Modified ferric phosphate and ferric sodium pyrophosphate positive electrode material, and preparation method and application of modified ferric phosphate and ferric sodium pyrophosphate positive electrode material

Abstract

The invention discloses a modified ferric phosphate and ferric sodium pyrophosphate positive electrode material as well as a preparation method and application thereof. The preparation method of the modified iron phosphate comprises the following steps: mixing an iron source, a phosphorus source and a surfactant, adjusting the pH value to 0.5-2, uniformly mixing with hydrogen-substituted graphdiyne aerogel, and carrying out a hydrothermal reaction to prepare the modified iron phosphate, wherein the mass ratio of the iron source to the hydrogen-substituted graphdiyne aerogel is (50-5000): 1. According to the prepared ferric sodium pyrophosphate positive electrode material, the rate capability is remarkably improved under the condition that the first charge capacity, the first discharge capacity and the coulombic efficiency are good.

Description

Technical Field

[0001] The present invention relates to a modified iron phosphate, sodium iron pyrophosphate phosphate cathode material, a preparation method thereof, and an application. Background Art

[0002] With the wide application of lithium-ion batteries in multiple fields, the shortage problem of the lithium resources they rely on has gradually emerged. In addition, the price of lithium is relatively high and its distribution is uneven, which restricts the long-term development of lithium-ion batteries. Therefore, it has become an urgent task to explore the next-generation high-performance secondary energy storage batteries. In recent years, sodium-ion batteries have received extensive attention due to their rich sodium resources, low cost, and similar chemical properties to lithium elements. Sodium-ion batteries have broad application prospects and are currently in the research stage of large-scale application. However, due to the relatively large radius of sodium ions, the ion transport kinetics is slow, which poses a challenge to the development of high-performance and stable sodium-ion batteries. This is one of the key points and difficulties in current research.

[0003] Regarding the research on the cathode materials of sodium-ion batteries, iron-based polyanion compounds such as sodium iron pyrophosphate (NFPP) have become ideal candidate materials for the application of sodium-ion batteries due to their advantages such as low cost, good stability, environmental friendliness, and rich reserves of iron elements. However, the NFPP material has the problem of poor electronic conductivity, which affects the full play of its capacity. In order to improve this situation, the method of coating a carbon layer on the surface of NFPP is often used in the prior art to enhance conductivity. For example, the technical solutions described in patents CN118213528A, CN118198293A, and CN118289725A use organic substances such as glucose or sucrose to carbonize at high temperature to form a carbon coating layer.

[0004] The structural feature of the NFPP material is that primary particles with a scale of several hundred nanometers form secondary particles with a scale of several micrometers. The traditional carbon coating process can only cover the surface of primary particles or secondary particles and fails to penetrate into the interior of primary particles to establish an effective carbon conductive network. Therefore, although surface carbon coating can improve the conductivity of the material, the internal conductivity of the NFPP material has not been significantly improved, thus affecting the overall rate performance of the material, and there is still a gap compared with oxide-based cathode materials.

[0005] Therefore, developing a new method that can effectively improve the internal conductivity of the NFPP material is the key to further optimizing the performance of sodium-ion batteries. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defect that the NFPP material has a low conductivity in the prior art, thereby reducing the rate performance, and provides a modified iron phosphate, sodium pyrophosphate iron phosphate cathode material, a preparation method thereof, and an application. The sodium pyrophosphate iron phosphate cathode material prepared by the present invention has a significantly improved rate performance while maintaining good initial charge capacity, initial discharge capacity, and Coulomb efficiency.

[0007] The present invention solves the above technical problems through the following technical solutions.

[0008] The present invention provides a preparation method of modified iron phosphate, which comprises the following steps: mixing an iron source, a phosphorus source, and a surfactant, adjusting the pH value to 0.5 - 2, then mixing uniformly with hydrogen-substituted graphdiyne aerogel, and performing a hydrothermal reaction to obtain modified iron phosphate;

[0009] Wherein, the mass ratio of the iron source to the hydrogen-substituted graphdiyne aerogel is (50 - 5000):1.

[0010] In the present invention, the iron source can be selected from one or more of ferric chloride, ferrous sulfate, and iron powder.

[0011] In the present invention, the phosphorus source can be selected from one or more of sodium carbonate, sodium phosphate, sodium pyrophosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate, such as ammonium dihydrogen phosphate.

[0012] In the present invention, the surfactant can be selected from one or more of citric acid, polyethylene glycol, cetyltrimethylammonium bromide, and sodium dodecylbenzenesulfonate, such as cetyltrimethylammonium bromide.

[0013] In the present invention, the molar ratio of the iron source to the phosphorus source can be 1:(0.5 - 2), such as 1:1.

[0014] In the present invention, the mass ratio of the iron source to the surfactant can be 1:(0.1 - 0.3), such as 1:0.11 or 1:0.15.

[0015] In the present invention, the mass ratio of the iron source to the hydrogen-substituted graphdiyne aerogel can be (60 - 2000):1, preferably (75 - 1000):1, such as 81:1, 162:1, 810:1, or 4050:1. In the present invention, if the content of the hydrogen-substituted graphdiyne aerogel is too low, the rate performance is poor; if the content is too high, the specific capacity of the material decreases.

[0016] In the present invention, the hydrogen-substituted graphdiyne aerogel can be prepared by the following steps: dissolving trialkynyl-substituted benzene and a catalyst in a solvent, and performing a Glaser coupling reaction to obtain the hydrogen-substituted graphdiyne aerogel.

[0017] Among them, the trialkynyl-substituted benzene can be selected from one or more of 1,3,5-triethynylbenzene, 1,3,5-tri-n-propynylbenzene, and 1,3,5-tri-n-butynylbenzene.

[0018] Among them, the catalyst can be selected from one or more of cuprous chloride, copper acetate, cuprous iodide, and cuprous thiophene-2-carboxylate, such as cuprous chloride.

[0019] Among them, the solvent can be selected from one or more of pyridine, N-methylpyrrolidone, DMF, and acetone, such as pyridine.

[0020] Among them, the mass ratio of the trialkynyl-substituted benzene to the catalyst can be 1:(0.1 - 0.5), such as 1:0.16 or 1:0.2.

[0021] Among them, the mass-volume ratio of the trialkynyl-substituted benzene to the solvent can be 1 g:(40 - 70) mL, such as 1 g:54 mL or 1 g:66.7 mL.

[0022] Among them, in the Glaser coupling reaction, the temperature can be 20 - 80 °C, such as 40 °C.

[0023] Among them, in the Glaser coupling reaction, the time can be 3 - 96 h, such as 72 h.

[0024] Among them, after the Glaser coupling reaction, it may further include the steps of washing and / or drying.

[0025] Preferably, the detergent used for washing is selected from one or more of pyridine, chloroform, methanol, ethanol, and water. For example, washing is carried out separately with pyridine, chloroform, methanol, ethanol, and water. The washing time for each detergent is preferably 12 h.

[0026] Preferably, the drying is freeze-drying. The freeze-drying time is preferably 12 - 48 h, such as 24 h. The freeze-drying temperature is preferably -40 - -120 °C, such as -60 °C.

[0027] In the present invention, the range of adjusting the pH value can be 0.9 - 1.6.

[0028] In the present invention, in the adjustment of the pH value, the pH regulator can be selected from sulfuric acid solutions. The concentration of the sulfuric acid solution can be 1 - 3 mol / L.

[0029] In the present invention, in the hydrothermal reaction, the temperature can be 100 - 130 °C, such as 120 °C.

[0030] In the present invention, in the hydrothermal reaction, the time can be 3 - 8 h, such as 5 h.

[0031] In the present invention, after the hydrothermal reaction, a ball milling step may further be included.

[0032] In the present invention, the D50 particle size of the modified iron phosphate may be 200 - 500 nm, such as 225 nm, 348 nm, 392 nm or 407 nm.

[0033] The present invention also provides a modified iron phosphate prepared by the above preparation method.

[0034] The present invention also provides a modified iron phosphate in which iron phosphate particles are uniformly dispersed on a carrier, and the carrier is a hydrogen-substituted graphdiyne aerogel; the mass ratio of the iron phosphate to the carrier is (50 - 5000):1.

[0035] In the present invention, the particle size of the modified iron phosphate is preferably 200 - 500 nm, such as 225 nm, 348 nm, 392 nm or 407 nm.

[0036] In the present invention, the mass ratio of the iron phosphate to the carrier is preferably (60 - 2000):1, more preferably (75 - 1000):1, such as 81:1, 162:1, 810:1 or 4050:1.

[0037] The present invention also provides a preparation method of a sodium iron pyrophosphate phosphate cathode material, which includes the following steps: spray drying and calcining a mixture including a sodium source, a phosphorus source, a carbon source and the above modified iron phosphate to obtain the sodium iron pyrophosphate phosphate cathode material.

[0038] In the present invention, the sodium source may be selected from one or more of sodium carbonate, sodium oxalate, sodium nitrate, sodium acetate, sodium phosphate, sodium pyrophosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and sodium pyrophosphate, such as sodium carbonate or sodium oxalate.

[0039] In the present invention, the phosphorus source may be selected from one or more of sodium phosphate, sodium pyrophosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate and ammonium dihydrogen phosphate, such as sodium phosphate, sodium dihydrogen phosphate or sodium pyrophosphate.

[0040] In the present invention, the carbon source may be selected from organic carbon-containing materials. The organic carbon-containing materials are preferably one or more of graphite, carbon black, carbon nanotubes, graphene, citric acid, glucose, sucrose, starch and polyvinyl alcohol, such as glucose or sucrose.

[0041] In the present invention, preferably, the amounts of the modified iron phosphate, the sodium source and the phosphorus source are weighed according to the stoichiometric ratio of Na4Fe3(PO4)2P2O7.

[0042] In the present invention, the dosage of the carbon source is determined according to the carbon content in the sodium iron pyrophosphate phosphate cathode material, and the carbon content can be 0.5-5%, preferably 2%.

[0043] In the present invention, ball milling and / or sand milling may also be included before spray drying.

[0044] In the present invention, before spray drying, the particle size D50 of the slurry can be 100-300 nm, such as 200 nm.

[0045] In the present invention, the inlet temperature of the spray drying can be 200-300 °C, such as 220 °C.

[0046] In the present invention, the outlet temperature of the spray drying can be 80-150 °C, such as 120 °C.

[0047] In the present invention, the feed flow rate of the spray drying can be 30-80 mL / h, such as 50 mL / h.

[0048] In the present invention, the air pressure of the spray drying can be 0.2-0.6 MPa, such as 0.4 MPa.

[0049] In the present invention, the calcination can be carried out in an inert atmosphere. The inert atmosphere is preferably nitrogen, argon or a hydrogen-argon mixture.

[0050] In the present invention, the temperature of the calcination can be 450-650 °C, such as 500 °C, 520 °C or 550 °C.

[0051] In the present invention, the heating rate of the calcination can be 1-5 °C / min, such as 2 °C / min, 3 °C / min or 5 °C / min.

[0052] In the present invention, the holding time of the calcination can be 5-20 h, such as 10 h, 11 h or 12 h.

[0053] The present invention also provides a sodium iron pyrophosphate phosphate cathode material prepared by the above preparation method.

[0054] The present invention also provides an application of the above modified iron phosphate or the above sodium iron pyrophosphate phosphate cathode material in a sodium ion battery.

[0055] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0056] The reagents and raw materials used in the present invention are all commercially available.

[0057] The positive progressive effect of the present invention lies in:

[0058] The present invention uses hydrogen-substituted graphdiyne aerogel as a carrier to prepare primary particles of iron phosphate with a three-dimensional conductive network inside, greatly improving the electronic conductivity and ionic conductivity of the material.

[0059] For the sodium iron pyrophosphate phosphate cathode material prepared by the present invention, while maintaining good initial charge capacity, initial discharge capacity and Coulomb efficiency, the retention rates of specific capacities at 0.2C, 0.5C, 1C, 2C, 5C and 10C are significantly improved compared with that at 0.1C, and the rate performance is significantly improved. Description of the Drawings

[0060] Figure 1 SEM image of the sodium iron pyrophosphate phosphate cathode material prepared in Example 1. Detailed Embodiments

[0061] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0062] Example 1

[0063] (1) Preparation of HGDY aerogel

[0064] Dissolve 3 g of 1,3,5-triethynylbenzene monomer and 0.6 g of CuCl in 200 mL of pyridine. Transfer the solution to a polytetrafluoroethylene-lined autoclave, seal it, and place it in a water bath at 40 °C. After reacting for three days, an HGDY organogel is formed. Wash the product with pyridine, chloroform, methanol and ethanol. The washing process for each solvent is repeated three times (12 h each time) to ensure complete removal of impurities. Finally, exchange the solvent in the gel with water. After freeze-drying for 24 h, HGDY aerogel can be obtained.

[0065] (2) Preparation of modified iron phosphate FePO4 / HGDY

[0066] Add 81 g of ferric chloride, 57.5 g of ammonium dihydrogen phosphate, and 0.86 g of surfactant CTAB (the molar ratio of ferric chloride to ammonium dihydrogen phosphate is 1:1, and the mass ratio of ferric chloride to CTAB is 1:0.11) to 500 mL of water, and then stir and dissolve evenly with a magnetic stirrer. Adjust the pH of the solution to 0.9 - 1.6. Transfer the solution to a polytetrafluoroethylene-lined autoclave containing HGBY aerogel (0.5 g of HGBY aerogel), and carry out an oil bath heating reaction at a temperature of 120 °C for a reaction time of 5 h. Separate, wash, and dry the solution after the hydrothermal reaction, and mill it to 200 - 500 nm by ball milling to obtain FePO4 / HGDY.

[0067] (3) Preparation of sodium iron pyrophosphate phosphate cathode material

[0068] Weigh 90.6 g of FePO4 / HGDY, 10.6 g of anhydrous sodium carbonate, 32.8 g of anhydrous trisodium phosphate, and 14 g of glucose. Add the above substances to water, carry out ball milling and sand milling, and control D50 at 200 nm to obtain a slurry.

[0069] Place the slurry in a spray dryer for spray drying. During the spray drying process, keep stirring the slurry. Set the inlet air temperature at 220 °C, the outlet temperature at 120 °C, the feed flow rate at 50 mL / h, and the air pressure at 0.4 MPa to obtain a precursor material.

[0070] Put the precursor material into a tubular furnace for calcination. Use an argon-protected atmosphere, raise the temperature at a rate of 3 °C / min to 500 °C, hold for 12 h, then cool naturally. Take out the material when the temperature is below 40 °C to obtain the Na4Fe3(PO4)2P2O7 cathode material.

[0071] Example 2

[0072] (1) Preparation of HGDY aerogel

[0073] Dissolve 3.7 g of 1,3,5-tripropynylbenzene monomer and 0.6 g of CuCl in 200 mL of pyridine. Transfer the solution to a polytetrafluoroethylene-lined autoclave, seal it, and place it in a 40 °C water bath. After reacting for three days, an HGDY organic gel is formed. Wash the product with pyridine, chloroform, methanol, and ethanol. The washing process with each solvent is repeated three times (12 h each time) to ensure complete removal of impurities. Finally, exchange the solvent in the gel with water. After freeze-drying for 24 h, HGDY aerogel can be obtained.

[0074] (2) Preparation of modified iron phosphate FePO4 / HGDY

[0075] Add 81 g of ferric chloride, 57.5 g of ammonium dihydrogen phosphate, and 0.86 g of surfactant CTAB (the molar ratio of ferric chloride to ammonium dihydrogen phosphate is 1:1, and the mass ratio of ferric chloride to CTAB is 1:0.11) to 500 mL of water, then stir and dissolve evenly with a magnetic stirrer. Adjust the pH of the solution to 0.9 - 1.6. Transfer the solution to a polytetrafluoroethylene-lined autoclave containing HGBY aerogel (1 g of HGBY aerogel), and carry out an oil bath heating reaction at a temperature of 120 °C for 5 h. Separate, wash, and dry the solution after the hydrothermal reaction, and obtain FePO4 / HGDY by ball milling to 200 - 500 nm.

[0076] (3) Preparation of sodium iron pyrophosphate cathode material

[0077] Weigh 90.6 g of FePO4 / HGDY, 42.4 g of anhydrous sodium carbonate, 23 g of ammonium dihydrogen phosphate, and 14 g of sucrose. Add the above substances to water, carry out ball milling and sand milling, and control D50 at 200 nm to obtain a slurry.

[0078] Place the slurry in a spray dryer for spray drying. During the spray drying process, keep stirring the slurry. Set the inlet air temperature at 220 °C, the outlet temperature at 120 °C, the feed flow rate at 50 mL / h, and the air pressure at 0.4 MPa to obtain a precursor material.

[0079] Put the precursor material into a tubular furnace for calcination. Use argon as a protective atmosphere, raise the temperature at a rate of 5 °C / min to 550 °C, hold for 10 h, then cool naturally. Take out the material when the temperature is below 40 °C to obtain the Na4Fe3(PO4)2P2O7 cathode material.

[0080] Example 3

[0081] (1) Preparation of HGDY aerogel

[0082] Dissolve 3 g of 1,3,5-triethynylbenzene monomer and 0.6 g of CuCl in 200 mL of pyridine. Transfer the solution to a polytetrafluoroethylene-lined autoclave, seal it, and place it in a 40 °C water bath. After reacting for three days, an HGDY organogel is formed. Wash the product with pyridine, chloroform, methanol, and ethanol. The washing process with each solvent is repeated three times (12 h each time) to ensure complete removal of impurities. Finally, exchange the solvent in the gel with water. After freeze-drying for 24 h, HGDY aerogel can be obtained.

[0083] (2) Preparation of modified iron phosphate FePO4 / HGDY

[0084] Add 81 g of ferric chloride, 57.5 g of ammonium dihydrogen phosphate, and 0.86 g of surfactant CTAB (the molar ratio of ferric chloride to ammonium dihydrogen phosphate is 1:1, and the mass ratio of ferric chloride to CTAB is 1:0.11) to 500 mL of water, then stir and dissolve evenly with a magnetic stirrer. Adjust the pH of the solution to 0.9 - 1.6. Transfer the solution to a polytetrafluoroethylene-lined autoclave containing HGBY aerogel (0.1 g of HGBY aerogel), and carry out an oil bath heating reaction at a temperature of 120 °C for 5 h. Separate, wash, and dry the solution after the hydrothermal reaction, and carry out ball milling to 200 - 500 nm to obtain FePO4 / HGDY.

[0085] (3) Preparation of sodium iron pyrophosphate phosphate cathode material

[0086] Weigh 90.6 g of FePO4 / HGDY, 26.8 g of sodium oxalate, 26.6 g of sodium pyrophosphate, and 14 g of sucrose. Add the above substances to water, carry out ball milling and sand milling, and control D50 at 200 nm to obtain a slurry.

[0087] Place the slurry in a spray dryer for spray drying. During the spray drying process, keep stirring the slurry. Set the inlet air temperature at 220 °C, the outlet temperature at 120 °C, the feed flow rate at 50 mL / h, and the air pressure at 0.4 MPa to obtain a precursor material.

[0088] Put the precursor material into a tubular furnace for calcination. Use an argon-protected atmosphere, raise the temperature to 520 °C at a heating rate of 2 °C / min, hold for 11 h, then cool naturally. Take out the material when the temperature is lower than 40 °C to obtain the Na4Fe3(PO4)2P2O7 cathode material.

[0089] Example 4

[0090] Based on Example 1, the HGBY aerogel added in step (2) of Example 4 is 0.02 g, other steps Same as Example 1.

[0091] Comparative Example 1

[0092] Weigh 90.6 g of FePO4, 26.8 g of sodium oxalate, 26.6 g of sodium pyrophosphate, and 14 g of sucrose. Add the above substances to water, carry out ball milling and sand milling, and control D50 at 200 nm to obtain a slurry.

[0093] Place the slurry in a spray dryer for spray drying. During the spray drying process, keep stirring the slurry. Set the inlet air temperature at 220 °C, the outlet temperature at 120 °C, the feed flow rate at 50 mL / h, and the air pressure at 0.4 MPa to obtain a precursor material.

[0094] Put the precursor material into a tubular furnace for calcination. Use an argon-protected atmosphere, raise the temperature to 520 °C at a heating rate of 2 °C / min, hold for 11 h, then cool naturally. Take out the material when the temperature is lower than 40 °C to obtain the Na4Fe3(PO4)2P2O7 cathode material.

[0095] Comparative Example 2

[0096] Based on Example 1, in Comparative Example 2, no surfactant was added in step (2), and the other steps were the same as in Example 1.

[0097] Morphology of Effect Example 1

[0098] The SEM image of the sodium iron pyrophosphate phosphate cathode material prepared in Example 1 is as Figure 1As shown. It can be seen from the figure that the size of the primary particles in the sodium iron pyrophosphate phosphate cathode material is about 200 nm.

[0099] The particle size of the modified iron phosphate FePO4 / HGDY prepared in Step (2) of Examples 1-4 was detected using a laser particle size analyzer (reference model Malvern 2000), and the test results are shown in Table 1 below.

[0100] Effect Example 2 Electrochemical Performance

[0101] The coin cell was assembled in a glove box with water and oxygen content below 0.5 ppm. The cathode sheet was prepared with a mass ratio of Na4Fe3(PO4)2P2O7:SP:PVDF of 8:1:1, the metal sodium sheet was used as the anode, and the electrolyte composition was 1M NaPF6 / (EC:DEC:PC = 1:1:1). The coin cell was charged and discharged in the range of 2V - 4V.

[0102] Test the initial discharge specific capacity and the first Coulombic efficiency at room temperature at a rate of 0.1 C (1 C = 110 mA / g). ; At 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, 5.0C, and 10C rates, each charge and discharge cycle was repeated 5 times, and then returned to 0.1C to measure the discharge specific capacity retention rate at each rate.

[0103] The test results are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] As shown in Table 1, Examples 1-4 can have excellent capacity retention while maintaining high initial charge capacity, initial discharge capacity, and Coulomb efficiency. At 0.2C, the capacity retention can be maintained above 99%, and at 10C, the capacity retention can also be maintained above 94%.

[0107] In Comparative Example 1, a conventional iron source was used, and in Comparative Example 2, a modified iron source prepared by other methods was used. The rate performance of the sodium iron pyrophosphate phosphate cathode material thus prepared was significantly reduced.

Claims

1. A preparation method of modified iron phosphate, characterized in that, It includes the following steps: Mix an iron source, a phosphorus source, and a surfactant. After adjusting the pH value to 0.5 - 2, mix it evenly with a hydrogen-substituted graphdiyne aerogel, and carry out a hydrothermal reaction to obtain modified iron phosphate. Among them, the mass ratio of the iron source to the hydrogen-substituted graphdiyne aerogel is (50 - 5000):

1.

2. The preparation method of the modified iron phosphate according to claim 1, characterized in that, The iron source is selected from one or more of ferric chloride, ferrous sulfate, and iron powder. And / or, the phosphorus source is selected from one or more of sodium carbonate, sodium phosphate, sodium pyrophosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate, such as ammonium dihydrogen phosphate. And / or, the surfactant is selected from one or more of citric acid, polyethylene glycol, cetyltrimethylammonium bromide, and sodium cetylbenzenesulfonate, such as cetyltrimethylammonium bromide. And / or, the molar ratio of the iron source to the phosphorus source is 1:(0.5 - 2), such as 1:

1. And / or, the mass ratio of the iron source to the surfactant is 1:(0.1 - 0.3), such as 1:0.11 or 1:0.

15. And / or, the mass ratio of the iron source to the hydrogen-substituted graphdiyne aerogel is (60 - 2000):1, preferably (75 - 1000):1, such as 81:1, 162:1, 810:1, or 4050:

1. And / or, the hydrogen-substituted graphdiyne aerogel is prepared through the following steps: Dissolve a trialkynyl-substituted benzene and a catalyst in a solvent, and carry out a Glaser coupling reaction to obtain the hydrogen-substituted graphdiyne aerogel. And / or, the pH value is adjusted to a range of 0.9 - 1.

6. And / or, in the adjustment of the pH value, the pH regulator is selected from sulfuric acid solution; the concentration of the sulfuric acid solution is 1 - 3 mol / L. And / or, in the hydrothermal reaction, the temperature is 100 - 130 °C, such as 120 °C. And / or, in the hydrothermal reaction, the time is 3 - 8 h, such as 5 h. And / or, after the hydrothermal reaction, it further includes a ball milling step. And / or, the particle size D50 of the modified iron phosphate is 200 - 500 nm, such as 225 nm, 348 nm, 392 nm, or 407 nm.

3. The preparation method of the modified iron phosphate according to claim 2, wherein, The trialkynyl-substituted benzene is selected from one or more of 1,3,5-triethynylbenzene, 1,3,5-tri(n-propynyl)benzene, and 1,3,5-tri(n-butynyl)benzene. And / or, the catalyst is selected from one or more of cuprous chloride, copper acetate, cuprous iodide, and thiophene-2-carboxylic acid cuprous, such as cuprous chloride. And / or, the solvent is selected from one or more of pyridine, N-methylpyrrolidone, DMF, and acetone, such as pyridine. And / or, the mass ratio of the trialkynyl-substituted benzene to the catalyst is 1:(0.1 - 0.5), such as 1:0.16 or 1:0.

2. And / or, the mass-volume ratio of the trialkynyl-substituted benzene to the solvent is 1 g:(40 - 70) mL, such as 1 g:54 mL or 1 g:66.7 mL. And / or, in the Glaser coupling reaction, the temperature is 20 - 80 °C, such as 40 °C. And / or, in the Glaser coupling reaction, the time is 3 - 96 h, such as 72 h. And / or, after the Glaser coupling reaction, it further includes the steps of washing and / or drying; Preferably, the detergent used for washing is selected from one or more of pyridine, chloroform, methanol, ethanol, and water. For example, washing is carried out with pyridine, chloroform, methanol, ethanol, and water respectively; the washing time for each detergent is preferably 12 h; Preferably, the drying is freeze-drying; the freeze-drying time is preferably 12 - 48 h, such as 24 h; the freeze-drying temperature is preferably -40 - -120 °C, such as -60 °C.

4. A modified iron phosphate, characterized in that, It is prepared by the preparation method described in any one of claims 1 - 3.

5. A modified iron phosphate, characterized in that, In the modified iron phosphate, iron phosphate particles are uniformly dispersed on the carrier, and the carrier is hydrogen-substituted graphdiyne aerogel; the mass ratio of the iron phosphate to the carrier is (50 - 5000):1; Preferably, the particle size D50 of the modified iron phosphate is 200 - 500 nm, such as 225 nm, 348 nm, 392 nm, or 407 nm; Preferably, the mass ratio of the iron phosphate to the carrier is (60 - 2000):1, more preferably (75 - 1000):1, such as 81:1, 162:1, 810:1, or 4050:

1.

6. A preparation method of a sodium iron pyrophosphate phosphate cathode material, characterized in that, It includes the following steps: Spray-drying and calcining a mixture including a sodium source, a phosphorus source, a carbon source, and the modified iron phosphate described in claim 4 or 5 to obtain a sodium iron pyrophosphate phosphate cathode material.

7. The preparation method of the sodium iron pyrophosphate phosphate cathode material according to claim 6, wherein The sodium source is selected from one or more of sodium carbonate, sodium oxalate, sodium nitrate, sodium acetate, sodium phosphate, sodium pyrophosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate, such as sodium carbonate or sodium oxalate; And / or, the phosphorus source is selected from one or more of sodium phosphate, sodium pyrophosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate, such as sodium phosphate, sodium dihydrogen phosphate, or sodium pyrophosphate; And / or, the carbon source is selected from organic carbon-containing materials; the organic carbon-containing materials are preferably one or more of graphite, carbon black, carbon nanotubes, graphene, citric acid, glucose, sucrose, starch, and polyvinyl alcohol, such as glucose or sucrose; And / or, the amounts of the modified iron phosphate, the sodium source, and the phosphorus source are weighed according to the stoichiometric ratio of Na4Fe3(PO4)2P2O7; And / or, the amount of the carbon source is determined according to the carbon content in the sodium iron pyrophosphate phosphate cathode material, and the carbon content is 0.5 - 5%, preferably 2%.

8. The preparation method of the sodium iron pyrophosphate phosphate cathode material according to claim 6, characterized in that, Before the spray-drying, it further includes ball milling and / or sand milling; And / or, before the spray-drying, the particle size D50 of the slurry is 100 - 300 nm, such as 200 nm; And / or, the inlet temperature of the spray-drying is 200 - 300 °C, such as 220 °C; And / or, the outlet temperature of the spray-drying is 80 - 150 °C, such as 120 °C; And / or, the feed flow rate of the spray-drying is 30 - 80 mL / h, such as 50 mL / h; And / or, the air pressure of the spray-drying is 0.2 - 0.6 MPa, such as 0.4 MPa; And / or, the calcining is carried out in an inert atmosphere; the inert atmosphere is preferably nitrogen, argon, or a hydrogen-argon mixture; And / or, the calcination temperature is 450 - 650 °C, such as 500 °C, 520 °C or 550 °C; And / or, the heating rate of the calcination is 1 - 5 °C / min, such as 2 °C / min, 3 °C / min or 5 °C / min; And / or, the heat preservation time of the calcination is 5 - 20 h, such as 10 h, 11 h or 12 h.

9. A sodium iron pyrophosphate phosphate cathode material, characterized in that It is prepared by the preparation method according to any one of claims 6 - 8.

10. An application of the modified iron phosphate or sodium iron pyrophosphate cathode material according to claim 4 or 5, or claim 9 in a sodium ion battery.

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