A sodium ferric pyrophosphate phosphate positive electrode material, a preparation method and application thereof

Abstract

This invention belongs to the field of battery cathode material technology, specifically relating to a sodium iron pyrophosphate cathode material, its preparation method, and its application. The preparation method of the sodium iron pyrophosphate cathode material provided by this invention includes the following steps: 1) dispersing iron phosphate, sodium source, phosphate, and reducing agent in water, forming a spray powder through spray granulation, and then pulverizing by airflow to obtain precursor particles with a D50 particle size of 2.0-6.0 μm; 2) mixing the precursor particles obtained in step 1) with ammonium oxalate, and then performing a first calcination to obtain a calcined material; 3) mixing the calcined material obtained in step 2) with silicon oxide, and then performing a second calcination and pulverization to obtain the sodium iron pyrophosphate cathode material. The preparation method provided by this invention improves the compaction density of the sodium iron pyrophosphate cathode material, making it suitable for the large-scale production of sodium-ion batteries with high volumetric energy density.

Description

Technical Field

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

[0002] Sodium-ion batteries have broad application prospects due to their cost advantage. Their working principle is similar to that of lithium-ion batteries, utilizing the reversible insertion and extraction of sodium ions between the positive and negative electrodes to store and release energy. Currently, the main cathode materials used in sodium-ion batteries fall into three categories: transition metal oxide systems, polyanionic compounds (phosphate systems, fluorophosphate systems, sodium superionic conductor structures, etc.), and Prussian blue systems. Among these, sodium iron phosphate pyrophosphate cathode materials have attracted widespread attention and research. However, due to the porous and bulky morphology of the products synthesized by traditional solid-state methods, the compaction density of sodium iron phosphate pyrophosphate cathode materials is low, only 2.0-2.1 g / cm³. 3 This limits its application in high volumetric energy density scenarios. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the low compaction density of sodium iron phosphate pyrophosphate cathode material synthesized by the conventional solid-state method in the prior art limits its application in high volumetric energy density scenarios, thereby providing a sodium iron phosphate pyrophosphate cathode material, its preparation method and application.

[0004] This invention provides a method for preparing sodium iron pyrophosphate cathode material, comprising the following steps: 1) Disperse iron phosphate, sodium source, phosphate and reducing agent in water, spray granulate to form spray powder, and then pulverize by airflow to obtain precursor particles with D50 particle size of 2.0-6.0μm; 2) Mix the precursor particles obtained in step 1) with ammonium oxalate, and then perform a first calcination to obtain a calcined material; 3) The calcined material obtained in step 2) is mixed with silicon oxide, subjected to a second calcination, and then pulverized to obtain the sodium iron pyrophosphate cathode material.

[0005] Preferably, the reducing agent in step 1) is selected from at least one of citric acid, glucose, and carotene; The sodium source is selected from at least one of sodium oxalate and sodium carbonate; The phosphate is selected from at least one of disodium hydrogen phosphate and sodium dihydrogen phosphate; The mass ratio of iron phosphate, sodium source, phosphate, and reducing agent is (2.5-5):(1.5-3):(1-2):(1.5-4).

[0006] Optionally, before the step of dispersing ferric phosphate, sodium source, phosphate, and reducing agent in water, the step of sand milling ferric phosphate can be further included. Sand milling can promote the full integration of raw materials.

[0007] Preferably, in step 1), ferric phosphate, sodium source, phosphate, and reducing agent are mixed and dispersed in water to form a slurry with a solid content of 20-40%. The solid content mentioned in this invention refers to the concentration of substances other than water in the slurry by mass relative to the total mass of the slurry.

[0008] The spray granulation described in step 1) is carried out using a centrifugal spray dryer. The inlet temperature of the centrifugal spray dryer is 180-250℃, and the rotation speed of the atomizing disc of the centrifugal spray dryer is 8000-12000rpm.

[0009] Preferably, the D50 particle size of the spray granulation in step 1) is 6-12 μm; In step 1), the air pressure during airflow pulverization is 0.5-1 MPa, the classifier frequency is 100-140 Hz, and the induced draft fan frequency is 40-60 Hz.

[0010] Preferably, the mass ratio of the precursor particles to ammonium oxalate in step 2) is 100:(1-2); The ammonium oxalate has a particle size range of 0.1-1.0 μm; The mixing speed in step 2) is 1400-1600 rpm, and the mixing time is 20-40 min.

[0011] This invention uses ammonium oxalate with a specific particle size range of 0.1-1.0 μm. When mixed at a specific mixing speed, nano-sized ammonium oxalate particles are formed, which further helps to improve the compaction density of sodium iron pyrophosphate cathode material.

[0012] Preferably, in step 2), the first calcination temperature is 280-320℃ and the first calcination time is 5-7h.

[0013] Preferably, the mass ratio of the sintered material to silicon dioxide in step 3) is 100:(0.3-0.8); The particle size of the silicon oxide is in the range of 0.1-1.0 μm; The mixing speed in step 3) is 1400-1600 rpm, and the mixing time is 25-35 min.

[0014] Optionally, the silicon oxide includes at least one of silicon monoxide and silicon dioxide.

[0015] This invention uses silicon oxide with a specific particle size range of 0.1-1.0 μm. When mixed at a specific mixing speed, nano-sized silicon oxide particles are formed, which further helps to improve the compaction density of sodium iron pyrophosphate cathode material.

[0016] Preferably, in step 3), the second calcination temperature is 550-600℃ and the second calcination time is 10-14h.

[0017] And / or, as described in step 3), the particle size is pulverized to a D50 particle size of 3.0-8.0 μm.

[0018] This invention provides a sodium iron pyrophosphate cathode material, which is prepared by the above-described method for preparing sodium iron pyrophosphate cathode materials.

[0019] This invention also provides an application of the above-described sodium iron pyrophosphate cathode material in a sodium-ion battery. The technical solution of this invention has the following advantages: The method for preparing sodium iron pyrophosphate cathode material provided by the present invention includes the following steps: 1) dispersing iron phosphate, sodium source, phosphate and reducing agent in water, forming spray powder by spray granulation, and then pulverizing by airflow to obtain precursor particles with a D50 particle size of 2.0-6.0 μm; 2) mixing the precursor particles obtained in step 1) with ammonium oxalate, and then performing a first calcination to obtain a calcined material; 3) mixing the calcined material obtained in step 2) with silicon oxide, and then performing a second calcination and pulverization to obtain the sodium iron pyrophosphate cathode material. This invention produces a spray-granulated material with mostly hollow shells and thin shells, resulting in a very light material. Subsequent air-jet milling breaks down the shells, causing the material volume to shrink and producing irregularly shaped particles with increased bulk density. This reduces crystal formation barriers during sintering, aiding in the synthesis of materials with high tap density. Ammonium oxalate preferentially decomposes upon heating, releasing ammonia and carbon dioxide. Pre-opening the material's exhaust channels allows for timely removal of gases from the decomposition of sodium oxalate and organic matter, reducing the volume expansion of the main reactants and thus increasing material density. Silica, with its high surface energy, induces precursor spheroidization, improving flowability and strengthening particle bonding points, thereby increasing material density. This invention utilizes spray granulation, air-jet milling, and calcination with ammonium oxalate, followed by further milling after calcination with silica. This overall process improves interfacial stress, thus enhancing material density. The preparation method provided by this invention increases the compaction density of sodium phosphate pyrophosphate cathode materials, making it suitable for the large-scale production of high-volume-density sodium-ion batteries. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 SEM image of the sodium iron pyrophosphate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0023] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0024] The FePO4 used in the embodiments and comparative examples of this invention is FePO4 that has undergone sand milling treatment, with a particle size range of 50-100 nm.

[0025] Example 1 This embodiment provides a method for preparing sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 7620g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer, inlet temperature 190℃, atomizing disc speed 10000rpm) to obtain spherical powder with a D50 particle size of 10μm. The powder was then subjected to air jet milling (air pressure 0.6MPa, classifier wheel frequency 120Hz, induced draft fan frequency 50Hz) to obtain irregularly shaped precursor particles with a D50 particle size of 2.0μm. 2) The precursor particles obtained in step 1) are mixed with ammonium oxalate (D50 particle size is 0.5μm) at a mass ratio of 100:1 in a high-speed mixer at 1500rpm for 30min, and then calcined at 300℃ for 6h to obtain a calcined material; 3) The calcined material obtained in step 2) and silica (D50 particle size of 0.5 μm) were mixed in a high-speed mixer at a mass ratio of 100:0.5 for 30 min at 1500 rpm. Then, the mixture was calcined at 550℃ for 12 h, followed by air jet milling until the D50 particle size was 3.0 μm (air pressure 0.6 MPa, classifier frequency 120 Hz, induced draft fan frequency 50 Hz) to obtain sodium iron pyrophosphate cathode material. The obtained sodium iron pyrophosphate cathode material was scanned using a scanning electron microscope (SEM), and the SEM image of the sodium iron pyrophosphate cathode material is shown below. Figure 1 As shown.

[0026] Example 2 This embodiment provides a method for preparing sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 8000g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer, inlet temperature 180℃, atomizing disc speed 12000rpm) to obtain spherical powder with a D50 particle size of 6μm. The powder was then subjected to air jet milling (air pressure 0.6MPa, classifier wheel frequency 120Hz, induced draft fan frequency 50Hz) to obtain irregularly shaped precursor particles with a D50 particle size of 2.0μm. 2) The precursor particles obtained in step 1) and ammonium oxalate (D50 particle size is 0.1μm) are placed in a high-speed mixer at a mass ratio of 100:2 and mixed at 1600rpm for 20min. Then, they are calcined at 320℃ for 5h to obtain a calcined material. 3) The calcined material obtained in step 2) and silicon dioxide (D50 particle size of 0.5μm) are placed in a high-speed mixer at a mass ratio of 100:0.8 and mixed at 1600rpm for 20min. Then, it is calcined at 580℃ for 10h and then air-jet milled until the D50 particle size is 3.0μm (air pressure of 0.6MPa, classifier frequency of 120Hz, and induced draft fan frequency of 50Hz) to obtain sodium iron pyrophosphate cathode material.

[0027] Example 3 This embodiment provides a method for preparing sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 7800g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer, inlet temperature 250℃, atomizing disc speed 8000rpm) to obtain spherical powder with a D50 particle size of 12μm. The powder was then subjected to air jet milling (air pressure 0.6MPa, classifier wheel frequency 120Hz, induced draft fan frequency 50Hz) to obtain irregularly shaped precursor particles with a D50 particle size of 2.0μm. 2) The precursor particles obtained in step 1) and ammonium oxalate (D50 particle size is 0.5μm) are placed in a high-speed mixer at a mass ratio of 100:1.5 and mixed at 1400rpm for 40min. Then, they are calcined at 280℃ for 7h to obtain a calcined material. 3) The calcined material obtained in step 2) and silicon dioxide (D50 particle size of 0.5μm) are placed in a high-speed mixer at a mass ratio of 100:0.3 and mixed at 1400rpm for 40min. Then, it is calcined at 600℃ for 10h and then air-jet milled until the D50 particle size is 3.0μm (air pressure of 0.6MPa, classifier frequency of 120Hz, and induced draft fan frequency of 50Hz) to obtain sodium iron pyrophosphate cathode material.

[0028] Comparative Example 1 This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 7620g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer with an inlet temperature of 190℃ and an atomizing disc speed of 10000rpm) to obtain spherical powder with a D50 particle size of 10μm, thus obtaining precursor particles. 2) The precursor particles obtained in step 1) are mixed with ammonium oxalate (D50 particle size is 0.5μm) at a mass ratio of 100:1 in a high-speed mixer at 1500rpm for 30min, and then calcined at 300℃ for 6h to obtain a calcined material; 3) The calcined material obtained in step 2) and silicon dioxide (D50 particle size of 0.5μm) are placed in a high-speed mixer at a mass ratio of 100:0.5 and mixed at 1500rpm for 30min. Then, it is calcined at 550℃ for 12h and then air-jet milled until the D50 particle size is 3.0μm (air pressure of 0.6MPa, classifier frequency of 120Hz, and induced draft fan frequency of 50Hz) to obtain sodium iron pyrophosphate cathode material.

[0029] Comparative Example 2 This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 7620g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer, inlet temperature 190℃, atomizing disc speed 10000rpm) to obtain spherical powder with a D50 particle size of 10μm. The powder was then subjected to air jet milling (air pressure 0.6MPa, classifier wheel frequency 120Hz, induced draft fan frequency 50Hz) to obtain irregularly shaped precursor particles with a D50 particle size of 2.0μm. 2) The precursor particles obtained in step 1) are placed in a high-speed mixer and mixed at 1500 rpm for 30 min, and then calcined at 300℃ for 6 h to obtain a calcined material; 3) The calcined material obtained in step 2) and silicon dioxide (D50 particle size of 0.5μm) are placed in a high-speed mixer at a mass ratio of 100:0.5 and mixed at 1500rpm for 30min. Then, it is calcined at 550℃ for 12h and then air-jet milled until the D50 particle size is 3.0μm (air pressure of 0.6MPa, classifier frequency of 120Hz, and induced draft fan frequency of 50Hz) to obtain sodium iron pyrophosphate cathode material.

[0030] Comparative Example 3 This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 7620g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer, inlet temperature 190℃, atomizing disc speed 10000rpm) to obtain spherical powder with a D50 particle size of 10μm. The powder was then subjected to air jet milling (air pressure 0.6MPa, classifier wheel frequency 120Hz, induced draft fan frequency 50Hz) to obtain irregularly shaped precursor particles with a D50 particle size of 2.0μm. 2) The precursor particles obtained in step 1) are mixed with ammonium oxalate (D50 particle size is 0.5μm) at a mass ratio of 100:1 in a high-speed mixer at 1500rpm for 30min, and then calcined at 300℃ for 6h to obtain a calcined material; 3) The calcined material obtained in step 2) is placed in a high-speed mixer and mixed at 1500 rpm for 30 min. Then it is calcined at 550℃ for 12 h and then air-jet pulverized to a D50 particle size of 3.0 μm (air pressure 0.6 MPa, classifier frequency 120 Hz, and induced draft fan frequency 50 Hz during air-jet pulverization) to obtain sodium iron phosphate pyrophosphate cathode material.

[0031] Comparative Example 4 This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material, including the following steps: 1350g of milled FePO4, 603g of Na2C2O4, 356g of NaH2PO4, and 946g of citric acid (C6H8O7·H2O) were uniformly dispersed in 7620g of pure water. The mixture was then spray-granulated (using a centrifugal spray dryer, inlet temperature 190℃, atomizing disc speed 10000rpm) to obtain spherical powder with a D50 particle size of 10μm. The powder was then subjected to air jet milling (air pressure 0.6MPa, classifier wheel frequency 120Hz, induced draft fan frequency 50Hz) to obtain irregularly shaped precursor particles with a D50 particle size of 2.0μm. 2) The precursor particles obtained in step 1) are placed in a high-speed mixer and mixed at 1500 rpm for 30 min, and then calcined at 300℃ for 6 h to obtain a calcined material; 3) The calcined material obtained in step 2) is placed in a high-speed mixer and mixed at 1500 rpm for 30 min. Then it is calcined at 550℃ for 12 h and then air-jet pulverized to a D50 particle size of 3.0 μm (air pressure 0.6 MPa, classifier frequency 120 Hz, and induced draft fan frequency 50 Hz during air-jet pulverization) to obtain sodium iron phosphate pyrophosphate cathode material.

[0032] Test case The compaction density of the sodium iron pyrophosphate cathode materials prepared in Examples 1-3 and Comparative Examples 1-4 was tested respectively. The test method was carried out in accordance with GB / T 44330-2024. The test results are shown in Table 1.

[0033] The sodium iron pyrophosphate positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-4 were mixed uniformly with acetylene black and PVDF at a mass ratio of 80:12:8. 1-Methyl-2-pyrrolidone was added and ball-milled for 1 hour to prepare a slurry. This slurry was then uniformly coated onto an aluminum sheet, dried, and cut into positive electrode sheets. A sodium metal sheet was used as the negative electrode, a Celgard 2500 type separator was used as the separator, and a propylene carbonate (PC) solution containing 1 mol / L NaClO4 was used as the electrolyte. These were assembled into 2032 coin cells. The performance of the above batteries was tested using the Land testing system. The test method was as follows: within a cutoff voltage range of 2.0-3.8V, the first cycle was performed at 0.1C, followed by 50 cycles at 1C. The specific capacity of the first cycle discharge and the capacity retention rate after 50 cycles (i.e., the specific capacity of the 51st cycle discharge / the specific capacity of the 2nd cycle discharge × 100%) were tested. The test results are shown in Table 1.

[0034] Table 1

[0035] As shown in Table 1, the compaction density of the sodium iron pyrophosphate cathode materials in Examples 1-3 of this invention is significantly better than that of the cathode materials in Comparative Examples 1-4. This indicates that the use of airflow pulverization after spray granulation helps to improve the compaction density of the cathode material. The coating of sodium oxalate and the coating of silicon oxide can synergistically improve the compaction density of the cathode material, thus making it suitable for the large-scale production of sodium-ion batteries with high volumetric energy density. Meanwhile, the first-cycle discharge specific capacity and 50-cycle cycle retention rate of the sodium iron pyrophosphate cathode materials in Examples 1-3 of this invention are basically similar to, or even slightly better than, those in Comparative Examples 1-4. This shows that the first-cycle discharge specific capacity and 50-cycle cycle retention rate of the sodium iron pyrophosphate cathode materials prepared by this invention are not affected.

[0036] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a sodium iron phosphate pyrophosphate positive electrode material, characterized in that, Includes the following steps: 1) Disperse iron phosphate, sodium source, phosphate and reducing agent in water, spray granulate to form spray powder, and then pulverize by airflow to obtain precursor particles with D50 particle size of 2.0-6.0μm; 2) Mix the precursor particles obtained in step 1) with ammonium oxalate, and then perform a first calcination to obtain a calcined material; The ammonium oxalate has a particle size range of 0.1-1.0 μm; The first calcination temperature is 280-320℃, and the first calcination time is 5-7h; 3) The calcined material obtained in step 2) is mixed with silicon oxide, and then subjected to a second calcination and pulverization to obtain the sodium iron pyrophosphate cathode material; The particle size of the silicon oxide is in the range of 0.1-1.0 μm; The second calcination temperature is 550-600℃, and the second calcination time is 10-14h.

2. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The reducing agent mentioned in step 1) is selected from at least one of citric acid, glucose, and carotene; The sodium source is selected from at least one of sodium oxalate and sodium carbonate; The phosphate is selected from at least one of disodium hydrogen phosphate and sodium dihydrogen phosphate; The mass ratio of iron phosphate, sodium source, phosphate, and reducing agent is (2.5-5):(1.5-3):(1-2):(1.5-4).

3. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step 1), ferric phosphate, sodium source, phosphate, and reducing agent are mixed and dispersed in water to form a slurry with a solid content of 20-40%. The spray granulation described in step 1) is carried out using a centrifugal spray dryer. The inlet temperature of the centrifugal spray dryer is 180-250℃, and the rotation speed of the atomizing disc of the centrifugal spray dryer is 8000-12000rpm.

4. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The D50 particle size of the spray granulation described in step 1) is 6-12 μm; In step 1), the air pressure during airflow pulverization is 0.5-1 MPa, the classifier frequency is 100-140 Hz, and the induced draft fan frequency is 40-60 Hz.

5. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The mass ratio of the precursor particles to ammonium oxalate in step 2) is 100:(1-2); The mixing speed in step 2) is 1400-1600 rpm, and the mixing time is 20-40 min.

6. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step 3), the mass ratio of the sintered material to silicon dioxide is 100:(0.3-0.8).

7. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The mixing speed in step 3) is 1400-1600 rpm, and the mixing time is 25-35 min.

8. The method for preparing the sodium iron pyrophosphate cathode material according to claim 1, characterized in that, The pulverization process described in step 3) involves grinding the particles to a D50 particle size of 3.0-8.0 μm.

9. A sodium iron pyrophosphate cathode material, characterized in that, It is prepared by the method for preparing sodium iron pyrophosphate cathode material according to any one of claims 1-8.

10. The application of the sodium iron pyrophosphate cathode material according to claim 9 in sodium-ion batteries.

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