Method for preparing composite sodium iron phosphate positive electrode material by using iron slag solid waste

Abstract

This invention discloses a method for preparing composite sodium iron phosphate cathode material using iron slag solid waste, belonging to the field of sodium-ion battery cathode materials. The method specifically includes the following steps: Iron slag is crushed and sieved, dissolved in sulfuric acid, then iron powder is added and reacted, followed by filtration. The filtrate is demagnetized, heated to a specific temperature and held, and sodium hydroxide solution is slowly added dropwise to precipitate impurity ions. A flocculant is then added and filtered, resulting in solid-liquid separation. Phosphoric acid is added dropwise to the filtrate, followed by vacuum evaporation, concentration, cooling, and crystallization to obtain solid ferrous phosphate. Ferrous phosphate, sodium pyrophosphate, sucrose, oxalic acid, and pure water are stirred to form a uniform slurry. The slurry is ground, treated to remove iron, and then spray-dried to obtain precursor powder. The precursor powder is sintered at high temperature, pulverized by airflow, and treated to remove iron under an inert atmosphere to obtain the composite sodium iron phosphate cathode material. This invention uses iron slag as an iron source, turning waste into resources, reducing costs and increasing efficiency. The prepared material exhibits good rate capability and cycle performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery positive electrode materials, in particular to a method for preparing a composite sodium iron phosphate positive electrode material by using iron slag solid waste. BACKGROUND

[0002] In recent years, with the rapid development of the new energy automobile market, the lithium ion battery industry has continued to grow rapidly, but the domestic lithium resources are scarce, and the supply is in a state of tension. Lithium ion batteries urgently need to find a high cost-effective replacement solution. Sodium ion batteries are currently the best replacement solution for lithium ion batteries due to their overall cost-effective advantage.

[0003] Polyanion-type materials have the characteristics of stable crystal structure, high thermal stability, adjustable voltage, and adjustable chemical composition, and are one of the most widely studied sodium ion battery positive electrode materials. PO4 3- and P2O7 4- The composite sodium iron phosphate positive electrode material (Na4Fe3(PO4)2(P2O7), abbreviated as NFPP) coexisting with polyanions has the advantages of low cost, good safety, simple preparation process, and strong cycle stability, and has become the most potential polyanion-type positive electrode material for sodium ion batteries.

[0004] According to the selection of the iron source, the mainstream production process of NFPP can be divided into four routes: ferrous phosphate process, ferrous oxalate process, red iron oxide process, and ferric nitrate process. Among the above technical routes, the ferrous phosphate process has high technical barriers and high process cost, and a large amount of wastewater containing nitrogen and phosphorus is generated during the production process of ferrous phosphate; the supply chain of ferrous oxalate is not complete, so the cost of the iron source is much higher than that of other routes; the production process of ferric nitrate has great environmental protection pressure, and the process control is difficult, so the production control is difficult; the positive electrode material prepared by the red iron oxide process has poor electrochemical performance, and the market competitiveness is weak.

[0005] China is a major steel producer, with the world's first steel production, and iron slag is a waste generated during the steel production process, and its main components are iron, as well as a small amount of SiO2, Al2O3, CaO, MgO, MnO, Fe2O3 and other impurities. Developing a process for preparing a composite sodium iron phosphate positive electrode material based on waste iron slag can realize the recycling of solid waste and reduce the cost of the material, and has very obvious economic and social benefits. SUMMARY

[0006] Therefore, the application aims to provide a method for preparing a composite sodium iron phosphate positive electrode material by using iron slag solid waste, so as to solve the problems of complex preparation process and high preparation cost of the existing composite sodium iron phosphate positive electrode material.

[0007] To achieve the above-mentioned purpose, the technical scheme of the application is as follows:

[0008] A method for preparing a composite sodium iron phosphate positive electrode material from iron slag solid waste, comprising the following steps:

[0009] 1) crushing and screening the iron slag to obtain iron slag particles;

[0010] 2) adding sulfuric acid to the iron slag particles for a dissolution reaction, with heating and stirring during the reaction to obtain acid hydrolysis solution A;

[0011] 3) adding iron powder to the acid hydrolysis solution A, stirring for a period of time, then filtering, and then removing the magnetism of the obtained filtrate to obtain solution B;

[0012] 4) heating the solution B to a specific temperature, then slowly adding sodium hydroxide solution, maintaining stirring during the addition, stopping the addition when the pH value reaches a specified pH value, then adding a flocculating agent and continuing to stir for a period of time, then filtering to separate the solid and the liquid, and obtaining filtrate C;

[0013] 5) detecting and analyzing the Fe 2+ concentration in the filtrate C, and then adding phosphoric acid to the filtrate C under the protection of an inert atmosphere, and then vacuum evaporation, concentration, cooling and crystallization to obtain solid ferrous phosphate;

[0014] 6) adding pure water, sodium pyrophosphate, sucrose and oxalic acid to the ferrous phosphate, stirring to obtain slurry D, grinding and removing the magnetism of the slurry D, and then spray drying to obtain a precursor powder;

[0015] 7) high-temperature sintering, airflow crushing and iron removal of the precursor powder under an inert atmosphere to obtain a composite sodium iron phosphate positive electrode material.

[0016] Optionally, the particle size of the iron slag particles in step 1) is ≤3mm.

[0017] Optionally, the mass concentration of the sulfuric acid in step 2) is 30%-40%, and the reaction liquid temperature of the dissolution reaction is 30-40℃.

[0018] Optionally, the particle size of the iron powder in step 3) is ≤50μm, the addition amount of the iron powder is 5% of the total mass of the iron slag particles, and the magnetic force strength of the demagnetization treatment is ≥8000GS.

[0019] Optionally, the mass concentration of the sodium hydroxide solution in step 4) is 8%-10%, the specified pH value is 4-5, and the specific temperature is 70-90℃.

[0020] Optionally, the flocculating agent in step 4) is polyacrylamide, and the addition amount of the flocculating agent is 1%-3% of the total mass of the solution in step 4).

[0021] Optionally, the Fe in the filtrate C in step 5) is 2+ and the molar ratio of the phosphoric acid is 3:(2.1-2.3).

[0022] Optionally, the molar ratio of the ferrous phosphate, the sodium pyrophosphate and the oxalic acid in step 6) is 1:(1-1.2):(0.8-1).

[0023] Optionally, the amount of the sucrose added in step 6) is 4-6% of the total mass of the ferrous phosphate and the sodium pyrophosphate

[0024] Optionally, the solid content of the slurry D in step 6) is 30-40%, and the magnetic intensity of the magnetic removal treatment is ≥8000GS.

[0025] Optionally, the iron removal treatment in step 7) is an electromagnetic iron removal mode, the iron removal current is 22-26A, and the iron removal voltage is 170-190V; the sintering temperature of the high-temperature sintering is 600-800℃, and the sintering time is 8-10h.

[0026] Compared with the prior art, the method for preparing the composite sodium iron phosphate positive material from the iron slag solid waste has the following advantages:

[0027] 1. For the impurities in the iron slag solid waste, the present application achieves purification and impurity removal through multi-stage impurity removal. The impurity cations are precipitated as hydroxides by adjusting the pH value of the solution with sodium hydroxide. Polyacrylamide is added to remove impurities through coagulation and flocculation. Deep impurity removal is achieved through permanent magnet iron removal and electromagnetic iron removal, effectively reducing impurity elements in the material.

[0028] 2. The iron slag solid waste is turned into a benefit, and the iron in the iron slag byproduct of the steel industry is efficiently utilized, greatly improving the added value of the iron slag solid waste. Using iron slag as the iron source of the composite sodium iron phosphate positive material significantly reduces the production cost of the composite sodium iron phosphate positive material.

[0029] 3. The industrial production of iron phosphate is mostly synthesized by liquid phase precipitation method, which has a complicated reaction process, high technical barriers and high process cost. The industrial production of ferric nitrate requires strong oxidizing nitric acid, and the production process generates nitrogen oxide byproducts, which has high environmental protection pressure, difficult process control and large production control difficulty. The cost of ferrous oxalate material is high, and the performance of red iron oxide is poor. Compared with the above iron sources, the present application uses iron slag as the iron source of the composite sodium iron phosphate positive material, which has low production cost, simple reaction process, easy operation and simple equipment.

[0030] 4. The material prepared by the method provided by the present invention has a small particle size and uniform particle size distribution. Oxalic acid and sucrose, as composite carbon sources, are transformed into carbon layers during high-temperature sintering and carbonization, uniformly coating the surface of the material. This can effectively improve the electrical conductivity of the material and provide an effective buffer for volume changes during the charging and discharging process. The prepared material has excellent rate performance and cycle performance. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 The image shown is a scanning electron microscope image of the composite sodium iron phosphate cathode material prepared in Example 1 of this invention.

[0033] Figure 2 This is a rate performance diagram of the composite sodium iron phosphate cathode material prepared in Example 1 of the present invention;

[0034] Figure 3 The diagram shows the cycle performance of the composite sodium iron phosphate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions and effects of the present invention, several embodiments will be provided below. Obviously, the following description is only an embodiment and does not limit the scope of protection of the present invention.

[0036] Example 1

[0037] A method for preparing composite sodium iron phosphate cathode material using iron slag solid waste includes the following steps:

[0038] 1) Crush and screen 100g of iron slag to obtain iron slag particles with a particle size ≤3mm;

[0039] 2) Place the iron slag particles in a reaction vessel, and then add sulfuric acid with a mass concentration of 30% for dissolution reaction. During the reaction, heat and stir at the same time, and maintain the temperature of the reaction solution in the vessel at 40℃ for 40 minutes to obtain acid hydrolysate A;

[0040] 3) Add 5g of iron powder with a particle size of 50μm to the acid hydrolysate A, stir and react for 30min, then filter. The resulting filtrate is demagnetized by passing it through an iron separator with a magnetic strength of 8000GS to obtain solution B.

[0041] 4) Heat solution B to 80℃ and keep it at that temperature. Then slowly add a 10% sodium hydroxide solution while stirring. Stop adding the sodium hydroxide solution when the pH reaches 4. Then weigh 3% of the total mass of the solution and add it to the solution. Continue stirring for 30 minutes. Then filter the solution to separate the solid and liquid and obtain the filtrate C.

[0042] 5) Detect and analyze Fe in filtrate C 2+ Concentration, under nitrogen atmosphere protection, according to Fe 2+ The molar ratio of ferrous phosphate to phosphoric acid is 3:2.3. Phosphoric acid is added to the filtrate C, and then the solution is concentrated under vacuum, cooled and crystallized to obtain solid ferrous phosphate.

[0043] 6) Weigh the three materials according to the molar ratio of ferrous phosphate, sodium pyrophosphate and oxalic acid of 1:1.2:1. Weigh sucrose according to 6% of the total mass of ferrous phosphate and sodium pyrophosphate. Then add pure water and stir the four materials of ferrous phosphate, sodium pyrophosphate and oxalic acid evenly to obtain slurry D with a solid content of 40%. After grinding slurry D, it is flowed through an iron separator with a magnetic strength of 8000GS for demagnetization treatment, and then spray dried to obtain precursor powder.

[0044] 7) The precursor powder was subjected to high-temperature sintering treatment under nitrogen atmosphere. The sintering temperature was 800℃ and the sintering time was 8h. After the sintered material was pulverized by airflow, it was subjected to electromagnetic iron removal treatment to obtain composite sodium iron phosphate cathode material. The electromagnetic iron removal current was 26A and the electromagnetic iron removal voltage was 190V.

[0045] Example 2

[0046] A method for preparing composite sodium iron phosphate cathode material using iron slag solid waste includes the following steps:

[0047] 1) Crush and screen 100g of iron slag to obtain iron slag particles with a particle size ≤3mm;

[0048] 2) Place the iron slag particles in a reaction vessel, and then add sulfuric acid with a mass concentration of 40% for dissolution reaction. During the reaction, heat and stir at the same time, and maintain the temperature of the reaction solution in the vessel at 30°C for 40 minutes to obtain acid hydrolysate A.

[0049] 3) Add 5g of iron powder with a particle size of 50μm to the acid hydrolysate A, stir and react for 30min, then filter. The resulting filtrate is demagnetized by passing it through an iron separator with a magnetic strength of 8000GS to obtain solution B.

[0050] 4) Heat solution B to 90℃ and keep it at that temperature. Then slowly add an 8% sodium hydroxide solution while stirring. Stop adding the sodium hydroxide solution when the pH reaches 5. Then weigh 1% of the total mass of the solution and add it to the solution. Continue stirring for 30 minutes. Then filter the solution to separate the solid and liquid and obtain the filtrate C.

[0051] 5) Detect and analyze Fe in filtrate C 2+ Concentration, under nitrogen atmosphere protection, according to Fe 2+ The molar ratio of ferrous phosphate to phosphoric acid is 3:2.1. Phosphoric acid is added to the filtrate C, and then the solution is concentrated under vacuum, cooled and crystallized to obtain solid ferrous phosphate.

[0052] 6) Weigh the three materials according to the molar ratio of ferrous phosphate, sodium pyrophosphate and oxalic acid of 1:1:0.8. Weigh sucrose according to 4% of the total mass of ferrous phosphate and sodium pyrophosphate. Then add pure water and stir the four materials of ferrous phosphate, sodium pyrophosphate, oxalic acid and sucrose evenly to obtain slurry D with a solid content of 30%. After grinding slurry D, it is flowed through an iron separator with a magnetic strength of 8000GS for demagnetization treatment. Then it is spray dried to obtain precursor powder.

[0053] 7) The precursor powder was subjected to high-temperature sintering treatment under nitrogen atmosphere. The sintering temperature was 600℃ and the sintering time was 10h. After the sintered material was pulverized by airflow, it was subjected to electromagnetic iron removal treatment to obtain composite sodium iron phosphate cathode material. The electromagnetic iron removal current was 22A and the electromagnetic iron removal voltage was 170V.

[0054] The microstructure and electrical properties of the composite sodium iron phosphate cathode material prepared in Example 1 of this invention were tested, and the test results are as follows: Figures 1-3 .

[0055] in, Figure 1 This is a scanning electron microscope image of the composite sodium iron phosphate cathode material prepared in Example 1 of this invention. Figure 1 It can be seen that the composite sodium iron phosphate material is a spherical nanomaterial with a particle size range of 200-500 nm.

[0056] Figure 2 The rate performance diagram of the composite sodium iron phosphate cathode material prepared in Example 1 is shown. The material was subjected to charge-discharge cycles at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C. Figure 2 It can be seen that the discharge capacities from 0.1C to 5C are 110.3, 108.1, 105.3, 101.5, 98.3, and 95.8 mAh·g, respectively. -1The discharge capacities at 0.1C and 50C are 110.3mAh / g and 95.8mAh / g, respectively, with a capacity retention rate of 86.9%. The material exhibits good rate performance and high rate capacity retention.

[0057] Figure 3 This is a cycle performance diagram of the composite sodium iron phosphate cathode material prepared in Example 1. (From...) Figure 3 It can be seen that, at a current density of 0.1C, the discharge capacity of the composite sodium iron phosphate cathode material is 109.6 mAh·g. -1 After 200 cycles, the capacity is 108.3 mAh·g. -1 The capacity retention rate is 98.8%. It is evident that the material shows almost no loss after 200 cycles, demonstrating excellent cycling performance.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing composite sodium iron phosphate cathode material using iron slag solid waste, characterized in that, Includes the following steps: 1) The iron slag is crushed and screened to obtain iron slag particles; 2) Add sulfuric acid to the iron slag particles to carry out a dissolution reaction. During the reaction, heat and stir simultaneously to obtain acid hydrolysate A; 3) Add iron powder to the acid hydrolysate A, stir and react for a period of time, then filter the solution. The resulting filtrate is demagnetized to obtain solution B. 4) Heat the solution B to a specific temperature and keep it at that temperature. Then slowly add sodium hydroxide solution dropwise while stirring. Stop adding sodium hydroxide solution dropwise when the pH value reaches the specified pH value. Then add flocculant and continue stirring for a period of time. Then filter the solution to separate the solid and liquid and obtain filtrate C. 5) Detect and analyze Fe in the filtrate C 2+ To determine the concentration, under an inert atmosphere, phosphoric acid was added dropwise to the filtrate C, followed by vacuum evaporation, concentration, cooling, and crystallization to obtain solid ferrous phosphate. 6) Add pure water, sodium pyrophosphate, sucrose and oxalic acid to the ferrous phosphate and stir evenly to obtain slurry D. The slurry D is ground and demagnetized, and then spray dried to obtain precursor powder. 7) The precursor powder is subjected to high-temperature sintering, air jet milling and iron removal treatment under an inert atmosphere to obtain a composite sodium iron phosphate cathode material. In step 3), the particle size of the iron powder is ≤50μm, the amount of iron powder added is 5% of the total mass of the iron slag particles, and the magnetic strength of the demagnetization treatment is ≥8000 GS. The flocculant mentioned in step 4) is polyacrylamide, and the amount of flocculant added is 1% to 3% of the total mass of the solution in step 4). Fe in the filtrate C described in step 5) 2+ The molar ratio of phosphoric acid to phosphoric acid is 3: (2.1 to 2.3). In step 6), the molar ratio of ferrous phosphate, sodium pyrophosphate, and oxalic acid is 1:(1-1.2):(0.8-1); the amount of sucrose added is 4-6% of the total mass of ferrous phosphate and sodium pyrophosphate. The iron removal process described in step 7) is an electromagnetic iron removal method, with an iron removal current of 22-26A and an iron removal voltage of 170-190V; the high-temperature sintering process is carried out at a sintering temperature of 600-800℃ and a sintering time of 8-10h.

2. The method for preparing composite sodium iron phosphate cathode material using iron slag solid waste according to claim 1, characterized in that, The particle size of the iron slag particles mentioned in step 1) is ≤3mm.

3. The method for preparing composite sodium iron phosphate cathode material using iron slag solid waste according to claim 1, characterized in that, The mass concentration of sulfuric acid in step 2) is 30% to 40%, and the reaction temperature of the dissolution reaction solution is 30-40℃.

4. The method for preparing composite sodium iron phosphate cathode material using iron slag solid waste according to claim 1, characterized in that, The sodium hydroxide solution in step 4) has a mass concentration of 8% to 10%, a specified pH value of 4 to 5, and a specific temperature of 70 to 90°C.

5. The method for preparing composite sodium iron phosphate cathode material using iron slag solid waste according to claim 1, characterized in that, The solid content of the slurry D in step 6) is 30% to 40%, and the magnetic strength of the demagnetization treatment is ≥8000 GS.

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