Positive electrode active material and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a positive electrode active material and a preparation method and application thereof. The invention provides a preparation method of a positive electrode active material, which comprises the following steps: S1, mixing a nickel manganese precursor, a first lithium source and a dopant, introducing oxygen-containing gas, and carrying out first sintering and microwave-assisted sintering to obtain a lithium nickel manganese oxide material; wherein the temperature of the first sintering is 800-950 DEG C, the temperature of the microwave-assisted sintering is 600-700 DEG C, and the flow of the oxygen-containing gas in the microwave-assisted sintering process is larger than that in the first sintering process; and S2, mixing the lithium nickel manganese oxide material and the LATP precursor gel, and carrying out microwave-assisted coating to obtain the positive electrode active material. According to the positive electrode active material provided by the invention, the capacity and the rate capability are further improved while the high-temperature cycle performance and the safety are improved.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a positive electrode active material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have advantages such as high operating voltage, large specific capacity, long cycle life, and low pollution. Commonly used cathode materials for lithium-ion batteries include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate. Among them, lithium cobalt oxide and lithium nickel cobalt manganese oxide pose significant safety risks when used as cathode materials for power batteries, and cobalt is expensive. While lithium manganese oxide is low-cost and has good safety performance, its specific capacity is relatively low, and excessive trivalent manganese can lead to Mn dissolution, Jahn-Teller distortion, and lattice instability, resulting in unsatisfactory electrical performance, especially cycle life. Lithium nickel manganese oxide, by doping nickel into lithium manganese oxide, can solve some of the Mn dissolution and Jahn-Teller distortion issues. While doping and coating can improve the conductivity and structural stability of lithium nickel manganese oxide (LiMO) to enhance its electrochemical performance, existing technologies offer limited improvements. However, LiMO suffers from numerous disordered phases, oxygen vacancies, and high trivalent manganese ion content. Under high temperature and pressure, it still undergoes numerous side reactions with the electrolyte, generating large amounts of gas and resulting in poor safety. Furthermore, it exhibits severe Mn dissolution, severe Jahn-Teller distortion, and poor lattice stability, leading to poor high-temperature cycling performance. Therefore, passive protection methods like doping or coating cannot effectively address the problems inherent in LiMO cathode materials. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this application is to overcome the defects in the internal structure of doped or coated modified lithium nickel manganese oxide materials in the prior art, which have many disordered phases, many oxygen vacancies, and a high content of trivalent manganese ions. Excessive trivalent manganese leads to severe Mn dissolution, severe Jahn-Teller distortion effect and poor lattice stability, resulting in poor high-temperature cycling performance of modified lithium nickel manganese oxide materials. This application provides a positive electrode active material, its preparation method and application.

[0004] Therefore, this application provides the following technical solution.

[0005] This application provides a method for preparing a positive electrode active material, comprising the following steps:

[0006] S1, mix the nickel-manganese precursor, the first lithium source and the dopant, and pass in oxygen-containing gas to perform the first sintering and microwave-assisted sintering to obtain lithium nickel manganese oxide material;

[0007] The temperature of the first sintering is 800-950℃, the temperature of the microwave-assisted sintering is 600-700℃, and the flow rate of oxygen-containing gas during the microwave-assisted sintering process is greater than the flow rate of oxygen-containing gas during the first sintering process.

[0008] S2, lithium nickel manganese oxide material and LATP precursor gel are mixed and microwave-assisted coating is performed to obtain positive electrode active material.

[0009] In one optional embodiment, the flow rate of oxygen-containing gas during the first sintering process is 10-30 L / min;

[0010] In one optional embodiment, the flow rate of oxygen-containing gas during the microwave-assisted sintering process is 40-50 L / min.

[0011] In one alternative embodiment, the nickel-manganese precursor comprises nickel-manganese hydroxide;

[0012] In one optional embodiment, the first lithium source includes at least one of lithium carbonate, lithium acetate, and lithium hydroxide.

[0013] In one optional embodiment, the ratio of the total molar amount of nickel and manganese in the nickel-manganese precursor to the molar amount of lithium in the first lithium source is 1:(1.01-1.05).

[0014] In one alternative embodiment, the dopant includes titanium-containing compounds, tungsten-containing compounds, and magnesium-containing compounds.

[0015] In one optional embodiment, the titanium-containing compound includes at least one of titanium dioxide, titanium chloride, titanium sulfate, and titanium nitrate;

[0016] In one alternative embodiment, the tungsten-containing compound includes at least one of tungsten trioxide, tungsten dioxide, and tungsten hexafluoride;

[0017] In one alternative embodiment, the magnesium-containing compound includes at least one of magnesium oxide, magnesium nitrate, and magnesium peroxide;

[0018] In one optional embodiment, the mass percentage of titanium in the titanium-containing compound is 2000-6000 ppm, based on the mass of the nickel-manganese precursor.

[0019] In one optional embodiment, the mass percentage of tungsten in the tungsten-containing compound is 500-3000 ppm, based on the mass of the nickel-manganese precursor.

[0020] In one alternative embodiment, the magnesium content in the magnesium-containing compound is 500-3000 ppm, based on the mass of the nickel-manganese precursor.

[0021] In one optional implementation, in step S1, the mixing parameters include: a rotation speed of 1500-2500 r / min and a time of 15-25 min; in step S2, the mixing does not require parameter limitation, and conventional parameters in the art can be used to mix evenly. As an example, conventional parameters of a high-speed disperser are used for mixing.

[0022] In one optional embodiment, the heating rate of the first sintering is 2-4 °C / min;

[0023] In one optional embodiment, the first sintering time is 8-10 hours;

[0024] In one optional embodiment, the cooling rate of the microwave-assisted sintering is 0.5-1℃ / min;

[0025] In one optional embodiment, the microwave-assisted sintering time is 1-2 hours;

[0026] In one optional embodiment, the frequency of the microwave-assisted sintering is 800-1000MHz;

[0027] In one alternative embodiment, the microwave-assisted sintering is followed by natural cooling to room temperature to obtain lithium nickel manganese oxide material.

[0028] In one optional embodiment, step S1 further includes a crushing process after microwave-assisted sintering, and the median particle size D50 of the processed lithium nickel manganese oxide material is 4-6 μm.

[0029] In one optional embodiment, the preparation steps of the LATP precursor gel include: mixing a second lithium source, an aluminum source, a titanium source and a phosphorus source to obtain a mixed slurry, adding a retarder and adjusting the pH value of the mixed slurry to obtain the LATP precursor gel.

[0030] Optionally, the molar ratio of lithium in the second lithium source, aluminum in the aluminum source, titanium in the titanium source, and phosphorus in the phosphorus source is (1.28-1.32):(0.28-0.32):(1.68-1.72):(2.98-3.02);

[0031] Optionally, the second lithium source includes at least one of lithium acetate and lithium hydroxide; optionally, the aluminum source includes at least one of aluminum nitrate and aluminum carbonate; optionally, the titanium source includes at least one of titanium diacetate and tetrabutyl titanate; optionally, the phosphorus source includes at least one of ammonium dihydrogen phosphate and lithium dihydrogen phosphate.

[0032] Optionally, the solid content of the mixed slurry is 50-70%;

[0033] Optionally, the retarder includes at least one of ethanol, ethylene glycol, propylene glycol, and glycerin;

[0034] Optionally, the amount of retarder added is 20-40 wt%, based on the mass of the solvent in the mixed slurry;

[0035] Optionally, the concentration of the retarder is 95-100 wt%.

[0036] Optionally, the pH value of the mixed slurry is 3.5-4.5.

[0037] The LATP precursor gel was prepared under stirring at a speed of 100-300 r / min for 0.5-1 h. Under stirring conditions, metal ions (such as Li+, Al) were stirred. 3 +、Ti 4 The alkoxide or aqueous solution of LATP undergoes a hydrolysis reaction to generate an active monomer, which is then converted into a transparent sol through a condensation reaction to obtain the LATP precursor gel.

[0038] In one optional embodiment, the mass percentage of phosphorus in the LATP precursor gel is 2000-3000 ppm, based on the mass of the lithium nickel manganese oxide material.

[0039] In one optional embodiment, in step S2, the lithium nickel manganese oxide material and LATP precursor gel are mixed and then heated to 800-900°C for microwave-assisted coating; optionally, the microwave-assisted coating time is 1-2 hours; optionally, the microwave-assisted coating frequency is 800-1000 MHz; optionally, the heating rate is 2-5°C / min.

[0040] In one alternative embodiment, the microwave-assisted coating is followed by natural cooling to room temperature to obtain the positive electrode active material.

[0041] Optionally, the positive electrode active material is subjected to crushing treatment, and the median particle size D50 of the treated positive electrode active material is 4-6 μm.

[0042] This application also provides a positive electrode active material, which is prepared by the above-described preparation method.

[0043] This application also provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the aforementioned positive active material.

[0044] This application also provides a secondary battery, including the aforementioned positive electrode plate.

[0045] The technical solution of this application has the following advantages:

[0046] 1. The method for preparing the positive electrode active material provided in this application includes the following steps: S1, mixing a nickel-manganese precursor, a first lithium source, and a dopant, and introducing oxygen-containing gas for a first sintering and microwave-assisted sintering to obtain a lithium nickel manganese oxide material; wherein, the temperature of the first sintering is 800-950℃, the temperature of the microwave-assisted sintering is 600-700℃, and the flow rate of the oxygen-containing gas during the microwave-assisted sintering process is greater than the flow rate of the oxygen-containing gas during the first sintering process; S2, mixing the lithium nickel manganese oxide material and LATP precursor gel, and microwave-assisted coating to obtain the positive electrode active material. The positive electrode active material provided in this application improves high-temperature cycling performance and safety, while also further enhancing capacity and rate performance. The first sintering is carried out at 800-950℃, during which the nickel-manganese precursor and the first lithium source undergo a solid-state reaction to form lithium nickel manganese oxide with a spinel crystal structure, giving it good electrochemical activity. Subsequently, microwave-assisted sintering is performed, during which the spinel lithium nickel manganese oxide transforms from a disordered phase to an ordered phase at 600-700℃. In this application, the oxygen content introduced in the microwave-assisted sintering stage is increased, which, together with the microwave-assisted sintering, excites the chemical bonds in the lithium nickel manganese oxide and accelerates the absorption of sufficient oxygen by the lithium nickel manganese oxide. This significantly reduces the disordered phase, oxygen defects, and trivalent manganese ions in the lithium nickel manganese oxide, thereby reducing manganese dissolution and distortion effects, improving the lattice stability of the material, and thus improving the cycle performance of the lithium nickel manganese oxide material. This application utilizes microwave-assisted coating to densely coat the LATP precursor gel onto the surface of lithium nickel manganese oxide material, further reducing manganese leaching. The dense coating layer LATP and the lithium nickel manganese oxide material with significantly improved internal ordered phase combine to jointly enhance the ionic and electronic conductivity of the cathode active material, thereby improving the capacity, rate performance, and high-temperature cycling performance of the cathode active material.

[0047] The positive electrode active material provided in this application can be used in solid-state batteries and liquid battery systems, with a wide range of applications. Specifically, the three-dimensional lithium-ion transport channels of LATP give LATP excellent ionic conductivity, allowing lithium ions to migrate rapidly between the positive and negative electrodes. Coating LATP onto the surface of lithium nickel manganese oxide material can improve the interfacial impedance phenomenon between the solid electrolyte and the positive electrode, thereby enhancing the battery's electrical performance.

[0048] 2. The cathode active material provided in this application is doped with titanium, magnesium, and tungsten. The co-doping of these three elements further enhances the structural stability and electrochemical performance of the cathode active material, thereby improving its capacity, rate performance, and high-temperature cycling performance. Specifically, titanium improves the crystal structure of the cathode active material, increasing its electronic conductivity and lithium-ion diffusion rate, thus reducing structural distortion and side reactions during charge and discharge processes, further enhancing its capacity and rate performance. Magnesium, on the one hand, increases the average valence state of manganese, inhibiting manganese ion disproportionation and MnO formation, reducing manganese dissolution, and thus improving the cycling performance of the cathode active material. On the other hand, magnesium also stabilizes the spinel structure of lithium nickel manganese oxide, reducing high-temperature phase transitions, thereby improving the stability of the cathode active material under high voltage and its high-temperature cycling performance. Tungsten suppresses harmful phase transitions in deep charge states, thereby inhibiting lattice shrinkage, avoiding lattice defects such as microcracks, and improving the high-temperature cycling performance of the cathode active material. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0050] Figure 1 These are the 0.1C charge-discharge curves of Embodiment 1 and Comparative Example 1 of this application;

[0051] Figure 2 These are the 45°C cycling curves of Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0052] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0053] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0055] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0056] 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 the specific 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. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to 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 herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0058] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0059] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0061] Example 1

[0062] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0063] (1) Ni 0.25 Mn 0.75 (OH)₂ and lithium carbonate are mixed (Li:M(Ni+Mn) atomic molar ratio is 1.03:1), TiO₂, WO₃ and MgO are added, and the mixture is stirred at 2000 r / min for 20 min with a stirring pump, wherein Ni is the dominant component. 0.25 Mn 0.75 Based on the mass of (OH)2, a mixture was obtained with the mass percentages of Ti, W, and Mg being 4000ppm, 1500ppm, and 1500ppm, respectively. Under an air atmosphere (gas flow rate of 20L / min), the mixture was heated to 950℃ at a rate of 3℃ / min and then sintered at a constant temperature for 10h. The gas flow rate was then changed to 50L / min, and the temperature was lowered to 700℃ at a rate of 0.5℃ / min. The mixture was then sintered at a constant temperature for 1h, while simultaneously being microwave-assisted at a microwave frequency of 800MHz for 1h. The mixture was then allowed to cool naturally to room temperature to obtain lithium nickel manganese oxide material, which was then crushed by an air jet mill to a median particle size D50 = 6μm.

[0064] (2) Li(CH3COO), Al(NO3), TiO(OOCCH3)2 and NH4H2PO4 were mixed in water at a molar ratio of Li:Al:Ti:P = 1.3:0.3:1.7:3 to obtain a mixed slurry with a solid content of 50%. 95wt% ethanol was added to adjust the pH of the mixed slurry to 3.5-4.5 to obtain LATP precursor gel. Step (2) was carried out at a stirring rate of 300r / min for 1h. The amount of ethanol added was 40wt% based on the mass of water in the mixed slurry.

[0065] (3) The lithium nickel manganese oxide material and LATP precursor gel were mixed and stirred evenly using a high-speed disperser. The mixture was heated to 850°C at a rate of 3°C / min, and then microwave-assisted coating was performed at a microwave frequency of 800MHz for 1.5 hours. After natural cooling to room temperature, the positive electrode active material was obtained. The material was then crushed by an air jet mill, and the particle size was controlled at D50 = 6μm. Based on the mass of the lithium nickel manganese oxide material, the mass percentage of phosphorus in the LATP precursor gel was 2500ppm.

[0066] Example 2

[0067] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0068] (1) Ni 0.25 Mn 0.75 (OH)₂ and lithium acetate were mixed (Li:M(Ni+Mn) atomic molar ratio of 1.01:1), magnesium nitrate, tungsten dioxide and titanium nitrate were added, and the mixture was stirred at 1500 r / min for 25 min with Ni as the main component. 0.25 Mn 0.75 Based on the mass of (OH)2, a mixture was obtained with the mass percentages of Ti, W, and Mg being 2000 ppm, 3000 ppm, and 500 ppm, respectively. Under an air atmosphere (gas flow rate of 10 L / min), the mixture was heated to 800 °C at a rate of 2 °C / min and then sintered at a constant temperature for 8 h. The gas flow rate was then changed to 50 L / min, and the temperature was lowered to 600 °C at a rate of 1 °C / min. The mixture was then sintered at a constant temperature for 2 h, while simultaneously being microwave-assisted at a microwave frequency of 1000 MHz for 2 h. The mixture was then allowed to cool naturally to room temperature to obtain lithium nickel manganese oxide material, which was then crushed by an air jet mill to a median particle size D50 = 4 μm.

[0069] (2) Lithium hydroxide, aluminum carbonate, tetrabutyl titanate and lithium dihydrogen phosphate were mixed and dissolved in water at a molar ratio of Li:Al:Ti:P = 1.3:0.3:1.7:3 to obtain a mixed slurry with a solid content of 70%. 100wt% ethanol was added to adjust the pH of the mixed slurry and the pH value was controlled to be 3.5-4.5 to obtain LATP precursor gel. Step (2) was carried out at a stirring rate of 200r / min for 0.5h. The amount of ethanol added was 20wt% based on the mass of water in the mixed slurry.

[0070] (3) The lithium nickel manganese oxide material and LATP precursor gel were mixed and stirred evenly using a high-speed disperser. The mixture was heated to 900°C at a rate of 5°C / min, and then microwave-assisted coating was performed at a microwave frequency of 1000MHz for 2 hours. After natural cooling to room temperature, the positive electrode active material was obtained. The material was then crushed by an air jet mill, and the particle size was controlled at D50 = 4μm. Based on the mass of the lithium nickel manganese oxide material, the mass percentage of phosphorus in the LATP precursor gel was 2000ppm.

[0071] Example 3

[0072] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0073] (1) Ni 0.25 Mn 0.75 A mixture of (OH)₂ and lithium hydroxide (Li:M(Ni+Mn) atomic molar ratio of 1.05:1) was added, along with titanium sulfate, tungsten hexafluoride, and magnesium peroxide. The mixture was stirred at 2500 rpm for 15 min using a stirrer, with Ni as the dominant component. 0.25 Mn 0.75 Based on the mass of (OH)2, a mixture was obtained with the mass percentages of Ti, W, and Mg being 6000ppm, 500ppm, and 3000ppm, respectively. Under an air atmosphere (gas flow rate of 30L / min), the mixture was heated to 850℃ at a rate of 4℃ / min and then sintered at a constant temperature for 9 hours. The gas flow rate was then changed to 40L / min, and the temperature was lowered to 650℃ at a rate of 0.5℃ / min. The mixture was then sintered at a constant temperature for 1.5 hours, while simultaneously being microwave-assisted at a microwave frequency of 900MHz for 1.5 hours. The mixture was then allowed to cool naturally to room temperature to obtain lithium nickel manganese oxide material, which was then crushed by an air jet mill to a median particle size D50 = 5μm.

[0074] (2) Li(CH3COO), aluminum carbonate, TiO(OOCCH3)2 and NH4H2PO4 were mixed in water at a molar ratio of Li:Al:Ti:P = 1.3:0.3:1.7:3 to obtain a mixed slurry with a solid content of 60%. 99wt% glycerol was added to adjust the pH of the mixed slurry to 3.5-4.5 to obtain LATP precursor gel. Step (2) was carried out at a stirring rate of 100r / min for 1h. The amount of glycerol added was 20wt% based on the mass of water in the mixed slurry.

[0075] (3) The lithium nickel manganese oxide material and LATP precursor gel were mixed and stirred evenly using a high-speed disperser. The mixture was heated to 800°C at a rate of 2°C / min, and then microwave-assisted coating was performed at a microwave frequency of 900MHz for 1 hour. After natural cooling to room temperature, the positive electrode active material was obtained. The material was then crushed by an air jet mill, and the particle size was controlled at D50 = 5μm. Based on the mass of the lithium nickel manganese oxide material, the mass percentage of phosphorus in the LATP precursor gel was 3000ppm.

[0076] Example 4

[0077] This embodiment provides a method for preparing a positive electrode active material, which differs from Example 1 only in that Ni is used. 0.25 Mn 0.75Based on the mass of (OH)2, the mass percentage of Ti element is 7000ppm; the mass percentages of Ti, W, and Mg elements used in Example 1 are 4000ppm, 1500ppm, and 1500ppm, respectively.

[0078] Example 5

[0079] This embodiment provides a method for preparing a positive electrode active material. The only difference from Embodiment 1 is that the temperature is lowered to 630°C at a rate of 0.5°C / min, and sintered at a constant temperature for 1 hour, while simultaneously being microwave-assisted at a microwave frequency of 800MHz for 1 hour; instead of Embodiment 1, the temperature is lowered to 700°C at a rate of 0.5°C / min, and sintered at a constant temperature for 1 hour, while simultaneously being microwave-assisted at a microwave frequency of 800MHz for 1 hour.

[0080] Example 6

[0081] This embodiment provides a method for preparing a positive electrode active material. The only difference from Embodiment 1 is that the temperature is lowered to 670°C at a rate of 0.5°C / min, and sintered at a constant temperature for 1 hour, while simultaneously being microwave-assisted at a microwave frequency of 800MHz for 1 hour; instead of Embodiment 1, the temperature is lowered to 700°C at a rate of 0.5°C / min, and sintered at a constant temperature for 1 hour, while simultaneously being microwave-assisted at a microwave frequency of 800MHz for 1 hour.

[0082] Example 7

[0083] This embodiment provides a method for preparing a positive electrode active material. The only difference from Embodiment 1 is that, under an air atmosphere (gas flow rate of 25 L / min), the mixture is heated to 950°C at 3°C / min and then sintered at a constant temperature for 10 h; the gas flow rate is changed to 50 L / min, the temperature is lowered to 700°C at 0.5°C / min, and sintered at a constant temperature for 1 h, while simultaneously using microwave assistance at a microwave frequency of 800 MHz for 1 h.

[0084] Instead of Example 1, the mixture was heated to 950°C at 3°C / min in an air atmosphere (gas flow rate of 20 L / min) and then sintered at a constant temperature for 10 h. The gas flow rate was changed to 50 L / min, and the temperature was lowered to 700°C at 0.5°C / min and sintered at a constant temperature for 1 h, while microwave assistance was performed at a microwave frequency of 800 MHz for 1 h.

[0085] Example 8

[0086] This embodiment provides a method for preparing a positive electrode active material. The only difference from Embodiment 1 is that, under an air atmosphere (gas flow rate of 10 L / min), the mixture is heated to 950°C at 3°C / min and then sintered at a constant temperature for 10 h; the gas flow rate is changed to 40 L / min, the temperature is lowered to 700°C at 0.5°C / min, and sintered at a constant temperature for 1 h, while simultaneously being microwave-assisted at a microwave frequency of 800 MHz for 1 h.

[0087] Instead of Example 1, the mixture was heated to 950°C at 3°C / min in an air atmosphere (gas flow rate of 20 L / min) and then sintered at a constant temperature for 10 h. The gas flow rate was changed to 50 L / min, and the temperature was lowered to 700°C at 0.5°C / min and sintered at a constant temperature for 1 h, while microwave assistance was performed at a microwave frequency of 800 MHz for 1 h.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a positive electrode active material, including the following steps:

[0090] (1) Ni 0.25 Mn 0.75 (OH)₂ and lithium carbonate are mixed (Li:M(Ni+Mn) atomic molar ratio is 1.03:1), TiO₂, WO₃ and MgO are added, and the mixture is stirred at 2000 r / min for 20 min with a stirring pump, wherein Ni is the dominant component. 0.25 Mn 0.75 Based on the mass of (OH)2, a mixture was obtained with Ti, W, and Mg at mass ratios of 4000ppm, 1500ppm, and 1500ppm, respectively. Under an air atmosphere (gas flow rate of 20L / min), the mixture was heated to 950℃ at a rate of 3℃ / min and sintered at a constant temperature for 10h. The gas flow rate remained at 20L / min, and the temperature was lowered to 700℃ at a rate of 0.5℃ / min. The mixture was sintered at a constant temperature for 1h, while simultaneously being microwave-assisted at a microwave frequency of 800MHz for 1h. The mixture was then allowed to cool naturally to room temperature to obtain lithium nickel manganese oxide material, which was then crushed by an air jet mill to a median particle size D50 = 6μm.

[0091] (2) Lithium nickel manganese oxide material and LATP powder (median particle size D50 = 600 nm) were mixed and stirred evenly using a high-speed disperser. Then, the mixture was heated to 800 °C at a rate of 3 °C / min under an air atmosphere (air flow rate of 20 L / min), held at that temperature for 5 h with the air flow rate unchanged, and then allowed to cool naturally to room temperature to obtain the positive electrode active material. Based on the mass of lithium nickel manganese oxide material, the mass percentage of phosphorus in LATP was 2500 ppm.

[0092] Comparative Example 2

[0093] This comparative example provides a method for preparing a positive electrode active material. Compared with Example 1, the only difference is that the gas flow rate is 20 L / min, the temperature is lowered to 700℃ at 0.5℃ / min, and the sintering is carried out at a constant temperature for 1 hour, instead of the gas flow rate of 50 L / min, the temperature is lowered to 700℃ at 0.5℃ / min, and the sintering is carried out at a constant temperature for 1 hour in Example 1.

[0094] Comparative Example 3

[0095] This comparative example provides a method for preparing a positive electrode active material. The only difference from Example 1 is that steps (2)-(3) are not performed.

[0096] Comparative Example 4

[0097] This comparative example provides a method for preparing a positive electrode active material. The only difference from Example 1 is that TiO2, WO3 and MgO are not added.

[0098] Comparative Example 5

[0099] This comparative example provides a method for preparing a positive electrode active material. Compared with Example 1, step (1) is different. The specific steps (1) of this comparative example are as follows:

[0100] Ni 0.25 Mn 0.75 (OH)₂ and lithium carbonate are mixed (Li:M(Ni+Mn) atomic molar ratio is 1.03:1), TiO₂, WO₃ and MgO are added, and the mixture is stirred at 2000 r / min for 20 min with a stirring pump, wherein Ni is the dominant component. 0.25 Mn 0.75 Based on the mass of (OH)2, a mixture was obtained with the mass percentages of Ti, W, and Mg being 4000ppm, 1500ppm, and 1500ppm, respectively. Under an air atmosphere (gas flow rate of 20L / min), the mixture was heated to 950℃ at a rate of 3℃ / min and then sintered at a constant temperature for 10h. The gas flow rate was then changed to 50L / min, and the temperature was lowered to 700℃ at a rate of 0.5℃ / min. The mixture was then sintered at a constant temperature for 1h and allowed to cool naturally to room temperature to obtain lithium nickel manganese oxide material. The material was then crushed by an air jet mill to a median particle size D50 = 6μm.

[0101] Comparative Example 6

[0102] This comparative example provides a method for preparing a positive electrode active material. Compared with Example 1, the only difference is that in step (1), the temperature is lowered to 800°C at 0.5°C / min, and constant temperature sintering is performed for 1 hour, while microwave assistance is performed at a microwave frequency of 800MHz for 1 hour; instead of the method in Example 1, the temperature is lowered to 700°C at 0.5°C / min, and constant temperature sintering is performed for 1 hour, while microwave assistance is performed at a microwave frequency of 800MHz for 1 hour.

[0103] Comparative Example 7

[0104] This comparative example provides a method for preparing a positive electrode active material. Compared with Example 1, the only difference is that in step (1), the temperature is lowered to 500°C at 0.5°C / min, and sintered at a constant temperature for 1 hour, while microwave assistance is performed at a microwave frequency of 800MHz for 1 hour; instead of the method in Example 1, the temperature is lowered to 700°C at 0.5°C / min, and sintered at a constant temperature for 1 hour, while microwave assistance is performed at a microwave frequency of 800MHz for 1 hour.

[0105] Test case

[0106] The performance of the positive electrode active materials in each embodiment and comparative example was tested, as follows:

[0107] The positive electrode active material, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 92:4:4 and dispersed in N-methylpyrrolidone (NMP) to form a uniform slurry. The slurry was then coated onto a 20 μm aluminum foil, achieving a coating areal density of 8.28 mg / cm³. 2 After drying, a positive electrode sheet is obtained; in a glove box, a lithium sheet is used as the negative electrode, a polyethylene membrane with a thickness of 12 μm is used as the separator, and 80 μL of electrolyte (1 mol / L LiPF6, solvent is ethylene carbonate EC: diethyl carbonate DEC with a volume ratio of 3:7) is added to assemble an R2032 coin cell.

[0108] The button cells were tested using a blue-light tester. The prepared button cells were placed in a 45°C high-temperature oven for charge-discharge testing within a voltage range of 3.5V-5.0V. The cells were charged at 0.1C to 5V, then charged at a constant 5V to 0.05C, and then discharged at a constant current of 0.1C to 3.5V, repeated twice. Then, they were charged at 1C to 5.0V, then charged at a constant 5V to 0.05C, and then discharged at 1C to 3.5V, repeated 200 times. The capacity retention rate after 200 cycles was obtained, and the results are shown in Table 1. Figure 2 .

[0109] The button cells were tested using a blue-light tester. The prepared button cells were placed in a 25°C room temperature oven for charge-discharge testing within a voltage range of 3.5V-5.0V. The cells were charged at 0.1C to 5V, then charged at a constant 5V to 0.05C, and then discharged at a constant current of 0.1C to 3.5V, repeated twice to obtain the initial charge-discharge capacity and initial efficiency. Initial efficiency = (initial discharge capacity / initial charge capacity) × 100%. Then, the cells were charged at 1C to 5.0V, then charged at a constant 5V to 0.05C, and then discharged at 1C to 3.5V, repeated twice. Finally, the cells were charged at 10C to 5.0V, then charged at a constant 5V to 0.05C, and then discharged at 10C to 3.5V, repeated twice to obtain the 1C and 10C discharge capacities. Rate performance = (10C discharge capacity / 1C discharge capacity) × 100%. The results are shown in Table 1 and [Table data would be inserted here]. Figure 1 .

[0110] Table 1

[0111]

[0112]

[0113] Depend on Figure 1 It can be seen that within the same voltage range during discharge or charging, a greater slope of voltage drop or rise indicates a lower content of trivalent manganese ions and less disproportionation reaction of trivalent manganese ions, thereby reducing the occurrence of undesirable phenomena such as manganese dissolution. In Example 1, the slope of voltage drop or rise is significantly greater than that of Comparative Example 1. Taking the range of approximately 4.1V as an example, the slope of voltage rise of the positive electrode active material provided in this application is greater in this range, and the trivalent manganese plateau segment is significantly shortened, indicating a reduction in trivalent manganese ions and a reduction in the disproportionation reaction of trivalent manganese ions, which can effectively reduce the dissolution of manganese from the positive electrode active material.

[0114] As can be seen from Table 1, the positive electrode active material provided in this application has good first discharge capacity, first charge capacity, first coulombic efficiency, rate performance and 200-cycle capacity retention. The high-temperature capacity retention shows that the oxygen vacancies and lattice defects of the positive electrode active material are reduced.

[0115] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: S1, mix the nickel-manganese precursor, the first lithium source and the dopant, and pass in oxygen-containing gas to perform the first sintering and microwave-assisted sintering to obtain lithium nickel manganese oxide material; The temperature of the first sintering is 800-950℃, the temperature of the microwave-assisted sintering is 600-700℃, and the flow rate of oxygen-containing gas during the microwave-assisted sintering process is greater than the flow rate of oxygen-containing gas during the first sintering process. S2, lithium nickel manganese oxide material and LATP precursor gel are mixed and microwave-assisted coating is performed to obtain positive electrode active material.

2. The method for preparing the positive electrode active material according to claim 1, characterized in that, The flow rate of oxygen-containing gas during the first sintering process is 10-30 L / min; And / or, the flow rate of oxygen-containing gas during the microwave-assisted sintering process is 40-50 L / min.

3. The method for preparing the positive electrode active material according to claim 1, characterized in that, The nickel-manganese precursor includes nickel-manganese hydroxide; And / or, the first lithium source includes at least one of lithium carbonate, lithium acetate, and lithium hydroxide; And / or, the ratio of the total molar amount of nickel and manganese in the nickel-manganese precursor to the molar amount of lithium in the first lithium source is 1:(1.01-1.05); And / or, the dopant includes titanium-containing compounds, tungsten-containing compounds, and magnesium-containing compounds.

4. The method for preparing the positive electrode active material according to claim 3, characterized in that, The titanium-containing compound includes at least one of titanium dioxide, titanium chloride, titanium sulfate, and titanium nitrate; And / or, the tungsten-containing compound includes at least one of tungsten trioxide, tungsten dioxide, and tungsten hexafluoride; And / or, the magnesium-containing compound includes at least one of magnesium oxide, magnesium nitrate, and magnesium peroxide; And / or, based on the mass of the nickel-manganese precursor, the mass percentage of titanium in the titanium-containing compound is 2000-6000 ppm; And / or, based on the mass of the nickel-manganese precursor, the mass percentage of tungsten in the tungsten-containing compound is 500-3000 ppm; And / or, based on the mass of the nickel-manganese precursor, the magnesium content in the magnesium-containing compound is 500-3000 ppm by mass.

5. The method for preparing the positive electrode active material according to claim 1, characterized in that, In step S1, the mixing parameters include: rotation speed of 1500-2500 r / min and time of 15-25 min; And / or, the heating rate of the first sintering is 2-4℃ / min; and / or, the time of the first sintering is 8-10h; And / or, the cooling rate of the microwave-assisted sintering is 0.5-1℃ / min; and / or, the microwave-assisted sintering time is 1-2h; and / or, the frequency of the microwave-assisted sintering is 800-1000MHz. And / or, microwave-assisted sintering is followed by natural cooling to room temperature to obtain lithium nickel manganese oxide material; And / or, in step S1, after microwave-assisted sintering, a crushing process is also included, and the median particle size D50 of the processed lithium nickel manganese oxide material is 4-6 μm.

6. The method for preparing the positive electrode active material according to claim 1, characterized in that, The preparation steps of the LATP precursor gel include: mixing a second lithium source, an aluminum source, a titanium source and a phosphorus source to obtain a mixed slurry, adding a retarder and adjusting the pH value of the mixed slurry to obtain the LATP precursor gel. Optionally, the molar ratio of lithium in the second lithium source, aluminum in the aluminum source, titanium in the titanium source, and phosphorus in the phosphorus source is (1.28-1.32):(0.28-0.32):(1.68-1.72):(2.98-3.02); Optionally, the second lithium source includes at least one of lithium acetate and lithium hydroxide; optionally, the aluminum source includes at least one of aluminum nitrate and aluminum carbonate; optionally, the titanium source includes at least one of titanium diacetate and tetrabutyl titanate; optionally, the phosphorus source includes at least one of ammonium dihydrogen phosphate and lithium dihydrogen phosphate. Optionally, the solid content of the mixed slurry is 50-70%; Optionally, the retarder includes at least one of ethanol, ethylene glycol, propylene glycol, and glycerin; Optionally, the amount of retarder added is 20-40 wt%, based on the mass of the solvent in the mixed slurry; Optionally, the concentration of the retarder is 95-100 wt%. Optionally, the pH value of the mixed slurry is 3.5-4.

5.

7. The method for preparing the positive electrode active material according to claim 1, characterized in that, Based on the mass of lithium nickel manganese oxide material, the mass percentage of phosphorus in the LATP precursor gel is 2000-3000 ppm. And / or, in step S2, the lithium nickel manganese oxide material and LATP precursor gel are mixed and heated to 800-900℃ for microwave-assisted coating; optionally, the microwave-assisted coating time is 1-2h; optionally, the microwave-assisted coating frequency is 800-1000MHz; optionally, the heating rate is 2-5℃ / min. And / or, after microwave-assisted coating, natural cooling to room temperature is also included to obtain the positive electrode active material.

8. A positive electrode active material, characterized in that, It is prepared by the method according to any one of claims 1-7.

9. A positive electrode sheet, characterized in that, It includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive active material as described in claim 8.

10. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

Images