Positive electrode active material and preparation method thereof, dry-method positive electrode plate and solid-state battery

Abstract

The invention discloses a positive electrode active material and a preparation method thereof, a dry-method positive electrode plate and a solid-state battery, the positive electrode active material comprises a lithium-rich manganese-based layered oxide, and the open pore porosity of the positive electrode active material is 3.0%-6.0%; the positive electrode active material meets the following conditions: R is more than or equal to 2 and less than or equal to 2.35, R = (Q90-Q10) / Q50, Q10 is the corresponding aperture value when the aperture volume distribution is accumulated to 10%, Q50 is the corresponding aperture value when the aperture volume distribution is accumulated to 50%, and Q90 is the corresponding aperture value when the aperture volume distribution is accumulated to 90%. Therefore, the porosity and pore size distribution of the lithium-rich manganese-based layered oxide are cooperatively regulated and controlled, so that the positive electrode active material has a compact and uniform secondary particle accumulation structure, and the interface contact coverage degree between the solid electrolyte and positive electrode active material particles is remarkably improved, thereby establishing a continuous lithium ion transmission channel; and thus, the specific discharge capacity, the rate capability and the cycling stability of the positive electrode active material in a solid-state battery system can be improved.

Description

Positive electrode active materials and their preparation methods, dry-process positive electrode sheets, solid-state batteries 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-rich manganese-based cathode active material (Li 1+x M 1-x O2 (M can be Mn, Ni, Co, etc.) is considered an important candidate cathode active material for next-generation high-energy-density lithium-ion batteries and all-solid-state batteries due to its combination of high specific capacity (>250mAh / g) and low cost. However, lithium-rich manganese-based materials still face the following prominent problems in solid-state battery systems: (1) Solid electrolytes are inorganic rigid phases, which make it difficult to achieve sufficient wetting and close contact with cathode active materials, resulting in poor interface contact and excessively high interface impedance; (2) The ion transport path inside the cathode particles is limited, making it difficult to achieve efficient lithium-ion diffusion. Therefore, lithium-rich manganese-based cathode active materials still have problems that need to be further solved in practical applications.

[0003] 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

[0004] In a first aspect, this application proposes a positive electrode active material comprising a lithium-rich manganese-based layered oxide, wherein the open porosity of the positive electrode active material is 3.0%-6.0%; the positive electrode active material satisfies: 2≤R≤2.35, where R = (Q 90 -Q 10 ) / Q 50 Q 10 Q represents the pore size value corresponding to 10% of the pore size distribution. 50 Q represents the pore size value corresponding to 50% accumulation of pore volume distribution. 90 This represents the pore size value corresponding to a cumulative pore volume distribution of 90%. Therefore, by synergistically controlling the porosity and pore size distribution of lithium-rich manganese-based substrate oxides, the cathode active material exhibits a dense and uniform secondary particle packing structure. This significantly improves the interfacial contact coverage between the solid electrolyte and the cathode active material particles, thereby establishing a continuous lithium-ion transport channel. This, in turn, helps improve the discharge specific capacity, rate performance, and cycle stability of the cathode active material in solid-state battery systems.

[0005] In some embodiments, the porosity of the positive electrode active material is 3.5%-5.0%. This results in a lower degree of particle density, higher mechanical stability, and a larger effective contact area with the solid electrolyte, which helps to form continuous lithium-ion transport channels.

[0006] In some embodiments, the closed-cell porosity of the positive electrode active material is 1.2%-2.5%. When the closed-cell porosity is within the aforementioned range, the positive electrode active material is less prone to volume expansion during charging and discharging, and the interparticle contact is good, which is beneficial to improving the structural stability of the positive electrode active material; moreover, a moderate closed-cell porosity helps to form a continuous electronic conductive network, thereby improving the overall electronic conductivity of the positive electrode active material.

[0007] In some embodiments, at least one of the following conditions is satisfied: 8nm ≤ Q 10 ≤15nm; 50nm≤Q 50 ≤80nm; 120nm≤Q 90 ≤200nm. Therefore, the positive electrode active material exhibits superior mechanical stability and high interfacial contact coverage with the solid electrolyte.

[0008] In some embodiments, the lithium-rich manganese-based substrate oxide comprises secondary particles formed by the agglomeration of primary particles, wherein the primary particles have a layered structure. This facilitates shortening the lithium-ion diffusion path and increasing the lithium-ion diffusion rate.

[0009] In some embodiments, the average aspect ratio of the primary particles is 2.5-9. This is beneficial for controlling the porosity of the positive electrode active material.

[0010] In some embodiments, the average major axis dimension of the primary particles is 400 nm-800 nm; and / or, the average minor axis dimension of the primary particles is 85 nm-200 nm. This helps to reduce the breakage of the positive electrode active material and improve the lithium-ion transport rate.

[0011] In some embodiments, the positive electrode active material satisfies: 0.6 ≤ K ≤ 1.0, where K = (D 90 -D 10 ) / D 50 Therefore, the secondary particles of the positive electrode active material have high particle size uniformity and good processing performance.

[0012] In some embodiments, the D of the positive electrode active material 50 The particle size is 2μm-6μm. Therefore, the lithium-ion diffusion distance is moderate, and there are many contact sites between the positive electrode active material particles, making it easy to form continuous electronic pathways, which in turn helps to improve the capacity utilization of the positive electrode active material.

[0013] In some embodiments, the specific surface area of the positive electrode active material is 1 m 2 / g - 5 m 2 / g. Thus, the positive electrode active material has both high reaction activity and good structural stability. On the one hand, the specific surface area within the foregoing range can provide sufficient electrochemically active sites, which helps to improve the rate performance of the positive electrode active material; on the other hand, a moderate specific surface area is not likely to cause intense interfacial side reactions and gas evolution, thereby significantly enhancing the first-cycle Coulombic efficiency and long cycle life of the positive electrode active material.

[0014] In some embodiments, the positive electrode active material satisfies the following chemical formula: Li 1+a Mn x Ni y Co z M b O2, where 0 < a < 0.33, 0 < x < 1, 0 < y < 1, 0 < z < 1,  0 ≤ b < 0.1; M includes at least one of Mg, Al, Fe, Zn, Ti, Mo, V, Cr, Nb, Zr, Ta, W, Y, Ca, Cu. Thus, the introduction of the M element is beneficial to improving the structural stability of the positive electrode active material and regulating the porosity of the positive electrode active material.

[0015] In some embodiments, 0.1 < a ≤ 0.25, 0.35 < x < 0.7, 0.05 < y < 0.25, 0.05 < z < 0.30. Thus, it is beneficial to further improve the structural stability of the positive electrode active material.

[0016] In the second aspect of the present application, the present application proposes a method for preparing the above positive electrode active material, including: mixing a manganese source, a nickel source, a cobalt source, a precipitating agent, a complexing agent, acetic acid, and deionized water and then performing a coprecipitation reaction to obtain a hydroxide precursor, the tap density of the hydroxide precursor being 0.9 g / cm 3 -1.6 g / cm 3 ; mixing the hydroxide precursor, a lithium source, and an M source and then performing a sintering treatment to obtain the positive electrode active material. The present application realizes the controllable adjustment of the internal and external pore structures of the positive electrode active material particles by regulating the tap density of the hydroxide precursor, and further obtains a closely packed positive electrode active material. Moreover, the preparation method is simple, easy to operate, and easy to realize industrial production.

[0017] In some embodiments, at least one of the following conditions is satisfied: the D 50 of the hydroxide precursor is from 2 μm to 6 μm; the specific surface area of the hydroxide precursor is 20 m 2 / g - 30 m 2 / g; the porosity of the hydroxide precursor is 18%-35%. This is beneficial for controlling the pore structure of the positive electrode active material.

[0018] In some embodiments, the temperature of the coprecipitation reaction is 45°C-65°C, and the pH of the coprecipitation reaction is 9.5-11.5. This facilitates the acquisition of hydroxide precursors with uniform particle size.

[0019] In some embodiments, the sintering temperature is 800℃-900℃, and the sintering time is 8h-15h. This helps to improve the crystallinity of the positive electrode active material, promotes stable and controllable grain growth, and, by controlling the sintering temperature, can adjust the open porosity of the positive electrode active material.

[0020] In some embodiments, the manganese source includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, and manganese tetroxide; and / or, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate; and / or, the cobalt source includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate; and / or, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; and / or, the M source includes at least one of the oxide, chloride, carbonate, and sulfate corresponding to element M; and / or, the precipitant includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and ammonium bicarbonate; and / or, the complexing agent includes at least one of ammonia, ammonium sulfate, ammonium nitrate, and citric acid. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is convenient.

[0021] In a third aspect, this application proposes a dry-process positive electrode sheet, comprising a positive electrode active material 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. The interfacial contact coverage between the positive electrode active material and the solid electrolyte is greater than or equal to 90%. Thus, the solid electrolyte can form a sufficiently uniform coating layer on the surface of the positive electrode active material, which not only facilitates the uniform insertion and extraction of lithium ions at the interface between the positive electrode active material and the solid electrolyte, thereby inducing synergistic and uniform changes in lattice parameters, but also effectively maintains the structural integrity of the positive electrode active material and its stable contact with the solid electrolyte during long-term cycling.

[0022] In a fourth aspect, this application proposes a solid-state battery comprising the dry-process positive electrode sheet described in the third aspect. Consequently, this solid-state battery exhibits high discharge specific capacity, excellent rate performance, and superior cycle stability. Attached Figure Description

[0023] 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, in which: Figure 1 is a SEM image of hydroxide precursor particles in Preparation Example 2 of this application; Figure 2 is a SEM image of positive electrode active material particles in Example 2 of this application; Figure 3 is a SEM image of hydroxide precursor particles in Comparative Preparation Example 1 of this application; Figure 4 is a SEM image of positive electrode active material particles in Comparative Example 1 of this application; Figure 5 is a pore size distribution curve of the positive electrode active material of Example 2 and Comparative Example 1 of this application; Figure 6 is a cumulative curve of pore size corresponding to volume ratio of the positive electrode active material of Example 2 and Comparative Example 1 of this application; Figure 7 is a cross-sectional SEM image of a dry-process positive electrode sheet prepared using the positive electrode active material of Example 2 of this application. Detailed Implementation

[0024] 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.

[0025] 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).

[0026] 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.

[0027] 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%.

[0028] 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.

[0029] 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.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] In a first aspect, this application proposes a positive electrode active material comprising a lithium-rich manganese-based layered oxide, wherein the open porosity of the positive electrode active material is 3.0%-6.0%; the positive electrode active material satisfies: 2≤R≤2.35, where R = (Q 90 -Q 10 ) / Q 50 Q 10 Q represents the pore size value corresponding to 10% of the pore size distribution. 50 Q represents the pore size value corresponding to 50% accumulation of pore volume distribution. 90 This is the pore size value corresponding to when the pore volume distribution accumulates to 90%.

[0033] As an example, the porosity P1 of the positive electrode active material can be 3.0%, 4.0%, 5.0%, or 6.0%, etc.

[0034] As an example, R can be 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, or 2.35, etc.

[0035] This application achieves a dense and uniform secondary particle stacking structure in the cathode active material by synergistically controlling the porosity and pore size distribution of lithium-rich manganese-based base oxides. This significantly improves the interfacial contact coverage between the solid electrolyte and the cathode active material particles, thereby establishing a continuous lithium-ion transport channel. This, in turn, helps to improve the discharge specific capacity, rate performance, and cycle stability of the cathode active material in solid-state battery systems.

[0036] The porosity and pore size distribution of the cathode active material are key factors in regulating the interfacial contact and ion diffusion performance of solid-state batteries. The open porosity and pore size distribution directly affect the interfacial contact coverage between the cathode active material and the solid electrolyte. Specifically, when the open porosity of the cathode active material is within the aforementioned range, the particle densification is lower, which helps reduce internal stress accumulation and uneven volume expansion, making it less prone to particle breakage and resulting in better electrochemical performance. Simultaneously, the cathode active material exhibits higher compaction density and mechanical stability, resulting in a larger effective contact area with the electrolyte, which helps form continuous lithium-ion transport channels and enhances compatibility with the solid electrolyte.

[0037] Furthermore, the density of the positive electrode active material affects the pore size distribution. When the positive electrode active material meets the above-mentioned pore size distribution, the pore size distribution inside the secondary particles of the positive electrode active material is highly uniform, the degree of lithium insertion / extraction during charging and discharging is more consistent, it has better mechanical stability, and the interfacial contact coverage with the solid electrolyte is higher, which is beneficial to improving the rate performance and cycle performance of the positive electrode active material.

[0038] In this application, the porosity P1 is determined by a combination of specific surface area and X-ray diffraction. The specific surface area analyzer is used to measure the pore volume V1 per unit mass using the BJH method. The framework volume V2 of the positive electrode active material is then refined using X-ray diffraction. P1 = V1 / (V1+V2)×100%.

[0039] It should be noted that the open pore volume of the positive electrode active material refers to the volume of the pores in the positive electrode active material; the framework volume of the positive electrode active material refers to the actual volume of the positive electrode active material excluding the open pore volume. In other words, the apparent total volume of the positive electrode active material in its natural state is the sum of the open pore volume and the framework volume.

[0040] As an example, the steps for testing the pore volume V1 include: adding the positive electrode active material into a specific surface area sample tube and pretreating the positive electrode active material in a degassing station; placing the pretreated positive electrode active material on a specific surface area analyzer and obtaining the adsorption-desorption isotherm of the positive electrode active material by measuring the gas adsorption amount corresponding to different relative pressures P / P0 at a constant temperature; and calculating the pore volume V1 from the adsorption-desorption isotherm according to a data processing model.

[0041] As an example, the steps for testing the framework volume V2 include: calibrating the X-ray diffractometer parameters using a standard and determining the test conditions; placing the positive electrode active material on the sample stage and performing the X-ray diffraction test under the test conditions, saving the test data for analysis; importing the test data into the refinement software for data processing to obtain the framework volume V2.

[0042] Furthermore, after arranging the average pore size of the positive electrode active material measured by the BJH method in ascending order, the pore size parameter Q was obtained. 10 Q 50 Q 90 .

[0043] In some embodiments, the porosity of the positive electrode active material is 3.5%-5.0%. This results in a lower degree of particle density, higher mechanical stability, and a larger effective contact area with the solid electrolyte, which helps maintain close contact between the positive electrode active material and the solid electrolyte, forming a continuous lithium-ion transport channel.

[0044] In some embodiments, the closed-pore porosity of the positive electrode active material is 1.2%-2.5%.

[0045] As an example, the closed-pore porosity P2 of the positive electrode active material can be 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, or 2.5%, etc.

[0046] The closed-pore porosity has a significant impact on the structural stability of the positive electrode active material. When the closed-pore porosity is within the aforementioned range, a moderate expansion buffer space is retained between the positive electrode active material particles, which can effectively alleviate stress accumulation during the charging and discharging process and inhibit particle breakage. At the same time, the structure of the positive electrode active material is not excessively loose, ensuring the continuity of the electron transport path.

[0047] In this application, the closed-cell porosity P2 is determined by true density combined with X-ray diffraction. The true density of the positive electrode active material is obtained by a true density meter, and the reciprocal is taken to obtain the true volume V3 per unit mass of the positive electrode active material. V3 = true framework volume V2 + closed-cell volume, and the closed-cell porosity P2 = (V3 - V2) / (V1 + V2) × 100%.

[0048] The aforementioned porosity characterization method, which combines specific surface area and XRD analysis with multiple physical quantities, can effectively solve the error problem caused by using SEM images to statistically analyze porosity in related technologies. By coupling the crystal structure information (XRD), surface adsorption characteristics (BET), and true density of the cathode active material, non-destructive, full-sample characterization of the open and closed pore porosity within the cathode active material can be achieved. Compared with the shortcomings of traditional cross-sectional morphology statistical methods, such as overgeneralization and insufficient statistical sample size, this method has stronger statistical significance and universality, ensuring high data accuracy. Therefore, open and closed pore porosity can more accurately reflect the densification degree of the cathode active material, and using cathode active materials that meet the porosity requirements can effectively improve battery capacity utilization, rate performance, and cycle stability.

[0049] In some embodiments, at least one of the following conditions is satisfied: 8nm ≤ Q 10 ≤15nm; 50nm≤Q 50 ≤80nm; 120nm≤Q 90 ≤200nm.

[0050] As an example, Q 10 It can be 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, or 15nm, etc., Q 50 It can be 50nm, 60nm, 70nm or 80nm, etc., Q 90 It can be 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm, etc.

[0051] If the above pore size distribution conditions are met, the positive electrode active material has better mechanical stability and higher interfacial contact coverage with the solid electrolyte.

[0052] As an example, Q 10 Q 50 Q 90 The specific testing method can be as follows: Take a certain mass of positive electrode active material, dehydrate and degas it in a sealed tube at 300℃, and then transfer it to a specific surface area test bottle. Use nitrogen as the adsorption gas, test and record the amount of nitrogen adsorbed by the positive electrode active material under different nitrogen pressures from vacuum to nitrogen saturated vapor pressure, and obtain the adsorption isotherm curve. Based on the BJH model, the pore size and corresponding volume ratio of the positive electrode active material can be calculated.

[0053] In some embodiments, the lithium-rich manganese-based substrate oxide comprises secondary particles formed by the agglomeration of primary particles, wherein the primary particles have a layered structure. This facilitates shortening the lithium-ion diffusion path and increasing the lithium-ion diffusion rate.

[0054] In some embodiments, the average aspect ratio of the primary particles is 2.5-9.

[0055] As an example, the average aspect ratio of a primary particle can be 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, or 9, etc.

[0056] When the average aspect ratio of the primary particles is within the above range, it is beneficial to control the porosity of the positive electrode active material.

[0057] As an example, a specific method for testing the average aspect ratio of a single particle can be as follows: SEM analysis is performed on the surface of the positive electrode active material particles to obtain the major and minor axes. The longest direction of the particle, measured by the maximum distance between its two ends, is the major axis; the maximum width in the direction perpendicular to the major axis is the minor axis. The ratio of the major axis to the minor axis is the aspect ratio. The average aspect ratio is obtained by calculating the aspect ratios of all particles in a single SEM image and then averaging the results.

[0058] In some embodiments, the average major axis dimension of the primary particles is 400nm-800nm; and / or, the average minor axis dimension of the primary particles is 85nm-200nm.

[0059] As an example, the average major axis size of a primary particle can be 400nm, 500nm, 600nm, 700nm, or 800nm, etc., and the average minor axis size of a primary particle can be 85nm, 100nm, 120nm, 140nm, 160nm, 180nm, or 200nm, etc.

[0060] When the average major axis size and average minor axis size of the primary particles are within the above range, it is beneficial to reduce the breakage of the positive electrode active material and improve the lithium-ion transport rate.

[0061] In some embodiments, the positive electrode active material satisfies: 0.6 ≤ K ≤ 1.0, where K = (D 90 -D 10 ) / D 50 .

[0062] As an example, K can be 0.6, 0.7, 0.8, 0.9, or 1.0, etc.

[0063] When K is within the above range, the particle size uniformity of the secondary particles of the positive electrode active material is relatively high, and the processing performance is good.

[0064] In particle size distribution, D 50 Also known as the median particle size, it means that 50% of the volume of particles are smaller than or equal to this value, D. 90This means that 90% of the volumetric particle size is less than or equal to this value, D 10 This means that 10% of the volume of particles are smaller than or equal to this value. (D) 10 D 50 D 90 It can be measured using a Malvern 3000 laser particle size analyzer.

[0065] In some embodiments, the D of the positive electrode active material 50 The range is 2μm-6μm.

[0066] As an example, the D of the positive electrode active material 50 It can be 2μm, 3μm, 4μm, 5μm or 6μm, etc.

[0067] D of positive electrode active material 50 Within the aforementioned range, the lithium-ion diffusion distance is moderate, and there are many contact sites between the positive electrode active material particles, making it easy to form a continuous electronic pathway, which is beneficial to improving the capacity utilization of the positive electrode active material.

[0068] In some embodiments, the specific surface area of ​​the positive electrode active material is 1 m². 2 / g-5m 2 / g.

[0069] As an example, the specific surface area of ​​the positive electrode active material can be 1 m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g or 5m 2 / g.

[0070] When the specific surface area is within the aforementioned range, the positive electrode active material possesses both high reactivity and good structural stability. On the one hand, a specific surface area within the aforementioned range can provide sufficient electrochemical active sites, which helps to improve the rate performance of the positive electrode active material; on the other hand, a moderate specific surface area is less likely to cause severe interfacial side reactions and gas evolution, thereby significantly improving the first-cycle coulombic efficiency and long cycle life of the positive electrode active material.

[0071] As an example, the specific surface area can be measured using the Tri-star 3020 specific surface area analyzer from Micron Technology, Inc.

[0072] In some embodiments, the positive electrode active material satisfies the following chemical formula: Li 1+a Mn x Ni y Co z M bO2, where 0 < a < 0.33, 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 ≤ b < 0.1; M includes at least one of Mg, Al, Fe, Zn, Ti, Mo, V, Cr, Nb, Zr, Ta, W, Y, Ca, and Cu. Thus, the introduction of M element is beneficial to improving the structural stability of the cathode active material and regulating the porosity of the cathode active material.

[0073] As an example, a can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or 0.33, etc.

[0074] As an example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc.

[0075] As an example, y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc.

[0076] As an example, z can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc.

[0077] As an example, b can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, etc.

[0078] In some embodiments, 0.1 < a ≤ 0.25, 0.35 < x < 0.7, 0.05 < y < 0.25, and 0.05 < z < 0.30. Thus, it is beneficial to further improve the structural stability of the cathode active material.

[0079] In the second aspect of the present application, the present application proposes a method for preparing the above-mentioned cathode active material. The present application realizes the controllable adjustment of the internal and external pore structures of the cathode active material particles by regulating the tapped density of the hydroxide precursor, and then obtains a cathode active material with a close packing structure. Moreover, the preparation method is simple, easy to operate, and easy to realize industrial production. Specifically, the method includes: S1: Mixing a manganese source, a nickel source, a cobalt source, a precipitating agent, a complexing agent, acetic acid, and deionized water and then carrying out a coprecipitation reaction to obtain a hydroxide precursor.

[0080] In some embodiments, the manganese source includes at least one selected from manganese sulfate, manganese carbonate, manganese nitrate, and manganese tetroxide; and / or, the nickel source includes at least one selected from nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate; and / or, the cobalt source includes at least one selected from cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate; and / or, the precipitant includes at least one selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and ammonium bicarbonate; and / or, the complexing agent includes at least one selected from ammonia, ammonium sulfate, ammonium nitrate, and citric acid. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is convenient.

[0081] In some embodiments, the concentration of acetic acid is 0.1 mol / L to 1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, or 1 mol / L. The introduction of acetic acid serves to form complexes with metal ions, ensuring uniform co-precipitation at the atomic level, moderating reaction kinetics to improve process controllability, and promoting the formation of regular, dense spherical particle morphologies.

[0082] In some embodiments, the tap density of the hydroxide precursor is 0.9 g / cm³. 3 -1.6g / cm 3 For example, it can be 0.9 g / cm³. 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 Or 1.6g / cm 3 There is a correlation between the tap density of the hydroxide precursor and the porosity of the cathode active material; as the tap density of the hydroxide precursor increases, the porosity of the cathode active material decreases.

[0083] In some embodiments, the D of the hydroxide precursor 50 The surface area is 2μm-6μm, for example, it can be 2μm, 3μm, 4μm, 5μm or 6μm, etc.; the specific surface area of ​​the hydroxide precursor is 20m². 2 / g-30m 2 / g, for example, can be 20m 2 / g、22m 2 / g、24m 2 / g、26m 2 / g、28m 2 / g or 30m 2 / g; the porosity of the hydroxide precursor is 18%-35%, for example, it can be 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32% or 35%, etc. This is beneficial for controlling the pore structure of the positive electrode active material.

[0084] The nucleation-growth equilibrium during the coprecipitation reaction is crucial in determining the microstructure density of the hydroxide precursor. Adjusting the pH and reaction temperature can alter the supersaturation of the system. Higher pH and lower temperatures enhance the nucleation driving force, causing the nucleation rate to far exceed the growth rate, easily generating small-sized, loosely packed hydroxide precursors with low tap density. Adjusting the process to a low pH and high temperature range can suppress excessively rapid nucleation and enhance growth kinetics, allowing primary particles to stack in an orderly manner, ultimately resulting in a hydroxide precursor with a high tap density.

[0085] In some embodiments, the temperature of the coprecipitation reaction is 45°C-65°C (e.g., 45°C, 50°C, 55°C, 60°C, or 65°C), and the pH of the coprecipitation reaction is 9.5-11.5 (e.g., 9.5, 10, 10.5, 11, or 11.5). This facilitates the control of the tap density of the hydroxide precursor, resulting in a hydroxide precursor with uniform particle size.

[0086] As an example, this step includes the following process: (1) Solution preparation: Manganese source, nickel source, cobalt source and acetic acid with a concentration of 0.1 mol / L-1 mol / L are mixed in deionized water to form a mixed salt solution with a total metal ion molar concentration of 0.4 mol / L-2 mol / L. At the same time, sodium hydroxide precipitant solution with a concentration of 2 mol / L-5 mol / L and ammonia complexing agent solution with a concentration of 0.2 mol / L-1.5 mol / L are prepared respectively.

[0087] (2) Reactor initialization: Add deionized water and some ammonia water to the reactor to prepare the base solution. Adjust the pH of the base solution to 9.5-11.5, maintain the temperature at 45℃-65℃, and introduce nitrogen gas as a protective atmosphere.

[0088] (3) Coprecipitation reaction: Under continuous stirring, the mixed salt solution, precipitant solution and complexing agent solution are pumped into the reactor in parallel at a flow rate of 5 L / min-30 L / min. During the reaction, the pH value of the system is stabilized in the range of 9.5-11.5 by dynamically adjusting the flow rate of the precipitant, and the temperature is maintained at 45℃-65℃.

[0089] (4) Post-treatment: The coprecipitated product obtained from the reaction is subjected to pressure filtration, washing and drying to obtain small-particle-size hydroxide precursor.

[0090] S2: The hydroxide precursor, lithium source and M source are mixed and then sintered to obtain the positive electrode active material.

[0091] In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate. Therefore, the raw materials are widely available, the cost is low, and large-scale deployment is easily facilitated.

[0092] In some embodiments, the M source includes at least one of the oxides, chlorides, carbonates, and sulfates corresponding to the M element. Therefore, introducing the M element is beneficial for improving the structural stability of the positive electrode active material and controlling its porosity.

[0093] In some embodiments, the sintering temperature is 800℃-900℃ (e.g., 800℃, 820℃, 840℃, 860℃, 880℃, or 900℃), and the sintering time is 8h-15h (e.g., 8h, 9h, 10h, 11h, 12h, 13h, 14h, or 15h). This helps to improve the crystallinity of the positive electrode active material, promotes stable and controllable grain growth, and, by controlling the sintering temperature, can adjust the open porosity of the positive electrode active material.

[0094] In a third aspect, this application proposes a dry-process positive electrode sheet, comprising a positive electrode active material 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. The interfacial contact coverage between the positive electrode active material and the solid electrolyte is greater than or equal to 90%. Thus, the solid electrolyte can form a sufficiently uniform coating layer on the surface of the positive electrode active material, which not only facilitates the uniform insertion and extraction of lithium ions at the interface between the positive electrode active material and the solid electrolyte, thereby inducing synergistic and uniform changes in lattice parameters, but also effectively maintains the structural integrity of the positive electrode active material and its stable contact with the solid electrolyte during long-term cycling.

[0095] As an example, the interfacial contact coverage between the positive electrode active material and the solid electrolyte can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 98%, etc.

[0096] As an example, a specific test method for interfacial contact coverage can be as follows: The positive electrode active material, solid electrolyte Li3InCl6, and vapor-grown carbon fiber are uniformly mixed in a mass ratio of 60:35:5, and then cold-pressed under 360 MPa pressure for 3 minutes. Subsequently, the pressed cross-section is cut using an ion polishing system to obtain a smooth, clean surface free of mechanical damage. The cross-sectional morphology is observed using a scanning electron microscope to obtain a clear image of the interfacial structure. Based on the SEM images, the total external perimeter of the positive electrode active material particles and the interfacial perimeter in contact with the solid electrolyte are statistically analyzed. By calculating the ratio of the contact perimeter to the total perimeter, the interfacial contact coverage between the positive electrode active material and the solid electrolyte can be quantitatively evaluated.

[0097] In a fourth aspect, this application proposes a solid-state battery comprising the dry-process positive electrode sheet described in the third aspect. Consequently, this solid-state battery exhibits high discharge specific capacity, excellent rate performance, and superior cycle stability.

[0098] 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.

[0099] 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.

[0100] [Preparation of Hydroxide Precursors] Preparation Example 1: Step 1: Prepare a mixed solution of Mn, Ni, Co, and acetic acid, wherein the total molar concentration of Mn, Ni, and Co in the mixed solution is 1 mol / L, the molar ratio of Mn, Ni, and Co is 0.67:0.16:0.17, and the concentration of acetic acid is 0.1 mol / L; prepare a 2 mol / L sodium hydroxide solution as a precipitant; prepare a 0.7 mol / L ammonia solution as a complexing agent; Step 2: Add the precipitant, pure water, and complexing agent to a sealed reaction vessel to prepare a base solution; control the pH of the base solution to 11.0-11.2, and the ammonia concentration in the base solution... The concentration of the solvent is 0.20 mol / L-0.30 mol / L, the temperature is maintained at 50℃, and nitrogen gas is introduced as a protective gas. Step 3: Keeping the reactor stirred, the mixed solution, precipitant, and complexing agent from Step 1 are continuously added to the reactor at a flow rate of 45 L / min-55 L / min to carry out a co-precipitation reaction. The pH value is maintained at 11.0-11.2, the reaction temperature is maintained at 50℃, and the reactor rotation speed is 400 r / min-500 r / min. Step 4: The co-precipitated product from Step 3 is filtered, washed, and dried to obtain a hydroxide precursor with the chemical formula Mn. 0.67 Ni 0.16 Co 0.17 (OH)2, D 50 The thickness is 2.0 μm, and the tap density is 0.9 g / cm³. 3 Specific surface area is 30m² 2 / g, with a porosity of 35%.

[0101] The difference between Preparation Example 2 and Preparation Example 1 is as follows: Step 1: Prepare ammonia water with a molar concentration of 0.9 mol / L as a complexing agent; Step 2: Control the pH of the base solution to 10.8-11.0, the ammonia concentration in the base solution to 0.25 mol / L-0.35 mol / L, maintain the temperature at 55℃, and start introducing nitrogen gas as a protective gas; Step 3: Keep the reactor stirred, and continuously add the mixed solution, precipitant, and complexing agent from Step 1 to the reactor at a flow rate of 40 L / min-50 L / min to carry out the co-precipitation reaction. During the reaction, maintain the pH value at 10.8-11.0, maintain the reaction temperature at 55℃, and the reactor rotation speed at 350 r / min-450 r / min; Step 4: Filter, wash, and dry the co-precipitated product from Step 3 to obtain a hydroxide precursor with the chemical formula Mn. 0.67 Ni 0.16 Co 0.17 (OH)2, D 50 The thickness is 3.5 μm, and the tap density is 1.25 g / cm³. 3 Specific surface area is 28m² 2 / g, with a porosity of 26%.

[0102] The difference between Preparation Example 3 and Preparation Example 1 is as follows: Step 1: Prepare ammonia water with a molar concentration of 1.1 mol / L as a complexing agent; Step 2: Control the pH of the base solution to 10.6-10.8, the ammonia concentration in the base solution to 0.30 mol / L-0.40 mol / L, maintain the temperature at 60℃, and start introducing nitrogen gas as a protective gas; Step 3: Keep the reactor stirred, and continuously add the mixed solution, precipitant, and complexing agent from Step 1 to the reactor at a flow rate of 35 L / min-40 L / min to carry out the co-precipitation reaction. During the reaction, maintain the pH value at 10.6-10.8, maintain the reaction temperature at 60℃, and the reactor rotation speed at 300 r / min-400 r / min; Step 4: Filter, wash, and dry the co-precipitated product from Step 3 to obtain a hydroxide precursor with the chemical formula Mn. 0.67 Ni 0.16 Co 0.17 (OH)2, D 50 The diameter is 5 μm, and the tap density is 1.5 g / cm³. 3 Specific surface area is 22m² 2 / g, with a porosity of 23%.

[0103] The difference between Preparation Example 4 and Preparation Example 1 is as follows: Step 1: Prepare ammonia water with a molar concentration of 1.2 mol / L as a complexing agent; Step 2: Control the pH of the base solution to 10.4-10.6, the ammonia concentration in the base solution to 0.32 mol / L-0.42 mol / L, maintain the temperature at 63℃, and start introducing nitrogen gas as a protective gas; Step 3: Keep the reactor stirred, and continuously add the mixed solution, precipitant, and complexing agent from Step 1 to the reactor at a flow rate of 30 L / min-35 L / min to carry out the co-precipitation reaction. During the reaction, maintain the pH value at 10.4-10.6, maintain the reaction temperature at 63℃, and the reactor rotation speed at 250 r / min-300 r / min; Step 4: Filter, wash, and dry the co-precipitated product from Step 3 to obtain a hydroxide precursor with the chemical formula Mn. 0.67 Ni 0.16 Co 0.17 (OH)2, D 50 The diameter is 6 μm, and the tap density is 1.6 g / cm³. 3 Specific surface area is 20m² 2 / g, with a porosity of 18%.

[0104] Preparation Example 5 was prepared using the same method as Preparation Example 3, except that the molar ratio of Mn, Ni, and Co was 0.65:0.25:0.1, and the chemical formula of the hydroxide precursor was Mn. 0.65Ni 0.25 Co 0.1 (OH)2, D 50 The thickness is 4.9 μm, and the tap density is 1.48 g / cm³. 3 Specific surface area is 21m² 2 / g, with a porosity of 21%.

[0105] The difference between Preparation Example 1 and Preparation Example 2 is as follows: Step 1: Prepare ammonia solution with a molar concentration of 1.5 mol / L as a complexing agent; Step 2: Control the pH of the base solution to 10.3-10.5, the ammonia concentration in the base solution to 0.35 mol / L-0.45 mol / L, maintain the temperature at 70℃, and begin introducing nitrogen gas as a protective gas; Step 3: Keep the reactor stirred, and continuously add the mixed solution, precipitant, and complexing agent from Step 1 to the reactor at a flow rate of 20 L / min-30 L / min to carry out the co-precipitation reaction. During the reaction, maintain the pH value at 10.2-10.4, maintain the reaction temperature at 70℃, and the reactor rotation speed at 180 r / min-220 r / min; Step 4: Filter, wash, and dry the co-precipitated product from Step 3 to obtain a hydroxide precursor with the chemical formula Mn. 0.67 Ni 0.16 Co 0.17 (OH)2, D 50 The thickness is 3.5 μm, and the tap density is 1.68 g / cm³. 3 Its specific surface area is 16.2 m². 2 / g, with a porosity of 15.4%.

[0106] [Preparation of Positive Electrode Active Material] Example 1: The hydroxide precursor, lithium carbonate, alumina, and niobium pentoxide from Preparation Example 1 were accurately weighed in a molar ratio of 0.99:1.50:0.005:0.005 and then uniformly mixed in a high-speed mixer. The molar amount of the hydroxide precursor was calculated as the total molar amount of (Mn+Ni+Co). The molar amount of lithium carbonate was calculated as the molar amount of lithium element. The uniformly mixed material was sintered in a muffle furnace. The sintering regime was as follows: heating at 5°C / min to 500°C, holding at that temperature for 5 hours, then heating at 2°C / min to 900°C, and sintering at 900°C for 10 hours, followed by furnace cooling to room temperature. The sintered product was sieved to obtain the positive electrode active material.

[0107] The preparation method of Comparative Example 5 is the same as that of Example 1.

[0108] The open porosity of the positive electrode active material was measured to be 7.2% using conventional SEM.

[0109] The differences between other embodiments and comparative examples and embodiment 1 are shown in Table 1.

[0110] Table 1

[0111] The above-prepared positive electrode active material was tested as follows. The porosity of the positive electrode active material in Comparative Example 5 was tested using the following method: (1) The positive electrode active material was cut using an ion milling machine, and the particles were cut in the middle. (2) The cut sample was photographed under a scanning electron microscope. A single particle was selected to fill the field of view and photographed. The grain boundaries of the particles were required to be clear in one photograph. More than 5 particles were selected for photographing. (3) The photographed image was analyzed using a lithium battery material image intelligent analysis system. The image contour was refined using calipers. Finally, the porosity was automatically calculated using software. The average value of 5 sets of data is the porosity of the sample. The test results are shown in Tables 2-1 and 2-2.

[0112] 1. Open porosity P1: The open porosity V1 per unit mass is measured by BJH method using a specific surface area analyzer, and the skeleton volume V2 per unit mass of the material is obtained by X-ray diffraction. P1 = V1 / (V1+V2)×100%.

[0113] 2. Closed-cell porosity P2: The true density of the material is obtained by a true density meter, and the reciprocal is taken to obtain the true volume V3 per unit mass of the material. V3 = true skeleton volume V2 + closed-cell volume. Closed-cell porosity P2 = (V3 - V2) / (V1 + V2) × 100%.

[0114] 3. Q 10 Q 50 Q 90 Test: A certain mass of positive electrode active material is dehydrated and degassed in a sealed tube at 300℃, and then transferred to a specific surface area test bottle. Nitrogen is used as the adsorption gas. The amount of nitrogen adsorbed by the material under different nitrogen pressures from vacuum to nitrogen saturated vapor pressure is tested and recorded to obtain the adsorption isotherm curve. Based on the BJH model, the pore size and corresponding volume ratio of the positive electrode active material can be calculated.

[0115] 4. Average Aspect Ratio: The major and minor axes are obtained by analyzing the SEM test results of the positive electrode active material particles. The longest direction of the particle, where the maximum distance between its two ends is measured, is the major axis; the maximum width perpendicular to the major axis is the minor axis. The ratio of the major axis to the minor axis is the aspect ratio. The average aspect ratio is obtained by calculating the aspect ratios of all particles in a photograph and averaging them.

[0116] 5. D 10 D 50 D 90 The particle size distribution was obtained using a Malvern 3000 laser particle size analyzer.

[0117] 6. Specific surface area: Measured using a Tri-star 3020 specific surface area analyzer from Micron Technology, USA.

[0118] 7. Interface Contact Coverage: The positive electrode active material, Li3InCl6 solid electrolyte, and vapor-grown carbon fiber were uniformly mixed at a mass ratio of 60:35:5 and then cold-pressed under 360 MPa pressure for 3 minutes. Subsequently, the pressed cross-section was cut using an ion polishing system to obtain a smooth, clean surface free of mechanical damage. The cross-sectional morphology was observed using a scanning electron microscope to obtain a clear image of the interface structure. Based on the SEM images, the total external perimeter of the positive electrode active material particles and the perimeter of the interface with the solid electrolyte were statistically analyzed. By calculating the ratio of the contact perimeter to the total perimeter, the interface contact coverage between the positive electrode active material and the solid electrolyte can be quantitatively evaluated.

[0119] Table 2-1

[0120] In this context, "-" indicates that the data was not measured.

[0121] Table 2-2

[0122] The above-prepared positive electrode active material is assembled into a solid-state battery. The specific steps are as follows: (1) Constructing a double-layer electrolyte layer: First, 40 mg of Li6PS5Cl powder is filled into a polyarylether ether ketone mold and cold-pressed for 2 minutes under a pressure of 360 MPa to form a dense bottom layer; then, 80 mg of Li3InCl6 powder is spread on the bottom layer and pressed again under the same pressure conditions to form a complete double-layer solid electrolyte structure.

[0123] (2) Preparation of dry positive electrode sheet: The obtained positive active material, solid electrolyte Li3InCl6 and vapor-grown carbon fiber are uniformly mixed at a mass ratio of 60:35:5 to obtain a positive electrode composite. About 15 mg of the positive electrode composite is transferred to the surface of the Li3InCl6 layer and pressed at 360 MPa for 3 minutes to form a dry positive electrode sheet.

[0124] (3) Assembling the composite negative electrode and encapsulation: On the other side of the double electrolyte, an indium foil with a diameter of 10 mm and a thickness of 100 μm and a lithium foil with a diameter of 10 mm and a thickness of 30 μm are placed in sequence to form the composite negative electrode. Finally, the entire battery core is fixed in a stainless steel shell and encapsulated under a constant pressure of about 500 MPa to obtain a solid-state battery.

[0125] The electrical performance of the assembled batteries was tested, and the results are shown in Table 3.

[0126] (1) Capacity test conditions: After the prepared mold battery was left to stand for 10 hours, it was charged and discharged at room temperature with 1C=250mA / g in the range of 0.1C and 1.9V-4.2V. The specific capacity of the first charge and discharge and the coulombic efficiency of the first cycle were recorded.

[0127] (2) Rate test conditions: Within the voltage range of 1.9V-4.2V, after two cycles of 0.1C, charge and discharge test is performed at 1C to obtain the discharge specific capacity at 1C.

[0128] (3) Cyclic test conditions: After the battery is activated for two cycles in the 0.1C, 1.9V-4.2V voltage range, it is subjected to 200 charge-discharge cycles in the 1C current density, 1.9V-4.2V voltage range, and the capacity retention rate is recorded.

[0129] Table 3

[0130] Figure 1 shows the hydroxide precursor obtained in Preparation Example 2, which exhibits a distinct lamellar structure with certain gaps between the primary particles. Figure 2 shows the lithium-rich manganese-based cathode active material prepared based on Preparation Example 2 (Example 2). The material as a whole inherits the lamellar morphology of the precursor and exhibits good sphericity.

[0131] Figure 3 shows the hydroxide precursor obtained in Comparative Preparation Example 1, which is observed to be very densely packed with primary particles that are tightly bound and of uneven thickness. Figure 4 shows the lithium-rich manganese-based cathode active material prepared based on Preparation Example 1 (Comparative Example 1), whose primary particle morphology is significantly different from that of Example 2. It is no longer lamellar but tends to be granular, and the overall packing is also more dense.

[0132] Figure 7 shows the image obtained by SEM testing of the positive electrode active material prepared in Example 2, which was uniformly mixed with solid electrolyte Li3InCl6 and vapor-grown carbon fiber at a mass ratio of 60:35:5, pressed at 360MPa for 3 minutes, and then the interface was cut using an ion polishing system to obtain a flat and clean material cross-section.

[0133] As can be seen from Table 3, compared with Comparative Examples 1-4, the positive electrode active materials of Examples 1-18 all meet the requirement that the open porosity is in the range of 3%-6% and that 2≤R≤2.35, which makes their discharge specific capacity, rate performance and cycle stability in solid-state battery systems better.

[0134] In Example 1, the porosity of the positive electrode active material was measured using the method described in this application, and the measured value was within the range of this application. In Comparative Example 5, the porosity of the positive electrode active material was measured using conventional SEM, and the measured value was outside the range of this application. In Comparative Example 5, due to factors such as sample preparation, shooting angle, and cross-sectional position, the porosity test data fluctuated significantly, was inaccurate, and had a large dispersion. Furthermore, SEM cross-sectional testing is a planar single-particle porosity test, which can greatly affect the uniformity between material particles. Using the specific testing method of this application (specific surface area + XRD), the densification degree of the positive electrode active material can be accurately reflected. Therefore, using the specific surface area combined with X-ray diffraction method to obtain a positive electrode active material with an open porosity of 3%-6% can effectively improve the battery's capacity utilization, rate performance, and cycle stability.

[0135] As shown in Table 3, with the increase of the tap density of the hydroxide precursor in Preparation Examples 1-4, the compactness of the hydroxide precursor gradually increases, i.e., the open porosity gradually decreases, and correspondingly, the open porosity of the positive electrode active materials obtained in Examples 1-4 gradually decreases. Furthermore, the porosity of the positive electrode active material can also be controlled by changing the type of M source. For example, in Example 5, compared to Example 3, the M source was changed from molybdenum trioxide to molybdenum disulfide. During sintering, the volatilization of sulfur generates gas, which can effectively increase the open porosity of the positive electrode active material; therefore, Example 5 has a higher open porosity. Examples 6-7 also achieved an increase in open porosity by lowering the sintering temperature. Thus, this application can achieve precise control of the open porosity of the positive electrode active material through various methods such as adjusting the porosity of the hydroxide precursor, the type of M source, and the sintering regime. The results show that when the open porosity of the positive electrode active material is controlled between 3% and 6%, the overall performance of the solid-state battery is better.

[0136] The pore structure of Example 2 and Comparative Example 1 was analyzed using the BJH adsorption model, and the results are shown in Figures 5 and 6. The pore size distributions of the two examples differ significantly: Comparative Example 1, with its more compact structure, exhibits a higher pore volume distribution at larger pore sizes. Figure 6 shows the Q... 10 Q 50 Q 90 The values ​​(see Table 2-1) show that the change in pore size distribution originates from the material densification process. This process minimizes the system's energy by reducing the high-energy surface area (i.e., reducing the specific surface area), specifically manifested as the gradual disappearance of small pores, the continuous merging and coarsening of pores, ultimately leading to an increase in the average pore size. Let R = (Q 90 - Q 10 ) / Q 50Measuring pore size uniformity reveals that the R values ​​of all embodiments are between 2 and 2.35; however, the R value of Comparative Example 1 is too large, indicating excessively dense particles; while the R value of Comparative Example 2 is too small, indicating excessively porous material. Both are detrimental to the specific capacity and rate performance of solid-state batteries.

[0137] The fundamental reason is that the porosity and pore size distribution directly affect the interfacial contact coverage between the positive electrode active material and the solid electrolyte. This application points out that only when the porosity is maintained at 3%-6% and the R value is maintained in the range of 2-2.35 can the interfacial contact coverage between the positive electrode active material and the solid electrolyte reach more than 90%, thereby ensuring that the solid-state battery obtains higher specific capacity and excellent rate performance.

[0138] Test results show that the open porosity and closed porosity of the positive electrode active material exhibit a significant negative correlation, meaning that positive electrode active materials with higher open porosity usually exhibit lower closed porosity. This phenomenon mainly stems from the microstructural characteristics of the positive electrode active material: in positive electrode active materials with high open porosity, the primary particle agglomeration is relatively loose, and there are large and tortuous gaps between particles; these structures are difficult to completely close during sintering, thus retaining more open channels and also limiting the formation of internal closed pores.

[0139] Further analysis revealed that the cathode active material with a closed-pore porosity in the range of 1.2%–2.5% exhibited the best electrochemical performance. This pore structure offers the following synergistic advantages: Volume change adaptability: A suitable expansion buffer space is maintained between primary particles, effectively alleviating stress accumulation during charging and discharging and inhibiting particle breakage; Conductive network integrity: The structure is not excessively porous, ensuring the continuity of electron transport paths and preventing a significant decrease in conductivity; Interfacial contact stability: The moderately open-pore structure helps maintain close contact between the electrode and the solid electrolyte, promoting lithium-ion interfacial transport.

[0140] Therefore, by adjusting the tap density of the hydroxide precursor, the type of M source, and the sintering process, the balance between open-pore and closed-pore structures can be optimized, which can significantly improve the cycle stability and reversible capacity of lithium-rich manganese-based cathode active materials in solid-state battery systems.

[0141] 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 cathode active material includes a lithium-rich manganese-based substrate oxide, wherein the open porosity of the cathode active material is 3.0%-6.0%; the cathode active material satisfies: 2≤R≤2.35, where R = (Q 90 -Q 10 ) / Q 50 Q 10 Q represents the pore size value corresponding to 10% of the pore size distribution. 50 Q represents the pore size value corresponding to 50% accumulation of pore volume distribution. 90 This is the pore size value corresponding to when the pore volume distribution accumulates to 90%.

2. The positive electrode active material according to claim 1, characterized in that, The porosity of the positive electrode active material is 3.5%-5.0%.

3. The positive electrode active material according to claim 1, characterized in that, The closed-pore porosity of the positive electrode active material is 1.2%-2.5%.

4. The positive electrode active material according to claim 1, characterized in that, At least one of the following conditions must be met: 8nm≤Q 10 ≤15nm; 50nm≤Q 50 ≤80nm; 120nm≤Q 90 ≤200nm.

5. The positive electrode active material according to claim 1, characterized in that, The lithium-rich manganese-based crystalline oxide comprises secondary particles formed by the agglomeration of primary particles, wherein the primary particles have a lamellar structure.

6. The positive electrode active material according to claim 5, characterized in that, The average aspect ratio of the primary particles is 2.5-9.

7. The positive electrode active material according to claim 6, characterized in that, The average major axis dimension of the primary particles is 400nm-800nm; and / or, the average minor axis dimension of the primary particles is 85nm-200nm.

8. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies: 0.6 ≤ K ≤ 1.0, where K = (D 90 -D 10 ) / D 50 ; and / or, the D of the positive electrode active material 50 The surface area is 2μm-6μm; and / or the specific surface area of ​​the positive electrode active material is 1m². 2 / g-5m 2 / g.

9. The positive electrode active material according to any one of claims 1-8, characterized in that, Satisfies the following chemical formula: Li 1+a Mn x Ni y Co z M b O2, where 0 < a < 0.33, 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 ≤ b < 0.1; M includes at least one of Mg, Al, Fe, Zn, Ti, Mo, V, Cr, Nb, Zr, Ta, W, Y, Ca, Cu.

10. The positive electrode active material according to claim 9, characterized in that, 0.1 <a≤0.25,0.35<x<0.7,0.05<y<0.25,0.05<z<0.30。 11. A method for preparing the positive electrode active material according to any one of claims 1-10, characterized in that, include: A co-precipitation reaction was carried out by mixing manganese source, nickel source, cobalt source, precipitant, complexing agent, acetic acid, and deionized water to obtain a hydroxide precursor with a tap density of 0.9 g / cm³. 3 -1.6g / cm 3 The hydroxide precursor, lithium source and M source are mixed and then sintered to obtain the positive electrode active material.

12. The method according to claim 11, characterized in that, At least one of the following conditions must be met: the D of the hydroxide precursor 50 The surface area is 2μm-6μm; the specific surface area of ​​the hydroxide precursor is 20m². 2 / g-30m 2 / g; the porosity of the hydroxide precursor is 18%-35%.

13. The method according to claim 11, characterized in that, The temperature of the coprecipitation reaction is 45℃-65℃, and the pH of the coprecipitation reaction is 9.5-11.

5.

14. The method according to claim 11, characterized in that, The sintering temperature is 800℃-900℃, and the sintering time is 8h-15h.

15. The method according to claim 11, characterized in that, The manganese source includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, and manganese tetroxide; and / or, the nickel source includes at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate; and / or, the cobalt source includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate; and / or, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; and / or, the M source includes at least one of the oxide, chloride, carbonate, and sulfate corresponding to element M; and / or, the precipitant includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and ammonium bicarbonate; and / or, the complexing agent includes at least one of ammonia, ammonium sulfate, ammonium nitrate, and citric acid.

16. A dry-process positive electrode sheet, characterized in that, The invention includes a positive electrode active material and a solid electrolyte, wherein the positive electrode active material includes the positive electrode active material according to any one of claims 1-10 or the positive electrode active material prepared by the method according to any one of claims 11-15, and the interfacial contact coverage between the positive electrode active material and the solid electrolyte is greater than or equal to 90%.

17. A solid-state battery, characterized in that, Includes the dry-process positive electrode sheet as described in claim 16.

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