Positive electrode active material, method for producing same, dry positive electrode sheet, and solid-state battery

Abstract

The application discloses a positive electrode active material, a preparation method thereof, a dry positive electrode sheet and a solid-state battery. The positive electrode active material comprises a nickel-cobalt-manganese ternary material, the nickel-cobalt-manganese ternary material comprises secondary particles formed by agglomeration of primary particles, and the aspect ratio of the primary particles is 1.60-2.50. The proportion of large-angle grain boundaries of the positive electrode active material is 89.0%-96.0%, and the D 50 meets 2.0 mu m<=D 50 <=13.0 mu m, and the porosity of the positive electrode active material is 0.2%-1.9%. Thus, the positive electrode active material has high compression resistance, and the particles are in close contact, which is beneficial to improving the capacity performance and initial efficiency of the solid-state battery.

Description

Technical Field

[0001] This application relates to the field of solid-state battery technology, specifically to positive electrode active materials and their preparation methods, dry-process positive electrode sheets, and solid-state batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in mobile consumer electronics, electric vehicles, and energy storage. However, as the demand for battery energy density continues to increase, it is gradually becoming insufficient to meet the needs of applications such as long-range electric vehicles and new low-altitude aircraft. Furthermore, increasing energy density in liquid battery systems also introduces risks such as gas expansion and thermal runaway, hindering the development of the lithium battery industry. All-solid-state batteries are considered one of the effective solutions. High-nickel cathode active materials are widely used in all-solid-state batteries due to their high energy density and high capacity.

[0003] Compared to liquid systems, all-solid-state batteries often require high pressure and the use of mixed particles of varying sizes to improve the solid-solid contact between the electrode and the solid electrolyte and to prevent volume changes caused by lithium insertion / extraction from the active material during cycling, which could lead to poor interfacial contact and degraded battery performance. However, under such high pressure, agglomerated particles are prone to breakage. After breakage, the unprotected fresh interface inside the positive electrode active material comes into contact with the solid electrolyte, causing serious side reactions that affect battery performance. Therefore, the positive electrode active materials used in solid-state batteries still require further improvement.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect, this application proposes a positive electrode active material, comprising a nickel-cobalt-manganese ternary material, wherein the nickel-cobalt-manganese ternary material comprises secondary particles formed by the agglomeration of primary particles, the aspect ratio of the primary particles being 1.60-2.50; the proportion of large-angle grain boundaries in the positive electrode active material is 89.0%-96.0%; the D of the positive electrode active material... 50 Satisfying 2.0μm≤D 50 The porosity of the positive electrode active material is 0.2%-1.9%, with a particle size ≤13.0μm. Therefore, the positive electrode active material exhibits high compressive strength and close contact between particles, which is beneficial for improving the capacity utilization and initial efficiency of solid-state batteries.

[0006] In some embodiments, the aspect ratio of the primary particles is 1.60-1.75, and the proportion of large-angle grain boundaries is 89.0%-91.7%. When the aspect ratio of the primary particles and the proportion of large-angle grain boundaries are within the aforementioned range, the transport of lithium ions along the grain direction can be further improved, the internal stress of the positive electrode active material during charging and discharging can be reduced, and the first-efficiency and cycle performance of the solid-state battery can be improved.

[0007] In some embodiments, the aspect ratio of the primary particles is 1.755-2.35, and the proportion of large-angle grain boundaries is 91.75%-96.0%. When the aspect ratio of the primary particles and the proportion of large-angle grain boundaries are within the aforementioned range, the transport of lithium ions along the grain direction can be further improved, the internal stress of the positive electrode active material during charging and discharging can be reduced, and the first-efficiency and cycle performance of the solid-state battery can be improved.

[0008] In some embodiments, the D of the positive electrode active material 50 Satisfying 8.0μm < D 50 The porosity of the positive electrode active material is 0.2%-1.1%, with a diameter ≤13.0 μm.

[0009] In some embodiments, the D of the positive electrode active material 50 Satisfying 6.0μm < D 50 The porosity of the positive electrode active material is 0.3%-1.5%, with a diameter of ≤8.0μm.

[0010] In some embodiments, the D of the positive electrode active material 50 Satisfying 2.0μm≤D 50 The porosity of the positive electrode active material is 1.0%-1.9%, with a diameter ≤6.0 μm. Different D... 50 Porosity ranges exist for positive electrode active materials, with an optimal porosity within this range. At this optimal porosity, primary particles are densely packed within secondary particles, resulting in the highest number of grain boundaries. Lithium ions that cannot contact the electrolyte internally can migrate outwards through transport channels formed within the densely packed particles, thus improving the capacity of solid-state batteries.

[0011] In some embodiments, the equivalent circular diameter of the primary particle is related to the D of the positive electrode active material. 50 The ratio is 0.05-0.20. Therefore, the primary particle size of the positive electrode active material is optimal, which is beneficial for the insertion and extraction of lithium ions and facilitates capacity utilization.

[0012] In some embodiments, the positive electrode active material includes a matrix and a coating layer at least partially located on the surface of the matrix; the matrix satisfies the chemical formula: Li a Ni x Mn y Co z M bO2, wherein 0.9≤a≤1.5, 0<x<1, 0<y<1, 0<z<1, x+y+z =1, 0≤b / (x+y+z)≤0.05, and M includes at least one of Ga, Sc, In, Y, Ce, Co, La, Cr, Mo, Mn, Fe, Hf, Zr, W, Nb, Sm, Sb, and Al; the coating layer includes oxides of Al, Mg, Co, B, Zr, W, and Nb, or lithium-containing fast ion conductors. Therefore, by setting a coating layer on the substrate surface, it helps to improve the structural stability of the positive electrode active material, provide a uniform, fast, and stable lithium-ion transport channel, alleviate volume strain, reduce the occurrence of side reactions between the positive electrode active material and the solid electrolyte, and improve the cycle performance of the positive electrode active material.

[0013] In a second aspect of this application, a method for preparing the aforementioned positive electrode active material is proposed, comprising: mixing a nickel-cobalt-manganese precursor, a lithium source, and an optional M source under an oxygen-containing atmosphere, followed by a first sintering treatment to obtain an intermediate; and mixing the intermediate with an optional M' source under an oxygen-containing atmosphere, followed by a second sintering treatment to form a coating layer, thereby obtaining the positive electrode active material; wherein the first sintering treatment comprises: sequentially performing a first heating treatment and a first holding treatment, the temperature of the first holding treatment being 650℃-800℃. This application, by simultaneously doping the substrate with elements and forming a coating layer with high ionic conductivity on the substrate surface, while controlling the sintering regime, obtains a positive electrode active material with high compressive strength, which helps to improve the capacity utilization and first-time efficiency of solid-state batteries. Furthermore, the process is simple, the production cost is low, and it is suitable for large-scale industrial production.

[0014] In some embodiments, the nickel-cobalt-manganese precursor includes at least one of nickel-cobalt-manganese hydroxide and nickel-cobalt-manganese oxide; and / or, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium acetate. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is easy.

[0015] In some embodiments, the M source includes at least one of the oxides, chlorides, carbonates, and sulfates corresponding to the M element. Therefore, doping with the M element helps to improve the structural stability of the positive electrode active material.

[0016] In some embodiments, the M' source includes oxides of Al, Mg, Co, B, Zr, W, and Nb, or has a lithium-containing fast ion conductor. This facilitates the formation of a coating layer with high ionic conductivity on the substrate surface, which not only helps improve the compressive strength of the positive electrode active material but also provides a uniform, fast, and stable lithium-ion transport channel.

[0017] In some embodiments, the first heating treatment lasts for 1-6 hours, and the first holding treatment lasts for 5-18 hours. This facilitates uniform doping of the M element.

[0018] In some embodiments, the temperature of the second sintering treatment is 300℃-800℃, and the time of the second sintering treatment is 5h-20h. This facilitates the uniform distribution of the coating layer on the substrate surface and improves the crystallinity of the positive electrode active material.

[0019] In a third aspect of the application, this application proposes a dry-process positive electrode sheet, comprising a positive electrode active material, a conductive agent, and a solid electrolyte. The positive electrode active material includes the positive electrode active material described in the first aspect of this application or a positive electrode active material prepared using the method described in the second aspect of this application. This dry-process positive electrode sheet possesses all the features and advantages of the aforementioned positive electrode active materials, which will not be elaborated upon here.

[0020] In some embodiments, based on the mass of the dry-processed positive electrode sheet, the mass percentage of the positive electrode active material is 70%-97%; and / or, based on the mass of the dry-processed positive electrode sheet, the mass percentage of the conductive agent is 1%-4%; and / or, based on the mass of the dry-processed positive electrode sheet, the mass percentage of the solid electrolyte is 1%-30%. Thus, the positive electrode sheet exhibits superior energy density, ionic conductivity, and electronic conductivity.

[0021] In some embodiments, the mass ratio of halides to sulfides in the solid electrolyte is 0-1; optionally, the mass ratio of halides to sulfides in the solid electrolyte is 0-0.67. This is beneficial for improving the ionic conductivity and high-voltage stability of the dry-process positive electrode.

[0022] In some embodiments, the halide includes at least one of Li3YCl6, Li2ZrCl6, Li3InCl6, Li3LaBr6, and LiAlCl4; and / or, the sulfide includes Li3PS4, Li2S-P2S5, Li6PS5Cl, and Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them. This is beneficial for further improving the ionic conductivity and high-voltage stability of the dry-process positive electrode.

[0023] In a fourth aspect, this application proposes a solid-state battery comprising the dry-process positive electrode sheet described in the third aspect. This solid-state battery possesses all the features and advantages of the aforementioned positive electrode active materials, which will not be elaborated upon here. Attached Figure Description

[0024] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1 This is a SEM image of the positive electrode active material of Example 4 of this application. Detailed Implementation

[0025] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0026] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0027] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0028] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0031] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0034] In a first aspect, this application proposes a positive electrode active material, comprising a nickel-cobalt-manganese ternary material, wherein the nickel-cobalt-manganese ternary material comprises secondary particles formed by the agglomeration of primary particles, the aspect ratio of the primary particles being 1.60-2.50; the proportion of large-angle grain boundaries in the positive electrode active material is 89.0%-96.0%; the D of the positive electrode active material... 50 Satisfying 2.0μm≤D 50The porosity of the positive electrode active material is 0.2%-1.9%, with a particle size ≤13.0μm. Therefore, the positive electrode active material exhibits high compressive strength and close contact between particles, which is beneficial for improving the capacity utilization and initial efficiency of solid-state batteries.

[0035] As an example, the aspect ratio of the primary particles can be 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, or 2.50, etc. When the aspect ratio of the primary particles is within the above range, the primary particles inside the positive electrode active material have a radial structure. When external pressure is applied to the positive electrode active material, the force is transmitted towards the center along the length direction of the primary particles, so that each primary particle mainly bears the compressive stress along its long axis, exhibiting higher compressive strength.

[0036] As an example, the proportion of large-angle grain boundaries in the positive electrode active material can be 89.0%, 90.0%, 91.0%, 92.0%, 93.0%, 94.0%, 95.0%, or 96.0%, etc. The higher the proportion of large-angle grain boundaries in the positive electrode active material, the fewer defects the positive electrode active material has, the more stable the structure, and the larger the aspect ratio of the primary particles of the resulting positive electrode active material.

[0037] When the aspect ratio of primary particles is within the aforementioned range, it facilitates lithium-ion transport along the grain direction, thereby reducing lithium-ion transport between grain boundaries and improving the capacity utilization and first-time efficiency of solid-state batteries. Simultaneously, primary particles meeting the aforementioned aspect ratio requirements are stacked and contacted in a face-to-edge or edge-to-edge manner, with a moderate proportion of large-angle grain boundaries. This allows for rapid release of lattice stress, reducing internal stress caused by lattice contraction and expansion during charging and discharging. This improves the application of cathode active materials under high applied pressure, enhances the cycle life and structural integrity of the cathode active material, and ultimately improves the cycle performance of solid-state batteries.

[0038] As an example, the D of the positive electrode active material 50 It can be 2.0μm, 4.0μm, 6.0μm, 8.0μm, 10.0μm, 12.0μm or 13.0μm, etc.

[0039] As an example, the porosity of the positive electrode active material can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, or 1.9%, etc.

[0040] Different D 50 Porosity ranges exist for positive electrode active materials, with an optimal porosity within this range. At this optimal porosity, primary particles are densely packed within secondary particles, resulting in the highest number of grain boundaries. Lithium ions that cannot contact the electrolyte internally can migrate outwards through transport channels formed within the densely packed particles, thus improving the capacity of solid-state batteries.

[0041] As an example, the aspect ratio of primary particles is obtained through EBSD testing: An electron beam from an EBSD (Electron Back-Scattered Difference) detector mounted on a scanning electron microscope (SEM) is irradiated onto an inclined sample. Backscattered electrons undergo diffraction, and the resulting diffracted electrons are projected onto the phosphor screen of the EBSD detector, forming a diffraction pattern. The aspect ratio of the equivalent fitted ellipse of the primary particles in the cross-section of the cathode active material is analyzed. The aspect ratios of the equivalent fitted ellipse of the primary particles from at least 10 secondary particles (e.g., all clear primary particles in a cross-sectional photograph) are randomly counted, and the average value is calculated; this average value is the aspect ratio of the primary particles of the cathode active material.

[0042] In the cross-section of a secondary particle, if the difference in particle orientation angle between adjacent primary particles is greater than 10°, then the grain boundary between these adjacent primary particles is a large-angle grain boundary. The proportion of the length of a large-angle grain boundary in the total length of all grain boundaries is the proportion of large-angle grain boundaries.

[0043] As an example, the method for testing the proportion of large-angle grain boundaries in positive electrode active materials includes: mounting an EBSD (Electron Back-Scattered Diffraction) detector on a scanning electron microscope (SEM), irradiating the tilted sample with an electron beam, causing backscattered electrons to diffract, and projecting the diffracted electrons onto the phosphor screen of the EBSD detector to form a diffraction pattern. Software is used to analyze the diffraction pattern, calibrate the phase and orientation, and obtain the proportion of large-angle grain boundaries. This application limits the numerical range to an average value obtained from statistical analysis of no fewer than 50 randomly selected particles.

[0044] As an example, the D of the positive electrode active material 50 The testing method is as follows: the particle size is obtained by testing with a Malvern 3000 laser particle size analyzer.

[0045] As an example, the test method for the porosity of positive electrode active materials is: porosity = V1 / (V1+V2).

[0046] The pore volume V1 can be obtained by testing and analyzing the N2 adsorption-desorption isotherms of the positive electrode active material, such as using a surface analyzer like the Tristar 3020 from Micromeritics. The N2 adsorption-desorption isotherm test specifically includes: using a conventional measuring device (such as the Tristar 3020), gradually adding N2 to the sample of the test material (after removing physically adsorbed components) under vacuum; calculating the pressure change caused by N2 adsorption using the constant volume method; and determining the amount of N2 adsorbed based on the gas equation. This yields the N2 adsorption isotherm from 0 atm to 0.995 atm at liquid nitrogen temperature. After reaching 0.995 atm, the N2 pressure is gradually reduced to 0 atm to obtain the N2 desorption isotherm from 0.995 atm to 0 atm, and the results are then summarized to obtain the N2 adsorption-desorption isotherms. Among them, the N2 adsorption-desorption isotherm analysis is: the pore volume is calculated from the amount of N2 adsorbed when the relative pressure (p / p0) of the N2 adsorption isotherm is 0.995.

[0047] The sum of the framework volume and closed-pore volume V2 of the positive electrode active material can be measured using the gas displacement method combined with a true density analyzer, such as the Micromeritics Accupy II 1345 true density analyzer. Specifically, the gas displacement method can involve using an inert gas N2 as the displacement medium, sealing the sample in an N2-filled sample chamber, opening the expansion chamber to allow gas diffusion, and then calculating the sum of the framework volume and closed-pore volume V2 by analyzing the pressure change before and after gas diffusion.

[0048] In some embodiments, the aspect ratio of the primary particles is 1.60-1.75 (e.g., 1.60, 1.62, 1.64, 1.66, 1.68, 1.70, 1.72, or 1.75), and the proportion of large-angle grain boundaries is 89.0%-91.7% (e.g., 89.0%, 89.2%, 89.5%, 89.7%, 90.0%, 90.2%, 90.5%, 90.7%, 91.0%, 91.2%, 91.5%, or 91.7%). When the aspect ratio of the primary particles and the proportion of large-angle grain boundaries are within the aforementioned range, lithium-ion transport along the grain direction can be further improved, the internal stress of the positive electrode active material during charging and discharging can be reduced, and the first-efficiency and cycle performance of the solid-state battery can be improved.

[0049] In some embodiments, the aspect ratio of the primary particles is 1.755-2.35 (e.g., 1.755, 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, or 2.35), and the proportion of large-angle grain boundaries is 91.75%-96.0% (e.g., 91.75%, 92.0%, 93.0%, 94.0%, 95.0%, or 96.0%). When the aspect ratio of the primary particles and the proportion of large-angle grain boundaries are within the aforementioned range, lithium-ion transport along the grain direction can be further improved, the internal stress of the positive electrode active material during charging and discharging can be reduced, and the first-efficiency and cycle performance of the solid-state battery can be improved.

[0050] In some embodiments, the D of the positive electrode active material 50 Satisfying 8.0μm < D 50 The porosity of the positive electrode active material is 0.2%-1.1% (e.g., 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or 1.1%), ≤13.0μm (e.g., 8.0μm, 9.0μm, 10.0μm, 11.0μm, 13.0μm, etc.).

[0051] In some embodiments, the D of the positive electrode active material 50 Satisfying 6.0μm < D 50 The porosity of the positive electrode active material is 0.3%-1.5% (e.g., 0.3%, 0.5%, 0.7%, 1.0%, 1.3% or 1.5%), ≤8.0μm (e.g., 6.0μm, 7.0μm or 8.0μm).

[0052] In some embodiments, the D of the positive electrode active material 50 Satisfying 2.0μm≤D 50 ≤6.0μm (e.g., 2.0μm, 3.0μm, 4.0μm, 5.0μm, or 6.0μm), and the porosity of the positive electrode active material is 1.0%-1.9% (e.g., 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, or 1.9%). Different D 50 Porosity ranges exist for positive electrode active materials, with an optimal porosity within this range. At this optimal porosity, primary particles are densely packed within secondary particles, resulting in the highest number of grain boundaries. Lithium ions that cannot contact the electrolyte internally can migrate outwards through transport channels formed within the densely packed particles, thus improving the capacity of solid-state batteries.

[0053] In some embodiments, the equivalent circular diameter of the primary particle is related to the D of the positive electrode active material. 50The ratio is 0.05-0.20.

[0054] As an example, the equivalent circular diameter of a primary particle is related to the D of the positive electrode active material. 50 The ratio can be 0.05, 0.08, 0.10, 0.12, 0.15, 0.18 or 0.20, etc.

[0055] Therefore, the primary particle size of the positive electrode active material is optimal, which is beneficial for the insertion and extraction of lithium ions and facilitates capacity utilization.

[0056] In this application, the equivalent circular diameter of the primary particle refers to the diameter of a circle that has the same area as the primary particle in the cross-section of the positive electrode active material particle, and can be determined by the following methods: An electron beam from an EBSD (Electron Back-Scattered Difference) detector mounted on a scanning electron microscope (SEM) is irradiated onto an inclined sample. Backscattered electrons undergo diffraction, and the diffracted electrons are projected onto the phosphor screen of the EBSD detector, forming a diffraction pattern. The area of ​​each primary particle in the cross-section of the positive electrode active material particle is analyzed, and the diameter of a circle with the same area is taken as the equivalent circle diameter of the primary particle of the positive electrode active material. The equivalent circle diameters of the primary particles in at least 10 secondary particles (for example, all clear primary particles in a cross-sectional image can be counted) are randomly selected, and the average value is calculated, which is the average equivalent circle diameter of the primary particles of the positive electrode active material.

[0057] In some embodiments, the positive electrode active material includes a matrix and a coating layer at least partially located on the surface of the matrix; the matrix satisfies the chemical formula: Li a Ni x Mn y Co z M b O2, wherein 0.9≤a≤1.5, 0<x<1, 0<y<1, 0<z<1, x+y+z =1, 0≤b / (x+y+z)≤0.05, and M includes at least one of Ga, Sc, In, Y, Ce, Co, La, Cr, Mo, Mn, Fe, Hf, Zr, W, Nb, Sm, Sb, and Al; the coating layer includes oxides of Al, Mg, Co, B, Zr, W, and Nb, or lithium-containing fast ion conductors. Therefore, by setting a coating layer on the substrate surface, the structural stability of the positive electrode active material is improved, a uniform, fast, and stable lithium-ion transport channel is provided, volume strain is alleviated, side reactions between the positive electrode active material and the solid electrolyte are reduced, and the cycle performance of the positive electrode active material is improved.

[0058] As an example, 'a' can be 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5, etc.

[0059] As an example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, etc.

[0060] As an example, y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, etc.

[0061] As an example, z can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, etc.

[0062] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material. This method involves elemental doping of the substrate and forming a coating layer with high ionic conductivity on the substrate surface, while simultaneously controlling the sintering process. This yields a positive electrode active material with high compressive strength, which helps improve the capacity and first-efficiency performance of solid-state batteries. Furthermore, the process is simple, has low production costs, and is suitable for large-scale industrial production. Specifically, the method includes: S1: Under an oxygen-containing atmosphere, the nickel-cobalt-manganese precursor, lithium source, and optional M source are mixed and subjected to a first sintering treatment to obtain an intermediate.

[0063] In some embodiments, the nickel-cobalt-manganese precursor includes at least one of nickel-cobalt-manganese hydroxide and nickel-cobalt-manganese oxide; and / or, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium acetate. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is easy.

[0064] In some embodiments, the M source includes at least one of the oxides, chlorides, carbonates, and sulfates corresponding to the M element. Therefore, doping with the M element helps to improve the structural stability of the positive electrode active material.

[0065] In some embodiments, the amount of lithium source added, based on the molar ratio, satisfies 0.90≤n(Li) / n(Ni+Co+Mn+M) ≤1.05, for example, it can be 0.90, 0.92, 0.95, 0.98, 1.00, 1.02 or 1.05, etc.

[0066] In some embodiments, the oxygen-containing atmosphere is air or oxygen.

[0067] In some embodiments, the first sintering process includes: sequentially performing a first heating process and a first holding process, wherein the temperature of the first holding process is 650℃-800℃, the duration of the first heating process is 1h-6h, and the duration of the first holding process is 5h-18h. It can be understood that the starting temperature of the first heating process is room temperature, and the ending temperature is the temperature of the first holding process. This facilitates the uniform doping of element M.

[0068] As an example, the temperature of the first heat preservation treatment can be 650℃, 680℃, 700℃, 720℃, 750℃, 780℃ or 800℃, etc., the time of the first heating treatment can be 1h, 2h, 3h, 4h, 5h or 6h, etc., and the time of the first heat preservation treatment can be 5h, 8h, 10h, 12h, 15h or 18h, etc.

[0069] S2: Under an oxygen-containing atmosphere, the intermediate is mixed with an optional M' source and then subjected to a second sintering process to form a coating layer to obtain the positive electrode active material.

[0070] In some embodiments, the M' source includes oxides of Al, Mg, Co, B, Zr, W, and Nb, or has a lithium-containing fast ion conductor. This facilitates the formation of a coating layer with high ionic conductivity on the substrate surface, which not only helps improve the compressive strength of the positive electrode active material but also provides a uniform, fast, and stable lithium-ion transport channel.

[0071] In some embodiments, the oxygen-containing atmosphere is air or oxygen.

[0072] In some embodiments, the temperature of the second sintering treatment is 300℃-800℃, and the time of the second sintering treatment is 5h-20h. This facilitates the uniform distribution of the coating layer on the substrate surface and improves the crystallinity of the positive electrode active material.

[0073] As an example, the temperature of the second sintering treatment can be 300℃, 400℃, 500℃, 600℃, 700℃ or 800℃, etc., and the time of the second sintering treatment can be 5h, 8h, 10h, 12h, 15h, 18h or 20h, etc.

[0074] In a third aspect of the application, this application proposes a dry-process positive electrode sheet, comprising a positive electrode active material, a conductive agent, and a solid electrolyte. The positive electrode active material includes the positive electrode active material described in the first aspect of this application or a positive electrode active material prepared using the method described in the second aspect of this application. This dry-process positive electrode sheet possesses all the features and advantages of the aforementioned positive electrode active materials, which will not be elaborated upon here.

[0075] In some embodiments, based on the mass of the dry-process positive electrode sheet, the mass percentage of the positive electrode active material is 70%-97%, for example, 70%, 75%, 80%, 85%, 90%, 95%, or 97%; and / or, based on the mass of the dry-process positive electrode sheet, the mass percentage of the conductive agent is 1%-4%, for example, 1%, 2%, 3%, or 4%; and / or, based on the mass of the dry-process positive electrode sheet, the mass percentage of the solid electrolyte is 1%-30%, for example, 1%, 5%, 8%, 10%, 15%, 20%, 25%, or 30%. Therefore, the dry-process positive electrode sheet exhibits superior energy density, ionic conductivity, and electronic conductivity.

[0076] In some embodiments, the solid electrolyte includes at least one of polymer electrolyte, inorganic solid electrolyte, and composite solid electrolyte.

[0077] In some embodiments, the mass ratio E1 of halides to sulfides in the solid electrolyte is 0-1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1; optionally, the mass ratio E1 of halides to sulfides in the solid electrolyte is 0-0.67. This is beneficial for improving the ionic conductivity and high-voltage stability of the dry-process positive electrode.

[0078] In some embodiments, the halide includes at least one of Li3YCl6, Li2ZrCl6, Li3InCl6, Li3LaBr6, and LiAlCl4; and / or, the sulfide includes Li3PS4, Li2S-P2S5, Li6PS5Cl, and Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them. This is beneficial for further improving the ionic conductivity and high-voltage stability of the dry-process positive electrode.

[0079] As an example, the preparation method of dry-process positive electrode sheets includes: (1) Mix the positive electrode active material and the halide in a certain proportion to obtain a mixture; (2) Mix the mixture with sulfide and conductive agent (such as conductive carbon) in a certain proportion to obtain dry positive electrode sheet.

[0080] In a fourth aspect, this application proposes a solid-state battery comprising the dry-process positive electrode sheet described in the third aspect. This solid-state battery possesses all the features and advantages of the aforementioned positive electrode active materials, which will not be elaborated upon here.

[0081] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0082] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0083] Example 1 (1) D 50 A first mixture was obtained by uniformly mixing a 7.5μm agglomerated nickel-cobalt-manganese hydroxide precursor with a molar ratio of 95:3:2, lithium hydroxide, and molybdenum oxide in a high-speed mixer at a ratio of n(Li) / n(Ni+Co+Mn+Mo) = 1.03 and n(Mo) / n(Ni+Co+Mn) = 0.01. Under an oxygen atmosphere, the first mixture is subjected to a first sintering treatment, which involves sequentially subjecting the first mixture to a first heating treatment and a first holding treatment. The first heating treatment lasts for 6 hours, the first holding treatment lasts for 8 hours at a temperature of 780°C, and the mixture is then naturally cooled to room temperature. The mixture is then crushed and sieved to obtain an intermediate. (2) The intermediate and LiNbO3 are uniformly mixed in a high-speed mixer at a ratio of m(LiNbO3) / m(intermediate)×100%=0.5wt.% to obtain a second mixture; The second mixture was subjected to a second sintering treatment under an oxygen atmosphere at a temperature of 330°C for 8 hours. After natural cooling to room temperature, the mixture was crushed and sieved to obtain an agglomerated positive electrode active material with the composition Li. 1.03 (Ni 0.95 Co 0.03 Mn 0.02 Mo 0.01 )O2.

[0084] The differences between other embodiments and comparative examples and embodiment 1 are shown in Table 1.

[0085] Table 1

[0086] The positive electrode active materials prepared in the examples and comparative examples were subjected to the aforementioned tests, and the test results are shown in Table 2.

[0087] Table 2

[0088] Assembly of all-solid-state molded batteries: First, the all-solid positive electrode active material, solid electrolyte, and conductive carbon are mixed in a mass ratio of 70:20:20 and pressed into a dry positive electrode sheet in a mold at a pressure of 450MPa. Then, the solid electrolyte powder is pressed into an electrolyte sheet at a pressure of 100MPa. Finally, the dry positive electrode sheet, electrolyte sheet, and lithium indium alloy negative electrode are stacked in the mold battery and tested under an external pressure of 200MPa. When E1=0, the solid electrolyte is Li3PS4; when E1=0.43, the solid electrolytes are Li3YCl6 and Li3PS4.

[0089] The performance evaluation of the mold battery is as follows: Charge-discharge performance test: The charge-discharge performance of the positive electrode active material was examined at a temperature of 25℃, a voltage range of 1.9V-3.7V, and a rate of 0.1C. The test results are shown in Table 3.

[0090] Table 3

[0091] As can be seen from Table 3, the aspect ratio of primary particles, the proportion of large-angle grain boundaries, and the D of the positive electrode active material in the embodiments of this application are... 50 The porosity is within the range specified in this application, which enables the positive electrode active material to have high compressive strength and close contact between particles, resulting in better capacity utilization and first-time efficiency of the solid-state battery.

[0092] In Comparative Examples 1 and 2, the temperature of the first heat preservation treatment during the preparation process was too high, resulting in excessively high porosity of the positive electrode active material and excessively small aspect ratio of the primary particles, leading to poor capacity utilization and poor first-time efficiency of the battery.

[0093] In Comparative Example 3, the temperature of the first heat preservation treatment during the preparation process was too high, resulting in an excessively high proportion of large-angle grain boundaries in the positive electrode active material, which led to poor capacity utilization and initial efficiency of the battery.

[0094] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The material includes a nickel-cobalt-manganese ternary material, wherein the nickel-cobalt-manganese ternary material comprises secondary particles formed by the agglomeration of primary particles, and the aspect ratio of the primary particles is 1.60-2.50; The proportion of large-angle grain boundaries in the positive electrode active material is 89.0%-96.0%; The positive electrode active material D 50 Satisfying 2.0μm≤D 50 The porosity of the positive electrode active material is 0.2%-1.9%, with a diameter ≤13.0μm.

2. The positive electrode active material according to claim 1, characterized in that, The aspect ratio of the primary particles is 1.60-1.75, and the proportion of large-angle grain boundaries is 89.0%-91.7%.

3. The positive electrode active material according to claim 1, characterized in that, The aspect ratio of the primary particles is 1.755-2.35, and the proportion of large-angle grain boundaries is 91.75%-96.0%.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The positive electrode active material D 50 Satisfying 8.0μm < D 50 The porosity of the positive electrode active material is 0.2%-1.1%, with a diameter ≤13.0 μm.

5. The positive electrode active material according to any one of claims 1-3, characterized in that, The positive electrode active material D 50 Satisfying 6.0μm < D 50 The porosity of the positive electrode active material is 0.3%-1.5%, with a diameter of ≤8.0μm.

6. The positive electrode active material according to any one of claims 1-3, characterized in that, The positive electrode active material D 50 Satisfying 2.0μm≤D 50 When the diameter is ≤6.0μm, the porosity of the positive electrode active material is 1.0%-1.9%.

7. The positive electrode active material according to claim 1, characterized in that, The equivalent circular diameter of the primary particle is related to the D of the positive electrode active material. 50 The ratio is 0.05-0.

20.

8. The positive electrode active material according to claim 1 or 2, characterized in that, The positive electrode active material includes a matrix and a coating layer located at least partially on the surface of the matrix; The matrix satisfies the chemical formula: Li a Ni x Mn y Co z M b O2, wherein 0.9≤a≤1.5, 0<x<1, 0<y<1, 0<z<1, x+y+z =1, 0≤b / (x+y+z)≤0.05, and M includes at least one of Ga, Sc, In, Y, Ce, Co, La, Cr, Mo, Mn, Fe, Hf, Zr, W, Nb, Sm, Sb, and Al; The coating layer includes oxides of Al, Mg, Co, B, Zr, W, and Nb or lithium-containing fast ion conductors.

9. A method for preparing the positive electrode active material according to any one of claims 1-8, characterized in that, include: In an oxygen-containing atmosphere, a nickel-cobalt-manganese precursor, a lithium source, and an optional M source are mixed and subjected to a first sintering treatment to obtain an intermediate. Under an oxygen-containing atmosphere, the intermediate is mixed with an optional M' source and then subjected to a second sintering process to form a coating layer, thereby obtaining the positive electrode active material. The first sintering process includes: sequentially performing a first heating process and a first heat preservation process, wherein the temperature of the first heat preservation process is 650℃-800℃.

10. The method according to claim 9, characterized in that, The nickel-cobalt-manganese precursor includes at least one of nickel-cobalt-manganese hydroxide and nickel-cobalt-manganese oxide; and / or, The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium acetate; and / or, The M source includes at least one of the oxides, chlorides, carbonates, and sulfates corresponding to the M element; and / or, The M' source includes oxides of Al, Mg, Co, B, Zr, W, and Nb, or has a lithium-containing fast ion conductor.

11. The method according to claim 9, characterized in that, The first heating treatment lasts for 1-6 hours, and the first heat preservation treatment lasts for 5-18 hours.

12. The method according to claim 11, characterized in that, The temperature of the second sintering treatment is 300℃-800℃, and the time of the second sintering treatment is 5h-20h.

13. A dry-process positive electrode sheet, characterized in that, It includes a positive electrode active material, a conductive agent, and a solid electrolyte, wherein the positive electrode active material includes the positive electrode active material according to any one of claims 1-8 or the positive electrode active material prepared by the method according to any one of claims 9-12.

14. The dry-process positive electrode sheet according to claim 13, characterized in that, Based on the mass of the dry-process positive electrode sheet, the mass percentage of the positive electrode active material is 70%-97%; and / or, Based on the mass of the dry-process positive electrode sheet, the mass percentage of the conductive agent is 1%-4%; and / or, Based on the mass of the dry-process positive electrode sheet, the mass ratio of the solid electrolyte is 1%-30%.

15. The dry-process positive electrode sheet according to claim 13, characterized in that, The mass ratio of halides to sulfides in the solid electrolyte is 0-1; Optionally, the mass ratio of halides to sulfides in the solid electrolyte is 0-0.

67.

16. The dry-process positive electrode sheet according to claim 15, characterized in that, The halide includes at least one of Li3YCl6, Li2ZrCl6, Li3InCl6, Li3LaBr6, and LiAlCl4; and / or, The sulfides include Li3PS4, Li2S-P2S5, Li6PS5Cl, and Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them.

17. A solid-state battery, characterized in that, Includes the dry-process positive electrode sheet as described in any one of claims 13-16.

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