Preparation method of composite sodium iron phosphate

Abstract

The application discloses a preparation method of composite sodium iron phosphate, and the composite sodium iron phosphate has a general formula of Na4Fe x P4O 12 +x, wherein the value range of x is 2.0<=x<=4.0. The preparation method of the composite sodium iron phosphate comprises dispersing a Na source, an Fe source, a P source, a dispersing agent and a metal doping additive which are hardly soluble in water into water, sand milling to obtain slurry A; dissolving a Na source, an Fe source, a P source and an organic carbon source which are easily soluble in water into water, stirring and dissolving to obtain solution B; fully mixing the slurry A and the solution B, spray granulating, and then sintering under atmosphere protection at high temperature to obtain the in-situ carbon-coated composite sodium iron phosphate material. The preparation method is simple in process, effectively reduces sand milling time, improves sand milling efficiency, is easy for industrial production, and the composite sodium iron phosphate prepared by using the method is high in purity and good in electric performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material technology, specifically relating to a method for preparing composite sodium iron phosphate. Background Technology

[0002] With the widespread use of fossil fuels, environmental pollution has become increasingly prominent. The development of new energy sources is undoubtedly a green and effective approach, and lithium / sodium-ion batteries are certainly a leader in the future of new energy. In recent years, the widespread adoption of new energy vehicles has driven the rapid development of lithium-ion batteries. However, the current global lithium reserves are scarce and unevenly distributed, unable to meet the needs of the electric vehicle sector, let alone the low-cost requirements for large-scale energy storage. This will inevitably lead to a surge in lithium carbonate prices, thereby increasing the manufacturing cost of lithium-ion batteries.

[0003] Sodium-ion batteries operate on a similar principle to lithium-ion batteries, and sodium resources are abundant and inexpensive to mine. Under the same conditions, the manufacturing cost of sodium-ion battery electrode materials is significantly lower, making them a promising candidate for widespread application in energy storage. Sodium-ion cathode materials include transition metal oxides, Prussian blue and its analogues, and polyanionic materials. These materials exhibit significant differences in capacity, rate capability, and structural stability. Current research indicates that transition metal oxides often undergo multiple phase transitions during the redox process of sodium ion insertion / extraction, leading to structural collapse and affecting the material's cycle stability. Prussian blue and its analogues contain a large amount of water of crystallization, which easily decomposes and generates gas at high potentials, causing battery swelling and failure. Compared to the first two types of materials, polyanionic sodium-ion battery cathode materials, with their stable framework structure and excellent electrochemical performance, are undoubtedly the best choice for sodium-ion battery cathodes.

[0004] Currently, the most studied cathode materials for polyanionic sodium-ion batteries include metal-based phosphates such as vanadium-based phosphates (V-based phosphates) like Na3V2(PO4)3 and NaVPO4F. Although V-based phosphates possess high redox potentials (3.4-3.6V) and specific capacities, their limited resources and high toxicity hinder their large-scale application. However, non-V metal-based phosphates, on the other hand, are non-toxic, pollution-free, and inexpensive, providing a solid foundation for their large-scale application.

[0005] Currently, there are two main processes for preparing metal-based phosphate cathode materials for polyanionic sodium-ion batteries: One involves solid-phase ball milling, where water-insoluble metal salts, sodium salts, phosphorus sources, and carbon sources (glucose, citric acid, sucrose, etc.) are mixed and milled, followed by spray drying to obtain precursor powder, which is then calcined to obtain the final product. However, solid-phase ball milling cannot guarantee uniform mixing of Na, M, and PO4, leading to the formation of a large number of impurity phases in the final product, affecting the material's electrochemical performance. The second process uses a liquid-phase method, where easily soluble metal salts, sodium salts (sodium carbonate, sodium hydroxide, sodium oxalate, sodium phosphate, etc.), phosphorus sources (sodium pyrophosphate, ammonium dihydrogen phosphate, sodium phosphate, monohydrogen / dihydrogen phosphate, etc.), and carbon sources (glucose, citric acid, sucrose, etc.) are mixed and dissolved, followed by spray drying to obtain precursor powder, which is then calcined to obtain the final product. However, the aforementioned water-soluble metal salts are highly hygroscopic, and the carbon sources used, such as glucose, citric acid, and sucrose, have low melting points and high viscosity, leading to severe powder adhesion to the walls during spray drying and making material collection impossible. Furthermore, phosphate-based metal salts have low solubility products and are extremely difficult to dissolve in water. The liquid-phase mixing process is often accompanied by the formation of phosphate precipitates, resulting in uneven mixing of Na, M, and PO4, leading to the formation of a large number of impurity phases in the final product. Summary of the Invention

[0006] To address the shortcomings of existing preparation processes, the present invention aims to provide a method for preparing polyanionic sodium-ion battery cathode materials, which features low production cost, high efficiency, and high product purity.

[0007] The purpose of this invention is to provide a method for preparing composite sodium iron phosphate, comprising the following steps:

[0008] S1. Raw material weighing: Based on the different values ​​of x, according to the general formula of sodium iron phosphate, Na4Fe x P4O 12 In the stoichiometric ratio of +x, weigh out the sparingly soluble Na source, Fe source, P source, dispersant, and water-soluble Na source, Fe source, and P source respectively;

[0009] S2. Preparation of slurry A: Disperse one or more of the following in water: a Na source, Fe source, P source, dispersant, and metal doping additive, which are difficult to dissolve in water, into water and perform sand milling. During the sand milling process, water is added in batches according to the viscosity to adjust the solid content, thus obtaining slurry A; Preparation of solution B: Dissolve one or more of the following in water: a Na source, Fe source, P source, and organic carbon source, which are easily soluble in water, into water and stir to dissolve, thus obtaining solution B;

[0010] S3. Precursor slurry mixing: Add solution B to slurry A and stir to mix thoroughly;

[0011] S4. Spray drying: Spray dry the precursor slurry from step S3 above to obtain dried precursor powder.

[0012] S5. Precursor powder sintering: The precursor powder from step S4 above is sintered at high temperature under an inert atmosphere to obtain a composite sodium iron phosphate cathode material.

[0013] Preferably, in step S1, the material has the general formula Na4Fe x P4 O 12 +x, where x can take values ​​of 2.0 ≤ x ≤ 4.0.

[0014] Preferably, in the slurry A obtained in step S2, the solution solid content is 20-60 wt%, the dispersant accounts for 1%-15 wt% of the total solid content in the solution, and the water-soluble carbon source accounts for 10-80 wt% of the total solid content in the solution B.

[0015] Preferably, in step S2, the water-insoluble Fe source includes one or more of iron oxide, ferrous oxalate, and ferric phosphate, and the water-soluble Fe source includes one or more of ferric sulfate, ferric nitrate, ferrous chloride, and ferric dihydrogen phosphate.

[0016] Sodium sources include one or more of the following: sodium formate, sodium acetate, sodium sulfate, sodium nitrate, sodium citrate, sodium phosphate, sodium pyrophosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium chloride.

[0017] The water-insoluble P source in step S2 includes one or more of ferric phosphate and ferric pyrophosphate, and the water-soluble P source includes one or more of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, phosphorus pentoxide, and ammonium hypophosphite.

[0018] Preferably, the dispersant in step S2 includes one or more of polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyethylene oxide, polytetrafluoroethylene, polyacrylic acid, polymethyl acrylate, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and carboxyethyl methyl cellulose.

[0019] Preferably, the metal doping additive in step S2 includes one or more of titanium dioxide and magnesium hydroxide.

[0020] Preferably, the organic carbon source in step S3 includes one or more of glucose, starch, carbon nanotubes, citric acid, polyvinyl alcohol, and polyvinyl acetate.

[0021] Preferably, in step S4, the spray drying inlet temperature is 200-300℃ and the outlet temperature is 80-120℃.

[0022] Preferably, in step S5, the protective atmosphere includes one or more of N2, Ar, CO2 / H2; the sintering temperature in step S5 is 400-650℃, and the sintering time is 6-20 hours.

[0023] Preferably, the carbon content of the composite sodium iron phosphate product in step S5 is 1%-5%.

[0024] Compared with existing technologies, the advantages of this invention are: the preparation method provided by this invention is simple, the sand milling efficiency is significantly improved, and the powder adheres very little to the wall during spray drying, making it suitable for industrial production. Using the preparation method of this invention, by controlling the change of the x value, single-phase or two-phase composite sodium iron phosphate materials can be synthesized very efficiently. Compared with traditional solid-phase synthesis methods, the preparation cost of this invention is lower, and the discharge specific capacity and rate performance of the composite sodium iron phosphate materials are superior. Attached Figure Description

[0025] Figure 1 The charge-discharge curve of the composite sodium iron phosphate sample prepared in Example 4 is shown. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Example 1

[0028] S1. Raw material weighing: According to the general formula Na4Fe3P4O 15 According to the stoichiometric ratio, ferric phosphate, sodium pyrophosphate and titanium dioxide, which are sparingly soluble in water, were weighed out respectively. First, 1 / 3 of the water was added, and the mixture was put into a sand mill and ground at a speed of 2000 r / min for 2 hours. Then, 1 / 3 of the water was added and the mixture was ground for another 2 hours to obtain slurry A.

[0029] S2. Weigh out sodium carbonate, glucose, and PEG, which are easily soluble in water, according to the stoichiometric ratio, and dissolve them in 1 / 3 of the water. Stir for 10 minutes to obtain solution B.

[0030] S3. Precursor slurry mixing: Add solution B to slurry A and mix thoroughly by sand milling at 1000 r / min for 30 min;

[0031] S4. Spray drying: The precursor solution in step S3 above is spray dried to obtain dried precursor powder.

[0032] S5. Precursor powder sintering: The precursor powder from step S4 above is transferred to a tube furnace and calcined at 600°C for 10 hours under a N2 protective atmosphere. Finally, it is pulverized by airflow to obtain the composite sodium iron phosphate cathode material.

[0033] Example 2

[0034] S1. Raw material weighing: According to the general formula Na4Fe3P4O 15 According to the stoichiometric ratio, ferric phosphate, ferrous oxalate and titanium dioxide, which are sparingly soluble in water, were weighed out respectively. First, 1 / 3 of the water was added, and the mixture was put into a sand mill and ground at a speed of 2000 r / min for 2 hours. Then, 1 / 3 of the water was added and the mixture was ground for another 2 hours to obtain slurry A.

[0035] S2. Weigh out sodium citrate, sodium pyrophosphate, fructose and PEG, which are easily soluble in water, according to the stoichiometric ratio, and dissolve them in 1 / 3 of the water. Stir for 10 minutes to obtain solution B.

[0036] S3. Precursor slurry mixing: Add solution B to slurry A and mix thoroughly by sand milling at 1000 r / min for 30 min;

[0037] S4. Spray drying: The precursor solution in step S3 above is spray dried to obtain dried precursor powder.

[0038] S5. Precursor powder sintering: The precursor powder from step S4 above is transferred to a tube furnace and calcined at 580°C for 10 hours under a N2 protective atmosphere. Finally, it is pulverized by airflow to obtain the composite sodium iron phosphate cathode material.

[0039] Example 3

[0040] S1. Raw material weighing: According to the general formula Na4Fe3P4O 15 According to the stoichiometric ratio in the text, weigh out the sparingly soluble iron phosphate and magnesium oxide, add 1 / 3 water first, transfer to a sand mill and grind at 2000 r / min for 2 hours, then add another 1 / 3 water and continue sand milling for 2 hours to obtain slurry A;

[0041] S2. Weigh out sodium citrate, phosphoric acid, and lactose, which are easily soluble in water, according to the stoichiometric ratio, and dissolve them in 1 / 3 of the water. Stir for 10 minutes to obtain solution B.

[0042] S3. Precursor slurry mixing: Add solution B to slurry A and mix thoroughly by sand milling at 1000 r / min for 30 min;

[0043] S4. Spray drying: The precursor solution in step S3 above is spray dried to obtain dried precursor powder.

[0044] S5. Precursor powder sintering: The precursor powder from step S4 above is transferred to a tube furnace and calcined at 550°C for 10 hours under a N2 protective atmosphere. Finally, it is pulverized by airflow to obtain the composite sodium iron phosphate cathode material.

[0045] Example 4

[0046] S1. Raw material weighing: According to the general formula Na4Fe3P4O15 According to the stoichiometric ratio, weigh out the sparingly soluble iron phosphate and titanium dioxide, add 1 / 3 water, transfer to a sand mill and grind at 2000 r / min for 2 hours, add another 1 / 3 water, and continue sand milling for 2 hours to obtain slurry A;

[0047] S2. According to the stoichiometric ratio, weigh out sodium bicarbonate, ammonium dihydrogen phosphate and glucose, which are easily soluble in water, and dissolve them in 1 / 3 of the water. Stir for 10 minutes to obtain solution B.

[0048] S3. Precursor slurry mixing: Add solution B to slurry A and mix thoroughly by sand milling at 1000 r / min for 30 min;

[0049] S4. Spray drying: The precursor solution in step S3 above is spray dried to obtain dried precursor powder.

[0050] S5. Precursor powder sintering: The precursor powder from step S4 above is transferred to a tube furnace and calcined at 550°C for 10 hours under a N2 protective atmosphere. Finally, it is pulverized by airflow to obtain the composite sodium iron phosphate cathode material.

[0051] Rate performance test: Using the composite sodium iron phosphate prepared in the above implementation case as the positive electrode material, coin cells were assembled and charged and discharged at current rates of 0.1C, 0.2C, 0.5C and 1C respectively to evaluate the rate performance of the material. The test results are shown in Table 1.

[0052] Table 1

[0053]

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite sodium iron phosphate, characterized by: The method comprises the following steps: S1, raw material weighing: according to the different x values, the general formula of sodium iron phosphate material Na4Fe x P4O 12+x , the stoichiometric ratio in the general formula Na4Fe x P4O 12+x x is in the range of 2.0≤x≤4.0; weigh the Na source, Fe source, P source, dispersant and water-soluble Na source, Fe source, P source which are difficult to dissolve in water respectively; S2, preparation of slurry A: dispersing one or more of water-insoluble Na source, Fe source, P source, and optionally dispersant and optional metal doping additive into water, sand milling, and adjusting solid content by adding water in batches according to viscosity during sand milling to obtain slurry A; preparation of solution B: dissolving one or more of water-soluble Na source, Fe source, P source, and organic carbon source into water, and stirring to obtain solution B; in the obtained slurry A, the solid content of the solution is 20-60wt%; in the solution B, the water-soluble carbon source accounts for 10-80wt% of the total solid content in the solution; S3, mixing of precursor slurry: adding solution B into slurry A and fully mixing by stirring; S4, spray drying: spray drying the precursor slurry in step S3 to obtain dry precursor powder; S5, sintering of precursor powder: sintering the precursor powder in step S4 under the protection of inert atmosphere at high temperature to obtain composite sodium iron phosphate positive electrode material.

2. The method for preparing composite sodium iron phosphate according to claim 1, characterized in that: In the slurry A obtained in step S2, the dispersant accounts for 1-15wt% of the total solid content in the solution.

3. The method for preparing the composite sodium iron phosphate according to claim 1, characterized in that: The water-insoluble Fe source in step S2 includes one or more of iron oxide, ferrous oxalate, and iron phosphate, and the water-soluble Fe source includes one or more of iron sulfate, iron nitrate, ferrous chloride, and ferrous phosphate; The water-soluble Na source includes one or more of sodium formate, sodium acetate, sodium sulfate, sodium nitrate, sodium citrate, sodium phosphate, sodium pyrophosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium chloride; The water-insoluble P source in step S2 includes one or more of iron phosphate and iron pyrophosphate, and the water-soluble P source includes one or more of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, diaphosphorus pentoxide, and ammonium hypophosphite.

4. The method for preparing the composite sodium iron phosphate according to claim 1, characterized in that: The dispersant in step S2 includes one or more of polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyethylene oxide, polytetrafluoroethylene, polyacrylic acid, polymethyl acrylate, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, carboxyethyl cellulose, carboxypropyl methyl cellulose, and carboxyethyl methyl cellulose.

5. The method for preparing the composite sodium iron phosphate according to claim 1, characterized in that: The metal doping additive in step S2 includes one or more of titanium dioxide and magnesium hydroxide.

6. The method for preparing the composite sodium iron phosphate according to claim 1, characterized in that: The organic carbon source in step S2 includes one or more of glucose, starch, carbon nanotube, citric acid, polyvinyl alcohol, and polyvinyl acetate.

7. The method for preparing composite sodium iron phosphate according to claim 1, characterized in that: The inlet temperature of spray drying in step S4 is 200-300℃, and the outlet temperature is 80-120℃.

8. The method for preparing composite sodium iron phosphate according to claim 1, characterized in that: The inert atmosphere in step S5 includes one or more of N2, Ar, and CO2; the sintering temperature in step S5 is 400-650℃, and the sintering time is 6-20 hours.

9. The method for preparing the composite sodium iron phosphate according to claim 1, characterized in that: The carbon content of the composite sodium iron phosphate product in step S5 is 1-5%.

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