Pyrophosphate ferric phosphate sodium positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a sodium ferric pyrophosphate positive electrode material as well as a preparation method and application thereof. The invention provides a preparation method of a sodium ferric pyrophosphate positive electrode material, which comprises the following steps: (1) mixing an iron source, a sodium source, a phosphorus source and citric acid for the first time, and performing spray drying for the first time to prepare a first precursor with D50 of 10-12 [mu] m; performing secondary mixing on an iron source, a sodium source, a phosphorus source and citric acid, and performing secondary spray drying to prepare a second precursor with D50 of 3-5 microns; the iron source comprises a first iron source with D50 of 1.1-1.8 [mu] m and a second iron source with D50 of 0.3-0.8 [mu] m; the mass ratio of the first iron source to the second iron source is (0.3-0.5): (0.5-0.7); and (2) mixing the first precursor, the second precursor and sodium metaborate, and sintering to obtain the sodium ferric pyrophosphate positive electrode material. After the prepared pyrophosphate ferric phosphate sodium positive electrode material is prepared into a pole piece, the compaction density is proper, and the prepared battery is high in specific capacity and cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a sodium iron pyrophosphate phosphate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium-ion batteries have a working principle similar to that of lithium-ion batteries, and utilize the reversible insertion and extraction of sodium ions between the positive and negative electrodes to achieve energy storage and release, but their cost is lower. Currently, the cathode materials used in sodium-ion batteries mainly include three categories: transition metal oxide systems, polyanion compounds (phosphate systems, fluorophosphate systems, sulfate systems), and Prussian blue systems.

[0003] Sodium iron pyrophosphate phosphate cathode material belongs to one of the polyanion compound phosphate systems, and is usually synthesized by a solid-phase method. The prepared sodium iron pyrophosphate phosphate cathode material has a porous and massive morphology, a low tap density (about 2.0 g / cm 3 ), and the compaction density of the electrode sheet is only 2.1 - 2.2 g / cm 3 , and the specific capacity and cycle retention rate are low. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects in the prior art such as the poor particle morphology of the sodium iron pyrophosphate phosphate cathode material, the low compaction density, specific capacity, and cycle retention rate after forming the electrode sheet, so as to provide a sodium iron pyrophosphate phosphate cathode material, a preparation method thereof, and an application thereof.

[0005] For this purpose, the present invention provides the following technical solutions.

[0006] The present invention provides a preparation method of a sodium iron pyrophosphate phosphate cathode material, comprising the following steps:

[0007] (1) First, mix an iron source, a sodium source, a phosphorus source, and citric acid, and perform first spray drying to obtain a first precursor with a D50 of 10 - 12 μm; then mix the iron source, the sodium source, the phosphorus source, and citric acid again, and perform second spray drying to obtain a second precursor with a D50 of 3 - 5 μm; the iron source includes a first iron source with a D50 of 1.1 - 1.8 μm and a second iron source with a D50 of 0.3 - 0.8 μm; the mass ratio of the first iron source to the second iron source is (0.3 - 0.5):(0.5 - 0.7);

[0008] (2) Mix the first precursor, the second precursor, and sodium metaborate, and sinter to obtain the sodium iron pyrophosphate phosphate cathode material.

[0009] The citric acid functions as a chelating agent and a reducing agent, which not only reduces to generate divalent iron ions, but also makes the sodium element, iron element, and phosphorus element evenly distributed, avoiding the generation of impurity phases due to uneven distribution;

[0010] Preferably, in step (2), the first precursor and the second precursor are mixed, and then sodium metaborate is added.

[0011] The first precursor is secondary particles formed by agglomeration of primary particles with a size of 100 - 300 nm. When the primary particles agglomerate to form secondary particles, pores are formed between the primary particles, giving the first precursor a porous structure with a porosity of 30 ± 5%.

[0012] The present invention controls the particle sizes of the first precursor and the second precursor by adjusting the parameters of spray drying.

[0013] The second precursor is secondary particles formed by agglomeration of primary particles with a size of 100 - 300 nm. When the primary particles agglomerate to form secondary particles, pores are formed between the primary particles, giving the second precursor a porous structure with a porosity of 30 ± 5%.

[0014] The first precursor and the second precursor with porous structures can be fully mixed, and then a cathode material with high density is formed after sintering.

[0015] In an alternative embodiment, in the first mixing, the molar ratio of iron, sodium, and phosphorus in the iron source, phosphorus source, and sodium source is (2.8 - 3):(3.9 - 4.1):(3.9 - 4.1).

[0016] In an alternative embodiment, in the first mixing, the molar ratio of iron in the iron source, phosphorus source, and sodium source to citric acid is (2.8 - 3):(1.5 - 2).

[0017] In an alternative embodiment, in the second mixing, the molar ratio of iron, sodium, and phosphorus in the iron source, phosphorus source, and sodium source is (2.8 - 3):(3.9 - 4.1):(3.9 - 4.1).

[0018] In an alternative embodiment, in the second mixing, the molar ratio of iron in the iron source, phosphorus source, and sodium source to citric acid is (2.8 - 3):(1.5 - 2).

[0019] In an alternative embodiment, the iron source includes at least one of iron phosphate, ferrous oxalate, and iron nitrate.

[0020] In an alternative embodiment, the sodium source includes at least one of sodium oxalate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and sodium bicarbonate.

[0021] In an alternative embodiment, the phosphorus source includes at least one of sodium dihydrogen phosphate, iron phosphate, and disodium hydrogen phosphate. It should be noted that the sodium source and the phosphorus source can come from the same compound or different compounds, and the iron source and the phosphorus source can come from the same compound or different compounds. For example, when the raw material includes sodium dihydrogen phosphate, it can provide both sodium and phosphorus; when the raw material includes iron phosphate, it can provide both iron and phosphorus.

[0022] In an alternative embodiment, in the first mixing, the first mixing further includes adding a solvent;

[0023] Preferably, the solvent includes water;

[0024] Preferably, the mass ratio of the sum of the masses of the iron source, sodium source, phosphorus source, and citric acid to the mass of the solvent is (2 - 4):(6 - 8).

[0025] In an alternative embodiment, in the second mixing, the second mixing further includes adding a solvent;

[0026] Preferably, the solvent includes water;

[0027] Preferably, the mass ratio of the sum of the masses of the iron source, sodium source, phosphorus source, and citric acid to the mass of the solvent is (2 - 4):(6 - 8).

[0028] In an alternative embodiment, the inlet temperature of the first spray drying is 190 - 210 °C;

[0029] In an alternative embodiment, the outlet temperature of the first spray drying is 90 - 100 °C;

[0030] In an alternative embodiment, the rotation speed of the first spray drying is 10000 - 15000 rpm;

[0031] In an alternative embodiment, the inlet temperature of the second spray drying is 220 - 230 °C;

[0032] In an alternative embodiment, the outlet temperature of the second spray drying is 90 - 100 °C;

[0033] In an alternative embodiment, the rotation speed of the second spray drying is 18000 - 20000 rpm.

[0034] In an alternative embodiment, the mass ratio of the first precursor to the second precursor is (6 - 8):(2 - 4);

[0035] In an alternative embodiment, the mass ratio of the sum of the masses of the first precursor and the second precursor to the mass of sodium metaborate is 1:(0.01 - 0.015).

[0036] In an alternative embodiment, the sintering includes a first sintering and a second sintering;

[0037] Preferably, the temperature of the first sintering is 200 - 400 °C;

[0038] Preferably, the time of the first sintering is 1 - 6 h;

[0039] Preferably, the temperature of the second sintering is 500 - 600 °C;

[0040] Preferably, the time of the second sintering is 8 - 24 h.

[0041] The present invention also provides a sodium iron pyrophosphate cathode material prepared by the above preparation method.

[0042] The sodium iron pyrophosphate cathode material prepared by the present invention has a tap density of 2.3 - 2.5 g / cm 3 after being made into a pole piece; the particle breakage rate < 3%;

[0043] The present invention also provides an application of the sodium iron pyrophosphate cathode material prepared by the above preparation method in a sodium-ion battery.

[0044] The technical solution of the present invention has the following advantages:

[0045] 1. The preparation method of the sodium iron pyrophosphate cathode material provided by the present invention includes the following steps: (1) First, mix an iron source, a sodium source, a phosphorus source, and citric acid, and perform first spray drying to obtain a first precursor with a D50 of 10 - 12 μm; then mix the iron source, the sodium source, the phosphorus source, and citric acid for the second time, and perform second spray drying to obtain a second precursor with a D50 of 3 - 5 μm; the iron source includes a first iron source with a D50 of 1.1 - 1.8 μm and a second iron source with a D50 of 0.3 - 0.8 μm; the mass ratio of the first iron source to the second iron source is (0.3 - 0.5):(0.5 - 0.7); (2) Mix the first precursor, the second precursor, and sodium metaborate, and sinter to obtain the sodium iron pyrophosphate cathode material. The sodium iron pyrophosphate cathode material prepared by the present invention has a moderate tap density after being made into a pole piece, the particle breakage rate < 3%, and the battery obtained has a high specific capacity and cycling performance.

[0046] The present invention prepares first precursors and second precursors with different particle sizes. After mixing, the small particles fill the gaps between the large particles, avoiding many holes; mixing the first precursor, the second precursor, and sodium metaborate, and sintering, enables the borate groups to penetrate into the grain boundaries, eliminating internal stress, reducing micro-voids, improving the tap density of the pole piece, and thus increasing the energy density of the battery obtained, thereby enhancing its specific capacity and cycling retention rate. The particle size grading of large and small particles and the borate groups can further improve the tap density of the pole piece;

[0047] The iron sources used in the present invention include a first iron source with a D50 of 1.1 - 1.8 μm and a second iron source with a D50 of 0.3 - 0.8 μm; the iron sources with different particle sizes enable the materials in spray drying to be packed more closely, reducing the void volume, and thus improving the tap density of the sodium iron pyrophosphate cathode material prepared into a pole piece. Detailed implementation manners

[0048] The following embodiments are provided to better understand the present invention further. They are not limited to the best implementation manner, and do not constitute a limitation to the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other existing technologies falls within the protection scope of the present invention.

[0049] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0050] Example 1

[0051] This example provides a preparation method of a sodium iron pyrophosphate cathode material, including the following steps:

[0052] (1) 1350 g of FePO4, 603 g of Na2C2O4, 356 g of NaH2PO4, and 946 g of C6H8O7·H2O are uniformly dispersed in 7620 g of pure water, and spray granulation is carried out with a centrifugal spray dryer at 10000 rpm (the inlet temperature is 190 °C, and the outlet temperature is 90 °C) to obtain a first precursor with a D50 of 10 μm; the first precursor is a secondary particle formed by the aggregation of primary particles of 100 - 300 nm, and the porosity of the first precursor is 30 ± 5%; among them, FePO4 is treated by sanding, and the composition is 30 wt% with a D50 = 1.1 μm and 70 wt% with a D50 = 0.3 μm;

[0053] (2) 1350 g of FePO4, 603 g of Na2C2O4, 356 g of NaH2PO4, and 946 g of C6H8O7·H2O are uniformly dispersed in 7620 g of pure water, and spray granulation is carried out with a centrifugal spray dryer at 18000 rpm (the inlet temperature is 220 °C, and the outlet temperature is 90 °C) to obtain a second precursor with a D50 of 4 μm; the second precursor is a secondary particle formed by the aggregation of primary particles of 100 - 300 nm, and the porosity of the second precursor is 30 ± 5%; among them, FePO4 is treated by sanding, and the composition is 30 wt% with a D50 = 1.1 μm and 70 wt% with a D50 = 0.3 μm;

[0054] (3) Mix 700 g of the first precursor and 300 g of the second precursor, then add 10 g of NaBO2 and mix evenly. After heating to 300 °C, sinter for 4 h for the first time, and then heat to 550 °C and sinter for 12 h for the second time to obtain the sodium iron pyrophosphate phosphate cathode material.

[0055] Example 2

[0056] This example provides a method for preparing a sodium iron pyrophosphate phosphate cathode material, which includes the following steps:

[0057] (1) Uniformly disperse 1350 g of FePO4, 603 g of Na2C2O4, 356 g of NaH2PO4, and 946 g of C6H8O7·H2O in 7620 g of pure water, and perform spray granulation with a centrifugal spray dryer at 15000 rpm (the inlet temperature is 210 °C and the outlet temperature is 100 °C) to obtain a first precursor with a D50 of 10 μm; the first precursor is a secondary particle formed by agglomeration of primary particles with a size of 100 - 300 nm, and the porosity of the first precursor is 30 ± 5%; among them, FePO4 is treated by sanding, and the composition is 30 wt% with a D50 = 1.1 μm and 70 wt% with a D50 = 0.3 μm;

[0058] (2) Uniformly disperse 1350 g of FePO4, 603 g of Na2C2O4, 356 g of NaH2PO4, and 946 g of C6H8O7·H2O in 7620 g of pure water, and perform spray granulation with a centrifugal spray dryer at 20000 rpm (the inlet temperature is 230 °C and the outlet temperature is 100 °C) to obtain a second precursor with a D50 of 4 μm; the second precursor is a secondary particle formed by agglomeration of primary particles with a size of 100 - 300 nm, and the porosity of the second precursor is 30 ± 5%; among them, FePO4 is treated by sanding, and the composition is 30 wt% with a D50 = 1.1 μm and 70 wt% with a D50 = 0.3 μm;

[0059] (3) Mix 700 g of the first precursor and 350 g of the second precursor, then add 15 g of NaBO2 and mix evenly. After heating to 200 °C, sinter for 6 h for the first time, and then heat to 600 °C and sinter for 8 h for the second time to obtain the sodium iron pyrophosphate phosphate cathode material.

[0060] Example 3

[0061] This example provides a method for preparing a sodium iron pyrophosphate phosphate cathode material, which includes the following steps:

[0062] (1) 1700 g of FePO4, 650 g of sodium bicarbonate, 550 g of disodium hydrogen phosphate, and 1500 g of C6H8O7·H2O were uniformly dispersed in 7620 g of pure water, and spray granulation was carried out at 13000 rpm with a centrifugal spray dryer (the inlet temperature was 200 °C and the outlet temperature was 90 °C) to obtain a first precursor with a D50 of 10 μm; the first precursor was composed of secondary particles formed by the aggregation of primary particles with a size of 100 - 300 nm, and the porosity of the first precursor was 30 ± 5%; among them, FePO4 was treated by sand grinding, and the composition was 40 wt% with D50 = 1.8 μm and 60 wt% with D50 = 0.8 μm;

[0063] (2) 1700 g of FePO4, 650 g of sodium bicarbonate, 550 g of disodium hydrogen phosphate, and 1500 g of C6H8O7·H2O were uniformly dispersed in 7620 g of pure water, and spray granulation was carried out at 18000 rpm with a centrifugal spray dryer (the inlet temperature was 220 °C and the outlet temperature was 90 °C) to obtain a second precursor with a D50 of 4 μm; the second precursor was composed of secondary particles formed by the aggregation of primary particles with a size of 100 - 300 nm, and the porosity of the second precursor was 30 ± 5%; among them, FePO4 was treated by sand grinding, and the composition was 40 wt% with D50 = 1.8 μm and 60 wt% with D50 = 0.8 μm;

[0064] (3) 700 g of the first precursor and 230 g of the second precursor were mixed, and then 10 g of NaBO2 was added and mixed evenly. After heating to 400 °C, the first sintering was carried out for 2 h, and then after heating to 500 °C, the second sintering was carried out for 24 h to obtain the sodium iron pyrophosphate phosphate cathode material.

[0065] Comparative Example 1

[0066] This comparative example provides a method for preparing a lithium iron phosphate cathode material, including the following steps:

[0067] (1) 1350 g of FePO4 (D50 = 0.6 μm), 603 g of Na2C2O4, 356 g of NaH2PO4, and 946 g of C6H8O7·H2O were uniformly dispersed in 7620 g of pure water, and spray granulation was carried out at 12000 rpm with a centrifugal spray dryer (the inlet temperature was 200 °C and the outlet temperature was 90 °C) to obtain a precursor with a D50 of 7 μm; the precursor was composed of secondary particles formed by the aggregation of primary particles with a size of 100 - 300 nm, and the porosity of the precursor was 30 ± 5%;

[0068] (2) 1000 g of the precursor was heated to 300 °C and then the first sintering was carried out for 4 h, and then after heating to 550 °C, the second sintering was carried out for 12 h to obtain the lithium iron phosphate cathode material.

[0069] Comparative Example 2

[0070] This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material. Compared with Example 1, the only difference is that 10 g of NaBO2 is not added in step (3).

[0071] Comparative Example 3

[0072] This comparative example provides a method for preparing a sodium iron pyrophosphate cathode material, including the following steps:

[0073] (1) 1350 g of FePO4 (D50 = 0.6 μm), 603 g of Na2C2O4, 356 g of NaH2PO4, and 946 g of C6H8O7·H2O were uniformly dispersed in 7620 g of pure water, and spray granulation was carried out with a centrifugal spray dryer at 12000 rpm (the inlet temperature was 200 °C and the outlet temperature was 90 °C) to obtain a precursor with D50 of 7 μm; the precursor was composed of secondary particles aggregated by primary particles of 100 - 300 nm, and the porosity of the precursor was 30 ± 5%;

[0074] (2) 1000 g of the precursor and 10 g of NaBO2 were mixed, heated to 300 °C and sintered for the first time for 4 h, and then heated to 550 °C and sintered for the second time for 12 h to obtain the sodium iron pyrophosphate cathode material.

[0075] Test Example

[0076] The cathode materials prepared in the above Examples 1 - 3 and Comparative Examples 1 - 3 were respectively mixed uniformly with acetylene black and PVDF in a mass ratio of 80:12:8, added with 1 - methyl - 2 - pyrrolidone and ball - milled for 1 h to make a slurry, uniformly coated on an aluminum sheet, dried, and pressed into a positive electrode sheet. Using a sodium metal sheet as the negative electrode and a PC solution of 1 mol / L NaClO4 as the electrolyte, a 2032 coin - type battery was assembled. The performance was tested with a Land test system.

[0077] (1) Compaction density detection method: The sheets prepared in Examples 1 - 3 and Comparative Examples 1 - 3 were tested according to GB / T7314 - 2017 "Metallic materials - Compression testing at ambient temperature", and the results are shown in Table 1.

[0078] (2) 0.1C charge specific capacity detection method: At room temperature, within the cut - off voltage of 2.0 - 4.5 V, charge once at 0.1C; the results are shown in Table 1;

[0079] (3) Cycle retention rate detection method: At room temperature, within the cut - off voltage of 2.0 - 4.5 V, charge once at 1C and discharge once at 1C, and cycle 50 times; the results are shown in Table 1.

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, the sodium iron pyrophosphate phosphate cathode material prepared by the present invention has a good tap density after being made into a pole piece, and the specific capacity and cycle performance of the prepared battery are high.

[0083] From the comparison between the examples and the comparative examples, it can be seen that the sodium iron pyrophosphate phosphate cathode material prepared by the present invention adopts the grading of precursor particles with different sizes and boron doping, which has a good synergistic effect, effectively improves the tap density of the cathode material after being made into a pole piece, and further improves the specific capacity and cycle retention rate.

[0084] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A preparation method of sodium iron pyrophosphate phosphate cathode material, characterized in that, It includes the following steps: (1) First, mix an iron source, a sodium source, a phosphorus source and citric acid, and perform first spray drying to obtain a first precursor with a D50 of 10 - 12 μm; second, mix an iron source, a sodium source, a phosphorus source and citric acid, and perform second spray drying to obtain a second precursor with a D50 of 3 - 5 μm; the iron source includes a first iron source with a D50 of 1.1 - 1.8 μm and a second iron source with a D50 of 0.3 - 0.8 μm; the mass ratio of the first iron source to the second iron source is (0.3 - 0.5):(0.5 - 0.7); (2) Mix the first precursor, the second precursor and sodium metaborate, and sinter to obtain a sodium iron pyrophosphate cathode material.

2. The preparation method according to claim 1, wherein, In the first mixing, the molar ratio of iron element, sodium element, and phosphorus element in the iron source, phosphorus source, and sodium source is (2.8 - 3):(3.9 - 4.1):(3.9 - 4.1); and / or, In the first mixing, the ratio of the molar amount of iron element in the iron source, phosphorus source, and sodium source to citric acid is (2.8 - 3):(1.5 - 2); and / or, In the second mixing, the molar ratio of iron element, sodium element, and phosphorus element in the iron source, phosphorus source, and sodium source is (2.8 - 3):(3.9 - 4.1):(3.9 - 4.1); and / or, In the second mixing, the ratio of the molar amount of iron element in the iron source, phosphorus source, and sodium source to citric acid is (2.8 - 3):(1.5 - 2).

3. The preparation method according to claim 1 or 2, characterized in that, The iron source includes at least one of iron phosphate, ferrous oxalate, and iron nitrate; and / or, The sodium source includes at least one of sodium oxalate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and sodium bicarbonate; and / or, The phosphorus source includes at least one of sodium dihydrogen phosphate, iron phosphate, and disodium hydrogen phosphate.

4. The preparation method according to any one of claims 1-3, characterized in that, In the first mixing, the first mixing further includes adding a solvent; Preferably, the solvent includes water; Preferably, the mass ratio of the sum of the masses of the iron source, sodium source, phosphorus source, and citric acid to the mass of the solvent is (2 - 4):(6 - 8).

5. The preparation method according to any one of claims 1-4, characterized in that, In the second mixing, the second mixing further includes adding a solvent; Preferably, the solvent includes water; Preferably, the mass ratio of the sum of the masses of the iron source, sodium source, phosphorus source, and citric acid to the mass of the solvent is (2 - 4):(6 - 8).

6. The preparation method according to any one of claims 1-5, characterized in that, The inlet temperature of the first spray drying is 190 - 210 °C; and / or, The outlet temperature of the first spray drying is 90 - 100 °C; and / or, The rotation speed of the first spray drying is 10000 - 15000 rpm; and / or, The inlet temperature of the second spray drying is 220 - 230 °C; and / or, The outlet temperature of the second spray drying is 90 - 100 °C; and / or, The rotation speed of the second spray drying is 18000 - 20000 rpm.

7. The preparation method according to any one of claims 1-6, characterized in that, The mass ratio of the first precursor to the second precursor is (6 - 8):(2 - 4); and / or, The mass ratio of the sum of the masses of the first precursor and the second precursor to the mass of sodium metaborate is 1:(0.01 - 0.015).

8. The preparation method according to any one of claims 1-7, characterized in that, The sintering includes first sintering and second sintering; Preferably, the temperature of the first sintering is 200 - 400 °C; Preferably, the time of the first sintering is 1-6 h; Preferably, the temperature of the second sintering is 500-600 °C; Preferably, the time of the second sintering is 8-24 h.

9. The sodium iron pyrophosphate cathode material prepared by the preparation method according to any one of claims 1-8.

10. The application of the sodium iron pyrophosphate cathode material prepared by the preparation method according to any one of claims 1-8 in a sodium ion battery.

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