Preparation method of pure-phase ferric sodium pyrophosphate with high specific surface area and low temperature sensitivity

Abstract

The invention discloses a preparation method of high-specific-surface low-temperature-sensitivity pure-phase ferric sodium pyrophosphate, which comprises the following steps: adding an iron source solution added with an antioxidant into a phosphorus source solution with adjusted pH at a specific dripping speed, heating and ultrasonically stirring to synthesize a sea urchin-like high-specific-surface precursor induction material mixed solution; adding a sodium source into the precursor induction material mixed solution, heating and stirring to obtain a precursor mixed solution, and performing closed spray drying under inert carrier gas to obtain a precursor material; the precursor material has the properties of being porous, high in specific surface area, stable in structure during high-temperature calcination and the like, the tap density of the material and the sodium ion conduction efficiency are improved through the porous high-specific-surface structure, and the phenomenon that due to the stable material structure, due to uneven temperatures of different parts in the sintering process, a phase is changed, and an impure phase is generated is avoided. And finally, calcining the precursor material at high temperature to obtain the pure-phase ferric sodium pyrophosphate material with high specific surface area and low temperature sensitivity.

Description

Technical Field

[0001] The present invention relates to a preparation method of sodium iron pyrophosphate phosphate with high specific surface area and low temperature sensitivity and pure phase. Background Art

[0002] With the continuous expansion and demand of the new energy-related market, large-scale energy storage technology has become an urgent problem for us to solve. Sodium-ion batteries have attracted more and more attention due to their rich sodium reserves, low cost, long cycle life, and the "rocking chair" working principle similar to that of lithium-ion batteries, and have become the main force for realizing large-scale energy storage.

[0003] The cathode material directly affects the battery performance. Currently, the cathode materials applied to sodium-ion batteries mainly include several categories: layered metal oxides, Prussian blue-based materials, and polyanion-based materials. Among them, the NASICON-type iron-based mixed phosphate material sodium iron pyrophosphate phosphate Na4Fe3(PO4)2P2O7 (NFPP) is considered one of the most promising cathode materials because of its high theoretical specific capacity and moderate voltage. However, during the large-scale synthesis of this material, it has a high temperature sensitivity, and the generation of impurity phases is caused by the different temperatures in different calcination parts. The capacities and conductivities of these impurity phases are lower than those of NFPP, thus affecting the battery performance. The structure and tap density of the material itself also affect the performance of the entire battery.

[0004] Therefore, developing a preparation method of pure-phase NFPP cathode material with high specific surface area and low temperature sensitivity is of great significance for the development of sodium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a preparation method of sodium iron pyrophosphate phosphate with high specific surface area and low temperature sensitivity and pure phase, which ensures the purity of the precursor-induced material, increases the specific surface area of the precursor-induced material, reduces the steps of precursor drying, reduces the production energy consumption, and at the same time, the sodium source added in the liquid phase is more uniformly mixed with the precursor-induced material. During the drying process, the sodium source is embedded in the folds of the sea urchin-like porous precursor-induced material, reducing the atomic diffusion path during sintering and lowering the sintering temperature sensitivity.

[0006] The technical solution to achieve the above purpose is: a preparation method of sodium iron pyrophosphate phosphate with high specific surface area and low temperature sensitivity and pure phase, comprising the following steps:

[0007] S1, preparation of sea urchin-like porous precursor-induced material, comprising the following processes:

[0008] S11, dissolving an iron source and an antioxidant in deionized water to obtain an iron salt solution;

[0009] S12. Dissolve the phosphorus source in deionized water to obtain a phosphate solution, and adjust the pH of the phosphate solution.

[0010] S13. Slowly add the iron salt solution drop by drop into the phosphate solution. During the dropping process, assist with heating, stirring, and ultrasonic treatment. After the titration is completed, continue to heat and stir the mixture to obtain a mixture of sea urchin-like porous precursor inducing materials.

[0011] S2. Add the sodium source to the mixture of precursor inducing materials obtained in step S1, heat and stir evenly to obtain a precursor mixture with pores, stable structure, and low temperature sensitivity.

[0012] S3. Spray-dry the precursor mixture obtained in step S2 to obtain a precursor material. The spray-drying is closed-loop spray-drying, and the carrier gas is an inert gas, nitrogen or argon.

[0013] S4. Perform high-temperature sintering on the precursor material obtained in step S3 under an inert atmosphere, and cool to obtain a pure-phase cathode sodium iron pyrophosphate material with high specific surface area and low temperature sensitivity.

[0014] In the above method for preparing a pure-phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity, wherein the iron source is at least one of ferrous acetate, ferrous chloride, ferrous sulfate, and ferrous phosphate;

[0015] The phosphorus source is at least one of phosphoric acid, ammonium phosphate, monoammonium phosphate, diammonium phosphate, and dibasic ammonium phosphate;

[0016] The sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium citrate, sodium oxalate, and sodium acetate;

[0017] The acid for regulating the pH value of the phosphate solution is one or more of acetic acid, citric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid;

[0018] The antioxidant is hydrogen peroxide or ascorbic acid;

[0019] The ratio of the iron source to the phosphorus source is from 1:1.5 to 1:5.

[0020] In the above method for preparing a pure-phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity, during the titration process in step S13, the heating and stirring temperature is 70 - 90 °C, the heating and stirring speed is 800 - 1500 r / min, and the ultrasonic power is 150 - 200 W.

[0021] In the above method for preparing a pure-phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity, in step S13, after the titration is completed, the heating and stirring temperature is 50 - 70 °C, and the heating and stirring speed is 300 - 800 r / min.

[0022] In the above method for preparing a high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate, in step S2, the heating and stirring temperature is 50 - 70 °C, the heating and stirring time is 2 - 10 h, and the heating and stirring speed is 300 - 800 r / min.

[0023] In the above method for preparing a high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate, in step S3, the spray drying temperature is 150 - 220 °C.

[0024] In the above method for preparing a high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate, in step S4, the sintering temperature is 500 - 750 °C, and the sintering time is 5 - 15 h.

[0025] The beneficial effects of the method for preparing a high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate of the present invention are as follows:

[0026] (1) During the preparation of the sea urchin-like porous precursor-induced material, an antioxidant is added, closed-loop spray drying is used during the spray drying process, and an inert gas protection is used during sintering. During the whole process, the Fe ions are in a reduced state, ensuring the purity of the material.

[0027] (2) During the preparation of the sea urchin-like porous precursor-induced material, the titration process is assisted by ultrasound, and both the heating temperature and the stirring rate are at relatively high and fast temperatures and rates, promoting the nucleation reaction and reducing the nucleation growth rate, thereby increasing the specific surface area of the precursor-induced material.

[0028] (3) The conventional preparation method is to dry the iron phosphate precursor (i.e., the sea urchin-like porous precursor-induced material in the present invention), then add a sodium source and a carbon source and mix them uniformly by solid-phase dry mixing, and then sinter to obtain the sodium iron pyrophosphate phosphate material. The present invention reduces the step of precursor drying, reduces the production energy consumption, and at the same time, the sodium source added in the liquid phase is more uniformly mixed with the precursor-induced material. During the drying process, the sodium source is embedded in the folds of the sea urchin-like porous precursor-induced material (see Figure 2 ), reducing the atomic diffusion path during sintering and lowering the sintering temperature sensitivity (the sintering temperature sensitivity refers to the response degree of the material to temperature changes during the sintering process, especially the characteristics of how the material properties change with the slight change of the sintering temperature. In the preparation process of sodium iron pyrophosphate phosphate material, it specifically shows that at the same sintering temperature, different positions in the same crucible or different crucibles in the furnace show different material characteristics due to the slight temperature difference). Description of the Drawings

[0029] Figure 1 SEM image of the sea urchin-like porous precursor-induced material;

[0030] Figure 2 Schematic diagram of the precursor material after sodium insertion;

[0031] Figure 3 Schematic diagram of the furnace chamber of the box furnace for sintering materials;

[0032] Figure 4 XRD test result diagram of the samples in the crucibles at different parts of the furnace in Example 1;

[0033] Figure 5 XRD test result diagram of the samples in the crucibles at different parts of the furnace in Comparative Example 1;

[0034] Figure 6 XRD test result diagram of the samples in the crucibles at different parts of the furnace in Comparative Example 2. Detailed implementation manners

[0035] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the following will specifically describe its implementation manners with reference to the accompanying drawings:

[0036] Example 1

[0037] Please refer to Figure 1 、 Figure 2 、 Figure 3 and Figure 4 , a preparation method of high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate. Respectively take ferric acetate, ammonium dihydrogen phosphate, and sodium acetate as the iron source, phosphorus source, and sodium source. Among them, control the molar ratio of iron element, phosphorus element, and sodium element to be 1:3:3. Hydrogen peroxide is used as an antioxidant. First, prepare a sea urchin-like porous precursor induction material. The precursor material synthesized through this induction material has properties such as high specific surface area, low temperature sensitivity, and stable structure at different calcination temperatures, thus ensuring the preparation of high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate material. The specific implementation steps are as follows:

[0038] S1. Preparation of the sea urchin-like porous precursor induction material, which specifically includes the following processes:

[0039] S11. Add ferric acetate and hydrogen peroxide into ionized water at the same time to prepare a ferric acetate solution with a concentration of 1 mol / L;

[0040] S12. Prepare an ammonium dihydrogen phosphate solution with a concentration of 3 mol / L, add acetic acid to this solution, and adjust the pH of the solution to 3;

[0041] S13. Slowly add the iron acetate solution drop by drop into the ammonium dihydrogen phosphate solution with the adjusted pH at a dropping rate of 500 ml / min. During the dropping process, assist with heating, stirring, and ultrasonic treatment. The heating and stirring temperature is 80 °C, the heating and stirring speed is 1000 r / min, and the ultrasonic power is 180 W. After the titration is completed, continue to heat and stir the mixed solution for 3 h, with the heating and stirring temperature of 60 °C and the heating and stirring speed of 500 r / min to obtain a mixed solution of a sea urchin-like porous precursor inducing material;

[0042] S2. Add sodium acetate to the mixed solution of the precursor inducing material obtained in step S1, and continue to heat and stir for 5 h, with the heating and stirring temperature of 60 °C and the heating and stirring speed of 500 r / min. Obtain a precursor mixture with pores, stable structure, and low temperature sensitivity;

[0043] S3. Perform closed-loop spray drying on the precursor mixture obtained in step S2, with the nozzle temperature of 200 °C and the carrier gas of nitrogen to obtain a precursor material;

[0044] S4. Under a nitrogen atmosphere, perform high-temperature sintering on the precursor material prepared in step S3 in a box furnace (see Figure 3 ) for 5 h, with the sintering temperature of 550 °C. After cooling, obtain a pure-phase cathode sodium iron pyrophosphate material with high specific surface area and low temperature sensitivity.

[0045] The sintering temperature sensitivity refers to the degree of response of the material to temperature changes during the sintering process, especially the characteristic of how the material properties change with small changes in the sintering temperature. In the preparation process of sodium iron pyrophosphate material, it is specifically manifested that at the same sintering temperature, different material properties are presented due to small temperature differences at different positions in the same crucible or in different crucibles in the furnace.

[0046] Please refer to Figure 3 , in the furnace chamber 8 of the box furnace, six crucibles (crucibles 1 - 6) and a temperature sensor 7 are placed. The placement positions of crucibles 1 - 6 are shown in Figure 3 .

[0047] Samples in crucibles at different furnace positions after sintering are taken for XRD testing (see Figure 4 ). The test results show that no impurity phases are detected in the products at different sampling positions. The main reason is that during the drying process, the sodium source 11 is embedded in the folds of the sea urchin-like porous precursor inducing material 10 (see Figure 2 ), reducing the atomic diffusion path during sintering and lowering the sintering temperature sensitivity.

[0048] Comparative Example 1

[0049] Iron acetate, ammonium dihydrogen phosphate, and sodium acetate were respectively used as the iron source, phosphorus source, and sodium source, and the molar ratio of iron, phosphorus, and sodium elements was controlled to be 1:3:3. Hydrogen peroxide was used as an antioxidant. The preparation method was as follows:

[0050] All the calculated raw materials were dissolved in deionized water, and then heated and stirred. The heating temperature was 60 °C, the stirring speed was 500 r / min, and the stirring time was 8 h to obtain a precursor mixture. Then, the mixture was subjected to closed-loop spray drying. The nozzle temperature was 200 °C, and the carrier gas was nitrogen to obtain a precursor material. Finally, in a nitrogen atmosphere, the precursor material was subjected to high-temperature sintering in a box furnace for 5 h at a sintering temperature of 550 °C. After cooling, the sodium iron pyrophosphate material of Comparative Example 1 was obtained.

[0051] Please refer to Figure 3 and Figure 5 , and samples in crucibles at different furnace positions after sintering were sampled and tested by XRD. The test results showed that there were impurity phases detected in the products at different sampling positions.

[0052] When the preparation process of Comparative Example 1 was adopted, since the preparation of the precursor-induced material mixture was not carried out, the structure of the generated precursor material was not stable and uniform. Therefore, under the same sintering system, impurity phases appeared in the samples of crucible 3 and crucible 4. After analysis, the impurity phase was mainly iron phosphate, which was caused by the fact that the furnace was heated from all around and the temperature sensor was located at the rear of the furnace, resulting in insufficient heating temperature in the middle area.

[0053] Example 2

[0054] As another example, this Example 2 was proposed based on Example 1. The raw material iron source, phosphorus source, and sodium source, as well as the raw material ratio and antioxidant, were the same as those in Example 1, and the preparation process of the precursor material was also the same. The difference was only that in the last step S4, the sintering temperature of the precursor material was changed, and the sintering temperature was increased to 600 °C, and the sintering time was still 5 h to judge the sensitivity of the material to the sintering temperature.

[0055] Similarly, finally, samples in crucibles at different furnace positions after sintering were sampled and tested by XRD. The test results were the same as those in Example 1 (see Figure 4 ), and the test results showed that there were still no impurity phases detected in the products at different sampling positions.

[0056] Comparative Example 2

[0057] As a comparative example, this Comparative Example 2 was proposed based on Comparative Example 1. The specific raw materials selected and the operation steps were the same as those in Comparative Example 1, except that the final sintering temperature of the precursor was increased to 600 °C, and the sintering time was still 5 h.

[0058] Please refer to Figure 3And Figure 6 Samples in the crucibles at different furnace positions after sintering were sampled and tested by XRD. The test results showed that there were impurity phases detected in the products at different sampling positions.

[0059] Due to the increase in temperature, the samples in the middle crucibles (crucibles 3 and 4) were pure phases, while the samples around showed impurity phases, which were analyzed to be sodium iron phosphate produced by overburning (the diffraction peak at 2θ = 25 degrees in XRD was sodium iron phosphate).

[0060] Example 3

[0061] As another example, this Example 3 is also proposed based on Example 1. The raw material iron source, phosphorus source, and sodium source, as well as the raw material ratio and antioxidant, are the same as in Example 1, and the preparation process of the precursor material is also the same. The difference is only that in the last step S4, the sintering temperature of the precursor material is changed to 650 °C, and the sintering time is still 5 h to judge the temperature sensitivity of the material.

[0062] Finally, samples in the crucibles at different furnace positions after sintering were also sampled and tested by XRD. The test results were the same as those in Example 1 (see Figure 4 ), and the test results showed that there were still no impurity phases detected in the products at different sampling positions.

[0063] Comparative Example 3

[0064] As a comparative example, this Comparative Example 3 is proposed based on Comparative Example 1. The specific raw materials selected and operation steps are the same as in Comparative Example 1, except that the final sintering temperature of the precursor is increased to 650 °C, and the sintering time is still 5 h.

[0065] The products at different furnace positions after sintering were tested by XRD. The test results showed that there were impurity phases detected in the products at different sampling positions.

[0066] Example 4

[0067] The difference between this Example 4 and Example 1 is that the iron source, phosphorus source, and sodium source are replaced with ferric chloride, diammonium hydrogen phosphate, and sodium carbonate respectively. The antioxidant is selected as ascorbic acid, and the acid used to adjust the pH of the phosphoric acid solution is citric acid. The molar ratio of iron element, phosphorus element, and sodium element is still 1:3:3, and other parameters are exactly the same as in Example 1. The specific implementation steps are as follows:

[0068] S1. Preparation of a sea urchin-like porous precursor-induced material, specifically including the following processes:

[0069] S11. Ferric chloride and ascorbic acid were simultaneously added to ionized water to prepare a ferric chloride solution with a concentration of 1 mol / L;

[0070] S12. Prepare a diammonium hydrogen phosphate solution with a concentration of 3 mol / L, add citric acid to this solution, and adjust the pH of the solution to 3;

[0071] S13. Slowly add the ferric chloride solution drop by drop into the adjusted pH diammonium hydrogen phosphate solution at a dropping rate of 500 ml / min. During the dropping process, assist with heating, stirring, and ultrasonic treatment. The heating and stirring temperature is 80 °C, the heating and stirring speed is 1000 r / min, and the ultrasonic power is 180 W. After the titration is completed, continue to heat and stir the mixture for 3 h, with a heating and stirring temperature of 60 °C and a heating and stirring speed of 500 r / min to obtain a sea urchin-like porous precursor-induced material mixture;

[0072] S2. Add sodium carbonate to the precursor-induced material mixture obtained in step S1, and continue to heat and stir for 5 h, with a heating and stirring temperature of 60 °C and a heating and stirring speed of 500 r / min. Obtain a porous, structurally stable, and low-temperature sensitivity precursor mixture;

[0073] S3. Conduct closed-loop spray drying on the precursor mixture obtained in step S2, with a nozzle temperature of 200 °C and a carrier gas of nitrogen to obtain a precursor material;

[0074] S4. Under a nitrogen atmosphere, perform high-temperature sintering on the precursor material prepared in step S3 in a box furnace (see Figure 3 ) for 5 h, with a sintering temperature of 550 °C. After cooling, obtain a pure-phase cathode sodium iron pyrophosphate material with a high specific surface area and low temperature sensitivity.

[0075] Samples in crucibles at different furnace positions after sintering are sampled and tested by XRD. The test results are the same as those in Example 1 (see Figure 4 ). The test results show that no impurity phases are detected in the products at different sampling positions.

[0076] Example 5

[0077] The difference between this Example 5 and Example 4 is that the precursor sintering temperature is increased to 600 °C, and other parameters are exactly the same as those in Example 4.

[0078] Samples in crucibles at different furnace positions after sintering are sampled and tested by XRD. The test results are the same as those in Example 1 (see Figure 4 ). The test results show that no impurity phases are detected in the products at different sampling positions.

[0079] Example 6

[0080] The difference between this Example 6 and Example 4 is that the precursor sintering temperature is increased to 650 °C, and other parameters are exactly the same as those in Example 4.

[0081] Samples of the crucibles at different parts of the furnace after sintering were taken for XRD testing, and the test results were the same as those of Example 1 (see Figure 4 ), and the test results showed that no impurity phases were detected in the products at different sampling parts.

[0082] Comparative Example 4

[0083] The difference between this Comparative Example 4 and Comparative Example 1 is that the iron source, phosphorus source, and sodium source were respectively replaced with ferric chloride, diammonium hydrogen phosphate, and sodium carbonate, and the molar ratios of iron, phosphorus, and sodium elements were still 1:3:3. Ascorbic acid was selected as the antioxidant, and all other parameters were exactly the same as those of Comparative Example 1. The preparation method is as follows:

[0084] All the calculated raw materials were dissolved in deionized water, and then heated and stirred at a heating temperature of 60 °C, a stirring speed of 500 r / min, and a stirring time of 8 h to obtain a precursor mixture; then the mixture was subjected to closed-loop spray drying at a nozzle temperature of 200 °C and a carrier gas of nitrogen to obtain a precursor material; finally, in a nitrogen atmosphere, the precursor material was subjected to high-temperature sintering in a box furnace for 5 h at a sintering temperature of 550 °C, and the sodium iron pyrophosphate material of Comparative Example 4 was obtained after cooling.

[0085] Comparative Example 5

[0086] The difference between this Comparative Example 5 and Comparative Example 4 is that the sintering temperature of the precursor was increased to 600 °C, and all other parameters were exactly the same as those of Comparative Example 4.

[0087] Comparative Example 6

[0088] The difference between this Comparative Example 6 and Comparative Example 4 is that the sintering temperature of the precursor was increased to 650 °C, and all other parameters were exactly the same as those of Comparative Example 4.

[0089] In Comparative Examples 4 - 6, samples of the crucibles at different parts of the furnace after sintering were taken for XRD testing, and the test results showed that impurity phases were detected in the products at different sampling parts.

[0090] Preparation method of high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate of the present invention: An iron source solution added with an antioxidant is added dropwise into a phosphorus source solution with adjusted pH at a specific dropping rate, and heated, ultrasonically stirred to synthesize a sea urchin-like high specific surface area precursor inducing material mixture. Then a sodium source is added into the precursor inducing material mixture, heated and stirred to obtain a precursor mixture, and the precursor material is obtained by closed-loop spray drying under an inert carrier gas. The precursor material has properties such as porous, high specific surface area and stable structure during high-temperature calcination. The porous high specific surface area structure improves the tap density and sodium ion conduction efficiency of the material, and the stable material structure will not cause phase change to generate impurity phases due to uneven temperature in different parts during the sintering process. Finally, the precursor material is calcined at high temperature to obtain a high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate material.

[0091] Compared with the traditional preparation method (after drying the iron phosphate precursor, adding a sodium source and a carbon source for solid-phase dry mixing and homogenization, and then sintering to obtain the sodium iron pyrophosphate phosphate material), the present invention reduces the step of drying the precursor, reduces the production energy consumption. At the same time, the sodium source added in the liquid phase is more uniformly mixed with the precursor inducing material. During the drying process, the sodium source is embedded in the folds of the sea urchin-like porous precursor inducing material, reducing the atomic diffusion path during sintering and reducing the sintering temperature sensitivity.

[0092] In summary, for the preparation method of high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate of the present invention, a sea urchin-like porous precursor inducing material is first prepared. The precursor material has properties such as porous, high specific surface area and stable structure during high-temperature calcination. The porous and high specific surface area structure improves the tap density and sodium ion conduction efficiency of the material, and the stable material structure will not cause phase change to generate impurity phases due to uneven temperature in different parts during the sintering process, and a high specific surface area and low temperature sensitivity pure-phase sodium iron pyrophosphate phosphate material can be obtained.

[0093] Those of ordinary skill in the art in this technical field should recognize that the above embodiments are only used to illustrate the present invention, rather than to limit the present invention. As long as it is within the scope of the essential spirit of the present invention, changes and modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for preparing pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity, characterized in that: The following steps are involved: S1, preparation of sea urchin-like porous precursor induction material, including the following steps: S11, dissolving an iron source and an antioxidant in deionized water to obtain an iron salt solution; S12, dissolving a phosphorus source in deionized water to obtain a phosphorus salt solution, and adjusting the pH of the phosphorus salt solution; S13, adding the iron salt solution dropwise into the phosphate salt solution, and during the dropping process, auxiliary heating, stirring and ultrasound are performed; after the titration is completed, the mixed solution is continued to be heated and stirred to obtain a sea urchin-like porous precursor inducing material mixed solution; S2, adding a sodium source to the precursor inducing material mixture obtained in step S1, heating and stirring the mixture to obtain a porous, structurally stable, and low temperature-sensitive precursor mixture; S3, spray drying the precursor mixture obtained in step S2 to obtain a precursor material, wherein the spray drying is closed spray drying, and the carrier gas is an inert gas, nitrogen or argon; S4, sintering the precursor material obtained in step S3 at high temperature under an inert atmosphere, and obtaining a pure-phase positive electrode sodium iron pyrophosphate material with high specific surface area and low temperature sensitivity after cooling.

2. The method for preparing a pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity according to claim 1, characterized in that: The iron source is at least one of ferrous acetate, ferrous chloride, ferrous sulfate and ferrous phosphate; The phosphorus source is at least one of phosphoric acid, ammonium phosphate, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, and diammonium hydrogen phosphate; The sodium source is at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium citrate, sodium oxalate and sodium acetate; The acid used to adjust the pH value of the phosphate solution is one or more of acetic acid, citric acid, hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid; The antioxidant is hydrogen peroxide or ascorbic acid; The ratio of the iron source to the phosphorus source is 1:1.5 to 1:

5.

3. The method for preparing a pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity according to claim 1, characterized in that: During the titration process of step S13, the heating and stirring temperature is 70-90°C, the heating and stirring speed is 800-1500 r / min, and the ultrasonic power is 150-200W.

4. The method for preparing a pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity according to claim 1, characterized in that: In step S13, after the titration is completed, the heating and stirring temperature is 50-70°C, and the heating and stirring speed is 300-800 r / min.

5. The method for preparing a pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity according to claim 1, characterized in that: In step S2, the heating and stirring temperature is 50-70°C, the heating and stirring time is 2-10 hours, and the heating and stirring speed is 300-800 r / min.

6. The method for preparing a pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity according to claim 1, characterized in that: In step S3, the spray drying temperature is 150-220°C.

7. The method for preparing a pure phase sodium iron pyrophosphate with high specific surface area and low temperature sensitivity according to claim 1, characterized in that: In step S4, the sintering temperature is 500-750° C., and the sintering time is 5-15 hours.

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