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

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a sodium ferric sulfate positive electrode material and a preparation method and application thereof. The preparation method of the sodium ferric sulfate positive electrode material comprises the following steps: obtaining a carbon foam substrate; weighing raw materials according to the stoichiometric ratio of the sodium ferric sulfate positive electrode material and adding the raw materials into a solvent to obtain a mixed solution; depositing the mixed solution on the carbon foam substrate by using an electrostatic spray deposition method to obtain a precursor film; and performing sintering treatment on the precursor film to obtain the sodium ferric sulfate positive electrode material. The carbon foam is used as a substrate material, the electrostatic spray deposition is simultaneously performed to prepare a sodium ferric sulfate precursor, and then sintering treatment is performed to obtain the sodium ferric sulfate material, so that the discharge specific capacity, the rate performance and the cycle performance of the sodium ferric sulfate material are all significantly improved.

Description

Technical Field

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

[0002] Sodium iron sulfate (FeSU) cathode materials have shown broad application prospects in sodium-ion batteries due to their advantages such as high specific capacity, good cycle stability, high temperature resistance, and low spontaneous combustion and explosiveness. This material typically has a high operating voltage (3.0-3.8V), is relatively abundant in resources, and has a relatively low cost, thus possessing potential economic advantages in energy storage systems. However, despite the high theoretical energy density of FeSU, in practical applications, its large band gap and low intrinsic conductivity limit the rapid transfer and reaction kinetics of charge carriers (sodium ions and electrons), resulting in poor discharge specific capacity and rate performance. Furthermore, the strong bonding between sodium and oxygen in FeSU makes it difficult for sodium ions to break free, leading to irreversible sodium ion insertion and extraction, increasing the migration resistance of sodium ions, resulting in higher internal impedance and reduced rate performance. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor discharge specific capacity and rate performance of existing sodium iron phosphate cathode materials, thereby providing a sodium iron sulfate cathode material, its preparation method and application to solve the above problems.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a sodium ferric sulfate cathode material includes:

[0006] Obtaining a carbon foam substrate;

[0007] The raw materials were weighed according to the stoichiometric ratio of sodium ferric sulfate cathode material and added to the solvent to obtain a mixture;

[0008] The mixture was deposited onto a carbon foam substrate using electrostatic spray deposition to obtain a precursor film.

[0009] The precursor film was sintered to obtain sodium ferric sulfate cathode material.

[0010] Preferably, the chemical formula of the sodium ferric sulfate cathode material is Na. x Fe y M z (SO4)3, 2.0≤x<3.0, 1.5<y≤2, 0≤z≤0.4, x+2y+2z=6, M is a transition metal element; wherein, preferably 0.05<z≤0.4.

[0011] Preferably, the raw materials for the sodium ferric sulfate cathode material include an iron source, a sodium source, and metal element additives;

[0012] And / or, antioxidants and antioxidant synergists are also added to the mixture.

[0013] Preferably, the iron source is ferrous sulfate heptahydrate;

[0014] And / or, the sodium source is anhydrous sodium sulfate;

[0015] And / or, the metal element additive is Ca 2+ Mg 2+ Al 3+ Cu 2+ Zn 2+ La 3+ Ti 4+ W 6+ At least one of them, and it is a sulfate.

[0016] Preferably, the process of obtaining the mixture includes: adding the raw material to nitrogen-saturated water to fully dissolve it, and then mixing it with a mixed reagent composed of an antioxidant, an antioxidant synergist, and an organic solvent to obtain the mixture.

[0017] Preferably, the water is ultrapure water;

[0018] And / or, the antioxidant is sodium acetate;

[0019] And / or, the synergist of the antioxidant is phosphoric acid;

[0020] And / or, the organic solvent is propylene glycol;

[0021] And / or, the mass of the raw material is 10-20% of the mass of water;

[0022] And / or, the water content is 7-15% of the organic solvent content;

[0023] And / or, the antioxidant is 0.2-3% of the raw material mass;

[0024] And / or, the mass of the synergist of the antioxidant is 1.5-6% of the mass of the raw material.

[0025] Preferably, the sintering temperature is 750°C;

[0026] And / or, the sintering treatment time is 8 hours;

[0027] And / or, the atmosphere for the sintering process is an inert atmosphere;

[0028] And / or, the sintering process is followed by crushing, sieving and demagnetizing.

[0029] Preferably, the process of obtaining the carbon foam substrate includes: heat-treating melamine sponge under an inert atmosphere; preferably, the heat treatment temperature is 750-820℃ and the heat treatment time is 2-4h.

[0030] The present invention also provides a sodium ferric sulfate cathode material, which is prepared by the above-described method for preparing sodium ferric sulfate cathode material.

[0031] The present invention also provides the application of the above-mentioned sodium iron sulfate cathode material in sodium-ion batteries.

[0032] In this invention, transition metal elements are metal element additives.

[0033] The technical solution of this invention has the following advantages:

[0034] 1. A method for preparing sodium ferric sulfate cathode material, comprising: obtaining a carbon foam substrate; weighing raw materials according to the stoichiometric ratio of sodium ferric sulfate cathode material and adding them to a solvent to obtain a mixture; depositing the mixture onto the carbon foam substrate using electrostatic spray deposition to obtain a precursor film; and sintering the precursor film to obtain the sodium ferric sulfate cathode material. This invention uses carbon foam as the substrate material, simultaneously preparing a sodium ferric sulfate precursor via electrostatic spray deposition, followed by sintering to obtain the sodium ferric sulfate material. The porous structure of the carbon foam provides more space for sodium ferric sulfate to accommodate active materials, which helps to improve the overall energy density of the cathode material. Simultaneously, the porous structure also provides a convenient channel for the rapid transport of sodium ions, thereby improving the rate performance of the battery. Electrostatic spray deposition is a chemical deposition method that utilizes a high-voltage DC electrostatic field to disperse charged electrosols under the dual effects of Coulomb repulsion and electrostatic attraction during spraying, and grows a film on a high-temperature metal substrate. This method can achieve high-precision and uniform material deposition, thereby improving the electrochemical performance of the material. Moreover, the sodium ferric sulfate material prepared by electrostatic spray deposition has a certain degree of disordered structure. This disordered structure can weaken the bonding force between sodium and oxygen, activate sodium storage sites, and realize the reversible insertion and extraction of multiple sodium ions, which greatly improves the discharge specific capacity and conductivity of the material. At the same time, it can stabilize the structure and improve the cycle performance.

[0035] 2. In the preparation method of the sodium ferric sulfate cathode material of the present invention, melamine sponge is used to make a carbon foam substrate, which has advantages such as high open porosity, low density, high stability, environmental friendliness, and multifunctionality. Specifically, the melamine sponge has a low density (e.g., 8.5 kg / m³). 3The high porosity and stability of melamine foam enable the cathode material to maintain good cycle stability even at high temperatures. Furthermore, the high porosity (up to 99%) of melamine foam creates a three-dimensional mesh structure, providing extremely high specific surface area and pore volume when used to prepare porous carbon materials. This structure not only facilitates the growth of materials such as carbon nanotubes but also enhances the mechanical strength and electrical conductivity of the materials. These characteristics make carbon foam substrates made from melamine foam an ideal choice for preparing high-performance electrode materials (e.g., cathode materials for supercapacitors).

[0036] 3. In the preparation method of sodium iron sulfate cathode material of the present invention, the doping of transition metal elements can improve the conductivity of cathode material, stabilize the crystal structure of cathode material, reduce interfacial reaction between material and electrolyte and loss of active material, reduce capacity loss rate of battery during cycle, and further effectively extend battery life.

[0037] 4. In the preparation method of the sodium ferric sulfate cathode material of the present invention, the addition of an antioxidant and an antioxidant synergist can prevent Fe 2+ Oxidized to Fe 3+ This reduces the impurity content in the material. Detailed Implementation

[0038] 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.

[0039] 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.

[0040] Example 1

[0041] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0042] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 820°C for 3 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0043] 2) According to Na2Fe 1.6 Mg 0.4The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined by weighing out the following ingredients: ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The ingredients are then dissolved in nitrogen-saturated ultrapure water to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed thoroughly with a mixed reagent consisting of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0044] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0045] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0046] Example 2

[0047] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0048] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 820°C for 3 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0049] 2) According to Na2Fe 1.7 Mg 0.3 The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined by weighing out the following ingredients: ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The ingredients are then dissolved in nitrogen-saturated ultrapure water to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed thoroughly with a mixed reagent consisting of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0050] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0051] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0052] Example 3

[0053] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0054] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 820°C for 3 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0055] 2) According to Na2Fe 1.8 Mg 0.2 The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined by weighing out the following ingredients: ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The ingredients are then dissolved in nitrogen-saturated ultrapure water to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed thoroughly with a mixed reagent consisting of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0056] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0057] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0058] Example 4

[0059] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0060] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 820°C for 3 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0061] 2) According to Na2Fe 1.7 Zn 0.3 The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined by weighing out the following ingredients: ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The ingredients are then dissolved in nitrogen-saturated ultrapure water to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed thoroughly with a mixed reagent consisting of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0062] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0063] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0064] Example 5

[0065] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0066] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 820°C for 3 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0067] 2) Weigh ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate according to the stoichiometric ratio of Na2Fe2(SO4)3. Add the raw materials to nitrogen-saturated ultrapure water and dissolve them completely to obtain an aqueous solution of the metal salt. Then, mix the aqueous solution of the metal salt with a mixed reagent composed of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate. After stirring continuously for 5 hours, pour the solution into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0068] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0069] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0070] Example 6

[0071] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0072] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 750°C for 4 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0073] 2) According to Na 2.6 Fe 1.6 Mg 0.1 The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined by weighing out the following ingredients: ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The ingredients are then dissolved in nitrogen-saturated ultrapure water to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed thoroughly with a mixed reagent consisting of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 10% of the mass of ultrapure water, the mass of ultrapure water is 7% of the mass of propylene glycol, the mass of sodium acetate is 3% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 6% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0074] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0075] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0076] Example 7

[0077] This embodiment provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0078] 1) Cut the melamine sponge into pieces measuring 5×3.5×0.4cm. 3 Thin blocks were placed in a tube furnace and an argon atmosphere was created. Then, the carbon foam was heat-treated at 820°C for 2 hours to obtain elastic porous carbon foam. Finally, the carbon foam was punched into round sheets with a diameter of 12 mm.

[0079] 2) According to Na2Fe 1.6 Mg 0.4 The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined by weighing out the following ingredients: ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The ingredients are then dissolved in nitrogen-saturated ultrapure water to obtain an aqueous solution of the metal salt. This aqueous solution is then mixed thoroughly with a mixed reagent consisting of sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 20% of the mass of ultrapure water, the mass of ultrapure water is 15% of the mass of propylene glycol, the mass of sodium acetate is 0.2% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 1.5% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0080] 3) During the electrostatic spraying process, the distance between the carbon foam disc from step 1) and the nozzle is fixed at 2.8 cm. The disc temperature is set to 235℃, and the voltage applied during electrostatic spraying is 7 kV, resulting in a precursor film.

[0081] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0082] Example 8

[0083] The difference between this embodiment and Embodiment 2 is that only ultrapure water is used as the solvent, and ferrous sulfate heptahydrate, anhydrous sodium sulfate, magnesium sulfate, sodium acetate, and phosphoric acid are added to the solvent simultaneously to obtain a mixture. Other conditions are the same as in Embodiment 2.

[0084] Example 9

[0085] The difference between this embodiment and Embodiment 2 is that only propylene glycol is used as the solvent, and ferrous sulfate heptahydrate, anhydrous sodium sulfate, magnesium sulfate, sodium acetate, and phosphoric acid are added to the solvent simultaneously to obtain a mixture. Other conditions are the same as in Embodiment 2.

[0086] Example 10

[0087] The difference between this embodiment and Embodiment 2 is that ultrapure water and propylene glycol are first mixed as a mixed solvent, and then ferrous sulfate heptahydrate, anhydrous sodium sulfate, magnesium sulfate, sodium acetate, and phosphoric acid are simultaneously added to the mixed solvent to obtain a mixed solution. Other conditions are the same as in Embodiment 2.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0090] 1) According to Na2Fe 1.7 Mg 0.3 The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined. The raw materials are added to nitrogen-saturated ultrapure water and dissolved thoroughly to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed evenly with sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate. The solution is vigorously magnetically stirred overnight at 80°C. After the water in the solution evaporates, a black gel is formed.

[0091] 2) Dry the gel obtained in step 1) in an oven at 120°C overnight;

[0092] 3) Place the dried gel from step 2) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally crush, sieve and demagnetize to obtain sodium iron sulfate cathode material.

[0093] Comparative Example 2

[0094] This comparative example provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0095] 1) Melamine is dissolved in methanol to form a melamine solution, wherein the mass of melamine is 15% of the mass of methanol. The melamine solution is then uniformly coated onto a fiber mesh and dried in an argon atmosphere to form a solid melamine film. The melamine film is then heat-treated in an argon atmosphere to a high temperature (800℃) for 6 hours to cause pyrolysis and carbonization of the melamine, transforming it into a carbon-rich structure. Finally, after cooling, washing, and drying, melamine carbon paper is obtained.

[0096] 2) Weigh out ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate according to the stoichiometric ratio of Na2Fe2(SO4)3. Add the raw materials to nitrogen-saturated ultrapure water and dissolve them completely to obtain an aqueous solution of the metal salt. Then mix the aqueous solution of the metal salt with sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate. After stirring continuously for 5 hours, pour the solution into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0097] 3) During the electrostatic spraying process, the distance between the carbon paper substrate and the nozzle in step 1) is fixed at 2.8 cm, the temperature of the carbon paper substrate is set to 235℃, and the voltage applied during the electrostatic spraying process is 7kV to obtain the precursor film.

[0098] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0099] Comparative Example 3

[0100] This comparative example provides a method for preparing sodium ferric sulfate cathode material, the specific steps of which are as follows:

[0101] 1) Melamine is dissolved in methanol to form a melamine solution, wherein the mass of melamine is 15% of the mass of methanol. The melamine solution is then uniformly coated onto a fiber mesh and dried in an argon atmosphere to form a solid melamine film. The melamine film is then heat-treated in an argon atmosphere to a high temperature (800℃) for 6 hours to cause pyrolysis and carbonization of the melamine, transforming it into a carbon-rich structure. Finally, after cooling, washing, and drying, melamine carbon paper is obtained.

[0102] 2) According to Na2Fe 1.7 Mg 0.3The stoichiometric ratio of ferrous sulfate heptahydrate, anhydrous sodium sulfate, and magnesium sulfate for (SO4)3 is determined. The raw materials are added to nitrogen-saturated ultrapure water and dissolved thoroughly to obtain an aqueous solution of the metal salt. The aqueous solution of the metal salt is then mixed evenly with sodium acetate, phosphoric acid, and propylene glycol to obtain a mixed solution. The total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate is 15% of the mass of ultrapure water, the mass of ultrapure water is 10% of the mass of propylene glycol, the mass of sodium acetate is 0.5% of the total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate, and the mass of phosphoric acid is 2% of the total mass of ferrous sulfate heptahydrate and anhydrous sodium sulfate. After stirring continuously for 5 hours, the solution is poured into a 20 mL syringe with a nozzle diameter of 1.2 mm.

[0103] 3) During the electrostatic spraying process, the distance between the carbon paper substrate and the nozzle in step 1) is fixed at 2.8 cm, the temperature of the carbon paper substrate is set to 235℃, and the voltage applied during the electrostatic spraying process is 7kV to obtain the precursor film.

[0104] 4) Place the precursor film from step 3) into a tube furnace and sinter it at 750°C for 8 hours under an argon atmosphere. Cool it in the furnace and finally obtain sodium iron sulfate cathode material by crushing, sieving and demagnetizing.

[0105] Test Example 1

[0106] The electrochemical properties of the sodium iron sulfate cathode materials prepared in the examples and comparative examples were tested. The test conditions were as follows: Electrodes were prepared by homogenizing and coating a slurry at a ratio of 95 (main material): 2.5 (PVDF): 2.5 (SP). Sodium metal was used as the counter electrode, glass fiber as the separator, and a 1 mol / L NaPF6 solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio 1:1) was used as the electrolyte. The cathode, sodium sheet, separator, gasket, and spring were assembled into a CR2032 coin cell. Finally, the coin cell was placed in a Blue Electric testing system for electrochemical performance testing. The electrical performance test parameters were set as follows: voltage range 2.0V-4.5V, capacity test was performed by 0.1C / 0.1C charge and discharge in the first cycle, rate performance was evaluated by 0.2C / 0.2C, 0.5C / 0.5C, and 1C / 1C charge and discharge tests, and cycle performance was evaluated by 50 cycles at 1C / 1C. The test results are shown in Table 1.

[0107] Table 1

[0108]

[0109] 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, include: Obtaining a carbon foam substrate; The process of obtaining the carbon foam substrate includes: heat-treating melamine sponge under an inert atmosphere; The raw materials were weighed according to the stoichiometric ratio of the sodium ferric sulfate cathode material and added to the solvent to obtain a mixture; the chemical formula of the sodium ferric sulfate cathode material is Na. x Fe y M z (SO4)3, 2.0≤x<3.0, 1.5<y≤2, 0<z≤0.4, x+2y+2z=6, M is a transition metal element; the process of obtaining the mixed solution includes: adding the raw material to nitrogen-saturated water to fully dissolve it, and then mixing it with a mixed reagent composed of an antioxidant, an antioxidant synergist, and an organic solvent to obtain the mixed solution; the antioxidant is sodium acetate; the antioxidant synergist is phosphoric acid; the organic solvent is propylene glycol; The mixture was deposited onto a carbon foam substrate using electrostatic spray deposition to obtain a precursor film. The precursor film was sintered to obtain sodium ferric sulfate cathode material.

2. The preparation method according to claim 1, characterized in that, The condition is 0.05 < z ≤ 0.

4.

3. The preparation method according to claim 1, characterized in that, The raw materials for the sodium ferric sulfate cathode material include an iron source, a sodium source, and metal element additives.

4. The preparation method according to claim 3, characterized in that, The iron source is ferrous sulfate heptahydrate; And / or, the sodium source is anhydrous sodium sulfate; And / or, the metal element additive is Ca 2+ Mg 2+ Al 3+ Cu 2+ Zn 2+ La 3+ Ti 4+ W 6+ At least one of them, and it is a sulfate.

5. The preparation method according to claim 1, characterized in that, The water is ultrapure water; And / or, the mass of the raw material is 10-20% of the mass of water; And / or, the water mass is 7-15% of the organic solvent mass; And / or, the antioxidant is 0.2-3% of the raw material mass; And / or, the mass of the synergist of the antioxidant is 1.5-6% of the mass of the raw material.

6. The preparation method according to any one of claims 1-5, characterized in that, The sintering temperature is 750℃; And / or, the sintering treatment time is 8 h; And / or, the atmosphere for the sintering process is an inert atmosphere; And / or, the sintering process is followed by crushing, sieving and demagnetizing.

7. The preparation method according to claim 1 or 2, characterized in that, The heat treatment temperature is 750-820℃, and the heat treatment time is 2-4 h.

8. 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 1-7.

9. The application of the sodium ferric sulfate cathode material according to claim 8 in sodium-ion batteries.

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