Sodium battery cathode material, preparation method thereof and battery

Abstract

The application belongs to the technical field of battery materials, and discloses a sodium battery positive electrode material, a preparation method thereof and a battery. The method comprises the following steps: obtaining iron concentrate by adopting iron ore and performing multi-stage magnetic separation and flotation treatment; mixing phosphoric acid and pyrophosphoric acid to obtain mixed acid; adding the iron concentrate into the mixed acid, and then performing filtration treatment so that the content of suspended solids in the filtrate is lower than 100 ppm, thereby obtaining an iron and phosphorus-containing solution material; uniformly mixing metatitanic acid and sodium carbonate, and then performing calcination, subsequent cooling and discharging, and grinding treatment, thereby obtaining a dopant; stirring the solution material at a second stirring speed, adding a sodium source, a carbon source and the dopant to obtain slurry, and performing spray drying on the slurry, thereby obtaining a sodium pyrophosphate iron phosphate material, and the sodium pyrophosphate iron phosphate material is a sodium battery positive electrode material. The preparation method of the battery positive electrode material has the advantages of low preparation cost, short process flow, good environmental protection and ideal electrical performance of the obtained sodium battery positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a sodium battery cathode material, its preparation method, and the battery itself. Background Technology

[0002] In recent years, with the continuous rise in lithium carbonate prices, sodium-ion batteries have attracted widespread attention due to their significant cost advantages, and their market penetration rate is expected to increase rapidly. Currently, the annual sales volume of sodium battery cathode materials has reached 50,000 tons, and it is projected to grow at a rate of 100% to 500% annually in the future, indicating a significant acceleration in industrialization. In existing technologies, the preparation of sodium battery cathode materials typically uses high-purity iron as a raw material, adding iron powder to reduce ferric iron to ferrous sulfate, and then further preparing iron phosphate to finally synthesize the sodium battery cathode material. This route uses a high-purity iron source to synthesize a precursor via liquid-phase co-precipitation, which is then mixed with sodium and carbon sources and sintered at high temperature to obtain the cathode active material. This process requires first converting the iron source into iron phosphate or a similar compound, followed by multiple filtrations, washing, and drying to obtain a solid precursor, which is then ground and mixed, and finally sintered under an inert atmosphere.

[0003] The above technical approach has many shortcomings: The process is lengthy and energy-intensive, involving multiple steps of liquid-phase reaction and solid-phase treatment. The procedures are complex and energy consumption is high. Co-precipitation and washing processes generate large amounts of acidic and saline wastewater, resulting in high treatment costs. To ensure electrochemical performance, a high-purity chemical-grade iron source must be used, severely undermining the cost advantage of low-cost ore raw materials. Solid-phase mixing makes it difficult to achieve a uniform distribution of elements at the atomic scale, easily leading to particle agglomeration and uneven ion distribution. Incomplete local reactions during sintering affect the consistency and purity of the product structure. This condensation reaction requires high temperatures, has a narrow reaction window, and is prone to generating impurity phases, limiting further improvement in the material's final performance.

[0004] Therefore, there is an urgent need to develop a new sodium battery cathode material preparation process that can make full use of low-cost, high-purity iron concentrate, simplify the process, be environmentally friendly, and ensure the uniformity of product structure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a sodium battery cathode material, its preparation method, and a battery, aiming to improve the problems of high preparation cost, long process flow, poor environmental performance, and unsatisfactory electrical performance of existing sodium battery cathode material preparation methods.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a sodium battery cathode material is provided, including the following steps: Iron concentrate is obtained by processing iron ore through multi-stage magnetic separation and flotation. Phosphoric acid and pyrophosphoric acid are mixed to obtain a mixed acid; The iron concentrate is added to the mixed acid and stirred at 90-110°C at the first stirring speed for 2-4 hours. Pure water is added for slurry treatment to bring the iron content to 1.0-2.0 mol / L. Then, the mixture is filtered to bring the suspended solids content in the filtrate to less than 100 ppm, thus obtaining a solution containing iron and phosphorus. After mixing metatitanic acid and sodium carbonate evenly, the mixture is calcined at a heating rate of 100~200℃ / h, and then heated to 700~800℃ and held for calcination for 3~6h. After cooling and discharging, the mixture is ground to obtain the dopant. The solution is stirred at a second stirring speed, and a sodium source, a carbon source, and a dopant are added to obtain a slurry. The slurry is then spray-dried under the following conditions: inlet air temperature of 200~350℃ and outlet air temperature of 80~100℃, so that the particle size of the spray-dried material is 5~25μm and the material moisture content is ≤1.5wt%, to obtain sodium iron phosphate pyrophosphate material, which is a cathode material for sodium batteries.

[0007] Furthermore, the iron concentrate has an iron content of ≥71wt%, wherein the content of iron(III) oxide is ≥97wt%.

[0008] The iron concentrate has the following particle size requirements: 90 wt% of the material passes through a 200-mesh sieve, and 50-70 wt% of the material passes through a 400-mesh sieve; the content of calcium, magnesium, and aluminum in the iron concentrate is less than 500 ppm each, and the content of nickel, cobalt, copper, and zinc is less than 50 ppm each.

[0009] Furthermore, the molar ratio of phosphoric acid to pyrophosphoric acid is 2:1.05~1.10, and the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid is 2.85-3.15:4.

[0010] Furthermore, the molar ratio of the metatitanic acid to the sodium carbonate is 4~6:1.5~3.

[0011] Furthermore, the particle size of the dopant is 0.3-0.6 μm.

[0012] Furthermore, the stirring speed of the first stirrer is 200~400 r / min; the stirring speed of the second stirrer is 500~1000 r / min.

[0013] Furthermore, the carbon source is at least one of glucose, sucrose, water-soluble starch, fructose, and PEG.

[0014] Furthermore, the sodium source is at least one of battery-grade sodium carbonate, battery-grade sodium bicarbonate, and battery-grade sodium hydroxide.

[0015] Furthermore, the amount of carbon source added results in a carbon content of 1.50~2.50 wt% in the final product; wherein the sodium source is added over a period of 15~45 min; and the amount of dopant added is 0.3~1.0% of the mass of the sodium source. The molar ratio of sodium in the sodium source to phosphorus in the filtrate is 1.01~1.05:1.

[0016] Furthermore, during the calcination process, nitrogen gas is introduced to ensure that the oxygen content in the atmosphere is ≤10ppm, and the furnace pressure inside the calcination furnace is maintained at 50~70Pa. Then, the material is cooled to ≤100℃ before being discharged to obtain sodium iron phosphate pyrophosphate material.

[0017] Sodium battery cathode materials are also provided, which are prepared by the above-described preparation method.

[0018] A battery is also provided, the positive electrode material of which is the aforementioned sodium battery positive electrode material.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention uses high-grade iron ore as raw material. The iron ore is subjected to magnetic separation and multi-stage flotation processes to obtain high-purity iron concentrate with an iron content of more than 97% based on iron oxide. The main phase is iron oxide, and the residual impurities are mainly oxides of elements such as aluminum, silicon, magnesium, manganese, and calcium. The contents of calcium, magnesium, and aluminum are all less than 500 ppm, and the contents of nickel, cobalt, copper, and zinc are all less than 50 ppm. The market price of this iron concentrate is about RMB 1,300 / ton, which is much lower than that of conventional chemical-grade iron powder. It has significant economic advantages and overcomes the problem of high cost that exists when using high-purity iron sources as raw materials.

[0020] (2) The present invention uses a mixture of phosphoric acid and pyrophosphate to directly leach iron concentrate. During the leaching stage, the pyrophosphate ions required for the target product are introduced. In the subsequent calcination process, there is no need to carry out high-temperature condensation conversion of phosphate ions to pyrophosphate ions, which avoids the problem of easily generating sodium iron phosphate impurity phase in the traditional high-temperature condensation reaction and ensures the phase purity of the product sodium iron phosphate pyrophosphate.

[0021] (3) In this invention, the filtrate after mixed acid leaching is an ionic solution. The sodium source, carbon source and dopant added subsequently enable molecular-level uniform mixing in the liquid phase. Micron-level mixing can be achieved without traditional solid-phase mechanical grinding, resulting in uniform distribution of each element at the atomic scale. This effectively avoids the problems of ion segregation and particle agglomeration, ultimately making the structure of the calcined product more consistent and the electrochemical performance more stable. The addition of dopant can also improve the ionic conductivity of the material and increase the capacity of the material.

[0022] (4) The present invention uses spray drying to granulate the liquid precursor. During the instantaneous drying process, the droplets naturally shrink into spherical particles. The spherical morphology is retained after calcination. The cathode material powder with good flowability and stacking characteristics can be obtained without secondary grinding. The grinding process in the traditional process is eliminated, the process is shortened, and energy consumption and equipment investment are reduced.

[0023] (5) In the entire production process of this invention, the filtrate after mixed acid leaching is directly used for subsequent synthesis without the need for co-precipitation, filtration, and washing processes. It basically does not generate acidic or salty wastewater, overcoming the problem of traditional methods that require large amounts of wastewater discharge, and significantly reducing the environmental burden. At the same time, iron concentrate is a widely available industrial mineral with stable output and sufficient supply, and the raw material supply is highly reliable, making it suitable for large-scale production and application.

[0024] (6) The process of this invention is short, low-cost and environmentally friendly. The overall cost is reduced by more than 15% compared with the traditional iron phosphate or iron oxide red process. The resulting sodium iron phosphate pyrophosphate material has high phase purity and high compaction density, and is suitable for large-scale low-cost production of sodium-ion batteries. Attached Figure Description

[0025] Figure 1 This is a SEM image of the sodium iron phosphate pyrophosphate material from Experiment Example 1.

[0026] Figure 2 This is the XRD pattern of Experiment Example 1. Detailed Implementation

[0027] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention have been shown, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0028] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a” and “the” as used in this invention and the appended claims are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0029] It should be understood that although the terms "first," "second," "third," etc., may be used in this invention to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this invention, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] Example 1 This embodiment provides a method for preparing a sodium battery cathode material, including the following steps: Preparation of iron concentrate: High-grade iron ore is subjected to multi-stage magnetic separation and flotation to obtain iron concentrate. In this embodiment, the iron concentrate has an iron content of 71 wt% and a magnetite (Fe3O4) content of 97 wt%; in terms of particle size, 90 wt% of the material passes through a 200-mesh sieve, and 50 wt% passes through a 400-mesh sieve; the impurity content is as follows: calcium, magnesium, and aluminum are all below 500 ppm, and nickel, cobalt, copper, and zinc are all below 50 ppm.

[0031] Preparation of mixed acid: Phosphoric acid and pyrophosphate are mixed at a molar ratio of 2:1.05 to obtain mixed acid.

[0032] Mixed acid leaching and filtration: The above-mentioned iron concentrate was added to a mixed acid, controlling the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid to be 2.85:4. Pure water was added for slurry treatment to control the iron content at 1.0 mol / L. The reaction was carried out at 90℃ with a stirring speed of 200 r / min for 4 hours, followed by filtration to ensure that the suspended solids content in the filtrate was below 100 ppm, yielding a solution containing iron and phosphorus.

[0033] Preparation of dopant: Metatitanic acid and sodium carbonate were mixed evenly at a molar ratio of 4:1.5 and then placed in a muffle furnace for calcination. The temperature was increased to 700℃ at a heating rate of 100℃ / h and held for calcination for 6h. After cooling, the material was discharged and ground to a particle size of 0.3μm using a pot mill. The material was then discharged for use.

[0034] Mixing and Spray Drying: A sodium source (battery-grade sodium carbonate), a carbon source (glucose), and a dopant were sequentially added to the resulting solution under stirring at a speed of 500 r / min. The molar ratio of sodium in the sodium source to phosphorus in the filtrate was 1.01:1; the sodium carbonate was added over a period of 5 min; the dopant was added at 0.3% of the sodium source mass; and the carbon source was added to achieve a final product carbon content of 1.50 wt%. The resulting slurry was then spray-dried at an inlet air temperature of 200℃ and an outlet air temperature of 80℃ to obtain a spray-dried material with a particle size of 5 μm and a moisture content of 1.5 wt%.

[0035] Calcination: The spray-dried material is placed in a calcination furnace, nitrogen is introduced to make the oxygen content in the furnace ≤10ppm, the furnace pressure is maintained at 50Pa, the temperature is raised to 500℃ at a heating rate of 100℃ / h, and calcined at this temperature for 8h. After cooling to the material temperature ≤100℃, the material is removed from the furnace, crushed, sieved, de-ironized and packaged to obtain sodium iron phosphate pyrophosphate material.

[0036] Example 2 This embodiment provides a method for preparing a sodium battery cathode material, including the following steps: Preparation of iron concentrate: High-grade iron ore is subjected to multi-stage magnetic separation and flotation to obtain iron concentrate. In this embodiment, the iron concentrate has an iron content of 73 wt% and a magnetite (Fe3O4) content of 98.5 wt%. Regarding particle size, 90 wt% of the material passes through a 200-mesh sieve, and 60 wt% passes through a 400-mesh sieve. The impurity content is as follows: calcium, magnesium, and aluminum are all below 500 ppm; nickel, cobalt, copper, and zinc are all below 50 ppm.

[0037] Preparation of mixed acid: Phosphoric acid and pyrophosphate are mixed at a molar ratio of 2:1.075 to obtain mixed acid.

[0038] Mixed acid leaching and filtration: The above-mentioned iron concentrate was added to a mixed acid, controlling the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid to be 3.0:4. Pure water was added for slurry treatment to control the iron content at 1.5 mol / L. The mixture was reacted at 100℃ with a stirring speed of 300 r / min for 3 h, followed by filtration to ensure that the suspended solids content in the filtrate was below 100 ppm, yielding a solution containing iron and phosphorus.

[0039] Preparation of dopant: Metatitanic acid and sodium carbonate were mixed evenly in a molar ratio of 5:2.05 and then calcined in a muffle furnace. The temperature was increased to 750℃ at a heating rate of 150℃ / h and held for calcination for 4.5h. After cooling, the material was discharged and ground in a mill to a particle size of 0.45μm. The material was then discharged for use.

[0040] Mixing and Spray Drying: A sodium source (battery-grade sodium bicarbonate), a carbon source (sucrose), and a dopant were added sequentially to the resulting solution under stirring at a speed of 750 r / min. The molar ratio of sodium in the sodium source to phosphorus in the filtrate was 1.03:1; the sodium bicarbonate was added over a period of 10 min; the dopant was added at 0.65% of the sodium source mass; and the carbon source was added to achieve a final product carbon content of 2.0 wt%. The resulting slurry was then spray-dried at an inlet air temperature of 275℃ and an outlet air temperature of 90℃ to obtain a spray-dried material with a particle size of 15 μm and a moisture content of 1.2 wt%.

[0041] Calcination: The spray-dried material is placed in a calcination furnace, nitrogen is introduced to make the oxygen content in the furnace ≤10ppm, the furnace pressure is maintained at 60Pa, the temperature is raised to 550℃ at a heating rate of 150℃ / h, and calcined at this temperature for 6h. After cooling to the material temperature ≤100℃, the material is removed from the furnace, crushed, sieved, iron removed and packaged to obtain sodium iron phosphate pyrophosphate material.

[0042] Example 3 This embodiment provides a method for preparing a sodium battery cathode material, including the following steps: Preparation of iron concentrate: High-grade iron ore is subjected to multi-stage magnetic separation and flotation to obtain iron concentrate. In this embodiment, the iron concentrate has an iron content of 75 wt% and a magnetite (Fe3O4) content of 99.5 wt%. Regarding particle size, 90 wt% of the material passes through a 200-mesh sieve, and 70 wt% passes through a 400-mesh sieve. The impurity content is as follows: calcium, magnesium, and aluminum are all below 500 ppm; nickel, cobalt, copper, and zinc are all below 50 ppm.

[0043] Preparation of mixed acid: Phosphoric acid and pyrophosphate are mixed at a molar ratio of 2:1.10 to obtain mixed acid.

[0044] Mixed acid leaching and filtration: The above-mentioned iron concentrate was added to a mixed acid, controlling the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid to be 3.15:4. Pure water was added for slurry treatment to control the iron content at 2.0 mol / L. The reaction was carried out at 110℃ with a stirring speed of 400 r / min for 2 h, followed by filtration to ensure that the suspended solids content in the filtrate was below 100 ppm, yielding a solution containing iron and phosphorus.

[0045] Preparation of dopant: Metatitanic acid and sodium carbonate were mixed evenly at a molar ratio of 6:3 and then placed in a muffle furnace for calcination. The temperature was increased to 800℃ at a heating rate of 200℃ / h and held for calcination for 3h. After cooling, the material was discharged and ground to a particle size of 0.6μm using a pot mill. The material was then discharged for use.

[0046] Mixing and Spray Drying: A sodium source (battery-grade sodium hydroxide), a carbon source (water-soluble starch), and a dopant were added sequentially to the resulting solution under stirring at a speed of 1000 r / min. The molar ratio of sodium in the sodium source to phosphorus in the filtrate was 1.05:1; the sodium hydroxide was added over a period of 15 min; the dopant was added at 1.0% of the sodium source mass; and the carbon source was added to achieve a final product carbon content of 2.50 wt%. The resulting slurry was then spray-dried at an inlet air temperature of 350℃ and an outlet air temperature of 100℃ to obtain a spray-dried material with a particle size of 25 μm and a moisture content of 1.0 wt%.

[0047] Calcination: The spray-dried material is placed in a calcination furnace, nitrogen is introduced to make the oxygen content in the furnace ≤10ppm, the furnace pressure is maintained at 70Pa, the temperature is raised to 600℃ at a heating rate of 200℃ / h, and calcined for 4h. After cooling to the material temperature ≤100℃, the material is taken out of the furnace, crushed, sieved, iron removed and packaged to obtain sodium iron phosphate pyrophosphate material.

[0048] Example 4 This embodiment provides a method for preparing a sodium battery cathode material, including the following steps: Preparation of iron concentrate: High-grade iron ore is subjected to multi-stage magnetic separation and flotation to obtain iron concentrate. In this embodiment, the iron concentrate has an iron content of 72 wt% and a magnetite (Fe3O4) content of 98 wt%; in terms of particle size, 90 wt% of the material passes through a 200-mesh sieve, and 55 wt% passes through a 400-mesh sieve; the impurity content is as follows: calcium, magnesium, and aluminum are all below 500 ppm, and nickel, cobalt, copper, and zinc are all below 50 ppm.

[0049] Preparation of mixed acid: Phosphoric acid and pyrophosphate are mixed at a molar ratio of 2:1.06 to obtain mixed acid.

[0050] Mixed acid leaching and filtration: The above-mentioned iron concentrate was added to a mixed acid, controlling the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid to be 2.90:4. Pure water was added for slurry treatment to control the iron content at 1.2 mol / L. The reaction was carried out at 95℃ with a stirring speed of 250 r / min for 3.5 h, followed by filtration to ensure that the suspended solids content in the filtrate was below 100 ppm, yielding a solution containing iron and phosphorus.

[0051] Preparation of dopant: Metatitanic acid and sodium carbonate were mixed evenly at a molar ratio of 4.5:1.8 and then placed in a muffle furnace for calcination. The temperature was increased to 720℃ at a heating rate of 120℃ / h and held for 5h. After cooling, the material was discharged and ground to a particle size of 0.35μm using a pot mill. The material was then discharged for use.

[0052] Mixing and Spray Drying: A sodium source (a mixture of battery-grade sodium carbonate and battery-grade sodium bicarbonate in an equimolar ratio), a carbon source (fructose), and a dopant were added sequentially to the resulting solution under stirring at a speed of 600 r / min. The molar ratio of sodium in the sodium source to phosphorus in the filtrate was 1.02:1; the sodium source was added over an 8-min period; the dopant was added at 0.5% of the sodium source mass; and the carbon source was added to achieve a final product carbon content of 1.8 wt%. The resulting slurry was then spray-dried at an inlet air temperature of 230℃ and an outlet air temperature of 85℃ to obtain a spray-dried material with a particle size of 10 μm and a moisture content of 1.3 wt%.

[0053] Calcination: The spray-dried material is placed in a calcination furnace, nitrogen is introduced to make the oxygen content in the furnace ≤10ppm, the furnace pressure is maintained at 55Pa, the temperature is raised to 520℃ at a heating rate of 120℃ / h, and calcined for 7h. After cooling to the material temperature ≤100℃, the material is taken out of the furnace, crushed, sieved, iron removed and packaged to obtain sodium iron phosphate pyrophosphate material.

[0054] Example 5 This embodiment provides a method for preparing a sodium battery cathode material, including the following steps: Preparation of iron concentrate: High-grade iron ore is subjected to multi-stage magnetic separation and flotation to obtain iron concentrate. In this embodiment, the iron concentrate has an iron content of 74 wt% and a magnetite (Fe3O4) content of 99 wt%; in terms of particle size, 90 wt% of the material passes through a 200-mesh sieve, and 65 wt% passes through a 400-mesh sieve; the impurity content is as follows: calcium, magnesium, and aluminum are all below 500 ppm, and nickel, cobalt, copper, and zinc are all below 50 ppm.

[0055] Preparation of mixed acid: Phosphoric acid and pyrophosphate are mixed at a molar ratio of 2:1.09 to obtain mixed acid.

[0056] Mixed acid leaching and filtration: The above-mentioned iron concentrate was added to a mixed acid, controlling the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid to be 3.10:4. Pure water was added for slurry treatment to control the iron content at 1.8 mol / L. The reaction was carried out at 105℃ with a stirring speed of 350 r / min for 2.5 h, followed by filtration to ensure that the suspended solids content in the filtrate was below 100 ppm, yielding a solution containing iron and phosphorus.

[0057] Preparation of dopant: Metatitanic acid and sodium carbonate were mixed evenly in a molar ratio of 5.5:2.5 and then calcined in a muffle furnace. The temperature was increased to 780℃ at a heating rate of 180℃ / h and held for 3.5h. After cooling, the material was discharged and ground to a particle size of 0.55μm using a pot mill. The material was then discharged for use.

[0058] Mixing and Spray Drying: A sodium source (battery-grade sodium carbonate), a carbon source (PEG), and a dopant were added sequentially to the resulting solution under stirring at a speed of 900 r / min. The molar ratio of sodium in the sodium source to phosphorus in the filtrate was 1.04:1; the sodium carbonate was added over a period of 12 min; the dopant was added at 0.8% of the sodium source mass; and the carbon source was added to achieve a final carbon content of 2.3 wt%. The resulting slurry was then spray-dried at an inlet air temperature of 320℃ and an outlet air temperature of 95℃ to obtain a spray-dried material with a particle size of 20 μm and a moisture content of 0.8 wt%.

[0059] Calcination: The spray-dried material is placed in a calcination furnace, nitrogen is introduced to make the oxygen content in the furnace ≤10ppm, the furnace pressure is maintained at 65Pa, the temperature is raised to 580℃ at a heating rate of 180℃ / h, and calcined for 5h. After cooling to the material temperature ≤100℃, the material is taken out of the furnace, crushed, sieved, iron removed and packaged to obtain sodium iron phosphate pyrophosphate material.

[0060] To further illustrate the effectiveness of the preparation method of the present invention, the following experiments were conducted: Experimental Example 1 After iron ore undergoes multi-stage magnetic separation and flotation, iron concentrate is obtained, the composition of which is shown in Table 1 below: Table 1 Properties of iron concentrate

[0061] Phosphoric acid and pyrophosphoric acid were mixed at a molar ratio of 2:1.07 to prepare a mixed acid solution with a density of 1.18 g / mL. The aforementioned iron concentrate was added to the mixed acid solution, controlling the molar ratio of iron in the iron source to phosphorus in the mixed acid to be 3.02:4. Pure water was added for slurry preparation to achieve an iron ion concentration of 1.55 mol / L in the reaction system. The reaction was carried out for 3 hours at a stirring speed of 300 r / min and a temperature of 99℃ to fully complete the acid leaching reaction, allowing iron to enter the solution in a soluble form. After the reaction, solid-liquid separation was performed, and the solution was filtered to obtain a clear filtrate, ensuring that the suspended solids (SS) content in the filtrate was below 100 ppm, thus obtaining a leachate containing iron and phosphorus.

[0062] The method for preparing the dopant is as follows: metatitanic acid and sodium carbonate are mixed evenly at a molar ratio of 5:2.05, and then placed in a muffle furnace for calcination. The temperature is raised to 750℃ at a heating rate of 150℃ / h, and held at this temperature for 4.5 hours. After cooling, the material is discharged and then ground in a can mill to a particle size of 0.45 micrometers to obtain dopant powder for later use.

[0063] The above leachate was placed in a high-speed shear stirring device, and battery-grade sodium carbonate, sucrose, and the aforementioned dopant were slowly added at a stirring speed of 800 r / min. The molar ratio of sodium in the sodium source to phosphorus in the filtrate was 1.03:1; the amount of sucrose added was controlled to ensure the final product carbon content was 2.01 wt%; the sodium carbonate was added over a period of 30 min; and the dopant was added at 0.65% of the sodium source mass. High-speed shearing achieved uniform mixing of the components at the molecular scale, forming a stable slurry.

[0064] The obtained slurry was spray-dried with an inlet air temperature of 300℃ and an outlet air temperature of 90℃ to obtain spherical or near-spherical precursor powder with an average particle size of 12.7μm and a moisture content of ≤1.5wt%.

[0065] The spray-dried powder is fed into a calcining furnace and sintered at high temperature under a nitrogen protective atmosphere, with the oxygen content inside the furnace controlled at ≤10ppm and the furnace pressure maintained at 65Pa. The temperature is increased to 550℃ at a rate of 150℃ / h and held at this temperature for 6 hours to complete the crystal phase transformation reaction. After the reaction is complete, the material is allowed to cool naturally to a temperature ≤100℃ before being removed from the furnace.

[0066] The material exiting the furnace is successively crushed, sieved, and de-ironed, and then packaged to finally obtain sodium iron phosphate pyrophosphate cathode material.

[0067] Scanning electron microscopy (SEM) is used to characterize the microstructure of sodium battery cathode materials, obtaining results such as... Figure 1 The results are shown. Figure 1 As shown, the primary particle size of the material is approximately 100 nm, exhibiting high density and uniform microstructure. The above sodium battery material was fabricated into a coin cell, and its electrical performance was measured, as shown in Table 2.

[0068] Table 2 Electrical properties of sodium battery materials

[0069] The physicochemical data of the above sodium battery materials are shown in Table 3 below.

[0070] Table 3 Physicochemical data of sodium battery materials

[0071] XRD patterns of sodium battery materials, such as Figure 2 As shown, the XRD pattern indicates that the main phase is a monocrystalline form of sodium iron pyrophosphate, with no obvious impurity phase peaks.

[0072] Economic analysis shows that, under the same auxiliary material conditions, the cost of this invention is 3,000 yuan per ton lower than that of the iron phosphate + sodium carbonate process and 2,500 yuan per ton lower than that of the iron oxide red + sodium dihydrogen phosphate process. The overall cost is less than 15,000 yuan / ton, which has a significant cost advantage.

[0073] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a sodium battery cathode material, characterized in that, Includes the following steps: Iron concentrate is obtained by processing iron ore through multi-stage magnetic separation and flotation. Phosphoric acid and pyrophosphoric acid are mixed to obtain a mixed acid; The iron concentrate is added to the mixed acid and stirred at 90-110°C at the first stirring speed for 2-4 hours. Pure water is added for slurry treatment to bring the iron content to 1.0-2.0 mol / L. Then, the mixture is filtered to bring the suspended solids content in the filtrate to less than 100 ppm, thus obtaining a solution containing iron and phosphorus. After mixing metatitanic acid and sodium carbonate evenly, the mixture is calcined at a heating rate of 100~200℃ / h, and then heated to 700~800℃ and held for calcination for 3~6h. After cooling and discharging, the mixture is ground to obtain the dopant. The solution is stirred at a second stirring speed, and a sodium source, a carbon source, and a dopant are added to obtain a slurry. The slurry is then spray-dried under the following conditions: inlet air temperature of 200~350℃ and outlet air temperature of 80~100℃, so that the particle size of the spray-dried material is 5~25μm and the material moisture content is ≤1.5wt%, to obtain sodium iron phosphate pyrophosphate material, which is a cathode material for sodium batteries.

2. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The iron concentrate contains ≥71 wt% iron, of which the content of iron(III) oxide is ≥97 wt%. The iron concentrate has the following particle size requirements: 90 wt% of the material passes through a 200-mesh sieve, and 50-70 wt% of the material passes through a 400-mesh sieve; the content of calcium, magnesium, and aluminum in the iron concentrate is less than 500 ppm each, and the content of nickel, cobalt, copper, and zinc is less than 50 ppm each.

3. The method for preparing the sodium battery cathode material according to claim 2, characterized in that, The molar ratio of phosphoric acid to pyrophosphate is 2:1.05~1.10, and the molar ratio of iron in the iron concentrate to phosphorus in the mixed acid is 2.85~3.15:

4.

4. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The molar ratio of metatitanic acid to sodium carbonate is 4~6:1.5~3.

5. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The particle size of the dopant is 0.3~0.6μm.

6. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The stirring speed of the first stirrer is 200~400 r / min; the stirring speed of the second stirrer is 500~1000 r / min.

7. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The carbon source is at least one of glucose, sucrose, water-soluble starch, fructose, and PEG.

8. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The sodium source is at least one of battery-grade sodium carbonate, battery-grade sodium bicarbonate, and battery-grade sodium hydroxide.

9. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, The amount of carbon source added results in a carbon content of 1.50~2.50 wt% in the final product; the sodium source is added over a period of 15~45 min; and the amount of dopant added is 0.3~1.0% of the mass of the sodium source. The molar ratio of sodium in the sodium source to phosphorus in the filtrate is 1.01~1.05:

1.

10. The method for preparing the sodium battery cathode material according to claim 1, characterized in that, During the calcination process, nitrogen gas is introduced to ensure that the oxygen content in the atmosphere is ≤10ppm, and the furnace pressure in the calcination furnace is maintained at 50~70Pa. Then, the material is discharged after cooling to ≤100℃ to obtain sodium iron phosphate pyrophosphate material.

11. A sodium battery cathode material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 10.

12. A battery, characterized in that, Its positive electrode material is the sodium battery positive electrode material as described in claim 11.

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