A high-entropy doped sodium iron phosphate pyrophosphate positive electrode material, a preparation method and application thereof

Abstract

This application belongs to the field of sodium-ion battery materials, and discloses a high-entropy doped sodium iron pyrophosphate cathode material, its preparation method, and its application. The high-entropy doped sodium iron pyrophosphate cathode material has the chemical formula Na₄Fe₄. 3‑9x (MgYTiZrNb) x (PO4)2P2O7 / C, where x = 0.01~0.1. This application prepares high-entropy doped sodium iron pyrophosphate cathode material through ball milling, blending, and calcination. The preparation process is simple, the raw materials are inexpensive and widely available, and it does not involve the use of hazardous chemicals. The high-entropy doped sodium iron pyrophosphate cathode material of this application suppresses the electrochemically inert sodium iron phosphate phase during the reaction process, improves the purity of the sodium iron pyrophosphate phase, achieves a discharge specific capacity close to its theoretical discharge specific capacity, good rate performance, and significantly improved cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material technology, and in particular relates to a high-entropy doped sodium iron pyrophosphate cathode material, its preparation method and application. Background Technology

[0002] Efficient energy storage technology is a prerequisite for utilizing sustainable energy. Over the past few decades, advanced lithium-ion batteries have successfully entered the energy storage market due to their high energy density and long lifespan. However, constrained by limited lithium resources and rising costs, a significant supply-demand gap remains in large-scale energy storage systems. Sodium-ion batteries have attracted widespread attention due to their similar working mechanism, low cost, abundant sodium resources, environmental friendliness, wide operating temperature range, and high safety.

[0003] Sodium iron pyrophosphate (SO4) exhibits significant commercial potential due to its moderate average voltage plateau of 3.1 V, large three-dimensional open sodium ion diffusion channels, minimal volume change, robust structure, and low cost. However, because the chemical potentials of phosphate and pyrophosphate ions in the crystal lattice are similar, thermodynamic competition is easily triggered during the preparation of SO4. The system tends to generate thermodynamically more stable mono-anion byproducts, i.e., the formation of sodium iron phosphate or sodium iron pyrophosphate impurity phases. Furthermore, these impurity phases will induce lattice distortion during long-term charge-discharge cycles, reducing structural stability and weakening the material's cycle stability and rate performance. Secondly, the low intrinsic conductivity of SO4 limits capacity release.

[0004] For example, Chinese patent CN119495724A discloses a carbon-coated sodium iron pyrophosphate cathode material, its preparation method, and its application. Utilizing the respective conductivity advantages of carbon nanotubes and organic carbon sources, a strong conductive network is formed, improving the material's conductivity. However, the problem of the sodium iron phosphate impurity phase remains unresolved. Chinese patent CN120709323A discloses a Se anion-doped sodium iron pyrophosphate / carbon cathode active material, its preparation method, and its application. This material utilizes Se anion doping within the crystal structure of the matrix material... 2- Partially replaces O 2- To address this issue, a Se-doped solid solution was constructed to modulate the electronic band structure of the material. The introduction of Se reduced the band gap and improved electronic conductivity, but its capacity release was insufficient, its crystal structure stability was inadequate, and its cycling performance was limited. Furthermore, the toxicity of Se cannot be ignored. Chinese patent CN120172384B discloses a method for preparing a composite sodium iron pyrophosphate material. By controlling the preparation temperature, the formation of impurity phases was suppressed, but the problem of intrinsic conductivity remained unresolved.

[0005] Based on this, this application was developed. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a high-entropy doped sodium iron pyrophosphate cathode material, which aims to suppress the electrochemically inert sodium iron phosphate that appears during the preparation process, stabilize the crystal structure, provide more redox centers, and improve the electrochemical performance of the sodium iron pyrophosphate cathode.

[0007] This invention also provides a method for preparing and applying the above-mentioned high-entropy doped sodium iron pyrophosphate cathode material.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A high-entropy doped sodium iron pyrophosphate cathode material with the chemical formula Na₄Fe 3-9x (MgYTiZrNb) x (PO4)2P2O7 / C, where x = 0.01~0.1.

[0009] The preparation method of the above-mentioned high-entropy doped sodium iron pyrophosphate cathode material includes the following steps: A precursor powder containing sodium, iron, phosphorus, carbon, and high-entropy raw materials is provided. The precursor is calcined at a temperature of 200~700°C in a non-oxidizing atmosphere to obtain the high-entropy doped sodium iron pyrophosphate cathode material.

[0010] As a preferred technical solution, the preparation method of the above-mentioned high-entropy doped sodium iron pyrophosphate cathode material includes the following steps: (1) Sodium source, iron source, phosphorus source, carbon source, high entropy raw material and solvent are wet ball milled and mixed evenly, and dried (drying at 100-140℃ for 12±2h) to obtain mixed precursor; (2) The mixed precursor obtained in step (1) is ground, pre-calcined, sintered, and cooled to obtain the high-entropy doped sodium iron pyrophosphate cathode material Na4Fe 3-9x (MgYTiZrNb) x (PO4)2P2O7 / C.

[0011] Specifically, the sodium source includes, but is not limited to, one or more of the following: sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium carbonate, sodium bicarbonate, sodium oxalate, and sodium citrate. The iron source includes, but is not limited to, one or more of the following: ferric phosphate, ferric nitrate, ferric chloride, and ferrous oxalate. The phosphorus source includes, but is not limited to, one or more of the following: phosphoric acid, pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and sodium pyrophosphate. The carbon source includes, but is not limited to, one or more of citric acid, glucose, sucrose, carbon nanotubes, reduced graphene oxide, etc.

[0012] Specifically, the high-entropy raw materials include magnesium sources, yttrium sources, titanium sources, zirconium sources, and niobium sources, etc.; the solvent is water, ethanol, or a mixture thereof, etc. The magnesium source includes, but is not limited to, one or more of magnesium acetate, magnesium chloride, magnesium carbonate, magnesium citrate, etc. The yttrium source includes, but is not limited to, one or more of yttrium chloride, yttrium acetate, yttrium phosphate, and yttrium carbonate; The titanium source includes, but is not limited to, one or more of the following: metatitanic acid, orthotitanic acid, titanium tetrachloride, and titanium oxysulfate; The zirconium source includes, but is not limited to, one or more of zirconium oxychloride, zirconium acetate, zirconium sulfate, and zirconium nitrate; The niobium source includes, but is not limited to, one or more of niobium acetate, niobium nitrate, niobium pentachloride, etc.

[0013] Furthermore, the molar ratio of the sodium source, iron source, and phosphorus source is: sodium:iron:phosphorus = 4.00:2.10~2.91:4.00; the molar ratio of the carbon source to the iron source can be 0.5~2:2.10~2.91. The magnesium source, yttrium source, titanium source, zirconium source, and niobium source in the high-entropy raw material are doped in the same proportion in the high-entropy doped sodium iron pyrophosphate cathode material, and the molar ratio of magnesium source, yttrium source, titanium source, zirconium source, niobium source to iron source is 0.01~0.1:2.10~2.91.

[0014] Specifically, in step (2), the preheating temperature is 200-400℃, the heating rate is 2-10℃ / min, and the preheating time is 2-8 hours.

[0015] Specifically, in step (2), the sintering temperature is 400-700℃, the heating rate is 2-10℃ / min, and the sintering time is 6-15 hours.

[0016] Furthermore, in step (2), the atmosphere for pre-firing and sintering is one or a mixture of nitrogen, argon, and argon-hydrogen mixture.

[0017] The present invention also provides the application of the above-mentioned high-entropy doped sodium iron pyrophosphate cathode material in the preparation of sodium-ion batteries, and conducts electrochemical performance tests.

[0018] This application describes the preparation of high-entropy doped sodium iron pyrophosphate cathode material via ball milling, blending, and calcination. The preparation process is simple, uses inexpensive and widely available raw materials, and does not involve the use of hazardous chemicals. The high-entropy doped sodium iron pyrophosphate cathode material of this application suppresses the electrochemically inert sodium iron phosphate phase during the reaction, improves the purity of the sodium iron phosphate pyrophosphate phase, achieves a discharge specific capacity close to its theoretical discharge specific capacity, exhibits good rate performance, and significantly improves cycle stability.

[0019] Compared with the prior art, this application has the following advantages: 1) The high-entropy doped sodium iron pyrophosphate cathode material described in this application has advantages such as good conductivity, high specific capacity, good cycle stability, and high rate capacity; for example, in the voltage range of 1.7 to 4.3V, the 0.1C discharge specific capacity can reach 125.8 mAh g. -1 ; 5C discharge specific capacity can reach 95.8mAh g -1 The stability rate of 5C at 800 cycles reaches 92.1%. 2) The high-entropy doped sodium iron pyrophosphate cathode material described in this application uses five elements to replace the Fe site, which increases the configuration entropy of the material, suppresses the generation of impurity phases, and greatly improves the electronic conductivity and sodium ion diffusion efficiency of the cathode material. 3) The method for preparing high-entropy doped sodium iron pyrophosphate cathode material in this application has a short process, simple technology, and is green and environmentally friendly. Attached Figure Description

[0020] Figure 1 The Na4Fe3(PO4)2P2O7 / C and Na4Fe were used to prepare the cathode material products of Comparative Example 1 and Examples 1-4. 2.64 (MgYTiZrNb) 0.04 (PO4)2P2O7 / C, Na4Fe 2.82 (MgYTiZrNb) 0.02 (PO4)2P2O7 / C, Na4Fe 2.73 (MgYTiZrNb) 0.03 (PO4)2P2O7 / C, Na4Fe 2.55 (MgYTiZrNb) 0.05 XRD pattern of (PO4)2P2O7 / C material; Figure 2 Scanning images of the cathode materials prepared in Comparative Example 1 and Example 1; Figure 3 TEM and HRTEM images of the cathode materials prepared in Comparative Example 1 and Example 1; Figure 4 The image shows the HAADF pattern of the cathode material prepared in Example 1. Figure 5 The charge-discharge curve of the button cell provided in this application at 0.1C; Figure 6 Rate test chart of the button cell provided in this application in the voltage range of 1.7 to 4.3V; Figure 7 The graph shows the cycle performance of the button cell provided in this application under 5C conditions. Detailed Implementation

[0021] The technical solutions of this application will be further described in detail below with reference to embodiments, but this application is not limited to the following embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art.

[0022] The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this application.

[0023] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the raw materials used in the embodiments are all commercially available products that can be purchased directly. Example 1

[0024] The chemical formula of the high-entropy doped sodium iron pyrophosphate cathode material in this embodiment is: Na₄Fe₂O₃ 2.64 (MgYTiZrNb) 0.04 (PO4)2P2O7 / C.

[0025] The preparation method includes the following steps: (1) Research reports indicate that the molecular formula of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7. After introducing a high-entropy element, the chemical formula can be written as Na4Fe3(PO4)2P2O7 according to the principle of charge balancing. 3-9x (MgYTiZrNb) x (PO4)2P2O7 was calculated to be produced by mixing 2.64 mol of ferrous oxalate dihydrate (FeC2O4·2H2O), 1 mol of anhydrous sodium pyrophosphate (Na4P2O7), 2 mol of ammonium dihydrogen phosphate (NH4H2PO4), and 1 mol of citric acid monohydrate (C6H8O7·H2O) in a ball mill jar. Then, 150 g of agate beads, 120 g of pure water, and 30 g of ethanol were added at a ball-to-solvent mass ratio of 1:1. Subsequently, 0.04 mol each of high-entropy raw materials magnesium acetate, yttrium chloride, metatitanic acid, zirconium oxychloride, and niobium pentachloride were added for wet ball milling at a speed of 450 rpm / min for 5 h to achieve uniform mixing. The slurry obtained from ball milling was dried in a forced-air drying oven at 120℃ for 12 h. The dried material was then ground in a mortar and pestle to obtain the precursor powder.

[0026] (2) The precursor powder obtained in step (1) was pre-sintered in nitrogen at 300°C for 6 hours at a heating rate of 5°C / min, and then sintered at 550°C for 10 hours. After cooling to room temperature in the furnace, the high-entropy doped sodium iron pyrophosphate cathode material Na4Fe was obtained. 2.64 (MgYTiZrNb) 0.04 (PO4)2P2O7 / C.

[0027] The XRD pattern of the cathode material prepared in this embodiment is as follows: Figure 1 As shown, from Figure 1 It can be seen that the synthesized high-entropy doped sodium iron pyrophosphate has an orthorhombic crystal structure with space group Pn21a, showing high phase purity and no sodium iron phosphate impurity phase.

[0028] The SEM image of the cathode material prepared in this embodiment is as follows: Figure 2 As shown, from Figure 2 As can be seen, the material is porous and has a uniform carbon layer on its surface.

[0029] TEM and HRTEM images of the cathode material prepared in this embodiment are as follows: Figure 3 As shown, from Figure 3 As can be seen, the material of Example 1 is covered by a thin and uniform carbon layer with a thickness of 4.69 nm. In addition, the lattice fringes with a spacing of 3.465 Å correspond to the (103) crystal plane of the sodium iron pyrophosphate lattice.

[0030] The HAADF-EDS image of the positive electrode material prepared in this embodiment is as follows: Figure 4 As shown, the material surface is porous, and all elements, including Na, Fe, P, O, C, Mg, Y, Ti, Zr and Nb, are uniformly distributed within it.

[0031] The positive electrode material, conductive carbon black, and PVDF prepared in this embodiment were weighed out in a ratio of 8:1:1 (0.48 g, 0.06 g, and 0.06 g respectively) and mixed evenly. The mixture was then coated with 6 g of N-methylpyrrolidone solvent to form a 10 wt% slurry. The slurry was coated onto aluminum foil. A sodium sheet was used as the negative electrode, and a 1 M NaPF6 solution of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) (1:1:1 Vol%, containing 5% fluoroethylene carbonate FEC) was used as the electrolyte. The cells were assembled into a CR2032 coin cell, and the electrochemical performance of the positive electrode material was tested.

[0032] The charge / discharge curves of the assembled battery are as follows: Figure 5 As shown, the 0.1C discharge specific capacity is 125.8 mAh g. -1 Ratio performance such as Figure 6 As shown, the 5C discharge specific capacity can reach 95.8 mAh g. -1 Cyclic performance such as Figure 7 As shown, the capacity retention rate can reach 92.1% after 800 cycles at 5C.

[0033] Comparative Example 1 (1) According to calculations, 3 mol ferrous oxalate dihydrate (FeC2O4·2H2O), 1 mol anhydrous sodium pyrophosphate (Na4P2O7), 2 mol ammonium dihydrogen phosphate (NH4H2PO4) and 1 mol citric acid monohydrate (C6H8O7·H2O) were mixed in a ball mill jar. Then, 150g of agate beads and 150g of pure water were added at a ball milling ratio of 1:1 for wet ball milling. The ball milling speed was 450rpm / min and the ball milling time was 5h. The slurry obtained from ball milling was dried in a forced-air drying oven at 120℃ for 12h. The dried material was then ground in a mortar to obtain the precursor powder.

[0034] (2) The precursor powder obtained in step (1) is pre-sintered in nitrogen at 300°C for 6 hours with a heating rate of 5°C / min. Then, it is heated to 550°C and sintered for 10 hours. After cooling to room temperature in the furnace, the sodium iron pyrophosphate cathode material Na4Fe3(PO4)2P2O7 / C is obtained.

[0035] The XRD pattern of the cathode material prepared in this comparative example is as follows: Figure 1 As shown, from Figure 1 It can be seen that the synthesized high-entropy doped sodium iron pyrophosphate has an orthorhombic crystal structure with space group Pn21a, but there is a clear sodium iron phosphate impurity phase present.

[0036] The SEM image of the cathode material prepared in this comparative example is as follows: Figure 2 As shown, from Figure 2 As can be seen, the material is porous and has a uniform carbon layer on its surface.

[0037] Using the same method as in Example 1, CR2032 coin cells were assembled, and the electrochemical performance of the cathode material was tested. The charge-discharge curves of the assembled cells are shown below. Figure 5 As shown, the 0.1C discharge specific capacity is 108.5 mAh g. -1 Ratio performance such as Figure 6 As shown, the discharge specific capacity at a 5C rate is 51.0 mAh g. -1 Cyclic performance such as Figure 7 As shown, after 800 cycles of 5C, the capacity retention rate was 62.6%, and all performance indicators were lower than those of Example 1. Example 2

[0038] The chemical formula of the high-entropy doped sodium iron pyrophosphate cathode material in this embodiment is: Na₄Fe₂O₃ 2.82 (MgYTiZrNb) 0.02 (PO4)2P2O7 / C.

[0039] The preparation method includes the following steps: (1) According to calculations, 2.82 mol of ferrous oxalate dihydrate (FeC2O4·2H2O), 1 mol of anhydrous sodium pyrophosphate (Na4P2O7), 2 mol of ammonium dihydrogen phosphate (NH4H2PO4) and 1 mol of citric acid monohydrate (C6H8O7·H2O) were mixed in a ball mill jar. Then, 150g of agate beads, 120g of pure water and 30g of ethanol were added at a ball milling bead to solvent mass ratio of 1:1. Subsequently, 0.02 mol each of high entropy raw materials magnesium acetate, yttrium chloride, metatitanic acid, zirconium oxychloride and niobium pentachloride were added for wet ball milling at a speed of 450 rpm / min for 5 hours to mix evenly. The slurry obtained from ball milling was dried in a forced-air drying oven at 120℃ for 12 hours. The dried material was then ground in a mortar to obtain the precursor powder.

[0040] (2) The precursor powder obtained in step (1) was pre-sintered in nitrogen at 300°C for 6 hours at a heating rate of 5°C / min, and then sintered at 550°C for 10 hours. After cooling to room temperature in the furnace, the high-entropy doped sodium iron pyrophosphate cathode material Na4Fe was obtained. 2.82 (MgYTiZrNb) 0.02 (PO4)2P2O7 / C. Example 3

[0041] The chemical formula of the high-entropy doped sodium iron pyrophosphate cathode material in this embodiment is: Na₄Fe₂O₃ 2.73 (MgYTiZrNb) 0.03 (PO4)2P2O7 / C.

[0042] The preparation method includes the following steps: (1) According to calculations, 2.73 mol of ferrous oxalate dihydrate (FeC2O4·2H2O), 1 mol of anhydrous sodium pyrophosphate (Na4P2O7), 2 mol of ammonium dihydrogen phosphate (NH4H2PO4) and 1 mol of citric acid monohydrate (C6H8O7·H2O) were mixed in a ball mill jar. Then, 150 g of agate beads, 120 g of pure water and 30 g of ethanol were added at a ball milling bead to solvent mass ratio of 1:1. Subsequently, 0.03 mol each of high entropy raw materials magnesium acetate, yttrium chloride, metatitanic acid, zirconium oxychloride and niobium pentachloride were added for wet ball milling at a speed of 450 rpm / min for 5 h to achieve uniform mixing. The slurry obtained from ball milling was dried in a forced-air drying oven at 120℃ for 12 h. The dried material was then ground in a mortar and pestle to obtain the precursor powder.

[0043] (2) The precursor powder obtained in step (1) was pre-sintered in nitrogen at 300°C for 6 hours at a heating rate of 5°C / min, and then sintered at 550°C for 10 hours. After cooling to room temperature in the furnace, the high-entropy doped sodium iron pyrophosphate cathode material Na4Fe was obtained.2.73 (MgYTiZrNb) 0.03 (PO4)2P2O7 / C. Example 4

[0044] The chemical formula of the high-entropy doped sodium iron pyrophosphate cathode material in this embodiment is: Na₄Fe₂O₃ 2.55 (MgYTiZrNb) 0.05 (PO4)2P2O7 / C.

[0045] The preparation method includes the following steps: (1) According to calculations, 2.55 mol of ferrous oxalate dihydrate (FeC2O4·2H2O), 1 mol of anhydrous sodium pyrophosphate (Na4P2O7), 2 mol of ammonium dihydrogen phosphate (NH4H2PO4) and 1 mol of citric acid monohydrate (C6H8O7·H2O) were mixed in a ball mill jar. Then, 150 g of agate beads, 120 g of pure water and 30 g of ethanol were added at a ball milling ball to solvent mass ratio of 1:1. Subsequently, 0.05 mol each of high entropy raw materials magnesium acetate, yttrium chloride, metatitanic acid, zirconium oxychloride and niobium pentachloride were added for wet ball milling at a speed of 450 rpm / min for 5 h to achieve uniform mixing. The slurry obtained from ball milling was dried in a forced-air drying oven at 120℃ for 12 h. The dried material was then ground in a mortar and pestle to obtain the precursor powder.

[0046] (2) The precursor powder obtained in step (1) was pre-sintered in nitrogen at 300°C for 6 hours at a heating rate of 5°C / min, and then sintered at 550°C for 10 hours. After cooling to room temperature in the furnace, the high-entropy doped sodium iron pyrophosphate cathode material Na4Fe was obtained. 2.55 (MgYTiZrNb) 0.05 (PO4)2P2O7 / C.

[0047] The 0.1C discharge specific capacity, 5C discharge specific capacity, and cycle performance of the high-entropy doped sodium iron pyrophosphate cathode materials prepared in Examples 1-4 and the sodium iron pyrophosphate cathode materials prepared in the comparative examples are listed in the table below.

[0048]

[0049] As can be seen from the data in the table above, the 0.1C discharge specific capacity of the high-entropy doped sodium iron pyrophosphate cathode materials described in Examples 1 and 3 of this application is significantly higher than that of the sodium iron pyrophosphate cathode material in Comparative Example 1. The 0.1C discharge specific capacity of Examples 2 and 4 is comparable to that of Comparative Example 1. The discharge specific capacity of Examples 1 to 4 at 5C is higher than that of Comparative Example 1, reaching 60.0 mAh g. -1In the above examples, the cycle performance of Examples 1-4 at 5C for 800 cycles is much higher than that of Comparative Example 1, reaching more than 83.5%.

[0050] In summary, the high-entropy doped sodium iron pyrophosphate cathode material and its preparation method described in this application are reasonably designed, have a simple process, and are easy to scale up for production. The synthesized high-entropy doped sodium iron pyrophosphate cathode material has faster electron transport speed, more electroactive reaction sites, high specific capacity, and stable electrochemical performance, and can be used as the preferred cathode material for future commercial sodium-ion batteries.

[0051] The above description is merely a preferred embodiment of the present invention and only describes the implementation of the present invention. It is not intended to limit the patent scope of the present invention. Any improvements made under the technical concept of the present invention and using the contents of the present invention specification and drawings should also be considered within the protection scope of the present invention.

Claims

1. A high-entropy doped sodium iron pyrophosphate cathode material, characterized in that, Its chemical formula is Na₄Fe 3-9x (MgYTiZrNb) x (PO4)2P2O7 / C, where x = 0.01~0.

1.

2. The method for preparing the high-entropy doped sodium iron pyrophosphate cathode material according to claim 1, characterized in that, Includes the following steps: A precursor powder containing sodium, iron, phosphorus, carbon, and high-entropy raw materials is provided. The precursor is calcined at a temperature of 200~700°C in a non-oxidizing atmosphere to obtain the high-entropy doped sodium iron pyrophosphate cathode material.

3. The preparation method according to claim 2, characterized in that, Includes the following steps: (1) Sodium source, iron source, phosphorus source, carbon source, high entropy raw material and solvent are wet ball milled and mixed, and dried to obtain mixed precursor; (2) Grind, pre-calcine, sinter, and cool the mixed precursor obtained in step (1) to obtain the high-entropy doped sodium iron pyrophosphate cathode material.

4. The preparation method according to claim 2, characterized in that, The sodium source is one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium carbonate, sodium bicarbonate, sodium oxalate, and sodium citrate. The iron source is one or more of ferric phosphate, ferric nitrate, ferric chloride, and ferrous oxalate; The phosphorus source is one or more of phosphoric acid, pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, ferric phosphate, and sodium pyrophosphate. The carbon source is one or more of citric acid, glucose, sucrose, carbon nanotubes, and reduced graphene oxide.

5. The preparation method according to claim 2, characterized in that, The high-entropy raw materials include magnesium sources, yttrium sources, titanium sources, zirconium sources, and niobium sources; the solvent is water, ethanol, or a mixture thereof; The magnesium source is one or more of magnesium acetate, magnesium chloride, magnesium carbonate, and magnesium citrate. The yttrium source is one or more selected from yttrium chloride, yttrium acetate, yttrium phosphate, and yttrium carbonate; The titanium source is one or more of metatitanic acid, orthotitanic acid, titanium tetrachloride, and titanium oxysulfate. The zirconium source is one or more of zirconium oxychloride, zirconium acetate, zirconium sulfate, and zirconium nitrate; The niobium source is one or more of niobium acetate, niobium nitrate, and niobium pentachloride.

6. The preparation method according to claim 2, characterized in that, The molar ratio of sodium source, iron source, and phosphorus source is: sodium:iron:phosphorus = 4.00:2.10~2.91:4.00; the molar ratio of carbon source to iron source is 0.5~2:2.10~2.91; the magnesium source, yttrium source, titanium source, zirconium source, and niobium source in the high-entropy raw material are doped in the same proportion in the high-entropy doped sodium iron pyrophosphate cathode material, and the molar ratio of magnesium source, yttrium source, titanium source, zirconium source, niobium source, and iron source is 0.01~0.1:2.10~2.

91.

7. The preparation method according to claim 3, characterized in that, In step (2), the pre-firing temperature is 200-400℃, the heating rate is 2-10℃ / min, and the pre-firing time is 2-8 hours.

8. The preparation method according to claim 3, characterized in that, In step (2), the sintering temperature is 400-700℃, the heating rate is 2-10℃ / min, and the sintering time is 6-15 hours.

9. The preparation method according to claim 3, characterized in that, In step (2), the atmosphere for pre-firing and sintering is one or a mixture of nitrogen, argon, and argon-hydrogen mixture.

10. The application of the high-entropy doped sodium iron pyrophosphate cathode material of claim 1 in the preparation of sodium-ion batteries.

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