Sodium ferric sulfate positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a sodium ferric sulfate positive electrode material as well as a preparation method and application thereof. The preparation method of the sodium ferric sulfate positive electrode material provided by the invention comprises the following steps: 1) stirring and mixing sodium sulfate, ferrous sulfate, an antioxidant, a conductive agent, nanoscale fluoride and water to form a mixed solution, and then performing spray drying to obtain a precursor; and 2) spraying an ammonium phosphate salt aqueous solution on the precursor obtained in the step 1) under a stirring condition, and then carrying out heat treatment under a protective atmosphere to obtain the sodium ferric sulfate positive electrode material. According to the preparation method of the sodium ferric sulfate positive electrode material provided by the invention, fluoride doping and ammonium phosphate surface modification are synergistically matched, so that the cycling stability, especially the high-temperature stability, of the prepared sodium ferric sulfate positive electrode material can be remarkably improved.

Description

Technical Field

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

[0002] Sodium-ion batteries have broad application prospects due to their cost advantage. Their working principle is similar to that of lithium-ion batteries, utilizing the reversible insertion and extraction of sodium ions between the positive and negative electrodes to store and release energy. Currently, the main cathode materials used in sodium-ion batteries fall into three categories: transition metal oxide systems, polyanionic compounds (phosphate systems, fluorophosphate systems, and sulfate systems), and Prussian blue systems. Among these, sodium ferric sulfate polyanionic cathode materials, with their high voltage platform, have attracted widespread attention and research. However, existing sodium ferric sulfate polyanionic cathode materials are prone to water absorption and exhibit issues with Fe during charging and discharging. 2+ Leaching leads to poor high-temperature cycling stability. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor high-temperature cycling stability of sodium ferric sulfate polyanionic cathode material, thereby providing a sodium ferric sulfate cathode material, its preparation method and application.

[0004] This invention provides a method for preparing sodium ferric sulfate cathode material, comprising the following steps: 1) Sodium sulfate, ferrous sulfate, antioxidant, conductive agent, nano-sized fluoride and water are stirred and mixed to form a mixture, and then spray dried to obtain the precursor; 2) The precursor obtained in step 1) is sprayed with an aqueous solution of ammonium phosphate under stirring conditions, and then heat-treated under a protective atmosphere to obtain the sodium iron sulfate cathode material.

[0005] Preferably, the molar ratio of sodium sulfate and ferrous sulfate in step 1) is 1:(1.0-2.0); The total mass ratio of sodium sulfate and ferrous sulfate to the mass ratio of nano-sized fluoride is 100:(0.5-1.0); The total mass ratio of sodium sulfate and ferrous sulfate to the mass ratio of the antioxidant is 100:(0.5-1.5); The total mass ratio of sodium sulfate and ferrous sulfate to the mass ratio of the conductive agent is 100:(2-5).

[0006] Preferably, the average particle size of the nano-sized fluoride in step 1) is 50-300 nm; The fluoride is selected from at least one of MgF2, AlF3, ZrF4, MnF2, and CrF2; The antioxidant is selected from at least one of ascorbic acid, vitamin E, citric acid, and glucose; The conductive agent is selected from at least one of carbon nanotubes and conductive carbon black.

[0007] Preferably, the stirring speed in step 1) is 100-400 rpm, and the stirring time is 1-24 h; The total mass of sodium sulfate, ferrous sulfate, antioxidant, conductive agent and nano-sized fluoride in the mixture is 30%.

[0008] Preferably, the inlet air temperature of the spray dryer in step 1) is 170-250°C, and the outlet air temperature of the spray dryer is 90-110°C. During the spray drying process, the atomizer frequency is 200-450Hz and the feed rate is 5-40mL / min.

[0009] Preferably, in step 2), the precursor obtained in step 1) is sprayed with an aqueous solution of ammonium phosphate under stirring at 1000-2000 rpm; The mass concentration of ammonium phosphate in the aqueous solution is 1-3 wt%. The ammonium phosphate salt is selected from at least one of (NH4)2HPO4, NH4H2PO4, and (NH4)3PO4.

[0010] Preferably, in step 2), the ratio of the precursor obtained in step 1) to the aqueous solution of ammonium phosphate is 500:(15-50), in g / mL.

[0011] Preferably, the protective atmosphere in step 2) is selected from at least one of nitrogen protective atmosphere and argon protective atmosphere; The heat treatment temperature is 330-400℃, and the heat treatment time is 8-12h; Optionally, after the heat treatment step described in step 2) is completed, a crushing step may also be included.

[0012] This invention provides a sodium ferric sulfate cathode material, which is prepared by the method described above for preparing sodium ferric sulfate cathode materials.

[0013] The present invention also provides an application of the above-described sodium iron sulfate cathode material in sodium-ion batteries.

[0014] The technical solution of this invention has the following advantages: 1. The preparation method of sodium ferric sulfate cathode material provided by the present invention includes the following steps: 1) Sodium sulfate, ferrous sulfate, antioxidant, conductive agent, nano-sized fluoride and water are stirred and mixed to form a mixed solution, and then spray-dried to obtain a precursor; 2) The precursor obtained in step 1) is sprayed with an ammonium phosphate aqueous solution under stirring conditions, and then heat-treated under a protective atmosphere to obtain the sodium ferric sulfate cathode material. In the preparation of the anion sodium ferric sulfate sodium-ion battery cathode material of the present invention, nano-sized fluoride is added as a dopant, which is incorporated into the target phase structure during sintering. F atoms occupy the O positions, enhancing the bond energy between F and Fe atoms, increasing the difficulty of Fe migration, and reducing Fe... 2+ Dissolution enhances the structural stability of the material; simultaneously, ammonium phosphate is used as a surface modifier, primarily for phosphate doping. Phosphate ions occupy sulfate sites, reducing the material's electronegativity, water absorption, and gas generation under high-temperature cycling, thus enhancing the material's processability and improving the cathode material's surface interface. Furthermore, ammonium phosphate, as a surface modifier, further restricts Fe migration, reduces water absorption, and synergistically works with the dopant fluoride to improve the cathode material's cycle stability, especially its high-temperature cycle stability.

[0015] 2. The method for preparing sodium ferric sulfate cathode material provided by the present invention, wherein the average particle size of the nano-sized fluoride in step 1) is 50-300 nm; the fluoride is selected from at least one of MgF2, AlF3, ZrF4, MnF2, and CrF2; the antioxidant is selected from at least one of ascorbic acid, vitamin E, citric acid, and glucose. The present invention specifically selects MgF2, AlF3, ZrF4, MnF2, and CrF2 fluorides, where Mg, Al, Zr, Mn, and Cr metal atoms occupy Fe sites, altering the coordination environment between Fe and O atoms, further restricting Fe migration, and further improving the cycle stability of the cathode material, especially its high-temperature cycle stability. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 SEM image of the sodium ferric sulfate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0018] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0019] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0020] Example 1 This embodiment provides a method for preparing sodium ferric sulfate cathode material, including the following steps: 1) Na₂SO₄, FeSO₄·7H₂O, ascorbic acid, carbon nanotubes, MgF₂, and water were mixed at 150 rpm for 1 hour to form a mixture. The average particle size of MgF₂ was 100 nm. The molar ratio of Na₂SO₄ to FeSO₄·7H₂O was 1:1.67. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to ascorbic acid was 100:1. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to MgF₂ was... The mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:0.5, and the mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:3. The total mass concentration of Na2SO4, FeSO4·7H2O, ascorbic acid, MgF2 and carbon nanotubes in the mixture was 30%. Then, spray drying was carried out. The inlet air temperature of spray drying was 180℃ and the outlet air temperature was 90℃. The atomizer frequency was 350Hz and the feed rate was 10mL / min. After spray drying, the precursor was obtained. 2) 500g of the precursor obtained in step 1) was sprayed with 15mL of a 2wt% (NH4)2HPO4 aqueous solution under stirring at 1500rpm. The mixture was then heat-treated at 350℃ for 10h under a nitrogen atmosphere. The heat-treated product was then pulverized into powder to obtain the sodium ferric sulfate cathode material. The obtained sodium ferric sulfate cathode material was examined using a scanning electron microscope (SEM) to obtain the following SEM image: Figure 1 As shown.

[0021] Example 2 This embodiment provides a method for preparing sodium ferric sulfate cathode material, including the following steps: 1) Na₂SO₄, FeSO₄·7H₂O, ascorbic acid, carbon nanotubes, ZrF₄, and water were mixed at 200 rpm for 22 h to form a mixture. The average particle size of ZrF₄ was 50 nm. The molar ratio of Na₂SO₄ to FeSO₄·7H₂O was 1:1. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to ascorbic acid was 100:0.5. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to ZrF₄ was 100:0.5. The mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:0.7, the mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:3, and the total mass concentration of Na2SO4, FeSO4·7H2O, ascorbic acid, ZrF4 and carbon nanotubes in the mixture was 30%. Then, spray drying was carried out. The inlet air temperature of spray drying was 200℃, the outlet air temperature was 100℃, the atomizer frequency was 200Hz, and the feed rate was 20mL / min. After spray drying, the precursor was obtained. 2) Spray 500g of the precursor obtained in step 1) with 30mL of (NH4)3PO4 aqueous solution with a mass concentration of 3wt% under stirring at 1000rpm, and then heat treat it at 330℃ for 12h under nitrogen protection atmosphere. Then, pulverize the heat-treated product into powder to obtain the sodium iron sulfate cathode material.

[0022] Example 3 This embodiment provides a method for preparing sodium ferric sulfate cathode material, including the following steps: 1) Na₂SO₄, FeSO₄·7H₂O, ascorbic acid, carbon nanotubes, CrF₂, and water were mixed at 100 rpm for 24 h to form a mixture. The average particle size of CrF₂ was 100 nm. The molar ratio of Na₂SO₄ to FeSO₄·7H₂O was 1:2. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to ascorbic acid was 100:1.5. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to CrF₂ was 1:1.5. The mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes is 100:1, the total mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes is 100:3, and the total mass concentration of Na2SO4, FeSO4·7H2O, ascorbic acid, CrF2 and carbon nanotubes in the mixture is 30%. Then, spray drying is performed with an inlet air temperature of 170℃ and an outlet air temperature of 110℃. The atomizer frequency during spray drying is 450Hz, and the feed rate is 40mL / min. After spray drying, the precursor is obtained. 2) Spray 500g of the precursor obtained in step 1) with 50mL of NH4H2PO4 aqueous solution with a mass concentration of 1wt% under stirring at 2000rpm, and then heat treat it at 400℃ for 8h under nitrogen protection atmosphere. Then, pulverize the heat-treated product into powder to obtain the sodium iron sulfate cathode material.

[0023] Comparative Example 1 This comparative example provides a method for preparing sodium ferric sulfate cathode material, including the following steps: 1) Na2SO4, FeSO4·7H2O, ascorbic acid, carbon nanotubes and water were stirred at 150 rpm for 1 h to form a mixture. The molar ratio of Na2SO4 to FeSO4·7H2O was 1:1.67, the mass ratio of the total mass of Na2SO4 and FeSO4·7H2O to ascorbic acid was 100:1, the mass ratio of the total mass of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:3, and the total mass concentration of Na2SO4, FeSO4·7H2O, ascorbic acid and carbon nanotubes in the mixture was 30%. Then, spray drying was carried out. The inlet air temperature of spray drying was 180℃, the outlet air temperature was 90℃, the atomizer frequency was 350Hz, and the feed rate was 10mL / min. After spray drying, the precursor was obtained. 2) Spray 500g of the precursor obtained in step 1) with 15mL of (NH4)2HPO4 aqueous solution with a mass concentration of 2wt% under stirring at 1500rpm, and then heat treat it at 350℃ for 10h under nitrogen protection atmosphere. Then, pulverize the heat-treated product into powder to obtain the sodium iron sulfate cathode material.

[0024] Comparative Example 2 This comparative example provides a method for preparing sodium ferric sulfate cathode material, including the following steps: 1) Na₂SO₄, FeSO₄·7H₂O, ascorbic acid, carbon nanotubes, MgF₂, and water were mixed at 150 rpm for 1 hour to form a mixture. The average particle size of MgF₂ was 100 nm. The molar ratio of Na₂SO₄ to FeSO₄·7H₂O was 1:1.67. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to ascorbic acid was 100:1. The mass ratio of the total mass of Na₂SO₄ and FeSO₄·7H₂O to MgF₂ was... The mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:0.5, and the mass ratio of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:3. The total mass concentration of Na2SO4, FeSO4·7H2O, ascorbic acid, MgF2 and carbon nanotubes in the mixture was 30%. Then, spray drying was carried out. The inlet air temperature of spray drying was 180℃ and the outlet air temperature was 90℃. The atomizer frequency was 350Hz and the feed rate was 10mL / min. After spray drying, the precursor was obtained. 2) Heat-treat 500g of the precursor obtained in step 1) at 350°C for 10h under a nitrogen protective atmosphere, and then pulverize the heat-treated product into powder to obtain the sodium iron sulfate cathode material.

[0025] Comparative Example 3 This comparative example provides a method for preparing sodium ferric sulfate cathode material, including the following steps: 1) Na2SO4, FeSO4·7H2O, ascorbic acid, carbon nanotubes and water were stirred at 150 rpm for 1 h to form a mixture. The molar ratio of Na2SO4 to FeSO4·7H2O was 1:1.67, the mass ratio of the total mass of Na2SO4 and FeSO4·7H2O to ascorbic acid was 100:1, the mass ratio of the total mass of Na2SO4 and FeSO4·7H2O to carbon nanotubes was 100:3, and the total mass concentration of Na2SO4, FeSO4·7H2O, ascorbic acid and carbon nanotubes in the mixture was 30%. Then, spray drying was carried out. The inlet air temperature of spray drying was 180℃, the outlet air temperature was 90℃, the atomizer frequency was 350Hz, and the feed rate was 10mL / min. After spray drying, the precursor was obtained. 2) Take 500g of the precursor obtained in step 1) and heat-treat it at 350°C for 10h under a nitrogen protective atmosphere. Then, pulverize the heat-treated product into powder to obtain the sodium iron sulfate cathode material.

[0026] Test case Sodium-ion batteries (CR2032 type button half-cells) were prepared using the sodium iron sulfate cathode materials obtained in Examples 1-3 and Comparative Examples 1-3 as the main materials, and their electrical performance was tested. Preparation of the button half-cell: The main material, polyvinylidene fluoride (PVDF), and acetylene black were mixed in an N-methylpyrrolidone solvent at a mass ratio of 86:7:7. The mixture was homogenized, coated, dried, and cut to form the cathode sheet (the areal density of the cathode material was 8.0 mg / cm³). 2 A CR2032 button cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode, a Celgard 2500 membrane as the separator, and a 1 mol / L sodium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio of 1:1) as the electrolyte. The cells were assembled in the following order: negative electrode, electrolyte, separator, electrolyte, and positive electrode. The button half-cells prepared above were placed in the Blue Electric testing system for electrical performance testing. The electrical performance testing conditions were: charge / discharge voltage range of 2.0V-4.5V, ambient temperature of 60℃, charging at a rate of 0.1C to 4.25V, and then discharging at a rate of 0.1C to 2.0V, constituting one cycle. The charge / discharge specific capacity of this cycle was recorded as the initial charge / discharge specific capacity, and the first-cycle efficiency was calculated as (first-discharge specific capacity / first-charge specific capacity × 100%). Then, the cells were charged at 1C and discharged at 1C for 50 cycles. The charge / discharge specific capacity of the second cycle and the 51st cycle were recorded. The cycle capacity retention rate was calculated as (51st cycle / 2nd cycle discharge specific capacity × 100%). The test results are shown in Table 1.

[0027] Table 1

[0028] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a sodium ferric sulfate cathode material, characterized in that, Includes the following steps: 1) Sodium sulfate, ferrous sulfate, antioxidant, conductive agent, nano-sized fluoride and water are stirred and mixed to form a mixture, and then spray dried to obtain the precursor; 2) The precursor obtained in step 1) is sprayed with an aqueous solution of ammonium phosphate under stirring conditions, and then heat-treated under a protective atmosphere to obtain the sodium iron sulfate cathode material.

2. The method for preparing the sodium ferric sulfate cathode material according to claim 1, characterized in that, The molar ratio of sodium sulfate and ferrous sulfate in step 1) is 1:(1.0-2.0); The total mass ratio of sodium sulfate and ferrous sulfate to the mass ratio of nano-sized fluoride is 100:(0.5-1.0); The total mass ratio of sodium sulfate and ferrous sulfate to the mass ratio of the antioxidant is 100:(0.5-1.5); The total mass ratio of sodium sulfate and ferrous sulfate to the mass ratio of the conductive agent is 100:(2-5).

3. The method for preparing the sodium ferric sulfate cathode material according to claim 1 or 2, characterized in that, The average particle size of the nano-sized fluoride mentioned in step 1) is 50-300 nm; The fluoride is selected from at least one of MgF2, AlF3, ZrF4, MnF2, and CrF2; The antioxidant is selected from at least one of ascorbic acid, vitamin E, citric acid, and glucose; The conductive agent is selected from at least one of carbon nanotubes and conductive carbon black.

4. The method for preparing the sodium ferric sulfate cathode material according to any one of claims 1-3, characterized in that, The stirring speed in step 1) is 100-400 rpm, and the stirring time is 1-24 h; The total mass of sodium sulfate, ferrous sulfate, antioxidant, conductive agent and nano-sized fluoride in the mixture is 20-30%.

5. The method for preparing the sodium ferric sulfate cathode material according to any one of claims 1-4, characterized in that, The inlet air temperature for spray drying in step 1) is 170-250℃, and the outlet air temperature for spray drying is 90-110℃. During the spray drying process, the atomizer frequency is 200-450Hz and the feed rate is 5-40mL / min.

6. The method for preparing the sodium ferric sulfate cathode material according to any one of claims 1-5, characterized in that, In step 2), the precursor obtained in step 1) is sprayed with an aqueous solution of ammonium phosphate under stirring at 1000-2000 rpm. The mass concentration of ammonium phosphate in the aqueous solution is 1-3 wt%. The ammonium phosphate salt is selected from at least one of (NH4)2HPO4, NH4H2PO4, and (NH4)3PO4.

7. The method for preparing the sodium ferric sulfate cathode material according to any one of claims 1-6, characterized in that, In step 2), the ratio of the precursor obtained in step 1) to the aqueous solution of ammonium phosphate is 500:(15-50), in g / mL.

8. The method for preparing the sodium ferric sulfate cathode material according to any one of claims 1-7, characterized in that, The protective atmosphere mentioned in step 2) is selected from at least one of nitrogen protective atmosphere and argon protective atmosphere; The heat treatment temperature is 330-400℃, and the heat treatment time is 8-12h; Optionally, after the heat treatment step described in step 2) is completed, a crushing step may also be included.

9. A sodium ferric sulfate cathode material, characterized in that, It is prepared by the method for preparing sodium ferric sulfate cathode material according to any one of claims 1-8.

10. The application of the sodium ferric sulfate cathode material according to claim 9 in sodium-ion batteries.

Images