Sodium-rich ferric sodium pyrophosphate positive electrode precursor as well as preparation method and application thereof

Abstract

The invention provides a sodium-rich ferric sodium pyrophosphate positive electrode precursor and a preparation method and application thereof.The preparation method comprises the following steps that a ferrite solution, a phosphoric acid source solution, a pyrophosphoric acid source solution, an alkaline solution and a sodium persulfate solution are injected into a base solution in a parallel flow mode for a co-precipitation reaction, the sodium-rich ferric sodium pyrophosphate positive electrode precursor is obtained; wherein the base solution is pure water. The method disclosed by the invention is simple to operate, the sodium-rich ferric sodium pyrophosphate positive electrode precursor with high sodium content, uniform element distribution and uniform phase can be prepared, the sodium-rich ferric sodium pyrophosphate positive electrode precursor is low in gas production rate in the subsequent sintering process, and the sodium-rich ferric sodium pyrophosphate positive electrode material with high compaction density can be prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries and relates to a sodium-rich sodium iron pyrophosphate positive electrode precursor and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries (SIBs), due to their similar electrochemical properties and abundant storage capacity to lithium-ion batteries, are considered one of the most promising power sources for large-scale energy storage systems. The main cathode materials for SIBs include layered oxides, polyanions, and Prussian blue. Polyanion-based cathode materials are considered the most promising due to their low cost, high safety, and long cycle life.

[0003] Sodium iron pyrophosphate (SFP) is the most typical polyanion sodium ion battery cathode material and has been widely researched and industrialized in the past two years. However, its compaction density is low, and it is not easy for the powder particles to form dense accumulation. At present, the compaction density of most prepared SFP cathode material powders is difficult to exceed 2.2g / cm 3 , resulting in low energy density of the final battery, hindering the application of this material. In order to improve the energy density of the battery, it is almost an industry consensus to develop a high-density sodium iron pyrophosphate positive electrode material.

[0004] CN120172382A discloses a method for preparing a sodium iron pyrophosphate positive electrode material, comprising the following steps: (1) weighing a sodium source, an iron source, a phosphorus source, and a carbon source, rapidly mixing them uniformly, and then performing low-temperature pre-sintering to obtain a precursor; wherein the low-temperature pre-sintering includes two stages, the first stage is heating to 60-150°C and maintaining for 1-3 hours, and the second stage is heating to 200-350°C and maintaining for 1-8 hours; (2) adding a carbon source to the precursor to prepare a slurry, and then sand-milling and centrifugal spray drying the slurry and then performing high-temperature sintering to obtain the sodium iron pyrophosphate positive electrode material.

[0005] CN119503753A discloses a sodium iron phosphate pyrophosphate cathode material and a preparation method thereof. The preparation method comprises mixing phosphoric acid, an iron source, a sodium source and a carbon source in water, freeze-drying to obtain a precursor and carbonizing the precursor to obtain a high-purity sodium iron phosphate pyrophosphate cathode material.

[0006] In the process of preparing sodium iron phosphate pyrophosphate positive electrode material by the above scheme, the element distribution uniformity in the prepared sodium iron phosphate pyrophosphate positive electrode precursor is poor, the phase is uneven, and a lot of gas is generated during the sintering process, which affects the performance of the prepared sodium iron phosphate pyrophosphate positive electrode material. Summary of the Invention

[0007] The object of the present invention is to provide a sodium-rich sodium ferric phosphate pyrophosphate positive electrode precursor and its preparation method and application. The method of the present invention is simple to operate and can produce a sodium-rich sodium ferric phosphate pyrophosphate positive electrode precursor with high sodium content, uniform element distribution and uniform physical phase. The sodium-rich sodium ferric phosphate pyrophosphate positive electrode precursor produces little gas in the subsequent sintering process, and can produce a sodium-rich sodium ferric phosphate pyrophosphate positive electrode material with a high compaction density.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a sodium-rich sodium iron pyrophosphate positive electrode precursor, the preparation method comprising the following steps:

[0010] The ferrous salt solution, the phosphoric acid source solution, the pyrophosphate source solution, the alkaline solution and the sodium persulfate (Na2S2O8) solution are injected into the bottom liquid in parallel to perform a co-precipitation reaction to obtain the sodium-rich sodium ferric pyrophosphate positive electrode precursor;

[0011] Wherein, the base liquid is pure water.

[0012] In the preparation process of the sodium-rich sodium ferric pyrophosphate positive electrode precursor of the present invention, pure water is used as the base liquid to avoid the introduction of other impurity anions and improve the purity of the product. By simultaneously injecting ferrous salt, phosphate source, pyrophosphate source, alkali solution and sodium persulfate into the base liquid, a dynamic balance of reactant concentrations is achieved, avoiding local supersaturation or component segregation caused by traditional step-by-step addition, and the product composition is more uniform. Sodium persulfate directly participates in the coprecipitation process and immediately oxidizes Fe2 + Fe3 + , avoiding the traditional method of first preparing Fe3 + The complex step of precursor remixing reduces the risk of phase separation. During the co-current co-precipitation reaction, adding base to maintain a stable pH and inhibit the formation of impurities.

[0013] Preferably, the ferrous salt solution comprises any one of ferrous sulfate solution, ferrous chloride solution or ferrous nitrate solution, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ferrous sulfate solution and ferrous nitrate solution, a combination of ferrous sulfate solution and ferrous chloride solution, or a combination of ferrous chloride solution and ferrous nitrate solution.

[0014] Preferably, the molar concentration of the ferrous salt solution is 0.5 mol / L to 2 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0015] Preferably, the phosphoric acid source solution comprises a sodium phosphate solution.

[0016] Preferably, the molar concentration of the phosphoric acid source solution is 0.1 mol / L to 1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0017] Preferably, the pyrophosphate source solution comprises a sodium pyrophosphate solution.

[0018] Preferably, the molar concentration of the pyrophosphate source solution is 0.1 mol / L to 1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0019] Preferably, the alkaline solution comprises sodium hydroxide solution.

[0020] Preferably, the molar concentration of the alkaline solution is 5 mol / L to 15 mol / L, for example, 5 mol / L, 8 mol / L, 10 mol / L, 12 mol / L or 15 mol / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0021] Preferably, the molar concentration of the sodium persulfate solution is 0.5 mol / L to 2 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2.0 mol / L, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0022] The sodium persulfate described in the present invention is an aqueous solution of Na2S2O8. The molar amount in the reaction system is calculated based on the molar amount of Na2S2O8.

[0023] Preferably, in the coprecipitation reaction system, the molar ratio of ferrous salt to phosphate source is 1:(0.5-0.8), for example: 1:0.5, 1:0.55, 1:0.6, 1:0.7 or 1:0.8, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, in the coprecipitation reaction system, the molar ratio of ferrous salt to pyrophosphate source is 1:(0.2-0.5), for example: 1:0.2, 1:0.25, 1:0.3, 1:0.4 or 1:0.5, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, in the coprecipitation reaction system, the molar ratio of ferrous salt to Na2S2O8 is 1:(0.05~0.1), for example: 1:0.05, 1:0.06, 1:0.08, 1:0.09 or 1:0.1, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the pH of the coprecipitation reaction is 6 to 8, for example, 6, 6.5, 7, 7.5 or 8, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0027] The pH of the coprecipitation reaction described in the present invention covers weak acid, neutral and weak alkalinity, among which the iron-phosphorus ratio of the precursor obtained under weak acid is also within the technical range, but slightly higher than the optimal value, the iron-phosphorus ratio of the precursor obtained under neutral conditions is close to the optimal value, and the iron-phosphorus ratio of the precursor obtained under weak alkalinity is also within the technical range, but slightly lower than the optimal value.

[0028] Preferably, the temperature of the coprecipitation reaction is 30°C to 90°C, for example, 30°C, 50°C, 60°C, 80°C or 90°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the coprecipitation reaction time is 30 h to 50 h, for example, 30 h, 35 h, 40 h, 45 h or 50 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the atmosphere of the coprecipitation reaction includes nitrogen and / or argon.

[0031] In a second aspect, the present invention provides a sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor, which is prepared by the preparation method described in the first aspect.

[0032] The sodium-rich sodium ferric phosphate pyrophosphate cathode precursor prepared by the method of the present invention has uniform element distribution, a uniform phase, and an amorphous phase. The sodium ferric phosphate pyrophosphate formed after sintering is relatively pure. The sodium-rich sodium ferric phosphate pyrophosphate cathode precursor has a suitable iron-to-phosphorus ratio and a high sodium content.

[0033] In a third aspect, the present invention provides a sodium-rich sodium iron phosphate pyrophosphate positive electrode material, which is prepared by mixing the sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor as described in the second aspect with a sodium source and then sintering.

[0034] The sodium-rich sodium phosphate iron pyrophosphate positive electrode precursor of the present invention is mainly composed of sodium, iron, phosphate, and pyrophosphate, does not contain carbonate, has low water content, and produces little gas during sintering. The obtained positive electrode material has a high compaction density. The sodium content in the positive electrode material precursor is high, and only a small amount of sodium carbonate needs to be added during sintering.

[0035] Preferably, the molar ratio of the sodium-rich sodium iron pyrophosphate positive electrode precursor to the sodium source is 1:(0.2-0.5), for example: 1:0.2, 1:0.3, 1:0.4 or 1:0.5, etc., not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0036] Preferably, the sodium source comprises sodium carbonate.

[0037] Preferably, the mixing comprises sequentially performing mechanical mixing, sand milling and spray granulation.

[0038] Preferably, the sintering temperature is 550°C to 750°C, for example, 550°C, 600°C, 650°C, 700°C or 750°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the sintering time is 6 hours to 12 hours, for example, 6 hours, 8 hours, 9 hours, 10 hours or 12 hours, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] In a fourth aspect, the present invention provides a sodium ion battery, which comprises the sodium-rich sodium iron pyrophosphate positive electrode material as described in the third aspect.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The method of the present invention is simple to operate and can produce a sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor with high sodium content, uniform element distribution and uniform physical phase. The sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor produces little gas during the subsequent sintering process, and can produce a sodium-rich sodium iron phosphate pyrophosphate positive electrode material with a high compaction density.

[0043] (2) The sodium-rich sodium ferric pyrophosphate cathode precursor prepared by the method of the present invention can be used to make the cathode of sodium ion battery with a compact density of up to 2.46 g / cm 3The average discharge voltage can reach above 3.1V, the discharge capacity can reach above 106.9mAh / g, and the volume energy density can reach above 807Wh / L. The sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor material prepared by the method of the present invention has uniform element distribution and low gas production during sintering. The final positive electrode material has high compaction density, high energy density, stable discharge voltage, and electrochemical performance significantly better than the sodium iron phosphate pyrophosphate positive electrode material prepared by conventional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the XRD diagram of the sodium-rich sodium iron pyrophosphate positive electrode precursor provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0046] Example 1

[0047] This embodiment provides a sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor, which is prepared by the following method:

[0048] 1.0 mol / L ferrous sulfate solution, 0.3 mol / L sodium phosphate solution, 0.2 mol / L sodium pyrophosphate solution, 1 mol / L sodium persulfate solution, and 10 mol / L sodium hydroxide solution were added to the pure water bottom liquid in parallel for co-precipitation reaction. In the co-precipitation reaction system, the molar ratio of ferrous sulfate, sodium phosphate, sodium pyrophosphate and sodium persulfate was 1:0.58:0.4:0.08. By controlling the flow rate of the sodium hydroxide solution, the pH value of the reaction system was controlled to 7.2. At the same time, under a nitrogen protective atmosphere, the reaction was kept at 60°C for 40 hours, and the precipitated product was washed and dried to obtain the sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor.

[0049] The XRD pattern of the sodium-rich sodium iron pyrophosphate positive electrode precursor is as follows: Figure 1 As shown by Figure 1 It can be seen that the precursor prepared in this example has an amorphous structure.

[0050] The elemental composition of the sodium-rich sodium iron pyrophosphate positive electrode precursor is as follows:

[0051] Na: 13.05%, Fe: 27.08%, P: 19.99%, O: 39.32% (the rest are impurities), and the molar ratio of sodium, iron and phosphorus in the sodium-rich sodium iron pyrophosphate positive electrode precursor is approximately 3.5:3:4.

[0052] Example 2

[0053] This embodiment provides a sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor, which is prepared by the following method:

[0054] 1.2 mol / L ferrous sulfate solution, 0.5 mol / L sodium phosphate solution, 0.3 mol / L sodium pyrophosphate solution, 2 mol / L sodium persulfate solution, and 10 mol / L sodium hydroxide solution were added to the pure water bottom liquid in parallel for co-precipitation reaction. In the co-precipitation reaction system, the molar ratio of ferrous sulfate, sodium phosphate, sodium pyrophosphate and Na2S2O8 was 1:0.62:0.38:0.06. By controlling the flow rate of the sodium hydroxide solution, the pH value of the reaction system was controlled to 8. At the same time, under a nitrogen protective atmosphere, the reaction was kept at 50°C for 45 hours, and the precipitated product was washed and dried to obtain the sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor.

[0055] Example 3

[0056] This embodiment provides a sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor, which is prepared by the following method:

[0057] 2mol / L ferrous sulfate solution, 1mol / L sodium phosphate solution, 1mol / L sodium pyrophosphate solution, 0.8mol / L sodium persulfate solution, and 15mol / L sodium hydroxide solution were added to the pure water bottom liquid in parallel for co-precipitation reaction. In the co-precipitation reaction system, the molar ratio of ferrous sulfate, sodium phosphate, sodium pyrophosphate and was 1:0.8:0.5:0.05. By controlling the flow rate of the sodium hydroxide solution, the pH value of the reaction system was controlled to 6. At the same time, under a nitrogen protective atmosphere, the reaction was kept at 60°C for 40 hours, and the precipitated product was washed and dried to obtain the sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor.

[0058] Example 4

[0059] This embodiment provides a sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor, which is prepared by the following method:

[0060] 0.5 mol / L ferrous sulfate solution, 0.1 mol / L sodium phosphate solution, 0.1 mol / L sodium pyrophosphate solution, 0.5 mol / L sodium persulfate solution, and 5 mol / L sodium hydroxide solution were added to the pure water bottom liquid in parallel for co-precipitation reaction. In the co-precipitation reaction system, the molar ratio of ferrous sulfate, sodium phosphate, sodium pyrophosphate and was 1:0.5:0.2:0.1. By controlling the flow rate of the sodium hydroxide solution, the pH value of the reaction system was controlled to 7.5. At the same time, under a nitrogen protective atmosphere, the reaction was kept at 60°C for 40 hours, and the precipitated product was washed and dried to obtain the sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor.

[0061] Example 5

[0062] The only difference between this embodiment and embodiment 1 is that the molar ratio of ferrous sulfate to Na2S2O8 is 1:0.02, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0063] Example 6

[0064] The only difference between this embodiment and embodiment 1 is that the molar ratio of ferrous sulfate to Na2S2O8 is 1:0.15, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0065] Example 7

[0066] The only difference between this embodiment and embodiment 1 is that the pH of the coprecipitation reaction is 5, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0067] Example 8

[0068] The only difference between this embodiment and embodiment 1 is that the pH of the coprecipitation reaction is 9, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 1 is that no sodium persulfate solution is added, and other conditions and parameters are exactly the same as those in Example 1.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 1 is that the sodium persulfate solution is replaced with hydrogen peroxide, and the other conditions and parameters are exactly the same as those in Example 1.

[0073] Comparative Example 3

[0074] The only difference between this comparative example and Example 1 is that the base liquid is a 0.01 mol / L sodium hydroxide solution, and the other conditions and parameters are exactly the same as those in Example 1.

[0075] Performance testing:

[0076] The sodium-rich sodium ferric phosphate pyrophosphate cathode precursor prepared in the embodiment and the comparative example was mechanically mixed with sodium carbonate in a molar ratio of 1:0.3, and then wet mixed sand milled for 4 hours, and then spray granulated; finally, the granulated material was sintered at 650° C. for 10 hours under a nitrogen atmosphere to obtain a sodium-rich sodium ferric phosphate pyrophosphate cathode material. The sodium-rich sodium ferric phosphate pyrophosphate cathode was used as the main positive electrode material, and a metal sodium sheet was used as the negative electrode. The batteries were assembled into CR2032 button batteries, and then electrochemical performance tests were carried out at a voltage range of 2.0 to 3.6 V and a discharge current density of 10 mA / g. The average discharge voltage and discharge capacity in the fifth cycle were taken. The test results are shown in Table 1:

[0077] Table 1

[0078]

[0079] As can be seen from Table 1, from Examples 1-8, the sodium-rich sodium ferric pyrophosphate cathode precursor prepared by the method of the present invention can achieve a positive electrode density of a sodium ion battery of up to 2.46 g / cm 3 The average discharge voltage can reach above 3.1V, the discharge capacity can reach above 106.9mAh / g, and the volume energy density can reach above 807Wh / L. The sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor material prepared by the method of the present invention has a high compaction density, high energy density, and stable discharge voltage after sintering, and its electrochemical performance is significantly better than that of the sodium iron phosphate pyrophosphate positive electrode material prepared by conventional methods.

[0080] By comparison of Example 1 and Example 5-6, it can be seen that in the preparation process of the sodium-rich sodium phosphate ferric pyrophosphate positive electrode precursor of the present invention, the amount of sodium persulfate added will affect its performance, and the molar ratio of ferrous sulfate and Na2S2O8 is controlled at 1: (0.05-0.1), and the effect of obtaining the sodium-rich sodium phosphate ferric pyrophosphate positive electrode precursor is better. If the amount of sodium persulfate added is too low, the divalent iron is not fully oxidized, resulting in more impurities in the final positive electrode material and a low capacity. If the amount of sodium persulfate added is too high, the divalent iron is excessively oxidized, which will also result in more impurities in the final positive electrode material and a low capacity.

[0081] By comparison of Example 1 and Example 7-8, it can be seen that in the preparation process of the sodium-rich phosphate sodium iron pyrophosphate positive electrode precursor of the present invention, the pH of the coprecipitation reaction will affect its performance. The pH of the coprecipitation reaction is controlled at 6 to 8, and the effect of obtaining the sodium-rich phosphate sodium iron pyrophosphate positive electrode precursor is better. If the pH of the coprecipitation reaction is too low, the iron-phosphorus ratio of the obtained precursor is too high, and the final sintered positive electrode material has a high content of sodium iron phosphate phase, and the reversible capacity of the positive electrode material is significantly reduced. If the pH of the coprecipitation reaction is too high, the iron-phosphorus ratio of the obtained precursor is too low, and the final sintered positive electrode material has a high content of sodium iron pyrophosphate phase, and the reversible capacity of the positive electrode material is also reduced.

[0082] From the comparison between Example 1 and Comparative Examples 1-3, it can be seen that in the preparation process of the sodium-rich phosphate sodium iron pyrophosphate positive electrode precursor of the present invention, pure water is used as the base liquid to avoid the introduction of other impurity anions and improve the purity of the product. By simultaneously injecting ferrous salt, phosphate source, pyrophosphate source, alkali solution and sodium persulfate into the base liquid, a dynamic balance of reactant concentrations is achieved, avoiding local supersaturation or component segregation caused by traditional step-by-step feeding, and the product composition is more uniform. Sodium persulfate directly participates in the coprecipitation process and immediately oxidizes Fe2 + Fe3 + Compared with conventional oxidants, it has excellent oxidation effect and can avoid the traditional method of preparing Fe3 + Complex steps of precursor remixing to reduce the risk of phase separation.

[0083] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a sodium-rich sodium iron pyrophosphate positive electrode precursor, characterized in that: The preparation method comprises the following steps: The ferrous salt solution, the phosphoric acid source solution, the pyrophosphate source solution, the alkaline solution and the sodium persulfate solution are injected into the bottom liquid in parallel to perform a co-precipitation reaction, thereby obtaining the sodium-rich sodium ferric pyrophosphate positive electrode precursor; Wherein, the base liquid is pure water.

2. The preparation method according to claim 1, wherein The ferrous salt solution includes any one of ferrous sulfate solution, ferrous chloride solution or ferrous nitrate solution, or a combination of at least two thereof; Preferably, the molar concentration of the ferrous salt solution is 0.5 mol / L to 2 mol / L; Preferably, the phosphoric acid source solution comprises a sodium phosphate solution; Preferably, the molar concentration of the phosphoric acid source solution is 0.1 mol / L to 1 mol / L; Preferably, the pyrophosphate source solution comprises a sodium pyrophosphate solution; Preferably, the molar concentration of the pyrophosphate source solution is 0.1 mol / L to 1 mol / L; Preferably, the alkaline solution comprises sodium hydroxide solution; Preferably, the molar concentration of the alkaline solution is 5 mol / L to 15 mol / L; Preferably, the molar concentration of the sodium persulfate solution is 0.5 mol / L to 2 mol / L.

3. The preparation method according to claim 1 or 2, wherein In the coprecipitation reaction system, the molar ratio of the ferrous salt to the phosphate source is 1:(0.5-0.8).

4. The preparation method according to any one of claims 1 to 3, wherein In the coprecipitation reaction system, the molar ratio of the ferrous salt to the pyrophosphate source is 1:(0.2-0.5).

5. The preparation method according to any one of claims 1 to 4, characterized in that In the coprecipitation reaction system, the molar ratio of ferrous salt to sodium persulfate is 1:(0.05-0.1).

6. The preparation method according to any one of claims 1 to 5, characterized in that The pH of the coprecipitation reaction is 6 to 8; Preferably, the temperature of the coprecipitation reaction is 30°C to 90°C; Preferably, the coprecipitation reaction time is 30h to 50h; Preferably, the atmosphere of the coprecipitation reaction includes nitrogen and / or argon.

7. A sodium-rich sodium iron pyrophosphate cathode precursor, characterized in that: The sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor is prepared by the preparation method according to any one of claims 1 to 6.

8. A sodium-rich sodium iron pyrophosphate positive electrode material, characterized in that The sodium-rich sodium iron phosphate pyrophosphate positive electrode material is prepared by mixing the sodium-rich sodium iron phosphate pyrophosphate positive electrode precursor according to claim 7 with a sodium source and then sintering.

9. The sodium-rich sodium iron pyrophosphate positive electrode material according to claim 8, characterized in that The molar ratio of the sodium-rich sodium iron pyrophosphate positive electrode precursor to the sodium source is 1:(0.2-0.5); Preferably, the sodium source comprises sodium carbonate; Preferably, the mixing comprises sequentially performing mechanical mixing, sand milling and spray granulation; Preferably, the sintering temperature is 550°C to 750°C; Preferably, the sintering time is 6 hours to 12 hours.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the sodium-rich sodium iron pyrophosphate positive electrode material as claimed in claim 8 or 9.

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