Sodium ferric sulfate positive electrode material and synthesis method thereof

Abstract

The application discloses a kind of sodium ferrosulphate positive electrode material and synthesis method thereof, it is related to sodium ferrosulphate positive electrode material technical field, to solve the problem of low yield or raw material consumption of existing synthesis method;The present application includes taking ferrous sulfate heptahydrate and anhydrous sodium sulfate into water saturated with nitrogen, fully dissolving to obtain the aqueous solution of metal salt, adding appropriate amount of organic alcohol and mixing uniformly to obtain mixed liquor;Keep the reaction environment to prevent oxidation of ferrous ion, control the temperature of mixed liquor, add appropriate amount of cationic surfactant, after fully stirring, collect the precipitate by suction filtration or centrifugation, the precipitate is washed with ethanol and then vacuum dried or freeze-dried, to obtain the required precursor;Grind the precursor, and obtain sodium ferrosulphate positive electrode material by low-temperature calcination under protective atmosphere;The method is simple, green and easy to scale up, the amount of raw materials is small, the yield is high, the product sodium ferrosulphate positive electrode material has excellent performance, and is more suitable for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ferric sulfate positive electrode materials, in particular to a sodium ferric sulfate positive electrode material and a synthesis method thereof. BACKGROUND

[0002] Sodium and lithium belong to the same main group in the periodic table, and their physical and chemical properties are very similar. The charging and discharging principles of sodium ion batteries and lithium ion batteries are similar, that is, lithium ions or sodium ions are embedded and de-embedded between the positive and negative electrodes. Compared with lithium ion batteries, sodium ion batteries have the advantages of abundant resources, low cost, good safety performance, good cycle performance and the like, and can meet the requirements of low cost, long service life and high safety in the energy storage field. As a key part determining the cost and performance of sodium ion batteries, the positive electrode material is crucial to the industrial development of sodium ion batteries. There are three mainstream technical routes for the positive electrode material, namely, layered oxides, polyanion compounds and prussian blue compounds. Compared with the other two kinds of positive electrode materials, the polyanion type positive electrode material has the characteristics of high working voltage, stable crystal structure and excellent sodium storage kinetics, and has attracted widespread attention. As one of the polyanion type positive electrode materials, sodium ferric sulfate has the advantages of low raw material cost, simple preparation process, green environmental protection and simple synthesis, and is considered to be one of the most promising positive electrode materials for the industrialization of sodium ion batteries.

[0003] The preparation method of sodium ferric sulfate generally comprises mixing iron salt and sodium salt to obtain a precursor, and then sintering at a low temperature to obtain the positive electrode material. Since the sulfate radical is easily decomposed at high temperature, the sintering temperature is generally not more than 400 DEG C. To obtain a sample with high phase purity at a relatively low temperature, the iron salt and the sodium salt in the precursor need to be uniformly mixed. Compared with the solid phase method, atomic-level uniform mixing can be achieved in the liquid phase, and by controlling the precipitation of iron salt and sodium salt, a highly mixed precursor can be obtained.

[0004] In the invention patent application with the publication number CN116093292A and the name of a method for preparing carbon-coated sodium ferric sulfate material, carbon-coated sodium ferric sulfate material and battery, it is disclosed that by using the action of cetyltrimethylammonium bromide (CTAB) and metal salt, ferrous sulfate heptahydrate and anhydrous sodium sulfate are precipitated, then the mixed solution is solid-liquid separated and dried to obtain a precursor powder, and finally the precursor powder is calcined in an inert atmosphere to obtain a sodium ferric sulfate positive electrode material. In this method, the saturation micellar concentration needs to be reached to make the precipitation precipitate, so although the amount of CTAB does not affect the performance of the product, a large amount of CTAB needs to be added to obtain the product, and the yield is also low.

[0005] In the invention patent application with the publication number CN114050246A and the title of Micro-porous sodium ferrous sulfate / carbon composite positive electrode material and preparation of sodium ion battery or sodium battery, a precursor is prepared by a precipitation method, that is, a certain proportion of ethylene glycol and graphene oxide powder are dispersed into deionized water, ultrasonic dispersion is uniform, then iron salt, sodium salt, antioxidant and organic carbon are added and stirred uniformly, then organic alcohol is added dropwise and stirred, then the obtained turbid solution is centrifuged and freeze-dried to obtain the required precursor; a large amount of alcohol is required to obtain a high precursor yield. SUMMARY

[0006] The purpose of the present application is to provide a sodium ferrite positive electrode material and a synthesis method thereof to solve the problems of low yield or large raw material consumption of existing synthesis methods.

[0007] To achieve the above purpose, the present application provides the following technical solution: a synthesis method of a sodium ferrite positive electrode material, comprising the following specific contents:

[0008] S1. Take ferrous sulfate heptahydrate and anhydrous sodium sulfate and add them into water saturated with nitrogen, fully dissolve to obtain an aqueous solution of metal salt, and then add an appropriate amount of organic alcohol to mix uniformly to obtain a mixed solution;

[0009] S2. Maintain the reaction environment to prevent oxidation of ferrous ions, control the temperature of the mixed solution, add an appropriate amount of cationic surfactant, fully stir, then collect the precipitate by filtration or centrifugation, wash the precipitate with ethanol, then vacuum dry or freeze-dry to obtain the required precursor;

[0010] S3. Grind the precursor, then low-temperature calcine under a protective atmosphere to obtain a sodium ferrite positive electrode material.

[0011] Preferably, the molar ratio of iron salt to sodium salt added to the mixed solution is (0.6-1.6):1; the volume ratio of water to organic alcohol added to the mixed solution is (1-5):1; and the mass ratio of iron salt and sodium salt to water added to the mixed solution is (0.5-0.8):1.

[0012] Preferably, the organic alcohol is one or more of methanol, ethanol, isopropanol, n-butanol, and sec-butanol.

[0013] Preferably, the temperature of the mixed solution is controlled at 10-70℃.

[0014] Preferably, the cationic surfactant is selected from CTAB, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium hexadecyl sulfate, and benzalkonium chloride.

[0015] Preferably, the mass of the cationic surfactant accounts for 0.5%-3% of the total mass of ferrous sulfate and anhydrous sodium sulfate in the mixed solution.

[0016] Preferably, the reaction environment for preventing ferrous oxidation is a nitrogen atmosphere or adding a sufficient amount of an antioxidant that does not participate in the reaction.

[0017] Preferably, the protective atmosphere is nitrogen or argon, the calcination temperature is 200-400 DEG C, and the calcination time is 6-20 h.

[0018] Preferably, the yield of the above synthesis method is 83-94%.

[0019] The application provides another technical scheme, i.e., a sodium ferric sulfate positive electrode material prepared by the above synthesis method, which has a stable rod-like structure under SEM, a capacity retention rate of more than 100% after 200 cycles of a button cell test, and a charge-discharge efficiency maintained at 100%.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] 1. The sodium ferric sulfate positive electrode material and the synthesis method thereof utilize the self-assembly characteristics of CTAB and other surfactants in a water / alcohol system, i.e., the surfactants are more likely to form micelles and precipitate in a water / alcohol system, so that a large amount of iron salt and sodium salt can be precipitated by using a small amount of alcohol and a small amount of surfactant, and the yield of the precursor is ensured by using a small amount of raw material, the method is simple in operation, green and environmentally friendly, and easy to scale up, and is more suitable for large-scale industrial application.

[0022] 2. The sodium ferric sulfate positive electrode material and the synthesis method thereof utilize the cationic surfactant to form spherical micelles with a dense ionic shell and a diffusion double layer in an aqueous solution, and after adding an organic alcohol, the alcohol can act as an auxiliary surfactant to induce a structure transition at a low surfactant concentration, and the spherical micelles are converted into rod-like micelles, the structure is highly ordered, the positive electrode material prepared after heat treatment has high phase purity and good structure stability, and the positive electrode material has better cycle stability and rate performance.

[0023] 3. The sodium ferric sulfate positive electrode material and the synthesis method thereof use a small amount of alcohol to form a water / alcohol mixed system, and then add CTAB and other surfactants to self-assemble into micelles and precipitate iron salt and sodium salt to obtain a precursor, the method is beneficial to reducing the production energy consumption because the iron and sodium are mixed uniformly and can be sintered into sodium ferric sulfate at a lower sintering temperature. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a scanning electron microscope (SEM) image of a sample prepared in Example 1 in the application.

[0025] Figure 2 is an X-ray powder diffraction (XRD) image of a sample prepared in Example 1 in the application.

[0026] Figure 3is the charge-discharge curve of the sample prepared in Example 1 of the present application.

[0027] Figure 4 is the discharge capacity of the sample prepared in Example 1 of the present application under 1C cycle condition. DETAILED DESCRIPTION

[0028] A synthesis method of sodium ferric sulfate positive electrode material, comprising the following specific contents:

[0029] S1. Take ferrous sulfate heptahydrate and anhydrous sodium sulfate into water saturated with nitrogen, and fully dissolve to obtain an aqueous solution of metal salt, wherein the molar ratio of iron salt to sodium salt can be further preferably (0.6-1.6):1, and the mass ratio of solute to solvent can be further preferably (0.5-0.8):1 of iron salt and sodium salt:water; an appropriate amount of organic alcohol is added to the aqueous solution and mixed uniformly to obtain a mixed solution, and the volume ratio of water to organic alcohol can be further preferably (1-5):1, and optionally, the organic alcohol is preferably one or more of methanol, ethanol, isopropanol, n-butanol, sec-butanol, etc.

[0030] S2. Maintain the reaction environment to prevent oxidation of ferrous iron (for example, maintain a nitrogen atmosphere, or add a sufficient amount of antioxidant that does not participate in the reaction, such as ascorbic acid, etc.), control the temperature of the mixed solution, which is generally room temperature, preferably controlled at 10-70℃, and add an appropriate amount of cationic surfactant (which can be selected from CTAB, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium hexadecyl sulfate, benzalkonium chloride, etc.), and the mass of the cationic surfactant can be 0.5%-3% of the total mass of ferrous sulfate and anhydrous sodium sulfate in the mixed solution, after fully stirring, the precipitate is collected by suction filtration or centrifugation, the precipitate is washed with ethanol and then vacuum dried or freeze-dried to obtain the desired precursor;

[0031] S3. After grinding the precursor, a sodium ferric sulfate positive electrode material is obtained by low-temperature calcination under a protective atmosphere, and in a more preferred embodiment, the protective atmosphere is nitrogen or argon, the calcination temperature is 200-400℃, and the calcination time is 6-20h.

[0032] The yield of the sodium ferric sulfate positive electrode material obtained by the above synthesis method is 83%-94%, as described in Figure 1, the prepared sodium ferric sulfate positive electrode material is a stable rod-like structure under SEM; the prepared sodium ferric sulfate material, conductive agent Super P and binder PVDF are mixed in a weight ratio of 8:1:1 to prepare a positive electrode slurry, which is coated on one side of an aluminum foil surface, dried to prepare a positive electrode sheet, and assembled into a button cell in the order of negative electrode shell, sodium sheet, separator, electrolyte, positive electrode sheet, gasket, spring and positive electrode shell, wherein the electrolyte is 1M NaClO4, the solvent is PC, the separator is GF / C type glass fiber, the test voltage is 2-4.5V, and the charging is carried out by constant current and then the discharging is carried out by constant current, wherein the theoretical capacity of the positive electrode material is 120mAh / g, the capacity test charging and discharging current is 0.1C, and the constant current charging and discharging is carried out under 1C current in the cycle test, and refer to Figure 4 After 200 cycles of the above conventional button cell test, the capacity retention rate is greater than 100%, and the charging and discharging efficiency is maintained at 100%.

[0033] Example 1

[0034] Take 172.8g of ferrous sulfate heptahydrate and 85.2g of anhydrous sodium sulfate and add them to 400ml of nitrogen-saturated water, fully dissolve to obtain a metal salt aqueous solution, then add 100ml of ethanol and fully stir. Keep the temperature of the above mixture at 40°C under a nitrogen atmosphere, then add 1.8g of CTAB, fully stir to obtain a precursor precipitate, collect the precipitate using suction filtration and wash it with ethanol, then dry it in a vacuum drying oven overnight to obtain the desired precursor. Grind the precursor into powder, then calcine it in a tube furnace under the condition of 300°C for 6h under nitrogen, then naturally cool to obtain the desired sodium ferric sulfate positive electrode material.

[0035] The XRD pattern of the sodium ferric sulfate positive electrode material prepared by the above method is shown in the patent Figure 2 The final yield of the sodium ferric sulfate positive electrode material of Example 1 is 92%. The SEM image of the sample prepared in Example 1 is shown in the patent Figure 1 , which is a rod-like structure. This ordered structure is beneficial to the rapid transmission of sodium ions and has good structural stability, so it has higher mass specific capacity and better cycle performance. The charge-discharge curve of the button cell prepared in Example 1 is shown in the patent Figure 3 , and the discharge specific capacity is 75.9mAh / g. The discharge capacity retention rate under 1C condition is 84.1%, and the capacity retention rate after 200 cycles of charging and discharging is 105.6%. The reason is that the electrolyte is fully soaked, the capacity increases, and the charging and discharging efficiency is maintained at 100%.

[0036] Comparative Example 1

[0037] This example is performed according to example 1, except that the ethanol added during the solution preparation is replaced by water. In this comparative example, no precipitate is formed upon addition of CTAB under vigorous stirring, because in the pure water system, the CTAB concentration is too low to reach the condition of micelle formation.

[0038] Comparative example 2

[0039] This example is performed according to example 1, except that the ethanol added during the solution preparation is replaced by water, and the amount of CTAB added is adjusted to 14.3 g. A precipitate is formed upon vigorous stirring, and the final product yield is 39%. Compared to example 1 and comparative example 1, the percentage of CTAB in the total mass of ferrous sulfate and anhydrous sodium sulfate in the mixture is increased from 1% to 8%. The discharge capacity retention under 1C is 63.5%, and the capacity retention after 200 charge-discharge cycles is 85.6%.

[0040] Comparative example 3

[0041] This example is performed according to example 1, except that no CTAB is added. No precipitate is formed in the water and ethanol system, because the ethanol content is too low to reach the condition of crystal precipitation.

[0042] Comparative example 4

[0043] This example is performed according to example 1, except that no CTAB is added, and the amount of ethanol added is adjusted to 800 ml. A precipitate is formed upon vigorous stirring, and the final product yield is 31%. Compared to example 1 and comparative example 2, the volume ratio of water to ethanol is changed from 4 to 0.5, i.e. more ethanol is needed. The discharge capacity retention under 1C is 72.4%, and the capacity retention after 200 charge-discharge cycles is 89.4%.

[0044] Example 2

[0045] This example is performed according to example 1, except that the amount of anhydrous sodium sulfate is changed to 53.3 g, i.e. the molar ratio of iron salt to sodium salt is 1.6:1.

[0046] Example 3

[0047] This example is performed according to example 1, except that the amount of anhydrous sodium sulfate is changed to 142.5 g, i.e. the molar ratio of iron salt to sodium salt is 0.6:1.

[0048] Example 4

[0049] This example is performed according to example 1, except that the organic alcohol ethanol is replaced by isopropanol.

[0050] Example 5

[0051] This example was carried out according to Example 1, except that the amount of ethanol was changed to 400 ml.

[0052] Example 6

[0053] This example was carried out according to Example 1, except that the precipitation reaction temperature was changed to 10°C.

[0054] Example 7

[0055] This example was carried out according to Example 1, except that the precipitation reaction temperature was changed to 70°C.

[0056] Example 8

[0057] This example was carried out according to Example 1, except that the surfactant CTAB was replaced by sodium dodecyl benzene sulfonate.

[0058] Example 9

[0059] This example was carried out according to Example 1, except that the amount of CTAB was changed to 0.9 g, i.e. CTAB accounted for 0.5% of the total mass percentage of ferrous sulfate and anhydrous sodium sulfate in the mixed solution.

[0060] Example 10

[0061] This example was carried out according to Example 1, except that the amount of CTAB was changed to 2.7 g, i.e. CTAB accounted for 3% of the total mass percentage of ferrous sulfate and anhydrous sodium sulfate in the mixed solution.

[0062] Example 11

[0063] This example was carried out according to Example 1, except that the calcination time was changed to 20 h.

[0064] Example 12

[0065] This example was carried out according to Example 1, except that the calcination temperature was changed to 200°C.

[0066] Example 13

[0067] This example was carried out according to Example 1, except that the calcination temperature was changed to 400°C.

[0068] The yield and battery capacity test results of the examples and comparative examples are shown in the following table:

[0069] Table 1: Yield and test results of comparative examples and examples

[0070]

[0071] As shown in the above table 1, the sodium ferric sulfate positive electrode material prepared by the method of the present application has high yield, which is between 83% and 94%, and relatively large battery capacity, so that the application in production can reduce resource waste, reduce production cost, and the product performance can be guaranteed.

[0072] The above only is the preferred embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be limited by the protection scope defined by the claims.

[0073] The part not described in the present application is the known technology of the person skilled in the art.

Claims

1. A method for synthesizing a sodium ferric sulfate cathode material, characterized in that, The application relates to a synthesis method of a sodium ferric sulfate positive electrode material. S1. Seven ferrous sulfate heptahydrate and anhydrous sodium sulfate are added into nitrogen-saturated water, fully dissolved to obtain a metal salt aqueous solution, and an appropriate amount of organic alcohol is added and uniformly mixed to obtain a mixed solution; S2. A reaction environment preventing ferrous oxidation is maintained, the temperature of the mixed solution is controlled, an appropriate amount of cationic surfactant is added, and after fully stirring, the precipitate is collected by filtration or centrifugation, the precipitate is washed with ethanol, and then vacuum drying or freeze drying is carried out to obtain the required precursor; S3. The precursor is ground into powder, and then low-temperature calcination is carried out under a protective atmosphere to obtain the sodium ferric sulfate positive electrode material; In the step S1, the molar ratio of the iron salt to the sodium salt added into the mixed solution is (0.6-1.6):1; the volume ratio of water to the organic alcohol added into the mixed solution is (1-5):1; and the mass ratio of the iron salt and the sodium salt to water added into the mixed solution is (0.5-0.8):

1. In the step S2, the temperature of the mixed solution is controlled to be 10-70 DEG C; and the mass of the cationic surfactant accounts for 0.5%-3% of the total mass of the ferrous sulfate and the anhydrous sodium sulfate in the mixed solution. In the step S3, the protective atmosphere is nitrogen or argon, the calcination temperature is 200-400 DEG C, and the calcination time is 6-20 h.

2. The method of claim 1, wherein the method is characterized by: In the step S1, the organic alcohol is one or more of methanol, ethanol, isopropyl alcohol, n-butyl alcohol and sec-butyl alcohol. 3.The method of claim 1, wherein the method further comprises: adding a sodium hydroxide solution to the mixture of claim 1 to form a precipitate; and washing the precipitate with water to obtain a sodium ferric sulfate product. In the step S2, the cationic surfactant is selected from CTAB and benzalkonium chloride. 4.The method of claim 1, wherein the method is characterized by: In the step S2, the reaction environment preventing ferrous oxidation is a nitrogen atmosphere or the addition of a sufficient amount of an antioxidant not participating in the reaction.

5. The method for synthesizing a sodium ferric sulfate positive material according to any one of claims 1 to 4, characterized in that: The yield of the synthesis method is 83%-94%.

6. The sodium iron sulfate positive electrode material according to any one of claims 1 to 4, characterized in that: The sodium ferric sulfate positive electrode material has a stable rod-like structure under SEM.

Images