Sodium-ion battery precursor and preparation method of sodium-ion battery

Abstract

The invention relates to the technical field of sodium-ion battery materials, in particular to a preparation method of a sodium-ion battery precursor and a sodium-ion battery. The preparation method comprises the following steps: preparing a manganese-iron mixed salt solution, and preparing a magnesium sulfate solution; the preparation method comprises the following steps: adding a manganese-iron mixed salt solution and a magnesium sulfate solution into a reaction kettle, then adding a sodium source, adjusting the pH value for reaction, washing the material after the reaction is finished, diluting and dissolving the washed material, then heating, then adding a phosphorus source to adjust the pH value for reaction, and aging after the reaction is finished to obtain doped manganese-iron-sodium pyrophosphate precursor slurry; and then washing and drying the slurry to obtain the doped sodium ferromanganese pyrophosphate precursor material. The precursor material, a sodium source, a phosphorus source and a carbon source are mixed, sanded and sintered to obtain the positive electrode material of the sodium ion battery, and then the positive electrode material is used for preparing the sodium ion battery. A sodium ferromanganese phosphate precursor is prepared by adopting a coprecipitation method, ferromanganese is uniformly distributed, and a product with a special structure is prepared by adopting a special process route.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials, and more particularly to a sodium-ion battery precursor and a method for preparing a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have become an important complementary technology to lithium-ion batteries due to their resource cost advantages, but their cathode materials generally suffer from drawbacks such as low specific capacity (<140mAh / g) and short cycle life (capacity retention <80% after 500 full cell cycles). Layered oxides (such as...) have seen faster commercialization progress.

[0003] NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 Taking O2 and polyanionic compounds (such as Na3V2(PO4)3) as examples, the former suffers from irreversible structural degradation due to the O′→P′ phase transition in the sodium interlayer, while the latter is limited by the single-electron reaction mechanism and low electronic conductivity (<10). -9 The energy density and rate performance are severely limited by the energy density (S / cm).

[0004] Sodium manganese ferric pyrophosphate (Na4Mn) x Fe 3-x (PO4)2P2O7) materials possess both high theoretical capacity (>120mAh / g) and are based on Mn 2+ / Mn 3+ with Fe 2+ / Fe 3+ With its dual redox couple and stable olivine-type structure, it is considered a breakthrough candidate material. Summary of the Invention

[0005] In view of this, the present invention provides a sodium-ion battery precursor and a method for preparing a sodium-ion battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a sodium-ion battery precursor, wherein the precursor has the molecular formula NaMn x Fe 1-x-y Mg y PO4, where 0.40≤x≤0.80, 0.001<y<0.02.

[0007] A method for preparing a sodium-ion battery precursor includes the following steps:

[0008] S1. Dissolve soluble divalent manganese salt in pure water, then add an antioxidant, and then add soluble divalent ferrous salt to prepare a manganese-iron mixed salt solution; prepare a doping solution, which is a magnesium sulfate solution.

[0009] S2. Add the manganese-iron mixed salt solution and magnesium sulfate solution to the reaction vessel, then add the sodium source, adjust the measured pH to the target value and carry out the reaction. After the reaction is completed, wash the materials.

[0010] S3. The washed material from step S2 is diluted and dissolved with pure water, then added to a reaction vessel and heated to the target temperature. Then a phosphorus source is added, followed by aging to obtain a doped sodium manganese phosphate pyrophosphate precursor slurry.

[0011] S4. Wash and dry the sodium manganese phosphate precursor slurry obtained in step S3 to obtain the doped sodium manganese phosphate precursor material.

[0012] As a further description of the above technical solution:

[0013] In step S1, the soluble divalent manganese salt is one or more of manganese sulfate, manganese acetate, manganese oxalate, and manganese chloride; the soluble divalent ferrous salt is one or more of ferrous chloride, ferrous nitrate, and ferrous sulfate; the antioxidant is one or more of ascorbic acid, dilute sulfuric acid, and citric acid; the molar concentration of manganese and ferrous salt in the manganese-ferrous mixed salt solution is 1.5-3.0 mol / L; the molar ratio of manganese ions to ferrous ions is x:1-xy, where 0.40≤x≤0.80, 0.001<y<0.02.

[0014] As a further description of the above technical solution:

[0015] The target temperature in step S3 is 70-100℃; the sodium source in step S2 is one or more of sodium hydroxide and sodium carbonate; the measured pH control range is 11.0-13.0; preferably, the measured pH is between 11.8-12.5.

[0016] As a further description of the above technical solution:

[0017] In step S3, the phosphorus source is one or more of 85% phosphoric acid and ammonium dihydrogen phosphate, and the molar ratio of the added phosphorus source to the total molar ratio of manganese and iron is 2-3:1; the aging time is 6-16 hours.

[0018] A method for preparing a sodium-ion battery cathode material includes the above-mentioned sodium-ion battery precursor: after mixing and milling a dry doped sodium manganese ferric pyrophosphate precursor material with a sodium source, a phosphorus source and a carbon source, the mixture is sintered at multiple temperatures under a protective atmosphere to obtain the sodium manganese ferric pyrophosphate sodium-ion battery cathode material.

[0019] As a further description of the above technical solution:

[0020] The sodium source is one or more of sodium carbonate and sodium acetate, and the total mass of the added sodium source is 10-15% of the total mass of the doped sodium manganese ferric pyrophosphate precursor; the phosphorus source is one or more of phosphoric acid and sodium dihydrogen phosphate, and the total mass of the added phosphorus source is 19-24% of the total mass of the doped sodium manganese ferric pyrophosphate precursor; the carbon source is one or more of glucose and sucrose, and the total mass of the added carbon source is 3-6% of the total mass of the sodium manganese ferric pyrophosphate precursor; the sintering temperature is controlled in multiple stages: the first stage is 300-400℃, with a holding time of 1-2 hours; the second stage is 550-650℃, with a holding time of 3-5 hours; the third stage is 700-750℃, with a holding time of 6-10 hours; the heating rate is controlled at 3-5℃ / min.

[0021] A sodium-ion battery includes the above-mentioned sodium-ion battery positive electrode material, wherein the sodium-ion battery is prepared using the sodium pyrophosphate manganese iron phosphate sodium-ion battery positive electrode material.

[0022] By employing the above technical solutions, the sodium-ion battery precursor and the method for preparing a sodium-ion battery of the present invention have at least the following beneficial effects:

[0023] 1. Compared with the prior art, the present invention provides a sodium-ion battery precursor and a method for preparing a sodium-ion battery. The precursor is prepared by co-precipitation, which yields a sodium manganese iron phosphate precursor with uniform manganese and iron distribution. At the same time, by optimizing the design of the synthesis process steps, a sodium manganese iron phosphate precursor with a similar symmetrical "boat-shaped" structure is prepared. The sodium-ion battery prepared from the precursor with this structure has higher capacity and better cycle performance.

[0024] 2. Compared with the prior art, the sodium-ion battery precursor and sodium-ion battery preparation method of the present invention, in the co-precipitation reaction process, metal ion doping can improve the uniform distribution of dopant elements and suppress Jahn-Teller distortion. Attached Figure Description

[0025] Figure 1 This is a SEM image of the sodium manganese phosphate iron pyrophosphate precursor prepared in Example 1 of the present invention;

[0026] Figure 2 This is a SEM image of the sodium manganese phosphate iron pyrophosphate precursor prepared in Comparative Example 1 of this invention. Detailed Implementation

[0027] Reference Figures 1-2 This invention provides a sodium-ion battery precursor with the molecular formula NaMn. x Fe 1-x- y Mg yPO4, where 0.40≤x≤0.80, 0.001<y<0.02.

[0028] A method for preparing a sodium-ion battery precursor includes the following steps:

[0029] S1. Dissolve a soluble divalent manganese salt in pure water, then add an antioxidant, followed by a soluble divalent ferrous salt to prepare a manganese-ferrous mixed salt solution. The soluble divalent manganese salt is one or more of manganese sulfate, manganese acetate, manganese oxalate, and manganese chloride; the antioxidant is one or more of ascorbic acid, dilute sulfuric acid, and citric acid; the soluble divalent ferrous salt is one or more of ferrous chloride, ferrous nitrate, and ferrous sulfate. Prepare a doping solution, which is a magnesium sulfate solution used as a dopant. The molar ratio of manganese ions to ferric ions is x:1-xy, where 0.40≤x≤0.80 and 0.001<y<0.02.

[0030] S2. Add the manganese-iron mixed salt solution and magnesium sulfate solution to the reaction vessel, then add a sodium source, adjust the measured pH to the target value and carry out the reaction. After the reaction is completed, wash the materials. The sodium source is one or more of sodium hydroxide and sodium carbonate. The measured pH is controlled within the range of 11.0-13.0. Preferably, the measured pH is between 11.8-12.5. Specifically, the manganese-iron mixed salt and the sodium source undergo a co-precipitation reaction.

[0031] S3. Dilute and dissolve the washed material from step S2 with pure water, then add it to a reaction vessel and heat it to the target temperature. Then add a phosphorus source and age it to obtain a doped sodium manganese ferric pyrophosphate precursor slurry. The phosphorus source is one or more of 85% phosphoric acid and ammonium dihydrogen phosphate. The molar ratio of the phosphorus source to the total molar ratio of manganese and iron is 2-3:1. The aging time is 6-16 hours.

[0032] S4. Wash and dry the sodium manganese phosphate precursor slurry obtained in step S3 to obtain the doped sodium manganese phosphate precursor material.

[0033] A method for preparing a sodium-ion battery cathode material includes the following steps: A dry, doped sodium manganese ferric pyrophosphate precursor material is mixed with a sodium source, a phosphorus source, and a carbon source, milled, and then sintered at multiple temperatures under a protective atmosphere to obtain the sodium manganese ferric pyrophosphate sodium-ion battery cathode material. Specifically, the sodium source is one or more of sodium carbonate and sodium acetate, and the total mass of the added sodium source is 10-15% of the total mass of the doped sodium manganese ferric pyrophosphate precursor; the phosphorus source is one or more of phosphoric acid and sodium dihydrogen phosphate, and the total mass of the added phosphorus source is... The total weight is 19-24% of the total weight of the doped sodium manganese ferric pyrophosphate precursor; the carbon source is one or more of glucose and sucrose, and the total weight of the added carbon source is 3-6% of the total weight of the sodium manganese ferric pyrophosphate precursor; the protective atmosphere is an inert gas such as nitrogen; the sintering temperature is controlled in multiple stages: the first stage is 300-400℃, and the holding time is 1-2h; the second stage is 550-650℃, and the holding time is 3-5h; the third stage is 700-750℃, and the holding time is 6-10h; the heating rate is controlled at 3-5℃ / min.

[0034] A sodium-ion battery, comprising the above-mentioned sodium-ion battery cathode material, and prepared by using sodium pyrophosphate manganese iron phosphate sodium-ion battery cathode material.

[0035] Example 1:

[0036] A sodium-ion battery is prepared as follows:

[0037] (1) Dissolve 13.246 kg of manganese sulfate crystals in 40 L of deionized water, add 400 ml of 5% dilute sulfuric acid, stir for 5 min, then add 11.010 kg of ferrous sulfate crystals, stir and dissolve to prepare a 2.475 mol / L manganese-iron mixed salt solution; dissolve 0.12 kg of magnesium sulfate crystals separately in 5 L of deionized water to prepare a 0.20 mol / L magnesium sulfate solution;

[0038] (2) At room temperature, add 20L of pure water to a 100L reactor, turn on nitrogen protection, then add 40L of manganese-iron mixed salt solution and 5L of magnesium sulfate solution, turn on the reactor to stir, slowly add 15.0L of 32% liquid alkali solution (to control the target measured pH), adjust the measured pH to 11.50, react for 30 minutes and then discharge the material, wash it with 200L of pure water to obtain material A;

[0039] (3) In a 100L reactor, add 60L of pure water, turn on nitrogen and stir, then add material A, and heat to 70℃ at the same time. After the material dissolves, add 15.15L of 85% phosphoric acid solution, adjust the measured pH to 1.37, and then perform dynamic aging for 8 hours to obtain sodium manganese phosphate pyrophosphate precursor slurry.

[0040] (4) The sodium manganese phosphate precursor slurry obtained in step (3) is washed and dried to obtain magnesium-doped sodium manganese phosphate precursor.

[0041] (5) The sodium manganese iron phosphate pyrophosphate precursor obtained in step (4) is mixed with 1.80 kg sodium carbonate, 2.20 L 85% phosphoric acid solution and 0.70 kg glucose and then milled. After that, multi-stage sintering is carried out. The first stage is 350℃, heating rate is 3℃ / min and constant temperature is 90 min; the second stage is 600℃, heating rate is 3℃ / min and constant temperature is 240 min; the third stage is 725℃, heating rate is 3℃ / min and constant temperature is 480 min. Then the temperature is lowered. After the cooling sintering is completed, sodium manganese iron phosphate pyrophosphate sodium-ion battery cathode material is obtained.

[0042] The sodium pyrophosphate (SMP) positive electrode material prepared above is used to prepare a sodium ion battery positive electrode sheet, and finally a sodium ion battery is prepared.

[0043] Example 2:

[0044] A sodium-ion battery is prepared as follows:

[0045] (1) Dissolve 15.499 kg of manganese sulfate crystals in 40 L of deionized water, add 400 ml of 5% dilute sulfuric acid, stir for 5 min, then add 8.202 kg of ferrous sulfate crystals, stir and dissolve to prepare a 2.475 mol / L manganese-iron mixed salt solution; dissolve 0.12 kg of magnesium sulfate crystals separately in 5 L of deionized water to prepare a 0.20 mol / L magnesium sulfate solution;

[0046] (2) At room temperature, add 20L of pure water to a 100L reactor, turn on nitrogen protection, then add 40L of manganese-iron mixed salt solution and 5L of magnesium sulfate solution, turn on the reactor to stir, slowly add 15.0L of 32% liquid alkali solution (to control the target measured pH), adjust the measured pH to 11.50, react for 30 minutes and then discharge the material, wash it with 200L of pure water to obtain material A;

[0047] (3) In a 100L reactor, add 60L of pure water, turn on nitrogen and stir, then add material A, and heat to 70℃ at the same time. After the material dissolves, add 15.15L of 85% phosphoric acid solution, adjust the measured pH to 1.37, and then perform dynamic aging for 8 hours to obtain sodium manganese phosphate pyrophosphate precursor slurry.

[0048] (4) The sodium manganese phosphate precursor slurry obtained in step (3) is washed and dried to obtain magnesium-doped sodium manganese phosphate precursor.

[0049] (5) The sodium manganese iron phosphate pyrophosphate precursor obtained in step (4) is mixed with 1.80 kg sodium carbonate, 2.20 L 85% phosphoric acid solution and 0.70 kg glucose and then milled. After that, multi-stage sintering is carried out. The first stage is 350℃, heating rate is 3℃ / min and constant temperature is 90 min; the second stage is 600℃, heating rate is 3℃ / min and constant temperature is 240 min; the third stage is 725℃, heating rate is 3℃ / min and constant temperature is 480 min. Then the temperature is lowered. After the cooling sintering is completed, sodium manganese iron phosphate pyrophosphate sodium-ion battery cathode material is obtained.

[0050] The sodium pyrophosphate (SMP) positive electrode material prepared above is used to prepare a sodium ion battery positive electrode sheet, and finally a sodium ion battery is prepared.

[0051] Example 3:

[0052] A sodium-ion battery is prepared as follows:

[0053] (1) Dissolve 13.246 kg of manganese sulfate crystals in 40 L of deionized water, add 400 ml of 5% dilute sulfuric acid, stir for 5 min, then add 11.010 kg of ferrous sulfate crystals, stir and dissolve to prepare a 2.475 mol / L manganese-iron mixed salt solution; dissolve 0.12 kg of magnesium sulfate crystals separately in 5 L of deionized water to prepare a 0.20 mol / L magnesium sulfate solution;

[0054] (2) At room temperature, add 20L of pure water to a 100L reactor, turn on nitrogen protection, then add 40L of manganese-iron mixed salt solution and 5L of magnesium sulfate solution, turn on the reactor to stir, slowly add 17.8L of 32% liquid alkali solution (to control the target measured pH), adjust the measured pH to 12.50, react for 30 minutes and then discharge the material, wash it with 200L of pure water to obtain material A;

[0055] (3) In a 100L reactor, add 60L of pure water, turn on nitrogen and stir, then add material A, and heat to 70℃ at the same time. After the material dissolves, add 15.15L of 85% phosphoric acid solution, adjust the measured pH to 1.37, and then perform dynamic aging for 8 hours to obtain sodium manganese phosphate pyrophosphate precursor slurry.

[0056] (4) The sodium manganese phosphate precursor slurry obtained in step (3) is washed and dried to obtain magnesium-doped sodium manganese phosphate precursor.

[0057] (5) The sodium manganese iron phosphate pyrophosphate precursor obtained in step (4) is mixed with 1.80 kg sodium carbonate, 2.20 L 85% phosphoric acid solution and 0.70 kg glucose and then milled. After that, multi-stage sintering is carried out. The first stage is 350℃, heating rate is 3℃ / min and constant temperature is 90 min; the second stage is 600℃, heating rate is 3℃ / min and constant temperature is 240 min; the third stage is 725℃, heating rate is 3℃ / min and constant temperature is 480 min. Then the temperature is lowered. After the cooling sintering is completed, sodium manganese iron phosphate pyrophosphate sodium-ion battery cathode material is obtained.

[0058] (6) The sodium pyrophosphate, manganese iron phosphate, sodium ion battery positive electrode material prepared above is used to prepare a sodium pyrophosphate, manganese iron phosphate, sodium ion battery positive electrode sheet, and finally a sodium ion battery is prepared.

[0059] Example 4:

[0060] A sodium-ion battery is prepared as follows:

[0061] (1) Dissolve 13.246 kg of manganese sulfate crystals in 40 L of deionized water, add 400 ml of 5% dilute sulfuric acid, stir for 5 min, then add 11.010 kg of ferrous sulfate crystals, stir and dissolve to prepare a 2.475 mol / L manganese-iron mixed salt solution; dissolve 0.12 kg of magnesium sulfate crystals separately in 5 L of deionized water to prepare a 0.20 mol / L magnesium sulfate solution;

[0062] (2) At room temperature, add 20L of pure water to a 100L reactor, turn on nitrogen protection, then add 40L of manganese-iron mixed salt solution and 5L of magnesium sulfate solution, turn on the reactor to stir, slowly add 15.0L of 32% liquid alkali solution (to control the target measured pH), adjust the measured pH to 11.50, react for 30 minutes and then discharge the material, wash it with 200L of pure water to obtain material A;

[0063] (3) In a 100L reactor, add 60L of pure water, turn on nitrogen and stir, then add material A, and simultaneously raise the temperature to 70℃. After the material dissolves, add 17.9L of 85% phosphoric acid solution, adjust the measured pH to 1.23, and then perform dynamic aging for 8 hours to obtain sodium manganese phosphate pyrophosphate precursor slurry.

[0064] (4) The sodium manganese phosphate precursor slurry obtained in step (3) is washed and dried to obtain magnesium-doped sodium manganese phosphate precursor.

[0065] (5) The sodium manganese iron phosphate pyrophosphate precursor obtained in step (4) is mixed with 1.80 kg sodium carbonate, 2.20 L 85% phosphoric acid solution and 0.70 kg glucose and then milled. After that, multi-stage sintering is carried out. The first stage is 350℃, heating rate is 3℃ / min and constant temperature is 90 min; the second stage is 600℃, heating rate is 3℃ / min and constant temperature is 240 min; the third stage is 725℃, heating rate is 3℃ / min and constant temperature is 480 min. Then the temperature is lowered. After the cooling sintering is completed, sodium manganese iron phosphate pyrophosphate sodium-ion battery cathode material is obtained.

[0066] The sodium pyrophosphate (SMP) positive electrode material prepared above is used to prepare a sodium ion battery positive electrode sheet, and finally a sodium ion battery is prepared.

[0067] Comparative Example 1:

[0068] (1) Dissolve 13.246 kg of manganese sulfate crystals in 40 L of deionized water, add 400 ml of 5% dilute sulfuric acid, stir for 5 min, then add 11.010 kg of ferrous sulfate crystals, stir and dissolve to prepare a 2.475 mol / L manganese-iron mixed salt solution; dissolve 0.12 kg of magnesium sulfate crystals separately in 5 L of deionized water to prepare a 0.20 mol / L magnesium sulfate solution;

[0069] (2) Preparation of the mixture: Use 85% phosphoric acid solution, dilute to prepare 10% phosphoric acid solution, and then add 32% liquid alkali solution in small amounts several times to adjust the pH of the mixture to 10.0-11.0. The preparation is then complete.

[0070] (3) At room temperature, add 20L of pure water to a 100L reactor, turn on nitrogen protection, then add 40L of manganese-iron mixed salt solution and 5L of magnesium sulfate solution, turn on the reactor to stir, quickly add a certain amount of ammonium bicarbonate solution, adjust the pH to 6.0-9.0 as measured during the process, and after reacting for 30 minutes, discharge the material and wash it with 200L of pure water to obtain material A;

[0071] (4) In a 100L reactor, add 60L of pure water, turn on nitrogen and stir, then add material A, and heat to 70℃ at the same time. After the material dissolves, add the mixture prepared in step (2), adjust the measured pH to 10.30, stop adding after the pH is in place, and then perform dynamic aging for 8 hours to obtain sodium manganese phosphate pyrophosphate precursor slurry.

[0072] (5) The sodium manganese phosphate precursor slurry obtained in step (3) is washed and dried to obtain magnesium-doped sodium manganese phosphate precursor.

[0073] (6) The sodium manganese iron phosphate pyrophosphate precursor obtained in step (4) is mixed with 1.80 kg sodium carbonate, 2.20 L 85% phosphoric acid solution and 0.70 kg glucose and then milled. After that, multi-stage sintering is carried out. The first stage is 350 °C, heating rate is 3 °C / min, and constant temperature is 90 min; the second stage is 600 °C, heating rate is 3 °C / min, and constant temperature is 240 min; the third stage is 725 °C, heating rate is 3 °C / min, and constant temperature is 480 min. Then the temperature is lowered. After the cooling sintering is completed, sodium manganese iron phosphate pyrophosphate sodium-ion battery cathode material is obtained.

[0074] The sodium pyrophosphate (SMP) positive electrode material prepared above is used to prepare a sodium ion battery positive electrode sheet, and finally a sodium ion battery is prepared.

[0075] The sodium manganese iron phosphate pyrophosphate cathode materials prepared in Examples 1-4 and Comparative Example 1 were used to prepare coin cells, and their electrochemical performance was tested. The test results are shown in Table 1.

[0076]

[0077] Table 1 Electrochemical performance test results

[0078] As can be seen from the results in Table 1, compared with the comparative examples, the coin cells prepared in Examples 1-4 have higher capacity and cycle retention, which is mainly due to the specific structure of the precursor prepared in this invention.

[0079] Working principle: Step 1: Generate hydroxide or carbonate compound; Step 2: React with phosphorus source to generate precursor, and then perform pyrophosphate; Through two steps, doped sodium manganese phosphate pyrophosphate precursor is synthesized to produce a specific product structure "ship-shaped".

[0080] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium-ion battery precursor, characterized in that: The sodium ion battery precursor is a pyrophosphate sodium manganese iron phosphate precursor, and a molecular formula of the pyrophosphate sodium manganese iron phosphate precursor is NaMn x Fe 1-x-y Mg y PO4, wherein 0.40≤x≤0.80, 0.001 y <0.

02.

2. A method for preparing a sodium-ion battery precursor, characterized in that, The method comprises the following steps: S1, dissolving a soluble divalent manganese salt in pure water, then adding an antioxidant, and then adding a soluble divalent iron salt to prepare a manganese-iron mixed salt solution; A doping solution is prepared, and the doping solution is a magnesium sulfate solution; S2, adding the manganese-iron mixed salt solution and the magnesium sulfate solution into a reaction kettle, then adding a sodium source, adjusting the measured pH to a target value, and then performing reaction, and then washing the material after the reaction is completed; S3, diluting and dissolving the washed material in step S2 with pure water, then adding the material into the reaction kettle and heating to a target temperature, then adding a phosphorus source, and then performing aging to obtain a doped pyrophosphoric acid manganese iron sodium precursor slurry; S4, washing and drying the pyrophosphoric acid manganese iron sodium precursor slurry obtained in step S3 to obtain a doped pyrophosphoric acid manganese iron sodium precursor material.

3. The method of claim 2, wherein: In the step S1, the soluble divalent manganese salt is one or more of manganese sulfate, manganese acetate, manganese oxalate and manganese chloride; the soluble divalent iron salt is one or more of ferrous chloride, ferrous nitrate and ferrous sulfate; the antioxidant is one or more of ascorbic acid, dilute sulfuric acid and citric acid; the molar concentration of the manganese-iron salt in the manganese-iron mixed salt solution is 1.5-3.0 mol / L; the molar ratio of manganese ions to iron ions is x:1-x-y, wherein 0.40≤x≤0.80 and 0.001 4. The method of claim 2, wherein: In the step S2, the sodium source is one or more of sodium hydroxide and sodium carbonate; the measured pH is controlled in the range of 11.0-13.

0.

5. The method of claim 2, wherein: In the step S3, the target temperature is 70-100℃; the phosphorus source is one or more of 85% phosphoric acid and ammonium dihydrogen phosphate, the molar amount of the added phosphorus source is 2-3:1 of the total molar amount of manganese and iron; and the aging time is 6-16h.

6. A method for preparing a sodium-ion battery cathode material, characterized in that, The method comprises the following steps: mixing a dry doped pyrophosphoric acid manganese iron sodium precursor material with a sodium source, a phosphorus source and a carbon source, sand grinding, and then adopting multi-stage temperature sintering in a protective atmosphere to obtain a pyrophosphoric acid manganese iron sodium sodium ion battery positive electrode material.

7. The method of claim 6, wherein the method further comprises: The sodium source is one or more of sodium carbonate and sodium acetate, the total mass of the added sodium source is 10-15% of the total mass of the doped pyrophosphoric acid manganese iron sodium precursor, the phosphorus source is one or more of phosphoric acid and sodium dihydrogen phosphate, the total mass of the added phosphorus source is 19-24% of the total mass of the doped pyrophosphoric acid manganese iron sodium precursor, the carbon source is one or more of glucose and sucrose, the total mass of the added carbon source is 3-6% of the total mass of the pyrophosphoric acid manganese iron sodium precursor, and the sintering temperature is controlled in a multi-stage mode, the first stage is 300-400℃, the constant temperature time is 1-2h, the second stage is 550-650℃, the constant temperature time is 3-5h, the third stage is 700-750℃, and the constant temperature time is 6-10h, and the heating rate is 3-5℃ / min.

8. A sodium-ion battery comprising the sodium-ion battery cathode material of claim 6, characterized in that: The pyrophosphoric acid manganese iron sodium sodium ion battery positive electrode material is used to prepare a sodium ion battery.

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