A method for preparing sodium pyrophosphate ferric phosphate with flexible adjustment of compaction and electrical performance

Abstract

This invention discloses a method for preparing sodium iron phosphate pyrophosphate with flexible adjustment of compaction and electrical properties, belonging to the field of sodium-ion battery cathode materials. The steps are as follows: S1, dispersing iron source 1, iron source 2, phosphorus source, sodium source, surfactant, and carbon source in water to form a uniform slurry; wherein: iron source 1 is FePO4, and iron source 2 is NH4Fe2(OH)(PO4)2·2H2O; S2, subjecting the slurry obtained in step S1 to multi-stage grinding, then spray drying, and finally sintering under an inert atmosphere to obtain sodium iron phosphate pyrophosphate. This invention achieves a comprehensive improvement in the compaction density and electrical properties of sodium iron phosphate pyrophosphate by simply using two different iron sources. The preparation is simple, requires no additional equipment, has good grinding efficiency, low production energy consumption, and has promising prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode materials, specifically relating to a method for preparing sodium iron pyrophosphate with adjustable compaction and electrical properties. Background Technology

[0002] Sodium-ion batteries not only possess the advantages of abundant and widely distributed sodium resources, low cost, no development bottlenecks, environmental friendliness, and compatibility with existing lithium-ion battery production equipment, but also offer superior power characteristics, wide temperature range adaptability, safety performance, and no over-discharge issues. Sodium-ion batteries will become a valuable supplement to lithium-ion batteries. Currently, my country's sodium-ion batteries are in a leading position internationally in terms of basic research, technological level, and industrialization speed, giving it a first-mover advantage.

[0003] Sodium iron phosphate pyrophosphate, as one of the technologies in sodium-ion batteries, possesses characteristics such as high theoretical specific capacity, high average operating voltage, and small volume change. Furthermore, it boasts low production costs, an environmentally friendly manufacturing process, and abundant raw material reserves, making it a promising candidate for applications in energy storage, low-speed electric vehicles, and two-wheeled vehicles. However, this material suffers from low electronic conductivity. Currently, the simplest and most readily available methods to improve conductivity are through extensive carbon coating, which sacrifices the material's compaction density; or through prolonged grinding to achieve smaller particle sizes and shorten the sodium ion migration path, thereby improving the material's electrical performance. However, these methods require lengthy grinding processes, increasing energy consumption and production costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing sodium iron pyrophosphate with flexible adjustment of compaction and electrical properties, achieving compatibility and flexible control of the electrical properties and compaction density of sodium iron pyrophosphate.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0006] A method for preparing sodium iron pyrophosphate with adjustable compaction and electrical properties is provided, comprising the following steps:

[0007] S1. Disperse iron source 1, iron source 2, phosphorus source, sodium source, surfactant and carbon source in water to form a uniform slurry; wherein: iron source 1 is FePO4 and iron source 2 is NH4Fe2(OH)(PO4)2·2H2O;

[0008] S2. The slurry obtained in step S1 is subjected to multi-stage grinding, then spray-dried, and finally sintered under an inert atmosphere to obtain sodium iron pyrophosphate.

[0009] According to the above scheme, in S1, NH4Fe2(OH)(PO4)2·2H2O is either the finished powder or the undried NH4Fe2(OH)(PO4)2·2H2O filter cake obtained during preparation.

[0010] According to the above scheme, in S1, FePO4 is FePO4 obtained by sintering, which has undergone a sintering process during conventional preparation.

[0011] According to the above scheme, in S1, the primary FePO4 particles have a rod-shaped structure and a size of 60-80 nm; the primary NH4Fe2(OH)(PO4)2·2H2O particles have a spherical shape and a size of 30-50 nm.

[0012] According to the above scheme, in S1, the molar ratio of iron source 1 to iron source 2 is 0.1 to 15:1; preferably 0.5 to 2:1.

[0013] According to the above scheme, in S1, the molar ratio of phosphorus source to sodium source is P:Na = 1:4 to 4.05.

[0014] According to the above scheme, in step S1, the amount of surfactant added is 1‰ to 8‰ of the total weight of the slurry.

[0015] According to the above scheme, in S1, the amount of carbon source added is 1% to 10% of the total weight of iron source 1, iron source 2, sodium source and phosphorus source; preferably, it is 5% to 8%.

[0016] According to the above scheme, in S1, the phosphorus source is one or more of phosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, and trisodium phosphate; the sodium source is one or more of sodium hydroxide, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate; the surfactant is one or more of silane coupling agent, polyethylene glycol, and sorbitol; and the carbon source is one or more of glucose, sucrose, PEG2000, and white sugar.

[0017] According to the above scheme, in S2, the multi-stage grinding method is a three-stage sand mill, which is divided into coarse grinding, fine grinding and fine grinding. The particle size of the coarse grinding output is D50≤800nm, the particle size of the fine grinding output is D50≤500nm, and the particle size of the fine grinding output is D50≤300nm.

[0018] Preferably, the particle size of the coarse grinding output is 500nm < D50 ≤ 800; the particle size of the fine grinding output is 300nm < D50 ≤ 500nm; and the particle size of the precision grinding output is 100nm ≤ D50 ≤ 300nm.

[0019] Preferably, the coarse grinding time is 0.5 to 1 hour, the fine grinding time is 1 to 2 hours, and the precision grinding time is 2 to 4 hours.

[0020] Preferably, the diameter of the zirconium beads used for coarse grinding is 0.6–0.8 mm; the diameter of the zirconium beads used for fine grinding is 0.25–0.4 mm; and the diameter of the zirconium beads used for precision grinding is 0.15–0.25 mm.

[0021] According to the above scheme, in step S2, the inlet air temperature of the spray dryer is 200-250°C, and the outlet air temperature is 80-130°C.

[0022] According to the above scheme, in S2, the sintering temperature is 500-600℃ and the sintering time is ≥12h.

[0023] Preferably, the sintering time is 12 to 15 hours.

[0024] Preferably, the heating rate is 5–10 °C / min.

[0025] This invention provides an application of sodium iron pyrophosphate prepared by the above method as a positive electrode material in sodium-ion batteries.

[0026] This invention provides a method for preparing sodium iron phosphate pyrophosphate using two different iron sources: FePO4 and NH4Fe2(OH)(PO4)2·2H2O. FePO4 undergoes a sintering process during conventional preparation, resulting in partial melting between particles, making it difficult to break the molten structure during grinding, which is beneficial for increasing the compaction density of sodium iron phosphate pyrophosphate. In contrast, NH4Fe2(OH)(PO4)2·2H2O does not involve a high-temperature sintering process during conventional preparation, and there is no melting between particles. This significantly shortens grinding time and improves grinding efficiency, which is beneficial for improving the electrical properties and rate performance of sodium iron phosphate pyrophosphate. Furthermore, the smaller spherical dihydrate basic ammonium phosphate particles can fill the gaps between rod-shaped anhydrous iron phosphate particles, achieving a gradation effect between particle sizes during the calcination preparation of sodium iron phosphate pyrophosphate, further improving the compaction density of the product. In addition, during the calcination of sodium iron phosphate pyrophosphate, the ammonium ions in basic iron ammonium phosphate are converted into NH3 gas. The released ammonia gas can inhibit the melting between particles, prevent grain growth, and generate more pores in the particles, thereby improving the electrical properties and rate performance of the product.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention provides a method for preparing sodium iron phosphate pyrophosphate, using two different types, morphologies, and particle size ranges of iron sources: FePO4 and basic ammonium iron phosphate dihydrate. This method improves the compaction density of sodium iron phosphate pyrophosphate while shortening the grinding time and enhancing the grinding effect. Simultaneously, basic ammonium iron phosphate dihydrate releases ammonia gas, which can inhibit grain growth and generate more pores within the particles, thereby improving the electrical and rate performance of the product. The prepared sodium iron phosphate pyrophosphate, used as a cathode material in sodium-ion batteries, achieves a comprehensive improvement in compaction density and electrical performance, resulting in excellent battery performance.

[0029] 2. This invention achieves a comprehensive improvement in the compaction density and electrical properties of sodium iron pyrophosphate by simply using two different iron sources. The preparation is simple, requires no additional equipment, has good grinding efficiency, low production energy consumption, and has promising prospects for industrial application. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of an embodiment of the present invention.

[0031] Figure 2 This is a scanning electron microscope image of sodium iron phosphate pyrophosphate prepared in Example 1 of the present invention.

[0032] Figure 3 This is a 10C charge-discharge curve of sodium iron pyrophosphate prepared in Example 1 of the present invention. Detailed Implementation

[0033] The embodiments of the present invention will now be described in detail with reference to examples.

[0034] In the following embodiments of the present invention, the raw material specifications are as follows:

[0035] The primary particle morphology of anhydrous ferric phosphate is rod-shaped, and the primary particle size is 60-80 nm.

[0036] The primary particle morphology of NH4Fe2(OH)(PO4)2·2H2O is spherical, and the primary particle size is 30-50 nm.

[0037] See the process flow diagram in the embodiments of the present invention. Figure 1 .

[0038] Example 1

[0039] A method for preparing sodium ferric pyrophosphate is provided, comprising the following steps:

[0040] 1. Weigh 151g of anhydrous ferric phosphate, 373g of basic ammonium ferric phosphate dihydrate, 164g of trisodium phosphate, 40g of sodium hydroxide, 50g of glucose, and 10g of polyethylene glycol and add them to 1500g of pure water and stir well.

[0041] 2. The slurry obtained in step 1, after being stirred evenly, is subjected to a three-stage sand milling process: coarse grinding, fine grinding, and precision grinding. The diameter of the zirconium beads used in coarse grinding is 0.6–0.8 mm, the grinding time is 0.5 h, and the particle size D50 of the coarse grinding output is 650 nm. The diameter of the zirconium beads used in fine grinding is 0.25–0.4 mm, the grinding time is 1.5 h, and the particle size D50 of the fine grinding output is 410 nm. The diameter of the zirconium beads used in precision grinding is 0.15–0.25 mm, the grinding time is 3 h, and the particle size D50 of the precision grinding output is 150 nm.

[0042] 3. Spray dry the grinding slurry obtained in step 2. The spray inlet temperature is 250℃ and the outlet temperature is 80℃ to obtain hollow spherical solid particles.

[0043] 4. The hollow spherical solid particles obtained in step 3 are heated from room temperature to 550℃ at a heating rate of 5℃ / min and held at that temperature for 14 hours for high-temperature calcination. Finally, after cooling, sodium iron phosphate pyrophosphate is obtained.

[0044] The sodium ferric phosphate pyrophosphate prepared in this embodiment is shown in the scanning electron microscope as follows: Figure 2 As shown, the primary particle morphology is a near-spherical structure, and the primary particle size is 50-150 nm.

[0045] When the sodium iron phosphate pyrophosphate prepared in this embodiment is used as a positive electrode material in a sodium-ion battery, its 10C charge-discharge curve is as follows: (The curve is missing from the provided text.) Figure 3 As shown, the charging capacity is 105.1 mAh / g, and the discharging capacity is 100.3 mAh / g.

[0046] Example 2

[0047] The preparation method of sodium ferric phosphate pyrophosphate in this embodiment differs from that in Example 1 only in that: the amount of anhydrous ferric phosphate added in step 1 is 392.6g, and the amount of basic ammonium ferric phosphate dihydrate added is 74.6g; the remaining steps are the same as in Example 1.

[0048] Example 3

[0049] The preparation method of sodium ferric phosphate pyrophosphate in this embodiment differs from that in Example 1 only in that: the amount of anhydrous ferric phosphate added in step 1 is 30.2g, and the amount of basic ammonium ferric phosphate dihydrate added is 522.2g; the remaining steps are the same as in Example 1.

[0050] The 1C and 10C charge / discharge data and compaction density of Examples 1, 2, and 3 are shown in Table 1.

[0051] Table 1

[0052]

[0053] Table 1 shows that when the ratio of anhydrous ferric phosphate to basic ferric ammonium phosphate is appropriate, as in Example 1, the prepared sodium ferric phosphate pyrophosphate exhibits good overall electrical and compaction performance, with a 10C discharge capacity of 100.3 mAh / g and a compaction density of 2.04 g / cm³. 3 Furthermore, by adjusting the ratio between anhydrous ferric phosphate and basic ferric ammonium phosphate, as in Examples 2 and 3, the compaction density and electrical properties can be flexibly controlled to meet different needs.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing sodium iron pyrophosphate with flexibly adjustable compaction and electrical properties, characterized in that, Includes the following steps: S1. Disperse iron source 1, iron source 2, phosphorus source, sodium source, surfactant, and carbon source in water to form a uniform slurry; wherein: iron source 1 is FePO4, with a primary particle morphology of rod-shaped structure and a primary particle size of 60~80nm; iron source 2 is NH4Fe2(OH)(PO4)2·2H2O, with a primary particle morphology of spherical shape and a primary particle size of 30~50nm; the molar ratio of iron source 1 to iron source 2 is 0.1~15:1; the molar ratio of phosphorus source to sodium source is P:Na=1:4~4.05; S2. The slurry obtained in step S1 is subjected to multi-stage grinding, then spray-dried, and finally sintered under an inert atmosphere to obtain sodium iron phosphate pyrophosphate; wherein: the multi-stage grinding method is a three-stage sand mill, which is divided into coarse grinding, fine grinding and fine grinding; the particle size of the coarse grinding output is D50≤800nm, the particle size of the fine grinding output is D50≤500nm, and the particle size of the fine grinding output is D50≤300nm.

2. The preparation method according to claim 1, characterized in that, In S1, the amount of surfactant added is 1‰ to 8‰ of the total weight of the slurry; the amount of carbon source added is 1% to 10% of the total weight of iron source 1, iron source 2, sodium source, and phosphorus source.

3. The preparation method according to claim 1, characterized in that, In S1, the phosphorus source is one or more of phosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, and trisodium phosphate; the sodium source is one or more of sodium hydroxide, disodium hydrogen phosphate, sodium dihydrogen phosphate, and trisodium phosphate; the surfactant is one or more of silane coupling agent, polyethylene glycol, and sorbitol; and the carbon source is one or more of glucose, sucrose, and PEG2000.

4. The preparation method according to claim 1, characterized in that, The coarse grinding time is 0.5~1h, the fine grinding time is 1~2h, and the precision grinding time is 2~4h.

5. The preparation method according to claim 1, characterized in that, In S2, the inlet air temperature of the spray drying is 200~250℃, the outlet air temperature is 80~130℃, the sintering temperature is 500~600℃, and the sintering time is ≥12h.

6. The application of sodium iron pyrophosphate prepared by the preparation method according to any one of claims 1-5 as a positive electrode material in sodium-ion batteries.

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