Method for preparing sodium ferric sulfate as sodium battery positive electrode material by using phosphoric acid iron black residue purification liquid

Abstract

The application discloses a method for preparing sodium ferric sulfate as a sodium battery positive electrode material from a purified iron phosphate black residue solution, and belongs to the technical field of lithium iron phosphate battery recycling and sodium ion battery positive electrode materials. The sodium ferric sulfate is prepared by using a gel method. First, the iron phosphate black residue acid leaching solution is purified, then mixed with sodium sulfate or sodium bicarbonate, and a small amount of citric acid is added to prepare a solution. After heating for a period of time, a sol system is obtained. The sol system is continuously stirred and heated, and the obtained dry material is ground and calcined to obtain sodium ferric sulfate with a molecular formula of NaFe(SO4)2. The application uses the iron phosphate black residue purification solution as a sulfur source and an iron source to prepare sodium ferric sulfate, realizes the recycling of battery recycling waste liquid, effectively reduces the sewage treatment cost and the production cost of sodium ferric sulfate, and meanwhile, the sodium ferric sulfate prepared by the method has the performance characteristics of excellent low-temperature performance and long cycle life, and can be used for sodium ion batteries.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium iron phosphate battery recycling and sodium ion battery positive electrode material, and relates to a method for preparing sodium ferrous sulfate as a sodium battery positive electrode material from a lithium iron phosphate black slag purification liquid. BACKGROUND

[0002] Compared with ternary battery recycling, the recycling cost of waste lithium iron phosphate batteries is high, and the value is low. At present, most enterprises adopt a wet recovery method to recover lithium, and the remaining lithium iron phosphate black slag is treated by stacking, which causes waste of resources. In recent years, with the increasing demand for lithium iron phosphate batteries in the market, the shipment of lithium iron phosphate batteries is rising and even overtaking ternary batteries. Therefore, battery recycling enterprises have carried out research on efficient and high-quality recycling of all components of lithium iron phosphate batteries.

[0003] Compared with lithium ion batteries, sodium ion batteries have low theoretical cost, wide working temperature, and are more suitable for energy storage environment, which can effectively solve the problem of low efficiency of energy storage power stations in high-cold regions. The price of lithium salt is high, and sodium ion batteries with price advantage are concerned by the energy storage market. At present, the positive electrode materials of sodium ion batteries mainly include transition metal oxides, polyanion compounds and prussian blue analogues. The transition metal oxide positive electrode material has high energy density, but poor cycle performance. The polyanion compound has good thermal stability and cycle performance, but low energy density and poor conductivity. The prussian blue analogue has good electrochemical performance, good stability and low cost, but is sensitive to water in production and has high production technology requirement. Sodium ferrous sulfate as a polyanion type iron-based material has the following advantages: pure iron base + sodium, very cost-competitive; simple process, low energy consumption, calcination temperature 300-400 DEG C, only single sintering is needed; high raw material utilization, very environmentally friendly.

[0004] CN115057425A discloses a method for preparing iron phosphate from waste lithium iron phosphate batteries. The method is to immerse the battery black powder in acid with a reducing agent to obtain an acid immersion liquid. Iron powder is added for one-stage purification, and two-stage purification is carried out in a reducing atmosphere. The two-stage purification liquid is precipitated with a phosphorus source and / or an iron source, and iron phosphate is obtained by filtration. In the patent, the purification liquid is prepared into iron phosphate, which needs to be prepared by liquid phase coprecipitation. The process flow is long, the energy consumption is high, and phosphoric acid needs to be added, which increases the cost.

[0005] CN115312903A discloses a method for preparing a rate type lithium iron phosphate from waste lithium iron phosphate, which comprises the following steps: mixing waste lithium iron phosphate powder and ferrous sulfide, adding acid and water to form a slurry, reacting in an autoclave, filtering, adding phosphorus source and lithium source to the filtrate, spray drying, and sintering under a protective atmosphere to obtain carbon-coated lithium iron phosphate positive electrode material. In this patent, waste lithium iron phosphate powder is prepared into regenerated lithium iron phosphate. The process involves slurry preparation and high-pressure reaction, which is complicated. Moreover, impurities are not removed, and the cost is increased compared with the high-temperature solid-phase method for preparing lithium iron phosphate.

[0006] CN109192982A discloses a method for synthesizing sodium iron sulfate positive electrode material, which comprises the following steps: weighing and mixing Na2SO4 and FeSO4·7H2O according to the molar ratio, adding a carbon source, high-energy ball milling several times, obtaining a highly dispersed uniform powder, and calcining the powder under a high-purity argon atmosphere to obtain sodium iron sulfate. This patent directly calcines to prepare sodium iron sulfate. The particles of sodium iron sulfate prepared by this method are not uniform.

[0007] CN116230888A discloses a method for preparing carbon-coated sodium iron sulfate material, carbon-coated sodium iron sulfate material and battery. The method comprises the following steps: ball milling a mixed solution of solvent, ferrous sulfate heptahydrate, sodium sulfate and inorganic carbon source in an inert gas atmosphere to obtain a viscous precursor slurry, and drying the slurry and then performing low-temperature sintering. The invention uses a solvent thermal method to prepare a sodium iron sulfate precursor, effectively controlling the uniformity of the product particles. However, the raw materials used are relatively traditional. SUMMARY

[0008] The present application aims to provide a method for preparing sodium iron sulfate as a sodium battery positive electrode material using phosphorus iron purification liquid as an iron and sulfur source. This method solves the problem of recycling phosphorus iron purification liquid in the recycling of lithium iron phosphate batteries. Moreover, a poly-anionic iron-based sodium ion battery positive electrode material with excellent low-temperature performance and long cycle life is prepared by a gel method.

[0009] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0010] The present application provides a method for preparing sodium iron sulfate as a sodium battery positive electrode material using phosphorus iron purification liquid as an iron and sulfur source. The method comprises the following steps:

[0011] Step 1: Acid leaching of lithium iron phosphate black powder obtained by discharging, crushing, screening, high-temperature calcination and sorting of waste lithium iron phosphate batteries. The acid leaching liquid is used for recycling lithium resources, and the acid leaching residue is continuously acid leached to obtain phosphorus iron purification liquid as a sulfur source and iron source. The iron content in the lithium iron phosphate black powder is 10% to 50%, and the phosphorus content is 5% to 20%. The acid used for acid leaching is one or more of inorganic acids.

[0012] Step 2: purifying the phosphorus-iron purified solution obtained in step 1, including adding an aluminum removal agent, a copper removal agent, and a flocculating agent to obtain a purified solution; wherein the copper removal agent includes one or more of iron powder and aluminum powder, and the flocculating agent includes one or more of polyaluminum chloride, polyferric sulfate, alum, sodium aluminate, ferric trichloride, polyacrylamide, and polyethyleneimine; the flocculating agent includes one or more of polyaluminum chloride, polyferric sulfate, alum, sodium aluminate, ferric trichloride, polyacrylamide, and polyethyleneimine;

[0013] Step 3: mixing the purified solution obtained in step 2 with sodium sulfate at a mass ratio of (100-300):(1-2), and adding a certain amount of citric acid, and stirring to obtain a solution; the solid-liquid ratio of citric acid to the solution is (1-5):(100-400);

[0014] Step 4: maintaining a certain stirring rate for the solution obtained in step 3, and heating for a period of time to obtain a sol system;

[0015] Step 5: continuously stirring and heating the sol system obtained in step 4 to obtain a gel system;

[0016] Step 6: drying the gel obtained in step 5, and crushing the dried gel to obtain a yellow powder;

[0017] Step 7: heating and calcining the yellow powder obtained in step 6 for a period of time to obtain a sodium ferric sulfate solid.

[0018] Preferably, in step 1, the solid-liquid ratio of the acid leaching is (1-5):(2-7).

[0019] Preferably, in step 2, the aluminum removal agent is ammonium bicarbonate, and the pH of the system is controlled to be 5-12 by adding the aluminum removal agent.

[0020] Preferably, in step 3, the mass ratio of the purified solution to sodium sulfate is 200:1.

[0021] Preferably, in step 3, the content of iron in the purified solution is 5%-30%, the content of phosphorus is 1%-10%, and the content of sulfate is 30%-50%.

[0022] Preferably, in step 3, the solid-liquid ratio of citric acid to the solution is 1:(50-300).

[0023] Preferably, in step 4, the stirring rate is 500-1000 rpm, the heating temperature is 30-80°C, and the heating time is 60-180 min.

[0024] Preferably, in step 5, the stirring rate is 300-800 rpm, the heating temperature is 30-80°C, and the heating time is 30-120 min.

[0025] Preferably, in step 6, the drying temperature is 100-200 DEG C, and the drying time is 60-180 min.

[0026] Preferably, in step 7, the calcination temperature is 300-400 DEG C, and the calcination time is 60-180 min.

[0027] The present application is recycled from lithium iron phosphate battery, the lithium iron phosphate waste battery is treated by physical method to obtain lithium iron phosphate black powder, and the lithium iron phosphate black powder is selectively leached to obtain lithium salt and phosphorus iron purification liquid. The acid leaching liquid contains iron and sulfuric acid, and the acid leaching liquid is purified as an iron and sulfur source, mixed with sodium sulfate, and prepared into sodium ion battery positive material sodium ferrous sulfate by gel method. The recycling of battery recovery waste liquid is realized, the sewage treatment cost and the production cost of sodium ferrous sulfate are effectively reduced, and the sodium ferrous sulfate prepared by the method has the performance characteristics of high capacity and high rate.

[0028] The present application has the following advantages: the sodium battery positive material sodium ferrous sulfate is prepared, sulfuric acid is added to the lithium iron phosphate black powder, and two acid leaching is carried out, lithium is recovered in the first acid leaching liquid, and phosphorus iron purification liquid is obtained in the second acid leaching. Then the phosphorus iron purification liquid is impurity-removed, first, ammonium bicarbonate is added to remove aluminum, iron powder is added to remove copper, and then a flocculating agent is added to remove impurities after copper removal. The purification liquid is collected, sodium sulfate is added according to the content of iron and sulfur in the purification liquid, citric acid is added according to the solid-liquid ratio, and sodium ferrous sulfate sol is prepared by heating and stirring. Continue to add and stir to obtain sodium ferrous sulfate gel, dry the gel, crush it after drying, put it into calcination, and obtain sodium ferrous sulfate solid after calcination. Compared with the preparation process of the existing sodium ion battery positive material sodium ferrous sulfate, the method of the present application has the following advantages: the present application uses the phosphorus iron black slag purification liquid as the iron and sulfur source, which not only saves the battery recycling waste liquid treatment cost, but also saves the preparation cost of sodium ferrous sulfate. No high-temperature solid-phase grinding method is used, the sodium ferrous sulfate prepared by the gel method has uniform particle size, good electrochemical performance, and the characteristics of excellent low-temperature performance and long cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating any inventive labor.

[0030] Figure 1 It is the process flow chart of the present application for preparing sodium battery positive material sodium ferrous sulfate by using phosphorus iron black slag purification liquid as iron and sulfur source. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0032] As shown in Figure 1 The method for preparing battery-grade sodium iron sulfate from iron phosphate black residue and sodium sulfate includes the following steps:

[0033] Step 1: The lithium iron phosphate black powder obtained by discharging, crushing, screening, high-temperature calcination and sorting of waste lithium iron phosphate batteries is subjected to acid leaching, and the acid leaching solution is used for recovering lithium resources. The acid leaching residue is continuously subjected to acid leaching, and the obtained phosphorus-iron purification liquid is used as a sulfur source and an iron source; wherein: the iron content in the lithium iron phosphate black powder is 10% to 50%, and the phosphorus content is 5% to 20%; the acid used for acid leaching is one or more of inorganic acids;

[0034] Step 1: The phosphorus-iron purification liquid obtained in step 1 is purified, including adding an aluminum removal agent, a copper removal agent and a flocculating agent to obtain a purification liquid; wherein: the copper removal agent includes one or more of iron powder and aluminum powder, and the flocculating agent includes one or more of polyaluminum chloride, polyferric sulfate, alum, sodium aluminate, ferric chloride, polyacrylamide and polyethyleneimine; the flocculating agent includes one or more of polyaluminum chloride, polyferric sulfate, alum, sodium aluminate, ferric chloride, polyacrylamide and polyethyleneimine;

[0035] Step 2: The purification liquid obtained in step 2 is mixed with sodium sulfate at a mass ratio of (100-300):(1-2), and a certain amount of citric acid is added, and the solution is prepared by stirring; the solid-liquid ratio of citric acid added to the solution is (1-5):(100-400);

[0036] Step 4: The solution obtained in step 3 is kept at a certain stirring rate and heated for a period of time to obtain a sol system;

[0037] Step 5: The sol system obtained in step 4 is continuously stirred and heated to obtain a gel system;

[0038] Step 6: The gel obtained in step 5 is dried, and the yellow powder is obtained after crushing;

[0039] Step 7: The yellow powder obtained in step 6 is heated and calcined for a period of time to obtain sodium iron sulfate solid.

[0040] The embodiment prepares sodium iron sulfate positive electrode material. Sulfuric acid is added to lithium iron phosphate black powder, and two acid leaching is performed. Lithium is recovered in the first acid leaching, and phosphorus iron purification liquid is obtained in the second acid leaching. Then, the phosphorus iron purification liquid is impurity-removed. First, ammonium bicarbonate is added to remove aluminum, iron powder is added to remove copper, and a flocculating agent is added after copper removal to remove impurities. The purification liquid is collected, sodium sulfate is added according to the iron and sulfur content in the purification liquid, citric acid is added according to the solid-liquid ratio, and sodium iron sulfate sol is prepared by heating and stirring. Then, sodium iron sulfate gel is obtained by continuing to add and stir. The gel is dried, crushed after drying, and calcined. After calcination, sodium iron sulfate solid is obtained.

[0041] In addition, the method of the embodiment has the following advantages: the present application uses phosphorus iron black slag purification liquid as a sulfur iron source, which not only saves the cost of battery recovery waste liquid treatment, but also saves the cost of preparing lithium iron sulfate. The high-temperature solid-phase grinding method is not used, the particle size of the prepared sodium iron sulfate is uniform, the electrochemical performance is good, and the sodium iron sulfate has the characteristics of high capacity and high rate.

[0042] Example 1

[0043] The iron content in the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached with sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:3. After two acid leaching, acid leaching slag is obtained. Pure water and ammonium bicarbonate (20% excess according to the aluminum content in the system) are added to the waste lithium iron phosphate black powder acid leaching slag to remove aluminum. The solution system PH is controlled to be 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction is completed, the filter residue is obtained by filtration. Pure water and iron powder (10% excess according to the copper content in the system) are added to the filter residue to remove copper. The stirring speed is 500 rpm, the reaction time is 30 min, and the copper-removed purification liquid is obtained by filtration. The flocculating agent polyethylene imine is added to the copper-removed purification liquid to remove impurities. The solid-liquid ratio is 1:800, the stirring speed is 500 rpm, the time is 10 min, and the purification liquid is obtained by filtration. The iron content in the purification liquid is 20%, the phosphorus content is 1%, and the sulfate content is 35%. Sodium sulfate is added to the purification liquid, the mass ratio is 200:1, the stirring speed is 800 rpm, and the time is 60 min to obtain a solution. Citric acid is added to the solution, the solid-liquid ratio is 100:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min to obtain a sol. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min to obtain a gel. The gel is collected and dried, the drying temperature is 180°C, and the drying time is 120 min to obtain a dried material. The dried material is collected and calcined, the calcination temperature is 350°C, the calcination time is 150 min, and light yellow sodium iron sulfate is obtained after calcination.

[0044] Example 2

[0045] The iron content of the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached using sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:3. After two acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (20% excess according to the aluminum content in the system) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled at 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction, the filter residue is obtained by filtration. Pure water is added to the filter residue, and iron powder (10% excess according to the copper content in the system) is added to remove copper, the stirring speed is 500 rpm, the reaction time is 30 min, and the copper removal purified liquid is obtained by filtration. The purified liquid is added to the flocculating agent polyethyleneimine to remove impurities, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, the time is 10 min, and the purified liquid is obtained by filtration. The iron content in the purified liquid is 20%, the phosphorus content is 1%, and the sulfate content is 45%. Sodium sulfate is added to the purified liquid, the mass ratio is 160:1, the stirring speed is 800 rpm, and the time is 60 min to obtain a solution. Citric acid is added to the solution, the solid-liquid ratio is 200:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min to obtain a sol. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min to obtain a gel. The gel is collected and dried, the drying temperature is 180°C, the drying time is 120 min, and the dried material is obtained. The dried material is collected and calcined, the calcination temperature is 350°C, the calcination time is 150 min, and the light yellow sodium iron sulfate is obtained after calcination.

[0046] Example 3

[0047] The iron content of the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached using sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:4. After two acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (20% excess according to the aluminum content in the system) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled at 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction, the filter residue is obtained by filtration. Pure water is added to the filter residue, and iron powder (10% excess according to the copper content in the system) is added to remove copper, the stirring speed is 500 rpm, the reaction time is 30 min, and the copper removal purified liquid is obtained by filtration. The purified liquid is added to the flocculating agent polyethyleneimine to remove impurities, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, the time is 10 min, and the purified liquid is obtained by filtration. The iron content in the purified liquid is 20%, the phosphorus content is 1%, and the sulfate content is 35%. Sodium sulfate is added to the purified liquid, the mass ratio is 200:1, the stirring speed is 800 rpm, and the time is 60 min to obtain a solution. Citric acid is added to the solution, the solid-liquid ratio is 100:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min to obtain a sol. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min to obtain a gel. The gel is collected and dried, the drying temperature is 180°C, the drying time is 120 min, and the dried material is obtained. The dried material is collected and calcined, the calcination temperature is 350°C, the calcination time is 150 min, and the light yellow sodium iron sulfate is obtained after calcination.

[0048] Example 4

[0049] The iron content of the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached using sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:4. After two acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (20% excess according to the aluminum content in the system) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled at 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction is completed, the filter residue is obtained by filtration. Pure water is added to the filter residue, and iron powder (10% excess according to the copper content in the system) is added to remove copper, the stirring speed is 500 rpm, the reaction time is 30 min, and the copper removal purified liquid is obtained by filtration. The impurities are removed from the copper removal purified liquid by adding a flocculating agent polyethyleneimine, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, the time is 10 min, and the purified liquid is obtained by filtration. The iron content in the purified liquid is 20%, the phosphorus content is 1%, and the sulfate content is 35%. Sodium sulfate is added to the purified liquid, the mass ratio is 160:1, the stirring speed is 800 rpm, and the time is 60 min to obtain a solution. Citric acid is added to the solution, the solid-liquid ratio is 200:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min to prepare a sol. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min to prepare a gel. The gel is collected and dried, the drying temperature is 180°C, the drying time is 120 min, and the dried material is obtained. The dried material is collected and calcined, the calcination temperature is 350°C, the calcination time is 150 min, and the light yellow sodium iron sulfate is obtained after calcination.

[0050] Example 5

[0051] The iron content of the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached using sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:5. After two acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (20% excess according to the aluminum content in the system) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled at 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction is completed, the filter residue is obtained by filtration. Pure water is added to the filter residue, and iron powder (10% excess according to the copper content in the system) is added to remove copper, the stirring speed is 500 rpm, the reaction time is 30 min, and the copper removal purified liquid is obtained by filtration. The impurities are removed from the copper removal purified liquid by adding a flocculating agent polyethyleneimine, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, the time is 10 min, and the purified liquid is obtained by filtration. The iron content in the purified liquid is 20%, the phosphorus content is 1%, and the sulfate content is 35%. Sodium sulfate is added to the purified liquid, the mass ratio is 100:1, the stirring speed is 800 rpm, and the time is 60 min to obtain a solution. Citric acid is added to the solution, the solid-liquid ratio is 100:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min to prepare a sol. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min to prepare a gel. The gel is collected and dried, the drying temperature is 180°C, the drying time is 120 min, and a light yellow dried material is obtained. The dried material is collected and calcined, the calcination temperature is 350°C, the calcination time is 150 min, and sodium iron sulfate is obtained after calcination.

[0052] Example 6

[0053] The iron content of the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached using sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:5. After two acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (20% excess according to the aluminum content in the system) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled at 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction, the filter residue is obtained by filtration. Pure water is added to the filter residue, and iron powder (10% excess according to the copper content in the system) is added to remove copper, the stirring speed is 500 rpm, the reaction time is 30 min, and the copper removal purified liquid is obtained by filtration. The impurities are removed from the copper removal purified liquid by adding a flocculating agent polyethyleneimine, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, the time is 10 min, and the purified liquid is obtained by filtration. The iron content in the purified liquid is 20%, the phosphorus content is 1%, and the sulfate content is 35%. Sodium sulfate is added to the purified liquid, the mass ratio is 200:1, the stirring speed is 800 rpm, and the time is 60 min to obtain a solution. Citric acid is added to the solution, the solid-liquid ratio is 200:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min to obtain a sol. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min to obtain a gel. The gel is collected and dried, the drying temperature is 180°C, the drying time is 120 min, and a light yellow dried material is obtained. The dried material is collected and calcined, the calcination temperature is 350°C, the calcination time is 150 min, and sodium iron sulfate is obtained after calcination.

[0054] Comparative Example 1

[0055] The iron content in the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached with sulfuric acid with a concentration of 30%, and the solid-liquid ratio is 1:1. After two times of acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (calculated according to the aluminum content in the system, but the amount is not limited) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled to be 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction is completed, the filter residue is obtained by filtration. Pure water and iron powder (calculated according to the copper content in the system, but the amount is not limited) are added to the filter residue to remove copper, the stirring speed is 500 rpm, and the reaction time is 30 min. The copper removal purified liquid is obtained by filtration. The flocculant polyethyleneimine is added to the copper removal purified liquid to remove impurities, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, and the time is 10 min. The purified liquid is obtained by filtration. The iron content in the purified liquid is 24%, the phosphorus content is 2%, and the sulfate content is 38%. Sodium sulfate is added to the purified liquid, the mass ratio is 200:1, the stirring speed is 800 rpm, and the time is 60 min. The solution is obtained. Citric acid is added to the solution, the solid-liquid ratio is 100:1, the stirring speed is 800 rpm, the heating temperature is 60°C, and the heating time is 150 min. The sol is prepared. The sol is continuously heated and stirred, the stirring speed is 500 rpm, the heating temperature is 80°C, and the heating time is 60 min. The gel is prepared. The gel is collected and dried, the drying temperature is 180°C, and the drying time is 120 min. The dry material with a light yellow color is obtained. The dry material is collected and calcined, the calcination temperature is 350°C, and the calcination time is 150 min. The sodium iron sulfate is obtained after the calcination is completed.

[0056] Comparative Example 2

[0057] The iron content in the lithium iron phosphate black powder is 30%, and the phosphorus content is 15%. The lithium iron phosphate black powder is acid leached with sulfuric acid with a concentration of 60%, and the solid-liquid ratio is 1:1. After two times of acid leaching, the acid leaching residue is obtained. Pure water and ammonium bicarbonate (calculated according to the aluminum content in the system, but the amount is not limited) are added to the waste lithium iron phosphate black powder acid leaching residue to remove aluminum, the solution system PH is controlled to be 6, the stirring speed is 500 rpm, and the reaction time is 60 min. After the reaction is completed, the filter residue is obtained by filtration. Pure water and iron powder (calculated according to the copper content in the system, but the amount is not limited) are added to the filter residue to remove copper, the stirring speed is 500 rpm, and the reaction time is 30 min. The copper removal purified liquid is obtained by filtration. The flocculant polyethyleneimine is added to the copper removal purified liquid to remove impurities, the solid-liquid ratio is 1:800, the stirring speed is 500 rpm, and the time is 10 min. The purified liquid is obtained by filtration. The iron content in the purified liquid is 24%, the phosphorus content is 2%, and the sulfate content is 38%. Sodium sulfate is added to the purified liquid, the mass ratio is 200:1, the stirring speed is 800 rpm, and the time is 60 min. The solution is obtained. The dry material is obtained by heating the solution for 180 min. The dry material is collected and calcined, the calcination temperature is 350°C, and the calcination time is 150 min. The sodium iron sulfate is obtained after the calcination is completed.

[0058] The physicochemical performance results of the sodium iron sulfate prepared in the above examples 1-6 and comparative examples 1-2 are shown in Table 1, and the rate charge-discharge test data results of the sodium iron sulfate prepared in the examples 1-6 and comparative examples 1-2 are shown in Table 2.

[0059] Table 1

[0060] Group Specific surface m 2 / g]] tapping g / cm 3 ]] Compacted g / cm 3 ]] Moisture % D10 pm D50 pm D99 pm Example 1 19.82 0.81 1.82 0.54 0.56 1.56 10.17 Example 2 19.91 0.85 1.88 0.48 0.51 2.10 10.35 Example 3 20.35 0.97 1.97 0.51 0.43 1.71 9.84 Example 4 20.60 1.04 2.01 0.55 0.39 1.98 10.13 Example 5 21.37 1.13 2.05 0.57 0.46 2.16 8.72 Example 6 21.45 1.20 2.06 0.49 0.52 1.82 9.44 Comparative Example 1 17.76 0.54 1.67 0.49 0.83 4.60 15.12 Comparative Example 2 17.98 0.60 1.69 0.52 0.75 5.75 14.21

[0061] Table 2

[0062] Group Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 0.1 C charge capacity (mAh / g) 110.7 111.2 112.2 112.7 114.1 115.2 98.7 10.1 0.1 C discharge capacity (mAh / g) 101.5 102.3 104.7 105.1 106.2 106.9 81.1 83.3 1 C discharge capacity (mAh / g) 95.1 95.5 96.3 96.5 97.2 98.1 80.5 80.8 3 C discharge capacity (mAh / g) 86.4 86.8 87.8 88.4 89.1 89.3 70.7 71.2 -20 °C capacity retention (%) 79.5 79.8 81.2 81.6 82.1 82.5 67.6 68.1 1 C room temperature cycle 500 cycles capacity retention (%) 93.2 93.5 94.6 95.2 95.2 95.5 87.5 88.1

[0063] From the analysis results in Table 1, it can be seen that the specific surface area of the polyanionic sodium ion battery positive electrode material sodium iron sulfate prepared in the present application is 19-22 m 2 / g, the vibration is 0.8-1.2 g / cm 3 , the pressure is 1.8-2.1 g / cm 3 , and D10 is about 0.5 μm. The specific surface area of the comparative examples 1-2 is about 17 m 2 / g, the vibration is about 0.5 g / cm 3 , the pressure is about 1.6 g / cm 3 , and D10 is about 0.8 μm.

[0064] From the test results in Table 2, it can be seen that the polyanionic sodium ion battery positive electrode material sodium iron sulfate prepared in the present application is made into a soft pack battery with a hard carbon negative electrode, the battery is activated after formation, and in the sodium iron sulfate-hard carbon battery system, the normal temperature rate charging test and the retention rate test are carried out. The normal temperature 0.1C charging capacity of the examples 1-6 is 110-120 mAh / g, the specific capacity under the normal temperature 3C rate state is 80-90 mAh / g, the capacity retention rate under the normal temperature 1C rate state after 500 cycles is 93%-95%, and the capacity retention rate at-20℃ is 70%-80%. The normal temperature 0.1C charging capacity of the comparative examples 1-2 is 90-100 mAh / g, the specific capacity under the normal temperature 3C rate state is about 70 mAh / g, the capacity retention rate under the normal temperature 1C rate state after 500 cycles is about 87%, and the capacity retention rate at-20℃ is about 67%. It can be seen that the polyanionic sodium ion battery positive electrode material sodium iron sulfate prepared in the present application has excellent electrochemical performance, and can meet the low temperature and long cycle life requirements of power batteries.

[0065] The above examples of the present application are described in detail, but the content described is only the preferred embodiment of the present application, and cannot be considered as limiting the scope of the present application. Any equivalent changes and improvements made within the scope of the present application should still be included in the scope of the present patent.

Claims

1. A method for preparing sodium ferrate as a sodium battery cathode material from a black iron phosphate sludge solution, characterized in that The method comprises the following steps: S1: the waste lithium iron phosphate battery is discharged, broken, screened, high-temperature calcined, and sorted to obtain lithium iron phosphate black powder, and the lithium iron phosphate black powder is subjected to acid leaching, the acid leaching liquid is used for recovering lithium resources, and the phosphorus iron black residue is continuously subjected to acid leaching to obtain a phosphorus iron purification liquid as a sulfur source and an iron source; wherein: the iron content in the lithium iron phosphate black powder is 10% to 50%, and the phosphorus content is 5% to 20%; the acid used for acid leaching is one or more of inorganic acids; S2: the phosphorus iron purification liquid obtained in step S1 is purified, including adding an aluminum removal agent, a copper removal agent, and a flocculating agent to obtain a purified liquid; wherein: the copper removal agent includes one or more of iron powder and aluminum powder, and the flocculating agent includes one or more of polyaluminum chloride, polyferric sulfate, alum, sodium aluminate, ferric chloride, polyacrylamide, and polyethyleneimine; S3: the purified liquid obtained in step S2 is mixed with sodium sulfate at a mass ratio of (100-300):(1-2), and a certain amount of citric acid is added, and the solution is prepared by stirring; the solid-liquid ratio of citric acid added to the solution is (1-5):(100-400); S4: the solution obtained in step S3 is kept at a certain stirring rate and heated for a period of time to obtain a sol system; S5: the sol system obtained in step S4 is continuously stirred and heated to obtain a gel system; S6: the gel obtained in step S5 is dried, and the yellow powder is obtained after breaking; S7: the yellow powder obtained in step S6 is heated and calcined for a period of time to obtain a sodium iron sulfate solid; In step S1, the solid-liquid ratio of acid leaching is 1:(2-7); In step S2, the aluminum removal agent is ammonium bicarbonate, and the pH of the system is controlled to be 5-12 by adding the aluminum removal agent; In step S3, the content of iron in the purified liquid is 5%-30%, the content of phosphorus is 1%-10%, and the content of sulfate is 30%-50%.

2. The process for the preparation of sodium ferrate as cathode material for sodium-ion batteries from iron phosphate black-dross solution as claimed in claim 1 wherein, In step S3, the mass ratio of the purified liquid to sodium sulfate is 200:

1.

3. The process for the preparation of sodium ferrate as cathode material for sodium-ion batteries from iron phosphate black-dross solution as claimed in claim 1 wherein, In step S3, the solid-liquid ratio of citric acid to the solution is 1:(50-300). ​ 4. The process for the preparation of sodium ferrate as cathode material for sodium-ion batteries from iron phosphate black-ash solution according to claim 1, characterized in that, In step S4, the stirring rate is 500-1000 rpm, the heating temperature is 30-80℃, and the heating time is 60-180 min.

5. The process for the preparation of sodium ferrate as cathode material for sodium-ion batteries from iron phosphate black-dross solution as claimed in claim 1 wherein, In step S5, the stirring rate is 300-800 rpm, the heating temperature is 30-80℃, and the heating time is 30-120 min. ​ 6. The process for the preparation of sodium ferrate as cathode material for sodium-ion batteries from iron phosphate black-dross solution as claimed in claim 1 wherein, In step S6, the drying temperature is 100-200℃, and the drying time is 60-180 min. ​ 7. The process for the preparation of sodium ferrate as cathode material for sodium-ion batteries from iron phosphate black-dross liquor as claimed in claim 1 wherein, In step S7, the calcination temperature is 300-400℃, and the calcination time is 60-180 min. ​

Images