Preparation method of sodium pyrophosphate ferric phosphate composite material

Abstract

The application provides a preparation method of sodium pyrophosphate ferric phosphate composite material. The preparation method can include: forming a mixed solution by mixing a sodium source, an iron source, a phosphorus source and a carbon source, adding a complexing agent, stirring to obtain a mixed solution; treating the mixed solution by using an atmospheric pressure jet plasma to obtain a gel precursor; drying the gel precursor, grinding, and sintering under a protective atmosphere to obtain the sodium pyrophosphate ferric phosphate composite material, wherein the gas introduced by the atmospheric pressure jet plasma is a nitrogen-containing and oxygen-containing gas. The preparation method has a simple process flow and low cost, and the prepared sodium pyrophosphate ferric phosphate composite material has high electronic conductivity and high purity, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more specifically, to a method for preparing a sodium iron phosphate pyrophosphate composite material. Background Technology

[0002] Currently, among numerous sodium-ion battery cathode materials, polyanionic iron-based mixed phosphate pyrophosphate sodium iron phosphate (Na4Fe3(PO4)2P2O7, NFPP) has advantages such as low cost, no resource limitations, environmental friendliness, and suitable theoretical specific capacity (129 mAh g / g). –1 The advantages of NFPP, such as small volume change during cycling (<4%), have attracted widespread attention. However, the low electronic conductivity of NFPP limits its specific capacity and rate performance. To improve electronic conductivity, highly conductive carbon materials are often added during its preparation. However, carbon materials with high electronic conductivity are difficult to disperse effectively in solution due to their low surface energy and hydrophobicity, thus failing to achieve the goal of efficiently improving the electronic conductivity of NFPP. In addition, during its sol-gel preparation process, the uneven distribution and precipitation of elements during gel formation inevitably produce electrochemically inert impurities such as sodium iron phosphate (NaFePO4, NFP). Its narrow ion channels and dense structure hinder the absorption of Na+. + The transport of these substances deteriorated the sodium storage performance of NFPP. Summary of the Invention

[0003] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for preparing a sodium iron phosphate pyrophosphate composite material with high electronic conductivity.

[0004] This invention provides a method for preparing sodium iron phosphate pyrophosphate composite material, which may include the following steps: forming a mixture of sodium source, iron source, phosphorus source and carbon source, adding a complexing agent, stirring to obtain a mixed solution; treating the mixed solution with atmospheric pressure jet plasma to obtain a gel precursor; drying the gel precursor, grinding it, and sintering it under a protective atmosphere to obtain sodium iron phosphate pyrophosphate composite material, wherein the gas introduced by the atmospheric pressure jet plasma is a nitrogen-containing and oxygen-containing gas.

[0005] Furthermore, the processing power of atmospheric pressure jet plasma can be 300W to 500W.

[0006] Furthermore, the processing time for atmospheric pressure jet plasma can be 30 to 50 minutes.

[0007] Furthermore, the gas flow rate can be from 0.5 L / min to 2.5 L / min.

[0008] Furthermore, sintering under a protective atmosphere may include heating to 280°C to 320°C at a heating rate of 1°C / min to 5°C / min, pre-firing for 2.5h to 3.5h, and then heating to 500°C to 600°C at a heating rate of 1°C / min to 5°C / min, followed by sintering for 8h to 14h.

[0009] Furthermore, the molar ratio of sodium in the sodium source, iron in the iron source, and phosphorus in the phosphorus source can be (3.9–4.1):(2.9–3.1):(3.9–4.1), and the molar ratio of sodium in the sodium source to carbon in the carbon source can be 1:(1.5–3).

[0010] Furthermore, the sodium source may include at least one of sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium acetate; the iron source may include at least one of ferric nitrate, ferrous nitrate, ferrous carbonate, ferrous oxalate, and ferrous phosphate; the phosphorus source may include at least one of sodium pyrophosphate, pyrophosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate; and the carbon source may include at least one of carbon black, graphite, graphene, carbon nanotubes, and carbon fibers.

[0011] Furthermore, the complexing agent can be citric acid or polyvinylpyrrolidone.

[0012] Furthermore, the sodium iron phosphate pyrophosphate composite material has a core-shell structure with sodium iron phosphate pyrophosphate as the core and carbon as the outer shell.

[0013] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0014] (1) The preparation method of the present invention has a simple process flow and low cost. The prepared sodium iron phosphate pyrophosphate composite material has high electronic conductivity and high purity, and is suitable for industrial production.

[0015] (2) The sodium iron phosphate pyrophosphate composite material prepared by the method of the present invention has good crystallinity, few impurities, and uniform and dispersed particle size;

[0016] (3) The preparation method of the present invention treats the mixed solution with atmospheric pressure jet plasma, which enables the surface of the low surface energy and high hydrophobicity high conductivity carbon material in the mixed solution to be grafted and generate nitrogen-containing polar functional groups, thereby improving the surface energy of the carbon material and improving its dispersion performance in water, thereby achieving the purpose of efficiently improving the electronic conductivity of sodium iron phosphate pyrophosphate composite material.

[0017] (4) The preparation method of the present invention uses atmospheric pressure jet plasma to treat the mixed solution. Atmospheric pressure jet plasma can introduce oxygen-containing functional groups and other oxygen-active substances. By fully anchoring metal ions, it avoids the uneven element distribution and element precipitation during gel formation, which leads to the generation of electrochemical inert impurities such as sodium iron phosphate and sodium ferric phosphate. This avoids the electrochemical inert impurities hindering the formation of Na+. + The transport of sodium iron phosphate pyrophosphate deteriorates the sodium storage performance of the composite material.

[0018] (5) The preparation method of the present invention can promote the hydrolysis process and condensation reaction through high-energy jet plasma, so as to rapidly form a stable gel precursor with a three-dimensional network. By bombarding and etching the gel precursor, a stable three-dimensional porous structure can be generated. Combined with the subsequent sintering process, a porous sodium pyrophosphate iron phosphate composite material can be generated, which can increase the contact area between the composite material and the electrolyte and thus have excellent sodium storage performance. Attached Figure Description

[0019] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 The image shows the XRD pattern of the sodium iron phosphate pyrophosphate composite material prepared in Example 1 of this invention.

[0021] Figure 2 This is a SEM image of the sodium iron phosphate pyrophosphate composite material prepared in Example 1 of the present invention;

[0022] Figure 3 The charge-discharge curve of the sodium iron phosphate pyrophosphate composite material prepared in Example 1 of this invention is shown.

[0023] Figure 4 The charge-discharge curve of the sodium iron phosphate pyrophosphate composite material prepared in Example 2 of this invention is shown.

[0024] Figure 5 The charge-discharge curve of the sodium iron phosphate pyrophosphate composite material prepared in Example 3 of this invention is shown.

[0025] Figure 6 The charge-discharge curve of the sodium iron phosphate pyrophosphate composite material prepared in Example 4 of this invention is shown.

[0026] Figure 7 The charge-discharge curve of the sodium iron phosphate pyrophosphate composite material prepared in Comparative Example 1 of this invention is shown.

[0027] Figure 8 This is a charge-discharge curve of the sodium iron phosphate pyrophosphate composite material prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0028] The method for preparing sodium iron phosphate pyrophosphate composite material according to the present invention will be described in detail below with reference to the accompanying drawings and exemplary embodiments.

[0029] This invention provides a method for preparing a sodium iron phosphate pyrophosphate composite material. In some embodiments, the method for preparing the sodium iron phosphate pyrophosphate composite material may include the following steps:

[0030] S01, after forming a mixture of sodium source, iron source, phosphorus source and carbon source, add complexing agent and stir to obtain a mixed solution;

[0031] S02, the mixed solution is treated with atmospheric pressure jet plasma to obtain a gel precursor;

[0032] S03, the gel precursor is dried, ground, and sintered under a protective atmosphere to obtain sodium iron phosphate pyrophosphate composite material, wherein the gas introduced by the atmospheric pressure jet plasma is a nitrogen-containing and oxygen-containing gas.

[0033] Specifically, this invention obtains a gel precursor by treating a mixture of raw materials with atmospheric pressure jet plasma. The gas introduced into the atmospheric pressure jet plasma is a nitrogen- and oxygen-containing gas. On the one hand, due to the nitrogen content of the system, the atmospheric pressure jet plasma generates nitrogen-based active substances, thereby grafting nitrogen-containing functional groups onto the surface of the carbon material, which can improve the surface energy and hydrophilicity of the carbon material and efficiently enhance the electronic conductivity of the sodium iron phosphate pyrophosphate composite material. On the other hand, due to the oxygen content of the system, the atmospheric pressure jet plasma can generate oxygen-based active substances. The oxygen-containing free radicals introduced into the solution can fully anchor metal ions, thereby avoiding the generation of electrochemically inert impurities caused by uneven distribution and precipitation of elements during gel formation. Furthermore, the continuous bombardment and etching of the gel precursor surface by the high-energy atmospheric pressure jet plasma can give it a three-dimensional porous structure. Combined with the subsequent sintering process, a porous sodium iron phosphate pyrophosphate composite material can be produced, which can increase the contact area between the composite material and the electrolyte, resulting in excellent sodium storage performance.

[0034] In some implementations, forming a mixture of sodium, iron, phosphorus and carbon sources includes forming a mixture of sodium, iron, phosphorus and carbon sources in deionized water.

[0035] In some embodiments, the gas introduced into the atmospheric pressure jet plasma can be air. Of course, the gas introduced in this invention is not limited to this; any gas containing nitrogen and oxygen may be used.

[0036] In some embodiments, the processing power of the atmospheric pressure jet plasma can be 300W to 500W. For example, in some embodiments, the processing power of the atmospheric jet plasma can be a combination of 320W to 470W, 350W to 440W, 385W to 418W, 397W to 405W or above.

[0037] In some embodiments, the processing time for atmospheric pressure jet plasma can be 30 min to 50 min. For example, in some embodiments, the processing time can be a combination of 32 min to 47 min, 35 min to 44 min, 40 min to 48 min, or more.

[0038] In some embodiments, the gas flow rate can be from 0.5 L / min to 2.5 L / min. For example, in some embodiments, the gas flow rate can be a combination of the ranges of 0.7 L / min to 2.3 L / min, 0.9 L / min to 2.1 L / min, 1.3 L / min to 1.8 L / min, 1.5 L / min to 1.7 L / min, or more.

[0039] In summary, under the aforementioned power, gas flow rate, and processing time, atmospheric pressure jet plasma generates nitrogen-based active substances, thereby grafting nitrogen-containing functional groups onto the surface of carbon materials. Simultaneously, it generates oxygen-based active substances, and the oxygen-containing free radicals introduced into the solution can effectively anchor metal ions, thus avoiding the generation of electrochemically inert impurities due to uneven element distribution and precipitation during gel formation. Furthermore, the continuous bombardment and etching of the gel precursor surface by the high-energy atmospheric pressure jet plasma can give it a three-dimensional porous structure. If the atmospheric pressure jet plasma power is below 300W and the gas flow rate is below 0.5L / min, it will be difficult for the atmospheric pressure jet plasma to fully graft and generate nitrogen-containing polar functional groups on the surface of highly conductive carbon materials, thus failing to effectively improve the surface energy and water dispersibility of the material. If the atmospheric pressure jet plasma power is greater than 500W and the gas flow rate is greater than 2.5L / min, the excessively high temperature generated will prevent the uniform distribution and precipitation of elements in the gel precursor, making it difficult to synthesize high-purity sodium iron phosphate pyrophosphate composite materials. If the atmospheric pressure jet plasma treatment time is less than 30 minutes, the gel formation will be incomplete; if the treatment time is greater than 50 minutes, some of the gel will be charred due to the long treatment time, affecting the purity of the sodium iron pyrophosphate composite material.

[0040] In some implementations, the pre-firing temperature can be 280℃~320℃, and the pre-firing time can be 2.5h~3.5h. For example, the pre-firing temperature can be 300℃, and the pre-firing time can be 3h. The sintering temperature can be 500℃~600℃, and the sintering time can be 8h~14h. Sintering temperatures above 500℃ can generate sodium iron phosphate pyrophosphate; if the sintering temperature is above 600℃, the sodium iron phosphate pyrophosphate will decompose and produce impurities due to high temperature heating. Therefore, the sintering temperature is set to 500℃~600℃. For example, the sintering temperature can be 520℃~570℃, and the sintering time can be 10h~12h. The pre-firing and sintering processes can be carried out in a tube furnace under a protective atmosphere. After sintering is completed and cooled to room temperature, the sodium iron phosphate pyrophosphate composite material is obtained.

[0041] In some embodiments, the pre-sintering heating rate can be 1°C / min to 5°C / min. The sintering heating rate can also be 1°C / min to 5°C / min. A sintering heating rate of 1°C / min to 5°C / min ensures uniform heating of the pre-sintered precursor powder, which is beneficial for the formation of sodium iron phosphate pyrophosphate composite materials. For example, the sintering heating rate can be a combination of 1.5°C / min to 3°C / min, 2°C / min to 4°C / min, or higher.

[0042] In some implementations, the molar ratio of sodium in the sodium source, iron in the iron source, and phosphorus in the phosphorus source can be (3.9–4.1):(2.9–3.1):(3.9–4.1). For example, the molar ratio of sodium in the sodium source, iron in the iron source, and phosphorus in the phosphorus source can be 4:3:4. The molar ratio of sodium in the sodium source to carbon in the carbon source can be 1:(1.5–3). For example, the molar ratio of sodium in the sodium source to carbon in the carbon source can be 1:(1.8–2.6).

[0043] Furthermore, the sodium source may include at least one of sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium acetate. The iron source may include at least one of ferric nitrate, ferrous nitrate, ferrous carbonate, ferrous oxalate, and ferrous phosphate. The phosphorus source may include at least one of sodium pyrophosphate, pyrophosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate. The carbon source may include at least one of carbon black, graphite, graphene, carbon nanotubes, and carbon fibers.

[0044] Furthermore, the complexing agent can be citric acid or polyvinylpyrrolidone.

[0045] Furthermore, the sodium iron phosphate pyrophosphate composite material has a core-shell structure with sodium iron phosphate pyrophosphate as the core and carbon as the outer shell. The chemical formula of the sodium iron phosphate pyrophosphate composite material can be Na4Fe3(PO4)2P2O7@C.

[0046] In some implementations, the drying in step S03 can be carried out in a vacuum drying oven. The drying temperature can be 80℃~100℃, and the drying time can be 2h~6h. For example, the drying temperature can be 80℃~95℃, and the drying time can be 3h~5h; another example is that the drying temperature can be 80℃, and the drying time can be 4h.

[0047] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0048] Example 1

[0049] A method for preparing a sodium iron phosphate pyrophosphate composite material may include the following steps:

[0050] S1. Sodium source, iron source, phosphorus source and carbon source are mixed in 20 mL of deionized water, then 0.5 g of citric acid is added, and the mixture is stirred again for 25 min to obtain a mixed solution.

[0051] S2, the mixed solution was treated with atmospheric pressure jet plasma with a power of 400W and a gas flow rate of 1.4L / min for 35 minutes to obtain the gel precursor.

[0052] S3. The gel precursor was vacuum dried at 80℃ for 4h and ground to obtain a solid powder. The solid powder was placed in a crucible and pre-calcined at 300℃ for 3h at a rate of 2℃ / min under a protective atmosphere to obtain a precursor powder. The precursor powder was ground and placed in a crucible and sintered at 500℃ for 10h at a rate of 2℃ / min under a protective atmosphere to obtain a sodium iron phosphate pyrophosphate composite material.

[0053] Coin cells were assembled in a glove box where the water and oxygen content were both below 0.1 ppm, and their electrochemical performance was then tested. Figure 1 The image shows the XRD pattern of the sodium iron phosphate pyrophosphate composite material prepared in this embodiment. It has high crystallinity and no obvious impurity peaks. Figure 2 The image shows a SEM image of the sodium iron phosphate pyrophosphate composite material prepared in this embodiment. The particles have irregular morphology and exhibit a porous structure, with particle sizes ranging from 0.1 μm to 10 μm. Figure 3 As shown, the sodium iron phosphate pyrophosphate composite material prepared in this embodiment exhibits a reversible specific capacity of 93.2 mAh g⁻¹ at a current density of 0.2 C. –1 .

[0054] Example 2

[0055] A method for preparing a sodium iron phosphate pyrophosphate composite material may include the following steps:

[0056] S1. Sodium source, iron source, phosphorus source and carbon source are mixed in 20 mL of deionized water, then 0.5 g of polyvinylpyrrolidone is added, and the mixture is stirred again for 30 min to obtain a mixed solution.

[0057] S2, the mixed solution was treated with atmospheric pressure jet plasma with a power of 350W and a gas flow rate of 1L / min for 40min to obtain the gel precursor.

[0058] S3, the gel precursor was vacuum dried at 100℃ for 4h and ground to obtain a solid powder; the solid powder was placed in a crucible, heated to 300℃ at a rate of 2℃ / min under a protective atmosphere and pre-calcined for 3h to obtain a precursor powder; the precursor powder was ground and placed in a crucible, heated to 500℃ at a rate of 3℃ / min under a protective atmosphere and sintered for 14h to obtain a sodium iron phosphate pyrophosphate composite material.

[0059] Coin cells were assembled in a glove box where the water and oxygen content were both below 0.1 ppm, and their electrochemical performance was subsequently tested. Figure 4 As shown, the sodium iron phosphate pyrophosphate composite material prepared in this embodiment exhibits a reversible specific capacity of 92.4 mAh g⁻¹ at a current density of 0.2 C. –1 .

[0060] Example 3

[0061] A method for preparing a sodium iron phosphate pyrophosphate composite material may include the following steps:

[0062] S1. Sodium source, iron source, phosphorus source and carbon source are mixed in 20 mL of deionized water, then 0.5 g of citric acid is added, and the mixture is stirred again for 40 min to obtain a mixed solution.

[0063] S2. The mixed solution was treated with atmospheric pressure jet plasma with a power of 300W and a gas flow rate of 0.5L / min for 30 minutes to obtain a gel precursor.

[0064] S3, the gel precursor was vacuum dried at 90℃ for 6h and ground to obtain a solid powder; the solid powder was placed in a crucible, heated to 300℃ at a rate of 2℃ / min under a protective atmosphere and pre-calcined for 3h to obtain a precursor powder; the precursor powder was ground and placed in a crucible, heated to 550℃ at a rate of 4℃ / min under a protective atmosphere and sintered for 12h to obtain a sodium iron phosphate pyrophosphate composite material.

[0065] Coin cells were assembled in a glove box where the water and oxygen content were both below 0.1 ppm, and their electrochemical performance was subsequently tested. Figure 5 As shown, the sodium iron phosphate pyrophosphate composite material prepared in this embodiment exhibits a reversible specific capacity of 89 mAh g⁻¹ at a current density of 0.2C. –1 .

[0066] Example 4

[0067] A method for preparing a sodium iron phosphate pyrophosphate composite material may include the following steps:

[0068] S1. Sodium source, iron source, phosphorus source and carbon source are mixed in 20 mL of deionized water, then 0.5 g of polyvinylpyrrolidone is added, and the mixture is stirred again for 30 min to obtain a mixed solution.

[0069] S2, the mixed solution was treated with atmospheric pressure jet plasma with a power of 450W and a gas flow rate of 2L / min for 45min to obtain a gel precursor.

[0070] S3. The gel precursor was vacuum dried at 85°C for 2 hours to obtain a solid powder. The solid powder was placed in a crucible and heated to 300°C at a rate of 2°C / min under a protective atmosphere and pre-calcined for 3 hours to obtain a precursor powder. The precursor powder was ground and placed in a crucible and heated to 600°C at a rate of 1°C / min under a protective atmosphere and sintered for 8 hours to obtain a sodium iron phosphate pyrophosphate composite material.

[0071] Coin cells were assembled in a glove box where the water and oxygen content were both below 0.1 ppm, and their electrochemical performance was subsequently tested. Figure 6 As shown, the sodium iron phosphate pyrophosphate composite material prepared in this embodiment exhibits a reversible specific capacity of 90.3 mAh g⁻¹ at a current density of 0.2 C. –1 .

[0072] Comparative Example 1

[0073] A method for preparing a sodium iron phosphate pyrophosphate composite material may include the following steps:

[0074] S1, mix sodium source, iron source, phosphorus source and carbon source in 20 mL of deionized water, then add 0.5 g of citric acid, stir again for 25 min to obtain a mixed solution;

[0075] S2, the mixed solution was treated with atmospheric pressure jet plasma with a power of 200W and a gas flow rate of 0.2L / min for 80min to obtain a gel precursor that was partially charred and had unevenly dispersed carbon material;

[0076] S3, the gel precursor was vacuum dried at 80℃ for 4h and ground to obtain a solid powder; the solid powder was placed in a crucible, heated to 300℃ at a rate of 2℃ / min under a protective atmosphere and pre-calcined for 3h to obtain a precursor powder; the precursor powder was ground and placed in a crucible, heated to 500℃ at a rate of 2℃ / min under a protective atmosphere and sintered for 10h to obtain a sodium iron phosphate pyrophosphate composite material.

[0077] Coin cells were assembled in a glove box where the water and oxygen content were both below 0.1 ppm, and their electrochemical performance was subsequently tested. Figure 7 As shown, the sodium iron phosphate pyrophosphate composite material prepared in this embodiment exhibits a reversible specific capacity of 72 mAh g⁻¹ at a current density of 0.2 C. –1 Compared with Example 1, this comparative example shows that the sodium iron phosphate pyrophosphate composite material with better electrochemical performance can be obtained under the power, gas flow rate and processing time set by the present invention.

[0078] Comparative Example 2

[0079] The difference between this comparative method and the preparation method in Example 1 is that the mixed solution in S1 was not subjected to atmospheric pressure jet plasma treatment, but was instead treated by oil bath heating to obtain a gel precursor with uneven element distribution and poor carbon material dispersion. All other aspects are the same.

[0080] like Figure 8 As shown, the sodium iron phosphate pyrophosphate composite material prepared in this embodiment has a reversible specific capacity of only 69 mAh g at a current density of 0.2C. –1 .

[0081] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing a sodium iron phosphate pyrophosphate composite material, characterized in that, Includes the following steps: After forming a mixture of sodium, iron, phosphorus and carbon sources, a complexing agent is added and the mixture is stirred to obtain a mixed solution. The mixed solution was treated with atmospheric pressure jet plasma to obtain a gel precursor; The gel precursor was dried, ground, and sintered under a protective atmosphere to obtain a sodium iron phosphate pyrophosphate composite material. The gas introduced by the atmospheric pressure jet plasma was a nitrogen-containing and oxygen-containing gas. The processing power of the atmospheric pressure jet plasma was 300W~500W, and the processing time was 30min~50min.

2. The method for preparing sodium iron phosphate pyrophosphate composite material according to claim 1, characterized in that, The gas flow rate is 0.5 L / min to 2.5 L / min.

3. The method for preparing sodium iron phosphate pyrophosphate composite material according to claim 1 or 2, characterized in that, Sintering under a protective atmosphere includes heating to 280 ℃ to 320 ℃ at a heating rate of 1 ℃ / min to 5 ℃ / min, pre-firing for 2.5 h to 3.5 h, and then heating to 500 ℃ to 600 ℃ at a heating rate of 1 ℃ / min to 5 ℃ / min, followed by sintering for 8 h to 14 h.

4. The method for preparing sodium iron phosphate pyrophosphate composite material according to claim 1 or 2, characterized in that, The molar ratio of sodium in the sodium source, iron in the iron source, and phosphorus in the phosphorus source is (3.9~4.1):(2.9~3.1):(3.9~4.1), and the molar ratio of sodium in the sodium source to carbon in the carbon source is 1:(1.5~3).

5. The method for preparing sodium iron phosphate pyrophosphate composite material according to claim 4, characterized in that, The sodium source includes at least one of sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium acetate; the iron source includes at least one of ferric nitrate, ferrous nitrate, ferrous carbonate, ferrous oxalate, and ferrous phosphate; the phosphorus source includes at least one of sodium pyrophosphate, pyrophosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate; and the carbon source includes at least one of carbon black, graphite, graphene, carbon nanotubes, and carbon fibers.

6. The method for preparing sodium iron phosphate pyrophosphate composite material according to claim 1, characterized in that, The complexing agent is citric acid or polyvinylpyrrolidone.

7. The method for preparing sodium iron phosphate pyrophosphate composite material according to claim 1, characterized in that, The sodium iron phosphate pyrophosphate composite material has a core-shell structure with sodium iron phosphate pyrophosphate as the core and carbon as the outer shell.

Images