WO2024131048A1 - 正极材料及钠离子电池 - Google Patents

正极材料及钠离子电池 Download PDF

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WO2024131048A1
WO2024131048A1 PCT/CN2023/107998 CN2023107998W WO2024131048A1 WO 2024131048 A1 WO2024131048 A1 WO 2024131048A1 CN 2023107998 W CN2023107998 W CN 2023107998W WO 2024131048 A1 WO2024131048 A1 WO 2024131048A1
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positive electrode
electrode material
sodium
phosphate
transition metal
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PCT/CN2023/107998
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English (en)
French (fr)
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骆亦琦
陈龙
李子坤
黄友元
吴小珍
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深圳市贝特瑞新能源技术研究院有限公司
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Publication of WO2024131048A1 publication Critical patent/WO2024131048A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of positive electrode materials, and in particular relates to a positive electrode material and a preparation method thereof, and a sodium ion battery.
  • EES electrochemical energy storage systems
  • Secondary battery energy storage has great potential in electrochemical energy storage.
  • lithium-ion batteries dominate the energy storage market due to their high theoretical specific capacity and specific energy density.
  • Sodium-based layered oxide cathode material is one of the most critical materials for sodium-ion batteries. Similar to lithium cobalt oxide and ternary structures of lithium batteries, the layered oxide structure has good ion channels. The cycle performance may have certain shortcomings, but the average maturity is relatively high. Transition metal oxide NaXMeO 2 is an embedded or intercalated compound, which theoretically has a higher discharge specific capacity, but poor cycle performance.
  • O3- type positive electrode materials have high capacity, low initial efficiency, and poor cycle performance
  • P2-type positive electrode materials have low first charge capacity, but good cycle and rate performance
  • P3-type positive electrode materials have low capacity, poor cycle performance, and high operating voltage.
  • the overall performance of each type of positive electrode material is not good.
  • the purpose of this application is to provide a positive electrode material and a sodium ion battery, wherein the positive electrode material has high voltage resistance, high capacity and cycle stability, thereby improving the comprehensive performance of the positive electrode material.
  • C1 is the discharge capacity difference of the half-cell between Von and 2.5V, wherein Von is the open circuit voltage of the first charge curve of the half-cell; and C2 is the discharge capacity difference between 2.5V and 2.0V.
  • the sodium-rich defect X of the positive electrode material satisfies: 0.3 ⁇ X ⁇ 0.6.
  • the cathode material includes a layered oxide having a P2 phase structure.
  • the crystal structure of the matrix material is a layered oxide having a P2 phase structure, and the crystal structure of the matrix material has the sodium-rich structural defects.
  • the positive electrode material when 0.8 ⁇ a ⁇ 0.85, has a diffraction peak at 41.4 ⁇ 0.2° as measured by XRD ray.
  • the positive electrode material has diffraction peaks at 15.80 ⁇ 0.5°, 31.95 ⁇ 0.5°, 35.90 ⁇ 0.5°, 36.81 ⁇ 0.5°, 39.45 ⁇ 0.5°, 43.56 ⁇ 0.5°, 48.84 ⁇ 0.5°, 62.08 ⁇ 0.5°, 64.56 ⁇ 0.5°, 66.93 ⁇ 0.5°, 73.87 ⁇ 0.5°, 76.16 ⁇ 0.5°, 78.35 ⁇ 0.5° and 84.97 ⁇ 0.5° as determined by XRD ray.
  • the positive electrode material further includes a coating layer located on the surface of the base material, and the coating layer includes at least one of a transition metal oxide and a phosphate.
  • the coating layer includes a phosphate
  • the phosphate includes at least one of a lithium phosphate, a sodium phosphate, a potassium phosphate, a titanium phosphate, an aluminum phosphate, an iron phosphate, and diammonium phosphate;
  • the coating layer includes phosphate, and the mass percentage of the phosphate in the base material is 0.05wt% to 5wt%;
  • the coating layer comprises a transition metal oxide, and the transition metal in the transition metal oxide comprises at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb and B;
  • the coating layer includes a transition metal oxide, and the mass percentage of the transition metal oxide in the base material is 0.05 wt % to 5 wt %.
  • M comprises at least one of a transition metal and a rare earth metal
  • M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb, and B;
  • the mass content of CO32- in the positive electrode material is ⁇ 2wt%, and the mass content of OH- in the positive electrode material is ⁇ 2wt%;
  • the tap density of the positive electrode material is ⁇ 1.6 g/cm3;
  • the specific surface area of the positive electrode material is 0.2 m2/g to 2 m2/g;
  • the median particle size D50 of the positive electrode material is 3 ⁇ m to 15 ⁇ m;
  • the pH value of the cathode material is 11 to 13;
  • the mass content of water in the positive electrode material is ⁇ 0.05wt%
  • the space group of the positive electrode material is P63/mmc.
  • the present application provides a sodium ion battery, the sodium ion battery comprising a positive electrode plate, the positive electrode plate comprising the positive electrode material described in the first aspect or the positive electrode material prepared by the method described in the second aspect.
  • the ratio of the number of Na positions occupied by surplus Na ions to the total number of Na positions available for Na ion embedding is defined as sodium-rich defectivity. Controlling the sodium-rich defectivity of the positive electrode material within an appropriate range can be beneficial to maintaining the crystal structure stability and structural stability of the positive electrode material. An appropriate amount of sodium-rich defectivity enables the positive electrode material to have a higher ability to release sodium ions and a higher specific capacity.
  • the positive electrode material can alleviate the irreversible phase change under high voltage caused by the large amount of sodium ions released during the charge and discharge process, which is beneficial to maintaining the crystal structure stability of the positive electrode material and alleviating metal dissolution, so that the positive electrode material has both high voltage resistance, high capacity and cycle stability, thereby improving the comprehensive performance of the positive electrode material.
  • FIG1 is a schematic flow chart of a method for preparing a positive electrode material provided in an embodiment of the present application.
  • FIG. 2 a is a scanning electron microscope image of the positive electrode material obtained in Example 1 of the present application.
  • FIG. 2 b is a charge and discharge curve diagram of a battery assembled with the positive electrode material prepared in Example 1 of the present application.
  • FIG. 2c is an XRD diffraction pattern of the positive electrode material obtained in Example 1 of the present application.
  • FIG3 a is a scanning electron microscope image of the positive electrode material obtained in Example 2 of the present application.
  • FIG3 b is a charge and discharge curve diagram of a battery assembled with the positive electrode material prepared in Example 2 of the present application.
  • FIG4 a is a scanning electron microscope image of the positive electrode material obtained in Example 3 of the present application.
  • FIG4 b is a charge and discharge curve diagram of a battery assembled with the positive electrode material prepared in Example 3 of the present application.
  • FIG5 a is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 1 of the present application.
  • FIG5 b is a charge and discharge curve diagram of a battery assembled with the positive electrode material prepared in Comparative Example 1 of the present application.
  • first and second are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.
  • features defined as “first” and “second” may explicitly or implicitly include one or more of the features.
  • Sodium-based layered oxide cathode material is one of the most critical materials for sodium-ion batteries. Similar to lithium cobalt oxide and ternary structures of lithium batteries, the layered oxide structure has good ion channels. The cycle performance may have certain shortcomings, but the average maturity is relatively high. Transition metal oxide NaXMeO 2 is an embedded or intercalated compound, which theoretically has a higher discharge specific capacity, but poor cycle performance.
  • Each type of existing layered oxide materials for sodium ion batteries has obvious disadvantages.
  • O3 - type positive electrode materials have high capacity, low initial efficiency, and poor cycle performance
  • P2-type positive electrode materials have low first charge capacity, but good cycle and rate performance
  • P3-type positive electrode materials have low capacity, poor cycle performance, and high operating voltage.
  • the overall performance of each type of positive electrode material is not good.
  • C1 is the discharge capacity difference of the half-cell between Von and 2.5V, wherein Von is the open circuit voltage of the first charge curve of the half-cell; C2 is the discharge capacity difference between 2.5V and 2.0V.
  • the positive electrode material provided in the present application can help maintain the crystal structure stability and structural stability of the positive electrode material.
  • the appropriate amount of sodium-rich defect makes the positive electrode material have a higher ability to release sodium ions and a higher specific capacity.
  • it can alleviate the irreversible phase change under high voltage caused by the large amount of sodium ions released during the charging and discharging process, which is beneficial to maintaining the crystal structure stability of the positive electrode material and alleviating metal dissolution, so that the positive electrode material has high voltage resistance, high capacity and cycle stability, thereby improving the comprehensive performance of the positive electrode material.
  • the ratio of the number of Na positions occupied by surplus Na ions to the total number of Na positions available for Na ions to be embedded is defined as the sodium-rich defect X.
  • the degree of sodium-rich defects in the positive electrode material is closely related to the ability of the material to deintercalate Na ions during charging and discharging, which can be characterized by the relative relationship of specific capacity in the CV curve obtained by the test.
  • the specific capacity of the tested CV curve is directly related to the number of Na ions deintercalated.
  • P2-type materials are that they can additionally embed sodium ions (the typical P2 material has a Na content of 0.67, and 0.33 Na ions can be additionally embedded in the half-cell).
  • the capacity interval corresponding to the additionally embedded Na is reflected in the 2.0-V interval of the discharge curve (where 2.0-2.5V corresponds to additional sodium embedding in the ideal P2 structure, corresponding to the redox reaction of Mn 4+ ⁇ Mn 3+ .
  • 2.5V ⁇ V corresponds to structural distortion and additional sodium embedding, which is different from the original P2-type prismatic structure, and the main corresponding redox reaction is Ni 3+ ⁇ Ni 2+ ). Therefore, the inventors found that the degree of sodium-rich defects can be reflected from the side through the correlation between these two capacity intervals.
  • the degree of sodium-rich defects represents the ratio of lattice distortion defects caused by additional Na ions to the total number of additional sodium that can be embedded.
  • the algorithm when the sodium-rich defects in the positive electrode material increase, the specific capacity of the C1 segment increases, the specific capacity of the C2 segment decreases, and the value of x increases; conversely, when the sodium-rich defects decrease, C1 decreases, C2 increases, and the value of x decreases.
  • the monotonicity of X is consistent with the monotonicity of the degree of sodium-rich defects, and can be used as an indicator of the degree of sodium-rich defects.
  • the sodium-rich degree of the positive electrode material is calculated by testing the interval specific capacity C1 and C2 in the first-cycle discharge curve of a button battery assembled from the positive electrode material.
  • the specific button battery manufacturing process and test conditions are known to those skilled in the art.
  • the manufacturing process of the positive electrode sheet is consistent with that of the lithium battery positive electrode sheet, and the mass ratio of the active material, PVDF (5130), and the conductive carbon is 90:5:5;
  • the button battery manufacturing process is also basically the same as the lithium-ion button battery manufacturing process, except that the electrolyte is replaced with NaPF6-DIGLYME electrolyte, the diaphragm uses a glass fiber diaphragm, and the negative electrode sheet is replaced with a commercial sodium sheet.
  • the test adopts the Xinwei test, 2.0-4.1V test range, 0.1C rate charge and discharge, to obtain the required C-V curve.
  • the positive electrode material, polyvinylidene fluoride and conductive carbon are dispersed in N-methylpyrrolidone in a mass ratio of 90:5:5 to prepare a positive electrode slurry with a solid content of 50%, which is coated on aluminum foil and dried as a positive electrode sheet.
  • a sodium sheet is used as a negative electrode sheet
  • the separator is a glass fiber membrane
  • the electrolyte is sodium hexafluorophosphate-diethylene glycol dimethyl ether (NaPF6 concentration is 1 mol/L) to form a button battery.
  • Charge and discharge tests are carried out at 2.0V to 4.1V and a rate of 0.1C.
  • the sodium-rich defect of the positive electrode material is X, 0.25 ⁇ X ⁇ 0.7, and the specific value of X can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65 or 0.7, etc., of course, it can also be other values within the above range, which are not limited here.
  • the right amount of sodium-rich defect makes the positive electrode material have a higher ability to remove Na ions and a higher specific capacity. At the same time, it can alleviate the irreversible phase change under high voltage caused by the large amount of Na ions being removed during the charge and discharge process, which is beneficial to maintain the crystal structure stability of the positive electrode material and alleviate metal dissolution.
  • the sodium-rich defect When the sodium-rich defect is too large, the excessive defects will hinder the sodium ion deintercalation, resulting in the deterioration of the capacity of the positive electrode material and the deterioration of the cycle performance. In addition, when the sodium-rich defect is too large, the residual alkali on the surface of the material will increase, affecting the processing performance of the material.
  • the cathode material includes a layered oxide having a P2 phase structure.
  • the crystal structure of the matrix material is a layered oxide with a P2 phase, and the crystal structure of the matrix material has sodium-rich structural defects.
  • the value of a may be, for example, 0.67, 0.69, 0.70, 0.72, 0.75, 0.79, 0.82 or 0.85.
  • the battery using the positive electrode material has a higher specific charge and discharge capacity; when the molar content of Na in the positive electrode material is less, the specific capacity of the battery is reduced, the energy density is reduced, and the electrochemical performance is significantly reduced.
  • the value of b may be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.3, 0.4, 0.45 or 0.5
  • the value of c may be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.3, 0.4, 0.45 or 0.5
  • the value of d may be, for example, 0.01, 0.05, 0.08, 0.1, 0.15, 0.16, 0.18, 0.2, 0.28 or 0.3, etc., which are not limited herein.
  • the value of e may be, for example, 0.5, 0.6, 0.7, 0.75, 0.79, 0.83, 0.87, 0.9 or 0.95, etc.
  • M includes at least one of a transition metal and a rare earth metal.
  • M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb, and B.
  • the battery has good electrochemical performance.
  • the crystal structure of the matrix material is a layered oxide having a P2 phase structure, and the crystal structure of the matrix material has sodium-rich structural defects.
  • Ni, Fe, and Mn form octahedral structures with adjacent oxygen atoms, and multiple octahedral structures are doped with M metal to form transition metal layers.
  • the oxygen atoms in the two adjacent transition metal layers and the sodium ions form a triangular prism structure, which in turn forms a layered structure.
  • the introduction of a high sodium content in the P2 phase structure will reduce the average valence of the transition metal ions in the crystal structure, prompting the transition metal with the lowest oxidation state in the crystal structure to transform to its high valence state, thereby achieving a higher specific capacity.
  • the excess sodium ions brought by the sodium-rich defects can alleviate the tendency of the positive electrode to undergo phase transition in the high sodium removal state during the process of large-scale sodium ion extraction, thereby improving the structural stability of the positive electrode material.
  • Na ions are embedded in Na positions.
  • the Na positions available for Na ions to embed in the crystal junction are constant. Excess Na ions occupying Na positions will cause lattice distortion defects, that is, the Na positions jointly occupied by excess Na ions will cause sodium-rich defects.
  • the space group of the cathode material is P63/mmc.
  • the positive electrode material further includes a coating layer located on the surface of the base material, and the coating layer includes at least one of a transition metal oxide and a phosphate.
  • the phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, titanium phosphate, aluminum phosphate, iron phosphate, and diammonium phosphate.
  • the phosphate in the coating layer not only has high sodium ion conductivity, inhibits the corrosion of the electrolyte to the matrix material, but is also conducive to the formation of a spatial sodium ion conductive network.
  • the transition metal includes at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb and B;
  • the mass percentage of the transition metal oxide in the matrix material is 0.05wt% to 5wt%, specifically 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt% or 5.0wt%, etc., and of course other values within the above range may also be used.
  • the mass percentage of the transition metal oxide in the matrix material is 0.05wt% to 2wt%.
  • the mass percentage of the phosphate in the matrix material is 0.05wt% to 5wt%, specifically 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt% or 5.0wt%. etc., and of course, it may be other values within the above range.
  • the mass percentage of the phosphate in the matrix material is 0.05wt% to 2wt%.
  • the mass content of CO 3 2- in the positive electrode material is ⁇ 2wt%, specifically 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%, etc., and of course other values within the above range may also be used.
  • the mass content of CO 3 2- in the positive electrode material is ⁇ 1wt%.
  • the mass content of OH - in the positive electrode material is ⁇ 2wt%, specifically 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%, etc., and of course other values within the above range may also be used.
  • the mass content of OH - in the positive electrode material is ⁇ 1wt%.
  • the median particle size D50 of the positive electrode material is 3 ⁇ m to 15 ⁇ m, specifically 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 8 ⁇ m, 10 ⁇ m, 12 ⁇ m, 14 ⁇ m or 15 ⁇ m, etc., and of course other values within the above range are also possible, which are not limited here. Controlling the particle size of the positive electrode material within the above range is beneficial to improving the structural stability, thermal stability and long cycle stability of the positive electrode material.
  • the median particle size D50 of the positive electrode material is 5 ⁇ m to 10 ⁇ m.
  • the particle size of the positive electrode material satisfies (D 90 -D 10 )/D 50 ⁇ 1.5, specifically 1.5, 1.4, 1.3, 1.2, 1.1, 0.9, 0.8, 0.5, 0.3, 0.1, etc., which are not limited here.
  • (D 90 -D 10 )/D 50 ⁇ 1.2.
  • the volume-based cumulative particle size distribution of the particle size distribution determination is measured by laser diffraction method
  • D10 represents the particle size corresponding to when the cumulative particle size distribution percentage of the powder reaches 10%
  • D50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%
  • D90 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.
  • the specific surface area of the positive electrode material is 0.2 m 2 /g to 2 m 2 /g. Specifically, it may be 0.2 m 2 /g, 0.4 m 2 /g, 0.5 m 2 /g, 0.6 m 2 /g, 0.7 m 2 /g, 1.2 m 2 /g, 1.5 m 2 /g, 1.6 m 2 / g , 1.8 m 2 /g or 2.0 m 2 /g, etc.
  • the specific surface area of the positive electrode material is controlled within the above range, it is beneficial to improve the cycle performance of the battery made of the positive electrode material.
  • the tap density of the positive electrode material is ⁇ 1.6 g/cm 3 , specifically 1.6 g/cm 3 , 1.7 g/cm 3 , 1.8 g/cm 3 , 1.85 g/cm 3 , 1.9 g/cm 3 , 1.95 g/cm 3 or 2.0 g/cm 3 , etc.
  • the tap density of the positive electrode material is ⁇ 1.8 g/cm 3 .
  • the pH value of the positive electrode material is 11-13; specifically, it can be 11.5, 11.9, 12.1, 12.3, 12.5, 12.7, 12.9 or 13, etc., and of course, it can also be other values within the above range.
  • the mass content of water in the positive electrode material is ⁇ 0.05wt%, specifically 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt% or 0.05wt%, etc., and of course other values within the above range can also be used. Controlling the water content of the positive electrode material is beneficial to suppressing the content of residual alkali and improving the processing performance of the material. Preferably, the mass content of water in the positive electrode material is ⁇ 0.03wt%.
  • the positive electrode material has diffraction peaks at 15.80 ⁇ 0.5°, 31.95 ⁇ 0.5°, 35.90 ⁇ 0.5°, 36.81 ⁇ 0.5°, 39.45 ⁇ 0.5°, 43.56 ⁇ 0.5°, 48.84 ⁇ 0.5°, 62.08 ⁇ 0.5°, 64.56 ⁇ 0.5°, 66.93 ⁇ 0.5°, 73.87 ⁇ 0.5°, 76.16 ⁇ 0.5°, 78.35 ⁇ 0.5° and 84.97 ⁇ 0.5° as determined by XRD ray.
  • the positive electrode material has diffraction peaks at 15.80 ⁇ 0.2°, 31.95 ⁇ 0.2°, 35.90 ⁇ 0.2°, 36.81 ⁇ 0.2°, 39.45 ⁇ 0.2°, 43.56 ⁇ 0.2°, 48.84 ⁇ 0.2°, 62.08 ⁇ 0.2°, 64.56 ⁇ 0.2°, 66.93 ⁇ 0.2°, 73.87 ⁇ 0.2°, 76.16 ⁇ 0.2°, 78.35 ⁇ 0.2°, and 84.97 ⁇ 0.2°, measured by XRD rays.
  • the positive electrode material when 0.8 ⁇ a ⁇ 0.85, has a diffraction peak at 41.4 ⁇ 0.2° as measured by XRD ray.
  • the present application provides a method for preparing a positive electrode material, as shown in FIG1 , comprising the following steps:
  • Step S10 mixing the nickel-iron-manganese-based precursor, the sodium salt and the dopant containing the M element to obtain a mixture; wherein, The ratio of the sum of the molar amounts of Ni, Fe and Mn to the molar amount of sodium is 1:(0.67-0.85), where M is a metal;
  • Step S20 sintering the mixture once in an oxygen-containing atmosphere to obtain a positive electrode material, wherein the ratio of the oxygen content in the oxygen-containing atmosphere in the heating section and the heat preservation section during the sintering treatment is controlled to be (0.4-0.65):1, and the sodium-rich defect degree of the positive electrode material is X, 0.25 ⁇ X ⁇ 0.7.
  • the sodium-rich defect X of the positive electrode material is controlled to meet the range of 0.25 ⁇ X ⁇ 0.7, thereby ensuring that the crystal structure stability of the sodium-rich positive electrode material is better, and the appropriate amount of sodium-rich defect can also make the positive electrode material have more ability to escape sodium ions, have a higher specific capacity, and at the same time can alleviate the irreversible phase change under high voltage caused by the large amount of sodium ions escaped during the charge and discharge process, which is beneficial to maintain the crystal structure stability of the positive electrode material and alleviate metal dissolution, so that the positive electrode material has both high voltage resistance, high capacity and cycle stability, and improves the comprehensive performance of the positive electrode material.
  • Step S10 mixing the nickel-iron-manganese-based precursor, the sodium salt and the dopant containing the M element to obtain a mixture.
  • the nickel-iron-manganese-based precursor includes at least one of a nickel-iron-manganese-based composite oxide and a nickel-iron-manganese-based hydroxide.
  • the general chemical formula of the nickel-iron-manganese-based precursor is Ni c Fe d Mne(OH) 2 , wherein 0.01 ⁇ c ⁇ 0.5, 0.01 ⁇ d ⁇ 0.3, and 0.5 ⁇ e ⁇ 1.
  • the sodium salt includes at least one of anhydrous sodium carbonate, sodium carbonate monohydrate, sodium carbonate decahydrate, sodium bicarbonate and sodium sulfate.
  • the dopant containing the M element includes at least one of an oxide of the M element, a sulfide of the M element, a nitride of the M element, and a hydroxide of the M element.
  • the amount of the dopant containing the M element added satisfies: the molar amount of M accounts for 0 mol% to 50 mol% in the total molar amount of Ni, Fe and Mn; specifically, it can be 1 mol%, 2 mol%, 5 mol%, 10 mol%, 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol% or 50 mol%, etc., which is not limited here.
  • M includes at least one of a transition metal and a rare earth metal.
  • M includes at least one of Cu, Al, Ti, Zr, W, Ta, Co, Mg, Ca, Mo, Nb, and B.
  • the mixing conditions for obtaining the mixture are: dry grinding at 10°C to 50°C for 0.3h to 2h, the grinding temperature can be specifically 10°C, 20°C, 30°C, 40°C, 45°C or 50°C, etc., and the grinding time can be specifically 0.3h, 0.5h, 1h, 1.5h, 1.8h or 2h.
  • the mixing conditions for obtaining the mixture are: placing the raw materials in a mechanical mixing device.
  • the mixing conditions for obtaining the mixture are: placing the raw materials in a high-speed mixer, controlling the linear speed of the high-speed mixer to be 5 m/s to 20 m/s, and mixing time to be 1 min to 30 min.
  • the mechanical mixing device is at least one of a ball mill, a three-dimensional mixer, a high-speed mixer, and a VC mixer.
  • Step S20 sintering the mixture once in an oxygen-containing atmosphere to obtain a positive electrode material, wherein the ratio of the oxygen content in the oxygen-containing atmosphere in the heating section and the heat preservation section during the sintering treatment is controlled to be (0.4-0.65):1, and the sodium-rich defect degree of the positive electrode material is X, 0.25 ⁇ X ⁇ 0.7.
  • the ratio of the oxygen content in the oxygen-containing atmosphere in the heating stage and the heat preservation stage during the sintering process can be specifically 0.4:1, 0.45:1, 0.48:1, 0.5:1, 0.55:1, 0.58:1, 0.61:1 or 0.65:1, etc. Of course, it can also be other values within the above range, which is not limited here.
  • the oxygen content in the oxygen-containing atmosphere of the temperature rising section is controlled to be 40% to 60%, specifically 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58% or 60%, etc., which is not limited here.
  • the oxygen content in the oxygen-containing atmosphere of the temperature rising section is 50% to 60%.
  • the transition metal elements in the precursor tend to be oxidized, the overall valence state increases, the ability of the transition metal to bind to oxygen atoms in the crystal structure becomes stronger, the crystallization strength of the P2 phase crystal structure is enhanced, and the ability of oxygen atoms to bind to sodium ions becomes weaker, thereby hindering the entry of excess sodium ions into the crystal lattice.
  • the heating rate of the heating section is 3°C/min to 5°C/min, specifically 3°C/min, 3.5°C/min, 4°C/min, 4.5°C/min or 5°C/min, etc., which is not limited here.
  • the oxygen content in the oxygen-containing atmosphere of the heat preservation section is controlled to be 80% to 100%, specifically 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98% or 100%, etc., which are not limited here.
  • the oxygen content in the oxygen-containing atmosphere of the heat preservation section is controlled to be 90% to 100%.
  • the crystal structure of the material is gradually optimized and completely. By increasing the oxygen content in the sintering atmosphere, the sodium ions compete for the sodium position in the crystal structure, resulting in a sodium-rich defect phenomenon.
  • the oxygen content in the oxygen-containing atmosphere of the temperature-lowering section is controlled to be 20% to 25%.
  • the temperature-lowering section is controlled to use an air atmosphere to reduce costs.
  • the temperature of the primary sintering treatment is 800°C to 950°C; specifically, it can be 800°C, 820°C, 850°C, 870°C, 880°C, 900°C, 920°C or 950°C, etc. Of course, it can also be other values within the above range, which is not limited here.
  • the time of the primary sintering treatment is 12 h to 24 h, specifically 12 h, 14 h, 15 h, 18 h, 20 h, 22 h or 24 h, etc.
  • 12 h, 14 h, 15 h, 18 h, 20 h, 22 h or 24 h etc.
  • it can also be other values within the above range, which is not limited here.
  • the oxygen-containing atmosphere includes at least one of air and oxygen.
  • the method further comprises:
  • Step S30 mixing at least one of phosphate and transition metal oxide and the primary sintering product, and performing secondary sintering on the mixed product to obtain a positive electrode material.
  • the mixing time is 0.3h to 2.0h, for example, 0.3h, 0.4h, 0.5h, 0.7h, 0.8h, 1.0h, 1.2h, 1.5h or 2.0h, etc., but it is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the mixing temperature is 10°C to 50°C, for example, 10°C, 15°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, etc.
  • the mixing temperature is 10°C to 40°C. The inventors have found through multiple experiments that under this mixing condition, both the mixing can be fully uniform and the side reactions of the mixed raw materials caused by excessive temperature can be prevented.
  • the temperature of the secondary sintering treatment is 300°C to 850°C, specifically 300°C, 400°C, 550°C, 600°C, 650°C, 700°C, 750°C or 850°C, etc., and of course other values within the above range, which are not limited here.
  • the temperature of the secondary sintering treatment is 350°C to 850°C. The inventors have found through multiple experiments that within this sintering temperature range, phosphate can be more evenly and firmly coated on the surface of the primary sintered product.
  • phosphate it is beneficial for phosphate to react with residual sodium on the surface of the primary sintered product, reduce residual alkali to form high sodium ion conductivity phosphate compounds, improve processing performance and rate performance, and prevent the sintered product from decomposing and sodium precipitating.
  • the secondary sintering treatment time is 4 hours to 10 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, etc., and of course, it can also be other values within the above range, which is not limited here.
  • the secondary sintering treatment time is 5 hours to 8 hours.
  • the oxygen-containing atmosphere includes at least one of air, oxygen, and nitrogen.
  • the phosphate includes at least one of lithium phosphate, sodium phosphate, potassium phosphate, titanium phosphate, aluminum phosphate, iron phosphate, and diammonium phosphate.
  • the lithium phosphate may be LiH 2 PO 4 and Li 3 PO 4 .
  • the average particle size of the phosphate is less than 10 ⁇ m, for example, it can be 0.01 ⁇ m, 0.1 ⁇ m, 1 ⁇ m, 2 ⁇ m, 4 ⁇ m, 5 ⁇ m, 8 ⁇ m or 9 ⁇ m, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the mass percentage of the phosphate in the primary sintered product is 0.05 wt % to 5 wt %.
  • the transition metal includes at least one of Cu, Al, Ti, Zr, Mg, Ta, W, Nb and B; specifically, it can be 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt% or 5.0wt%, etc., and of course, it can also be other values within the above range.
  • the mass proportion of the phosphate in the matrix material is 0.05wt% to 2wt%.
  • the mass percentage of the transition metal oxide in the matrix material is 0.05wt% to 5wt%; specifically, it can be 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt% or 5.0wt%, etc., and of course, it can also be other values within the above range.
  • the mass percentage of the transition metal oxide in the matrix material is 0.05wt% to 2wt%.
  • the secondary sintering is performed in air and/or oxygen.
  • the method further comprises:
  • the product after the secondary sintering is shaped, and the shaping includes at least one of crushing, grinding, ball milling or graded gas crushing.
  • the median particle size of the positive electrode material after shaping ranges from 3 ⁇ m to 15 ⁇ m.
  • grinding the sintered product can effectively control the particle size to reach the expected particle size range, within which the pore size range can not only ensure the penetration of the electrolyte, reduce the impedance of the positive electrode active material, improve the low temperature performance and rate performance of the material, but also will not affect the volume energy density of the battery.
  • An embodiment of the present application also provides a sodium ion battery, comprising a positive electrode plate, a negative electrode plate, a separator, a non-aqueous electrolyte and a casing, wherein the positive electrode plate comprises a current collector and a positive electrode active material coated on the current collector, and the positive electrode active material comprises the positive electrode material as described above or the positive electrode material prepared by the method for preparing the positive electrode material as described above, as well as a conductive agent and a binder.
  • the conductive agent is one of conductive carbon black, Ketjen black, graphite, and acetylene black.
  • the binder is one of sodium carboxymethyl cellulose, cyclodextrin, and polyvinylidene fluoride.
  • the solvent in the positive electrode active material is selected from one of deionized water, N-methylpyrrolidone, and N,N-dimethylformamide.
  • the positive electrode material, polyvinylidene fluoride and conductive carbon are dispersed in N-methylpyrrolidone in a mass ratio of 90:5:5 to prepare a positive electrode slurry with a solid content of 50%, which is coated on aluminum foil and dried as a positive electrode sheet.
  • a sodium sheet is used as a negative electrode sheet, a glass fiber membrane is used as a separator, and sodium hexafluorophosphate-diethylene glycol dimethyl ether (NaPF 6 concentration is 1 mol/L) is used as an electrolyte to assemble into a button battery.
  • a charge and discharge test is carried out at 2.0V to 4.1V and a rate of 0.1C.
  • the discharge specific capacity difference between V open and 2.5V in the first discharge process of the button battery is recorded as C1
  • the discharge specific capacity difference between 2.5V and 2.0V is recorded as C2
  • X C1/(C1+C2).
  • the LAND battery testing system was used to conduct discharge specific capacity, first coulombic efficiency and rate performance tests at 25°C, 2.0V ⁇ 4.1V and 0.1C rate.
  • the reference capacity was set to 100mA/g, and 0.1C corresponded to a current density of 10mA/g.
  • the alkaline impurity content on the surface of the positive electrode material is a characteristic of the material surface, which can be quantitatively measured by analyzing the reaction products between the surface and water. If the positive electrode material powder is immersed in water, a surface reaction occurs. During the reaction, the pH of the water increases (as the alkaline impurities dissolve), and the alkali content is quantified by pH titration. The result of the titration is the alkaline impurity content.
  • the content of alkaline impurities can be measured as follows: 5.0g of positive electrode material powder is immersed in 100ml of deionized water and stirred in a sealed glass flask for 10 minutes.
  • the suspension of the powder in water is filtered to obtain a clear solution.
  • 0.1M HCl is added at a rate of 0.5ml/min, and 90ml of the clear solution is titrated by recording the pH curve until the pH reaches 3.
  • a reference voltage curve is obtained by titrating a suitable mixture of NaOH and Na2CO3 dissolved in deionized water at a low concentration. In almost all cases, two different platforms are observed.
  • the upper plateau with end point y1 (in ml) between pH 8 and 9 is the equilibrium OH - /H 2 O, followed by the equilibrium CO 3 2- /HCO 3 - , and the lower plateau with end point y2 (in ml) between pH 4 and 6 is HCO 3 - /H 2 CO 3.
  • the inflection point y1 between the first and second plateaus and the inflection point y2 after the second plateau are obtained from the corresponding minimum values of the derivative dpH/dVol of the pH curve.
  • the second inflection point is generally close to pH 4.7.
  • the results are then expressed in terms of OH - and CO 3 2- weight percentages as shown in the following formulas (3) and (4):
  • Cu-K ⁇ rays are used as the X-ray source, and the testing conditions are 10-90° (2 ⁇ ) and a scanning step of 0.05°.
  • the particle size distribution range of the composite negative electrode material was tested by Malvern laser particle size analyzer.
  • the positive electrode sample is heated in a heating furnace, and the water evaporates into water vapor, which is transferred to the titration cup of the moisture meter by the dry carrier gas for measurement.
  • electrolysis produces iodine ions, and water reacts with iodine ions.
  • the water content is measured by measuring the charge used to produce iodine ions.
  • the LAND battery testing system was used to conduct capacity, first coulombic efficiency, and rate performance tests at 25°C, 2.0V ⁇ 4.1V.
  • the reference capacity was set to 200mA/g, and the current density corresponding to 1C was 200mA/g.
  • a method for preparing a positive electrode material comprises the following steps:
  • the mixed material is sintered at 700° C. for 8 h in a box-type atmosphere furnace in an air atmosphere, and the positive electrode material is obtained after crushing and sieving.
  • FIG2a is a scanning electron microscope image of the positive electrode material prepared in this embodiment.
  • the positive electrode material includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.9 g/cm 3 , the specific surface area is 0.9 m 2 /g, the median particle size D 50 is 7 ⁇ m, the pH value is 12.7, and the mass content of water in the positive electrode material is 0.016 wt%.
  • Figure 2c is the XRD diffraction pattern of the positive electrode material obtained in Example 1 of the present application. As shown in Figure 2c, using XRD ray measurement, the positive electrode material has diffraction peaks at 15.80 ⁇ 0.5°, 31.95 ⁇ 0.5°, 35.90 ⁇ 0.5°, 36.81 ⁇ 0.5°, 39.45 ⁇ 0.5°, 43.56 ⁇ 0.5°, 48.84 ⁇ 0.5°, 62.08 ⁇ 0.5°, 64.56 ⁇ 0.5°, 66.93 ⁇ 0.5°, 73.87 ⁇ 0.5°, 76.16 ⁇ 0.5°, 78.35 ⁇ 0.5° and 84.97 ⁇ 0.5°.
  • a method for preparing a positive electrode material comprises the following steps:
  • the mixed material is sintered in a box-type atmosphere furnace at 400° C. for 6 h in an air atmosphere, and the positive electrode material is obtained after crushing and sieving.
  • FIG3a is a scanning electron microscope image of the positive electrode material prepared in this embodiment.
  • the positive electrode material includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle, the positive electrode material has a tap density of 2.0 g/cm 3 , a specific surface area of 0.4 m 2 /g, a median particle size D 50 of 5 ⁇ m, a pH value of 12.5, and a water content of 0.034 wt % in the positive electrode material.
  • a method for preparing a positive electrode material comprises the following steps:
  • the inner core layered matrix material 1 wt% of titanium oxide, 0.5 wt% of copper oxide, 0.5 wt% of ammonium dihydrogen phosphate, and 1 wt% of boron oxide are placed in a high-speed mixer and mixed evenly to obtain a mixed material.
  • the mixed material is sintered in a box-type atmosphere furnace at 500° C. for 6 h in an air atmosphere, and the positive electrode material is obtained after crushing and sieving.
  • FIG4a is a scanning electron microscope image of the positive electrode material prepared in this embodiment.
  • the positive electrode material includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.8 g/cm 3 , the specific surface area is 1.24 m 2 /g, the median particle size D 50 is 6 ⁇ m, the pH value is 12.85, and the mass content of water in the positive electrode material is 0.009 wt%.
  • a method for preparing a positive electrode material comprises the following steps:
  • the positive electrode material prepared in this embodiment includes a base material.
  • the positive electrode material is a secondary particle.
  • the positive electrode material has a tap density of 1.8 g/cm 3 , a specific surface area of 1.4 m 2 /g, a median particle size D 50 of 6 ⁇ m, a pH value of 12.95, and a mass content of water in the positive electrode material of 0.012 wt %.
  • step (3) and step (4) are not performed.
  • the positive electrode material prepared in this embodiment includes a base material.
  • the positive electrode material is a secondary particle.
  • the positive electrode material has a tap density of 2.0 g/cm 3 , a specific surface area of 0.6 m 2 /g, a median particle size D 50 of 5 ⁇ m, a pH value of 12.7, and a water content of 0.038 wt % in the positive electrode material.
  • Example 2 in a box-type atmosphere furnace, the temperature is raised to 950°C at a heating rate of 4°C/min in an atmosphere with an oxygen content of 50%, and then the oxygen content of the atmosphere is adjusted to 10%. High-temperature calcination is carried out at 950°C for 12 hours. During the cooling process, the atmosphere is adjusted to air, and the matrix material is obtained after crushing and sieving.
  • the positive electrode material prepared in this embodiment includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.95 g/cm 3 , the specific surface area is 0.8 m 2 /g, the median particle size D 50 is 7.5 ⁇ m, the pH value is 12.85, and the mass content of water in the positive electrode material is 0.027 wt%.
  • a doping element precursor 5 mol% of copper oxide and 2.5 mol% of aluminum oxide
  • the positive electrode material prepared in this embodiment includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.9 g/cm 3 , the specific surface area is 0.88 m 2 /g, the median particle size D 50 is 7.1 ⁇ m, the pH value is 12.8, and the mass content of water in the positive electrode material is 0.027 wt%.
  • Example 2 The difference from Example 1 is that the layered base material, 1 wt% of titanium oxide, 0.5 wt% of copper oxide, and 0.5 wt% of LiH 2 PO 4 are placed in a high-speed mixer and mixed evenly to obtain a mixed material.
  • the positive electrode material prepared in this embodiment includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle, the tap density of the positive electrode material is 1.9 g/cm 3 , the specific surface area is 0.8 m 2 /g, the median particle size D 50 is 7.0 ⁇ m, the pH value is 12.8, and the mass content of water in the positive electrode material is 0.024 wt %.
  • the positive electrode material prepared in this embodiment includes a base material and a coating layer located on the surface of the base material.
  • the general formula of the base material is Na 0.67 Ni 0.25 Fe 0.25 Mn 0.5 O 2
  • the coating layer includes boron oxide, copper oxide and titanium oxide.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.98g/cm 3
  • the specific surface area is 0.6m 2 /g
  • the median particle size D 50 is 5 ⁇ m
  • the pH value is 12.6, and the mass content of water in the positive electrode material is 0.036wt%.
  • a doping element precursor 5 mol% of copper oxide and 2.5 mol% of aluminum oxide
  • the positive electrode material prepared in this embodiment includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.98g/cm 3 , the specific surface area is 0.8m 2 /g, the median particle size D 50 is 7 ⁇ m, the pH value is 12.9, and the mass content of water in the positive electrode material is 0.036wt%.
  • a method for preparing a positive electrode material comprises the following steps:
  • a doping element precursor 5 mol% of copper oxide, 5 mol% of titanium oxide, and 1.5 mol% of aluminum oxide
  • FIG4a is a scanning electron microscope image of the positive electrode material obtained in this comparative example.
  • the positive electrode material obtained in this comparative example includes a base material, the general formula of the base material is Na 0.99 M 0.13 Ni 0.23 Fe 0.3 Mn 0.34 O 2 , the positive electrode material is a secondary particle, and the positive electrode material is vibrated.
  • the density is 1.9 g/cm 3
  • the specific surface area is 1.0 m 2 /g
  • the median particle size D 50 is 7 ⁇ m
  • the pH value is 13.15
  • the mass content of water in the positive electrode material is 0.063 wt %.
  • a method for preparing a positive electrode material comprises the following steps:
  • the base material 1 wt% of titanium oxide, 0.5 wt% of copper oxide, 0.5 wt% of ammonium dihydrogen phosphate, and 1 wt% of boron oxide are placed in a high-speed mixer and mixed evenly to obtain a mixed material.
  • the mixed material is sintered in a box-type atmosphere furnace at 300° C. for 6 h in an air atmosphere, and the positive electrode material is obtained after crushing and sieving.
  • the positive electrode material prepared in this comparative example includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.78g/cm 3 , the specific surface area is 1.28m 2 /g, the median particle size D 50 is 6.2 ⁇ m, the pH value is 12.9, and the mass content of water in the positive electrode material is 0.019wt%.
  • a method for preparing a positive electrode material comprises the following steps:
  • the positive electrode material prepared in this comparative example includes a base material and a coating layer located on the surface of the base material.
  • the positive electrode material is a secondary particle.
  • the tap density of the positive electrode material is 1.8 g/cm 3 , the specific surface area is 1.3 m 2 /g, the median particle size D 50 is 6.1 ⁇ m, the pH value is 12.9, and the mass content of water in the positive electrode material is 0.033 wt%.
  • Example 4 The difference from Example 4 is that (2) the mixture is heated at 5°C/min in a box-type atmosphere furnace under an atmosphere of 35% oxygen content. The heating rate was increased to 870° C., and then the oxygen content of the atmosphere was adjusted to 100%. High-temperature calcination was carried out at 870° C. for 15 hours. During the cooling process, the atmosphere was adjusted to air, and the matrix material was obtained after crushing and sieving.
  • the positive electrode material prepared in this comparative example includes a base material.
  • the positive electrode material is a secondary particle.
  • the positive electrode material has a tap density of 1.8 g/cm 3 , a specific surface area of 1.4 m 2 /g, a median particle size D 50 of 6 ⁇ m, a pH value of 12.95, and a mass content of water in the positive electrode material of 0.069 wt %.
  • Example 4 The difference from Example 4 is that (2) in a box-type atmosphere furnace, in an atmosphere with an oxygen content of 60%, the mixture is heated to 870°C at a heating rate of 5°C/min, and then the oxygen content of the atmosphere is adjusted to 75%, and high-temperature calcination is carried out at 870°C for 15 hours. During the cooling process, the atmosphere is adjusted to air, and the matrix material is obtained after crushing and sieving.
  • the positive electrode material prepared in this comparative example includes a base material.
  • the positive electrode material is a secondary particle.
  • the positive electrode material has a tap density of 1.8 g/cm 3 , a specific surface area of 1.5 m 2 /g, a median particle size D 50 of 6.5 ⁇ m, a pH value of 12.9, and a water content of 0.053 wt % in the positive electrode material.
  • controlling the sodium-rich defect degree of the positive electrode material within an appropriate range can be beneficial to maintaining the crystal structure stability of the positive electrode material and the structural stability of the positive electrode material.
  • the appropriate amount of sodium-rich defect degree enables the positive electrode material to have a higher ability to remove sodium ions and a higher specific capacity.
  • it can alleviate the irreversible phase change under high voltage caused by the large amount of sodium ions being removed during the charge and discharge process, which is beneficial to maintaining the crystal structure stability of the positive electrode material and relieving metal dissolution, so that the positive electrode material has both high voltage resistance, high capacity and cycle stability, and improves the comprehensive performance of the positive electrode material.
  • the ratio of the oxygen content in the oxygen-containing atmosphere in the heating section and the holding section during the first sintering treatment is too high, and the oxygen content in the holding section during the sintering treatment is too low, which is not conducive to promoting sodium ions to compete for sodium positions in the crystal structure, resulting in a reduction in the sodium ion content in the crystal structure.
  • the sodium ion content in the crystal structure is low, the P2 phase crystal structure will undergo a phase transition, which is not conducive to maintaining the stability of the crystal structure and affects the cycle performance of the battery.

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Abstract

本申请涉及一种正极材料及钠离子电池，所述正极材料具有富钠的结构缺陷，所述正极材料的富钠缺陷度为X，0.25≤X≤0.7，所述X＝C1/(C1+C2)；其中，所述C1为半电池在V开至2.5V间的放电比容量差值，其中V开为半电池首次充电曲线的开路电压；所述C2为2.5V至2.0V的放电比容量差值。本申请正极材料，正极材料兼具耐高压性能、高容量及循环稳定性，提升正极材料的综合性能。

Description

正极材料及钠离子电池
相关申请的交叉引用
本申请要求于2022年12月22日提交中国国家知识产权局的申请号为202211657757.9、名称为“正极材料及钠离子电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请属于正极材料技术领域，尤其涉及一种正极材料及其制备方法、钠离子电池。
背景技术
由于传统化石能源短缺和能源安全等因素的制约以及人们对生态环境保护观念的增强，能源的可持续发展利用和存储受到世界各国的高度重视。在各种储能系统中，电化学储能系统(EES)因其使用寿命长、成本低、投资少、易于安装等优点，被认为是平衡可再生能源循环特性的有效方法，而电化学储能中二次电池储能具有巨大潜力。其中，锂离子电池因其高的理论比容量和比能量密度在储能市场占据主导地位，但由于锂(Li)资源储量有限且分布不均以及锂的多方面消耗，受制于提锂技术、地理环境、交通条件等客观因素，动力电池领域锂资源仍存在瓶颈。为了缓解该问题，目前提出用丰度大的元素，如钠(Na)、钾(K)、镁(Mg)、铝(Al)、钙(Ca)等替代锂，以制备新一代低成本、环保的二次离子电池发展钠离子电池具备国家层面的战略意义，钠离子电池已经受到越来越多国家的关注和支持。
钠基层状氧化物正极材料是钠离子电池的最关键材料之一，类似于锂电的钴酸锂、三元结构，层状氧化物结构拥有良好的离子通道，循环性能可能存在一定短板，但平均成熟度相对较高。过渡金属氧化物NaXMeO2是一种嵌入型或插层型化合物，理论上具有较高的放电比容量，但循环性能较差。
现有的钠离子电池层状氧化物材料中各个类型缺点明显，例如O3型正极材料容量高，首效低，循环性能差；P2型正极材料的首次充电容量低，循环、倍率性能好；P3型正极材料容量低，循环差，工作电压高，各类型正极材料的综合性能不佳。
发明内容
本申请的目的是为了提供一种正极材料、钠离子电池，正极材料兼具耐高压性能、高容量及循环稳定性，提升正极材料的综合性能。
第一方面，本申请一种正极材料，所述正极材料具有富钠的结构缺陷，所述正极材料的富钠缺陷度为X，0.25≤X≤0.7，所述X＝C1/(C1+C2)；
其中，所述C1为半电池在V开至2.5V间的放电比容量差值，其中V开为半电池首次充电曲线的开路电压；所述C2为2.5V至2.0V的放电比容量差值。
在一些实施方式中，所述正极材料的富钠缺陷度X满足：0.3≤X≤0.6。
在一些实施方式中，所述正极材料包括具有P2相结构的层状氧化物。
在一些实施方式中，所述正极材料包括基体材料，所述基体材料的化学通式为NaMbNicFedMneO2，其中，0.67≤a≤0.85，0≤b≤0.5，0.01≤c≤0.5，0.01≤d≤0.3，0.5≤e＜1，b+c+d+e＝1；M为金属；
所述基体材料的晶体结构为具有P2相结构的层状氧化物，且所述基体材料的晶体结构具有所述富钠的结构缺陷。
在一些实施方式中，当0.8≤a≤0.85时，利用XRD射线测定，所述正极材料在41.4±0.2°处具有衍射峰。
在一些实施方式中，利用XRD射线测定，所述正极材料在15.80±0.5°、31.95±0.5°、35.90±0.5°、36.81±0.5°、39.45±0.5°、43.56±0.5°、48.84±0.5°、62.08±0.5°、64.56±0.5°、66.93±0.5°、73.87±0.5°、76.16±0.5°、78.35±0.5°和84.97±0.5°处具有衍射峰。
在一些实施方式中，所述正极材料还包括位于所述基体材料表面的包覆层，所述包覆层包括过渡金属氧化物及磷酸盐中至少一种。
在一些实施方式中，所述包覆层包括磷酸盐，所述磷酸盐包括锂的磷酸盐、钠的磷酸盐、钾的磷酸盐、钛的磷酸盐、铝的磷酸盐、铁的磷酸盐和磷酸二氢铵中的至少一种；
在一些实施方式中，所述包覆层包括磷酸盐，所述磷酸盐在所述基体材料中的质量占比为0.05wt％～5wt％；
在一些实施方式中，所述包覆层包括过渡金属氧化物，所述过渡金属金属氧化物中的过渡金属包括Cu、Al、Ti、Zr、Mg、Ta、W、Nb和B中的至少一种；
在一些实施方式中，所述包覆层包括过渡金属氧化物，所述过渡金属氧化物在所述基体材料中的质量占比为0.05wt％～5wt％。
在一些实施方式中，M包括过渡金属和稀土金属中的至少一种；
在一些实施方式中，M包括Cu、Al、Ti、Zr、W、Ta、Co、Mg、Ca、Mo、Nb和B中的至少一种；
在一些实施方式中，所述正极材料中CO32-的质量含量≤2wt％，所述正极材料中OH-的质量含量≤2wt％；
在一些实施方式中，所述正极材料的振实密度为≥1.6g/cm3；
在一些实施方式中，所述正极材料的比表面积为0.2m2/g～2m2/g；
在一些实施方式中，所述正极材料的中值粒径D50为3μm～15μm；
在一些实施方式中，所述正极材料的pH值为11～13；
在一些实施方式中，所述正极材料中的水的质量含量≤0.05wt％；
在一些实施方式中，所述正极材料的空间群为P63/mmc。
第二方面，本申请提供一种钠离子电池，所述钠离子电池包括正极极片，所述正极极片包括第一方面所述的正极材料或第二方面所述的方法制备的正极材料。
本申请与现有技术相比，具备如下有益效果：
本申请提供的正极材料，将富余Na离子抢占的Na位置数量与可供Na离子嵌入的Na位置总数量的比值定义为富钠缺陷度，控制正极材料的富钠缺陷度在合适范围内，可以有利于保持正极材料的晶体结构稳定性及正极材料的结构稳定性，适量的富钠缺陷度使得正极材料具有更高的可脱出钠离子能力，具有更高的比容量，同时能够缓解充放电过程中由于钠离子大量脱出带来的高电压下的不可逆相变，有利于保持正极材料的晶体结构稳定性，缓解金属溶出，从而使得正极材料兼具耐高压性能、高容量及循环稳定性，提升正极材料的综合性能。
附图说明
为了更清楚的说明本申请实施例或现有技术的技术方案，下面将对实施例或现有技术描述中所 需要使用的附图作简单的介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本申请实施例提供的正极材料的制备方法的流程示意图。
图2a为本申请实施例1制得正极材料的扫描电镜图。
图2b为本申请实施例1制得正极材料组装的电池的充放电曲线图。
图2c为本申请实施例1制得正极材料的XRD衍射图。
图3a为本申请实施例2制得正极材料的扫描电镜图。
图3b为本申请实施例2制得正极材料组装的电池的充放电曲线图。
图4a为本申请实施例3制得正极材料的扫描电镜图。
图4b为本申请实施例3制得正极材料组装的电池的充放电曲线图。
图5a为本申请对比例1制得正极材料的扫描电镜图。
图5b为本申请对比例1制得正极材料组装的电池的充放电曲线图。
具体实施方式
为了更好的理解本申请的技术方案，下面结合附图对本申请实施例进行详细描述。
应当明确，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其它实施例，都属于本申请保护的范围。
此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多个该特征。
为了容易理解本申请，特定术语在本申请中被恰当地定义。除非本文中另外定义，本申请中使用的科学术语和技术术语具有本申请所属领域中的技术人员通常理解的含义。
钠基层状氧化物正极材料是钠离子电池的最关键材料之一，类似于锂电的钴酸锂、三元结构，层状氧化物结构拥有良好的离子通道，循环性能可能存在一定短板，但平均成熟度相对较高。过渡金属氧化物NaXMeO2是一种嵌入型或插层型化合物，理论上具有较高的放电比容量，但循环性能较差。
现有的钠离子电池层状氧化物材料中各个类型缺点明显，例如O3型正极材料容量高，首效低，循环性能差；P2型正极材料的首次充电容量低，循环、倍率性能好；P3型正极材料容量低，循环差，工作电压高，各类型正极材料的综合性能不佳。
因此，本申请提供一种正极材料，具有富钠的结构缺陷，正极材料的富钠缺陷度为X，0.25≤X≤0.7，X＝C1/(C1+C2)；
其中，C1为半电池在V开至2.5V间的放电比容量差值，其中V开为半电池首次充电曲线的开路电压；C2为2.5V至2.0V的放电比容量差值。
本申请提供的正极材料，可以有利于保持正极材料的晶体结构稳定性及正极材料的结构稳定性，适量的富钠缺陷度使得正极材料具有更高的可脱出钠离子能力，具有更高的比容量，同时能够缓解充放电过程中由于钠离子大量脱出带来的高电压下的不可逆相变，有利于保持正极材料的晶体结构稳定性，缓解金属溶出，从而使得正极材料兼具耐高压性能、高容量及循环稳定性，提升正极材料的综合性能。
在本申请的技术方案中，将富余Na离子抢占的Na位置数量与可供Na离子嵌入的Na位置总数量的比值定义为富钠缺陷度X。
正极材料中的富钠缺陷程度与材料充放电过程中脱嵌Na离子的能力息息相关，其在测试得到的C-V曲线图中可以通过比容量的相对关系来表征。测试的C-V曲线的比容量与脱嵌Na离子的个数直接相关。P2型材料最主要的特点就是可以额外嵌入钠离子(典型的P2材料Na含量0.67，半电池中可以额外嵌入0.33的Na离子)，额外嵌入的Na对应的容量区间都反应在放电曲线2.0-V开间(其中2.0-2.5V对应理想P2结构中额外嵌钠，对应于Mn4+→Mn3+的氧化还原反应。2.5V～V开对应结构扭曲额外嵌钠，区别于原有P2型棱柱结构，主要对应氧化还原反应为Ni3+→Ni2+)。因此本发明人发现可以通过这两个容量区间的相关关系，侧面映衬出富钠缺陷的程度。特别的，富钠缺陷程度表示由于额外Na离子带来的晶格扭曲缺陷占总共可额外嵌入钠的数量的比值。根据算法，当正极材料中富钠缺陷增加的时候，C1段比容量增加，C2段比容量减少，x的值增大；反之当富钠缺陷减少时，C1减少，C2增加，x的值减少。X的单调性与富钠缺陷程度单调性一致，可作为富钠缺陷程度的指标。
本申请中，正极材料的富钠缺程度是通过测试由该正极材料组装而成的扣式电池首圈放电曲线中的区间比容量C1、C2，经计算得到的。具体的扣式电池制作流程以及测试条件对于本领域技术人员来说，是已知的。例如，其正极极片制作过程，与锂电正极极片制作过程一致，活性物质、PVDF(5130)、导电碳的质量比为90：5：5；其扣电制作流程与锂离子扣式电池制作过程也基本一致，仅电解液更换为NaPF6-DIGLYME电解液，隔膜采用玻璃纤维的隔膜以及负极片改用商业钠片。测试采用新威测试，2.0-4.1V测试区间，0.1C倍率充放电，得到所需C-V曲线图。
具体地，将正极材料、聚偏氟乙烯与导电碳按照质量比90:5:5分散于N-甲基吡咯烷酮，配制成固含量为50％的正极浆料，涂布在铝箔上烘干之后作为正极片，采用钠片作为负极片，隔膜为玻璃纤维膜，电解液为六氟磷酸钠-二乙二醇二甲醚(NaPF6浓度为1mol/L)组装形成扣式电池，在2.0V～4.1V、0.1C倍率下进行充放电测试，记录扣式电池首次放电过程中V开至2.5V间的放电比容量差值为C1，2.5V至2.0V的放电比容量差值为C2，X＝C1/(C1+C2)。
可以理解地，不同电压下的放电比容量差值可以对应表征出这个电压区间内脱出嵌入钠离子的数量。
正极材料的富钠缺陷度为X，0.25≤X≤0.7，X取值具体可以是0.25、0.3、0.35、0.4、0.45、0.5、0.55、0.6、0.65或0.7等，当然也可以是上述范围内的其他值，在此不做限定。适量的富钠缺陷度使得正极材料具有更高的可脱出Na离子能力，具有更高的比容量，同时能够缓解充放电过程中由于Na离子大量脱出带来的高电压下的不可逆相变，有利于保持正极材料的晶体结构稳定性，缓解金属溶出。当富钠缺陷度过大时，过量缺陷会阻碍钠离子脱嵌，导致正极材料的容量发挥恶化，循环性能变差，另外富钠缺陷度过大时还会使得材料表面的残碱增加，影响材料的加工性能。
在一些实施方式中，0.3≤X≤0.6。
在一些实施方式中，所述正极材料包括具有P2相结构的层状氧化物。
在一些实施方式中，正极材料包括基体材料，基体材料的化学通式为NaaMbNicFedMneO2，其中，0.67≤a≤0.85，0≤b≤0.5，0.01≤c≤0.5，0.01≤d≤0.3，0.5≤e＜1，b+c+d+e＝1；M为金属；
基体材料的晶体结构为具有P2相的层状氧化物，且基体材料的晶体结构存在富钠的结构缺陷。
具体地，a的值例如可以是0.67、0.69、0.70、0.72、0.75、0.79、0.82或0.85等。当正极材料 中的Na的摩尔含量在上述范围内，使用该正极材料的电池具有较高的充放电比容量；当正极材料中的Na摩尔含量较少时，电池的比容量降低，能量密度下降，导致电化学性能显著下降。当正极材料中的Na摩尔含量较多时，材料表面会形成多余的残碱，在制备浆料过程中很容易形成果冻状，影响涂布的效果；其次，残碱对电化学性能的影响主要体现在增加了不可逆容量损失，同时恶化循环性能。
b的值例如可以是0.01、0.05、0.08、0.1、0.15、0.16、0.18、0.2、0.3、0.4、0.45或0.5等，c的值例如可以是0.01、0.05、0.08、0.1、0.15、0.16、0.18、0.2、0.3、0.4、0.45或0.5等，d的值例如可以是0.01、0.05、0.08、0.1、0.15、0.16、0.18、0.2、0.28或0.3等，在此不做限定。e的值例如可以是0.5、0.6、0.7、0.75、0.79、0.83、0.87、0.9或0.95等。
在一些实施方式中，M包括过渡金属和稀土金属中的至少一种。
在一些实施方式中，M包括Cu、Al、Ti、Zr、W、Ta、Co、Mg、Ca、Mo、Nb和B中的至少一种。
当正极材料中的Ni、Fe、Mn与M的总摩尔含量在上述范围内，电池具有良好的电化学性能。
在一些实施方式中，所述基体材料的晶体结构为具有P2相结构的层状氧化物，且所述基体材料的晶体结构存在富钠的结构缺陷。
在NaaMbNicFedMneO2+f的晶体结构中，Ni、Fe、Mn分别与邻近的氧原子形成八面体结构，多个八面体结构之间掺杂M金属并构成过渡金属层，相邻两层过渡金属层中的氧原子与钠离子构成三棱柱结构，进而构成层状结构。在P2相结构中引入高的钠含量，会降低晶体结构中过渡金属离子的平均价态，促使晶体结构中最低氧化态的过渡金属向其高价态转变，实现更高的比容量。富钠缺陷带来的多余的钠离子能够在钠离子大量脱出过程中缓解高脱钠状态下正极发生相变的趋向性，从而提高正极材料的结构稳定性。
在基体材料的晶体结构中，Na离子嵌入于Na位置上，晶体结中可供Na离子嵌入的Na位置是恒定的，富余的Na离子抢占Na位置会带来晶格扭曲缺陷，即富余的Na离子共同抢占的Na位置则会造成富钠缺陷现象。
在一些实施方式中，正极材料的空间群为P63/mmc。
在一些实施方式中，所述正极材料还包括位于所述基体材料表面的包覆层，所述包覆层包括过渡金属氧化物及磷酸盐中的至少一种。
在一些实施方式中，所述磷酸盐包括锂的磷酸盐、钠的磷酸盐、钾的磷酸盐、钛的磷酸盐、铝的磷酸盐、铁的磷酸盐和磷酸二氢铵中的至少一种。
包覆层中的磷酸盐不仅具有高钠离子电导率，抑制电解液腐蚀基体材料，有利于形成空间型钠离子导电网络。
在一些实施方式中，所述过渡金属包括Cu、Al、Ti、Zr、Mg、Ta、W、Nb和B中的至少一种；
在一些实施方式中，所述过渡金属氧化物在所述基体材料中的质量占比为0.05wt％～5wt％，具体可以是0.05wt％、0.1wt％、0.3wt％、0.5wt％、0.7wt％、0.9wt％、1.0wt％、2.0wt％、3.0wt％、4.0wt％或5.0wt％等，当然也可以是上述范围内的其他值。优选地，所述过渡金属氧化物在所述基体材料中的质量占比为0.05wt％～2wt％。
在一些实施方式中，所述磷酸盐在所述基体材料中的质量占比为0.05wt％～5wt％，具体可以是0.05wt％、0.1wt％、0.3wt％、0.5wt％、0.7wt％、0.9wt％、1.0wt％、2.0wt％、3.0wt％、4.0wt％或5.0wt％ 等，当然也可以是上述范围内的其他值。优选地，所述磷酸盐在所述基体材料中的质量占比为0.05wt％～2wt％。
在一些实施方式中，所述正极材料中CO3 2-的质量含量≤2wt％，具体可以是0.1wt％、0.3wt％、0.5wt％、0.7wt％、0.9wt％、1.0wt％、1.2wt％、1.5wt％、1.8wt％或2wt％等，当然也可以是上述范围内的其他值。优选地，正极材料中CO3 2-的质量含量≤1wt％。
在一些实施方式中，所述正极材料中OH-的质量含量≤2wt％，具体可以是0.1wt％、0.3wt％、0.5wt％、0.7wt％、0.9wt％、1.0wt％、1.2wt％、1.5wt％、1.8wt％或2wt％等，当然也可以是上述范围内的其他值。优选地，正极材料中OH-的质量含量≤1wt％。
在一些实施方式中，所述正极材料的中值粒径D50为3μm至15μm，具体可以是3μm、3.5μm、4μm、5μm、6μm、8μm、10μm、12μm、14μm或15μm等，当然也可以上述范围内的其他数值，在此不做限定。将正极材料的粒径控制在上述范围内，有利于提高正极材料的结构稳定性、热稳定性和长循环稳定性。优选地，正极材料的中值粒径D50为5μm至10μm。
在一些实施方式中，所述正极材料的颗粒径距满足(D90-D10)/D50≤1.5，具体可以是1.5、1.4、1.3、1.2、1.1、0.9、0.8、0.5、0.3、0.1等，在此不做限定。优选地，(D90-D10)/D50≤1.2。
需要说明的是，采用激光衍射法测得粒径分布测定的体积基准累计粒度分布，D10表示粉末累计粒度分布百分比达到10％时所对应的粒径，D50表示累计粒度分布百分比达到50％时所对应的粒径，D90表示累计粒度分布百分比达到90％时所对应的粒径。
在一些实施方式中，正极材料的比表面积为0.2m2/g～2m2/g。具体可以是0.2m2/g、0.4m2/g、0.5m2/g、0.6m2/g、0.7m2/g、1.2m2/g、1.5m2/g、1.6m2/g、1.8m2/g或2.0m2/g等。正极材料的比表面积控制在上述范围内时，有利于提高由该正极材料制成的电池的循环性能。
在一些实施方式中，正极材料的振实密度≥1.6g/cm3，具体可以是1.6g/cm3、1.7g/cm3、1.8g/cm3、1.85g/cm3、1.9g/cm3、1.95g/cm3或2.0g/cm3等。正极材料的振实密度控制在上述范围内时，有利于提高由该正极材料制成的电池的能量密度。优选地，正极材料的振实密度≥1.8g/cm3。
在一些实施方式中，正极材料的pH值为11～13；具体可以是11.5、11.9、12.1、12.3、12.5、12.7、12.9或13等，当然也可以是上述范围内的其他值。
在一些实施方式中，正极材料中的水的质量含量≤0.05wt％，具体可以是0.01wt％、0.02wt％、0.03wt％、0.04wt％或0.05wt％等，当然也可以是上述范围内的其他值。控制正极材料的水含量，有利于抑制残碱的含量，提高材料的加工性能。优选地，正极材料中的水的质量含量≤0.03wt％。
在一些实施方式中，利用XRD射线测定，所述正极材料在15.80±0.5°、31.95±0.5°、35.90±0.5°、36.81±0.5°、39.45±0.5°、43.56±0.5°、48.84±0.5°、62.08±0.5°、64.56±0.5°、66.93±0.5°、73.87±0.5°、76.16±0.5°、78.35±0.5°和84.97±0.5°处具有衍射峰。
在一些实施方式中，利用XRD射线测定，所述正极材料在15.80±0.2°、31.95±0.2°、35.90±0.2°、36.81±0.2°、39.45±0.2°、43.56±0.2°、48.84±0.2°、62.08±0.2°、64.56±0.2°、66.93±0.2°、73.87±0.2°、76.16±0.2°、78.35±0.2°、84.97±0.2°处具有衍射峰。
在一些实施方式中，当0.8≤a≤0.85时，利用XRD射线测定，所述正极材料在41.4±0.2°处具有衍射峰。
本申请实施例提供一种正极材料的制备方法，如图1所示，包括以下步骤：
步骤S10，将镍铁锰基前驱体、钠盐以及含M元素的掺杂剂进行混合，得到混合物；其中， Ni、Fe及Mn的摩尔量总和与钠的摩尔量的比值为1：(0.67～0.85)，M为金属；
步骤S20，在含氧气氛下将混合物进行一次烧结处理，得到正极材料，其中，控制烧结处理时升温段与保温段的含氧气氛中氧气含量的比值为(0.4～0.65):1，所述正极材料的富钠缺陷度为X，0.25≤X≤0.7。
在上述技术方案中，通过控制Ni、Fe及Mn的摩尔量总和与钠的摩尔量的比值，以及烧结处理时升温段以及保温段的氧气含量的比值，从而控制正极材料的富钠缺陷度X满足0.25≤X≤0.7范围内，从而可以保障富钠的正极材料的晶体结构稳定性更好，适量的富钠缺陷度还能使得正极材料具有更多可以脱出钠离子的能力，具有更高的比容量，同时能够缓解充放电过程中由于钠离子大量脱出带来的高电压下的不可逆相变，有利于保持正极材料的晶体结构稳定性，缓解金属溶出，从而使得正极材料兼具耐高压性能、高容量及循环稳定性，提升正极材料的综合性能。
以下结合实施例具体介绍本申请的制备方法：
步骤S10，将镍铁锰基前驱体、钠盐以及含M元素的掺杂剂进行混合，得到混合物。
在一些实施方式中，所述镍铁锰基前驱体包括镍铁锰基复合氧化物和镍铁锰基氢氧化物中的至少一种。
在一些实施方式中，所述镍铁锰基前驱体的化学通式为NicFedMne(OH)2，其中0.01≤c≤0.5，0.01≤d≤0.3，0.5≤e＜1。
在一些实施方式中，所述钠盐的包括无水碳酸钠、一水合碳酸钠、十水合碳酸钠、碳酸氢钠和硫酸钠中的至少一种。
在一些实施方式中，所述含M元素的掺杂剂包括M元素的氧化物、M元素的硫化物、M元素的氮化物、M元素的氢氧化物中的至少一种。
在一些实施方式中，所述含M元素的掺杂剂的加入量满足：M的摩尔量在Ni、Fe及Mn的摩尔量总和中的占比为0mol％～50mol％；具体可以是1mol％、2mol％、5mol％、10mol％、15mol％、20mol％、25mol％、30mol％、35mol％或50mol％等，在此不做限定。
在一些实施方式中，M包括过渡金属和稀土金属中的至少一种。
在一些实施方式中，M包括Cu、Al、Ti、Zr、W、Ta、Co、Mg、Ca、Mo、Nb和B中的至少一种。
在一些实施方式中，得到所述混合物的混合条件为：在10℃～50℃下干法研磨0.3h～2h，研磨温度具体可以是10℃、20℃、30℃、40℃、45℃或50℃等，研磨时间具体可以是0.3h、0.5h、1h、1.5h、1.8h或2h。
在一些实施方式中，得到所述混合物的混合条件为：将原料置于机械混合设备中。
在一些实施方式中，得到所述混合物的混合条件为：将原料置于高混机中，控制高混机的线速度为5m/s～20m/s，混料时间为1min～30min。
在一些实施方式中，机械混合设备为球磨机、三维混料机、高速混料机和VC混料机中的至少一种。
步骤S20，在含氧气氛下将混合物进行一次烧结处理，得到正极材料，其中，控制烧结处理时升温段与保温段的含氧气氛中氧气含量的比值为(0.4～0.65):1，所述正极材料的富钠缺陷度为X，0.25≤X≤0.7。
在一些实施方式中，控制烧结处理时升温段与保温段的含氧气氛中氧气含量的比值具体可以是 0.4:1、0.45:1、0.48:1、0.5:1、0.55:1、0.58:1、0.61:1或0.65:1等，当然也可以是上述范围内的其他值，在此不做限定。
在一些实施方式中，在所述一次烧结处理过程中，控制升温段的含氧气氛中氧气含量为40％～60％，具体可以是40％、42％、45％、48％、50％、52％、55％、58％或60％等，在此不做限定。优选地，升温段的含氧气氛中氧气含量为50％～60％。通过控制升温段的氧气含量，可有利于钠离子尽可能进入晶格内，当氧含量过高时，前驱体中的过渡金属元素趋于被氧化状态，整体价态升高，晶体结构中过渡金属与氧原子结合能力变强，P2相晶体结构的结晶化强度增强，氧原子与钠离子结合的能力变弱，进而阻碍富余钠离子进入晶格。
在一些实施方式中，所述升温段的升温速率为3℃/min～5℃/min，具体可以是3℃/min、3.5℃/min、4℃/min、4.5℃/min或5℃/min等，在此不做限定。
在一些实施方式中，在所述一次烧结处理过程中，控制保温段的含氧气氛中氧气含量为80％～100％，具体可以是80％、82％、85％、88％、90％、92％、95％、98％或100％等，在此不做限定。优选地，控制保温段的含氧气氛中氧气含量为90％～100％。在保温段，材料的晶体结构逐步完整优化，通过增加烧结气氛中的氧含量，使得钠离子争抢晶体结构中的钠位置，造成富钠缺陷现象。
在一些实施方式中，在所述一次烧结处理过程中，控制降温段的含氧气氛中氧气含量为20％～25％。优选地，在所述一次烧结处理过程中，控制降温段采用空气气氛，可以降低成本。
在一些实施方式中，所述一次烧结处理的温度为800℃～950℃；具体可以是800℃、820℃、850℃、870℃、880℃、900℃、920℃或950℃等，当然也可以是上述范围内的其他值，在此不做限定。
在一些实施方式中，所述一次烧结处理的时间为12h～24h，具体可以是12h、14h、15h、18h、20h、22h或24h等，当然也可以是上述范围内的其他值，在此不做限定。
在一些实施方式中，所述含氧气氛包括空气、氧气中的至少一种。
在一些实施方式中，所述方法还包括：
步骤S30，将磷酸盐及过渡金属氧化物中的至少一种、一次烧结产物进行混合，混合产物进行二次烧结，得到正极材料。
在一些实施方式中，所述一次烧结产物与磷酸盐、过渡金属氧化物混合过程中，混合时间为0.3h～2.0h，例如可以是0.3h、0.4h、0.5h、0.7h、0.8h、1.0h、1.2h、1.5h或2.0h等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。混合温度为10℃～50℃，例如10℃、15℃、25℃、30℃、35℃、40℃、45℃或50℃等，优选地，混合温度为10℃～40℃。发明人通过多次试验发现，在该混合条件下，既可以充分混合均匀，又可以防止温度过高导致混合原料发生副反应。
在一些实施方式中，所述二次烧结处理的温度为300℃～850℃，具体可以是300℃、400℃、550℃、600℃、650℃、700℃、750℃或850℃等，当然也可以是上述范围内的其他值，在此不做限定。优选地，所述二次烧结处理的温度为350℃～850℃。发明人通过多次试验发现，在该烧结温度范围内，能使磷酸盐更加均匀、牢固地包覆在一次烧结产物的表面，同时，有利于磷酸盐与一次烧结物表面残余钠反应，降低残碱形成高钠离子电导磷酸化合物，改善加工性能和倍率性能，又不至于使烧成物发生分解和钠析出。
在一些实施方式中，所述二次烧结处理的时间为4h～10h，具体可以是4h、5h、6h、7h、8h、9h或10h等，当然也可以是上述范围内的其他值，在此不做限定。优选地，所述二次烧结处理的时间为5h～8h。
在一些实施方式中，所述含氧气氛包括空气、氧气和氮气中的至少一种。
在一些实施方式中，所述磷酸盐包括锂的磷酸盐、钠的磷酸盐、钾的磷酸盐、钛的磷酸盐、铝的磷酸盐、铁的磷酸盐和磷酸二氢铵中的至少一种。示例性地，锂的磷酸盐可以是LiH2PO4和Li3PO4。
其中，所述磷酸盐的平均粒径小于10μm，例如可以是0.01μm、0.1μm、1μm、2μm、4μm、5μm、8μm或9μm等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
在一些实施方式中，所述磷酸盐在所述一次烧结产物中的质量占比为0.05wt％～5wt％。
在一些实施方式中，所述过渡金属包括Cu、Al、Ti、Zr、Mg、Ta、W、Nb和B中的至少一种；具体可以是0.05wt％、0.1wt％、0.3wt％、0.5wt％、0.7wt％、0.9wt％、1.0wt％、2.0wt％、3.0wt％、4.0wt％或5.0wt％等，当然也可以是上述范围内的其他值。优选地，所述磷酸盐在所述基体材料中的质量占比为0.05wt％～2wt％。
在一些实施方式中，所述过渡金属氧化物在所述基体材料中的质量占比为0.05wt％～5wt％；具体可以是0.05wt％、0.1wt％、0.3wt％、0.5wt％、0.7wt％、0.9wt％、1.0wt％、2.0wt％、3.0wt％、4.0wt％或5.0wt％等，当然也可以是上述范围内的其他值。优选地，所述过渡金属氧化物在所述基体材料中的质量占比为0.05wt％～2wt％。
在一些实施方式中，二次烧结在空气和/或氧气中进行。
在一些实施例中，方法还包括：
对二次烧结后的产物进行整形，整形包括粉碎、研磨、球磨或分级气碎中的至少一种。
整形后的正极材料的中值粒径范围为3μm至15μm。示例性地，将烧结后的产物进行研磨，可以有效控制颗粒粒径，使其达到预期的粒径范围，在该孔径范围内不仅可以保证电解液的渗透，降低正极活性材料的阻抗，提升材料的低温性能和倍率性能，还不会影响电池的体积能量密度。
本申请实施例还提供一种钠离子电池，包括正极极片、负极极片、隔膜、非水电解液和外壳，所述正极极片包括集流体和涂覆在所述集流体上的正极活性物质，正极活性物质包括如上述正极材料或如上述正极材料的制备方法制备的正极材料及导电剂、粘结剂。
在一些实施方式中，所述导电剂为导电炭黑、科琴黑、石墨、乙炔黑中的一种。
在一些实施方式中，所述粘结剂为羧甲基纤维素钠、环糊精、聚偏氟乙烯中的一种。
在一些实施方式中，正极活性物质中的溶剂选自去离子水、N-甲基吡咯烷酮、N,N-二甲基甲酰胺中的一种。
下面分多个实施例对本申请实施例进行进一步的说明。其中，本申请实施例不限定于以下的具体实施例。在不变主权利的范围内，可以适当的进行变更实施。
测试方法：
(1)正极材料的富钠缺陷度及电化学性能测试
将正极材料、聚偏氟乙烯与导电碳按照质量比90:5:5分散于N-甲基吡咯烷酮，配制成固含量为50％的正极浆料，涂布在铝箔上烘干之后作为正极片，采用钠片作为负极片，隔膜为玻璃纤维膜，电解液为六氟磷酸钠-二乙二醇二甲醚(NaPF6浓度为1mol/L)组装形成扣式电池，在2.0V～4.1V、0.1C倍率下进行充放电测试，记录扣式电池首次放电过程中V开至2.5V间的放电比容量差值为C1，2.5V至2.0V的放电比容量差值为C2，X＝C1/(C1+C2)。
采用LAND电池测试系统，在25℃，2.0V～4.1V、0.1C倍率下进行放电比容量、首次库伦效率和倍率性能测试，参比容量设置为100mA/g，0.1C对应电流密度为10mA/g。
(2)正极材料的碱性杂质测试：
正极材料表面碱性杂质含量是材料表面的特性，其可通过分析表面与水之间的反应产物定量测量。如果正极材料粉末浸入水中，则发生表面反应。在反应期间，水的pH增加(随着碱性杂质的溶解)，并且通过pH滴定将碱含量定量。滴定的结果为碱性杂质含量。碱性杂质的含量可如下测量：将5.0g正极材料粉末浸入100ml去离子水中，并且在密封的玻璃烧瓶中搅拌10分钟。在搅拌以溶解碱后，将粉末在水中的悬浮液过滤以得到澄清溶液。然后，在搅拌下在以0.5ml/min的速率添加0.1M HCl期间，通过记录pH曲线来滴定90ml澄清溶液，直至pH达到3。通过滴定以低浓度溶解于去离子水中的NaOH和Na2CO3的合适的混合物，获得参考电压曲线。在几乎所有情况下，观察到两个不同的平台。在pH 8～9之间具有终点y1(以ml为单位)的上平台是平衡OH-/H2O，之后是平衡CO3 2-/HCO3 -，在pH 4～6之间具有终点y2(以ml为单位)的下平台是HCO3 -/H2CO3。在第一与第二平台之间的拐点y1以及在第二平台之后的拐点y2由pH曲线的导数dpH/dVol的相应最小值获得。第二拐点一般接近pH 4.7。然后将结果以OH-和CO3 2-重量百分比表示如下式(3)和(4)所示：

(3)正极材料的XRD测试：
对材料进行XRD测试时，X射线的以Cu-Kα射线作为射线源，测试的条件为在10-90°(2θ)，扫描的步距0.05°。
(4)正极材料的比表面积的测试方式：
采用北京精微高博科学技术有限公司的动态比表面积快速测定仪JW-DX测试，单位为m2/g。
(5)正极材料的振实密度的测试方式：
采用百特振实，称取一定量样品，以300times/min，振动3000次测试振实密度。
(6)正极材料的粒径的测试方法：
通过马尔文激光粒度仪测试复合负极材料的粒径分布范围。
(7)正极材料的SEM的测试方法：
扫描电镜表征在透射电子显微镜上进行，操作电压为200kV，观察正极材料的结构。
(8)正极材料的水含量的测试方法：
正极样品在加热炉中加热，水分蒸发成水蒸气，被干燥的载气转移至水分仪的滴定杯中测定。在滴定杯中，电解产生碘离子，水与碘离子发生反应。通过测量产生碘离子所用的电荷，衡量水分的含量。
(9)正极材料的pH的测试方法：
将10wt％的正极材料粉末分散在水中，超声后通过pH计测试上清液的pH值。
(10)电化学性能测试：
采用LAND电池测试系统，在25℃，2.0V～4.1V下进行容量、首次库伦效率、和倍率性能测试，参比容量设置为200mA/g，1C对应电流密度为200mA/g。
实施例1
一种正极材料的制备方法，包括以下步骤：
(1)将3.13kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.74)、掺杂元素前驱物(5mol％的氧化铜、2.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在50％氧含量气氛下，将混合物以4℃/min升温速率升温至850℃，之后调整气氛氧含量至95％，850℃下进行高温煅烧15小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
(3)将层状的基体材料与1wt％的氧化钛、0.5wt％的氧化铜、0.5wt％的磷酸二氢铵放置于高速混料机中混合均匀，得到混合物料。
(4)将混合物料在箱式气氛炉中700℃下烧结8h，烧结气氛为空气，破碎过筛后得到正极材料。
图2a为本实施例制得正极材料的扫描电镜图，如图2a所示，正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.704M0.1Ni0.2Fe0.2Mn0.5O2，M＝Cu、Al，包覆层包括氧化钛、氧化铜及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.9g/cm3，比表面积为0.9m2/g，中值粒径D50为7μm，pH值为12.7，所述正极材料中的水的质量含量0.016wt％。
图2b为本申请实施例制得正极材料组装的电池的充放电曲线图，如图2b所示，V开＝2.83V，C1＝16.93mAh/g，C2＝17.5mAh/g，正极材料的富钠缺陷度X为0.49。
图2c为本申请实施例1制得正极材料的XRD衍射图，如图2c所示，利用XRD射线测定，所述正极材料在15.80±0.5°、31.95±0.5°、35.90±0.5°、36.81±0.5°、39.45±0.5°、43.56±0.5°、48.84±0.5°、62.08±0.5°、64.56±0.5°、66.93±0.5°、73.87±0.5°、76.16±0.5°、78.35±0.5°和84.97±0.5°处具有衍射峰。
实施例2
一种正极材料的制备方法，包括以下步骤：
(1)将2.98kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为5:6:9，且nNi+Fe+Mn：nNa＝1：0.703)、掺杂元素前驱物(5mol％的氧化镁、5mol％的氧化钛)，通过高速混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在40％氧含量气氛下，将混合物以5℃/min升温速率升温至900℃，之后调整气氛氧含量至90％，900℃下进行高温煅烧12小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
(3)将内核层状基体材料与1wt％的硼氧化物、0.5wt％的氧化铜、0.5wt％的氧化钛放置于高速混料机中混合均匀，得到混合物料。
(4)将混合物料在箱式气氛炉中400℃下烧结6h，烧结气氛为空气，破碎过筛后得到正极材料。
图3a为本实施例制得正极材料的扫描电镜图，如图3a所示，正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.67M0.1Ni0.25Fe0.2Mn0.45O2，M＝Mg、Ti，包覆层包 括硼氧化物、氧化铜及氧化钛。正极材料为二次颗粒，所述正极材料的振实密度为2.0g/cm3，比表面积为0.4m2/g，中值粒径D50为5μm，pH值为12.5，所述正极材料中的水的质量含量为0.034wt％。
图3b为本申请实施例制得正极材料组装的电池的充放电曲线图，如图3b所示，V开＝2.82V，C1＝9.81mAh/g，C2＝21.34mAh/g，正极材料的富钠缺陷度X为0.315。
实施例3
一种正极材料的制备方法，包括以下步骤：
(1)将3.34kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.788)、掺杂元素前驱物(5mol％的氧化铜、5mol％的氧化钛、1.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在60％氧含量气氛下，将混合物以3℃/min升温速率升温至870℃，之后调整气氛氧含量至98％，870℃下进行高温煅烧15小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
(3)将内核层状基体材料与1wt％的氧化钛、0.5wt％的氧化铜、0.5wt％的磷酸二氢铵、1wt％的硼氧化物放置于高速混料机中混合均匀，得到混合物料。
(4)将混合物料在箱式气氛炉中500℃下烧结6h，烧结气氛为空气，破碎过筛后得到正极材料。
图4a为本实施例制得正极材料的扫描电镜图，如图4a所示，正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.75M0.13Ni0.2Fe0.2Mn0.47O2，M＝Cu、Ti及Al，包覆层包括硼氧化物、氧化铜、氧化钛及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.8g/cm3，比表面积为1.24m2/g，中值粒径D50为6μm，pH值为12.85，所述正极材料中的水的质量含量为0.009wt％。
图4b为本申请实施例制得正极材料组装的电池的充放电曲线图，如图4b所示，V开＝2.75V，C1＝24.85mAh/g，C2＝16.97mAh/g，正极材料的富钠缺陷度X为0.594。
实施例4
一种正极材料的制备方法，包括以下步骤：
(1)将3.34kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.788)、掺杂元素前驱物(5mol％的氧化铜、5mol％的氧化钛、1.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在60％氧含量气氛下，将混合物以5℃/min升温速率升温至870℃，之后调整气氛氧含量至100％，870℃下进行高温煅烧15小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
本实施例制得正极材料包括基体材料，基体材料的通式为Na0.75M0.13Ni0.2Fe0.2Mn0.47O2，M＝Cu、Ti及Al，正极材料为二次颗粒，所述正极材料的振实密度为1.8g/cm3，比表面积为1.4m2/g，中值粒径D50为6μm，pH值为12.95，所述正极材料中的水的质量含量为0.012wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.74V，C1＝24.89mAh/g， C2＝16.87mAh/g，正极材料的富钠缺陷度X为0.596。
实施例5
与实施例2不同的是：未进行步骤(3)以及步骤(4)。
本实施例制得正极材料包括基体材料，基体材料的通式为Na0.67M0.1Ni0.25Fe0.2Mn0.45O2，M＝Mg、Ti，正极材料为二次颗粒，所述正极材料的振实密度为2.0g/cm3，比表面积为0.6m2/g，中值粒径D50为5μm，pH值为12.7，所述正极材料中的水的质量含量为0.038wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.82V，C1＝10.61mAh/g，C2＝20.64mAh/g，正极材料的富钠缺陷度X为0.339。
实施例6
与实施例1不同的是：(2)在箱式气氛炉中，在50％氧含量气氛下，以4℃/min升温速率升温至950℃，之后调整气氛氧含量至10％，950℃下进行高温煅烧12小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
本实施例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.7M0.1Ni0.2Fe0.2Mn0.5O2，M＝Cu、Al，包覆层包括氧化钛、氧化铜及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.95g/cm3，比表面积为0.8m2/g，中值粒径D50为7.5μm，pH值为12.85，所述正极材料中的水的质量含量为0.027wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.84V，C1＝16.24mAh/g，C2＝17.91mAh/g，正极材料的富钠缺陷度X为0.476。
实施例7
与实施例1不同的是：将4.193kg硫酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.74)、掺杂元素前驱物(5mol％的氧化铜、2.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
本实施例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.7M0.1Ni0.2Fe0.2Mn0.5O2，M＝Cu、Al，包覆层包括氧化钛、氧化铜及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.9g/cm3，比表面积为0.88m2/g，中值粒径D50为7.1μm，pH值为12.8，所述正极材料中的水的质量含量为0.027wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.83V，C1＝16.52mAh/g，C2＝17.61mAh/g，正极材料的富钠缺陷度X为0.484。
实施例8
与实施例1不同的是：将层状的基体材料与1wt％的氧化钛、0.5wt％的氧化铜、0.5wt％的LiH2PO4放置于高速混料机中混合均匀，得到混合物料。
本实施例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为 Na0.7M0.1Ni0.2Fe0.2Mn0.5O2，M＝Cu、Al，包覆层包括氧化钛、氧化铜及LiH2PO4。正极材料为二次颗粒，所述正极材料的振实密度为1.9g/cm3，比表面积为0.8m2/g，中值粒径D50为7.0μm，pH值为12.8，所述正极材料中的水的质量含量为0.024wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.84V，C1＝16.11mAh/g，C2＝17.76mAh/g，正极材料的富钠缺陷度X为0.475。
实施例9
与实施例2不同的是：将2.98kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.703)通过高速混料机混合均匀，得到混合物。
本实施例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.67Ni0.25Fe0.25Mn0.5O2，包覆层包括硼氧化物、氧化铜及氧化钛。正极材料为二次颗粒，所述正极材料的振实密度为1.98g/cm3，比表面积为0.6m2/g，中值粒径D50为5μm，pH值为12.6，所述正极材料中的水的质量含量为0.036wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.83V，C1＝8.41mAh/g，C2＝23.94mAh/g，正极材料的富钠缺陷度X为0.259。
实施例10
与实施例1不同的是：将3.78kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.893)、掺杂元素前驱物(5mol％的氧化铜、2.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
本实施例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.85M0.1Ni0.2Fe0.2Mn0.5O2，M＝Cu、Al，包覆层包括氧化钛、氧化铜及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.98g/cm3，比表面积为0.8m2/g，中值粒径D50为7μm，pH值为12.9，所述正极材料中的水的质量含量0.036wt％。
本申请实施例制得正极材料组装的电池的充放电测试过程中，V开＝2.82V，C1＝18.23mAh/g，C2＝8.19mAh/g，正极材料的富钠缺陷度X为0.690。
对比例1
一种正极材料的制备方法，包括以下步骤：
(1)将4.4kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:1，且nNi+Fe+Mn：nNa＝1：1)、掺杂元素前驱物(5mol％的氧化铜、5mol％的氧化钛、1.5mol％的氧化铝)，通过三维混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在空气气氛下，将混合物以4℃/min升温速率升温至850℃煅烧15小时，自然冷却，破碎过筛后得到基体材料。
图4a为本对比例制得正极材料的扫描电镜图，如图4a所示，本对比例制得正极材料包括基体材料，基体材料的通式为Na0.99M0.13Ni0.23Fe0.3Mn0.34O2，正极材料为二次颗粒，所述正极材料的振实 密度为1.9g/cm3，比表面积为1.0m2/g，中值粒径D50为7μm，pH值为13.15，所述正极材料中的水的质量含量为0.063wt％。
图4b为本对比例制得正极材料组装的电池的充放电曲线图，如图4b所示，V开＝2.99V，C1＝33.69mAh/g，C2＝7.32mAh/g，正极材料的富钠缺陷度X为0.821。
对比例2
一种正极材料的制备方法，包括以下步骤：
(1)将3.34kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.788)、掺杂元素前驱物(5mol％的氧化铜、5mol％的氧化钛、1.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在纯氧气氛下，将混合物以4℃/min升温速率升温至900℃煅烧12小时，自然冷却，破碎过筛后得到基体材料。
(3)将基体材料与1wt％的氧化钛、0.5wt％的氧化铜、0.5wt％的磷酸二氢铵、1wt％的硼氧化物放置于高速混料机中混合均匀，得到混合物料。
(4)将混合物料在箱式气氛炉中300℃下烧结6h，烧结气氛为空气，破碎过筛后得到正极材料。
本对比例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.75M0.13Ni0.2Fe0.2Mn0.47O2，M＝Cu、Ti及Al，包覆层包括氧化钛、氧化铜、硼氧化物及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.78g/cm3，比表面积为1.28m2/g，中值粒径D50为6.2μm，pH值为12.9，所述正极材料中的水的质量含量为0.019wt％。
本对比例制得正极材料组装的电池的充放电测试过程中，V开＝2.77V，C1＝7.02mAh/g，C2＝21.16mAh/g，正极材料的富钠缺陷度X为0.249。
对比例3
一种正极材料的制备方法，包括以下步骤：
(1)将3.34kg无水碳酸钠、7.2kg共沉淀法制备的镍铁锰基前驱体(其中Ni：Fe：Mn的摩尔比为1:1:2，且nNi+Fe+Mn：nNa＝1：0.788)、掺杂元素前驱物(1mol％的氧化铜、1mol％的氧化钛、0.5mol％的氧化铝)，通过高速混料机混合均匀，得到混合物。
(2)在箱式气氛炉中，在纯氧气氛下，将混合物以4℃/min升温速率升温至850℃煅烧12小时，降温段调整气氛为空气，破碎过筛后得到基体材料。
本对比例制得正极材料包括基体材料及位于所述基体材料表面的包覆层，基体材料的通式为Na0.75M0.13Ni0.2Fe0.2Mn0.47O2，M＝Cu、Ti及Al，，包覆层包括氧化钛、氧化铜、硼氧化物及磷酸二氢铵。正极材料为二次颗粒，所述正极材料的振实密度为1.8g/cm3，比表面积为1.3m2/g，中值粒径D50为6.1μm，pH值为12.9，所述正极材料中的水的质量含量为0.033wt％。
本对比例制得正极材料组装的电池的充放电测试过程中，V开＝2.75V，C1＝8.13mAh/g，C2＝25.02mAh/g，正极材料的富钠缺陷度X为0.245。
对比例4
与实施例4不同之处在于，(2)在箱式气氛炉中，在35％氧含量气氛下，将混合物以5℃/min 升温速率升温至870℃，之后调整气氛氧含量至100％，870℃下进行高温煅烧15小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
本对比例制得正极材料包括基体材料，基体材料的通式为Na0.75M0.13Ni0.2Fe0.2Mn0.47O2，M＝Cu、Ti及Al，正极材料为二次颗粒，所述正极材料的振实密度为1.8g/cm3，比表面积为1.4m2/g，中值粒径D50为6μm，pH值为12.95，所述正极材料中的水的质量含量为0.069wt％。
本对比例制得正极材料组装的电池的充放电测试过程中，V开＝2.86V，C1＝24.89mAh/g，C2＝10.56mAh/g，正极材料的富钠缺陷度X为0.702。
对比例5
与实施例4不同之处在于，(2)在箱式气氛炉中，在60％氧含量气氛下，将混合物以5℃/min升温速率升温至870℃，之后调整气氛氧含量至75％，870℃下进行高温煅烧15小时，降温过程将气氛调整为空气，破碎过筛后得到基体材料。
本对比例制得正极材料包括基体材料，基体材料的通式为Na0.75M0.13Ni0.2Fe0.2Mn0.47O2，M＝Cu、Ti及Al，正极材料为二次颗粒，所述正极材料的振实密度为1.8g/cm3，比表面积为1.5m2/g，中值粒径D50为6.5μm，pH值为12.9，所述正极材料中的水的质量含量为0.053wt％。
本对比例制得正极材料组装的电池的充放电测试过程中，V开＝2.72V，C1＝7.23mAh/g，C2＝21.87mAh/g，正极材料的富钠缺陷度X为0.248。
表1实施例与对比例的电化学性能数据对比表
如表1所示，根据实施例1至8的测试数据可知，控制正极材料的富钠缺陷度在合适范围内，可以有利于保持正极材料的晶体结构稳定性及正极材料的结构稳定性，适量的富钠缺陷度使得正极材料具有更高的可脱出钠离子能力，具有更高的比容量，同时能够缓解充放电过程中由于钠离子大量脱出带来的高电压下的不可逆相变，有利于保持正极材料的晶体结构稳定性，缓解金属溶出，从而使得正极材料兼具耐高压性能、高容量及循环稳定性，提升正极材料的综合性能。
如表1所示，对比例1至对比例3在制备过程中，一次烧结处理时，全程采用空气气氛或纯氧气氛，氧气含量保持稳定，升温段与保温段不存在氧含量差异，不利于钠离子尽可能进入晶格内，晶体结构中的钠离子过少，充电时当晶体结构中的钠离子含量少，P2相晶体结构会发生相转变，不利于保持晶体结构的稳定性，影响电池的循环性能。
同样地，对比例4在制备过程中，一次烧结处理时升温段与保温段的含氧气氛中氧气含量的比值过低，烧结处理时升温段的氧气含量过低，不利于钠离子尽可能进入晶格内，晶体结构中的钠离子过少，充电时当晶体结构中的钠离子含量少，P2相晶体结构会发生相转变，不利于保持晶体结构的稳定性，影响电池的循环性能。
同样地，对比例5在制备过程中，一次烧结处理时升温段与保温段的含氧气氛中氧气含量的比值过高，烧结处理时保温段的氧气含量过低，不利于促进钠离子争抢晶体结构中的钠位置，使得晶体结构中的钠离子含量减少，充电时当晶体结构中的钠离子含量少，P2相晶体结构会发生相转变，不利于保持晶体结构的稳定性，影响电池的循环性能。
以上所述仅为本申请的优选实施例而已，并不用于限制本申请，对于本领域的技术人员来说，本申请可以有各种更改和变化。凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (10)

  1. 一种正极材料，其特征在于，所述正极材料具有富钠的结构缺陷，所述正极材料的富钠缺陷度为X，0.25≤X≤0.7，所述X＝C1/(C1+C2)；
    其中，所述C1为半电池在V开至2.5V间的放电比容量差值，其中V开为半电池首次充电曲线的开路电压；所述C2为2.5V至2.0V的放电比容量差值。
  2. 根据权利要求1所述的正极材料，其特征在于，所述正极材料的富钠缺陷度X满足：0.3≤X≤0.6。
  3. 根据权利要求1或2所述的正极材料，其特征在于，所述正极材料包括具有P2相结构的层状氧化物。
  4. 根据权利要求1～3任一项所述的正极材料，其特征在于，所述正极材料包括基体材料，所述基体材料的化学通式为NaaMbNicFedMneO2，其中，0.67≤a≤0.85，0≤b≤0.5，0.01≤c≤0.5，0.01≤d≤0.3，0.5≤e＜1，b+c+d+e＝1；M为金属；
    所述基体材料的晶体结构为具有P2相结构的层状氧化物，且所述基体材料的晶体结构具有所述富钠的结构缺陷。
  5. 根据权利要求1～4任一项所述的正极材料，其特征在于，当0.8≤a≤0.85时，利用XRD射线测定，所述正极材料在41.4±0.2°处具有衍射峰。
  6. 根据权利要求1～4任一项述的正极材料，其特征在于，利用XRD射线测定，所述正极材料在15.80±0.5°、31.95±0.5°、35.90±0.5°、36.81±0.5°、39.45±0.5°、43.56±0.5°、48.84±0.5°、62.08±0.5°、64.56±0.5°、66.93±0.5°、73.87±0.5°、76.16±0.5°、78.35±0.5°和84.97±0.5°处具有衍射峰。
  7. 根据权利要求6所述的正极材料，其特征在于，所述正极材料包括如下特征(1)～(5)中的至少一种：
    (1)所述正极材料还包括位于所述基体材料表面的包覆层，所述包覆层包括过渡金属氧化物及磷酸盐中至少一种。
    (2)所述包覆层包括磷酸盐，所述磷酸盐包括锂的磷酸盐、钠的磷酸盐、钾的磷酸盐、钛的磷酸盐、铝的磷酸盐、铁的磷酸盐和磷酸二氢铵中的至少一种；
    (3)所述包覆层包括磷酸盐，所述磷酸盐在所述基体材料中的质量占比为0.05wt％～5wt％；
    (4)所述包覆层包括过渡金属氧化物，所述过渡金属氧化物中的过渡金属包括Cu、Al、Ti、Zr、Mg、Ta、W、Nb和B中的至少一种；
    (5)所述包覆层包括过渡金属氧化物，所述过渡金属氧化物在所述基体材料中的质量占比为0.05wt％～5wt％。
  8. 根据权利要求4～7任一项所述的正极材料，其特征在于，所述正极材料包括如下特征(1)～(2)中的至少一种：
    (1)M包括过渡金属和稀土金属中的至少一种；
    (2)M包括Cu、Al、Ti、Zr、W、Ta、Co、Mg、Ca、Mo、Nb和B中的至少一种。
  9. 根据权利要求1～8任一项所述的正极材料，其特征在于，所述正极材料包括如下特征(1)～(7)中的至少一种：
    (1)所述正极材料中CO3 2-的质量含量≤2wt％，所述正极材料中OH-的质量含量≤2wt％；
    (2)所述正极材料的振实密度为≥1.6g/cm3；
    (3)所述正极材料的比表面积为0.2m2/g～2m2/g；
    (4)所述正极材料的中值粒径D50为3μm～15μm；
    (5)所述正极材料的pH值为11～13；
    (6)所述正极材料中的水的质量含量≤0.05wt％；
    (7)所述正极材料的空间群为P63/mmc。
  10. 一种钠离子电池，其特征在于，所述钠离子电池包括权利要求1～9任一所述的正极材料。
PCT/CN2023/107998 2022-12-22 2023-07-18 正极材料及钠离子电池 WO2024131048A1 (zh)

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