Preparation method of sodium ion battery positive electrode material, positive electrode material, sodium ion battery and electric equipment

Abstract

The invention discloses a preparation method of a sodium ion battery positive electrode material, the positive electrode material, a sodium ion battery and electric equipment, the preparation method comprises the following steps: S1, mixing an iron source, a sodium source, a phosphorus source, a conductive agent, an antioxidant and a solvent according to a certain mass ratio, and uniformly stirring to obtain precursor slurry; s2, granulating the precursor slurry through a solution method to obtain a spherical or sphere-like precursor material; and S3, sintering the precursor material in an inert atmosphere at the temperature of 300-450 DEG C for 1-48 hours to obtain the sodium-ion battery positive electrode material Na < 2 + 2x > Fe < 2-x > (SO4) < 3-3x > (PO4) 2x, and x is greater than or equal to 0 and less than or equal to 1. The sodium-ion battery positive electrode material prepared by the preparation method has relatively high compaction density and proper porosity, can effectively inhibit generation of impure phases and iron ion migration, and improves the specific capacity, cycling stability and capacity retention ratio of a sodium-ion battery compared with a traditional solid-phase synthesis method.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a method for preparing a sodium-ion battery cathode material, the cathode material, the sodium-ion battery, and related electrical equipment. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries have significant advantages in safety, rate performance, low-temperature performance, and cost potential. However, they still have significant shortcomings in cycle life and energy density, which is directly related to the four key materials of the battery: positive electrode, negative electrode, electrolyte, and separator.

[0003] Sodium ferrous sulfate is a cathode material for sodium-ion batteries. It is a three-dimensional network structure polyanionic compound with a relatively high voltage platform, excellent environmental friendliness, structural stability, and long cycle life. However, its structural limitations pose significant challenges to practical applications. In the sodium ferrous sulfate framework structure, two [FeO6] octahedra are connected along a common edge to form [Fe2O] 10 The dimer then connects pointwise with the [SO4] tetrahedron, resulting in three Na groups. + Ion sites and two Fe 2+ Ion sites. Small-sized [SO4] tetrahedral connections [Fe2O] 10 The dimerization process shortens the Fe-Fe distance, resulting in strong Coulomb repulsion between Fe atoms. This leads to a metastable structure and the formation of impurity phases such as FeSO4 and Fe2O3. During the initial charge / discharge process, this structural instability is further exacerbated, as the Coulomb repulsion causes irreversible migration of iron ions to sodium ion sites, thus impairing cycle stability.

[0004] Previous studies have shown that introducing iron defects can weaken the Fe-Fe Coulomb repulsion force within the structure, effectively reducing the impurity content. However, due to the presence of Fe... 2+ / Fe 3+ Reducing the amount of charge significantly decreases the theoretical capacity of the battery, and this still does not solve the fundamental problem stemming from the inherent structural instability. Therefore, there is an urgent need for a method that can reduce the Fe-Fe Coulomb repulsion and suppress Fe-Na exchange without sacrificing capacity. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a sodium-ion battery cathode material, the cathode material, a sodium-ion battery, and an electrical device thereof. The preparation method involves introducing PO4. 3- Groups that replace part of SO4 2-By using functional groups to regulate the structure and composition of materials, the formation of impurity phases and the migration of iron ions can be effectively suppressed while maintaining high capacity. Furthermore, the prepared sodium-ion battery cathode material has high compaction density and suitable porosity, which also improves the specific capacity, cycle stability and capacity retention of sodium-ion batteries.

[0006] To achieve the above objectives, this invention proposes a method for preparing a sodium-ion battery cathode material, comprising the following steps: S1. Mix a certain mass ratio of iron source, sodium source, phosphorus source, conductive agent, antioxidant and solvent, and stir evenly to obtain precursor slurry; S2. Granulate the precursor slurry prepared in S1 by solution method to obtain spherical or near-spherical precursor materials. S3. The precursor material prepared in S2 is sintered in an inert gas atmosphere at a temperature of 300-450℃ for 1-48 hours to obtain the sodium-ion battery cathode material Na. 2+2x Fe 2-x (SO4) 3-3x (PO4) 2x , where 0≤x≤1.

[0007] As a further aspect of the present invention: in S1, the molar ratio of Na:Fe:P in the sodium source, iron source, and phosphorus source is (8-10):(6-8):(0.1-2); the amount of conductive agent added is 0.1-30wt% of the total mass of the raw materials; the amount of antioxidant added is 0.5-50wt% of the total weight of the raw materials; and the solid content of the prepared precursor slurry is 10-70wt%.

[0008] As a further aspect of the present invention: in S1, the stirring method of the precursor slurry includes at least one of magnetic stirring, planetary stirring, vibration stirring, tumbling mixing, ultrasonic circulation, and microjet.

[0009] As a further aspect of the present invention: in S1, the phosphorus source includes at least one of sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium hexametaphosphate, and sodium pyrophosphate; the sodium source includes at least one of sodium sulfate, sodium phosphate, sodium carbonate, sodium nitrate, sodium acetate, sodium oxalate, and sodium chloride; and the iron source includes at least one of hydrated ferrous sulfate, ferrous oxalate, and ferrous nitrate.

[0010] As a further aspect of the present invention: in S1, the conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes, and graphene; the antioxidant includes at least one of ascorbic acid, citric acid, oxalic acid, carotenoids, sodium sulfite, tea polyphenols, hypophosphite, and glucose; and the solvent includes at least one of deionized water and alcohols.

[0011] As a further aspect of the present invention: in S2, solution granulation includes at least one of freeze drying and spray drying; the inlet temperature of the spray dryer is 100-200℃, the outlet temperature is 80-130℃, the feed rate is 0.1-20mL / min, the atomizer speed is 1000-20000r / min, and the atomization method includes at least one of pressure type and airflow type.

[0012] As a further aspect of the present invention: in S3, the inert gas includes at least one of argon, nitrogen, helium, nitrogen-hydrogen mixture, and carbon dioxide-nitrogen mixture.

[0013] The present invention also proposes a positive electrode material, which is prepared by the above-described preparation method.

[0014] The present invention also proposes a sodium-ion battery, comprising: the above-mentioned positive electrode material.

[0015] The present invention also proposes an electrical device comprising: the aforementioned sodium-ion battery.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of this invention requires low-cost raw materials and has a conventional operation process. The prepared sodium-ion battery cathode material can have high compaction density and suitable porosity, effectively suppressing the formation of impurity phases and iron ion migration. Compared with the traditional solid-phase synthesis method, it improves the specific capacity, cycle stability and capacity retention of sodium-ion batteries.

[0017] This invention introduces PO4 3- Structural improvements enhance performance: Introduction of PO4 3- The cathode material exhibits superior performance compared to the PO4-free material in terms of compaction density, first-discharge specific capacity, and cycle stability. 3- The material has a compacted density of up to 2.35 g / cm³. 3 It has an initial discharge specific capacity of up to 108.8 mAh / g and excellent cycle stability.

[0018] The spray drying process proposed in this invention has significant advantages: Comparative Example 2, which uses a solid-phase method, has significantly lower compaction density, capacity, and cycle performance than the examples using the spray drying process. This demonstrates that the spray drying process has significant advantages in controlling the uniformity of material morphology and improving electrochemical performance. Detailed Implementation

[0019] S1. Mix a certain mass ratio of iron source, sodium source, phosphorus source, conductive agent, antioxidant and solvent, and stir evenly to obtain precursor slurry.

[0020] S2. The precursor slurry prepared in S1 is granulated by solution granulation to obtain spherical or near-spherical precursor materials.

[0021] S3. The precursor material prepared in S2 is heated to 200-300℃ in an inert gas atmosphere and held at that temperature for 1-3 hours. Then, it is calcined at a high temperature of 300-450℃ for 1-48 hours with a heating rate of 1-8℃ / min. Next, the powder material is refined to achieve a particle size D50 < 4μm to obtain the composite sodium-ion battery cathode material Na. 2+2x Fe 2-x (SO4) 3-3x (PO4) 2x , where 0≤x≤1.

[0022] Take Na 2+2x Fe 2-x (SO4) 3-3x (PO4) 2x The mass ratio of PVDF:SP / CNT = (80-95):(1-5):(1-10) was quantitatively weighed, and 0.1%-10% sodium supplement was added. The mixture was dissolved in the organic solvent NMP (N-methylpyrrolidone) and the solid content was controlled at 25%-50%. After homogenization at 400 r / min for 4 hours, the mixture was coated onto an aluminum foil with a thickness of 13 μm. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. The separator was a 16 μm thick base film. The electrolyte was a solution of 1.0 mol / L NaPF6 dissolved in EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0023] Example 1 (Spray Drying Method) S1. Weigh FeSO4·mH2O, anhydrous Na2SO4 and Na3PO4 in a molar ratio of Na:Fe:P=10:7:2. Add CNTs and ascorbic acid at 5% and 3% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 30%.

[0024] S2. Spray dry the above precursor slurry at an outlet temperature of 130°C, a feed rate of 3 mL / min, an atomizer speed of 1000 r / min, and a pressure atomization method to obtain spherical or near-spherical precursor materials.

[0025] S3. In a mixed gas atmosphere of N2:H2=97:3, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 1 hour. Then, the temperature is increased to 400℃ at a rate of 2℃ / min and calcined for 10 hours. Following this, the powder material is ball-milled to achieve a particle size D50 < 4μm, thus obtaining the sodium-ion battery cathode material Na. 2.5 Fe1.75 (SO4) 2.25 (PO4) 0.5 .

[0026] Take Na 2.5 Fe 1.75 (SO4) 2.25 (PO4) 0.5 The mass ratio of PVDF:SP / CNT = 90:5:5 was quantitatively weighed, and 5% sodium formate was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 40%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was 1.0 mol / L NaPF6 dissolved in a solution of EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0027] Example 2 (Spray Drying): The difference from Example 1 is that... S1. Weigh FeSO4·mH2O, anhydrous Na2SO4 and Na3PO4 at a molar ratio of Na:Fe:P = 8.4:7.8:0.4. Add CNTs and citric acid at 5% and 4% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 60%.

[0028] S2. Spray dry the above precursor slurry at an outlet temperature of 120°C, a feed rate of 5 mL / min, an atomizer speed of 3000 r / min, and a pressure atomization method to obtain spherical or near-spherical precursor materials.

[0029] S3. In a mixed gas atmosphere of N2:H2=96:4, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 1 hour. Then, the temperature is increased to 360℃ at a rate of 2℃ / min and calcined for 12 hours. The powder material is then ball-milled to achieve a particle size D50 < 4μm, yielding the sodium-ion battery cathode material Na. 2.1 Fe 1.95 (SO4) 2.85 (PO4) 0.1 .

[0030] Take Na 2.1 Fe 1.95 (SO4) 2.85 (PO4) 0.1The mass ratio of PVDF:SP / CNT = 85:5:10 was quantitatively weighed, and 10% sodium citrate was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 40%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was 1.0 mol / L NaPF6 dissolved in a solution of EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0031] Example 3 (Spray Drying): The difference from Example 1 is that... S1. Weigh FeSO4·mH2O, anhydrous Na2SO4 and Na3PO4 in a molar ratio of Na:Fe:P = 8.8:7.6:0.8. Add CNTs and oxalic acid at 4% and 4% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 50%.

[0032] S2. Spray dry the above precursor slurry at an outlet temperature of 110°C, a feed rate of 5 mL / min, an atomizer speed of 4000 r / min, and a pressure atomization method to obtain spherical or near-spherical precursor materials.

[0033] S3. In a mixed gas atmosphere of N2:H2=98:2, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 2h. Then, the temperature is increased to 380℃ at a rate of 2℃ / min and calcined for 11h. The powder material is then ball-milled to achieve a particle size D50 < 4μm, yielding the sodium-ion battery cathode material Na. 2.2 Fe 1.9 (SO4) 2.7 (PO4) 0.2 .

[0034] Take Na 2.2 Fe 1.9 (SO4) 2.7 (PO4) 0.2 The mass ratio of PVDF:SP / CNT = 80:10:10 was quantitatively weighed, and 8% sodium squartz was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 30%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was 1.0 mol / L NaPF6 dissolved in a solution of EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0035] Example 4 (Spray Drying): The difference from Example 1 is that... S1. Weigh FeSO4·mH2O, anhydrous Na2SO4 and Na3PO4 at a molar ratio of Na:Fe:P = 9.2:7.4:1.2. Add CNTs and glucose at 3% and 4% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 40%.

[0036] S2. Spray dry the above precursor slurry at an outlet temperature of 100°C, a feed rate of 10 mL / min, an atomizer speed of 5000 r / min, and an airflow atomization method to obtain spherical or near-spherical precursor materials.

[0037] S3. In a mixed gas atmosphere of N2:H2=95:5, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 2h. Then, the temperature is increased to 420℃ at a rate of 2℃ / min and calcined for 10h. The powder material is then ball-milled to achieve a particle size D50 < 4μm, yielding the sodium-ion battery cathode material Na. 2.3 Fe 1.85 (SO4) 2.55 (PO4) 0.3 .

[0038] Take Na 2.3 Fe 1.85 (SO4) 2.55 (PO4) 0.3 The mass ratio of PVDF:SP / CNT = 90:5:5 was quantitatively weighed, and 5% sodium bromide was added. The mixture was dissolved in the organic solvent NMP (N-methylpyrrolidone) to control the solid content at 30%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was 1.0 mol / L NaPF6 dissolved in a solution of EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0039] Example 5 (Spray Drying): The difference from Example 1 is that... S1. Weigh FeSO4·mH2O, anhydrous Na2SO4 and Na3PO4 at a molar ratio of Na:Fe:P = 9.6:7.2:1.6. Add CNTs and sodium sulfite at 4% and 3% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 20%.

[0040] S2. Spray dry the above slurry at an outlet temperature of 90°C, a feed rate of 15 mL / min, an atomizer speed of 10000 r / min, and an airflow atomization method to obtain spherical or near-spherical precursor materials.

[0041] S3. In a mixed gas atmosphere of N2:H2=94:6, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 3h. Then, the temperature is increased to 420℃ at a rate of 2℃ / min and calcined for 8h. The powder material is then ball-milled to achieve a particle size D50 < 4μm, yielding the sodium-ion battery cathode material Na. 2.5 Fe 1.8 (SO4) 2.4 (PO4) 0.4 .

[0042] Take Na 2.5 Fe 1.8 (SO4) 2.4 (PO4) 0.4 The PVDF:SP / CNT ratio was quantitatively weighed at 85:5:10, and 4% sodium iodide was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 50%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was a solution of 1.0 mol / L NaPF6 dissolved in EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0043] Example 6 (Spray Drying): The difference from Example 1 is that... S1. Weigh FeSO4·mH2O, anhydrous Na2SO4 and Na3PO4 at a molar ratio of Na:Fe:P = 10.4:6.8:2.4. Add CNTs and hypophosphoric acid at 3% and 3% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 40%.

[0044] S2. Spray dry the above precursor slurry at an outlet temperature of 130°C, a feed rate of 20 mL / min, an atomizer speed of 20000 r / min, and an airflow atomization method to obtain spherical or near-spherical precursor materials.

[0045] S3. In a mixed gas atmosphere of N2:H2=93:7, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 3h. Then, the temperature is increased to 400℃ at a rate of 2℃ / min and calcined for 10h. The powder material is then ball-milled to achieve a particle size D50 < 4μm, yielding the sodium-ion battery cathode material Na. 2.6 Fe1.7 (SO4) 2.1 (PO4) 0.6 .

[0046] Take Na 2.6 Fe 1.7 (SO4) 2.1 (PO4) 0.6 The PVDF:SP / CNT ratio was quantitatively weighed at 80:10:10, and 2% sodium bismuthate was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 40%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was a solution of 1.0 mol / L NaPF6 dissolved in EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0047] Comparative Example 1 (Spray Drying): The difference from Example 1 is that... S1. Weigh FeSO4·mH2O and anhydrous Na2SO4 at a molar ratio of Na:Fe=10:7. Add CNTs and ascorbic acid at 5% and 4% of the total mass, respectively. Mix with deionized water and stir until homogeneous to obtain a precursor slurry with a solid content of 30%.

[0048] S2. Spray dry the above slurry at an outlet temperature of 130°C to obtain spherical or near-spherical precursor materials.

[0049] S3. In a mixed gas atmosphere of N2:H2=97:3, the temperature is increased to 200℃ at a rate of 3℃ / min and held for 1 hour. Then, the temperature is increased to 400℃ at a rate of 2℃ / min and calcined for 10 hours. Following this, the powder material is ball-milled to achieve a particle size D50 < 4μm, thus obtaining the sodium-ion battery cathode material Na. 2.5 Fe 1.75 (SO4)3.

[0050] Take Na 2.5 Fe 1.75The following materials were weighed quantitatively: (SO4)3:PVDF:SP / CNT = 90:5:5 by mass, and 5% sodium citrate was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 40%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed. Hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was a solution of 1.0 mol / L NaPF6 dissolved in EC:EMC:FEC = 4:5:1. The batteries were assembled into button / pouch cells in an argon-filled glove box, and the performance of each battery was tested.

[0051] Comparative Example 2 (Solid Phase Method): S1. Weigh FeSO4·mH2O, anhydrous Na2SO4, and Na3PO4 in a molar ratio of Na:Fe:P = 10:7:2. Add conductive agent CNTs and ascorbic acid at 5% and 3% of the total mass, respectively, and mix evenly by magnetic stirring.

[0052] S2. Place the uniformly mixed raw materials in a tube furnace, and heat them to 200°C at a rate of 3°C / min and hold for 1 hour in a mixed gas atmosphere of N2:H2=97:3. Then heat them to 400°C at a rate of 2°C / min and calcine for 10 hours.

[0053] S3. After pressing and coarse grinding the sintered material, disperse and grind it in a ball mill (ball-to-material ratio 8:1, speed 600-1000 r / min) for 4-6 hours, then sieve it to make the particle size D50 < 4 μm, to obtain sodium-ion battery cathode material Na. 2.5 Fe 1.75 (SO4) 2.25 (PO4) 0.5 .

[0054] Take Na 2.5 Fe 1.75 (SO4) 2.25 (PO4) 0.5 The PVDF:SP / CNT ratio was quantitatively weighed at 90:5:5, and 5% sodium citrate was added and dissolved in the organic solvent NMP (N-methylpyrrolidone). The solid content was controlled at 40%. The mixture was homogenized at 400 r / min for 4 h and then coated onto a 13 μm thick aluminum foil. After drying and rolling, the positive electrode sheet was formed, and hard carbon was used as the negative electrode. A 16 μm thick base film was used as the separator. The electrolyte was a solution of 1.0 mol / L NaPF6 dissolved in EC:EMC:FEC = 4:5:1. The cells were assembled into button / pouch cells in an argon-filled glove box, and the performance of the cells was tested.

[0055] Experimental test results of the examples and comparative examples:

[0056] in conclusion: 1. Introduce PO4 3- Structural improvements enhance performance: Introduction of PO4 3- The cathode material exhibits superior performance compared to the PO4-free material in terms of compaction density, first-discharge specific capacity, and cycle stability. 3- The material has a compacted density of up to 2.35 g / cm³. 3 It has an initial discharge capacity of up to 108.8 mAh / g and excellent cycle stability.

[0057] 2. Spray drying process has obvious advantages: Comparative Example 2 uses the solid phase method, and its compaction density, volume and cycle performance are significantly lower than those of the example using the spray drying process. It can be seen that spray drying has significant advantages in material morphology control and performance improvement.

[0058] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The method comprises the following steps: S1, mixing an iron source, a sodium source, a phosphorus source, a conductive agent, an antioxidant, and a solvent in a certain mass ratio, and stirring uniformly to obtain a precursor slurry; S2, granulating the precursor slurry prepared in S1 by a solution method to obtain a spherical or spherical-like precursor material; S3, sintering the precursor material prepared in S2 in an inert gas atmosphere at a temperature of 300-450°C for 1-48h to obtain a sodium ion battery cathode material Na 2+2x Fe 2-x (SO4) 3-3x (PO4) 2x wherein 0≤x≤1.

2. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In S1, the molar ratio of Na:Fe:P in the sodium source, the iron source, and the phosphorus source is (8-10):(6-8):(0.1-2); the addition amount of the conductive agent is 0.1-30wt% of the total mass of the raw materials; the addition amount of the antioxidant is 0.5-50wt% of the total weight of the raw materials; and the solid content of the prepared precursor slurry is 10-70wt%.

3. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In S1, the stirring mode of the precursor slurry includes at least one of magnetic stirring, planetary stirring, vibration stirring, overturning mixing, ultrasonic circulation, and micro-jet.

4. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In S1, the phosphorus source includes at least one of sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium hexametaphosphate, and sodium pyrophosphate; the sodium source includes at least one of sodium sulfate, sodium phosphate, sodium carbonate, sodium nitrate, sodium acetate, sodium oxalate, and sodium chloride; and the iron source includes at least one of ferrous sulfate hydrate, ferrous oxalate, and ferrous nitrate.

5. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In S1, the conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon nanotubes, and graphene; the antioxidant includes at least one of ascorbic acid, citric acid, oxalic acid, carotenoids, sodium sulfite, tea polyphenols, hypophosphorous acid, and glucose; and the solvent includes at least one of deionized water and an alcohol.

6. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In S2, the solution granulation includes at least one of freeze-drying and spray drying; the inlet temperature of the spray drying is 100-200℃, the outlet temperature is 80-130℃, the feeding speed is 0.1-20mL / min, the atomizer rotation speed is 1000-20000r / min, and the atomization mode includes at least one of pressure type and airflow type.

7. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In S3, the inert gas includes at least one of argon, nitrogen, helium, nitrogen-hydrogen mixed gas, and carbon dioxide-nitrogen mixed gas.

8. A positive electrode material, characterized by, The positive electrode material is prepared by the preparation method in any one of claims 1-7.

9. A sodium-ion battery, characterized in that, The method comprises: The positive electrode material in claim 8.

10. An electric device, characterized by The method comprises: The sodium-ion battery in claim 9.

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