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

Abstract

The invention belongs to the technical field of secondary 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 comprises the following steps: S1, mixing a sodium source, an iron source, a sulfur source, an antioxidant, multilayer graphene oxide and water to obtain spray slurry; the number of layers of the multi-layer graphene oxide is 10-50; s2, performing spray drying on the spray slurry to obtain a spray material; and S3, sintering and crushing the spray material obtained in the step S2 to obtain the sodium ferric sulfate positive electrode material. The sodium ferric sulfate positive electrode material prepared by the method has good compaction density, and the energy density and the cycling stability of the sodium ferric sulfate positive electrode material can be improved through the compaction density.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a sodium iron sulfate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasingly prominent energy problem, new renewable energy has become a popular direction pursued by all sectors. Lithium-ion batteries are a good sustainable energy source and are now widely used in various portable mobile devices, electric vehicles and other fields. However, the global lithium resources are unevenly distributed, and they are consumed too quickly in the existing secondary battery environment, and their costs will be affected. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, which uses the reversible insertion and extraction of sodium ions between the positive and negative electrodes to achieve energy storage and release. However, the source of sodium is more extensive and the resource distribution is more average, so it has broad application prospects due to its cost advantage.

[0003] In sodium-ion batteries, indicators such as the cycle stability, output voltage, thermal stability, output capacity, and power density of the cathode material play a decisive role in the overall performance of the battery. Among the existing sodium-ion battery cathode materials, sodium iron sulfate polyanion cathode materials have a high voltage platform and are one of the important research directions. In the prior art, in the mixing step of preparing sodium iron sulfate polyanion cathode materials, since the main raw materials can be completely dissolved in water to form a solution state, the spray process is mostly used. However, on the one hand, the particles obtained by the spray process are mostly hollow shells, and the shells are very thin, with a small loose bulk density, a small loading amount in the crucible, and a very low production capacity. The sintering energy is not fully utilized, resulting in waste of resources. On the other hand, the tap density of the cathode material finally synthesized by sintering the air spray particles is also relatively low, which makes the energy density of the material relatively low. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects that when using the spray drying method to prepare polyanion-type sodium iron sulfate cathode materials in the prior art, the loose bulk density of the obtained spray particles is small, which in turn leads to a low tap density of the cathode material, etc., so as to provide a sodium iron sulfate cathode material, a preparation method thereof, and an application thereof.

[0005] To this end, the present invention provides the following technical solutions.

[0006] The present invention provides a preparation method of a sodium iron sulfate cathode material, comprising the following steps: S1: mixing a sodium source, an iron source, a sulfur source, an antioxidant, multi-layer graphene oxide, and water to obtain a spray slurry; the number of layers of the multi-layer graphene oxide is 10-50 layers; S2: spray-drying the spray slurry to obtain a spray material; S3: sintering and pulverizing the spray material obtained in S2 to obtain a sodium iron sulfate cathode material.

[0007] Among them, graphene oxide is an oxidized derivative or functionalized graphene of graphene, which is a complex compound generated after the oxidation reaction of graphene. Its surface and edges contain a large number of oxygen-containing functional groups, such as carboxyl groups, hydroxyl groups, oxygen ions, etc. Graphene oxide is mostly prepared by oxidizing graphene with strong acids.

[0008] Optionally, in the step S1, the mass of the multi-layer graphene oxide is 0.1% to 2.5% of the total mass of the sodium source, iron source, and sulfur source; optionally, the mass of the multi-layer graphene oxide is 0.7% to 1% of the total mass of the sodium source, iron source, and sulfur source.

[0009] Optionally, in the step S1, a carbon source is further added; optionally, the mass ratio of the multi-layer graphene oxide to the carbon source is 1:1 to 3; further optionally, the mass ratio of the multi-layer graphene oxide to the carbon source is 1:2. The addition of the carbon source can further improve the electronic conductivity of the material, thereby improving the rate performance of the material.

[0010] Optionally, in the step S2, the inlet air temperature of the spray drying is 140 to 200 °C, the outlet air temperature is 80 to 100 °C, the atomizer frequency is 200 to 400 Hz, and the feeding speed is 20 to 50 mL / min; optionally, in the step S2, the inlet air temperature of the spray drying is 180 to 190 °C, the outlet air temperature is 85 to 95 °C, the atomizer frequency is 270 to 330 Hz, and the feeding speed is 25 to 35 mL / min.

[0011] Optionally, in the step S1, the amount of water added is such that the solid content of the spray slurry is 20% to 50%; optionally, the solid content of the spray slurry is 25% to 35%. In the spray slurry, the solid mass is the sum of the masses of the sodium source, iron source, sulfur source, antioxidant, and multi-layer graphene oxide. When a carbon source is added, the solid mass also includes the carbon source.

[0012] Optionally, in the step S1, the mass of the antioxidant is 0.5% to 1.5% of the total mass of the sodium source, iron source, and sulfur source; optionally, the mass of the antioxidant is 1% to 1.5% of the total mass of the sodium source, iron source, and sulfur source.

[0013] Optionally, the amounts of the sodium source, iron source, and sulfur source are taken according to the stoichiometric number of sodium iron sulfate. When taking, an excessive amount of iron source can be used to ensure the full progress of the reaction; optionally, the sodium iron sulfate is non-stoichiometric sodium iron sulfate; optionally, the chemical formula of the sodium iron sulfate is Na x Fe(SO4) 1+x / 2 , where 1 ≤ x ≤ 2.

[0014] Optionally, in the step S3, the sintering temperature is 300 to 400 °C and the time is 8 to 16 h; optionally, the sintering temperature is 360 to 380 °C and the time is 10 to 14 h.

[0015] Optionally, in S3, the sintering is carried out in a protective atmosphere; optionally, the protective atmosphere includes a noble gas atmosphere and / or a nitrogen atmosphere.

[0016] Optionally, the D50 of the particles of the multi-layer graphene oxide is 0.5 to 10 μm.

[0017] Optionally, in S1, the method of mixing the sodium source, iron source, sulfur source, antioxidant, multi-layer graphene oxide, and water includes stirring; optionally, the stirring speed is 100 to 300 revolutions per minute, and the time is 0.5 to 2 hours; further optionally, the stirring speed is 130 to 170 revolutions per minute, and the time is 1 to 1.5 hours.

[0018] Optionally, the sodium source is a sodium-containing soluble salt; optionally, the sodium source includes at least one of sodium sulfate and sodium bisulfate.

[0019] Optionally, the iron source is an iron-containing soluble salt; optionally, the iron source is ferrous sulfate.

[0020] Optionally, the sulfur source is a sulfur-containing soluble salt; optionally, the sulfur source includes at least one of ferrous sulfate, sodium sulfate, and sodium bisulfate.

[0021] In the present invention, when compounds such as sodium sulfate, sodium bisulfate, and ferrous sulfate that contain both sodium and sulfur, or both iron and sulfur are used as raw materials, the raw materials can serve as a sulfur source while serving as a sodium source or an iron source.

[0022] Optionally, the carbon source includes at least one of carbon nanotubes, carbon black, acetylene black, and Ketjen black.

[0023] Optionally, the antioxidant includes at least one of ascorbic acid, citric acid, vitamin A, vitamin E, lutein, canthaxanthin, and astaxanthin.

[0024] The present invention provides a sodium iron sulfate cathode material prepared by the above preparation method.

[0025] The present invention also provides the application of the above sodium iron sulfate cathode material in secondary batteries; optionally, the secondary battery includes a sodium ion battery. Typically and non-limitingly, an assembly method of a sodium ion coin half-cell can be: mixing the obtained cathode material with a conductive agent acetylene carbon black and a binder PVDF in a mass ratio of 80 to 95:2 to 12:2 to 8, adding an appropriate amount of 1-methyl-2-pyrrolidone and ball milling for 1 to 3 hours to obtain a slurry, coating it on an aluminum sheet, drying and pressing to form a cathode sheet, using a sodium metal sheet as the anode, sodium hexafluorophosphate (NaPF6) as the electrolyte, and a mixture of dimethyl carbonate and ethylene carbonate with a volume ratio of 1:1 as the solvent, and assembling it into a 2032 coin cell.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention provides a method for preparing a sodium iron sulfate cathode material, which includes the following steps: S1: Mix a sodium source, an iron source, a sulfur source, an antioxidant, multi-layer graphene oxide, and water to obtain a spray slurry; the number of layers of the multi-layer graphene oxide is 10 to 50 layers; S2: Spray-dry the spray slurry to obtain a spray material; S3: Sinter and crush the spray material obtained in S2 to obtain the sodium iron sulfate cathode material. In the step of mixing raw materials, multi-layer graphene oxide is added. The multi-layer graphene oxide can play a role as a supporting carrier, improve the density of the obtained spray material, and further improve the tap density of the obtained sodium iron sulfate cathode material, and finally improve its energy density and cycle stability. In the step of mixing various raw materials to obtain a spray slurry, because the oxygen-containing functional groups such as carboxyl and hydroxyl on the multi-layer graphene oxide have a certain attraction to sodium ions, ferrous ions, and sulfate ions, the multi-layer graphene oxide makes the sodium ions, ferrous ions, and sulfate ion solutes in the spray slurry accumulate between the layers of the multi-layer graphene oxide through this special surface property and layered structure. When spray-drying, the water in the spray slurry evaporates instantaneously, and the sodium ions, ferrous ions, and sulfate ion solutes in the spray slurry accumulate rapidly in the multi-layer graphene oxide as a supporting carrier to obtain a relatively dense spray material. Description of the Drawings

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is the SEM image of the sodium iron sulfate cathode material obtained in Example 1 of the present invention, with a magnification of 1000 times. Specific Embodiments

[0030] The following embodiments are provided to better further understand the present invention. It is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features and being the same as or similar to the present invention falls within the protection scope of the present invention.

[0031] For those examples where specific experimental procedures or conditions are not specified, the operations or conditions of the conventional experimental procedures described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchases.

[0032] Example 1

[0033] This example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0034] (1) Weigh Na2SO4 and FeSO4·7H2O according to a molar ratio of 1:1.5, and take ascorbic acid accounting for 1% of the total mass of Na2SO4 and FeSO4·7H2O as an antioxidant; weigh multi-layer graphene oxide (with the number of layers being 10 - 20 layers and D50 being 0.6 μm) accounting for 1.5% of the total mass of Na2SO4 and FeSO4·7H2O; weigh carbon nanotubes as a carbon source according to a mass ratio of multi-layer graphene oxide to carbon nanotubes of 1:1. Weigh deionized water according to a solid content of 30% of the final spray slurry. Place the deionized water in a stirring tank and stir at 150 revolutions per minute. Pour Na2SO4, FeSO4·7H2O, ascorbic acid, multi-layer graphene oxide, and carbon nanotubes into the stirring tank in sequence, and continue stirring for 1 h to obtain a spray slurry.

[0035] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 150 °C, the outlet air temperature is 80 °C, the atomizer frequency is 300 Hz, and the feeding speed is 20 mL / min.

[0036] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 350 °C for 10 h under a nitrogen protection atmosphere, and pulverize to obtain the sodium iron sulfate cathode material.

[0037] Example 2

[0038] This example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0039] (1) Weigh Na2SO4 and FeSO4·7H2O according to a molar ratio of 1:1.5, and take ascorbic acid accounting for 1% of the total mass of Na2SO4 and FeSO4·7H2O as an antioxidant; weigh multi-layered graphene oxide (with 10 - 20 layers and D50 of 0.6 μm) accounting for 1% of the total mass of Na2SO4 and FeSO4·7H2O; weigh carbon nanotubes as a carbon source according to a mass ratio of multi-layered graphene oxide to carbon nanotubes of 1:2. Weigh deionized water according to the solid content of the final spray slurry being 25%. Place the deionized water in a stirring tank and stir at 130 revolutions per minute. Pour Na2SO4, FeSO4·7H2O, ascorbic acid, multi-layered graphene oxide, and carbon nanotubes into the stirring tank in sequence, and continue stirring for 1.5 h to obtain a spray slurry.

[0040] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 190 °C, the outlet air temperature is 95 °C, the atomizer frequency is 270 Hz, and the feeding speed is 25 mL / min.

[0041] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 360 °C for 14 h under a nitrogen protection atmosphere, and pulverize to obtain a sodium iron sulfate cathode material.

[0042] Example 3

[0043] This example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0044] (1) Weigh Na2SO4 and FeSO4·7H2O according to a molar ratio of 1:1.5, and take ascorbic acid accounting for 1.5% of the total mass of Na2SO4 and FeSO4·7H2O as an antioxidant; weigh multi-layered graphene oxide (with 10 - 20 layers and D50 of 0.6 μm) accounting for 0.7% of the total mass of Na2SO4 and FeSO4·7H2O; weigh carbon nanotubes as a carbon source according to a mass ratio of multi-layered graphene oxide to carbon nanotubes of 1:2. Weigh deionized water according to the solid content of the final spray slurry being 35%. Place the deionized water in a stirring tank and stir at 170 revolutions per minute. Pour Na2SO4, FeSO4·7H2O, ascorbic acid, multi-layered graphene oxide, and carbon nanotubes into the stirring tank in sequence, and continue stirring for 1 h to obtain a spray slurry.

[0045] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 180 °C, the outlet air temperature is 85 °C, the atomizer frequency is 330 Hz, and the feeding speed is 35 mL / min.

[0046] (3) Transfer the spray material obtained in (2) into a box furnace, and sinter it at 380 °C for 10 h under a nitrogen protection atmosphere, then pulverize it to obtain the sodium iron sulfate cathode material.

[0047] Example 4

[0048] This example provides a sodium iron sulfate cathode material and its preparation method, which includes the following steps:

[0049] (1) Weigh NaHSO4 and FeSO4·7H2O according to a molar ratio of 2:1, and take citric acid accounting for 0.5% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; weigh multi-layer graphene oxide (with 25 - 35 layers and D50 of 1 μm) accounting for 2.5% of the total mass of Na2SO4 and FeSO4·7H2O; weigh carbon black as a carbon source according to a mass ratio of multi-layer graphene oxide to carbon black of 1:1. Weigh deionized water according to a solid content of 50% in the final spray slurry. Place the deionized water in a stirring tank and stir at 100 revolutions per minute. Pour NaHSO4, FeSO4·7H2O, citric acid, multi-layer graphene oxide, and carbon black into the stirring tank in sequence, and continue stirring for 2 h to obtain the spray slurry.

[0050] (2) Spray-dry the spray slurry obtained in (1) to obtain the spray material; the inlet air temperature of the spray dryer is 140 °C, the outlet air temperature is 80 °C, the atomizer frequency is 400 Hz, and the feeding speed is 50 mL / min.

[0051] (3) Transfer the spray material obtained in (2) into a box furnace, and sinter it at 300 °C for 16 h under a nitrogen protection atmosphere, then pulverize it to obtain the sodium iron sulfate cathode material.

[0052] Example 5

[0053] This example provides a sodium iron sulfate cathode material and its preparation method, which includes the following steps:

[0054] (1) Weigh NaHSO4 and FeSO4·7H2O according to a molar ratio of 1:1, and take lutein accounting for 1.5% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; weigh multi-layer graphene oxide (with 35 - 45 layers and D50 of 1.3 μm) accounting for 0.125% of the total mass of Na2SO4 and FeSO4·7H2O; weigh Ketjen black as a carbon source according to a mass ratio of multi-layer graphene oxide to Ketjen black of 1:3. Weigh deionized water according to a solid content of 20% in the final spray slurry. Place the deionized water in a stirring tank and stir at 300 revolutions per minute. Pour NaHSO4, FeSO4·7H2O, lutein, multi-layer graphene oxide, and Ketjen black into the stirring tank in sequence, and continue stirring for 0.5 h to obtain the spray slurry.

[0055] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 200 °C, the outlet air temperature is 100 °C, the atomizer frequency is 200 Hz, and the feeding rate is 20 mL / min.

[0056] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 400 °C for 8 h under a nitrogen protection atmosphere, and pulverize to obtain a sodium iron sulfate cathode material.

[0057] Example 6

[0058] This example provides a sodium iron sulfate cathode material and a preparation method thereof, including the following steps:

[0059] (1) Weigh NaHSO4 and FeSO4·7H2O in a molar ratio of 1:1, and take lutein accounting for 3% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; weigh multilayer graphene oxide (with 35 - 45 layers and D50 of 1.3 μm) accounting for 0.125% of the total mass of Na2SO4 and FeSO4·7H2O. Weigh deionized water according to the solid content of the final spray slurry being 20%. Place the deionized water in a stirring tank, stir at 300 revolutions per minute, and pour NaHSO4, FeSO4·7H2O, lutein, and multilayer graphene oxide into the stirring tank in sequence, and continue stirring for 0.5 h to obtain a spray slurry.

[0060] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 200 °C, the outlet air temperature is 100 °C, the atomizer frequency is 200 Hz, and the feeding rate is 20 mL / min.

[0061] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 400 °C for 8 h under a nitrogen protection atmosphere, and pulverize to obtain a sodium iron sulfate cathode material.

[0062] Comparative Example 1

[0063] This comparative example provides a sodium iron sulfate cathode material and a preparation method thereof, including the following steps:

[0064] (1) Weigh NaHSO4 and FeSO4·7H2O in a molar ratio of 1:1, and take lutein accounting for 3% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; use Ketjen black as a carbon source, and weigh Ketjen black accounting for 0.5% of the total mass of NaHSO4 and FeSO4·7H2O. Weigh deionized water according to the solid content of the final spray slurry being 20%. Put the deionized water in a stirring tank, stir at 300 revolutions per minute, and pour NaHSO4, FeSO4·7H2O, lutein, and Ketjen black into the stirring tank in sequence, and continue stirring for 0.5 h to obtain a spray slurry.

[0065] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 200 °C, the outlet air temperature is 100 °C, the atomizer frequency is 200 Hz, and the feeding speed is 20 mL / min.

[0066] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 400 °C for 8 h under a nitrogen protection atmosphere, and pulverize to obtain a sodium iron sulfate cathode material.

[0067] Comparative Example 2

[0068] This comparative example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0069] (1) Weigh NaHSO4 and FeSO4·7H2O in a molar ratio of 1:1, and take lutein accounting for 3% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; weigh multi-layer graphene (using multi-layer graphene with a similar number of layers range and particle size range as the multi-layer graphene oxide used in Example 5) accounting for 0.125% of the total mass of Na2SO4 and FeSO4·7H2O; weigh Ketjen black as a carbon source according to the mass ratio of multi-layer graphene to Ketjen black being 1:3. Weigh deionized water according to the solid content of the final spray slurry being 20%. Put the deionized water in a stirring tank, stir at 300 revolutions per minute, and pour NaHSO4, FeSO4·7H2O, lutein, multi-layer graphene, and Ketjen black into the stirring tank in sequence, and continue stirring for 0.5 h to obtain a spray slurry.

[0070] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 200 °C, the outlet air temperature is 100 °C, the atomizer frequency is 200 Hz, and the feeding speed is 20 mL / min.

[0071] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 400 °C for 8 h under a nitrogen protection atmosphere, and pulverize to obtain a sodium iron sulfate cathode material.

[0072] Comparative Example 3

[0073] This comparative example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0074] Weigh NaHSO4 and FeSO4·7H2O according to a molar ratio of 1:1, and take lutein accounting for 3% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; weigh multi-layered graphene oxide (with 35 - 45 layers and D50 of 1.3 μm) according to 0.125% of the total mass of Na2SO4 and FeSO4·7H2O; weigh Ketjen black as a carbon source according to a mass ratio of multi-layered graphene oxide to Ketjen black of 1:3. Pour NaHSO4, FeSO4·7H2O, lutein, multi-layered graphene oxide, and Ketjen black into a stirring tank in sequence, and stir at 300 revolutions per minute for 0.5 h; transfer it into a box furnace, and sinter at 400 °C for 8 h under a nitrogen protection atmosphere, then pulverize to obtain the sodium iron sulfate cathode material.

[0075] Comparative Example 4

[0076] This comparative example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0077] (1) Weigh NaHSO4 and FeSO4·7H2O according to a molar ratio of 1:1; weigh multi-layered graphene oxide (with 35 - 45 layers and D50 of 1.3 μm) according to 0.125% of the total mass of Na2SO4 and FeSO4·7H2O; weigh Ketjen black as a carbon source according to a mass ratio of multi-layered graphene oxide to Ketjen black of 1:3. Weigh deionized water according to the solid content of the final spray slurry being 20%. Place the deionized water in a stirring tank, stir at 300 revolutions per minute, pour NaHSO4, FeSO4·7H2O, multi-layered graphene oxide, and Ketjen black into the stirring tank in sequence, and continue to stir for 0.5 h to obtain a spray slurry.

[0078] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 200 °C, the outlet air temperature is 100 °C, the atomizer frequency is 200 Hz, and the feeding speed is 20 mL / min.

[0079] (3) Transfer the spray material obtained in (2) into a box furnace, and sinter at 400 °C for 8 h under a nitrogen protection atmosphere, then pulverize to obtain the sodium iron sulfate cathode material.

[0080] Comparative Example 5

[0081] This comparative example provides a sodium iron sulfate cathode material and its preparation method, including the following steps:

[0082] (1) Weigh NaHSO4 and FeSO4·7H2O in a molar ratio of 1:1, and take lutein accounting for 3% of the total mass of NaHSO4 and FeSO4·7H2O as an antioxidant; weigh graphene oxide (using graphene oxide with a particle size range similar to that of the multi-layer graphene oxide used in Example 5) accounting for 0.125% of the total mass of Na2SO4 and FeSO4·7H2O; weigh Ketjen black as a carbon source in a mass ratio of graphene oxide to Ketjen black of 1:3. Weigh deionized water according to the solid content of the final spray slurry being 20%. Place the deionized water in a stirring tank and stir at 300 revolutions per minute. Pour NaHSO4, FeSO4·7H2O, lutein, graphene oxide, and Ketjen black into the stirring tank in sequence, and continue stirring for 0.5 h to obtain a spray slurry.

[0083] (2) Spray-dry the spray slurry obtained in (1) to obtain a spray material; the inlet air temperature of the spray dryer is 200 °C, the outlet air temperature is 100 °C, the atomizer frequency is 200 Hz, and the feeding speed is 20 mL / min.

[0084] (3) Transfer the spray material obtained in (2) to a box furnace, sinter at 400 °C for 8 h under a nitrogen protection atmosphere, and pulverize to obtain a sodium iron sulfate cathode material.

[0085] Test Example 1

[0086] Observe the SEM image of the sodium iron sulfate cathode material prepared in Example 1, as shown in Figure 1 , it can be seen that the obtained sodium iron sulfate cathode material is in the shape of quasi-solid spheres with very few shell-like substances, which proves that the multi-layer graphene oxide indeed plays a role as a supporting carrier.

[0087] Test Example 2

[0088] Take the spray materials obtained in the examples and test examples, and test their loose bulk density according to GB / T 1479.1-2011 "Determination of loose bulk density of metallic powders - Part D1: Funnel method". The obtained test data are shown in Table 1.

[0089] Test Example 3

[0090] Take the sodium iron sulfate cathode materials obtained in the examples and test examples, and test their cathode material tap density according to GB / T 44330-2024 "Determination of tap density of lithium-ion battery cathode material powders". The obtained test data are shown in Table 1.

[0091] Test Example 4

[0092] Take the sodium iron sulfate cathode material obtained in the examples and test examples. Mix the sodium iron sulfate cathode material with the conductive agent acetylene black and the binder PVDF evenly according to the mass ratio of 80:12:8. Add an appropriate amount of 1-methyl-2-pyrrolidone and ball mill for 1 h to obtain a slurry. Coat it on an aluminum sheet, dry it, and press it into a positive electrode sheet. Use a sodium metal sheet as the negative electrode, sodium hexafluorophosphate (NaPF6) as the electrolyte, and a mixture of dimethyl carbonate and ethylene carbonate with a volume ratio of 1:1 as the solvent to assemble a 2032 coin-type half-cell. Use a Siken test system to conduct electrical performance tests. In the range of charge-discharge cut-off voltages of 2.0 - 4.5 V, test the discharge specific capacity at 0.1C. Rate performance test: The charge-discharge cut-off voltage is 2.0 - 4.5 V. Test the discharge capacity C1 under the condition of 1C and the discharge capacity C2 under the condition of 0.1C. Its rate performance is C1 / C2. The test results are shown in Table 1. At room temperature, test its 50-cycle capacity retention rate under charge-discharge of 1C / 1C. The obtained test data are shown in Table 1.

[0093] Table 1

[0094]

[0095] Comparative Example 1 is compared with Example 5, and an equal amount of Ketjen black is used to replace the multi-layer graphene oxide; Comparative Example 2 is compared with Example 5, and an equal amount of multi-layer graphene is used to replace the multi-layer graphene oxide; Comparative Example 3 is compared with Example 5, and a preparation method of directly mixing each solid raw material and then sintering is used instead of first preparing a spray slurry and then sintering the spray material; Comparative Example 4 is compared with Example 5 and no antioxidant is added; Comparative Example 5 is compared with Example 5, and an equal amount of graphene oxide is used to replace the multi-layer graphene oxide. It can be seen from Table 1 that the loose bulk density of the spray material, the tap density of the cathode material, and the tap density of the cathode material obtained in the examples are significantly better than those obtained in the comparative examples. And after the material becomes more compact, the rate performance does not decrease significantly. The preparation method provided by the present invention improves the tap density of the material while maintaining the rate performance of the cathode material.

[0096] It can also be seen from Table 1 that compared with Examples 2 and 3 in which each raw material ratio, operating parameters, etc. are within the preferred range, the loose bulk density of the spray material and the tap density of the cathode material in Example 1 in which only some parameters are within the preferred range decrease significantly; compared with Example 1, the loose bulk density of the spray material and the tap density of the cathode material in Examples 4 and 5 in which each raw material ratio, operating parameters, etc. are not within the preferred range decrease significantly; this shows that the preferred raw material ratio, operating parameters, etc. improve the performance of the obtained cathode material. Compared with Example 5, the rate performance of Example 6 without adding a carbon source shows a decline, which indicates that the addition of a carbon source can improve the rate performance of the material.

[0097] Obviously, the above embodiments are merely examples given for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to exhaustively list all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for preparing a sodium iron sulfate positive electrode material, characterized in that: The steps include: S1: mixing a sodium source, an iron source, a sulfur source, an antioxidant, multilayer graphene oxide, and water to obtain a spray slurry; The number of layers of the multilayer graphene oxide is 10 to 50; S2: spray drying the spray slurry to obtain a spray material; S3: Sintering and crushing the spray material obtained in S2 to obtain a sodium iron sulfate positive electrode material.

2. The preparation method according to claim 1, characterized in that: In S1, the mass of the multilayer graphene oxide is 0.1% to 2.5% of the total mass of the sodium source, the iron source, and the sulfur source; optionally, the mass of the multilayer graphene oxide is 0.7% to 1% of the total mass of the sodium source, the iron source, and the sulfur source; And / or, in S1, a carbon source is further added; optionally, the mass ratio of the multilayer graphene oxide to the carbon source is 1:1 to 3; further optionally, the mass ratio of the multilayer graphene oxide to the carbon source is 1:

2.

3. The preparation method according to claim 1 or 2, characterized in that: In the S2, the inlet air temperature of the spray drying is 140-200°C, the outlet air temperature is 80-100°C, the atomizer frequency is 200-400Hz, and the feed rate is 20-50mL / min; optionally, in the S2, the inlet air temperature of the spray drying is 180-190°C, the outlet air temperature is 85-95°C, the atomizer frequency is 270-330Hz, and the feed rate is 25-35mL / min.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In S1, the amount of water added is such that the solid content of the spray slurry is 20% to 50%; optionally, the solid content of the spray slurry is 25% to 35%; And / or, in S1, the mass of the antioxidant is 0.5% to 1.5% of the total mass of the sodium source, the iron source, and the sulfur source; optionally, the mass of the antioxidant is 1% to 1.5% of the total mass of the sodium source, the iron source, and the sulfur source; And / or, the amount of sodium source, iron source and sulfur source is calculated according to the stoichiometric ratio of sodium ferric sulfate; Optionally, the sodium ferric sulfate is a non-stoichiometric sodium ferric sulfate; Optionally, the chemical formula of the sodium ferric sulfate is Na x Fe(SO4) 1+x / 2 , where 1≤x≤2.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In S3, the sintering temperature is 300-400°C and the time is 8-16 hours; optionally, the sintering temperature is 360-380°C and the time is 10-14 hours; And / or, in S3, sintering is performed under a protective atmosphere; optionally, the protective atmosphere includes a rare gas atmosphere and / or a nitrogen atmosphere.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The multilayer graphene oxide particles have a D50 of 0.5 to 10 μm.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In S1, the sodium source, iron source, sulfur source, antioxidant, multilayer graphene oxide and water are mixed by stirring; optionally, the stirring speed is 100 to 300 rpm and the time is 0.5 to 2 h; further optionally, the stirring speed is 130 to 170 rpm and the time is 1 to 1.5 h.

8. The preparation method according to any one of claims 2 to 7, characterized in that: The sodium source is a soluble salt containing sodium; optionally, the sodium source includes at least one of sodium sulfate and sodium bisulfate; And / or, the iron source is a soluble salt containing iron; optionally, the iron source is ferrous sulfate; And / or, the sulfur source is a soluble salt containing sulfur; optionally, the sulfur source includes at least one of ferrous sulfate, sodium sulfate, and sodium bisulfate; And / or, the carbon source comprises at least one of carbon nanotubes, carbon black, acetylene black and Ketjen black; And / or, the antioxidant includes at least one of ascorbic acid, citric acid, vitamin A, vitamin E, lutein, canthaxanthin and astaxanthin.

9. A sodium iron sulfate positive electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the sodium iron sulfate positive electrode material as claimed in claim 9 in a secondary battery; optionally, the secondary battery comprises a sodium ion battery.

Images