A method for regenerating a sodium ferric sulfate material and a regenerated sodium ferric sulfate material

Abstract

The application discloses a sodium ferric sulfate material regeneration method and a regenerated sodium ferric sulfate material, relates to the technical field of sodium ferric sulfate material regeneration, and comprises the following steps: adding the sodium ferric sulfate material into a weak alkaline cleaning solution and heating and stirring, filtering to obtain first filter residue, and washing the first filter residue; adding the washed first filter residue into a reducing cleaning solution and heating and stirring in an inert gas atmosphere, filtering to obtain second filter residue, and washing and drying the second filter residue; adding the dried second filter residue into a solvent, ultrasonic dispersion to obtain a suspension, adding an iron source, a sodium source and a composite modifier into the suspension and heating and stirring to obtain a precursor solution, and spray drying the precursor solution to obtain a precursor powder; under an inert gas atmosphere, the precursor powder is subjected to stage sintering, and after sintering, cooling to room temperature to obtain the regenerated sodium ferric sulfate material. The application improves the purification effect through double cleaning of the weak alkaline cleaning solution and the reducing cleaning solution.

Description

Technical Field

[0001] This application relates to the technical field of sodium ferric sulfate material regeneration, specifically to a method for regenerating sodium ferric sulfate material and the regenerated sodium ferric sulfate material. Background Technology

[0002] With the large-scale application of sodium-ion batteries, the efficient recycling and regeneration of sodium iron sulfate cathode materials has become a key issue; however, existing recycling technologies still have significant limitations. While conventional acid leaching can leach out active metal components, this process easily induces Fe... 2+ Oxidized to Fe 3+ This damages the integrity of the sodium ferric sulfate crystal structure and makes it difficult to effectively remove electrolyte decomposition products such as carbonate derivatives attached to the surface of the sodium ferric sulfate cathode material, resulting in severe performance degradation of the recycled material due to surface contamination and valence imbalance. Summary of the Invention

[0003] The first aspect of this application provides a method for regenerating sodium ferric sulfate material, comprising the following steps: Step S1: Provide sodium ferric sulfate material to be processed; Step S2: Add the sodium ferric sulfate material to be treated to a weakly alkaline cleaning solution and heat and stir at a first temperature. Then filter to obtain the first filter residue and wash the first filter residue. Step S3: Add the washed first filter residue to the reducing cleaning solution and heat and stir in an inert gas atmosphere and at a second temperature. Then filter to obtain the second filter residue, and wash and dry the second filter residue. Step S4: Add the dried second filter residue to the solvent, ultrasonically disperse to obtain a suspension, add iron source, sodium source and composite modifier to the suspension and heat and stir at a third temperature to obtain a precursor solution, spray dry the precursor solution to obtain precursor powder; Step S5: Under an inert gas atmosphere, the precursor powder is sintered in stages, and then cooled to room temperature to obtain recycled sodium ferric sulfate material.

[0004] In some optional embodiments of the first aspect of this application, the first temperature in step S2 is 30°C to 40°C; The heating and stirring time at the first temperature is 30 min to 60 min; Washing the first filter residue includes washing it with deionized water until the pH of the filtrate is 7.0 to 7.5.

[0005] In some optional embodiments of the first aspect of this application, the weakly alkaline cleaning solution is selected from sodium bicarbonate solution, wherein the concentration of sodium bicarbonate in the sodium bicarbonate solution is 0.05 mol / L to 0.1 mol / L; The solid-liquid ratio of the sodium ferric sulfate material to be treated to the weakly alkaline cleaning solution is 1:(10~20), with units of g / mL.

[0006] In some optional embodiments of the first aspect of this application, the second temperature in step S3 is 40°C to 50°C; The heating and stirring time in an inert gas atmosphere and at the second temperature is 60 min to 90 min. Washing and drying the second filter residue includes: washing the second filter residue with deionized water until the filtrate is no longer reducing, and then vacuum drying the washed second filter residue at 80℃~100℃ for 4h~6h.

[0007] In some optional embodiments of the first aspect of this application, the reducing cleaning solution includes sodium bisulfite and citric acid, wherein the concentration of sodium bisulfite in the reducing cleaning solution is 0.1 mol / L to 0.2 mol / L; Based on the total mass of the reducing cleaning solution, the mass fraction of citric acid is 0.5%~1%; The solid-liquid ratio between the first filter residue after washing and the reducing cleaning solution is 1:(15~25), with the unit being g / mL.

[0008] In some optional embodiments of the first aspect of this application, the mass fraction of the composite modifier is 2% to 5% based on the total mass of the precursor powder; The composite modifier includes ammonium dihydrogen phosphate and sucrose, with a mass ratio of ammonium dihydrogen phosphate to sucrose of 1:(2~3). The molar ratio of Na to Fe in the precursor powder is (1.0~1.05):1.

[0009] In some optional embodiments of the first aspect of this application, the third temperature in step S4 is 50°C to 60°C; The heating and stirring time at the third temperature is 60-90 minutes.

[0010] In some optional embodiments of the first aspect of this application, the staged sintering in step S5 includes: First, the temperature is increased to 300℃~350℃ at a rate of 2℃ / min~3℃ / min, and held for 2h~3h for pre-sintering; then the temperature is increased to 600℃~650℃ at a rate of 1℃ / min~2℃ / min, and held for 4h~6h for secondary sintering.

[0011] In some optional embodiments of the first aspect of this application, the sodium ferric sulfate material to be treated in step S1 includes: The sodium iron sulfate sodium ion battery to be processed is disassembled to obtain the positive electrode sheet, and the positive electrode sheet is mechanically crushed to a particle size of 5mm~10mm. Under an inert gas atmosphere, the broken positive electrode sheet is added to a mixed solvent, and then ultrasonically exfoliated for 20 min to 40 min at 25℃~35℃ and ultrasonic power of 200W~300W to obtain active material powder. The active material powder was vacuum dried at 60℃~80℃ for 8h~12h to obtain sodium ferric sulfate material to be treated. The mixed solvent includes sodium dodecylbenzenesulfonate, anhydrous ethanol, and deionized water; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 1:(3~5); based on the total mass of the mixed solvent, the mass fraction of sodium dodecylbenzenesulfonate is 0.1%~0.3%.

[0012] The second aspect of this application provides a regenerated sodium ferric sulfate material, which is prepared by the above-described method for regenerating sodium ferric sulfate material.

[0013] Beneficial effects: The method for regenerating sodium ferric sulfate material provided in the first aspect of this application involves first cleaning the sodium ferric sulfate material to be treated with a weakly alkaline cleaning solution to remove electrolyte decomposition byproducts, obtaining a first filter residue, and then cleaning the first filter residue with a reducing cleaning solution to remove Fe. 3+ Reduced to Fe 2+ Organic impurities are removed to obtain a second filter residue. An iron source, a sodium source, and a composite modifier are introduced into the second filter residue, followed by staged calcination. This process repairs crystal defects in the sodium ferric sulfate material while simultaneously forming protective PO4 on the sodium ferric sulfate material. 3- Carbon doping is used to coat the interface layer to improve the stability of sodium ferric sulfate materials.

[0014] The recycled sodium ferric sulfate material provided in the second aspect of this application has a low content of organic impurities and a low water absorption rate at room temperature. At the same time, the recycled sodium ferric sulfate material has good electrochemical performance and stability. Attached Figure Description

[0015] Figure 1 This is a flowchart of a method for regenerating sodium ferric sulfate material in one embodiment of this application. Detailed Implementation

[0016] The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present application and are not intended to limit the present application.

[0017] In one embodiment, a method for regenerating sodium ferric sulfate material includes the following steps: Step S1: Provide sodium ferric sulfate material to be processed; Step S2: Add the sodium ferric sulfate material to be treated to a weakly alkaline cleaning solution and heat and stir at a first temperature. Then filter to obtain the first filter residue and wash the first filter residue. Step S3: Add the washed first filter residue to the reducing cleaning solution and heat and stir in an inert gas atmosphere and at a second temperature. Then filter to obtain the second filter residue, and wash and dry the second filter residue. Step S4: Add the dried second filter residue to the solvent, ultrasonically disperse to obtain a suspension, add iron source, sodium source and composite modifier to the suspension and heat and stir at a third temperature to obtain a precursor solution, spray dry the precursor solution to obtain precursor powder; Step S5: Under an inert gas atmosphere, the precursor powder is sintered in stages, and then cooled to room temperature to obtain recycled sodium ferric sulfate material.

[0018] In this embodiment, the sodium ferric sulfate material to be processed is obtained from the dismantling of recycled sodium ferric sulfate sodium-ion batteries. The sodium ferric sulfate material to be processed has a high particle size and a dense crystal lattice. First, the sodium ferric sulfate material to be processed is added to a weakly alkaline cleaning solution and heated and stirred. Filtering is then performed to obtain a first filter residue, which removes electrolyte decomposition products such as sodium salts and carbonate derivatives from the surface of the sodium ferric sulfate material. The first filter residue is washed to remove residual weakly alkaline cleaning solution. After washing, the first filter residue is added to a reducing cleaning solution, and the Fe in the first filter residue is removed by heating and stirring under an inert gas atmosphere. 3+ Reduced to Fe 2+ The second filter residue is obtained by filtration to remove residual organic impurities on the surface of the sodium ferric sulfate material. After washing and drying, the second filter residue is mixed with deionized water to form a suspension. An iron source, a sodium source, and a composite modifier are added, and the mixture is heated and stirred to obtain a precursor solution. The precursor solution is spray-dried to obtain a precursor powder. Under an inert gas atmosphere, the precursor powder is sintered in stages, and after cooling to room temperature, the regenerated sodium ferric sulfate material is obtained.

[0019] This embodiment abandons the strong oxidizing acid leaching system and adopts a two-stage cleaning process. First, the carbonate polymer is hydrolyzed with a weakly alkaline cleaning solution to remove electrolyte decomposition byproducts. Then, under an inert atmosphere to prevent oxygen introduction, a reducing cleaning solution is used to remove Fe. 3+ Reduced to Fe 2+ It removes organic impurities, improves purification efficiency, and avoids incomplete purification or material damage caused by single cleaning. At the same time, the optimized cleaning process avoids secondary adhesion of salt crystals, significantly reduces interfacial resistance, and provides a clean reaction substrate for subsequent repair.

[0020] In this embodiment, a composite modifier and staged sintering are introduced during the sodium ferric sulfate regeneration stage. This repairs the crystal defects of the sodium ferric sulfate material while forming a protective PO4 layer on the material. 3- Carbon doping is used to coat the interface layer to improve the stability of sodium ferric sulfate materials.

[0021] In some optional embodiments of this application, the first temperature in step S2 is 30°C to 40°C, and the heating and stirring time at the first temperature is 30 min to 60 min. Under this first temperature range and heating and stirring time, the surface electrolyte decomposition products and organic impurities are gently removed by a weakly alkaline cleaning solution without significantly damaging the main sodium ferric sulfate crystals.

[0022] In some optional embodiments of this application, washing the first filter residue includes washing the first filter residue with deionized water until the pH of the filtrate is 7.0 to 7.5.

[0023] In some optional embodiments of this application, the weakly alkaline cleaning solution is selected from sodium bicarbonate solution, wherein the concentration of sodium bicarbonate in the sodium bicarbonate solution is 0.05 mol / L to 0.1 mol / L.

[0024] In some optional embodiments of this application, the solid-liquid ratio of the sodium ferric sulfate material to be treated to the weakly alkaline cleaning solution is 1:(10~20), in g / mL.

[0025] In some optional embodiments of this application, the second temperature in step S3 is 40°C to 50°C, and the heating and stirring time in the inert gas atmosphere and at the second temperature is 60 min to 90 min.

[0026] In some optional embodiments of this application, washing and drying the second filter residue includes: washing the second filter residue with deionized water until the filtrate is non-reducible, and then vacuum drying the washed second filter residue at 80°C to 100°C for 4 to 6 hours.

[0027] In this embodiment, the absence of color fading in the filtrate is considered a sign of "non-reducing properties of the filtrate" when tested with potassium permanganate solution.

[0028] In some optional embodiments of this application, the reducing cleaning solution includes sodium bisulfite and citric acid; the concentration of sodium bisulfite in the reducing cleaning solution is 0.1 mol / L to 0.2 mol / L; and the mass fraction of citric acid is 0.5% to 1% based on the total mass of the reducing cleaning solution. The buffering and weak reducing effect of the 0.1 mol / L to 0.2 mol / L sodium bisulfite in the reducing cleaning solution maintains the pH of the reducing cleaning solution within the range of 6.5 to 7.0, avoiding the risk of acidic leaching; and combined with low-temperature stirring, a mild impurity removal environment is constructed, achieving efficient removal of organic impurities while minimizing the breaking and complexation dissolution of the sodium ferric sulfate bulk lattice.

[0029] In some optional embodiments of this application, the solid-liquid ratio between the washed first filter residue and the reducing cleaning solution is 1:(15~25), in g / mL.

[0030] In some optional embodiments of this application, the mass fraction of the composite modifier is 2% to 5% based on the total mass of the precursor powder; the composite modifier includes ammonium dihydrogen phosphate and sucrose, and the mass ratio of ammonium dihydrogen phosphate to sucrose is 1:(2 to 3).

[0031] In this embodiment, ammonium dihydrogen phosphate and sucrose are introduced as composite modifiers. During sintering, ammonium dihydrogen phosphate decomposes to provide PO4. 3- In-situ doping into the crystal lattice surface forms stable NaFe(SO4). 1-x (PO4) x The gradient interface layer effectively blocks moisture intrusion, inhibits water absorption by the material, and suppresses Fe... 2+ Oxidation; at the same time, the continuous conductive carbon network formed by the pyrolysis of sucrose provides the electronic conductivity of the material and enhances the structural integrity between particles.

[0032] In some optional embodiments of this application, the molar ratio of Na to Fe in the precursor powder is (1.0~1.05):1.

[0033] In this embodiment, the sodium source is selected from anhydrous sodium sulfate, and the iron source is selected from ferrous ammonium sulfate. The amount of iron and sodium source supplemented is determined based on the amount of Fe and Na lost from the dried second filter residue.

[0034] In some optional embodiments of this application, the third temperature in step S4 is 50°C to 60°C; the heating and stirring time at the third temperature is 60 min to 90 min.

[0035] In some optional embodiments of this application, the spray drying conditions are an inlet temperature of 180°C to 200°C and an outlet temperature of 80°C to 100°C.

[0036] In some optional embodiments of this application, the staged sintering in step S5 includes: First, the temperature is increased to 300℃~350℃ at a rate of 2℃ / min~3℃ / min, and held for 2h~3h for pre-sintering; then the temperature is increased to 600℃~650℃ at a rate of 1℃ / min~2℃ / min, and held for 4h~6h for secondary sintering.

[0037] In this embodiment, residual organic matter is removed by pre-sintering, and then the material lattice defects are repaired by secondary sintering. This avoids the generation of impurity phases or structural damage caused by single-temperature sintering, ensures crystal integrity, and achieves crystal structure repair and interface coating.

[0038] In some optional embodiments of this application, the sodium ferric sulfate material to be treated in step S1 includes: The sodium iron sulfate sodium ion battery to be processed is disassembled to obtain the positive electrode sheet, and the positive electrode sheet is mechanically crushed to a particle size of 5mm~10mm. Under an inert gas atmosphere, the broken positive electrode sheet is added to a mixed solvent, and then ultrasonically exfoliated for 20 min to 40 min at 25℃~35℃ and ultrasonic power of 200W~300W to obtain active material powder. The active material powder was vacuum dried at 60℃~80℃ for 8h~12h to obtain sodium ferric sulfate material to be treated. The mixed solvent comprises sodium dodecylbenzenesulfonate, anhydrous ethanol, and deionized water; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 1:(3~5); based on the total mass of the mixed solvent, the mass fraction of sodium dodecylbenzenesulfonate is 0.1%~0.3%. With this configuration, the use of anhydrous ethanol in the mixed solvent reduces the polarity of water molecules and their ability to penetrate the crystal lattice, thus only removing impurities from the surface of the sodium ferric sulfate material without significantly dissolving the main crystal of the sodium ferric sulfate material.

[0039] In this embodiment, the surface of the regenerated sodium ferric sulfate material has no organic solvent residue, which avoids side reactions with the electrolyte and improves the cycle stability of the battery.

[0040] This embodiment achieves comprehensive and systematic repair through gradient purification to remove surface contaminants, composite modifier doping to repair lattice distortion and replenish lost ions, and high-temperature sintering to reconstruct the conductive network. The "purify first, then repair" process effectively prevents the formation of impurities during high-temperature sintering. Simultaneously, the introduction of the composite modifier inhibits particle agglomeration at high temperatures, promoting the formation of uniform and dense PO4. 3- The formation of a carbon-doped coating creates an efficient electron / ion transport channel, enhancing the material's conductivity and structural stability.

[0041] In another embodiment, a regenerated sodium ferric sulfate material is provided, which is prepared by the above-described method for regenerating sodium ferric sulfate material.

[0042] The present application is further illustrated below with reference to embodiments and comparative examples. Unless otherwise specified, the raw materials, reagents, materials and equipment used in this application are all commercially available sodium ferric sulfate commonly used in the art.

[0043]

Example 1

[0044] Step 2: Add the sodium ferric sulfate material to be treated to a 0.08 mol / L sodium bicarbonate solution. The solid-liquid ratio between the sodium ferric sulfate material to be treated and the sodium bicarbonate solution is 1:15 (g / mL). Heat and stir at 35℃ for 45 min, then filter to obtain the first filter residue. Wash the first filter residue with deionized water until the pH of the filtrate is 7.2.

[0045] Step 3: Add the washed first filter residue to a reducing cleaning solution containing 0.15 mol / L sodium bisulfite and 0.8% citric acid. The solid-liquid ratio between the washed first filter residue and the reducing cleaning solution is 1:20 (g / mL). Then, under nitrogen protection, heat and stir at 45°C for 75 min. After that, filter to obtain the second filter residue. Wash the second filter residue with deionized water until the washing filtrate shows no fading when tested with potassium permanganate solution. Dry the washed second filter residue under vacuum at 90°C for 5 h.

[0046] Step 4: Use ICP to detect the molar ratio of Na to Fe in the dried second filter residue. Add the dried second filter residue to deionized water and ultrasonically disperse for 30 min to obtain a suspension. Add ferrous ammonium sulfate and anhydrous sodium sulfate to the suspension according to the stoichiometric ratio of Na:Fe = 1.02:1. At the same time, add 3% of the total mass of the precursor powder as a composite modifier (ammonium dihydrogen phosphate: sucrose = 1:2.5 in the composite modifier). Heat and stir at 55℃ for 75 min to obtain a precursor solution. Spray dry the precursor solution (inlet temperature 190℃, outlet temperature 90℃) to obtain the precursor powder.

[0047] Step 5: Place the precursor powder in an argon furnace, heat it to 320℃ at 2.5℃ / min and hold for 2.5h, then heat it to 620℃ at 1.5℃ / min and hold for 5h, and cool it to room temperature under argon protection to obtain the regenerated sodium ferric sulfate material.

[0048]

Example 2

[0049] Step 2: Add the sodium ferric sulfate material to be treated to a 0.05 mol / L sodium bicarbonate solution. The solid-liquid ratio between the sodium ferric sulfate material to be treated and the sodium bicarbonate solution is 1:10 (g / mL). Heat and stir at 30℃ for 60 min, then filter to obtain the first filter residue. Wash the first filter residue with deionized water until the pH of the filtrate is 7.0.

[0050] Step 3: Add the washed first filter residue to a reducing cleaning solution containing 0.1 mol / L sodium bisulfite and 0.5% citric acid. The solid-liquid ratio between the washed first filter residue and the reducing cleaning solution is 1:15 (g / mL). Then, under nitrogen protection, heat and stir at 40°C for 90 min. After that, filter to obtain the second filter residue. Wash the second filter residue with deionized water until the washing filtrate shows no fading when tested with potassium permanganate solution. Dry the washed second filter residue under vacuum at 90°C for 5 h.

[0051] Step 4: Use ICP to detect the molar ratio of Na to Fe in the dried second filter residue. Add the dried second filter residue to deionized water and ultrasonically disperse for 30 min to obtain a suspension. Add ferrous ammonium sulfate and anhydrous sodium sulfate to the suspension according to the stoichiometric ratio of Na:Fe = 1.0:1. At the same time, add 2% of the total mass of the precursor powder as a composite modifier (ammonium dihydrogen phosphate: sucrose = 1:2 in the composite modifier). Heat and stir at 50℃ for 90 min to obtain a precursor solution. Spray dry the precursor solution (inlet temperature 180℃, outlet temperature 80℃) to obtain the precursor powder.

[0052] Step 5: Place the precursor powder in an argon furnace, heat it to 300℃ at 2℃ / min and hold for 3 hours, then heat it to 600℃ at 1℃ / min and hold for 6 hours. Cool it to room temperature under argon protection to obtain the regenerated sodium ferric sulfate material.

[0053]

Example 3

[0054] Step 2: Add the sodium ferric sulfate material to be treated to a 0.1 mol / L sodium bicarbonate solution. The solid-liquid ratio between the sodium ferric sulfate material to be treated and the sodium bicarbonate solution is 1:20 (g / mL). Heat and stir at 40℃ for 30 min, then filter to obtain the first filter residue. Wash the first filter residue with deionized water until the pH of the filtrate is 7.5.

[0055] Step 3: Add the washed first filter residue to a reducing cleaning solution containing 0.2 mol / L sodium bisulfite and 1% citric acid. The solid-liquid ratio between the washed first filter residue and the reducing cleaning solution is 1:25 (g / mL). Then, under nitrogen protection, heat and stir at 50°C for 60 min. After that, filter to obtain the second filter residue. Wash the second filter residue with deionized water until the washing filtrate shows no fading when tested with potassium permanganate solution. Dry the washed second filter residue under vacuum at 90°C for 5 h.

[0056] Step 4: Use ICP to detect the molar ratio of Na to Fe in the dried second filter residue. Add the dried second filter residue to deionized water and ultrasonically disperse for 30 min to obtain a suspension. Add ferrous ammonium sulfate and anhydrous sodium sulfate to the suspension according to the stoichiometric ratio of Na:Fe = 1.05:1. At the same time, add a composite modifier (ammonium dihydrogen phosphate: sucrose = 1:3 in the composite modifier) ​​accounting for 5% of the total mass of the precursor powder. Heat and stir at 60℃ for 60 min to obtain a precursor solution. Spray dry the precursor solution (inlet temperature 200℃, outlet temperature 100℃) to obtain the precursor powder.

[0057] Step 5: Place the precursor powder in an argon furnace, heat it to 350℃ at 3℃ / min and hold for 2 hours, then heat it to 650℃ at 2℃ / min and hold for 4 hours. Cool it to room temperature under argon protection to obtain the regenerated sodium ferric sulfate material.

[0058] Comparative Example 1 Step 1 is the same as step 1 in Example 1.

[0059] Step 2: Use ICP to detect the molar ratio of Na to Fe in the sodium ferric sulfate material to be treated. Add the sodium ferric sulfate material to be treated to deionized water and ultrasonically disperse for 30 min to obtain a suspension. Add ferrous ammonium sulfate and anhydrous sodium sulfate to the suspension according to the stoichiometric ratio Na:Fe = 1.02:1. At the same time, add 3% of the total mass of the precursor powder as a composite modifier (ammonium dihydrogen phosphate: sucrose = 1:2.5 in the composite modifier). Heat and stir at 55℃ for 75 min to obtain a precursor solution. Spray dry the precursor solution (inlet temperature 190℃, outlet temperature 90℃) to obtain the precursor powder. Step 3: Place the precursor powder in an argon furnace, heat it to 320℃ at 2.5℃ / min and hold it for 2.5h, then heat it to 620℃ at 1.5℃ / min and hold it for 5h. Cool it to room temperature under argon protection to obtain the regenerated sodium ferric sulfate material.

[0060] Comparative Example 2 Step 1 is the same as step 1 in Example 1.

[0061] Step 2 is the same as step 2 in Example 1.

[0062] Step 3 is the same as step 3 in Example 1.

[0063] Step 4: Use ICP to detect the molar ratio of Na to Fe in the dried second filter residue. Add the dried second filter residue to deionized water and ultrasonically disperse for 30 min to obtain a suspension. Add ferrous ammonium sulfate and anhydrous sodium sulfate to the suspension according to the stoichiometric ratio Na:Fe = 1.02:1. Heat and stir at 55℃ for 75 min to obtain a precursor solution. Spray dry the precursor solution (inlet temperature 190℃, outlet temperature 90℃) to obtain precursor powder.

[0064] Step 5 is the same as step 5 in Example 1.

[0065] [Performance Testing] (a) The dried second filter residue obtained in step 3 of Examples 1 to 3 and Comparative Example 2, and the sodium ferric sulfate material to be treated obtained in step 1 of Comparative Example 1 were used as samples to determine the Na and Fe contents. The test results are shown in Table 1.

[0066] The testing method is as follows: The following analysis was performed using an inductively coupled plasma optical emission spectrometer (ICP-OES, Thermoi CAP7400): 200 ± 10 mg of sample was weighed, 5 mL of concentrated nitric acid was added, and the mixture was digested in a microwave digester at 180 °C for 30 minutes. After cooling, the solution was diluted to 100 mL with deionized water. The concentrations C of Na and Fe in the solution were measured using ICP-OES. Na C Fe .

[0067] According to the formula, the mass fraction w Na =[(C Na [×V1) / m1]×100%, w Fe =[(C Fe [×V1)(m1)×100%, where V1 is 0.1L and m1 is the sample mass, calculate the mass fraction w of Na and Fe. Na w Fe Then the obtained mass fraction w Na w Fe Divide by the atomic weights of Na (22.99) and Fe (55.85) respectively to obtain the molar numbers of Na and Fe. The ratio of the two molar numbers of Na and Fe is the molar ratio of Na to Fe in the sample.

[0068] It should be noted that the commercially available sodium ferric sulfate used in the following text was purchased from Shanghai Puna Energy Technology Co., Ltd., with the product name being sodium ferric sulfate, model number PN-D1, and production batch number D16B1A01-01.

[0069] Table 1

[0070] (ii) The dried second filter residue obtained in step 3 of Examples 1 to 3 and Comparative Example 2, and the sodium ferric sulfate material to be treated obtained in step 1 of Comparative Example 1 were used as samples for the determination of residual sodium carbonate Na2CO3, as shown in Table 2.

[0071] The testing method is as follows: Ion chromatography (Dionex ICS-1100, equipped with an IonPac AS11-HC column, using 20 mmol / L KOH solution as eluent) was performed as follows: 200 ± 10 mg of sample was weighed, 20 mL of deionized water was added, and the sample was extracted by sonication at 100 W for 30 minutes. The sample was then centrifuged at 8000 rpm for 10 minutes, and the supernatant was collected. The carbonate ions (CO3-) in the supernatant were determined using ion chromatography. 2- The concentration of (C) 碳酸根 (mg / L).

[0072] According to formula m 碳酸根 =C碳酸根 Calculate CO3 in the extract by multiplying by V2 (V2 is 0.02L). 2- The total mass, and then based on the stoichiometric relationship m 碳酸钠 =m 碳酸根 ×(M 碳酸钠 / M 碳酸根 ), where M 碳酸钠 ≈105.99, M 碳酸根 ≈60.01, convert the carbonate mass to sodium carbonate mass, divide the sodium carbonate mass by the sample mass m2, and multiply by 100% to obtain the mass fraction of residual Na2CO3 in the sample.

[0073] Table 2

[0074] According to the data in Table 2, the sodium carbonate content in Comparative Example 1 sample was 2.25%. After treatment with weak alkaline cleaning solution and reducing cleaning solution, the sodium carbonate content in the samples of each example decreased significantly, confirming that the cleaning process has a good removal effect on sodium carbonate impurities.

[0075] (III) The dried second filter residue obtained in step 3 of Examples 1 to 3 and Comparative Example 2, and the sodium ferric sulfate material to be treated obtained in step 1 of Comparative Example 1, were used as samples for Fe... 2+ Fe 3+ The determination and test results are shown in Table 3.

[0076] The testing method is as follows: Weigh 250±10 mg of sample, dissolve it in 10 mL of 1 mol / L HCl solution, and take two 2 mL portions of the solution; add 1 mL of 10% hydroxylamine hydrochloride solution to the first portion to reduce all iron ions to Fe. 2+ After standing for 5 minutes, add 2 mL of 0.1% o-phenanthroline solution and 5 mL of acetate-sodium acetate buffer solution with pH 5.5, bring the volume to 25 mL, and let stand for 15 minutes. Measure the absorbance at 510 nm (using a UV-2600 UV-Vis spectrophotometer). Calculate the total iron content (w / w) using a standard curve. 总铁 The second sample underwent a colorimetric reaction without the addition of a reducing agent, and the Fe content in the original sample was determined. 2+ Content (w) 二价铁 Fe in the sample 3+ Content (w) 三价铁 The difference between the two is w. 总铁 -w 二价铁 ), while Fe 3+ The proportion of iron in the total iron is calculated using the formula [w 三价铁 / (w 三价铁 +w 二价铁 The result is calculated as ] × 100%.

[0077] w 总铁 =100%*[C 总铁 *V 显色定容体积 *(V) 样品溶剂总体积 / V 取样体积 [) / sample mass m3; where V 显色定容体积 For 0.025L, V 样品溶剂总体积 For 10 mL, V 取样体积 It is 2 mL.

[0078] w 二价铁 =100%*[C 二价铁 *V 显色定容体积 *(V) 样品溶剂总体积 / V 取样体积 [) / sample mass m3; where V 显色定容体积 For 0.025L, V 样品溶剂总体积 For 10 mL, V 取样体积 It is 2 mL.

[0079] Table 3

[0080] Table 3 shows that Fe in the sample of Comparative Example 1 3+ The content accounted for 6.74% of the total Fe. The Fe content in the samples of each example after treatment with a reducing cleaning solution... 3+ The content of iron as a percentage of total Fe decreased significantly, indicating that step S4 in this embodiment can effectively reduce high-valence iron in the material to a low-valence state.

[0081] (iv) The water absorption rate of the recycled sodium ferric sulfate materials obtained in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 was measured after 24 hours. The results are shown in Table 4.

[0082] The testing method is as follows: Accurately weigh 1 ± 0.05 g of the dried sample to constant weight (recorded as m0), place it in a standard environment at 25 ± 2℃ and 50 ± 5% relative humidity for 24 hours, and then quickly weigh its mass after moisture absorption (recorded as m1). The water absorption rate (%) of the sample after 24 hours is calculated using the formula: Water absorption rate (%) = (m0 - m1) / m2. x -m0) / m0×100%.

[0083] Table 4

[0084] As shown in Table 4, the water absorption rate of each embodiment was significantly reduced compared to Comparative Examples 1 and 2, demonstrating good moisture resistance. Comparative Example 1 lacked purification treatment, and Comparative Example 2 did not introduce a composite modifier. The data in Table 4 show that Examples 1 to 3 simultaneously incorporated purification treatment and a composite modifier, further reducing the water absorption rate to 1.2%~1.3%. This indicates that the synergistic effect of purification treatment and the composite modifier can achieve a more significant reduction in water absorption, and a single process is unlikely to achieve the desired performance target.

[0085] (v) The total carbon content of the recycled sodium ferric sulfate materials obtained in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 was tested respectively. The test results are shown in Table 5.

[0086] The testing method is as follows: Elemental analysis was performed using a VarioELIII instrument. An appropriate amount of sample was weighed and placed in the sample boat of the instrument. Under high-temperature combustion conditions, the carbon in the sample was completely oxidized to carbon dioxide. The carbon dioxide content was measured using a thermal conductivity detector and converted to the total carbon content. Each sample was tested in triplicate, and the average value was taken as the final result. The relative standard deviation (RSD) was required to be ≤2.5% to ensure the reliability of the test data.

[0087] Table 5

[0088] As shown in Table 5, the total carbon content in Examples 1 to 3 is significantly lower than that in Comparative Example 1, indicating that the weakly alkaline cleaning solution and reducing cleaning solution used in the examples can effectively reduce organic impurities in the materials.

[0089] (vi) The electrochemical performance, stability and physical properties of the recycled sodium ferric sulfate materials obtained in Examples 1 to 3, Comparative Example 1 and Comparative Example 2 were tested respectively. The test results are shown in Table 6.

[0090] The testing methods for electrochemical performance, stability, and physical properties are as follows: 1. Electrochemical performance testing Regenerated sodium ferric sulfate positive electrode sheets were prepared from the recycled sodium ferric sulfate materials obtained in Examples 1 to 3, Comparative Examples 1 and 2, respectively, and then assembled into CR2032 coin cells, as detailed below: The positive electrode preparation method is as follows: Regenerated sodium ferric sulfate material, conductive agent SuperP and binder PVDF are uniformly mixed at a mass ratio of 88:7:5, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added and ground into a uniform slurry; then the slurry is coated on an aluminum foil current collector, dried at 80°C for 12 hours to remove the solvent, and finally processed by a rolling process to obtain the regenerated sodium ferric sulfate positive electrode.

[0091] Battery assembly: In an argon-protected glove box (water and oxygen content <0.1ppm), a CR2032 coin cell was assembled by injecting an electrolyte containing 1mol / L NaPF6 (the electrolyte solvents are EC and DMC, with a volume ratio of EC to DMC of 1:1) using a regenerated sodium ferric sulfate positive electrode, a hard carbon negative electrode, and a polypropylene separator, and then allowing it to stand for 12 hours to age.

[0092] 0.1C initial discharge capacity and initial coulombic efficiency: Using the assembled CR2032 coin cell as described above, the cells were charged to 4.5V (cutoff current 0.01C) at 25℃ using a NEWARE battery testing system (CT-4008T-5V6A-S4) with a constant current of 0.1C (1C=120mAh / g). After standing for 1 minute, the cells were discharged to 2.0V with a constant current of 0.1C. The initial charge capacity (C0) and initial discharge capacity (D0) were recorded. The initial coulombic efficiency (%) was calculated as (D0 / C0)×100%.

[0093] Capacity retention rate after 5000 cycles at 1C: Using the assembled CR2032 coin cell battery, constant current charge and discharge was performed at 25℃ at a 1C rate (charged to 4.5V, cutoff current 0.01C, rested for 1 minute, discharged to 2.0V), and the cycle was repeated 5000 times. The discharge capacity was recorded each time. Capacity retention rate (%) = (5000th discharge capacity / first discharge capacity) × 100%.

[0094] -20℃ Capacity Retention: The CR2032 coin cell was placed in a -20℃ high and low temperature test chamber (GDW-100) for 2 hours and a single charge-discharge cycle was completed at a 0.1C rate (charged to 4.5V, discharged to 2.0V). The low-temperature discharge capacity (Q) was recorded. 低温 The battery was then restored to 25°C and tested using the same procedure to obtain the room temperature discharge capacity (Q). 常温 -20℃ capacity retention rate (%) = (Q 低温 / Q 常温 )×100%.

[0095] 10C discharge capacity retention: The CR2032 coin cell was activated at 0.1C rate for 3 cycles at 25℃, and the discharge capacity (Q) of the 3rd cycle was recorded. 0.1C The capacitor was then charged at a constant current of 1C to 4.5V (cutoff current 0.01C), allowed to stand for 1 minute, and then discharged at a high rate of 10C to 2.0V. The capacity Q was then recorded. 10C 10C discharge capacity retention rate (%) = (Q 10C / Q 0.1C )×100%.

[0096] Interfacial impedance: A three-electrode system (regenerated sodium ferric sulfate positive electrode as the working electrode, sodium sheet as the counter electrode and reference electrode) was used. AC impedance testing was conducted at 25℃ using a CHI660E electrochemical workstation (frequency 10 Hz). 6 ~10 -2 The interface impedance is obtained by fitting the Nyquist spectrum using ZsimpWin software (Hz, disturbance voltage 5mV) and obtaining the charge transfer impedance (Rct).

[0097] Electronic conductivity: 0.5g of recycled sodium ferric sulfate material was pressed into a disc with a diameter of 10mm and a thickness of 2mm under a pressure of 10MPa. The disc was tested in parallel 5 times under a current of 1mA using an RTS-9 four-probe tester. The electronic conductivity σ was calculated according to the formula σ=L / (R×S) (where L is the thickness of the disc, R is the test resistance, and S is the cross-sectional area of ​​the disc), and the average value of the 5 tests was taken.

[0098] 2. Stability Test Capacity decay rate after 12 months of air exposure: The regenerated sodium ferric sulfate materials obtained in Examples 1 to 3, Comparative Examples 1 and 2 were sealed in polyethylene bags and placed in an environment with room temperature (25±2℃) and relative humidity (50±5%) for 12 months. CR2032 coin cells were assembled from the regenerated sodium ferric sulfate materials before and after air exposure, and their 0.1C initial discharge capacity (denoted as Q) was tested. 初始 and Q 放置后 ), Capacity decay rate (%) = [(Q 初始 -Q 放置后 ) / Q_initial]×100%.

[0099] 3. Physical performance testing Particle D50 (median particle size): Take 50 mg of regenerated sodium ferric sulfate material, add 10 mL of deionized water and 1 drop of 0.1% sodium dodecylbenzenesulfonate dispersant, ultrasonically disperse for 10 min (100 W), and then inject into the sample cell of Malvern Mastersizer 3000 laser particle size analyzer. Set the refractive index to 1.52 and the medium refractive index to 1.33. Perform three parallel tests and take the average D50 as the final result.

[0100] Table 6

[0101] As shown in Table 6, in terms of electrochemical performance, Examples 1 to 3 are close to commercially available sodium ferric sulfate in terms of initial discharge capacity at 0.1C and initial coulombic efficiency at 0.1C, and are superior to Comparative Examples 1 and 2.

[0102] Regarding cycle stability, the capacity retention of Examples 1 to 3 after 5000 cycles at 1C is comparable to that of commercially available sodium ferric sulfate and superior to Comparative Examples 1 and 2. In terms of low-temperature performance, the capacity retention of Examples 1 to 3 at -20°C is comparable to that of commercially available sodium ferric sulfate and significantly higher than that of Comparative Examples 1 and 2.

[0103] In terms of rate performance, the 10C discharge capacity retention of Examples 1 to 3 is close to that of commercially available sodium ferric sulfate and is superior to that of Comparative Examples 1 and 2.

[0104] Regarding interfacial impedance, Examples 1 to 3 were significantly lower than Comparative Examples 1 and 2, and close to commercially available sodium ferric sulfate.

[0105] In terms of electronic conductivity, Examples 1 to 3 are superior to Comparative Examples 1 and 2, and are close to commercially available sodium ferric sulfate.

[0106] In terms of air stability, the capacity decay rates of Examples 1 to 3 after 12 months of air exposure were better than those of Comparative Examples 1 and 2, and were comparable to those of commercially available sodium ferric sulfate.

[0107] Regarding particle size, the D50 of Examples 1 to 3 is close to that of commercially available sodium ferric sulfate and is significantly smaller than that of Comparative Examples 1 and 2.

[0108] Overall, Examples 1 to 3 are superior to Comparative Examples 1 and 2 in all performance indicators, and their comprehensive performance is close to or reaches the level of commercially available sodium ferric sulfate.

[0109] (vii) Calculate the total yield in Examples 1 to 3, Comparative Example 1 and Comparative Example 2. The calculation results are shown in Table 7.

[0110] Total yield (%) = (mass of regenerated sodium ferric sulfate material / mass of sodium ferric sulfate material to be treated) × 100%.

[0111] Table 7

[0112] As shown in Table 7, the overall yields of Examples 1 to 3 were 92.7%, 93.7%, and 93.9%, respectively, with an average yield of 93.4%. This indicates that the regeneration method used in this application not only ensures a high yield but also possesses excellent material properties, achieving dual optimization of yield and quality, and demonstrating good process stability.

[0113] It should be noted that, in this document, "comprising," "including," or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0114] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0115] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A method for regenerating sodium ferric sulfate material, characterized in that, Includes the following steps: Step S1: Provide sodium ferric sulfate material to be processed; Step S2: Add the sodium ferric sulfate material to be treated to a weakly alkaline cleaning solution and heat and stir at a first temperature. Then filter to obtain the first filter residue and wash the first filter residue. Step S3: Add the washed first filter residue to the reducing cleaning solution and heat and stir in an inert gas atmosphere and at a second temperature. Then filter to obtain the second filter residue, and wash and dry the second filter residue. Step S4: Add the dried second filter residue to the solvent, ultrasonically disperse to obtain a suspension, add iron source, sodium source and composite modifier to the suspension and heat and stir at a third temperature to obtain a precursor solution, spray dry the precursor solution to obtain precursor powder; Step S5: Under an inert gas atmosphere, the precursor powder is sintered in stages, and then cooled to room temperature to obtain recycled sodium ferric sulfate material.

2. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, In step S2, the first temperature is 30℃~40℃; The heating and stirring time at the first temperature is 30 min to 60 min; The washing of the first filter residue includes: washing the first filter residue with deionized water until the pH of the filtrate is 7.0~7.

5.

3. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, The weakly alkaline cleaning solution is selected from sodium bicarbonate solution, and the concentration of sodium bicarbonate in the sodium bicarbonate solution is 0.05 mol / L to 0.1 mol / L; The solid-liquid ratio of the sodium ferric sulfate material to be treated to the weakly alkaline cleaning solution is 1:(10~20), with units of g / mL.

4. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, In step S3, the second temperature is 40℃~50℃; The heating and stirring time under an inert gas atmosphere and at a second temperature is 60 min to 90 min; The washing and drying of the second filter residue includes: washing the second filter residue with deionized water until the filtrate is no longer reducing, and then vacuum drying the washed second filter residue at 80°C to 100°C for 4 to 6 hours.

5. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, The reducing cleaning solution includes sodium bisulfite and citric acid, wherein the concentration of sodium bisulfite in the reducing cleaning solution is 0.1 mol / L to 0.2 mol / L; Based on the total mass of the reducing cleaning solution, the mass fraction of citric acid is 0.5%~1%; The solid-liquid ratio between the washed first filter residue and the reducing cleaning solution is 1:(15~25), with units of g / mL.

6. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, Based on the total mass of the precursor powder, the mass fraction of the composite modifier is 2% to 5%; The composite modifier includes ammonium dihydrogen phosphate and sucrose, with the mass ratio of ammonium dihydrogen phosphate to sucrose being 1:(2~3). The molar ratio of Na to Fe in the precursor powder is (1.0~1.05):

1.

7. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, The third temperature in step S4 is 50℃~60℃; The heating and stirring time at the third temperature is 60 min to 90 min.

8. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, The staged sintering in step S5 includes: First, the temperature is increased to 300℃~350℃ at a rate of 2℃ / min~3℃ / min, and held for 2h~3h for pre-sintering; then the temperature is increased to 600℃~650℃ at a rate of 1℃ / min~2℃ / min, and held for 4h~6h for secondary sintering.

9. The method for regenerating sodium ferric sulfate material as described in claim 1, characterized in that, The sodium ferric sulfate material to be treated in step S1 includes: The sodium iron sulfate sodium ion battery to be processed is disassembled to obtain the positive electrode sheet, and the positive electrode sheet is mechanically crushed to a particle size of 5mm~10mm. Under an inert gas atmosphere, the broken positive electrode sheet is added to a mixed solvent, and then ultrasonically exfoliated for 20 min to 40 min at 25℃~35℃ and ultrasonic power of 200W~300W to obtain active material powder. The active material powder is vacuum dried at 60℃~80℃ for 8h~12h to obtain the sodium ferric sulfate material to be treated. The mixed solvent comprises sodium dodecylbenzenesulfonate, anhydrous ethanol, and deionized water; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 1:(3~5); and the mass fraction of sodium dodecylbenzenesulfonate is 0.1%~0.3% based on the total mass of the mixed solvent.

10. A recycled sodium ferric sulfate material, characterized in that, It is prepared by the method for regenerating sodium ferric sulfate material according to any one of claims 1 to 9.

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