage) of the main material.

[0040] Exemplarily, the positive electrode active material is a magnetic-doped single-crystal-like secondary particle. Specifically, it can be: Material 1: high-nickel NCM doped with 1 mol% Fe (such as Li(Ni 0.83 Co 0.12 Mn 0.05 ) 0.99 Fe 0.01 O2).

[0041] Material 2: high-voltage lithium cobaltate doped with 0.5 mol% Nd (neodymium).

[0042] As a preferred embodiment, the percentage of atoms of the magnetic element doping all transition metal sites is 0.1 mol% to 2 mol%.

[0043] All transition metal sites in the embodiments of the present application refer to all elements occupying transition metal sites in the general formula LiM （1-x） A x O2 (i.e., the sum of M and A).

[0044] The application further sets the concentration range of the atoms of the doped magnetic element. The concentration of the atoms of the doped magnetic element is not less than 0.1 mol%, which can ensure that the number of introduced magnetic centers is sufficient to produce a collective effect, so that the entire particle obtains an effective magnetic moment in the magnetic field that is sufficient to overcome the viscous resistance of the slurry, and the orientation is realized. The concentration of the atoms of the doped magnetic element is not greater than 2 mol%, which can avoid excessive doping from causing the main lattice to be excessively distorted, thereby triggering negative effects such as material structure instability, electronic / ionic conductivity reduction, or introduction of electrochemically active impurities.

[0045] In the application, the percentage of the atoms of the doped magnetic element in all transition metal sites can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, or any value within the above defined range, which is not limited in the application.

[0046] As an optional embodiment, the particle size of the single crystal particles and / or quasi-single crystal secondary particles is 8 μm to 20 μm.

[0047] In the application, the particle size of the single crystal particles and / or quasi-single crystal secondary particles can refer to D50, which is the median particle size or the cumulative distribution median. It indicates that in a powder sample, the particle size value corresponding to the cumulative volume (or mass) reaching 50% of the total sample.

[0048] In the application, the particle size of the single crystal particles and / or quasi-single crystal secondary particles is not less than 8 μm, which can ensure that the particles have sufficient mass to produce effective rotational torque in the magnetic field or flow field, and help to reduce the specific surface area and reduce side reactions. The particle size of the single crystal particles and / or quasi-single crystal secondary particles is not greater than 20 μm, which can prevent the particle size from being too large to cause the lithium ion solid-phase diffusion path to be too long, affecting the rate performance; at the same time, it can prevent the particles from being too large to be more easily peeled off from the current collector under the bending or stress of the electrode.

[0049] The application sets the particle size range of the single crystal particles and / or quasi-single crystal secondary particles to be 8 μm to 20 μm, which can meet the demand for high energy density and ensure good kinetics and structural stability.

[0050] In the application, the particle size range of the single crystal particles and / or quasi-single crystal secondary particles can be 8 μm, 10 μm, 15 μm, 20 μm, or any value within the above defined range, which is not limited in the application.

[0051] As an optional embodiment, the positive electrode active layer further includes a conductive agent and a binder.

[0052] As a preferred embodiment, the conductive agent includes a first conductive agent and a second conductive agent, the first conductive agent includes carbon nanotubes, and the second conductive agent includes Super P and / or acetylene black.

[0053] The present application adopts a composite conductive agent, wherein the first conductive agent (carbon nanotube) acts as a "high aspect ratio conductive agent", and its fibrous structure can build long-range and firm conductive bridges between active particles. More importantly, the high strength and toughness of the carbon nanotube enable it to play a role similar to that of fibers in fiber-reinforced composites, bridging micro-cracks and inhibiting the initiation and propagation of cracks.

[0054] The second conductive agent (Super P / acetylene black) acts as an elastic spherical conductive agent, and its nanoscale spherical particles can provide a large number of point contacts and fill gaps. Under local stress, these soft carbon black particles can elastically deform, acting as a micro-cushion and cooperating with the carbon nanotube to build a stable and elastic three-dimensional conductive network.

[0055] As a preferred embodiment, the binder includes a first binder and a second binder, the first binder includes polyvinylidene fluoride, and the second binder includes a polyacrylate-based elastic binder and / or styrene-butadiene rubber.

[0056] The present application adopts a composite binder, and the first binder (PVDF) provides a basic and strong adhesive strength and excellent adhesion to the aluminum current collector, ensuring the basic integrity of the electrode coating.

[0057] The second binder (polyacrylate-based elastic binder / styrene-butadiene rubber) acts as an elastic component, and its molecular chain can form a physical entanglement or interpenetrating network structure with PVDF. Under cyclic stress, the elastic component can undergo large deformation, effectively absorbing and dissipating strain energy, and preventing stress concentration from causing adhesive failure or coating cracking.

[0058] As a preferred embodiment, the first conductive agent accounts for 0.5% to 2% of the mass percentage of the positive electrode active layer.

[0059] In the present application, the first conductive agent (carbon nanotube) accounts for 0.5% to 2% of the mass percentage of the positive electrode active layer, which can ensure the formation of an effective long-range conductive network and enhance the network; at the same time, it can prevent excessive slurry dispersion difficulties, viscosity surge or reduction of active material ratio.

[0060] In the present application, the first conductive agent accounts for 0.5%, 1%, 2% or any value within the above range of the mass percentage of the positive electrode active layer, and the present application does not limit it.

[0061] As a preferred embodiment, the second conductive agent accounts for 1% to 3% of the mass percentage of the positive electrode active layer. In the embodiment of the present application, the second conductive agent (spherical carbon black) accounts for 1% to 3% of the mass percentage of the positive electrode active layer, which can ensure sufficient point contact and pore filling; at the same time, it can avoid excessive filling to affect ion transmission or reduce the effective concentration of the binder.

[0062] In the embodiment of the present application, the second conductive agent can account for 1%, 2%, 3% or any value within the above limited range of the mass percentage of the positive electrode active layer, which is not limited in the present application.

[0063] As a preferred embodiment, the first binder accounts for 1% to 3% of the mass percentage of the positive electrode active layer. In the embodiment of the present application, the first binder (PVDF) accounts for 1% to 3% of the mass percentage of the positive electrode active layer, which can provide the necessary matrix strength; at the same time, it can control the cost and prevent the excessive insulating layer from affecting the conductivity.

[0064] In the embodiment of the present application, the first binder can account for 1%, 2%, 3% or any value within the above limited range of the mass percentage of the positive electrode active layer, which is not limited in the present application.

[0065] As a preferred embodiment, the second binder accounts for 0.5% to 2.5% of the mass percentage of the positive electrode active layer.

[0066] In the embodiment of the present application, the second binder (elastomer) accounts for 0.5% to 2.5% of the mass percentage of the positive electrode active layer, which can ensure the formation of an effective energy dissipation phase; at the same time, it can prevent excessive amount from causing the overall modulus of the electrode to be too low or compatibility problems with PVDF.

[0067] In the embodiment of the present application, the second binder can account for 0.5%, 1%, 2% or any value within the above limited range of the mass percentage of the positive electrode active layer, which is not limited in the present application.

[0068] Corresponding to the foregoing application function implementation method embodiment, the present application also provides a preparation method of a positive electrode sheet and corresponding embodiments.

[0069] The embodiment of the present application also provides a preparation method of a positive electrode sheet, which comprises: S10, preparing a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material, the positive electrode active material comprising single crystal particles and / or single crystal-like secondary particles, and the positive electrode active material satisfying at least one of the following conditions: The ratio of the intensity of the diffraction peak of the (003) crystal face to the intensity of the diffraction peak of the (104) crystal face in the X-ray diffraction spectrum of the positive electrode active material is A, and A≥1.5; The half-peak width of the (003) crystal face diffraction peak in the X-ray diffraction spectrum of the positive electrode active material is B, and B≤0.15°; The texture coefficient of the (003) crystal plane of the positive electrode active material is C, and C>1.5.

[0070] S20, coating the positive electrode slurry on the positive electrode current collector.

[0071] S30, before the positive electrode slurry is dried and solidified, an external magnetic field with a preset angle with the plane of the positive electrode current collector is applied, so that the angle between the (003) crystal plane of the single crystal particle and / or the plurality of primary crystal grains of the quasi-single crystal secondary particle and the plane of the positive electrode current collector is 15°-75°.

[0072] S40, drying and rolling the oriented positive electrode slurry to obtain a positive electrode sheet.

[0073] The embodiment of the present application applies an external magnetic field after the slurry is coated and before it is dried and solidified; wherein the direction of the external magnetic field is set at a preset angle with the plane of the positive electrode current collector, so as to promote the rotation and orientation of the single crystal particles and / or quasi-single crystal secondary particles in the slurry, so that the angle between the (003) crystal plane of the plurality of primary crystal grains constituting the particles and the plane of the positive electrode current collector is controlled within the range of 15°-75°. Wherein, the key time window for applying the magnetic field is after coating and before drying and solidification. At this time, the slurry still maintains fluidity, and the particles can freely rotate under the action of the magnetic moment; at the same time, the solvent has not yet completely evaporated, and the slurry system has sufficient deformability to respond to the rotation of the particles.

[0074] The embodiment of the present application converts the inherent magnetic properties of the material into the macroscopic structural advantage (specific crystal plane orientation) of the electrode through a controllable external field process. By adjusting the magnetic field strength, direction and slurry rheological state, positive electrode sheets with specific stress-orientation resistance can be stably and repeatedly produced in batches, solving the performance dispersion problem caused by random orientation. The magnetic field application device can be integrated between the existing coating-drying equipment, without the need to completely change the production line, and the process window is clear (viscosity, magnetic field strength, timing), with good prospects for large-scale production. This method is not passive to enhance the strength of the electrode, but actively designs the arrangement of the particles, so that they have the ability to dissipate stress through crystal plane slip from the source, improving the durability of the electrode in the silicon-carbon system.

[0075] As an optional embodiment, the strength of the magnetic field is 0.5T-2T.

[0076] The embodiment of the present application sets the strength of the magnetic field to be 0.5T-2T: The magnetic field strength is not less than 0.5T, which provides a magnetic moment sufficient to overcome the viscous resistance of the slurry and drive the rotation of the particles; the magnetic field strength is not greater than 2T, which ensures the orientation effect while taking into account the equipment cost and process safety.

[0077] As an optional embodiment, the viscosity of the slurry in step S1 is in the range of 3000 mPa·s~8000 mPa·s.

[0078] Setting the viscosity of the slurry to be no less than 3000 mPa·s can ensure that the slurry has sufficient structural viscosity to "fix" the particles in the subsequent magnetic field orientation step, preventing the particles from randomly turning again due to Brownian motion or gravity after orientation is completed, thereby maintaining the stability of the orientation. At the same time, the appropriate viscosity is also conducive to obtaining a uniform coating.

[0079] Setting the viscosity of the slurry to be no more than 8000 mPa·s can prevent the slurry from having too high a viscosity, causing the particles to experience too much viscous resistance when rotating in the magnetic field, making it difficult to complete effective orientation within a given magnetic field strength and process time, and even affecting the uniformity of the coating.

[0080] As an optional embodiment, the method for preparing the positive active material comprises: S11, reacting a mixed salt solution of nickel, cobalt and manganese with a precipitating agent and ammonia water to prepare a spherical transition metal hydroxide precursor.

[0081] The embodiments of the present application use a co-precipitation method to synthesize the precursor, which can prepare a spherical transition metal hydroxide (Ni 0.8 Co 0.1 Mn 0.1 )(OH)2precursor with uniform chemical composition and concentrated particle size distribution.

[0082] In the embodiments of the present application, the salt solution can be prepared according to the target ratio of nickel, cobalt and manganese (such as 8:1:1) to prepare a mixed aqueous solution of its sulfate or nitrate with a concentration of 1.5 mol / L~2.5 mol / L. The precipitating agent can be a sodium hydroxide NaOH solution with a certain concentration. The complexing agent can be an ammonia water solution with a certain concentration. Among them, ammonia water can form a complex with metal ions to control the precipitation rate and ensure uniform composition.

[0083] The co-precipitation reaction can be carried out in a continuous stirred tank reactor (CSTR). The conditions of the co-precipitation reaction can be: temperature of 50℃~60℃, pH value of 10.5~11.5 (which can be controlled by automatically adding NaOH and ammonia water), stirring speed of 300rpm~500rpm, to ensure sufficient mixing and mass transfer. The reaction time can be tens of hours to obtain the required D50 (for example ~10μm) particles.

[0084] Exemplarily, the salt solution, the base solution and the ammonia water are simultaneously and continuously pumped into a reaction kettle, and the metal hydroxide is slowly and uniformly precipitated out to grow into spherical secondary particles at a constant temperature and pH. The obtained slurry is filtered and washed to remove residual sodium ions and sulfate ions. The precursor powder is obtained by drying at 100-120℃ for 10-15 hours.

[0085] S21, mixing the precursor with a lithium source.

[0086] The lithium source in the embodiments of the present application can be lithium hydroxide or lithium carbonate. For high-nickel materials, LiOH is more commonly used.

[0087] The molar ratio of lithium to transition metal can be slightly higher than the stoichiometric ratio, for example, 1.02-1.08, to compensate for lithium evaporation at high temperatures. And it can be ensured that the lithium source and the precursor are fully and uniformly mixed by high-speed dry mixing or wet ball milling.

[0088] S31, the mixed material is subjected to first-stage sintering.

[0089] The first-stage sintering can make the precursor react with the lithium source to generate a layered oxide and control the grain growth morphology, so that the (003) plane dominates.

[0090] The conditions of the first-stage sintering can be as follows: The temperature is 750-850℃. If the temperature is too low, the reaction will not be complete, and if the temperature is too high, it will lead to excessive evaporation of lithium and excessive growth of grains.

[0091] Pure oxygen atmosphere, which helps to oxidize Ni 2+ to Ni 3+ , reduces cationic disordering, and forms an ideal layered structure.

[0092] The reaction time is 10-20 hours. Longer holding time is beneficial to the full growth and fusion of the grains to form dense single-crystal-like large particles.

[0093] The heating / cooling rate can be 2-5℃ / min to avoid thermal stress-induced particle cracking.

[0094] S41, the product after the first-stage sintering is subjected to second-stage heat treatment to obtain a positive electrode active material.

[0095] The second-stage heat treatment can be used for morphology control and stress relief.

[0096] The conditions of the second-stage heat treatment can be as follows: The temperature can be slightly lower than that of the first-stage sintering, for example, 600-750℃.

[0097] The reaction is carried out for 5-15 hours in an oxygen or air atmosphere.

[0098] At a slightly lower temperature, the atoms have sufficient mobility to undergo surface diffusion and rearrangement, but do not initiate vigorous bulk growth. In this stage, the non-(003) facets (such as (101) facets) with higher surface energy gradually "dissolve" or "transform" into more stable (003) facets through atomic rearrangement. This process is called surface reconstruction or thermal etching, effectively increasing the exposed area of the (003) facets, making them dominant in the particle morphology.

[0099] The embodiments of the present application can further include a subsequent processing step.

[0100] The sintered material is washed with deionized water or a weak acid to remove residual lithium salts (such as Li2CO3, LiOH) on the surface.

[0101] A short-time (such as 3-5 hours) annealing at 400-500°C is performed to repair the surface structure damage that may be caused during the washing process and ensure the stability of the material surface.

[0102] Corresponding to the foregoing application function implementation method embodiments, the present application also provides a battery and corresponding embodiments.

[0103] The embodiments of the present application do not have special restrictions on the specific type of battery, which can be a secondary battery, a power battery, an energy storage battery, etc. The shell of the battery can be used to package the battery cell and the electrolyte. The shell of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. It can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed. The present application does not have special restrictions on the shape of the battery, which can be cylindrical, square or any other shape.

[0104] The battery cell of the embodiments of the present application can be formed by winding the positive electrode sheet, the negative electrode sheet and the separator. Specifically, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, with the separator between the positive and negative electrodes to play a separating role, and then the stacked electrode sheet and the separating film are wound to obtain the battery cell.

[0105] The electrolyte of the embodiments of the present application includes an organic solvent, a lithium salt and a first additive, and the first additive includes a compound with an unsaturated hydrocarbon group. The compound with an unsaturated hydrocarbon group is used as the first additive, which can coordinate with lithium ions, promote the dissociation of the lithium salt, and improve the conduction of polymer electrolyte lithium ions.

[0106] In one specific embodiment, the separator includes a porous sheet or non-woven fabric-like substance with excellent liquid retention, and the separator includes a resin or glass fiber separator material, including but not limited to polyolefin, aramid, polytetrafluoroethylene, polyethersulfone, etc.

[0107] In the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material coated on at least one side of the positive electrode current collector.

[0108] The present application does not limit the selection of the positive electrode current collector, which can be selected according to actual needs, for example, a copper foil can be selected. The positive electrode active material layer of the present application can be coated on at least one side of the positive electrode current collector.

[0109] In the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material coated on at least one side of the negative electrode current collector.

[0110] The present application does not limit the selection of the negative electrode current collector, which can be selected according to actual needs, for example, a copper foil can be selected. The negative electrode active material layer of the present application includes a negative electrode active material and a negative electrode binder, the negative electrode active material includes a carbon material and a silicon material, the present application does not limit the selection of the carbon material, which can be selected according to actual needs, for example, graphite, carbon black, hard carbon, soft carbon, etc. can be selected. The present application does not limit the selection of the silicon material, which can be selected according to actual needs, for example, silicon oxide, pre-lithiated silicon oxide, pre-magnesiumized silicon oxide material, silicon-carbon composite material, elemental silicon, etc. The negative electrode binder of the present application includes a polypropylene compound and a butadiene rubber, the polypropylene compound refers to a polypropylene derivative, for example, polyacrylic acid, polyacrylonitrile, polyacrylamide, poly(methyl acrylate), etc.

[0111] The liquid electrolyte of the present application includes an electrolyte salt, an organic solvent and an additive. In the present application, the electrolyte salt includes one or more of lithium hexafluorophosphate LiPF6, lithium difluoro(oxalato)borate LiODFB, lithium bis(oxalato)borate LiBOB, lithium difluorodiphosphate LiDFOP, lithium tetrafluoroborate LiBF4, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium difluorophosphate LiPOF2, and the concentration of the electrolyte salt can be 0.4 mol / L to 2.2 mol / L.

[0112] In the present application, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, ethyl propionate, gamma-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0113] In the embodiments of the present application, the electrolyte additive further includes other additives, which include but are not limited to several of vinylene carbonate VC, 1,3-propane sultone PS, vinyl sulfate DTD, butanedinitrile SN, adipodinitrile ADN, 1,3,6-hexanetricarbonitrile HTCN, propylene sulfite PST, methane dimethyl sulfite MMDS, ethylene glycol bis (propionitrile) ether EGBE, pentafluoroethoxy phosphazene, dicyclohexyl carbonyl, phosphoric acid trimethyl imide, hexamethylene diisocyanate, etc.

[0114] Corresponding to the foregoing application function implementation method embodiments, the present application also provides an electronic device and corresponding embodiments.

[0115] The present application also provides an electronic device, which includes the foregoing battery.

[0116] Exemplarily, the above-mentioned power consumption device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0117] In order to further understand the present application, the present application is described below in conjunction with embodiments, which are only used to illustrate the present application and do not limit the scope of the present application.

[0118] Embodiment 1: 1. Preparation of the positive electrode sheet S10, preparation of the positive electrode slurry, the positive electrode slurry including a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material includes a single crystal LiNi0.8Co0.1Mn0.1O2 material with a D50 of 12 μm, which is made to have a (003) crystal face as a dominant crystal face in the particle (i.e. to meet at least one of conditions ①, ② and ③) through a co-precipitation precursor sintering and subsequent heat treatment process. The conductive agent is Super P, and the mass percentage of Super P in the positive electrode slurry is 3%. The binder is PVDF, and the mass percentage of PVDF in the positive electrode slurry is 3%.

[0119] S20, coating the positive electrode slurry on the positive electrode current collector.

[0120] S30, before the positive electrode slurry is dried and solidified, an external magnetic field at 45° to the plane of the positive electrode current collector is applied, so that the (003) crystal face of the single crystal particle and / or the plurality of primary crystal grains of the single-crystal-like secondary particle has an angle of 45° with the plane of the positive electrode current collector.

[0121] S40, drying and rolling the oriented positive electrode slurry to obtain the positive electrode sheet.

[0122] 2. Preparation of negative electrode sheet The negative electrode active material graphite, silicon particles, conductive agent acetylene black (Super P), thickening agent CMC and binder SBR were mixed uniformly in a mass ratio of 84:10:2:1.2:2.8, and uniformly dispersed in deionized water to prepare a uniform black slurry. The mixed slurry was coated on both sides of the copper foil current collector, and then baked, rolled, and cut to obtain the negative electrode sheet.

[0123] 3. Preparation of electrolyte Commercially available electrolyte.

[0124] 4. Preparation of lithium ion battery The prepared positive electrode sheet, separator and negative electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets. After winding and tab welding, a bare cell was obtained. The bare cell was placed in an aluminum plastic film, and then liquid injection, packaging and other processes were performed to obtain a lithium ion battery. According to the formulations and preparation methods in Table 1, the preparation of lithium ion batteries of each example and comparative example was completed. In Table 1, the "content of magnetic element" refers to the percentage of atoms of the doped magnetic element occupying all transition metal sites.

[0125] Table 1 Formulation and preparation method table

[0126] Note: (003) crystal plane dominant refers to the positive electrode active material meeting at least one of conditions ①, ② and ③, and (003) crystal plane not dominant refers to the positive electrode active material not meeting conditions ①, ② and ③.

[0127] II. Performance test Each example and comparative example was subjected to the following performance tests, and the test results are shown in Table 2.

[0128] (1) Cycle performance At 25°C ± 2°C, 1C constant current charging to 4.25V, constant voltage to current ≤0.05C; stand for 5 minutes; 1C constant current discharge to 3.0V, cycle 500 times. Record the discharge capacity of the Nth cycle, and calculate the retention rate relative to the discharge capacity of the 5th cycle.

[0129] (2) Observation of positive electrode sheet after disassembly 1. Battery disassembly and electrode sheet acquisition: The battery that completed the 500-cycle performance test was moved to an argon-filled glove box (H2O & O2 <0.1 ppm) in the discharged state (3.0V).

[0130] Depending on the battery type (pouch / hard case), carefully disassemble the casing using specialized tools to remove the battery cells.

[0131] Immerse the battery cell in sufficient anhydrous dimethyl ether (DME) or dimethyl carbonate (DMC) solvent for 24 hours to fully dissolve and wash away residual electrolyte.

[0132] Separate the positive electrode, separator, and negative electrode inside the glove box. Gently rinse the surface of the positive electrode with DME solvent, and then place it in the vacuum transition chamber inside the glove box.

[0133] 2. Macroscopic morphological observation and sampling: Remove the dried positive electrode from the glove box.

[0134] In a drying room (relative humidity <5%), observe the overall condition of the electrode sheets with the naked eye or with the aid of an optical microscope (50-100x), paying particular attention to: a. Integrity of the active layer: Are there any visible cracks, wrinkles, bulges, or peeling?

[0135] b. Color uniformity: Whether the surface color is uniform, and whether there is any darkening or mottled due to local side reactions or metal dissolution.

[0136] c. Current collector condition: Whether the aluminum foil has corroded, discolored, or broken.

[0137] 3. Microscopic morphology and structural analysis (SEM): Samples approximately 1cm × 1cm in size were cut from both the central and edge regions of each electrode for subsequent microscopic analysis. The positive electrode samples were fixed to the sample stage using conductive adhesive. Observation was performed using a scanning electron microscope (SEM, such as a Hitachi SU8000) in low-vacuum mode. Key focus areas: Ⅰ. Low magnification (500-2000 times): Observe the overall morphology of the active material layer, the uniformity of particle distribution, the bonding between the coating and the current collector, and whether there is a microscopic origin of macroscopic cracks.

[0138] II. High magnification (5000-20000x): Focusing on one or several secondary particles / single crystal particles for detailed observation: a. Particle integrity: Whether the particle surface is smooth, and whether there are cracks (especially through cracks), breakage or pulverization.

[0139] b. Particle state: Whether the network formed by the conductive agent and binder is intact, and whether there is obvious separation or aggregation between particles.

[0140] c. Surface coating: Observe the coverage of the positive electrode electrolyte interface film (CEI film) (whether it is uniform, too thick or locally piled up).

[0141] d. Cross-section observation: Part of the positive electrode sheet sample was subjected to liquid nitrogen brittle fracture or focused ion beam (FIB) cutting to prepare a cross-section sample. Observation was performed: (a) Coating thickness uniformity and the degree of tightness of the coating to the current collector.

[0142] (b) The direction and depth of the crack, to determine whether it is a cohesive failure in the coating or an interfacial peeling between the coating and the current collector.

[0143] Table 2 Test results

[0144] In combination with Table 1 and Table 2, by comparing Example 1 to Example 5, and Comparative Example 1 to Comparative Example 3, it can be seen that when the positive active material includes single crystal particles and / or single-crystal-like secondary particles, and the (003) crystal plane of the plurality of primary crystal grains of the single crystal particles and / or single-crystal-like secondary particles is dominant, and the angle between the (003) crystal plane of the plurality of primary crystal grains of the single crystal particles and / or single-crystal-like secondary particles and the plane of the positive current collector is 15°~75°, when the stress from the silicon-carbon negative electrode expansion (mainly manifested as tensile / compressive stress in the electrode sheet plane) acts on this particle, this orientation is conducive to converting the harmful stress that causes particle cracking into relatively harmless slip along the (003) crystal plane direction, thereby safely dissipating mechanical energy with controllable micro-deformation, preventing particle internal grain boundary cracking (for polycrystalline particles) or overall breakage, fundamentally solving the mechanical failure problem of the positive active material in the silicon-carbon system, thereby significantly improving the cycle life of the battery. Further by comparing Example 1 to Comparative Example 2 and Comparative Example 3, it can be seen that even if the positive active material only has an angle between the (003) crystal plane and the plane of the positive current collector that is not 15°~75°, its structural stability and electrochemical performance cannot be improved. Further by comparing Example 1 to Comparative Example 8, Example 6 and Comparative Example 9, and Example 9 and Comparative Example 10, it can be seen that even if the positive active material only has a (003) crystal plane that is not dominant, its structural stability and electrochemical performance cannot be improved.

[0145] It can be seen from the comparison between Example 1 and Example 6 that the single crystal particles and / or quasi-single crystal secondary particles can be doped or not doped with magnetic elements, preferably doped with magnetic elements, which can significantly enhance the response ability of the particles to an external magnetic field, and provide a material basis for realizing high-precision and high-efficiency magnetic field orientation arrangement. It can be further seen from Example 11 that the concentration of atoms doped with magnetic elements is not more than 2 mol%, which can avoid excessive doping leading to too large lattice distortion, thereby causing material structure instability, electronic / ionic conductivity decline, or introducing electrochemically active impurities and other negative effects. It can be further seen from the comparison between Comparative Example 4 and Comparative Example 5 that even if the positive electrode active material only has a (003) crystal plane with an angle of 15°-75° with the plane of the positive electrode current collector, the structure stability and electrochemical performance cannot be improved.

[0146] It can be seen from the comparison between Example 1, Example 7 to Example 9 that the use of composite conductive agents and composite binders can construct a stable and elastic three-dimensional conductive network, and under the action of cyclic stress, it can effectively absorb and dissipate strain energy, preventing stress concentration from leading to adhesion failure or coating cracking. It can be further seen from the comparison between Comparative Example 6 and Comparative Example 7 that even if the positive electrode active material only has a (003) crystal plane with an angle of 15°-75° with the plane of the positive electrode current collector, the structure stability and electrochemical performance cannot be improved.

[0147] It can be seen from the comparison between Example 1, Example 13 to Example 16 that the particle size range of the single crystal particles and / or quasi-single crystal secondary particles is set to 8 μm-20 μm, which can meet the demand for high energy density and ensure good kinetics and structure stability.

[0148] Although the present application has been described with reference to preferred embodiments, those skilled in the art will appreciate that various modifications can be made and equivalents can be substituted for elements thereof without departing from the scope of the present application. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the present application without departing from the essential scope thereof. Therefore, the present application is not intended to be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present application, but it will include all embodiments falling within the scope of the appended claims.

[0149] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are combinable with the ranges.

[0150] Having described various embodiments of the application, it is to be understood that the above description is meant to be illustrative only, and that many modifications and variations of the embodiments described herein are possible. It is therefore to be understood that within the scope of the appended claims, and their equivalents, many alternatives to the embodiments described herein are possible. The selection of terms to be used in the description is not intended to limit the scope of the embodiments described herein, but rather to best explain the principles of the embodiments, practical application, or improvement over the technology in the art, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A positive electrode plate, characterized in that, The device includes a positive current collector and a positive active layer coated on at least one side of the positive current collector. The positive active layer includes a positive active material, which includes single-crystal particles and / or quasi-single-crystal secondary particles. The (003) crystal planes of a plurality of primary grains of the single-crystal particles and / or the quasi-single-crystal secondary particles form an angle of 15° to 75° with the plane of the positive current collector. The positive active material satisfies at least one of the following conditions: The ratio of the intensity of the diffraction peaks of the (003) crystal plane to the intensity of the (104) crystal plane in the X-ray diffraction pattern of the positive electrode active material is A, where A≥1.5; The full width at half maximum (FWHM) of the (003) crystal plane diffraction peak in the X-ray diffraction pattern of the positive electrode active material is B, where B ≤ 0.15°. The texture coefficient of the (003) crystal plane in the X-ray diffraction pattern of the positive electrode active material is C, where C>1.

5.

2. The positive electrode sheet according to claim 1, characterized in that, The general formula of the single-crystal particles and / or single-crystal-like secondary particles is LiM. （1-x） A x O2, wherein M includes one or more of Ni, Co, and Mn; A is at least one magnetic doping element selected from Fe, Cr, Al, Mg, Zr, Ti, Y, W, Mo, Nb, Ta, and rare earth elements; 0≤x≤0.

08.

3. The positive electrode sheet according to claim 2, characterized in that, The percentage of the atoms of the doped magnetic element in all transition metal sites is 0.1 mol% to 2 mol%.

4. The positive electrode sheet according to claim 1, characterized in that, The particle size of the single crystal particles and / or quasi-single crystal secondary particles is 8μm~20μm.

5. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active layer also includes a conductive agent and a binder.

6. The positive electrode sheet according to claim 5, characterized in that, The conductive agent includes a first conductive agent and a second conductive agent, the first conductive agent including carbon nanotubes, and the second conductive agent including Super P and / or acetylene black; and / or, the adhesive includes a first adhesive and a second adhesive, the first adhesive including polyvinylidene fluoride, and the second adhesive including polyacrylate elastic adhesive and / or styrene-butadiene rubber.

7. The positive electrode sheet according to claim 6, characterized in that, The first conductive agent accounts for 0.5% to 2% of the mass percentage of the positive electrode active layer, and / or the second conductive agent accounts for 1% to 3% of the mass percentage of the positive electrode active layer, and / or the first adhesive accounts for 1% to 3% of the mass percentage of the positive electrode active layer, and / or the second adhesive accounts for 0.5% to 2.5% of the mass percentage of the positive electrode active layer.

8. A method for preparing a positive electrode sheet, characterized in that, include: A positive electrode slurry is prepared; the positive electrode slurry includes a positive electrode active material, the positive electrode active material includes single crystal particles and / or single crystal-like secondary particles, and the positive electrode active material satisfies at least one of the following conditions: The ratio of the intensity of the diffraction peaks of the (003) crystal plane to the intensity of the (104) crystal plane in the X-ray diffraction pattern of the positive electrode active material is A, where A≥1.5; The full width at half maximum (FWHM) of the (003) crystal plane diffraction peak in the X-ray diffraction pattern of the positive electrode active material is B, where B ≤ 0.15°. The texture factor of the (003) crystal plane of the positive electrode active material is C, where C>1.5; The positive electrode slurry is coated onto the positive electrode current collector; Before the positive electrode slurry is dried and cured, an external magnetic field is applied at a preset angle to the plane of the positive electrode current collector, so that the angle between the (003) crystal plane of the single crystal particle and / or the multiple primary crystals of the quasi-single crystal secondary particle and the plane of the positive electrode current collector is 15°~75°. The oriented positive electrode slurry is dried and rolled to obtain the positive electrode sheet.

9. The preparation method according to claim 8, characterized in that, It also includes a method for preparing the positive electrode active material, comprising: A spherical transition metal hydroxide precursor was prepared by reacting a mixed salt solution of nickel, cobalt, and manganese with a precipitant and ammonia. The precursor is mixed with a lithium source; The mixed materials are then subjected to the first stage of sintering. The product after the first stage of sintering is subjected to a second stage of heat treatment to obtain the positive electrode active material.

10. A battery, characterized in that, The battery includes a positive electrode sheet as described in any one of claims 1 to 7, or a positive electrode sheet prepared by the preparation method described in claim 8 or 9; the battery also includes a negative electrode sheet.

11. The battery according to claim 10, characterized in that, The negative electrode active material of the negative electrode sheet includes silicon-based materials.

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