Sodium-ion positive electrode material, preparation method and application thereof

Abstract

This invention belongs to the field of battery technology, specifically disclosing a sodium-ion cathode material, its preparation method, and its application. The general chemical formula of the cathode material is: Na （1‑a） A a [Ni x Fe y Mn z M b M' c O （2‑d） B d Wherein, A is one or more of Li, K, Ca, and Mg; M is one or more of Ti, Zr, and Nb; M' is one or more of Zn, Cu, and Al; and B is F. ‑ PO4 3‑ BO3 3‑ One or more of the above-mentioned sodium-ion cathode materials. This invention employs the above-mentioned sodium-ion cathode material, its preparation method, and its application. Through the preparation method of alkali-site pillar doping, transition site synergistic regulation, in-situ anion interface stabilization, and special sintering, the prepared pure-phase O3-type layered oxide sodium-ion cathode material possesses the characteristics of crystal structure and interface stability.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a sodium-ion cathode material, its preparation method, and its application. Background Technology

[0002] With the large-scale expansion of the energy storage and power battery industry, lithium-ion batteries have dominated the mainstream market due to their mature technology. However, lithium resources are limited in reserves, unevenly distributed, and subject to volatile prices, making it difficult to meet the long-term low-cost application needs of large-scale energy storage, low-speed electric vehicles, and grid peak shaving. Sodium-ion batteries, due to the abundance of sodium in the Earth's crust, low cost, and high compatibility of electrochemical properties with lithium-ion batteries, have become an ideal energy storage system to replace lithium-ion batteries and are currently a research and industrialization hotspot in the field of new energy materials.

[0003] Cathode materials are the core component of sodium-ion batteries, directly determining the battery's specific capacity, cycle life, rate performance, and safety performance. They are also a key bottleneck restricting the industrialization of sodium-ion batteries. Existing sodium-ion battery cathode materials are mainly divided into three major systems: layered oxides, Prussian blue-based materials, and phosphate-based materials. Among them, layered oxide cathode materials have advantages such as high theoretical specific capacity, excellent ionic conductivity, simple preparation process, and high compaction density, making them the most promising for commercial applications. Based on differences in sodium ion coordination environment, crystal stacking mode, and oxygen layer arrangement, layered oxides are mainly divided into two types: O3 phase and P2 phase. O3 phase layered oxides possess characteristics such as high initial charge-discharge efficiency, moderate operating voltage platform, and good full-cell matching, making them more suitable for practical commercial needs.

[0004] However, conventional O3-phase layered oxide sodium-ion cathode materials (general formula NaTMO2, where TM represents a transition metal element) have insurmountable technical defects: during charge and discharge, with repeated insertion and extraction of sodium ions, the crystal structure is prone to irreversible phase transitions of O3-P3-OP2, accompanied by significant shrinkage and expansion of the lattice volume. After long-term cycling, particle pulverization and grain boundary cracking occur, leading to a sharp capacity decay. The transition metal-oxygen bond strength is relatively weak, and oxygen is easily lost under high-voltage conditions. At the same time, transition metal ions are easily dissolved in the electrolyte, which damages the stability of the electrode-electrolyte interface, exacerbates interfacial side reactions, and increases battery impedance. Conventional preparation processes easily lead to excessive lattice defects and uneven grain growth, obstructing sodium ion diffusion channels and resulting in poor rate charge and discharge performance, which cannot meet the requirements of high-power applications.

[0005] Therefore, there is a need in this field to develop a sodium-ion cathode material, its preparation method, and its application, which can effectively solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a sodium ion cathode material, its preparation method, and its application. Through a preparation method involving alkali-site pillar doping, transition site synergistic regulation, in-situ anion interface stabilization, and special sintering, the prepared pure-phase O3-type layered oxide sodium ion cathode material possesses the characteristics of crystal structure and interface stability.

[0007] To achieve the above objectives, the present invention provides a sodium ion cathode material with the general chemical formula: Na （1-a） A a [Ni x Fe y Mn z M b M' c ]O （2-d） B d ; Wherein, A is one or more of Li, K, Ca, and Mg; M is one or more of Ti, Zr, and Nb; M' is one or more of Zn, Cu, and Al; and B is F. - PO4 3- BO3 3- One or more of the following; 0≤a≤0.05, 0.01≤b≤0.08, 0≤c≤0.05, 0≤d≤0.04; x:y:z=(0.3-0.38):(0.15-0.25):(0.4-0.5); 0.32≤x≤0.36, 0.18≤y≤0.22, 0.42≤z≤0.48; x+y+z+b+c=1.

[0008] Preferably, the secondary particles of the sodium ion cathode material are spherical with a particle size D50 of 4-10 μm; the primary grain size is 100-300 nm, and there are no impurities or obvious agglomeration.

[0009] This invention also provides a method for preparing a sodium-ion cathode material, comprising the following steps: Step S1: Weigh the sodium source, nickel source, iron source, manganese source, source A, source M, source M', and source B according to the stoichiometric ratio of the general chemical formula; wherein the sodium source is in excess by 2-5%; Step S2: Dissolve the nickel source, iron source, manganese source, M source, and M' source in water and mix them to obtain a mixed solution with a total metal concentration of 1.0-2.0 mol / L; Step S3: Prepare spherical hydroxide precursors from the mixed solution; Step S4: The spherical hydroxide precursor is mixed with sodium source, source A and source B by dry ball milling to obtain a mixed powder; Step S5: Pre-calcining the mixed powder to obtain a pre-calcined intermediate; Step S6: Sinter the pre-fired intermediate to obtain sintered material blocks; Step S7: The sintered material blocks are crushed, sieved, and iron removed in sequence to obtain sodium ion cathode material.

[0010] Preferably, in step S1, the sodium source is one or more of sodium carbonate, sodium bicarbonate, and sodium acetate; the nickel source, iron source, manganese source, M source, and M' source are all corresponding oxides, carbonates, or sulfates; the A source is one or more of the corresponding element's carbonate, acetate, oxide, or hydroxide; and the B source is one or more of fluoride, phosphate, and borate.

[0011] Preferably, step S3 specifically includes: Step S3-1: Prepare a NaOH solution with a concentration of 4.0-8.0 mol / L as the main precipitant, and prepare an NH3·H2O solution with a concentration of 0.5-2.0 mol / L as a complexing agent and pH auxiliary adjuster; Step S3-2: After adjusting the temperature to 50-70℃, stir the mixed solution, NaOH solution and NH3·H2O at 300-800r / min to ensure that the solution is mixed evenly, without local over-concentration and without particle deposition. Step S3-3: The pH value of the reaction is 9.5-11.5, and the reaction time is 6-24h, so that the metal ions are uniformly deposited in the form of hydroxides to form hydroxide precursors with uniform particle size, regular morphology and high sphericity. Steps S3-4: After the reaction is complete, the overflow product is aged at 50-70℃ for 2-6 hours to further improve the particle density and particle size uniformity, thus obtaining the spherical hydroxide precursor.

[0012] Preferably, in step S4, the rotation speed of the dry ball mill is 300-500 r / min, the dry ball milling time is 8-12 h, and the material-to-ball ratio is 1:(3-5).

[0013] Preferably, in step S5, the pre-firing specifically involves first raising the temperature to 350-450℃ and holding it at that temperature for 3-5 hours; then raising the temperature to 550-650℃ and holding it at that temperature for 4-6 hours; and finally cooling it to 23-25℃.

[0014] Preferably, in step S6, sintering specifically involves: first raising the temperature to 500-650℃ in an air atmosphere, then holding it at that temperature for 4-8 hours to complete the initial lattice construction; Pretreatment in an air atmosphere allows the pre-calcined intermediate to fully decompose, decarburize, and dehydrate, initially constructing a layered oxide lattice framework, reducing the risk of impurity phase formation during high-temperature sintering, and laying the foundation for the subsequent formation of a pure phase O3 structure.

[0015] Then, under an oxygen atmosphere, the temperature is raised to 680-850℃ and kept at that temperature for 6-15 hours to form a pure O3 phase and suppress oxygen defects and impurities. After the temperature is lowered to 600℃ at a rate of 1-3℃ / min, it is allowed to cool naturally to 23-25℃ in air. The cooling process utilizes anionic dopant (F... - PO4 3- BO3 3- The surface segregation effect generates a uniform and dense interface stabilizing layer in situ on the surface of the cathode material.

[0016] Preferably, step S7 specifically involves: sequentially crushing the sintered material into coarse, medium and air-jet pulverizers, classifying it by double sieve 200-400 mesh, and then removing iron in multiple stages with a magnetic field strength of ≥8000Gs to obtain pure O3 phase layered oxide sodium ion cathode material.

[0017] The present invention also provides an application of sodium-ion cathode material in sodium-ion batteries.

[0018] This invention employs the aforementioned sodium-ion cathode material, its preparation method, and its application, with the following beneficial effects: (1) In this invention, by first oxidizing with air at low temperature and then controlling the dynamic atmosphere with oxygen-rich temperature, the pure O3 phase and high lattice order can be ensured; then by gradient cooling and air cooling in the low temperature section, an interface stability layer is generated in situ, without the need for secondary coating, simplifying the process and strengthening the bonding force; and by using dual doping of alkaline sites and transition sites, the phase transition and volume deformation are suppressed through the pillar effect and bonding strengthening synergy.

[0019] (2) The raw materials used in this invention are all common metal oxides, carbonates or sulfates, which are widely available and inexpensive. There are no rare precious metals or toxic and harmful raw materials, and they are environmentally friendly. Moreover, the preparation process adopts dry mixing and conventional high-temperature sintering, which does not require precision control equipment. It can be adapted to existing lithium-ion battery cathode material mass production lines without the need for additional large-scale equipment investment.

[0020] (3) The sodium-ion cathode material prepared by the present invention has excellent electrochemical performance, and the assembled sodium-ion battery meets commercial indicators and can be directly applied to various energy storage and power scenarios, and has extremely high industrial application value.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a performance comparison diagram of various cathode materials in the experimental examples of sodium ion cathode material, its preparation method, and application of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0025] Example 1 A method for preparing a sodium-ion cathode material includes the following steps: Step S1, according to the general chemical formula: Na 0.98 Mg 0.02 [Ni 0.33 Fe 0.18 Mn 0.43 Ti 0.04 Al 0.02 ]O 1.98 F 0.02 The following components were weighed in the specified proportions: Na₂CO₃, NiSO₄·6H₂O, FeSO₄·7H₂O, MnSO₄·H₂O, Mg(OH)₂·4MgCO₃·5H₂O, Ti(SO₄)₂, Al₂(SO₄)₃·18H₂O, and NaF. The sodium source was in 3% excess.

[0026] Step S2: Dissolve NiSO4·6H2O, FeSO4·7H2O, MnSO4·H2O, Ti(SO4)2, and Al2(SO4)3·18H2O in water and mix them to obtain a mixed solution with a total metal concentration of 1.5 mol / L.

[0027] Step S3: Prepare spherical hydroxide precursors from the mixed solution.

[0028] Step S3-1: Prepare a 6.0 mol / L NaOH solution as the main precipitant, and prepare a 1.0 mol / L NH3·H2O solution as a complexing agent and pH auxiliary adjuster.

[0029] Step S3-2: After adjusting the temperature to 60℃, stir the mixed solution, NaOH solution and NH3·H2O at 500r / min to carry out the reaction.

[0030] Step S3-3: The pH value of the reaction is 10.0, and the reaction time is 15 hours, so that the metal ions are uniformly deposited in the form of hydroxide.

[0031] Steps S3-4: After the reaction is complete, the overflow product is aged at 60°C for 4 hours to obtain the spherical hydroxide precursor.

[0032] Step S4: The spherical hydroxide precursor is mixed with Na2CO3, Mg(OH)2·4MgCO3·5H2O and NaF by dry ball milling to obtain a mixed powder.

[0033] The dry ball milling speed was 400 r / min, the dry ball milling time was 10 h, and the material-to-ball ratio was 1:3.

[0034] Step S5: First, raise the temperature of the mixed powder to 400℃ and hold for 4 hours. Then, raise the temperature to 600℃ and hold for 5 hours. Finally, cool to 25℃ to obtain the pre-calcined intermediate.

[0035] Step S6: First, heat the pre-sintered intermediate to 600°C in air and hold for 6 hours. Then, heat it to 700°C in oxygen and hold for 10 hours. Finally, reduce the temperature to 600°C at a rate of 3°C / min and allow it to cool naturally to 25°C in air to obtain sintered blocks.

[0036] Step S7: The sintered material blocks are successively subjected to coarse crushing, medium crushing and air jet milling, then classified by 300-mesh double sieve, and then subjected to multi-stage iron removal with a magnetic field strength of ≥8000Gs to obtain sodium ion cathode material.

[0037] Example 2 A method for preparing a sodium-ion cathode material includes the following steps: Step S1, according to the general chemical formula: Na 0.98 Mg 0.02 [Ni 0.33 Fe 0.18 Mn 0.43 Ti 0.04 Al 0.02 ]O 1.98 F 0.02 The following components were weighed in the specified proportions: Na₂CO₃, NiSO₄·6H₂O, FeSO₄·7H₂O, MnSO₄·H₂O, Mg(OH)₂·4MgCO₃·5H₂O, Ti(SO₄)₂, Al₂(SO₄)₃·18H₂O, and NaF. The sodium source was in 3% excess.

[0038] Step S2: Dissolve NiSO4·6H2O, FeSO4·7H2O, MnSO4·H2O, Ti(SO4)2, and Al2(SO4)3·18H2O in water and mix them to obtain a mixed solution with a total metal concentration of 1.5 mol / L.

[0039] Step S3: Prepare spherical hydroxide precursors from the mixed solution.

[0040] Step S3-1: Prepare a 6.0 mol / L NaOH solution as the main precipitant, and prepare a 1.0 mol / L NH3·H2O solution as a complexing agent and pH auxiliary adjuster.

[0041] Step S3-2: After adjusting the temperature to 60℃, stir the mixed solution, NaOH solution and NH3·H2O at 500r / min to carry out the reaction.

[0042] Step S3-3: The pH value of the reaction is 10.0, and the reaction time is 15 hours, so that the metal ions are uniformly deposited in the form of hydroxide.

[0043] Steps S3-4: After the reaction is complete, the overflow product is aged at 60°C for 4 hours to obtain the spherical hydroxide precursor.

[0044] Step S4: The spherical hydroxide precursor is mixed with Na2CO3, Mg(OH)2·4MgCO3·5H2O and NaF by dry ball milling to obtain a mixed powder.

[0045] The dry ball milling speed was 400 r / min, the dry ball milling time was 10 h, and the material-to-ball ratio was 1:3.

[0046] Step S5: First, raise the temperature of the mixed powder to 350℃ and hold it at that temperature for 4 hours. Then, raise the temperature to 550℃ and hold it at that temperature for 5 hours. Finally, cool it to 25℃ to obtain the pre-calcined intermediate.

[0047] Step S6: First, heat the pre-sintered intermediate to 600°C in air and hold for 6 hours. Then, heat it to 700°C in oxygen and hold for 10 hours. Finally, reduce the temperature to 600°C at a rate of 3°C / min and allow it to cool naturally to 25°C in air to obtain sintered blocks.

[0048] Step S7: The sintered material blocks are successively subjected to coarse crushing, medium crushing and air jet milling, then classified by 300-mesh double sieve, and then subjected to multi-stage iron removal with a magnetic field strength of ≥8000Gs to obtain sodium ion cathode material.

[0049] Example 3 A method for preparing a sodium-ion cathode material includes the following steps: Step S1, according to the general chemical formula: Na 0.98 Mg 0.02 [Ni 0.33 Fe 0.18 Mn 0.43 Ti 0.04 Al 0.02 ]O 1.98 F 0.02 The following components were weighed in the specified proportions: Na₂CO₃, NiSO₄·6H₂O, FeSO₄·7H₂O, MnSO₄·H₂O, Mg(OH)₂·4MgCO₃·5H₂O, Ti(SO₄)₂, Al₂(SO₄)₃·18H₂O, and NaF. The sodium source was in 3% excess.

[0050] Step S2: Dissolve NiSO4·6H2O, FeSO4·7H2O, MnSO4·H2O, Ti(SO4)2, and Al2(SO4)3·18H2O in water and mix them to obtain a mixed solution with a total metal concentration of 1.5 mol / L.

[0051] Step S3: Prepare spherical hydroxide precursors from the mixed solution.

[0052] Step S3-1: Prepare a 6.0 mol / L NaOH solution as the main precipitant, and prepare a 1.0 mol / L NH3·H2O solution as a complexing agent and pH auxiliary adjuster.

[0053] Step S3-2: After adjusting the temperature to 60℃, stir the mixed solution, NaOH solution and NH3·H2O at 500r / min to carry out the reaction.

[0054] Step S3-3: The pH value of the reaction is 10.0, and the reaction time is 15 hours, so that the metal ions are uniformly deposited in the form of hydroxide.

[0055] Steps S3-4: After the reaction is complete, the overflow product is aged at 60°C for 4 hours to obtain the spherical hydroxide precursor.

[0056] Step S4: The spherical hydroxide precursor is mixed with Na2CO3, Mg(OH)2·4MgCO3·5H2O and NaF by dry ball milling to obtain a mixed powder.

[0057] The dry ball milling speed was 400 r / min, the dry ball milling time was 10 h, and the material-to-ball ratio was 1:3.

[0058] Step S5: First, raise the temperature of the mixed powder to 400℃ and hold for 4 hours. Then, raise the temperature to 600℃ and hold for 5 hours. Finally, cool to 25℃ to obtain the pre-calcined intermediate.

[0059] Step S6: First, heat the pre-sintered intermediate to 600°C in air and hold for 6 hours. Then, heat it to 700°C in oxygen and hold for 10 hours. Finally, reduce the temperature to 600°C at a rate of 3°C / min and allow it to cool naturally to 25°C in air to obtain sintered blocks.

[0060] Step S7: The sintered material blocks are successively subjected to coarse crushing, medium crushing and air jet milling, then classified by 300-mesh double sieve, and then subjected to multi-stage iron removal with a magnetic field strength of ≥8000Gs to obtain sodium ion cathode material.

[0061] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S1, according to the general chemical formula: Na 0.98 [Ni 0.33 Fe 0.18 Mn 0.43 Ti 0.04 Al 0.02 ]O 1.98 F 0.01 The following components were weighed in a specific ratio: Na₂CO₃, NiSO₄·6H₂O, FeSO₄·7H₂O, MnSO₄·H₂O, Ti(SO₄)₂, Al₂(SO₄)₃·18H₂O, and NaF. The sodium source was in 3% excess.

[0062] The remaining steps are the same as in Example 1.

[0063] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S1, according to the general chemical formula: Na 0.98 Mg 0.02 [Ni 0.33 Fe 0.18 Mn 0.43 Ti 0.06 ]O 1.98 F 0.02 The following components were weighed in a specific ratio: Na₂CO₃, NiSO₄·6H₂O, FeSO₄·7H₂O, MnSO₄·H₂O, TiO₂, Mg(OH)₂·4MgCO₃·5H₂O, and NaF. The sodium source was in 3% excess.

[0064] The remaining steps are the same as in Example 1.

[0065] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S5, the temperature of the mixed powder is raised to 600°C and held for 9 hours. Finally, it is cooled to 25°C to obtain the pre-calcined intermediate.

[0066] The remaining steps are the same as in Example 1.

[0067] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S6, the pre-calcined intermediate is heated to 700°C directly in an air atmosphere (the entire process is carried out in an air atmosphere) and held at that temperature for 16 hours. It is then naturally cooled to 25°C to obtain sintered material blocks.

[0068] The remaining steps are the same as in Example 1.

[0069] Experimental Example The cathode materials prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in Table 1.

[0070] A positive electrode slurry was prepared using N-methylpyrrolidone (NMP) as solvent, with a mass ratio of positive electrode material: conductive agent Super P: binder polyvinylidene fluoride of 93:3:4. This slurry was coated onto an aluminum foil current collector, and then dried, rolled, and die-cut to obtain the positive electrode sheet. A CR2032 coin cell was assembled in an argon-atmosphere glove box using sodium metal as the negative electrode, glass fiber as the separator, and 1.0 mol / L NaPF6 (ethylene carbonate: dimethyl carbonate = 1:1, volume ratio) as the electrolyte.

[0071] The Blue Battery Testing System was used to test the material's 0.1C initial discharge specific capacity, initial coulombic efficiency, 1C 100-cycle capacity retention, and 5C rate capacity retention, with a test voltage range of 2.0-4.0V.

[0072] Table 1 Performance Test Results

[0073] like Figure 1 As shown, the O3-phase sodium ion cathode materials prepared in Examples 1-3 of this invention possess high specific capacity, high initial coulombic efficiency, excellent cycle stability, and rate performance.

[0074] The cathode materials prepared in Comparative Examples 1-2 have inferior performance compared to the examples, demonstrating that Al-assisted doping can effectively control lattice defects, optimize sodium ion diffusion channels, and improve rate and cycle performance; it also demonstrates that the pillar effect of Mg base site doping is the core of suppressing the irreversible phase transition of O3 phase and stabilizing the lattice, and that the synergistic doping of the two can achieve optimal performance.

[0075] The cathode materials prepared in Comparative Examples 3-4 exhibited extremely poor performance, demonstrating that segmented gradient pre-sintering can promote the complete decomposition of the precursor and reduce impurity phases. Dynamic atmosphere sintering and gradient cooling are crucial for preparing pure-phase O3 structures and constructing an in-situ interface stabilizing layer. In particular, Comparative Example 4, without low-temperature air pretreatment, high-temperature oxygen sintering, and gradient cooling, relied entirely on air and natural cooling, which easily led to the formation of impurity phases, numerous lattice defects, and the absence of an interface stabilizing layer, directly resulting in a significant performance degradation.

[0076] Therefore, the present invention employs the above-mentioned sodium ion cathode material, its preparation method and application, and through the preparation method of alkaline site pillar doping, transition site synergistic regulation, in-situ anion interface stabilization and special sintering, the prepared pure phase O3 type layered oxide sodium ion cathode material has the characteristics of crystal structure and interface stability.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A sodium-ion cathode material, characterized in that, The general chemical formula is: Na （1-a） A a [Ni x Fe y Mn z M b M' c ]O （2-d） B d ; Wherein, A is one or more of Li, K, Ca, and Mg; M is one or more of Ti, Zr, and Nb; M' is one or more of Zn, Cu, and Al; and B is F. - PO4 3- BO3 3- One or more of the following; 0≤a≤0.05, 0.01≤b≤0.08, 0≤c≤0.05, 0≤d≤0.04; x:y:z=(0.3-0.38):(0.15-0.25):(0.4-0.5); 0.32≤x≤0.36, 0.18≤y≤0.22, 0.42≤z≤0.48; x+y+z+b+c=1.

2. The sodium-ion cathode material according to claim 1, characterized in that: The secondary particles of the sodium ion cathode material are spherical with a particle size D50 of 4-10 μm; the primary grain size is 100-300 nm.

3. A method for preparing a sodium-ion cathode material as described in any one of claims 1-2, characterized in that, Includes the following steps: Step S1: Weigh the sodium source, nickel source, iron source, manganese source, source A, source M, source M', and source B according to the stoichiometric ratio of the general chemical formula; wherein the sodium source is in excess by 2-5%; Step S2: Dissolve the nickel source, iron source, manganese source, M source, and M' source in water and mix them to obtain a mixed solution with a total metal concentration of 1.0-2.0 mol / L; Step S3: Prepare spherical hydroxide precursors from the mixed solution; Step S4: The spherical hydroxide precursor is mixed with sodium source, source A and source B by dry ball milling to obtain a mixed powder; Step S5: Pre-calcining the mixed powder to obtain a pre-calcined intermediate; Step S6: Sinter the pre-fired intermediate to obtain sintered material blocks; Step S7: The sintered material blocks are crushed, sieved, and iron removed in sequence to obtain sodium ion cathode material.

4. The method for preparing a sodium-ion cathode material according to claim 3, characterized in that: In step S1, the sodium source is one or more of sodium carbonate, sodium bicarbonate, and sodium acetate; the nickel source, iron source, manganese source, M source, and M' source are all corresponding oxides, carbonates, or sulfates; the A source is one or more of the corresponding element's carbonate, acetate, oxide, or hydroxide; and the B source is one or more of fluoride, phosphate, and borate.

5. The method for preparing a sodium-ion cathode material according to claim 3, characterized in that, Step S3 is as follows: Step S3-1: Prepare a NaOH solution with a concentration of 4.0-8.0 mol / L as the main precipitant, and prepare an NH3·H2O solution with a concentration of 0.5-2.0 mol / L as a complexing agent and pH auxiliary adjuster; Step S3-2: After adjusting the temperature to 50-70℃, stir the mixed solution, NaOH solution and NH3·H2O at a speed of 300-800r / min to carry out the reaction. Step S3-3: The pH value of the reaction is 9.5-11.5, and the reaction time is 6-24h, so that the metal ions are uniformly deposited in the form of hydroxides. After the reaction is complete in steps S3-4, the overflow product is aged at 50-70℃ for 2-6 hours to obtain the spherical hydroxide precursor.

6. The method for preparing a sodium-ion cathode material according to claim 3, characterized in that: In step S4, the rotation speed of the dry ball mill is 300-500 r / min, the dry ball milling time is 8-12 h, and the material-to-ball ratio is 1:(3-5).

7. The method for preparing a sodium-ion cathode material according to claim 3, characterized in that: In step S5, the preheating process specifically involves first raising the temperature to 350-450℃ and holding it at that temperature for 3-5 hours; then raising the temperature to 550-650℃ and holding it at that temperature for 4-6 hours; and finally cooling it to 23-25℃.

8. The method for preparing a sodium-ion cathode material according to claim 3, characterized in that, In step S6, the sintering process is as follows: first, in an air atmosphere, the temperature is raised to 500-650℃ and held for 4-8 hours; then, in an oxygen atmosphere, the temperature is raised to 680-850℃ and held for 6-15 hours; the temperature is lowered to 600℃ at a rate of 1-3℃ / min, and then naturally cooled to 23-25℃ in an air atmosphere.

9. The method for preparing a sodium-ion cathode material according to claim 3, characterized in that, Step S7 specifically involves: sequentially crushing the sintered material into coarse, medium and air-jet mills, classifying it by double sieve 200-400 mesh, and then removing iron in multiple stages with a magnetic field strength of ≥8000Gs to obtain sodium ion cathode material.

10. The application of the sodium-ion cathode material as described in any one of claims 1-2 in a sodium-ion battery.

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