High-stability layered oxide sodium-ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses a high-stability layered oxide sodium-ion battery positive electrode material and a preparation method thereof.The high-stability layered oxide sodium-ion battery positive electrode material comprises a layered oxide matrix and a surface coating layer, a sodium source, a nickel source, a manganese source, a lithium source and a magnesium source are mixed according to the stoichiometric ratio, a pre-sintered product is heated to 850-950 DEG C at the speed of 0.5-2 DEG C / min to be calcined, and the high-stability layered oxide sodium-ion battery positive electrode material is obtained. The calcined product, lithium phosphate and aluminum nitrate are subjected to ball milling and mixing in a citric acid solution with the pH value of 3-5 according to the mass ratio of 1: (0.005-0.03): (0.002-0.02), and the capacity retention ratio of the battery is larger than or equal to 88% after 500 times of circulation under the voltage range of 2.0-4.0 V and the multiplying power of 0.5 C. The comprehensive protection from the bulk phase to the interface is realized by triple doping and gradient coating, and the cycle life is prolonged by two times. Interlayer spacing expansion and coating layer ion conduction cooperate to reduce polarization, and the applicable temperature range is widened to-30 DEG C to 60 DEG C. Seed crystal induction and segmented sintering ensure batch consistency, and the method is suitable for large-scale production. Cheap Fe / Mn is adopted to replace part of Ni, and the material cost is reduced by 40% compared with similar products.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery materials, and in particular to a high-stability layered oxide sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] Layered transition metal oxides (NaxMO2) have become the mainstream cathode material for sodium-ion batteries due to their high specific capacity and tunable structure. However, conventional O3-type materials are prone to irreversible phase transitions during charge and discharge, resulting in poor cycling stability. Furthermore, surface side reactions and insufficient sodium ion diffusion kinetics limit their rate capability and low-temperature performance. Existing technologies, single-element doping or simple coating methods struggle to achieve both structural stability and interface optimization. Furthermore, the uneven particle size of materials synthesized using conventional solid-phase methods exacerbates capacity degradation. Summary of the Invention

[0003] In order to overcome the shortcomings of the existing technical solutions, the present invention provides a high-stability layered oxide sodium ion battery positive electrode material and a preparation method thereof, which can effectively solve the problems raised by the background technology.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] A high-stability layered oxide sodium ion battery positive electrode material comprises a layered oxide matrix and a surface coating layer. The general chemical formula of the layered oxide matrix is NaxM1-a-bLiaMgbO2, wherein the M element is at least two of Ni, Mn, and Fe, 0.6≤x≤1.0, 0.01≤a≤0.15, and 0.005≤b≤0.1; the surface coating layer is a composite layer of Li3PO4 and AlPO4, the thickness of the surface coating layer is 5-30 nm, and the coating amount of the surface coating layer accounts for 0.5-3% of the matrix mass.

[0006] As a further description of the above technical solution, the layered oxide matrix has an O3 type crystal structure, the interlayer spacing of the O3 type crystal structure is 0.52-0.58nm, the BET specific surface area of the O3 type crystal structure is 0.5-2.5m2 / g, the median particle size D50 of the secondary particles is 5-15μm, and it is formed by the agglomeration of primary particles of 50-200nm.

[0007] As a further description of the above technical solution, the molar ratio of Ni:Mn in the M element is 1:1-3:1, and the M element contains 0.5-5at% of Ti doping in the total amount of transition metals.

[0008] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0009] Step S1: Mix a sodium source, a nickel source, a manganese source, a lithium source, and a magnesium source in a stoichiometric ratio, add 0.1-1% ZrO2 seed crystals accounting for the total mass of the raw materials, and heat to 300-450°C at a rate of 2-5°C / min under a protective atmosphere for 2-5 hours;

[0010] Step S2: heating the pre-calcined product to 850-950°C at a rate of 0.5-2°C / min and calcining for 8-15 hours while controlling the oxygen partial pressure to be 5-15 vol%;

[0011] Step S3: ball-milling the calcined product with lithium phosphate and aluminum nitrate in a citric acid solution with a pH of 3-5 at a mass ratio of 1:(0.005-0.03):(0.002-0.02), spray-drying the mixture, and heat-treating the mixture at 400-550° C. for 2-6 hours to form a surface coating layer.

[0012] As a further description of the above technical solution, in step S1, the sodium source is a mixture of sodium carbonate and sodium acetate, and the mixing mass ratio is 1:0.2-0.5; the nickel source is nickel oxyhydroxide, and the manganese source is trimanganese tetraoxide.

[0013] As a further description of the above technical solution, in step S3, the inlet air temperature of the spray drying is 180-220°C, the outlet air temperature is 80-120°C, and the water content of the obtained precursor powder is ≤0.5wt%.

[0014] As a further description of the above technical solution, it also includes classifying the product after calcination in step S2, obtaining active particles with D90≤18μm by airflow classification, and then entering step S3 for coating.

[0015] A sodium ion battery has a capacity retention rate of ≥88% after 500 cycles at a rate of 0.5C within a voltage range of 2.0-4.0V, and a low-temperature capacity retention rate of ≥82% at -20°C.

[0016] As a further description of the above technical solution, the positive electrode material, conductive carbon and binder are made into a positive electrode sheet in a mass ratio of 90:7:3. The positive electrode sheet has a compaction density of 3.2-3.6 g / cm3 and a porosity of 20-30%.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The high-stability layered oxide sodium ion battery positive electrode material and the preparation method thereof of the present invention have at least one of the following beneficial effects during use:

[0019] Triple doping plus gradient coating achieves comprehensive protection from bulk to interface, doubling cycle life. Extended interlayer spacing and ionic conduction in the coating layer synergistically reduce polarization, extending the applicable temperature range to -30°C to 60°C. Seed induction and staged sintering ensure batch consistency, making it suitable for large-scale production. Using inexpensive Fe / Mn to partially replace Ni reduces material costs by 40% compared to similar products. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of a high-stability layered oxide sodium ion battery positive electrode material of the present invention.

[0021] Figure 2 The figure is a schematic flow chart of a method for preparing a high-stability layered oxide sodium-ion battery positive electrode material.

[0022] Numbers in the figure:

[0023] 101. Surface coating layer; 201. Layered oxide matrix. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] like Figure 1-2 As shown, the present invention provides a high-stability layered oxide sodium ion battery positive electrode material, including a layered oxide matrix and a surface coating layer, the chemical formula of the layered oxide matrix is NaxM1-a-bLiaMgbO2, wherein the M element is at least two of Ni, Mn, and Fe, 0.6≤x≤1.0, 0.01≤a≤0.15, and 0.005≤b≤0.1, the surface coating layer is a composite layer of Li3PO4 and AlPO4, the thickness of the surface coating layer is 5-30nm, and the coating amount of the surface coating layer accounts for 0.5-3% of the mass of the matrix.

[0026] Matrix material: The general chemical formula is NaxM1-a-bLiaMgbO2 (M=Ni / Mn / Fe). Through Li / Mg synergistic doping and partial substitution of Ti elements, triple optimization is achieved:

[0027] Li+ doping: occupies transition metal sites, expands the interlayer spacing (0.52-0.58nm), and reduces the energy barrier for sodium ion migration.

[0028] Mg2+ doping: acts as a "pillar ion" to suppress lattice distortion and reduce structural collapse under high voltage.

[0029] Ti4+ doping (accounting for 0.5-5at% of transition metals): stabilizes the oxygen framework through strong Ti-O bonds and inhibits oxygen precipitation.

[0030] Surface coating: Li3PO4 / AlPO4 composite layer (5-30nm) works synergistically through the following mechanisms:

[0031] Li3PO4: High ionic conductivity (>10-4S / cm) promotes Na+ interfacial transport.

[0032] AlPO4: Dense structure blocks electrolyte corrosion and reduces transition metal dissolution.

[0033] Gradient composite: The inner layer Li3PO4 forms a chemical bond with the outer layer AlPO4 to enhance the interface bonding strength.

[0034] Li + Radius (0.076nm) and Ni 2+ (0.069nm), which can replace some transition metal ions to occupy octahedral sites and inhibit the migration of transition metal ions during the cycle (such as Ni 2+ The structural disorder caused by the migration of the tetrahedral sites stabilizes the layered structure.

[0035] Mg 2+ As a high-valent cation (+2 valence), it enhances the interlayer Coulomb force through electrostatic interaction, inhibiting the Na + The interlayer expansion and contraction caused by deintercalation, especially in the high voltage range (such as close to 4.0V), can effectively slow down the phase transition from O3 to O'3 phase and maintain the integrity of the crystal structure.

[0036] The molar ratio of Ni:Mn in the M element is 1:1-3:1, Ni 2+ / Ni 3+ and Mn 3+ / Mn 4+ The redox couple provides the main capacity (Ni contributes to high specific capacity, Mn stabilizes the lattice structure), and Fe element (if present) can adjust the electronic conductivity of the material. In addition, Ti, which accounts for 0.5-5at% of the total transition metal content, 4+ doping, because its ionic radius (0.061nm) is smaller than that of Na + , which can form a stable coordination structure at the grain boundary, inhibit the propagation of intergranular cracks and improve the mechanical stability of the material.

[0037] It is further explained that the layered oxide matrix has an O3 type crystal structure, the interlayer spacing of the O3 type crystal structure is 0.52-0.58nm, the BET specific surface area of the O3 type crystal structure is 0.5-2.5m2 / g, the median particle size D50 of the secondary particles is 5-15μm, and it is formed by the agglomeration of primary particles of 50-200nm.

[0038] The ion transport properties of the O3 type crystal structure are based on the O3 type crystal structure (oxygen atoms are densely packed in a cubic manner), and the interlayer spacing is 0.52-0.58nm, which is significantly larger than that of sodium ions (Na + ) ionic radius (0.102nm), providing ample channels for sodium ions to intercalate / eject between layers. The BET specific surface area of the structure is controlled in the range of 0.5-2.5m 2 / g, which not only avoids the increase in electrolyte side reactions caused by excessive specific surface area, but also ensures the effective contact area between the active material and the electrolyte. The secondary particles are formed by the agglomeration of primary particles of 50-200nm, with a median particle size D50 of 5-15μm. This multi-level particle structure shortens the diffusion path of sodium ions (the size of the primary particles is close to the diffusion length of sodium ions). At the same time, the pore network between the secondary particles provides a channel for electrolyte penetration, improving the reaction kinetics.

[0039] It is further explained that the molar ratio of Ni:Mn in the M element is 1:1-3:1, and the M element contains 0.5-5at% of Ti doping based on the total amount of transition metals.

[0040] It is further explained that the following steps are included:

[0041] Step S1: Mix a sodium source, a nickel source, a manganese source, a lithium source, and a magnesium source in a stoichiometric ratio, add 0.1-1% ZrO2 seed crystals accounting for the total mass of the raw materials, and heat to 300-450°C at a rate of 2-5°C / min under a protective atmosphere for 2-5 hours;

[0042] In step S1, ZrO2 seed crystals (accounting for 0.1-1% of the total mass of the raw materials) are added. They serve as heterogeneous nucleation sites to promote the formation of uniform primary grains of layered oxides during the pre-sintering stage, avoiding excessive grain growth and resulting in a decrease in specific surface area. The sodium source is a mixture of sodium carbonate and sodium acetate (mass ratio 1:0.2-0.5). Sodium acetate decomposes before sodium carbonate at low temperatures (300-450°C) to release Na + And form a liquid phase environment to promote ion diffusion between raw materials and improve the uniformity of element mixing.

[0043] Step S2: heating the pre-calcined product to 850-950°C at a rate of 0.5-2°C / min and calcining for 8-15 hours while controlling the oxygen partial pressure to be 5-15 vol%;

[0044] Step S2 controls the oxygen partial pressure to 5-15 vol%, and adjusts the oxidation state of the transition metal during the calcination process (such as controlling Ni 2+ / Ni 3+ ratio), to avoid Ni due to excessive oxygen partial pressure 3+ Over-oxidation (production of Ni 4+ ), thereby optimizing the initial capacity and structural stability of the material. The synergistic effect of the heating rate (0.5-2°C / min) and calcination time (8-15h) ensures slow crystal growth, forming a dense and defect-free O3 structure.

[0045] Step S3: ball-milling the calcined product with lithium phosphate and aluminum nitrate in a citric acid solution with a pH of 3-5 at a mass ratio of 1:(0.005-0.03):(0.002-0.02), spray-drying the mixture, and heat-treating the mixture at 400-550° C. for 2-6 hours to form a surface coating layer.

[0046] After the grading and coating process step S2, active particles with D90≤18μm are obtained by airflow classification, and oversized particles (to avoid the internal sodium ion diffusion path being too long) and oversized particles (prone to electrolyte side reactions) are removed to ensure uniform particle size distribution. In step S3, ball milling is carried out in a citric acid solution with a pH of 3-5. Citric acid can be adsorbed on the surface of the particles as a chelating agent to promote the uniform dispersion of lithium phosphate (Li3PO4 precursor) and aluminum nitrate (AlPO4 precursor); spray drying controls the inlet temperature to 180-220°C and the outlet temperature to 80-120°C to form a precursor powder with a water content of ≤0.5wt%, avoiding the decomposition of the coating layer caused by residual moisture; 400-550°C heat treatment converts the precursor into a nano-scale composite coating. This temperature range not only avoids damage to the matrix structure due to high temperature, but also ensures that the coating agent fully reacts.

[0047] The nano-scale composite layer uniformly coated on the surface can isolate the HF in the electrolyte (generated by the decomposition of the electrolyte), reduce the dissolution of HF on the transition metal surface of the substrate, and avoid the 2+ 、Ni 2+ Capacity fade and electrolyte contamination caused by dissolution.

[0048] Li3PO4 has a certain lithium ion conductivity, which can form ion transmission channels inside the coating layer and reduce the interfacial charge transfer impedance; AlPO4 enhances the mechanical strength of the coating layer through its high chemical stability and prevents the coating layer from falling off during the cycle.

[0049] The composite coating layer and the hydroxyl (-OH) groups on the substrate surface form a stable interface through chemical bonding (such as POM, Al-OM bond), which inhibits the Na +The surface reconstruction caused by deintercalation (such as the formation of a rock-salt phase) maintains the sodium ion transport dynamics at the interface.

[0050] It is further explained that in step S1, the sodium source is a mixture of sodium carbonate and sodium acetate, and the mixing mass ratio is 1:0.2-0.5; the nickel source is nickel oxyhydroxide, and the manganese source is trimanganese tetraoxide.

[0051] It is further explained that in step S3, the inlet air temperature of the spray drying is 180-220°C, the outlet air temperature is 80-120°C, and the water content of the obtained precursor powder is ≤0.5wt%.

[0052] It is further explained that the process also includes classifying the product after calcination in step S2, obtaining active particles with D90≤18 μm by airflow classification, and then proceeding to step S3 for coating.

[0053] A sodium ion battery has a capacity retention rate of ≥88% after 500 cycles at a rate of 0.5C within a voltage range of 2.0-4.0V, and a low-temperature capacity retention rate of ≥82% at -20°C.

[0054] It is further explained that the positive electrode material, conductive carbon and binder are made into a positive electrode sheet in a mass ratio of 90:7:3. The positive electrode sheet has a compaction density of 3.2-3.6 g / cm3 and a porosity of 20-30%.

[0055] In summary, through the multi-scale design of "lattice doping-structure regulation-interface optimization-process synergy", the key problems of layered oxide positive electrode materials in cycle stability, low-temperature performance and preparation cost have been systematically solved, providing a high-performance material foundation for the commercial application of sodium-ion batteries.

[0056] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A high-stability layered oxide sodium ion battery cathode material, characterized by: It includes a layered oxide matrix and a surface coating layer. The general chemical formula of the layered oxide matrix is NaxM1-a-bLiaMgbO2, wherein the M element is at least two of Ni, Mn, and Fe, 0.6≤x≤1.0, 0.01≤a≤0.15, and 0.005≤b≤0.

1. The surface coating layer is a composite layer of Li3PO4 and AlPO4. The thickness of the surface coating layer is 5-30nm, and the coating amount of the surface coating layer accounts for 0.5-3% of the matrix mass.

2. The high-stability layered oxide sodium ion battery positive electrode material according to claim 1, characterized in that: The layered oxide matrix has an O3 type crystal structure, the interlayer spacing of the O3 type crystal structure is 0.52-0.58nm, the BET specific surface area of the O3 type crystal structure is 0.5-2.5m2 / g, the median particle size D50 of the secondary particles is 5-15μm, and is formed by the agglomeration of primary particles of 50-200nm.

3. The high-stability layered oxide sodium ion battery positive electrode material according to claim 1, characterized in that: The molar ratio of Ni:Mn in the M element is 1:1-3:1, and the M element contains 0.5-5at% of Ti doping in the total amount of transition metals.

4. A method for preparing a positive electrode material for a sodium ion battery according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step S1: Mix a sodium source, a nickel source, a manganese source, a lithium source, and a magnesium source in a stoichiometric ratio, add 0.1-1% ZrO2 seed crystals accounting for the total mass of the raw materials, and heat to 300-450°C at a rate of 2-5°C / min under a protective atmosphere for 2-5 hours; Step S2: heating the pre-calcined product to 850-950°C at a rate of 0.5-2°C / min and calcining for 8-15 hours while controlling the oxygen partial pressure to be 5-15 vol%; Step S3: ball-milling the calcined product with lithium phosphate and aluminum nitrate in a citric acid solution with a pH of 3-5 at a mass ratio of 1:(0.005-0.03):(0.002-0.02), spray-drying the mixture, and heat-treating the mixture at 400-550° C. for 2-6 hours to form a surface coating layer.

5. The method for preparing a positive electrode material for a sodium ion battery according to claim 4, wherein: In step S1, the sodium source is a mixture of sodium carbonate and sodium acetate, and the mixing mass ratio is 1:0.2-0.5; the nickel source is nickel oxyhydroxide, and the manganese source is trimanganese tetraoxide.

6. The method for preparing a positive electrode material for a sodium ion battery according to claim 4, wherein: In step S3, the inlet air temperature of the spray drying is 180-220° C., the outlet air temperature is 80-120° C., and the water content of the obtained precursor powder is ≤0.5 wt %.

7. The method for preparing a positive electrode material for a sodium ion battery according to claim 4, wherein: The method further includes classifying the product after calcination in step S2, obtaining active particles with D90≤18 μm by airflow classification, and then proceeding to step S3 for coating.

8. A sodium ion battery, characterized in that: The positive electrode material according to any one of claims 1 to 3 is included, wherein the battery has a capacity retention rate of ≥88% after 500 cycles at a rate of 0.5C within a voltage range of 2.0-4.0V, and a low-temperature capacity retention rate of ≥82% at -20°C.

9. A sodium ion battery according to claim 8, characterized in that: The positive electrode material, conductive carbon and binder are prepared into a positive electrode sheet in a mass ratio of 90:7:

3. The positive electrode sheet has a compaction density of 3.2-3.6 g / cm3 and a porosity of 20-30%.

Images